Preprocedural mouth rinses for preventing transmission of infectious diseases through aerosols in dental healthcare providers

Abstract

Background

Aerosols and spatter are generated in a dental clinic during aerosol‐generating procedures (AGPs) that use high‐speed hand pieces. Dental healthcare providers can be at increased risk of transmission of diseases such as tuberculosis, measles and severe acute respiratory syndrome (SARS) through droplets on mucosae, inhalation of aerosols or through fomites on mucosae, which harbour micro‐organisms. There are ways to mitigate and contain spatter and aerosols that may, in turn, reduce any risk of disease transmission. In addition to personal protective equipment (PPE) and aerosol‐reducing devices such as high‐volume suction, it has been hypothesised that the use of mouth rinse by patients before dental procedures could reduce the microbial load of aerosols that are generated during dental AGPs.

Objectives

To assess the effects of preprocedural mouth rinses used in dental clinics to minimise incidence of infection in dental healthcare providers and reduce or neutralise contamination in aerosols.

Search methods

We used standard, extensive Cochrane search methods. The latest search date was 4 February 2022.

Selection criteria

We included randomised controlled trials and excluded laboratory‐based studies. Study participants were dental patients undergoing AGPs. Studies compared any preprocedural mouth rinse used to reduce contaminated aerosols versus placebo, no mouth rinse or another mouth rinse. Our primary outcome was incidence of infection of dental healthcare providers and secondary outcomes were reduction in the level of contamination of the dental operatory environment, cost, change in mouth microbiota, adverse events, and acceptability and feasibility of the intervention.

Data collection and analysis

Two review authors screened search results, extracted data from included studies, assessed the risk of bias in the studies and judged the certainty of the available evidence. We used mean differences (MDs) and 95% confidence intervals (CIs) as the effect estimate for continuous outcomes, and random‐effects meta‐analysis to combine data 

Main results

 We included 17 studies with 830 participants aged 18 to 70 years. We judged three trials at high risk of bias, two at low risk and 12 at unclear risk of bias. 

None of the studies measured our primary outcome of the incidence of infection in dental healthcare providers. 

The primary outcome in the studies was reduction in the level of bacterial contamination measured in colony‐forming units (CFUs) at distances of less than 2 m (intended to capture larger droplets) and 2 m or more (to capture droplet nuclei from aerosols arising from the participant's oral cavity). It is unclear what size of CFU reduction represents a clinically significant amount.

There is low‐ to very low‐certainty evidence that chlorhexidine (CHX) may reduce bacterial contamination, as measured by CFUs, compared with no rinsing or rinsing with water. There were similar results when comparing cetylpyridinium chloride (CPC) with no rinsing and when comparing CPC, essential oils/herbal mouthwashes or boric acid with water. There is very low‐certainty evidence that tempered mouth rinses may provide a greater reduction in CFUs than cold mouth rinses. There is low‐certainty evidence that CHX may reduce CFUs more than essential oils/herbal mouthwashes. The evidence for other head‐to‐head comparisons was limited and inconsistent. 

The studies did not provide any information on costs, change in micro‐organisms in the patient's mouth or adverse events such as temporary discolouration, altered taste, allergic reaction or hypersensitivity. The studies did not assess acceptability of the intervention to patients or feasibility of implementation for dentists. 

Authors' conclusions

None of the included studies measured the incidence of infection among dental healthcare providers. The studies measured only reduction in level of bacterial contamination in aerosols. None of the studies evaluated viral or fungal contamination. We have only low to very low certainty for all findings. We are unable to draw conclusions regarding whether there is a role for preprocedural mouth rinses in reducing infection risk or the possible superiority of one preprocedural rinse over another. Studies are needed that measure the effect of rinses on infectious disease risk among dental healthcare providers and on contaminated aerosols at larger distances with standardised outcome measurement.

Plain language summary

Does use of mouth rinse before a dental procedure reduce the risk of infection transmission from patient to health professional?

Why is this question important?

Many dental procedures generate droplets that settle on a surface quickly. If high‐speed instruments, such as a drill, are used, aerosols are generated, which consist of tiny particles that remain suspended in the air and that can be inhaled or that settle farther away on surfaces. These aerosols contain a variety of micro‐organisms and may transmit infections either through direct contact or indirectly through the contaminated surfaces. To prevent the spread of infection, it may help to reduce the number of micro‐organisms that are present in these aerosols. The use of mouth rinses before a dental procedure ('preprocedural mouth rinse') has been suggested as a possible way to reduce the amount of contamination of these aerosols. Chlorhexidine, povidone iodine and cetylpyridinium chloride (CPC) are some of the commonly used mouth rinses. They act by killing or inactivating the micro‐organisms in the mouth and thereby reducing the level of contamination in the aerosol that is generated. We wanted to find out whether rinsing the mouth before a dental procedure reduces the contamination of aerosols produced during dental procedures in practice and helps prevent the transmission of infectious diseases.

How did we identify and evaluate the evidence?

We searched for all relevant studies that compared mouth rinses used before dental procedures against placebo (fake treatment), no intervention or another mouth rinse considered to be inactive. We then compared the results, and summarised the evidence from all the studies. Finally, we assessed our confidence in the evidence. To do this, we considered factors such as the way studies were conducted, study sizes and consistency of findings across studies.

What did we find?

We found 17 studies that met our inclusion criteria. These studies used chlorhexidine, CPC, essential oil/herbal mouth rinses, povidone iodine and boric acid in comparison to no rinsing, or rinsing with water, saline (salt water) or another mouth rinse. None of the studies measured the how often dental healthcare providers became infected with micro‐organisms. All the included studies measured the level of bacterial contamination in droplets or aerosols in the dental clinic. They did not examine contamination with viruses or fungi. 

Most rinses decreased bacterial contamination in aerosols to some extent, but there was considerable variation in the effects and we do not know what size of reduction is necessary to reduce infection risk. 

The studies did not provide any information on costs, change in micro‐organisms in the patient's mouth or side effects such as temporary discolouration, altered taste, allergic reaction or hypersensitivity. The studies did not assess whether patients were happy to use a mouth rinse or whether it was easy for dentists to implement. 

Overall, the results suggest that using a preprocedural mouth rinse may reduce the level of bacterial contamination in aerosols compared with no rinsing or rinsing with water, but we have only low or very low certainty that the evidence is reliable and we do not know how this reduction in contamination relates to the risk of infection.

What does this mean?

We have very little confidence in the evidence, and further studies may change the findings of our review. No studies measured infection risk or investigated viral or fungal contamination. 

How up‐to‐date is this review?

The evidence in this Cochrane Review is current to February 2022.

Summary of findings

Summary of findings 1. Chlorhexidine compared to no rinsing for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Chlorhexidine compared with no rinsing for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic
Population: dental patients undergoing aerosol‐generating procedures and dental healthcare professionals treating them Settings: university hospital Intervention: CHX Comparison: no rinsing
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with no rinsing	Risk with CHX
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	High heterogeneity in the meta‐analysis (I² = 89%; 2 studies)
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CHX: chlorhexidine; CI: confidence interval.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

Summary of findings 2. Chlorhexidine compared to water for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Chlorhexidine compared to water for preventing transmission of infectious diseases through aerosols in dental healthcare providers
Population: dental patients undergoing aerosol‐generating procedures and dental healthcare professionals treating them Setting: university hospital Intervention: CHX Comparison: water (distilled)
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with distilled water	Risk with CHX
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – combined patient and operator level	The range of mean reduction in level of contamination was 114.7 to 1963 CFUs	MD 632.94 CFUs lower (1267.33 lower to 1.45 higher)	—	80 (3 RCTs)	⊕⊝⊝⊝ Very lowa,b,c	Since heterogeneity was high (I² = 92%), we repeated the sensitivity analysis by removing Reddy 2012, which used 0.2% CHX (the other 2 studies used 0.12% CHX). The result was MD 956.11 CFUs lower (95% CI 1626.04 lower to 286.19 lower).
Reduction in the level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – combined operator, assistant and patient level	The mean reduction in the level of contamination was 114.7 CFUs	MD 101.1 CFUs lower (107.01 lower to 95.19 lower)	—	20 (1 RCT)	⊕⊕⊝⊝ Lowb,c	Study compared tempered CHX vs distilled water.
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CHX: chlorhexidine; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded two levels due to inconsistency.
^bDowngraded one level due to imprecision.
^cDowngraded one level due to risk of bias.

Summary of findings 3. Chlorhexidine compared to saline for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Chlorhexidine compared to saline for preventing transmission of infectious diseases through aerosols in dental healthcare providers
Population: dental patients undergoing aerosol‐generating procedures and dental care professionals treating them Setting: university hospital Intervention: CHX Comparison: saline
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with saline	Risk with CHX
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction in the level of contamination was 46.5 CFUs	MD 21.33 CFUs lower (36.80 lower to 5.86 lower)	—	12 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in the level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CHX: chlorhexidine; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded two levels due to serious risk of bias.
^bDowngraded two levels due to serious imprecision.

Summary of findings 4. Chlorhexidine compared to essential oils/herbal mouthwashes for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Chlorhexidine compared to essential oils/herbal mouthwashes for preventing transmission of infectious diseases through aerosols in dental healthcare providers
Population: dental patients undergoing aerosol‐generating procedures and dental care professionals treating them Setting: university hospital Intervention: CHX Comparison: essential oils/herbal mouthwash
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with essential oils/herbal mouthwash	Risk with CHX
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction in level of contamination ranged from 24.68 to 56.2 CFUs	MD 23.09 CFUs lower (34.4 lower to 11.78 lower)	—	76 (3 RCTs)	⊕⊕⊝⊝ Lowa,b	The studies compared 0.2% CHX to tea tree essential oil, herbal mouthwash A and herbal mouthwash B (see Table 5).
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – assistant level	The mean reduction in the level of contamination ranged from 19.25 to 26 CFUs	MD 12.21 CFUs lower (15.58 lower to 8.83 lower)	—	76 (3 RCTs)	⊕⊕⊝⊝ Lowa,b	The studies compared 0.2% CHX to tea tree essential oil, herbal mouthwash A and herbal mouthwash B (see Table 5).
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CHX: chlorhexidine; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded one level due to risk of bias.
^bDowngraded one level due to imprecision.

1. Details of essential oil and herbal mouth rinses.

Study	Intervention name in study	Composition
Bay 1993	Essential oil mouthwash C	Listerine (active ingredients: menthol (mint) 0.042%, thymol (thyme) 0.064%, methyl salicylate (wintergreen) 0.06%, and eucalyptol (eucalyptus) 0.092%)
Gupta 2014	Herbal mouthwash B	Natural herb bibhitaki (terminilia bellirica) 10 mg, Nagavalli (Piper betle) 10 mg, peelu (Salvadora persica) 5 mg, powders peppermint satva (mentha spp) 1.6 mg, yavani satva (caraway) 0.4 mg, oils gandhapura taila (wintergreen) 1.2 mg and cardamom 0.2 mg
Nayak 2020	Herbal mouthwash A	Befresh, which contains cinnamomum zeylanicum, mentha spicata, syzygium aromaticum, and eucalyptusglobulus
Shetty 2013	Essential oil mouthwash A	Tea tree oil
Suresh 2011	Essential oil mouthwash B	Eucalyptol + thymol + methyl salicylate + menthol

Summary of findings 5. Chlorhexidine compared to povidone iodine for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Chlorhexidine compared to povidone iodine for reduction in the level of contamination in aerosols
Population: dental patients undergoing aerosol‐generating procedures and dental care professionals treating them Setting: university hospital Intervention: CHX Comparison: povidone iodine
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with povidone iodine	Risk with CHX
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level (aerobic cultures)	The range of mean reduction in level of contamination was 30 to 52 CFUs	MD 10.75 CFUs lower (26.24 lower to 4.74 higher)	—	52 (2 RCTs)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level (aerobic and anaerobic cultures combined)	The mean reduction in level of contamination was 35.4 CFUs	MD 4.7 CFUs lower (7.01 lower to 2.39 lower)	—	30 (1 RCT)	⊕⊝⊝⊝ Very lowb,c	—
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment – aerobic cultures	The mean reduction in level of contamination was 18.5 CFUs	MD 0.20 CFUs higher (7.28 lower to 7.68 higher)	—	40 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment – anaerobic cultures	The mean reduction in level of contamination was 19.5 CFUs	MD 0.8 CFUs lower (11.65 lower to 10.05 higher)	—	40 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CHX: chlorhexidine; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded two levels due to risk of bias.
^bDowngraded two levels due to imprecision.
^c Downgraded one level due to risk of bias.

Summary of findings 6. Chlorhexidine compared to cetylpyridinium chloride (CPC) for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Chlorhexidine compared to cetylpyridinium chloride (CPC) for preventing transmission of infectious diseases through aerosols in dental healthcare providers
Population: dental patients undergoing aerosol‐generating procedures and dental care professionals treating them Setting: university hospital Intervention: CHX Comparison: CPC
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with CPC	Risk with CHX
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator	The mean reduction in level of contamination was 62.2 CFUs	MD 2.20 CFUs lower (9.07 lower to 4.67 higher)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	Tempered CHX vs tempered CPC
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – assistant	The mean reduction in level of contamination was 38.7 CFUs	MD 0.20 CFUs lower (6.30 lower to 5.90 higher)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	Tempered CHX vs tempered CPC
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator	The range of mean reduction in level of contamination was 6.9 to 71.5 CFUs	MD 4.43 CFUs higher (2.27 lower to 11.13 higher)	—	50 (2 RCTs)	⊕⊝⊝⊝ Very lowa,b	Cold CHX vs cold CPC
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – assistant	The mean reduction in level of contamination was 47.3 CFUs	MD 8.80 CFUs higher (2.70 higher to 14.90 higher)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	Cold CHX vs cold CPC
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator	The mean reduction in level of contamination was 71.5 CFUs	MD 11.50 CFUs lower (18.37 lower to 4.63 lower)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	Tempered CHX vs cold CPC
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – assistant	The mean reduction in level of contamination was 47.3 CFUs	MD 8.80 CFUs lower (14.90 lower to 2.70 lower)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	Tempered CHX vs cold CPC
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator	The mean reduction in level of contamination was 62.2 CFUs	MD 13.60 CFUs higher (6.73 higher to 20.47 higher)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	Cold CHX vs tempered CPC
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – assistant	The mean reduction in level of contamination was 38.7 CFUs	MD 17.40 CFUs higher (11.30 higher to 23.50 higher)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	Cold CHX vs tempered CPC
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction in level of contamination  was 61 CFUs	MD 30 CFUs lower (85.86 lower to 25.86 higher)	—	30 (1 RCT)	⊕⊝⊝⊝ Very lowb,c	CHX vs CPC+Zn+F (CPC plus zinc and sodium fluoride)
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CHX: chlorhexidine; CI: confidence interval; CPC: cetylpyridinium chloride; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded one level due to risk of bias.
^bDowngraded two levels due to imprecision.
^cDowngraded one level due to inconsistency,

Summary of findings 7. Tempered chlorhexidine compared to non‐tempered chlorhexidine for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Tempered chlorhexidine compared to non‐tempered chlorhexidine for preventing transmission of infectious diseases through aerosols in dental healthcare providers
Population: dental patients undergoing aerosol‐generating procedures and dental care professionals treating them Setting: university hospital Intervention: tempered CHX Comparison: non‐tempered CHX
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with non‐tempered CHX	Risk with tempered CHX
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction in level of contamination was 75.8 CFUs	MD 15.8 CFUs lower (22.67 lower to 8.93 lower)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – assistant level	The mean reduction in level of contamination was 56.1 CFUs	MD 17.60 CFUs lower (23.70 lower to 11.50 lower)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – combined	The mean reduction in level of contamination was 24.4 CFUs	MD 10.80 CFUs lower (15.15 lower to 6.45 lower)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in the level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded one level due to risk of bias.
^bDowngraded two levels due to imprecision.

Background

The use of high‐speed hand pieces, ultrasonic scalers and similar devices in dental clinics contributes to the generation of contaminated aerosols and spatter (Meng 2020), which have the potential to harbour harmful viral, bacterial and fungal organisms, and can be a source of infection (Mosaddad 2019). Over 700 microbial species have been detected in saliva, including the recent coronavirus‐19 (COVID‐19) virus; though they become diluted in the water during aerosol‐generating procedures (AGPs), they may pose a risk of infection in dental healthcare providers (Li 2020; To 2020). Such contaminated aerosols and spatter generated during dental procedures can also remain suspended in the air or settle on surfaces in a dental clinic (Laheij 2012), through which the transmission of diseases such as tuberculosis, measles and severe acute respiratory syndrome (SARS) can occur directly through inhalation of these droplets or aerosols, or indirectly from contact with contaminated surfaces (Harrel 2004). The droplets generated during coughing, sneezing and speaking are usually larger than 5 μm in diameter and settle in the near vicinity (less than 1 m), whereas bioaerosols produced during AGPs remain afloat for a considerable amount of time and spread virulent pathogens over a distance of 1.8 m, causing potential risk to dental healthcare providers and patients (Jones 2015).

In March 2020, the highly pathogenic and transmissible COVID‐19 (severe acute respiratory syndrome coronavirus (SARS‐CoV‐2)) virus emerged and spread rapidly around the world. Due to the unknown modes of transmission and uncertainty in the management of the viral infection, most dental practices were suspended across the globe (Fallahi 2020; Hughes 2020). Clinical studies with a small sample size have evaluated body fluids of people with COVID‐19 and reported remarkably high levels of SARS‐CoV‐2 in saliva and the oropharynx (Jeong 2020; Yoon 2020), pointing towards a potential source of infective aerosols during dental treatment of SARS‐CoV‐2‐positive people.

One study on the impact of adhering to infection control guidelines by 2195 dentists in the USA showed that the existing infection control recommendations may be sufficient to prevent COVID‐19 infection in dental settings (Estrich 2020). This could be attributed to the adherence of dentists to currently recommended Centers for Disease Control and Prevention (CDC) infection prevention and control guidelines such as disinfection (99.1%), using personal protective equipment (PPE) (85.2%), COVID‐19 screening (98.5%), use of masks by staff members (99.1%), social distancing (98.9%), preprocedural mouth rinse (12%) and use of extraoral suction (4%). It can be assumed that any intervention to reduce the ambient microbial load during AGPs would further mitigate the risk of infection transmission.

In view of this, organisations such as the UK's Faculty of General Dental Practice (FGDP) and the CDC published strict guidelines for safe and effective practice including preprocedural mouth rinsing (CDC 2020; FGDP 2020). Yoon 2020 reported a short‐term reduction of SARS‐CoV‐2 viral load in saliva following chlorhexidine (CHX) mouth rinse. One randomised control trial in 2021 involving 16 SARS‐CoV‐2‐positive patients showed sustained reduction in viral loads with the use of two commercially available mouth rinses (Seneviratne 2021).

In vitro studies have provided some evidence on commercially available oral rinses reducing the viral load including that of SARS‐CoV‐2 (Bidra 2020; Meister 2020), and other enveloped viruses such as SARS‐CoV, MERS‐CoV, influenza A, parainfluenza, cytomegalovirus, hepatitis B, herpes simplex virus type‐1, herpes simplex virus type‐2, human immunodeficiency virus‐1 and human papilloma virus (HPV) (Reis 2021). Effect of mouth rinses on viral load may not always correlate with their effect on the infectivity (replicating virus) of the viral culture (Gottsauner 2020). This advocates for a systematic evaluation of available clinical trials utilising these oral rinse formulations in prevention of infection transmission through contaminated aerosols.

Interventions that could possibly reduce the volume of aerosols generated during dental procedures, or their level of contamination, are evaluated in one Cochrane rapid review (Nagraj 2020). Our planned Cochrane Review will complement Nagraj 2020 by exploring the available evidence on the effectiveness and safety of preprocedural mouth rinses for preventing transmission of infectious diseases in a dental clinic. 

Description of the condition

Dental AGPs are used during endodontic treatment, periodontal and restorative procedures involving the use of high‐speed hand pieces, ultrasonic scalers and high‐pressure air syringes, which are responsible for most aerosols generated in a dental clinic (Barnes 1998; Eliades 2020; Gross 1992; Harrel 2004; Veena 2015). The Scottish Dental Clinical Effectiveness Programme (SDCEP) have categorised AGPs as those procedures that will produce aerosol particles such as ultrasonic scaling, using high‐speed air rotor and air polishing (Group A), that may produce aerosol particles such as slow‐speed/electric hand piece, prophylaxis with pumice, 3‐in‐1 syringe (either air or water) and diathermy (Group B) and that may produce spatter but are unlikely to produce aerosol particles such as dental examination without the use of 3‐in‐1 syringe, dental extraction, impression and intraoral radiography (Group C) (SDCEP 2021). However, there is no global consensus on the list of dental procedures that can be considered AGPs (Jackson 2020).

Some dental procedures can indirectly generate aerosols by agitating the airway (e.g. intraoral radiography or maxillary impressions). These procedures may induce the patient to cough forcibly, thereby releasing aerosols filled with microbes (Mair 2020). However, AGPs have been more commonly attributed to cross‐infection in dentistry (Chanpong 2020; Harrel 2004). While performing AGPs, the quantifiable risk of disease transmission is based on patient factors (i.e. whether they are infected with, or the carrier of, any disease), virulence of the pathogenic micro‐organism, type of procedure, duration of procedure, ability to employ mitigation factors such as aerosol‐reducing interventions and the probability of success of the intervention (Koletsi 2020). Bacteria can multiply rapidly by replicating their DNA, unlike most viruses that need entry into a living cell (such as a human cell) to be able to reproduce (Munita 2016). This is of significance in a compromised host that has increased susceptibility to allow micro‐organisms to colonise, replicate and survive.

Considering that dental treatment involves close contact between the patient and the treating dentist, any type of aerosol that is generated can lead to cross‐infection, and minimising the number of contaminated aerosols generated is key to infection control (Eliades 2020; Zemouri 2017). The aerosols generated can be differentiated into spatter, droplet and droplet nuclei, based on the particle size (Harrel 2004; Mair 2020). 'Spatter' are the larger droplets that are greater than 50 µm in diameter and are airborne for only a brief period of time (Wells 1934). The smaller 'droplets' remain suspended in the air for varying amounts of time, after which the water content evaporates, leaving the solid particles called 'droplet nuclei' (5 µm or less) to freely float in the air (Harrel 2004; James 2016; Mair 2020). The smaller droplets and droplet nuclei are responsible for airborne transmission of infectious diseases (James 2016) (Figure 1). In addition to pathogenic and non‐pathogenic bacteria, viruses and other micro‐organisms, bioaerosols also contain components of plaque, nasopharyngeal and oral secretions, and traces of materials used in dental procedures (Eliades 2020; Zemouri 2017).

1.

Aerosols and spatter generated in the dental clinic. mtrs: metres.

Description of the intervention

The chain of spread of infection consists of a reservoir, portal of exit from the reservoir (such as aerosols), an infectious agent, a susceptible host and a portal of entry into the host through a nasal or oral cavity (Mupparapu 2019). 'Infective dose' is of relevance when it comes to transmission of infectious diseases, and any technique that mitigates this dose would be beneficial in dental procedures (Li 2004). Therefore, it is reasonable to assume that any strategy used for reducing the viable microbial content of aerosols could lower the risk of cross‐contamination in the dental setting (Fine 1992). Preprocedural mouth rinses would supplement this endeavour, along with PPE, rubber dam isolation, high‐volume suction, high‐efficiency particulate air (HEPA) filters, UV lights, and ozonisation. The layering of infection control steps, as described by Harrel 2004, reduces risk with ultimate aim of breaking the transmission chain, preventing cross‐infection, and ensuring safe and effective dental practice. Most of the tested oral rinses have shown broad‐spectrum antibacterial, antimicrobial and virucidal properties (Corner 1988; Meister 2020). A detailed infographic is presented in Figure 2 (Nagraj 2020).

2.

Layering of infection control steps in the dental clinic. HEPA: high‐efficiency particulate air; UV: ultraviolet.

Layering of infection control steps

Layer 1: personal protective barriers

PPE includes masks or respirators, gowns or coveralls, protective eye wear and face shields that reduce and protect from exposure to aerosols. A Cochrane Review evaluated the use of PPE for infection control (Verbeek 2020). Hence this intervention is not included in this review.

Layer 2: preprocedural rinses and antimicrobial coolants

Layer 2 involves interventions such as preprocedural use of mouth rinses and antimicrobial coolants that prevent contamination of aerosols in the mouth. Antimicrobial agents such as CHX and povidone iodine are used as coolants along with ultrasonic scalers. The effectiveness of antimicrobial coolants is presented in a Cochrane Review (Nagraj 2020). The use of preprocedural mouth rinses is included in this review and is described in the next section of this review.

Layers 3, 4, 5 and 6

Layers 3, 4, 5 and 6 are interventions that prevent contaminated aerosols from escaping the mouth (e.g. rubber dam and saliva ejector), prevent contaminated aerosols from escaping the immediate operatory (e.g. high‐volume evacuation), reduce overall concentration of aerosol in the operatory using HEPA filters, and that decontaminate aerosols in air (such as UV light and ozonisation), respectively. The effectiveness of these interventions to reduce contaminated aerosols in a dental operatory is evaluated in another Cochrane Review (Nagraj 2020).

How the intervention might work

Chlorhexidine

CHX, chemically a bisbiguanide, is considered as a gold standard disinfectant in dentistry (Mandel 1994). It is a superior antiplaque agent with broad antimicrobial spectrum that includes gram‐positive and gram‐negative organisms, certain bacterial spores, lipophilic viruses, yeasts and dermatophytes (Jones 1997; Mandel 1994). This mouth rinse is commercially available in concentrations of 0.12% to 0.2% of CHX gluconate, with or without alcohol (Ciancio 2000). Although some studies on the virucidal effects of CHX against SARS‐CoV and related viral infections under biologically mimicked conditions have shown proven benefit (Yoon 2020), other studies have reported no antiviral property with the use of CHX (Jones 1997; Marui 2019; Meister 2020).

The most important property of CHX is the intrinsic ability to be retained by the oral surfaces and released gradually into the oral cavity over a period of time (Carrilho 2010). Staining of teeth and gingiva has been reported with use of CHX for more than seven days, except in formulations that contain polyvinylpyrrolidone in addition to CHX (Tartaglia 2019). Taste alteration and increased calculus formation are other reported adverse effects (Ciancio 2000).

Cetylpyridinium chloride

Cetylpyridinium chloride (CPC) is a cationic quaternary ammonium with broad‐spectrum antimicrobial and antiviral properties (Popkin 2017). It acts by penetrating the cell wall of organisms causing lysis and destruction. It is a surface‐active agent specifically active against gram‐positive organisms and yeast. It is commercially available in concentrations ranging from 0.05% to 0.10%. It is an established antiplaque agent and is used as an adjuvant in mild‐to‐moderate gingivitis (Ciancio 2000).

Essential oils

Essential oils are plant extracts obtained by distillation or cold press and are mixed with a carrier oil base to be used commercially. They are powerful antioxidants with regenerating, oxygenating and immune‐strengthening properties (Araujo 2015). Tea tree oil, helichrysum oil, chamomile oil, clove oil, eucalyptus oil and lavender oil are commonly used. Generally, mouth rinses contain oil of thymol, menthol, eucalyptol, and methyl salicylate in a hydroalcohol solution (Claffey 2003). Essential oils have antimicrobial properties and work by killing planktonic and biofilm‐associated bacteria and a broad spectrum of bacteria and yeasts associated with halitosis, gingivitis and periodontitis. They disrupt bacterial cell membranes and cell walls, inhibit bacterial growth and development, inhibit glucosyltransferase enzymes, reduce extracellular polysaccharide formation, and reduce plaque endotoxin levels (Alshehri 2018; Araujo 2015). Essential oils have also shown antiviral properties by causing capsid disintegration and viral expansion and thus making them ineffective (Wani 2021).

Herbal mouth rinses

Herbal mouth rinses are available as non‐prescription medications, and are widely used due to the belief that alternative or complementary therapy offers no or minimal adverse effects (Sridharan 2016). Botanical sources such as neem, basil, lemon grass, chamomile, linseed, leaf extracts such as from Carica papaya or guava leaf, peppermint, turmeric (Cai 2020), and green propolis (Pedrazzi 2015) have been incorporated into aqueous solutions to be used as mouth rinses. These are phytotherapeutic plants, containing a mixture of active agents such as catechins, tannins and sterols (Manipal 2016). These mouth rinses from botanical sources have been shown to have significant effects on both gram‐positive and gram‐negative organisms, including Escherichia coli, Streptococcus species and Salmonella species (Dua 2015). They possess significant antimicrobial and superoxide scavenging properties, leading to reduction in the bacterial load, decrease in overall inflammation and reduction in oxidative stress, ultimately leading to healing and recovery (Dua 2015; Mathur 2018).

Povidone iodine

Povidone iodine is a broad‐spectrum antimicrobial agent with established in vitro efficacy against many gram‐positive and gram‐negative bacteria including mycobacteria; bacterial spores; and a wide range of enveloped and non‐enveloped viruses, fungi and protozoa (Kanagalingam 2015). The microbicidal action of povidone iodine is related to the non‐complexed, freely mobile elemental iodine (Kanagalingam 2015). This activated iodine reacts in electrophilic reactions with enzymes of the respiratory chain as well as with amino acids from the cell membrane proteins both located in the cell wall. As a result, the well‐balanced tertiary structure necessary for maintaining the respiratory chain is destroyed and the micro‐organism is irreversibly damaged (Eggers 2018).

There were significant reductions in SARS‐CoV‐2 viral load when povidone iodine mouth rinse was tested under biologically mimicked conditions (Meister 2020). Povidone iodine as gargles and throat sprays demonstrated rapid virucidal activity against coronavirus strains, especially SARS‐CoV, after 10 seconds' exposure (Kariwa 2004). The exposure of 120 seconds was effective against Candida albicans that reduced the overall treatment cost of fungal infections (Kanagalingam 2015).

C31G

C31G is an equimolar mixture of alkyl dimethylglycine and alkyl dimethyl amine oxide that is buffered with citric acid (Corner 1988). It is a surface‐active agent effective against gram‐positive and gram‐negative bacteria and is used in a concentration of 0.5%. It acts by inhibition of bacterial glycolysis, bacterial adherence and low minimum inhibitory concentration (MIC) against a host of microbes (Corner 1988).

Hydrogen peroxide

Hydrogen peroxide in low concentrations is used in mouth rinses, dentifrices and teeth‐whitening agents (Mandel 1994; Walsh 2000). Commercially available mouth rinses contain 1% to 3% of hydrogen peroxide (Hossainian 2011). Being a strong oxidising agent, it exerts good antimicrobial effects against gram‐positive and gram‐negative organisms. Nevertheless, there is no evidence to support the use of hydrogen peroxide mouth rinses as an antiviral agent (Ortega 2020).

Saline

Saline is known to have antibacterial properties. One study using home‐made saline with a concentration of 2% and 5.8% showed marked activity on gram‐positive bacteria and the antibacterial effect for a 2% solution lasted three hours and for a 5.8% solution lasted five hours (Nokam Kamdem 2022). Nokam Kamdem and colleagues found the 5.8% saline to be as effective as 0.1% CHX.

Ozonated water

Ozone (O₃) is an allotropic form of oxygen and has the ability to oxidise organic material. Because of this property, it has been topically used to reduce infections affecting the oral cavity (Nagayoshi 2004).

Boric acid

Boric acid 0.75% to 3% has been used as antimicrobial and antifungal agent because of its potential fungicidal and bacteriostatic action. It contains AN0128, a boron‐containing compound that has demonstrated antimicrobial and anti‐inflammatory properties (Luan 2008), and has been successfully used in the field of dentistry as irrigation agent to reduce the periodontal pocket depth in people with periodontitis (Sağlam 2013).

Why it is important to do this review

Although aerosols produced during AGPs in the dental clinic have always been considered a potential threat for transmission of diseases among dentists and dental personnel, there are virtually no documented transmission episodes of any of these through dental practices. This concern of transmission has become even more important in the context of the current pandemic challenge posed by COVID‐19. Epidemics such as those of SARS, Middle East respiratory syndrome (MERS) and now COVID‐19 warrant superior infection control practices in dental clinics to sustain and provide necessary services during challenging times (Meng 2020). People attending dental clinics can cough, sneeze or undergo dental procedures that aerosolise dental materials, saliva and blood along with micro‐organisms. People who are infected can be in the incubation period, be asymptomatic or choose to conceal their infection (Meng 2020). Hence, it is the duty of healthcare professionals to take necessary precautions to the highest possible level.

Following the suspension of most dental practices due to the COVID‐19 pandemic, strict infection control guidelines are being proposed by major governing bodies across the world in order to resume routine practices, without which people with oral health problems will go untreated, and dental practices will have financial impact (CDC 2020; FGDP 2020). CDC guidelines recommend that dental settings need to balance providing necessary services to patients while minimising the risk of transmission of infectious diseases in the dental clinic. The Occupational Safety and Health Administration (OSHA) classified dentists as in the very high‐risk category due to the potential exposure to pathogenic micro‐organisms through AGPs. Also, according to the US Department of Labor, dental hygienists have the highest occupational risk at 99.7%, followed by the dental assistants at 92.5% and general dentists at 92.1%.

With current concerns about the transmission of infectious diseases and cross‐contamination in the dental setting, several methods have been proposed to reduce the risk of infection spread. Use of mouth rinses by the patient before the commencement of any dental procedure has been proposed and tested in various clinical and laboratory studies as a possible measure to reduce the amount of contamination in the aerosols generated during AGPs (Fine 1996; Hunter 2014; Joshi 2017). In one recently published rapid review on AGPs and their mitigation in International Dental Guidance documents, 82% (51/63) of documents recommended preprocedural mouth rinse for people without COVID; however, only 10/51 documents provided references to support the recommendation (Clarkson 2020). Different types of mouth rinses are commercially available, but there is uncertainty regarding the use of these preprocedural mouth rinses as we do not know if they are effective for preventing the risk of infection in dental healthcare providers and contamination of aerosols, and if so, whether one might work better than another. This review may help dental professionals prepare themselves to adopt best practices to reduce the risk of infection and help in the reduction of contaminated aerosols.

Objectives

To assess the effects of preprocedural mouth rinses used in dental clinics to minimise incidence of infection in dental healthcare providers and reduce or neutralise contamination in aerosols.

Methods

Criteria for considering studies for this review

Types of studies

We included randomised controlled trials (RCTs) either with parallel arm or cluster‐RCT design in dental patients. We included cross‐over design for secondary objectives but planned to include first‐period data from cross‐over trials as parallel‐arm studies. We excluded quasi‐RCTs, split‐mouth studies, controlled clinical trials and experimental studies conducted in a laboratory environment.

Types of participants

We included studies with dental patients undergoing AGPs.

Types of interventions

We included any preprocedural rinse that aimed to reduce contaminated aerosols in dental clinics, compared to placebo, no mouth rinse or another mouth rinse. We excluded studies that combined preprocedural rinse with other methods to reduce the aerosols, as this is beyond the scope of the review.

Types of outcome measures

We could not find any recommended core outcomes related to this review published in the Core Outcome Measures in Effectiveness Trials (COMET) initiative (COMET 2020). Hence, the review authors decided on the outcomes by consensus.

Primary outcomes

• Incidence of infection of dental healthcare providers (dentists, dental surgery assistants, dental hygienists, dental technologists, dental laboratory staff, dental aides or trainee students)

Measurement of outcomes: whether a participant infected any dental healthcare provider; if so, we planned to count it as one event.

Secondary outcomes

• Reduction in the level of contamination by particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment

• Reduction in the level of contamination by particles of 5 µm or less (droplet nuclei) at distances of 2 m or more from patient's oral cavity in the operative environment

• Cost

• Change of microbiota in the patient's mouth

• Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity

• Acceptability and feasibility of the intervention to patients and dental healthcare providers

Measurement of outcomes: we planned to measure the reduction in the level of contamination using colony‐forming units (CFUs), where the samples could be collected with culture plates, or the results of polymerase chain reaction (PCR) or index of microbial air contamination (IMA). We planned to measure cost in GBP or USD, and change of microbiota using CFUs or viral load. Adverse events are described qualitatively. Acceptability and feasibility of the interventions was to be measured using ordinal (e.g. Likert scale) or dichotomous (e.g. yes/no) data.

Search methods for identification of studies

Electronic searches

Cochrane Oral Health's Information Specialist conducted systematic searches in the following databases for RCTs and controlled clinical trials. There were no language, publication year or publication status restrictions:

• Cochrane Oral Health's Trials Register (searched 4 February 2022) (Appendix 1);

• Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Register of Studies (searched 4 February 2022) (Appendix 2);

• MEDLINE Ovid (1946 to 4 February 2022) (Appendix 3);

• Embase Ovid (1980 to 4 February 2022) (Appendix 4);

• World Health Organization COVID‐19 Global Literature on Coronavirus Disease Database (search.bvsalud.org/global-literature-on-novel-coronavirus-2019-ncov) (searched 4 February 2022) (Appendix 5);

• Cochrane COVID‐19 Study Register (covid-19.cochrane.org/) (searched via the Cochrane Register of Studies) (searched 4 February 2022) (Appendix 6).

Subject strategies were modelled on the search strategy designed for MEDLINE Ovid, presented in Appendix 3. Where appropriate, they were combined with subject strategy adaptations of the highly sensitive search strategies designed by Cochrane for identifying RCTs as described in the Cochrane Handbook for Systematic Reviews of Interventions, Technical Supplement to Chapter 4 (Lefebvre 2020). We also used a search filter to identify non‐randomised studies, as presented in Waffenschmidt 2020.

Searching other resources

Cochrane Oral Health's Information Specialist searched the following trials registries to identify ongoing studies:

• US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov (clinicaltrials.gov/) (searched 4 February 2022) (Appendix 7);

• World Health Organization International Clinical Trials Registry Platform (apps.who.int/trialsearch) (searched 4 February 2022) (Appendix 8).

We searched the reference lists of included studies and relevant systematic reviews for further studies.

We did not perform a separate search for adverse effects.

We checked to ensure that none of the included studies were retracted due to error or fraud.

We contacted the original authors for clarification and further data if trial reports were unclear.

Data collection and analysis

Selection of studies

Two review authors independently screened the titles and abstracts. The search was designed to be sensitive and include controlled clinical trials, these were filtered out early in the selection process if they were not randomised. We resolved any conflicts during the screening process by discussion. If this was not possible, we consulted a third review author (arbiter) and reached consensus through discussion. We used online Rayyan software to screen the titles and abstracts (Rayyan 2016).

Two review authors independently screened the full‐text articles. We resolved any conflicts during the screening by mutual discussion. If this was not possible, we consulted a third review author (arbiter) and reached consensus through discussion. For included studies, we extracted useful information and data from the full‐text articles. These are presented in the Characteristics of included studies table. We also present the Characteristics of excluded studies tables, stating the reasons for the exclusion of studies.

Data extraction and management

One review author designed the data extraction form and another review author tested its suitability. Two review authors independently extracted the data using the data extraction form. We limited the data extraction to a minimal set of required data items.

Where studies had multiple publications, we collated the reports of the same study, so that each study, rather than each report, was the unit of interest for the review. Such studies had a single identifier with multiple references.

Assessment of risk of bias in included studies

Two review authors independently assessed risk of bias using the Cochrane RoB 1 tool for RCTs, the results of which were reported in a table; Higgins 2011). For RCTs, we classified each domain as being at high, low or unclear risk of bias. We attempted to contact the trial authors if there was insufficient information or it was unclear. We resolved any disagreements by discussion between the review authors. If consensus was not reached, we consulted a third review author (arbiter).

Measures of treatment effect

We reported continuous outcomes as means differences (MDs) with 95% confidence intervals (CIs). If the included trials reported continuous outcomes obtained from different instruments, we used the standardised mean difference (SMD) as the effect measure, with 95% CIs.

We planned to qualitatively describe the costs for the interventions used. For ordinal data, we planned to dichotomise the data and present the effect sizes as risk ratios (RRs) with 95% CIs. We planned to present the effect sizes for dichotomous outcomes as RRs with 95% CIs. However, none of the included studies reported costs for the interventions, dichotomous and ordinal data.

Unit of analysis issues

For the primary outcome, the unit of analysis was the event of infection in any of the dental healthcare providers. For the secondary outcomes, the unit of analysis was the participant undergoing the AGP. In multi‐arm trials, we selected the relevant arms for inclusion in our analyses. If more than two arms were relevant to this review, we planned to split the control group between multiple comparisons so that participants were not double‐counted in a meta‐analysis. However, none of the meta‐analyses had this issue.

Dealing with missing data

When we encountered trials with missing data, we contacted the investigators or sponsors of these studies, if the contact author's email address was available. We calculated missing data from other data, such as standard deviations (SDs) and P values. We planned to re‐analyse the data according to the intention‐to‐treat (ITT) principle whenever possible. However, we did not encounter such trials.

Assessment of heterogeneity

We assessed heterogeneity by visually inspecting the forest plots to determine closeness of point estimates with each other and overlap of CIs. We used the Chi² test with a P value of 0.1 to indicate statistical significance. We also used the I² statistic, following the interpretation recommended in the Cochrane Handbook for Systematic Reviews of Interventions (0% to 40% might not be important; 30% to 60% may represent moderate heterogeneity; 50% to 90% may represent substantial heterogeneity; 75% to 100% represents considerable heterogeneity) (Higgins 2019).

Assessment of reporting biases

If we had included 10 or more studies, we planned to construct a funnel plot to investigate any potential reporting bias. However, most of the analyses were based on fewer than 10 studies.

Data synthesis

We analysed the data using Review Manager 5 (Review Manager 2020). In the absence of substantial clinical or methodological heterogeneity, we performed meta‐analysis using the random‐effects model. If there was substantial or considerable heterogeneity, we investigated this using a subgroup analysis. Where a meta‐analysis was not appropriate, we discussed the data narratively.

Subgroup analysis and investigation of heterogeneity

We planned to investigate heterogeneity by performing the following subgroup analyses.

• Type of AGP (e.g. ultrasonic and sonic scaling, tooth preparation using air turbine hand piece or air abrasion, three‐way syringe).

• Duration or dosage (or both) of mouth rinse.

• Position of the culture plates (for CFU).

• Type of culture media used (aerobic and anaerobic).

• Type of air sampler used (Reynier's, Andersen cascade, Surface Air System sampler, Active Casella slit sampler).

Of these, we had sufficient data to conduct subgroup analyses based on position of the culture plates and type of culture media used.

Sensitivity analysis

To explore the possible effect of losses to follow‐up on the effect estimates for the secondary outcomes, we planned to perform sensitivity analyses. We planned to remove those studies at high risk of bias (studies assessed to have high risk of bias in at least one domain) and report if any there were significant differences between the results of these analyses. However, most comparisons were based on single studies, or all the included studies were at high risk of bias or we could not meta‐analyse the data due to high heterogeneity for which we had no explanation.

For dichotomous outcomes, we planned to vary the event rate within the missing participants from intervention and control groups within plausible limits. However, none of the included studies reported the outcomes dichotomously.

Summary of findings and assessment of the certainty of the evidence

We planned to summarise the results of the analyses in summary of findings tables for the following outcomes, for all comparisons.

• Incidence of infection of dental healthcare providers.

• Reduction in the level of contamination by particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment.

• Reduction in the level of contamination by particles 5 µm or less (droplet nuclei) at distances of 2 m or more from patient's oral cavity in the operative environment.

• Adverse events.

However, we did not find any included studies reporting the primary outcome (incidence of infection of dental healthcare providers). Hence, we summarised the results of the analyses in summary of findings tables for the other three outcomes for seven comparisons only.

To identify the most important seven comparisons, we engaged stakeholders (four general dental practitioners and six specialists) who ranked the comparisons. We have presented the top seven comparisons identified by stakeholders as summary of findings tables (Table 1; Table 2; Table 3; Table 4; Table 6; Table 7; Table 8). For the other nine comparisons, we presented the summary of findings as additional tables (Table 9; Table 10; Table 11; Table 12; Table 13; Table 14; Table 15; Table 16; Table 17).

2. Cetylpyridinium chloride compared to no rinsing for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Cetylpyridinium chloride compared to no rinsing for preventing transmission of infectious diseases through aerosols in dental healthcare providers
Population: dental patients undergoing aerosol‐generating procedures and dental healthcare professionals treating them Setting: university hospital Intervention: CPC Comparison: no rinsing
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with no rinsing	Risk with CPC
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction in level of contamination was 41.7 CFUs	MD 34.8 CFUs lower (65.92 lower to 3.68 lower)	—	30 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction in level of contamination was 644 CFUs	MD 583 CFUs lower (958.36 lower to 207.64 lower)	—	30 (1 RCT)	⊕⊕⊝⊝ Lowb	CPC+Zn+F vs no rinsing
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – combined	The range of mean reduction in level of contamination was 803.3 to 875 CFUs	MD 0.75 CFUs lower (1.32 lower to 0.18 lower)	—	200 (2 RCTs)	⊕⊝⊝⊝ Very lowa,b	CPC formulation vs no rinsing
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CI: confidence interval; CPC: cetylpyridinium chloride; CPC+Zn+F: cetylpyridinium chloride + zinc + fluoride; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded one level due to risk of bias.
^bDowngraded two levels due to imprecision.

3. Cetylpyridinium chloride compared to water for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Cetylpyridinium chloride compared to water for preventing transmission of infectious diseases through aerosols in dental healthcare providers
Population: dental patients undergoing aerosol‐generating procedures and dental healthcare professionals treating them Setting: university hospital Intervention: CPC Comparison: water
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with water	Risk with CPC
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction in level of contamination was 55.6 CFUs	MD 48.7 CFUs lower (67.82 lower to 29.58 lower)	—	30 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	CPC vs water
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction in level of contamination was 307 CFUs	MD 246 CFUs lower (437.96 lower to 54.04 lower)	—	30 (1 RCT)	⊕⊕⊝⊝ Lowb	CPC+ZN+F vs water
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – combined	The mean reduction in level of contamination was 569 CFUs	MD 0.78 CFUs lower (1.24 lower to 0.31 lower)	—	105 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	CPC formulation vs water
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CI: confidence interval; CPC: cetylpyridinium chloride; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded one level due to risk of bias.
^bDowngraded two levels due to imprecision.

4. Tempered cetylpyridinium chloride compared to cold cetylpyridinium chloride for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Tempered cetylpyridinium chloride compared to cold cetylpyridinium chloride for preventing transmission of infectious diseases through aerosols in dental healthcare providers
Population: dental patients undergoing aerosol‐generating procedures and dental healthcare professionals treating them Setting: university hospital Intervention: tempered CPC Comparison: cold CPC
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with cold CPC	Risk with tempered  CPC
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator	The mean reduction in level of contamination was 71.5 CFUs	MD 9.3 CFUs lower (16.17 lower to 2.43 lower)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – assistant	The mean reduction in level of contamination was 47.3 CFUs	MD 8.6 CFUs lower (14.7 lower to 2.5 lower)	—	20 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CI: confidence interval; CPC: cetylpyridinium chloride; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded one level due to risk of bias.
^bDowngraded two levels due to imprecision.

5. Povidone iodine compared to saline for preventing transmission of infectious diseases through aerosols in dental healthcare providers.

Povidone iodine compared to saline for preventing transmission of infectious diseases through aerosols in dental healthcare providers
Population: dental patients undergoing aerosol‐generating procedures and dental care professionals treating them Setting: university hospital Intervention: povidone iodine Comparison: saline
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with saline	Risk with povidone iodine
Incidence of infection of dental healthcare providers	Not reported
Reduction in the level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction was 46.5 CFUs	MD 16.5 CFUs lower (32.65 lower to 0.35 lower)	—	12 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in the level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded two levels due to risk of bias.
^bDowngraded two levels due to imprecision.

6. Essential oil/herbal mouthwash compared to water for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Essential oil/herbal mouthwash compared to water for preventing transmission of infectious diseases through aerosols in dental healthcare providers
Population: dental patients undergoing aerosol‐generating procedures and dental healthcare professionals treating them Setting: university hospital Intervention: essential oil/herbal mouthwash Comparison: water
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with water	Risk with essential oil/herbal mouthwash
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	High heterogeneity in the meta‐analysis (3 studies)
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – assistant level	High heterogeneity in the meta‐analysis (3 studies)
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CHX: chlorhexidine; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

7. Chlorhexidine compared to ozonated water for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Chlorhexidine compared to ozonated water for reduction in the level of contamination of aerosols
Population: dental patients undergoing aerosol‐generating procedures and dental healthcare professionals treating them Setting: university hospital Intervention: CHX Comparison: ozonated water
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with ozonated water	Risk with CHX
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level aerobic assessed with CFUs	The mean reduction in level of contamination was 48.5 CFUs	MD 17.8 lower (33.70 lower to 1.90 lower)	—	40 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment – aerobic assessed with CFUs	The mean reduction in level of contamination was 31 CFUs	MD 12.3 lower (27.12 lower to 2.52 higher)	—	40 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,c	—
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment – anaerobic assessed with CFUs	The mean reduction in level of contamination was 22.1 CFUs	MD 3.4 lower (14.66 lower to 7.86 higher)	—	40 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,c	—
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded two levels due to high risk of bias.
^bDowngraded two levels due to imprecision.
^cDowngraded one level due to inconsistency.

8. Povidone iodine compared to ozonated water for preventing risk of infection in dental healthcare providers and contamination of aerosols in dental clinic.

Povidone iodine compared to ozonated water for reduction in the level of contamination in aerosols
Population: dental patients undergoing aerosol‐generating procedures and dental healthcare professionals treating them Setting: university hospital Intervention: povidone iodine Comparison: ozonated water
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with ozonated water	Risk with povidone iodine
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level aerobic assessed with CFUs	The mean reduction in level of contamination was 48.5	MD 3.5 higher (17.1 lower to 24.1 higher)	—	40 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,c	—
Reduction in level of contamination by particles ≤  5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment – aerobic assessed with CFUs	The mean reduction in level of contamination aerobic was 31	MD 12.5 lower (26.33 lower to 1.33 higher)	—	40 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,c	—
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment – anaerobic assessed with CFUs	The mean reduction in level of contamination was 22.1	MD 2.6 lower (9.54 lower to 4.34 higher)	—	40 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,c	—
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CHX; chlorhexidine; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded two levels due to high risk of bias.
^bDowngraded one level due to inconsistency.
^cDowngraded two levels due to imprecision.

9. Chlorhexidine compared to boric acid for reduction in the level of contamination in aerosols.

Chlorhexidine compared to boric acid for reduction in the level of contamination in aerosols
Population: dental patients undergoing aerosol‐generating procedures and dental healthcare professionals treating them Setting: university hospital Intervention: CHX Comparison: boric acid
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with boric acid	Risk with CHX
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction in level of contamination was 49.8 CFUs	MD 26.6 CFUs lower (28.24 lower to 24.96 lower)	—	60 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – assistant level	The mean reduction in level of contamination was 20.9 CFUs	MD 8.03 CFUs lower (9.65 lower to 6.41 lower)	—	60 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CHX: chlorhexidine; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded one level due to unclear risk of bias.
^bDowngraded two levels due to imprecision.

10. Boric acid compared to water for reduction in the level of contamination in aerosols.

Boric acid compared to water for reduction in the level of contamination in aerosols
Population: dental patients undergoing aerosol‐generating procedures and dental healthcare professionals treating them Setting: university hospital Intervention: boric acid Comparison: water
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with water	Risk with boric acid
Incidence of infection of dental healthcare providers	Not reported
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – operator level	The mean reduction in level of contamination was 79.1 CFUs	MD 29.3 CFUs lower (32.65 lower to 25.95 lower)	—	60 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles > 5 µm (droplets) at distances of < 2 m from patient's oral cavity in the operative environment – assistant level	The mean reduction in level of contamination was 34.13 CFUs	MD 14.04 CFUs lower (16.47 lower to 11.61 lower)	—	60 (1 RCT)	⊕⊝⊝⊝ Very lowa,b	—
Reduction in level of contamination by particles ≤ 5 µm (droplet nuclei) at distances of ≥ 2 m from patient's oral cavity in the operative environment	Not reported
Adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony‐forming unit; CI: confidence interval; MD: mean difference; RCT: randomised controlled trial.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of the effect.

^aDowngraded one level due to unclear risk of bias.
^bDowngraded two levels due to imprecision.

We used the GRADE framework to evaluate the certainty of evidence for each outcome as high, moderate, low or very low, as described in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2019). We justified all decisions to downgrade the certainty of the evidence using footnotes and provided comments to aid readers' understanding where necessary.

Results

Description of studies

See Characteristics of included studies, Characteristics of excluded studies, and Characteristics of ongoing studies tables.

Results of the search

The electronic search strategies identified 6356 records, and five records from cross‐references of the included studies and non‐Cochrane systematic reviews on this topic. We had 4319 records after deduplication. We excluded 4269 records after screening the abstracts as they were irrelevant and requested full‐text copies of 50 articles. From the 50 articles, we excluded 23 studies (25 reports) and identified four ongoing studies. The remaining 17 studies (21 reports) met the inclusion criteria of this review. See Figure 3 for the selection process.

3.

Study flow diagram.

Included studies

We included 17 studies with 830 participants. See the Characteristics of included studies table for further details.

Countries of origin

Eleven trials were from India (Gupta 2014; Joshi 2017; Kaur 2014; Mohan 2016; Nayak 2020; Nisha 2021; Reddy 2012; Shetty 2013; Suresh 2011; Tasneem 2017; Verma 2017); three from the USA (Bay 1993; Fine 1993a; Mohammed 1964); two from Brazil (Feres 2010; Retamal‐Valdes 2017); and one from Puerto Rico (Mohammed 1970).

All the included studies were published in the English language.

Trial design

All included studies were RCTs with parallel‐arm designs except one, which had a cross‐over design (Fine 1993a). Five studies had two arms (Fine 1993a; Mohammed 1970; Mohan 2016; Suresh 2011; Tasneem 2017); nine had three arms (Bay 1993; Gupta 2014; Kaur 2014; Mohammed 1964; Nayak 2020; Nisha 2021; Reddy 2012; Shetty 2013; Verma 2017); and three had four arms (Feres 2010; Joshi 2017; Retamal‐Valdes 2017).

Sample size

The minimum sample size was 18 (Fine 1993a; Verma 2017); and the maximum sample size was 185 (Mohammed 1964). None of the included studies mentioned the sample size calculation or power of the study.

Aerosol‐generating procedures tested

Fourteen studies tested interventions during ultrasonic scaling procedures (Feres 2010; Fine 1993a; Gupta 2014; Joshi 2017; Kaur 2014; Mohan 2016; Nayak 2020; Nisha 2021; Reddy 2012; Retamal‐Valdes 2017; Shetty 2013; Suresh 2011; Tasneem 2017; Verma 2017). Of these 14, four studies used a magnetostrictive ultrasonic scaler (Feres 2010; Fine 1993a; Retamal‐Valdes 2017; Suresh 2011); four studies used a piezoelectric scaler (Gupta 2014; Joshi 2017; Nayak 2020; Verma 2017); and the remaining six studies did not report the type of scaler used.

One study tested interventions during air‐abrasive polishing (Bay 1993); and two studies during tooth preparation with a high‐speed hand piece (Mohammed 1964; Mohammed 1970).

Funding

Private companies funded five trials were funded by private companies that manufactured the tested mouth rinses or the tested mouth rinses were sponsored by those companies (Bay 1993; Feres 2010; Fine 1993a; Nayak 2020; Retamal‐Valdes 2017). One study had university funding (Nisha 2021). Four trials did not disclose any funding details or conflict of interest (Gupta 2014; Mohammed 1964; Mohammed 1970; Mohan 2016), and the remaining seven trials reported that they had not received any funding and had no conflicts of interest (Joshi 2017; Kaur 2014; Reddy 2012; Shetty 2013; Suresh 2011; Tasneem 2017; Verma 2017).

Clinical set‐up

Disinfection of the operating room

Three trials fumigated the operatory used in the trial before starting the procedure (Joshi 2017; Nisha 2021; Verma 2017), one of which, Joshi 2017, used 34% formaldehyde. Other studies did not report any details regarding fumigation.

Dental unit waterlines

Two trials flushed the dental unit waterlines before the procedure (Fine 1993a; Nayak 2020). Bay 1993 flushed the polisher waterlines for two minutes before each use. Two trials flushed the ultrasonic scaler with distilled water before treatment (Feres 2010; Shetty 2013).

Participants

The maximum participant age reported was 70 years (Retamal‐Valdes 2017); the minimum was 18 years (Retamal‐Valdes 2017). Eleven studies recruited adults only (Fine 1993a; Gupta 2014; Joshi 2017; Kaur 2014; Mohan 2016; Nayak 2020; Nisha 2021; Retamal‐Valdes 2017; Shetty 2013; Suresh 2011; Tasneem 2017). Mohammed 1964 recruited university students. Reddy 2012 recruited people of any age. The remaining four studies did not mention any details about the age group (Bay 1993; Feres 2010; Mohammed 1970; Verma 2017).

One trial recruited only males (Mohammed 1970). Six studies recruited both males and females (Bay 1993; Gupta 2014; Mohammed 1964; Nisha 2021; Reddy 2012; Retamal‐Valdes 2017). The remaining 10 trials did not mention the sex of the study participants (Feres 2010; Fine 1993a; Joshi 2017; Kaur 2014; Mohan 2016; Nayak 2020; Shetty 2013; Suresh 2011; Tasneem 2017; Verma 2017).

Inclusion/exclusion criteria

Eight studies recruited medically healthy people (Feres 2010; Fine 1993a; Joshi 2017; Kaur 2014; Nisha 2021; Retamal‐Valdes 2017; Tasneem 2017; Verma 2017); and seven studies recruited people who were not taking any antibiotic treatment or with a recent history of antibiotic treatment (Gupta 2014; Mohan 2016; Nayak 2020; Nisha 2021; Reddy 2012; Shetty 2013; Suresh 2011). Two studies did not mention any such inclusion/exclusion criteria (Mohammed 1964; Mohammed 1970).

Outcomes

The included studies did not measure our primary outcome, incidence of infection of dental healthcare providers. The outcomes reported in the included studies were the reduction in the level of contamination in particles larger than 5 µm at distances of less than 2 m in the operative environment and reduction in the level of contamination in particles 5 µm or less at distances of 2 m or more in the operative environment. Both these outcomes were measured in CFUs. None of the included studies used automatic colony counters for the assessment of the outcome. Four trials used manual colony counters (Bay 1993; Feres 2010; Joshi 2017; Retamal‐Valdes 2017). Fine 1993a counted colonies using a dissecting microscope, with results reported as total CFUs per filter. Other trials did not report the details of colony counting.

Eleven trials reported the mean CFUs either at operator or assistant levels. One trial reported the mean CFUs at 3 feet (91 cm) distance from the patient and did not mention the precise location of the culture media (Mohan 2016). Four trials reported only the combined mean CFUs from the culture media placed at different locations in the dental clinic (Mohammed 1964; Mohammed 1970; Reddy 2012; Tasneem 2017).

Sixteen studies used passive aerosol sampling where the aerosols drop down to settle on the culture media. Bay 1993 used active aerosol sampling from the oropharynx of patients undergoing dental air‐abrasive polishing.

Interventions

Ten trials compared CHX to either water or saline (or both) or no rinsing reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment.

1. Chlorhexidine rinsing versus no rinsing

Two trials compared 0.12% CHX to no rinsing at operator mouth‐mask level (operator level) (Feres 2010; Retamal‐Valdes 2017). 

Feres 2010 used a one‐minute rinsing protocol and Retamal‐Valdes 2017 did not mention the rinsing duration.

2. Chlorhexidine versus water

Six trials compared CHX to distilled water at the operator level (Feres 2010; Gupta 2014; Nayak 2020; Nisha 2021; Retamal‐Valdes 2017; Shetty 2013). Of these, three trials used 0.2% CHX (Gupta 2014; Nayak 2020; Shetty 2013), and three used 0.12% CHX (Feres 2010; Nisha 2021; Retamal‐Valdes 2017). Four trials also evaluated the outcome at assistant level (Gupta 2014; Nayak 2020; Nisha 2021; Shetty 2013).

One trial compared non‐tempered 0.2% CHX and tempered 0.2% CHX with sterile water at operator level and assistant level; however, the combined data was presented (Reddy 2012).

Five studies used a one‐minute rinsing protocol (Feres 2010; Gupta 2014; Nayak 2020; Nisha 2021; Reddy 2012). Gupta 2014 performed rinsing 10 minutes prior to the dental procedure and Nayak 2020 30 minutes prior to treatment. Two studies did not mention the rinsing time (Retamal‐Valdes 2017; Shetty 2013).

Bay 1993 used a 30‐second rinsing time directly prior to treatment and evaluated the outcome at the patient level. Therefore, the data from this study were not included in the meta‐analysis.

3. Chlorhexidine versus saline

One trial compared 0.2% CHX to saline for the same outcome at 3 feet (91 cm) away from patient's mouth (exact location of the culture plate placement was not reported) (Mohan 2016), and another trial compared 0.2% CHX to saline at the operator level (Verma 2017). 

Mohan 2016 followed a one‐minute rinsing protocol and Verma 2017 used a two‐minute rinsing time.

4. Chlorhexidine versus essential oils/herbal mouthwash

We combined trials using essential oil mouth rinse or herbal mouth rinse versus CHX mouth rinse under this comparison as herbal mouth rinse is prepared using the essential oil from the plant extracts (Cai 2020). We presented the composition of the essential oil mouth washes in Table 5.

Five trials compared CHX mouth rinse to essential oil/herbal mouthwash for the outcome reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from the patient's oral cavity in the operative environment (Bay 1993; Gupta 2014; Nayak 2020; Shetty 2013; Suresh 2011). Four trials used 0.2% CHX (Gupta 2014; Nayak 2020; Shetty 2013; Suresh 2011), and Bay 1993 used 0.12% CHX. Three trials assessed the contamination at the operator and assistant levels (Gupta 2014; Nayak 2020; Shetty 2013). One trial assessed at the assistant level and at 6 inches (30 cm) from the patient's mouth (Suresh 2011). Another trial assessed at the Andersen's level 2 (oropharynx) (Bay 1993).

Shetty 2013 compared 0.2% CHX with essential oil mouthwash A (tea tree oil). Suresh 2011 trial compared 0.2% CHX with essential oil mouthwash B (combination of eucalyptol, thymol, methyl salicylate and menthol essential oil). Bay 1993 compared 0.12% CHX with essential oil mouthwash C (Listerine), which contains essential oils (such as 0.042% menthol (mint), 0.064% thymol (thyme), 0.06% methyl salicylate (wintergreen) and 0.092% eucalyptol (eucalyptus)).

Nayak 2020 compared 0.2% CHX mouthwash with herbal mouthwash A (Befresh, which contains Cinnamomum zeylanicum, Mentha spicata, Syzygium aromaticum and Eucalyptus globulus) and Gupta 2014 compared 0.2% CHX mouthwash with herbal mouthwash B (which contains Terminilia bellirica, Piper betle, Salvadora persica, powders peppermint (Mentha spp) and Caraway, Wintergreen oil and cardamom).

Three studies used a one‐minute rinsing time (Gupta 2014; Nayak 2020; Suresh 2011). Shetty 2013 did not mention the rinsing time. Gupta 2014 performed rinsing 10 minutes prior to the dental procedure and Nayak 2020 30 minutes prior to the dental procedure. Bay 1993 used a 30‐second rinsing time directly prior to treatment.

5. Chlorhexidine versus povidone iodine

For reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment at operator level, two trials compared 0.2% CHX mouthwash to povidone iodine mouthwash using aerobic culture (Tasneem 2017; Verma 2017), and one trial assessed using both aerobic and anaerobic cultures (Kaur 2014). Kaur 2014 used 1% povidone Iodine while Verma 2017 used 5%.

For reduction in the level of contamination in particles 5 µm or less (droplet nuclei) at distances of 2 m or more from patient's oral cavity in the operative environment, Kaur 2014 compared the same mouthwashes using both aerobic and anaerobic cultures.

Kaur 2014 used a one‐minute rinsing protocol and Verma 2017 used a two‐minute rinsing protocol. Tasneem 2017 did not mention the rinsing time. None of the studies mentioned when the rinsing was performed prior to the procedure.

6. Chlorhexidine versus cetylpyridinium chloride

Three trials reported reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment. Feres 2010 compared cold 0.12% CHX with cold 0.05% CPC at operator level. Joshi 2017 compared tempered 0.2% CHX with tempered 0.05% CPC, cold 0.2% CHX with cold 0.05% CPC, tempered 0.2% CHX with cold 0.05% CPC and cold 0.2% CHX with tempered 0.05% CPC at operator and assistant level. Retamal‐Valdes 2017 compared 0.12% CHX and 0.075% CPC plus 0.28% zinc + 0.05% sodium fluoride (CPC+Zn+F) at operator level.

Two studies used the specified mouth rinse for one minute (Feres 2010; Joshi 2017). Joshi 2017 used the mouth rinse 10 minutes prior to the dental procedure. Retamal‐Valdes 2017 did not mention rinsing time.

7. Tempered chlorhexidine versus non‐tempered chlorhexidine

Two trials compared tempered 0.2% CHX versus non‐tempered 0.2% CHX and reported reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment. Joshi 2017 compared the outcome at operator and assistant levels and Reddy 2012 reported the outcome as combined reduction in the level of contamination.

Both trials reported the comparison after one minute of rinsing (Joshi 2017; Reddy 2012). Joshi 2017 used the mouth rinse 10 minutes prior to dental procedure.

8. Cetylpyridinium chloride versus no rinsing

Four trials reported reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment at operator level. Feres 2010 compared 0.05% CPC versus no rinsing. Retamal‐Valdes 2017 compared CPC+Zn+F versus no rinsing. Two trials compared CPC plus domiphen bromide plus quaternary ammonium compounds with water and reported the same outcome as the combined results (Mohammed 1964; Mohammed 1970).

One study used the mouth rinse for one minute (Feres 2010). Three trials did not report the timing of rinsing (Mohammed 1964; Mohammed 1970; Retamal‐Valdes 2017).

9. Cetylpyridinium chloride versus water

Three trials reported reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment at operator level. Feres 2010 compared 0.05% CPC with distilled water. Retamal‐Valdes 2017 compared CPC+Zn+F with distilled water. Mohammed 1964 compared CPC plus domiphen bromide plus quaternary ammonium compounds with water and reported the same outcome as the combined results.

One study used the specified mouth rinse for one minute (Feres 2010). Three trials did not report the timing of rinsing (Mohammed 1964; Mohammed 1970; Retamal‐Valdes 2017).

10. Tempered cetylpyridinium chloride versus cold cetylpyridinium chloride

One trial compared tempered 0.05% CPC and cold 0.05% CPC and reported reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment at operator and assistant levels (Joshi 2017).

Joshi 2017 used the mouth rinse for one minute, 10 minutes prior to the dental procedure.

11. Povidone iodine versus saline

One trial compared 5% povidone iodine versus saline and reported reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment at operator level (Verma 2017). 

Verma 2017 used a two‐minute rinsing time.

12. Essential oil/herbal mouthwash versus water

Four trials reported reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from the patient's oral cavity in the operative environment under this comparison. Nayak 2020 compared herbal mouthwash A with water and Gupta 2014 compared herbal mouthwash B with distilled water at operator and assistant levels. Shetty 2013 compared essential oil mouthwash A with distilled water at operator and assistant levels. Bay 1993 compared essential oil mouthwash C with distilled water and reported the combined outcome. We presented the composition of the essential oil mouth washes in Table 5. 

Two studies used a one‐minute rinsing protocol (Gupta 2014; Nayak 2020). Gupta 2014 performed rinsing 10 minutes prior to the dental procedure and Nayak 202030 minutes prior. Bay 1993 used a 30‐second rinsing time directly prior to the treatment. Shetty 2013 did not report rinsing time.

13. Chlorhexidine versus ozonated water

One trial reported two outcomes, reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m and more than 2 m from patient's oral cavity in the operative environment (Kaur 2014). Kaur 2014 used 0.2% CHX rinse or ozonated water rinse with 0.082 mg/hour ozone output as preprocedural rinse before ultrasonic scaling procedure at operator level (mask of the operator) and 9 feet behind the patient. 

Kaur 2014 used a one‐minute rinsing time.

14. Povidone iodine versus ozonated water

One trial reported two outcomes, reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m and more than 2 m from patient's oral cavity in the operative environment (Kaur 2014). Kaur 2014 used 1% povidone iodine rinse or ozonated water rinse with 0.082 mg/hour ozone output as preprocedural rinse after ultrasonic scaling procedure at operator level (mask of the operator) and 9 feet behind the patient.

This study used a one‐minute rinsing time.

15. Chlorhexidine versus boric acid

One trial reported reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment at operator and assistant levels (Nisha 2021). Nisha 2021 used 0.12% CHX and 0.75% boric acid mouth rinse as preprocedural rinses 15 minutes before an ultrasonic scaling procedure at operator level (mask of the operator).

Nisha 2021 used a one‐minute rinsing time.

16. Boric acid versus water

One trial reported reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity in the operative environment at operator and assistant levels (Nisha 2021). Nisha 2021 used 0.75% boric acid mouth rinse and water as preprocedural rinses 15 minutes before an ultrasonic scaling procedure at operator level (mask of the operator).

Nisha 2021 used a one‐minute rinsing time.

17. Essential oil versus hydroalcohol mouthwash

One study compared essential oil mouthwash C (Listerine) with coloured and flavoured 5% hydroalcohol mouthwash in a cross‐over study design for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity at operator level using aerobic culture method during ultrasonic scaling (Fine 1993a). The study reported the mean log 10 values in a graph format and the data for the first phase were not reported. Hence, we could not include the results of the study in a meta‐analysis.

The participants followed a 30‐second rinsing protocol 40 minutes before the ultrasonic scaling procedure.

Excluded studies

We excluded 23 studies (25 reports) for the reasons listed in the Characteristics of excluded studies table. Of these, we could not access two trials from the clinical trial registry (CTRI/2017/10/010189; CTRI/2018/05/013935). Eight trials were not RCTs (Altonen 1976; Ciancio 1994; Dawson 2016; Litsky 1970; Paul 2020; Rajachandrasekaran 2019; Toroglu 2001; Worrall 1987). Six trials had split‐mouth design (Devker 2012; Fine 1992; Fine 1993b; Klyn 2001; Narayana 2016; Sawhney 2015). One trial checked bacterial contamination in the bone debris collected from the osteotomy site (Young 2002). One trial had a crossover design and the crossover sequence was not randomised (Santos 2014). NCT02319668 used toothpaste as the control and NCT04659928 used different high‐volume evacuation devices and hydrogen peroxide mouth rinse in combination. Three trials used high‐volume evacuation device in combination with preprocedural rinse (Logothetis 1995; Ramesh 2015; Swaminathan 2014).

Studies awaiting classification

There are no studies awaiting classification.

Ongoing studies

We identified four ongoing trials (CTRI/2021/03/031653; CTRI/2021/10/037528; NCT03839719; NCT04717063; see Characteristics of ongoing studies).

Risk of bias in included studies

We assessed three trials at high risk of bias overall (Bay 1993; Kaur 2014; Verma 2017), and 12 trials as unclear risk of bias overall because they each had at least one risk of bias domains that we judged to be unclear (Feres 2010; Fine 1993a; Gupta 2014; Joshi 2017; Mohammed 1964; Mohammed 1970; Mohan 2016; Nisha 2021; Reddy 2012; Shetty 2013; Suresh 2011; Tasneem 2017) (Figure 4; Figure 5). Two trials had low risk of bias overall (Nayak 2020; Retamal‐Valdes 2017).

4.

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.

5.

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

Allocation

Only four trials gave the details of random sequence generation and allocation concealment (Fine 1993a;  Kaur 2014; Nayak 2020; Retamal‐Valdes 2017). Four trials had low risk of bias in random sequence generation and had not provided any information on allocation concealment (Joshi 2017; Nisha 2021; Shetty 2013; Tasneem 2017). One trial provided no information on random sequence generation and had low risk of bias for allocation concealment (Gupta 2014), and one trial had provided the details of random sequence generation and was assessed to have high risk of bias for allocation concealment based on the details provided through personal communication (Verma 2017). The other seven trials did not provide any information on random sequence generation and allocation concealment and thus we assessed them to have unclear risk of bias (Bay 1993; Feres 2010; Mohammed 1964; Mohammed 1970; Mohan 2016; Reddy 2012; Suresh 2011).

Blinding

We assessed two trials to have high risk of performance bias as the dentists who carried out the AGPs were not blinded (Bay 1993; Verma 2017). Five trials did not give any details on blinding and were assessed to have unclear risk of bias  (Mohammed 1964; Mohammed 1970; Mohan 2016; Reddy 2012; Shetty 2013), and nine trials were at low risk of bias (Feres 2010; Fine 1993a; Gupta 2014; Joshi 2017; Kaur 2014; Nayak 2020; Nisha 2021; Retamal‐Valdes 2017; Tasneem 2017). None of the trials used automated colony counters. Therefore, we assessed trials to have low risk of bias if they used manual colony counting with assessor blinding. One trial had unclear performance bias and low risk of detection bias (Suresh 2011).

Incomplete outcome data

Three trials did not provide any details regarding the dropouts and hence we assessed these trials to have unclear risk of bias (Bay 1993; Feres 2010; Shetty 2013). We assessed the other 13 trials, which had no or minimal dropouts, at low risk of bias.

Selective reporting

Only two trials followed the reporting according to their registered protocols and thus were at low risk of bias (Nayak 2020; Retamal‐Valdes 2017). One trial had registered the trial retrospectively and the sample size mentioned was 10 per group (Nisha 2021). We are not sure if the outcomes reported were same as the planned ones and thus judged this at unclear risk of bias. Another two trials had deviated from the protocol, thus being assessed at high risk of bias (Kaur 2014; Verma 2017). The remaining trials provided no details of the trial registration and hence we could not evaluate if all the planned outcomes were adequately reported. Therefore, these trials were at unclear risk of bias.

Other potential sources of bias

We identified no other potential sources of bias and thus assessed all studies at low risk of other bias.

Effects of interventions

See: Table 1; Table 2; Table 3; Table 4; Table 6; Table 7; Table 8

We presented the results for 16 comparisons for two outcomes (reduction in the level of contamination at distances less than 2 m and 2 m or more from patient's oral cavity). We combined similar interventions with similar control in the analyses (e.g. different concentrations of CHX (0.12% and 0.2%), water and distilled water as 'water'). The unit of measurement in all 16 analyses was CFUs.

We analysed the level of contamination at operator and assistant levels and omitted the patient‐level data. If the studies reported the combined data for level of contamination (i.e. mean CFUs from operator and assistant levels), we analysed it.

Wherever appropriate, we analysed similar interventions as subgroups. For example, CHX and tempered CHX and CPC, CPC+Zn+F and CPC plus domiphen bromide plus quaternary ammonium compounds.

As the active ingredient in any herbal mouthwash is the essential oil, we analysed different herbal mouthwashes and essential oil mouthwashes as subgroups.

We imputed data or calculated MDs or SDs either using the graphs or based on the available information (Table 18; Table 19; Table 20; Table 21). We imputed the P value (0.001) based on the description of results and calculated the SE in the Mohammed 1964 and Mohammed 1970 trials.

11. Data imputed in Feres 2010.

Dentist	n	Mean (mm)	SE (mm)	Meana	SEa	SDa
No intervention	15	3	1	41.7	13.9	53.83
Water	15	4	0.5	55.6	6.9	26.72
CHX	15	1	1	13.9	13.9	53.83
CPC	15	0.5	0.5	6.9	6.9	26.72
Participant	n	Mean (mm)	SE (mm)	Meana	SEa	SDa
No intervention	15	71	10	986.1	138.9	537.96
Water	15	44	10	611.1	138.9	537.96
CHX	15	15	3	208.3	41.7	161.5
CPC	15	17	4	236.1	55.6	215.34
Combined (all locations)	n	Mean (mm)	SE (mm)	Meana	SEa	SDa
No intervention	15	99	12	1375.0	166.7	645.63
Water	15	70	12	972.2	166.7	645.63
CHX	15	21	3	291.7	41.7	161.5
CPC	15	22	4.5	305.6	62.5	242.06

Data (mean and standard error (SE)) are derived from graph. SE was converted to standard deviation (SD) using the SD calculator. We used data reported at patient level, dentist level and all locations (combined). Authors also discussed the CFUs collected at the support board, which was not considered in analysis.
^aData are derived; CFU: colony‐forming unit; CHX: chlorhexidine; CPC: cetylpyridinium chloride; n: number of participants.

12. Data imputed in Joshi 2017.

Area	Mean	SE	SDa
Patient	Tempered CPC 76.4 Cold CPC 103.6 Tempered CHX 70.2 Cold CHX 102.9	± 4.08	± 12.9
Assistant	Tempered CPC 38.7 Cold CPC 47.3 Tempered CHX 38.5 Cold CHX 56.1	± 2.20	± 6.96
Operator	Tempered CPC 62.2 Cold CPC 71.5 Tempered CHX 60 Cold CHX 75.8	± 2.48	± 7.84

Data given as mean and standard error (SE); SE converted to standard deviation (SD) using SD calculator based on the sample size of 10.
^aData were derived.
CHX: chlorhexidine; CPC: cetylpyridinium chloride.

13. Data imputed in Retamal‐Valdes 2017.

Clinician	Mean (cm)	SE (cm)	Meana	SDa
No rinsing	2.1	2.4	644	736
Water	1	1.2	307	368
CPC+ZN+F	0.2	0.3	61	92
CHX	0.1	0.2	31	61
Volunteer/patient	Mean (cm)	SE (cm)	Meana	SDa
No rinsing	2.9	1.8	890	552
Water	3	1.2	920	368
CPC+ZN+F	1.3	1	399	307
CHX	1.2	0.6	368	184
Combined (all locations)	Mean (cm)	SE (cm)	Meana	SDa
No rinsing	8.2	7.5	2515	2301
Water	6.4	4.5	1963	1380
CPC+ZN+F	2.5	1.85	767	567
CHX	1.9	1	583	307

Data (mean and standard error (SE)) were derived from graph. SE was converted to standard deviation (SD) using the Review Manager 5 calculator. We used the data reported at patient level, dentist level and all locations (combined). Authors also discussed the CFU collected at the support board, which was not considered in analysis.
^aData were derived; CHX: chlorhexidine; CPC+Zn+F: cetylpyridinium chloride + zinc + fluoride.

14. Data imputed in Shetty 2013.

Site	CHX (mean ± SDa)	Distilled water (mean ± SDa)
Operator	10.35 ± 107.13	131.15 ± 107.13
Patient	1.95 ± 43.28	50.75 ± 43.28
Assistant	8 ± 100.08	120.85 ± 100.08
Site	CHX (mean ± SDa)	Essential oil mouthwash A (tea tree oil) (mean ± SDa)
Operator	10.35 ± 12.71	24.68 ± 12.71
Patient	1.95 ± 7.54	10.45 ± 7.54
Assistant	8 ± 10.9	20.29 ± 10.9
Site	Essential oil mouthwash A (tea tree oil) (mean ± SDa)	Distilled water (mean ± SDa)
Operator	24.68 ± 94.42	131.15 ± 94.42
Patient	10.45 ± 35.74	50.75 ± 35.74
Assistant	20.29 ± 89.18	120.85 ± 89.18

Data given in graph. Mean for chlorhexidine (CHX) and distilled water was given in graph. However, for essential oil mouthwash A (tea tree oil), mean was derived from digital graph analyser. Standard deviation (SD) calculated using mean and P value (P < 0.001). We used data reported at operator level, patient level and assistant level.
^aData were derived.

1. Chlorhexidine versus no rinsing

Two studies with 60 participants evaluated reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity using a 0.12% CHX preprocedural rinse compared to no rinsing (Feres 2010; Retamal‐Valdes 2017). They evaluated the level of contamination at operator level but not assistant level.

At operator level

At the operator level, because of the high heterogeneity (I² = 89%), which we could not explain, we decided not to meta‐analyse the results (Analysis 1.1; Table 1).

1.1. Analysis.

Comparison 1: Chlorhexidine versus no rinsing, Outcome 1: Reduction in the level of contamination at < 2 m

2. Chlorhexidine versus water

At operator level

Six studies with 196 participants evaluated reduction in the level of contamination in particles larger than 5 µm (droplets) at distances of less than 2 m from patient's oral cavity using a CHX preprocedural rinse compared to distilled water at operator level (Feres 2010; Gupta 2014; Nayak 2020; Nisha 2021; Retamal‐Valdes 2017; Shetty 2013). Because of the high heterogeneity (I² = 98%), which we could not explain, we decided not to meta‐analyse the results (Analysis 2.1).

2.1. Analysis.

Comparison 2: Chlorhexidine versus water, Outcome 1: Reduction in the level of contamination at < 2 m

At assistant level

Four studies with 136 participants evaluated reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity using a 0.2% CHX preprocedural rinse compared to distilled water at assistant level (Gupta 2014; Nayak 2020; Nisha 2021; Shetty 2013). Because of the high heterogeneity (I² = 96%), which we could not explain, we decided not to meta‐analyse the results (Analysis 2.1).

Bay 1993 evaluated the outcome at patient level and thus the data from this study were not included in the meta‐analysis.

Because of the high heterogeneity in these three analyses, we decided to perform sensitivity analysis by excluding studies in which the SDs were derived. However, this did not explain the heterogeneity.

Combined levels

Three studies with 80 participants evaluated reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity using a CHX preprocedural rinse compared to distilled water (Feres 2010; Reddy 2012; Retamal‐Valdes 2017). The outcome was assessed as a combination of mean CFUs at different levels (patient, operator and assistant levels) (MD –632.94 CFUs, 95% CI –1267.33 to 1.45; I² = 92%; 3 studies, 80 participants; Analysis 2.1). Because of the high heterogeneity, we decided to perform a sensitivity analysis. Feres 2010 and Retamal‐Valdes 2017 used 0.12% CHX and presented the combined data from patient and operator level whereas Reddy 2012 used 0.2% CHX and presented the combined data from all three levels. After exclusion of the data from Reddy 2012, heterogeneity was less and the meta‐analysis suggested a benefit from CHX as a preprocedural rinse compared to distilled water (MD –956.11 CFUs, 95% CI –1626.04 to –286.19; I² = 67%; 2 studies, 60 participants; Analysis 2.1). See Table 2.

Tempered chlorhexidine

One study with 20 participants evaluated reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity using tempered 0.2% CHX preprocedural rinse compared to rinsing with distilled water (Reddy 2012). The outcome was assessed as a combination of mean CFUs different levels (operator, assistant and patient levels). The results showed a benefit from the tempered CHX as a preprocedural rinse compared to distilled water (MD –101 CFUs, 95% CI –107.01 to –95.19; 1 study, 20 participants; Analysis 2.1). See Table 2.

3. Chlorhexidine versus saline

Two studies with 32 participants evaluated reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity using a 0.2% CHX preprocedural rinse compared to saline (Mohan 2016; Verma 2017). See Table 3. The outcome was assessed as mean CFUs at different levels (Analysis 3.1).

3.1. Analysis.

Comparison 3: Chlorhexidine versus saline, Outcome 1: Reduction in the level of contamination at < 2 m

At three feet away from patient's mouth

One study compared 0.2% CHX preprocedural mouth rinse with saline on contamination at distances of 3 feet from the patient's mouth (exact location of the culture plate placement was not given in the report) (MD –668.40 CFUs, 95% CI –1044.45 to –292.35; 20 participants; Analysis 3.1) (Mohan 2016).

At operator level

One study evaluated this outcome at the operator level and the meta‐analysis suggested a benefit from the 0.2% CHX preprocedural mouth rinse compared to saline (MD –21.33 CFUs, 95% CI –36.80 to –5.86; 12 participants; Analysis 3.1) (Mohan 2016).

4. Chlorhexidine versus essential oils/herbal mouthwash

Five trials compared CHX with different types of essential oil/herbal preprocedural mouth rinse for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity (Bay 1993; Gupta 2014; Nayak 2020; Shetty 2013; Suresh 2011). See Table 4. The outcome was assessed as a combination of mean CFUs at different levels (operator, assistant, pharynx, or a combination) (Analysis 4.1).

4.1. Analysis.

Comparison 4: Chlorhexidine versus essential oils or herbal mouthwash, Outcome 1: Reduction in the level of contamination at < 2 m

Three trials compared 0.2% CHX mouthwash with essential oil/herbal mouthwashes at operator level (Gupta 2014; Nayak 2020; Shetty 2013). The effect estimates at both levels showed benefit from CHX compared to essential oil/herbal mouthwash (MD –23.09 CFUs, 95% CI –34.40 to –11.78; I² = 67%; 76 participants; Analysis 4.1).

Three trials compared 0.2% CHX mouthwash with essential oil/herbal mouthwashes at assistant level (Gupta 2014; Nayak 2020; Shetty 2013). The effect estimates at both levels showed benefit from CHX compared to essential oil/herbal mouthwash (MD –12.21 CFUs, 95% CI –15.58 to –8.83; I² = 7%; 76 participants; Analysis 4.1).

One trial compared 0.2% CHX with essential oil mouthwash B at 15 cm from the participant's mouth (exact location of the culture plate placement is not given in the report) (Suresh 2011). The effect estimates showed benefit from the CHX mouthwash compared to essential oil mouthwash B (MD –44.10 CFUs, 95% CI –59.12 to –29.08; 20 participants; Analysis 4.1).

Bay 1993 compared 0.12% CHX with essential oil mouthwash C (Listerine) at pharynx level (level 2), which was considered as patient level and hence was not analysed.

5. Chlorhexidine versus povidone iodine

Three studies compared CHX with povidone iodine for reduction in level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity (Kaur 2014; Tasneem 2017; Verma 2017). See Table 6.

At operator level 

Aerobic

Two trials compared 0.2% CHX with 1% and 5% povidone iodine preprocedural mouth rinses at operator level using aerobic culture media (povidone iodine: 1%: Kaur 2014; 5%: Verma 2017). The analysis showed 95% CI crossing the line of no effect and the effect estimate was thus not robust (MD –10.75 CFUs, 95% CI –26.24 to 4.74; I² = 44%; 52 participants; Analysis 5.1). Both studies had high risk of bias and hence we did not perform a sensitivity analysis.

5.1. Analysis.

Comparison 5: Chlorhexidine versus povidone iodine, Outcome 1: Reduction in the level of contamination at < 2 m

Aerobic and anaerobic combined

Tasneem 2017 compared 0.2% CHX with povidone iodine preprocedural mouth rinses at operator level using both aerobic and anaerobic culture media (presented as combined mean CFUs). The effect estimate shows benefit from the CHX mouthwash compared with povidone iodine mouthwash (MD –4.70 CFUs, 95% CI –7.01 to –2.39; 30 participants; Analysis 5.1).

One of the studies compared CHX with povidone iodine for reduction in level of contamination in particles 5 µm or less (droplet nuclei) at distances of 2 m or more from patient's oral cavity (Kaur 2014). They compared 0.2% CHX with 1% povidone iodine preprocedural mouth rinse using aerobic and anaerobic culture media at 9 feet behind the patient. The analysis showed 95% CI crossing the line of no effect and the effect estimates are thus not robust (aerobic: MD 0.20 CFUs, 95% CI –7.28 to 7.68; 40 participants; anaerobic: MD –0.80 CFUs, 95% CI –11.65 to 10.05; 40 participants; Analysis 5.2).

5.2. Analysis.

Comparison 5: Chlorhexidine versus povidone iodine, Outcome 2: Reduction in level of contamination at ≥ 2 m

6. Chlorhexidine versus cetylpyridinium chloride

Three trials compared CHX with CPC mouthwash for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity (Feres 2010; Joshi 2017; Retamal‐Valdes 2017). See Table 7.

Tempered 0.2% chlorhexidine versus tempered 0.05% cetylpyridinium chloride

Joshi 2017 reported the effect estimates at operator and assistant levels for this comparison. The analysis showed the 95% CI crossing the line of no effect (operator: MD –2.20 CFUs, 95% CI –9.07 to 4.67; 20 participants; assistant: MD –0.20 CFUs, 95% CI –6.30 to 5.90; 20 participants; Analysis 6.1).

6.1. Analysis.

Comparison 6: Chlorhexidine versus cetylpyridinium chloride (CPC), Outcome 1: Reduction in the level of contamination at < 2 m

Cold 0.12% or 0.2% chlorhexidine versus cold 0.05% cetylpyridinium chloride

Two trials reported the effect estimates at operator level for this comparison using 0.12% (Feres 2010) and 0.2% (Joshi 2017) CHX. The analysis showed the 95% CI crossing the line of no effect (MD 4.43 CFUs, 95% CI –2.27 to 11.13; I² = 0%; 50 participants; Analysis 6.1). Joshi 2017 reported the effect estimate at assistant level only, which showed benefit of using cold CPC (MD 8.80, 95% CI 2.70 to 14.90;  20 participants; Analysis 6.1).

Tempered 0.2% chlorhexidine versus cold 0.05% cetylpyridinium chloride

Joshi 2017 reported the effect estimates at operator and assistant levels for this comparison. The meta‐analyses showed benefit in the tempered CHX group at both the levels (operator: MD –11.50 CFUs, 95% CI –18.37 to –4.63; 20 participants; assistant: MD –8.80 CFUs, 95% CI –14.90 to –2.70; 20 participants; Analysis 6.1).

Cold 0.2% chlorhexidine versus tempered 0.05% cetylpyridinium chloride

Joshi 2017 reported the effect estimates at operator and assistant levels for this comparison. The meta‐analyses showed benefit in the tempered CPC group at both the levels (operator: MD 13.60 CFUs, 95% CI 6.73 to 20.47; 20 participants; assistant: MD 17.40 CFUs, 95% CI 11.30 to 23.50; 20 participants; Analysis 6.1).

Chlorhexidine 0.12% versus cetylpyridinium chloride plus zinc plus sodium fluoride

Retamal‐Valdes 2017 reported the effect estimates at operator level for this comparison. The analysis showed 95% CI crossing the line of no effect (MD –30.00 CFUs, 95% CI –85.86 to 25.86; 30 participants; Analysis 6.1).

7. Tempered chlorhexidine versus non‐tempered chlorhexidine

Two trials compared tempered 0.2% CHX with non‐tempered CHX for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity (Joshi 2017; Reddy 2012). See Table 8.

Joshi 2017 reported the effect estimates at operator and assistant levels for this comparison. The meta‐analyses showed benefit in the tempered CHX group at operator and assistant levels (operator: MD –15.80 CFUs, 95% CI –22.67 to –8.93; 20 participants; 1 study; assistant: MD –17.60 CFUs, 95% CI –23.70 to –11.50; 20 participants; Analysis 7.1).

7.1. Analysis.

Comparison 7: Tempered chlorhexidine versus non‐tempered chlorhexidine, Outcome 1: Reduction in the level of contamination at < 2 m

Reddy 2012 reported the effect estimate as combined mean CFUs (patient, operator and assistant levels). The meta‐analyses showed benefit in the tempered CHX group (MD –10.80 CFUs, 95% CI –15.15 to –6.45; 20 participants; 1 study; Analysis 7.1).

8. Cetylpyridinium chloride versus no rinsing

One study compared 0.05% CPC with no rinsing  (Feres 2010), and another study compared CPC+Zn+F with no rinsing (Retamal‐Valdes 2017). Two studies compared, CPC plus domiphen bromide plus quaternary ammonium compounds with no rinsing (Mohammed 1964; Mohammed 1970). All comparisons were for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity. Feres 2010 and Retamal‐Valdes 2017 reported the mean CFUs at the operator level. The other two studies combined the CFUs and expressed the outcomes as count data. Therefore, we decided to use the generic inverse variance method to analyse the data. See Table 9 for summary of findings.

At the operator level, Feres 2010 and Retamal‐Valdes 2017 studies showed benefit from using CPC or CPC+Zn+F versus no rinsing (CPC: MD –34.80 CFUs, 95% CI –65.92 to –3.68; 30 participants; 1 study; CPC+Zn+F: MD –583.00 CFUs, 95% CI –958.36 to –207.64; 30 participants; 1 study; Analysis 8.1).

8.1. Analysis.

Comparison 8: Cetylpyridinium chloride (CPC) versus no rinsing, Outcome 1: Reduction in level of contamination at < 2 m [CFUs]

The meta‐analysis of Mohammed 1964 and Mohammed 1970 showed benefit from using CPC plus domiphen bromide plus quaternary ammonium compounds (MD –0.75 CFUs, 95% CI –1.32 to –0.18; 200 participants; I² = 60%; Analysis 8.1).

9. Cetylpyridinium chloride versus water

Feres 2010 compared 0.05% CPC with water rinsing, and Retamal‐Valdes 2017 compared CPC+Zn+F with water rinsing. Mohammed 1964 compared CPC plus domiphen bromide plus quaternary ammonium compounds with water rinsing. All comparisons were for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity. Feres 2010 and Retamal‐Valdes 2017 reported the mean CFUs at the operator level. Mohammed 1964 combined the CFUs and expressed the outcomes as count data. Therefore, we decided to use the generic inverse variance method to analyse the data. See Table 10 for summary of findings.

At the operator level, two trials showed benefit from using CPC (Feres 2010) and CPC+Zn+F (Retamal‐Valdes 2017) (CPC: MD –48.70 CFUs, 95% CI –67.82 to –29.58; 1 study, 30 participants; CPC+Zn+F: MD –246.00 CFUs, 95% CI –437.96 to –54.04; 1 study, 30 participants; Analysis 9.1).

9.1. Analysis.

Comparison 9: Cetylpyridinium chloride (CPC) versus water, Outcome 1: Reduction in level of contamination at < 2 m [CFUs]

Mohammed 1964 showed benefit from using CPC plus domiphen bromide plus quaternary ammonium compounds (MD –0.78 CFUs, 95% CI –1.24 to –0.31; 105 participants; Analysis 9.1).

10. Tempered cetylpyridinium chloride versus cold cetylpyridinium chloride

Joshi 2017 compared tempered 0.05% CPC with cold 0.05% CPC for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity at operator and assistant levels. See Table 11 for summary of findings.

The effect estimates showed benefit from using the tempered CPC at both the levels (operator: MD –9.30 CFUs, 95% CI –16.17 to –2.43; 20 participants; assistant: MD –8.60 CFUs, 95% CI –14.70 to –2.50; 20 participants; Analysis 10.1).

10.1. Analysis.

Comparison 10: Tempered cetylpyridinium chloride (CPC) versus cold CPC, Outcome 1: Reduction in the level of contamination at < 2 m

11. Povidone iodine versus saline

 Verma 2017 compared 5% povidone iodine with saline as preprocedural mouth rinse for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity at operator level. See Table 12 for a summary of findings.

The effect estimates showed benefit from using the povidone iodine (MD –16.50 CFUs, 95% CI –32.65 to –0.35; 12 participants; Analysis 11.1).

11.1. Analysis.

Comparison 11: Povidone iodine versus saline, Outcome 1: Reduction in the level of contamination at < 2 m

12. Essential oil/herbal mouthwash versus water

Three studies compared mouthwashes containing different essential oils versus water at operator and assistant level for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity (Gupta 2014; Nayak 2020; Shetty 2013). One study compared another mouthwash containing essential oils versus water and reported CFUs at the different levels using Andersen's air sampler (Bay 1993). Level 2 (pharynx level) is considered as patient level and was not analysed.

At both the operator and assistant levels, because of the high heterogeneity (operator: I² = 98%; assistant: I² = 99%), which we could not explain, we decided not to meta‐analyse the results.

See Analysis 12.1 and Table 13 for a summary of findings.

12.1. Analysis.

Comparison 12: Essential oils/herbal mouthwash versus water, Outcome 1: Reduction in the level of contamination at < 2 m

13. Chlorhexidine versus ozonated water

One study of 40 participants comparing 0.2% CHX rinsing versus ozonated water rinsing reported two outcomes: reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity at operator level using aerobic culture method and reduction in the level of contamination in particles 5 µm or less (droplet nuclei) at distances 2 m or more from patient's oral cavity using aerobic and anaerobic culture methods (Kaur 2014). See Table 14 for a summary of findings.

For reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity, the study showed benefit from CHX rinsing at operator level compared to ozonated water (MD –17.80 CFUs, 95% CI –33.70 to –1.90). However, for reduction in the level of contamination in particles 5 µm or less (droplet nuclei) at distances 2 m or more from patient's oral cavity, the 95% CI crossed the line of no effect for aerobic and anaerobic types of culture methods (aerobic: MD –12.30 CFUs, 95% CI –27.12 to 2.52; anaerobic: MD –3.40 CFUs, 95% CI –14.66 to 7.86; Analysis 13.1; Analysis 13.2).

13.1. Analysis.

Comparison 13: Chlorhexidine versus ozonated water, Outcome 1: Reduction in the level of contamination at < 2 m

13.2. Analysis.

Comparison 13: Chlorhexidine versus ozonated water, Outcome 2: Reduction in the level of contamination at ≥ 2 m

14. Povidone iodine versus ozonated water

One study of 40 participants comparing 1% povidone iodine rinsing versus ozonated water rinsing reported two outcomes: reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity at operator level using an aerobic culture method and reduction in the level of contamination in particles 5 µm or less (droplet nuclei) at distance 2 m or more from patient's oral cavity using aerobic and anaerobic culture methods (Kaur 2014). See Table 15 for a summary of findings.

The study found no benefit for either outcome from povidone iodine rinsing at operator level compared to ozonated water as the 95% CI crossed the line of no effect (operator level at less than 2 m: MD 3.50 CFUs, 95% CI –17.10 to 24.10; more than 2 m with aerobic culture method: MD –12.50 CFUs, 95% CI –26.33 to 1.33; more than 2 m with anaerobic culture method: MD –2.60 CFUs, 95% CI –9.54 to 4.34; Analysis 14.1; Analysis 14.2).

14.1. Analysis.

Comparison 14: Povidone iodine versus ozonated water, Outcome 1: Reduction in the level of contamination at < 2 m

14.2. Analysis.

Comparison 14: Povidone iodine versus ozonated water, Outcome 2: Reduction in the level of contamination at ≥ 2 m

15. Chlorhexidine versus boric acid

One study of 60 participants compared 0.12% CHX versus 0.75% boric acid as preprocedural mouth rinse for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity at operator level and assistant level (Nisha 2021). The effect estimates showed benefit from using the CHX mouth rinse compared to boric acid mouth rinse (operator level: MD –26.60 CFUs, 95% CI –28.24 to –24.96; assistant level: MD –8.03 CFUs, 95% CI –9.65 to –6.41; Analysis 15.1). See Table 16 for a summary of findings.

15.1. Analysis.

Comparison 15: Chlorhexidine versus boric acid, Outcome 1: Reduction in the level of contamination at < 2 m

16. Boric acid versus water

One study of 60 participants compared 0.75% boric acid versus water as preprocedural mouth rinse for reduction in the level of contamination in particles larger than 5 µm (droplets) at distances less than 2 m from patient's oral cavity (Nisha 2021). The effect estimates showed benefit from using the boric acid mouth rinse compared to water (operator: MD –29.30 CFUs, 95% CI –32.65 to –25.95; assistant: MD –14.04 CFUs, 95% CI –16.47 to –11.61; Analysis 16.1). See Table 17 for a summary of findings.

16.1. Analysis.

Comparison 16: Boric acid versus water, Outcome 1: Reduction in the level of contamination at < 2 m

Discussion

Summary of main results

We found 17 studies that evaluated 16 comparisons in this Cochrane Review. None of the studies measured the incidence of infection of dental healthcare providers. Sixteen studies reported the results for reduction in the level of bacterial contamination by particles larger than 5 µm (droplets) in the operative environment.

Two trials compared CHX versus no rinsing at operator (dentist) level. One of the two trials showed beneficial effect; however, the 95% CI crossed the midline in one trial and the meta‐analysis showed high heterogeneity (Table 1).

Five trials compared CHX versus water at operator and assistant level but showed high heterogeneity that prevented meta‐analysis. All trials showed a beneficial effect, but the MDs ranged from –1380 CFUs to –16 CFUs (Table 2).

One trial compared CHX versus saline at operator level and found a beneficial effect in the CHX group to reduce the level of contamination (MD –21.33 CFUs, 95% CI –36.80 to –5.86; 12 participants) (Table 3).

Five trials compared CHX versus three different essential oils. At operator level, CHX reduced the level of contamination more than essential oil/herbal mouthwash (MD –23.09 CFUs, 95% CI –34.40 to –11.78; 3 studies, 76 participants; very low‐certainty evidence) and at assistant level (MD –12.21 CFUs, 95% CI –15.58 to –8.83; 3 studies, 76 participants; very low‐certainty evidence) (Table 4).

There was no evidence of an effect of CHX on contamination at less than 2 m compared to povidone iodine in two trials measured as aerobic cultures only (MD –10.75 CFUs, 95% CI –26.24 to 4.74; 52 participants; very low‐certainty evidence), but there was a small effect when measured with combined aerobic and anaerobic cultures in a third trial (MD –4.70 CFUs, 95% CI –7.01 to –2.39; 30 participants; very low‐certainty evidence). There was also no effect at more than 2 m distance measured in aerobic or anaerobic cultures (aerobic: MD 0.20 CFUs, 95% CI –7.28 to 7.68; 1 study, 40 participants; anaerobic: MD –0.80 CFUs, 95% CI –11.65 to 10.05; 1 study, 40 participants; both very low‐certainty evidence) (Table 6).

Three trials compared CHX to CPC or CPC+Zn+F. There was no evidence of a difference between CHX and CPC at operator level in two trials (MD 4.43 CFUs, 95% CI –2.27 to 11.13; 50 participants; very low‐certainty evidence), but there was an effect at the assistant level (MD 8.80 CFUs, 95% CI 2.70 to 14.90; 20 participants; very low‐certainty evidence). There was no evidence of an effect compared to CPC+Zn+F at operator level (MD –30.00 CFUs, 95% CI –85.86 to 25.86; 30 participants; very low‐certainty evidence). One trial compared various combinations of tempered CHX and CPC and found that the tempered rinse was better than the cold regardless of the content (Table 7).

Tempered (47 °C) CHX reduced contamination more than non‐heated CHX at operator level in one study (MD –15.80 CFUs, 95% CI –22.67 to –8.93; 20 participants; very low‐certainty evidence) with similar results for the assistant level and for the combined operator and assistant level in another study (Table 8).

None of the 17 studies provided data on costs or change of microbiota in the patient's mouth or adverse events such as transient discolouration, altered taste, allergic reaction, hypersensitivity, or acceptability and feasibility of the intervention to patients.

The certainty of the evidence was low to very low for all comparisons due to risk of bias, imprecision, inconsistency, or a combination of these.

Overall completeness and applicability of evidence

‐The primary objective of this review was to measure the incidence of infection among dental healthcare providers who were exposed to aerosols. We understand that it is difficult to conduct trials to focus on this primary objective. Dental healthcare providers could become infected in many ways other than aerosols produced during the AGPs in a dental clinic and practically it is difficult to differentiate the origin of infection.

All included studies reported reduction in the level of contamination in the operative environment at operator and assistant levels. The outcome measure was bacterial CFUs, which were counted in an aerobic or anaerobic culture media or both. However, none of these studies checked for the viral or fungal organisms in the aerosols. This could be because of the difficulties in viral culture or comparatively lower prevalence of aerosol‐borne fungal infections. The CFU is a surrogate measure for this outcome and may not represent the reduction of aerosol in the operative environment. In addition to this, we found no information on minimally important clinical difference (MICD) for CFUs in order to determine the effectiveness of the preprocedural mouth rinse interventions. For these reasons, we are unsure how these results can be interpreted.

The acceptable bacterial load (total viable count) in dental unit water lines must be between 100 CFU/mL and 200 CFU/mL (DoH 2013), and a heterotrophic bacterial load of 500 CFU or less for infection control in dental healthcare system (ADA 1996; CDC 2003). However, none of the included studies tested or reported this.

One study used active aerosol sampling (Bay 1993). The other 16 studies used passive aerosol sampling where the aerosols drop down to settle on the culture media. Such measurements are useful in a surgical theatre where wound contamination is possible due to the contaminated aerosols. However, in a dental clinic, it would be more apt to measure both the active aerosols (using devices such as slit sampler and the N6‐Andersen sampler in combination with DG18 (dichloran 18% glycerol agar) and MEA (malt extract agar) (Pasquarella 2000)) and passive aerosols.

There is no standardisation of outcome measurement methods. The most commonly agreed measure, index of microbial air contamination (IMA), was not established until 2000. The IMA for a dental clinic is 25 (which equates to 10 CFU/dm²/hour to 39 CFU/dm²/hour), which is a good performance indicator at a high‐risk venue such as a dental clinic. The IMA is based on the microbial count on Petri dishes of 9 cm in diameter left open to the air for one hour, 1 m from the floor, at least 1 m away from walls or any obstacle (Pasquarella 2000). Even after 2000, many trials did not use this standard. The varied duration, height and distances used in the included studies could be one of the possible reasons for high heterogeneity in meta‐analyses in our review.

Patarakulwiwat 2018, in their experimental study, showed that magnetostrictive ultrasonic scalers produce more droplets compared to piezoelectric scalers. As we included four studies using each type of scaler, we explored the possibility of heterogeneity due to the difference in the type of scaler. However, this was not the reason for heterogeneity in the meta‐analyses in this review.

All 17 included studies tested the aerosols generated during ultrasonic scaling, tooth preparation procedures using high‐speed air rotor instruments or air polishing. No studies tested other AGPs such as cavity preparation of carious teeth or surgical extractions. Procedures such as impressions or intraoral radiography that can induce cough were also not tested. Therefore, it is difficult to extrapolate the results of this review to all procedures in dentistry.

Only one included study tested the contamination due to particles 5 µm or less (droplet nuclei) at 2 m or more from patient's oral cavity. Dental surgeon and dental assistants are usually seated at less than 2 m from the patient's mouth and it is probable that this is the reason few studies have tested the contamination at greater distances.

There is also a possibility of contamination in the dental operative environment that could have been cultured along with the bacteria from the aerosols. Only three included studies had fumigated the rooms where the procedures were carried out (Joshi 2017; Nisha 2021; Verma 2017). Another possibility of contamination is through the bacteria present in the waterlines. Only five included studies addressed this issue by flushing the water for few minutes before starting the AGP (Bay 1993; Feres 2010; Fine 1993a; Nayak 2020; Shetty 2013). This issue of contamination could have been investigated by using the control culture media (baseline data). However, only seven included studies reported such baseline data (Bay 1993; Feres 2010; Fine 1993a; Kaur 2014; Reddy 2012; Retamal‐Valdes 2017; Verma 2017).

Although we had 17 trials included in this review, most of the comparisons were based on the results of single trials and could not be combined in meta‐analyses. It appears that tempered or tempered CHX and CPC mouthwashes show better reduction in contamination compared with colder versions of the same mouthwashes in individual trials. However, the evidence was of very low certainty for all comparisons. High‐quality RCTs are required to test the contamination of the dental operative environment with different micro‐organisms (aerobic and anaerobic bacteria, fungi and viruses).

We could not meta‐analyse a cross‐over trial as the authors did not report the data from the first phase of the study (Fine 1993a). We could not include Bay 1993 in the meta‐analysis as the aerosols were sampled directly from the patient's oropharynx and thus did not measure the contamination at operator or assistant level.

Quality of the evidence

The certainty of the evidence for all comparisons was low or very low for the considered outcomes. Most comparisons were evaluated by single trials with a relatively small number of participants and low event rates. We downgraded the certainty of the evidence mainly for high/unclear risk of bias, imprecision and inconsistency.

Potential biases in the review process

There is a possibility of unpublished data that we could have missed in this review. The Analyses 1.1.2 (Analysis 1.1), Analysis 2.1, Analysis 3.1.1 (Analysis 3.1) and 5.1.1 (Analysis 5.1) showed considerable heterogeneity and we were unable to explain this. There were huge differences in the CFUs between the included studies, which could be related multiple factors such as varying inclusion criteria of participants in the studies, oral hygiene status of those participants, different rinsing times, different AGPs, waterline contamination, varying fallow time and disinfection of dental clinic. Moreover, the included studies did not provide any details on the variation in the duration and speed of using high‐speed rotary instruments or ultrasonic scalers between different dentists and combination of AGPs in a single dental procedure (e.g. use of 3‐in‐1 syringe with both air and water and use of high‐speed rotary instruments), which could influence the quantity of droplets and droplet nuclei generated.

Agreements and disagreements with other studies or reviews

There are several systematic reviews on the use of preprocedural mouthwashes to reduce viral load in dental aerosols.

Samaranayake 2021 investigated the efficacy of preprocedural rinses, high‐volume evacuators and rubber dam in reducing bioaerosols produced during AGPs. They included 17 clinical trials, of which seven tested the efficacy of preprocedural mouth rinses (we included three of these studies in our review (Feres 2010; Fine 1993a; Retamal‐Valdes 2017) and excluded four (Dawson 2016; Fine 1992; Klyn 2001; Logothetis 1995)). All but one study included in their review showed a significant bacterial reduction after preprocedural rinsing with either CHX, CPC or essential oils. In contrast to our review, their review analysed the effect of the interventions at patient level also. We also analysed the outcome at various distances from the point of aerosol generation.

Mohd‐Said 2021 conducted a systematic review on the effectiveness of preprocedural mouth rinses in reducing aerosol contamination during periodontal prophylaxis. The review included 21 RCTs and reported significant reductions in bacterial contaminations measured in CFUs. Unlike our review, Mohd‐Said 2021 included split‐mouth trials and cross‐over trials (although cross‐over trials were not excluded from our review, we planned to include only first‐period data). We judged two of the included studies in that review to be non‐RCTs (Paul 2020; Rajachandrasekaran 2019), and it had a cross‐over trial that we excluded as the cross‐over sequence was not randomised (Santos 2014). The review authors used the Cochrane RoB 2 tool.

The Moosavi 2020 review included five original studies that used mouth washes as preprocedural or as a regular home use mouth rinse, after brushing. The review also included studies that used mouthwashes in people with COVID‐19. The outcome of interest was the reduction of viral load in saliva in people using mouthwashes, reduction of viral load in people with COVID‐19 and prevention of ventilator‐assisted pneumonia. Most included studies used C31G, povidone iodine and CHX as mouth rinses. Other mouth rinses were not discussed in this review. This is in contrast to our review which included all the other mouth rinses. The authors concluded that the use of mouthwash before dental procedures reduces the risk of transmission of the virus through the aerosol and saliva to the dental team and the use of this mouthwash in people with COVID‐19 improves systemic problems associated with oral microbial flora.

A systematic review by Marui 2019 also investigated the effect of preprocedural mouth rinses on the reduction of CFUs in dental aerosols. It included 13 RCTs that tested the efficacy of CHX, essential oils, CPC and herbal products. Meta‐analysis of 12 studies showed that mouth rinses with CHX, essential oils and CPC significantly reduced percentage of CFU reduction. The authors concluded that there is moderate evidence that preprocedural mouth rinses significantly reduce the number of micro‐organisms in the dental aerosols. In contrast to our review, this meta‐analysis did not include subgroups at various levels such as assistant, operator or patient, neither did they considered distance. They used 'mean percentage of CFU reduction' as the outcome measure and did not explain at which levels they had taken the CFU counts, which could be the reason for disagreement with our results.

Two Cochrane Reviews carried out by Burton and colleagues focused specifically on COVID‐19. They aimed to evaluate the RCT evidence for patient use of antimicrobial mouth washes before any AGP to prevent possible transmission of COVID‐19 to healthcare workers (Burton 2020a; Burton 2020b). They identified no trials, but these reviews are currently being updated.

Authors' conclusions

Implications for practice.

None of the included studies reported incidence of infection among dental healthcare providers. The analyses suggest that chlorhexidine, especially when tempered, and other mouth rinses may reduce bacterial contamination in aerosols, but it is not possible to draw any reliable conclusions because we have only low‐ to very low‐certainty evidence and we do not know how colony‐forming unit (CFU) measurement relates to infection risk. None of the included trials tested the reduction in level of viral or fungal contamination in droplets or aerosols. Overall, we are unable to draw conclusions regarding whether there is a role for preprocedural mouth rinses in reducing infection risk or the possible superiority of one preprocedural rinse over another.

Implications for research.

Research could determine the most effective methods to reduce contaminated aerosols generated during dental procedures (Group A, B and C aerosol‐generating procedures (AGPs); SDCEP 2021) by conducting well‐planned randomised controlled trials (RCTs) including the outcomes developed through any of the core outcome consortiums such as COMET (COMET 2020) and reporting following CONSORT 2010 recommendations. 

In designing such clinical trials, we suggest the following be considered.

Evidence:

• trials focusing on testing similar mouth rinses (concentration and dose);

• trials focusing on measuring contamination through droplets and droplet nuclei;

• studies measuring patient‐reported outcomes (acceptability and feasibility) and cost‐effectiveness.

Population:

• trials testing different types of AGPs (Group A, B and C (SDCEP 2021));

• trials of participants' head position while conducting the AGPs to allow standardisation and reporting.

Intervention:

• focusing on similar mouth rinses used in earlier studies such as chlorhexidine 0.2% rinsing for one minute. This will supplement the existing evidence base allowing us to draw more robust conclusions;

• methods to eliminate all possible contamination such as fumigation of dental operative environment and waterline disinfection;

• tempered mouthwashes compared with the colder versions to evaluate the role of temperature;

• standardisation of participant inclusion criteria, oral hygiene status, rinsing time, fallow time and disinfection methods.

Comparison:

• trials comparing the active intervention to rinsing with saline or water as the best placebo.

Outcomes:

• testing contamination of droplets near the operating dental surgeon and dental assistant seating positions rather than in other different directions;

• testing contamination of aerosols at distances further than 2 m;

• undertaking a consensus exercise to establish what to measure as the contamination outcome and how it should be measured, for example through a COMET initiative. This could include active air sampling and the standard index of microbial air contamination;

• experiments or calculations on how contamination outcomes can be transformed to reflect infection risk.

History

Protocol first published: Issue 12, 2020

Appendices

Appendix 1. Cochrane Oral Health's Trials Register search strategy  

Cochrane Oral Health’s Trials Register is available via the Cochrane Register of Studies. For information on how the register is compiled, see https://oralhealth.cochrane.org/trials 

1          MESH DESCRIPTOR Air Microbiology AND INREGISTER
2          MESH DESCRIPTOR Air Pollution, Indoor AND INREGISTER
3          MESH DESCRIPTOR Aerosols AND INREGISTER
4          MESH DESCRIPTOR Inhalation Exposure AND INREGISTER
5          (aerosol* or bioaerosol*) AND INREGISTER 
6          (droplet* or splatter* or spatter* or microbe* or bacillus or germ* or microorganism* or virus* or viral or coronavirus* or COVID* or "middle east? respiratory syndrome*" or MERS or MERS‐CoV or "camel flu" or SARS or "sudden acute respiratory syndrome*" or "Wuhan virus*" or 2019‐nCoV or SARS‐CoV‐2 or SARS‐CoV or SARS‐CoV‐1 or SARS‐1) AND INREGISTER
7          (air near5 (pollut* or quality or impur*)) AND INREGISTER
8          #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7
9          MESH DESCRIPTOR Mouthwashes EXPLODE ALL AND INREGISTER
10        (mouthwash* or gargl* or mouthrins*) AND INREGISTER
11        ((oral or mouth or larynx* or pharynx* or intraoral) and (irrigat* or lavag* or wash* or rins* or decontaminat* or mist or clean*)) AND INREGISTER          
12        MESH DESCRIPTOR Chlorhexidine EXPLODE ALL AND INREGISTER
13        MESH DESCRIPTOR Povidone‐Iodine EXPLODE ALL AND INREGISTER
14        MESH DESCRIPTOR Cetylpyridinium EXPLODE ALL AND INREGISTER 
15        MESH DESCRIPTOR Hexetidine EXPLODE ALL AND INREGISTER
16        MESH DESCRIPTOR Anti‐Infective Agents, Local EXPLODE ALL AND INREGISTER
17        MESH DESCRIPTOR Hydrogen Peroxide EXPLODE ALL AND INREGISTER
18        MESH DESCRIPTOR Carbamide Peroxide EXPLODE ALL AND   INREGISTER
19        MESH DESCRIPTOR Triclosan EXPLODE ALL AND INREGISTER
20        MESH DESCRIPTOR Oils, Volatile EXPLODE ALL AND INREGISTER
21        MESH DESCRIPTOR Plant oils EXPLODE ALL AND INREGISTER
22        MESH DESCRIPTOR Plant Extracts EXPLODE ALL AND INREGISTER
23        MESH DESCRIPTOR Menthol AND INREGISTER
24        MESH DESCRIPTOR Lavandula AND INREGISTER
25        MESH DESCRIPTOR Thymus plant AND INREGISTER
26        MESH DESCRIPTOR Mentha piperita AND INREGISTER
27        MESH DESCRIPTOR Eugenol AND INREGISTER
28        MESH DESCRIPTOR Cinnamomum verum AND INREGISTER
29        MESH DESCRIPTOR Muramidase AND INREGISTER
30        MESH DESCRIPTOR Lactoferrin AND INREGISTER
31        MESH DESCRIPTOR Glucose oxidase AND INREGISTER 
32        MESH DESCRIPTOR Lactoperoxidase AND INREGISTER 
33        MESH DESCRIPTOR Benzethonium AND INREGISTER
34        MESH DESCRIPTOR Teas, Herbal AND INREGISTER
35        MESH DESCRIPTOR Cymbopogon AND INREGISTER
36        MESH DESCRIPTOR Sesame Oil AND INREGISTER
37        (povidone or chlorhexidine or CHX or PVP or Polyvinylpyrrolidone or Betadine* or Providine* or Disadine* or Isodine* or Pharmadine* or Alphadine* or Betaisodona or Tubulicid or Novalsan or Sebidin or MK‐412A or MK412A)  AND INREGISTER         
38        (Chlorhexamed or Corsodyl or Curasept or Dyna‐Hex or Eludril or Gibitan or Hexidine or Hibiclens or Hibident or Hibiscrub or Hibisol or Hibitane or Peridex or avagard)  AND INREGISTER
39        (Hexadecylpyridinium or Cetylpyridium or Biosept or Ceepryn or Cetamium or Catamium or Sterogenol or Dobendan or Merocets or Pristacin or Pyrisept or Angifonil or Cetylyre)  AND INREGISTER
40        (Hexigel or Steri‐sol or "Steri sol" or Hextril or Oraldine or Oralspray or Hexoral or Bactidol or Elsix or Duranil or Doreperol or Hexetidine) AND INREGISTER
41        (Hydrogen Peroxide or H2O2 or Hydroperoxide or Superoxol or Oxydol or Perhydrol or Urea Peroxide or Perhydrol Urea) AND INREGISTER         
42        (Methyl salicylate or methylsalicylate or Rheumabal or Metsal Liniment or Hewedolor or Linsal) AND INREGISTER
43        (Tricolsan or Hydroxydiphenyl or trichlorodiphenyl or Clearasil or Cliniclean or Irgasan or Trisan or Oxy Skin Wash or pHisoHex or Sapoderm or Tersaseptic or Aquasept or Ster‐Zac or Manusept or Microshield) AND INREGISTER
44        ((irrigat* or rins* or wash* or lavag* or intraoral* or topical) and (antimicrobial or anti‐microbial or disinfect* or antisept* or anti‐infect* or herbal)) AND INREGISTER
45        ("essential oil*" or "plant oil*" or menthol or menthyl or (mint near2 oil*) or lavender or thyme or peppermint or "mentha piperita" or eugenol or eucalyptus or "blue gum*" or cajeput or clove or cinnamon) AND INREGISTER
46        (muramidase or lysozyme* or leftose or lactoferrin or lactotransferrin or "glucose oxidase" or lactoperoxidase or "saliva substitute") AND INREGISTER
47        (Listerine or Biotene) AND INREGISTER
48        ("chlorine dioxide" or "Benzethonium chloride" or "Bencetonium Chloride" or "Formula Magic" or "Hyamine 1622" or "Orchid Fresh II" or Phemeride or Phemerol or Phemethryn or Puri‐Clens or Quatrachlor or Solamin or "Vital Oxide")  AND INREGISTER
49        ("zinc salt*" or "green tea" or "lemon grass" or lemongrass or citronella or "Cymbopogon nardus" or "Andropogon nardus" or sesame or Triphala or Ela) AND INREGISTER
50        #9 OR #10 OR #11 OR #12 OR #13 OR #14 OR #15 OR #16 OR #17 OR #18 OR #19 OR #20 OR #21 OR #22 OR #23 OR #24 OR #25 OR #26 OR #27 OR #28 OR #29 OR #30 OR #31 OR #32 OR #33 OR #34 OR #35 OR #36 OR #37 OR #38 OR #39 OR #40 OR #41 OR #42 OR #43 OR #44 OR #45 OR #46 OR #47 OR #48 OR #49
51        #8 AND #50

Appendix 2. Cochrane Central Register of Controlled Clinical Trials (CENTRAL) search strategy  

1          MESH DESCRIPTOR dentistry EXPLODE ALL AND CENTRAL:TARGET 
2          MESH DESCRIPTOR dental facilities EXPLODE ALL AND CENTRAL:TARGET
3          MESH DESCRIPTOR infection control, dental AND CENTRAL:TARGET
4          MESH DESCRIPTOR dentists EXPLODE ALL AND CENTRAL:TARGET
5          MESH DESCRIPTOR dental staff AND CENTRAL:TARGET
6          MESH DESCRIPTOR Dental Auxiliaries EXPLODE ALL AND CENTRAL:TARGET
7          (dental or dentist* or hygienist*) AND CENTRAL:TARGET
8          ((oral or maxillofacial) and (care* or procedure* or surgery or surgical or medicine)) AND CENTRAL:TARGET  
9          orthodonti* AND CENTRAL:TARGET
10        periodont*  AND CENTRAL:TARGET
11        (tooth or teeth or gum* or endodont* or plaque* or pulpotom* or pulpectom* or "cavity      prep*" or molar* or bicuspid* or premolar* or pre‐molar* or incisor* or canine* or eyetooth or eyeteeth or cuspid*) AND CENTRAL:TARGET
12        ((scal* near2 polish*) or "root canal" or (root near6 resect*) or (root* near3 planing) or apicectom* or apicoectom*) AND CENTRAL:TARGET
13        ((root* or periodont* or dental or subgingiv* or gingiv* or supragingiv*) and (scale or scaling or scaler* or curettage))  AND CENTRAL:TARGET
14        MESH DESCRIPTOR Dental High‐Speed Equipment AND CENTRAL:TARGET
15        ("high speed air rotor*" or "low speed handpiece*" or "low speed hand piece*" or micromotor* or "turbine handpiece*" or "electrosurgery unit" or "air polisher*" or "prophy angle*" or "air‐water syringe*" or "high speed hand piece*" or "high speed handpiece*" or "three‐way air syringe*" or "threeway air syringe*" or "ultrasonic scaler*" or "hard‐tissue laser*" or "dental drill*" or "piezo unit*" or "piezo hand piece*" or "piezo handpiece*" or "rotary instrument*" or "air abrasion" or "water spray*")  AND CENTRAL:TARGET
16        #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10 OR #11 OR #12 OR #13 OR #14 OR #15
17        MESH DESCRIPTOR Air microbiology AND CENTRAL:TARGET
18        MESH DESCRIPTOR Air Pollution, Indoor AND CENTRAL:TARGET
19        MESH DESCRIPTOR Aerosols AND CENTRAL:TARGET
20        MESH DESCRIPTOR Inhalation Exposure AND CENTRAL:TARGET
21        (aerosol* or bioaerosol*)  AND CENTRAL:TARGET
22        (droplet* or splatter* or spatter* or microbe* or bacillus or germ* or microorganism* or virus* or viral or coronavirus* or COVID* or "middle east? respiratory syndrome*" or MERS or MERS‐CoV or "camel flu" or SARS or "sudden acute respiratory syndrome*" or "Wuhan virus*" or 2019‐nCoV or SARS‐CoV‐2 or SARS‐CoV or SARS‐CoV‐1 or SARS‐1) AND CENTRAL:TARGET
23        (air near5 (pollut* or quality or impur*))  AND CENTRAL:TARGET
24        #17 OR #18 OR #19 OR #20 OR #21 OR #22 OR #23
25        MESH DESCRIPTOR Mouthwashes EXPLODE ALL AND CENTRAL:TARGET
26        (mouthwash* or gargl* or mouthrins*)  AND CENTRAL:TARGET   4319
27        ((oral or mouth or larynx* or pharynx* or intraoral) and (irrigat* or lavag* or wash* or rins* or decontaminat* or mist or clean*)) AND CENTRAL:TARGET
28        MESH DESCRIPTOR Chlorhexidine EXPLODE ALL AND CENTRAL:TARGET
29        MESH DESCRIPTOR Povidone‐Iodine EXPLODE ALL AND CENTRAL:TARGET
30        MESH DESCRIPTOR Cetylpyridinium EXPLODE ALL AND CENTRAL:TARGET
31        MESH DESCRIPTOR Hexetidine EXPLODE ALL AND CENTRAL:TARGET
32        MESH DESCRIPTOR Anti‐Infective Agents, Local EXPLODE ALL AND CENTRAL:TARGET
33        MESH DESCRIPTOR Hydrogen Peroxide EXPLODE ALL AND CENTRAL:TARGET
34        MESH DESCRIPTOR Carbamide Peroxide EXPLODE ALL AND CENTRAL:TARGET     
35        MESH DESCRIPTOR Triclosan EXPLODE ALL AND CENTRAL:TARGET
36        MESH DESCRIPTOR Oils, volatile EXPLODE ALL AND CENTRAL:TARGET
37        MESH DESCRIPTOR Plant oils EXPLODE ALL AND CENTRAL:TARGET           
38        MESH DESCRIPTOR Plant extracts EXPLODE ALL AND CENTRAL:TARGET
39        MESH DESCRIPTOR Menthol EXPLODE ALL AND CENTRAL:TARGET
40        MESH DESCRIPTOR Lavandula EXPLODE ALL AND CENTRAL:TARGET
41        MESH DESCRIPTOR Thymus plant AND CENTRAL:TARGET
42        MESH DESCRIPTOR Mentha piperita AND CENTRAL:TARGET
43        MESH DESCRIPTOR Eugenol AND CENTRAL:TARGET
44        MESH DESCRIPTOR Cinnamomum verum AND CENTRAL:TARGET
45        MESH DESCRIPTOR Muramidase AND CENTRAL:TARGET
46        MESH DESCRIPTOR Lactoferrin AND CENTRAL:TARGET
47        MESH DESCRIPTOR Glucose oxidase AND CENTRAL:TARGET
48        MESH DESCRIPTOR Lactoperoxidase AND CENTRAL:TARGET
49        MESH DESCRIPTOR Benzethonium AND CENTRAL:TARGET
50        MESH DESCRIPTOR Teas, Herbal AND CENTRAL:TARGET
51        MESH DESCRIPTOR Cymbopogon AND CENTRAL:TARGET
52        MESH DESCRIPTOR Sesame oil AND CENTRAL:TARGET
53        (povidone or chlorhexidine or CHX or PVP or Polyvinylpyrrolidone or Betadine* or Providine* or Disadine* or Isodine* or Pharmadine* or Alphadine* or Betaisodona or Tubulicid or Novalsan or Sebidin or MK‐412A or MK412A)  AND CENTRAL:TARGET
54        (Chlorhexamed or Corsodyl or Curasept or Dyna‐Hex or Eludril or Gibitan or Hexidine or Hibiclens or Hibident or Hibiscrub or Hibisol or Hibitane or Peridex or avagard)  AND CENTRAL:TARGET
55        (Hexadecylpyridinium or Cetylpyridium or Biosept or Ceepryn or Cetamium or Catamium or Sterogenol or Dobendan or Merocets or Pristacin or Pyrisept or Angifonil or Cetylyre)  AND CENTRAL:TARGET
56        (Hexigel or Steri‐sol or "Steri sol" or Hextril or Oraldine or Oralspray or Hexoral or Bactidol or Elsix or Duranil or Doreperol or Hexetidine) AND CENTRAL:TARGET
57        (Hydrogen Peroxide or H2O2 or Hydroperoxide or Superoxol or Oxydol or Perhydrol or Urea Peroxide or Perhydrol Urea) AND CENTRAL:TARGET
58        (Methyl salicylate or methylsalicylate or Rheumabal or Metsal Liniment or Hewedolor or Linsal) AND CENTRAL:TARGET
59        (Tricolsan or Hydroxydiphenyl or trichlorodiphenyl or Clearasil or Cliniclean or Irgasan or Trisan or Oxy Skin Wash or pHisoHex or Sapoderm or Tersaseptic or Aquasept or Ster‐Zac or Manusept or Microshield) AND CENTRAL:TARGET
60        ((irrigat* or rins* or wash* or lavag* or intraoral* or topical) and (antimicrobial or anti‐microbial or disinfect* or antisept* or anti‐infect* or herbal)) AND CENTRAL:TARGET
61        ("essential oil*" or "plant oil*" or menthol or menthyl or (mint near2 oil*) or lavender or thyme or peppermint or "mentha piperita" or eugenol or eucalyptus or "blue gum*" or cajeput or clove or cinnamon) AND CENTRAL:TARGET
62        (muramidase or lysozyme* or leftose or lactoferrin or lactotransferrin or "glucose oxidase" or lactoperoxidase or "saliva substitute") AND CENTRAL:TARGET
63        (Listerine or Biotene) AND CENTRAL:TARGET
64        ("chlorine dioxide" or "Benzethonium chloride" or "Bencetonium Chloride" or "Formula Magic" or "Hyamine 1622" or "Orchid Fresh II" or Phemeride or Phemerol or Phemethryn or             Puri‐Clens or Quatrachlor or Solamin or "Vital Oxide")  AND CENTRAL:TARGET
65        ("zinc salt*" or "green tea" or "lemon grass" or lemongrass or citronella or "Cymbopogon nardus" or "Andropogon nardus" or sesame or Triphala or Ela) AND CENTRAL:TARGET
66        #25 OR #26 OR #27 OR #28 OR #29 OR #30 OR #31 OR #32 OR #33 OR #34 OR #35 OR #36 OR #37 OR #38 OR #39 OR #40 OR #41 OR #42 OR #43 OR #44 OR #45 OR #46 OR #47 OR #48 OR #49 OR #50 OR #51 OR #52 OR #53 OR #54 OR #55 OR #56 OR #57 OR #58 OR #59 OR #60 OR #61 OR #62 OR #63 OR #64 OR #65
67        #16 AND #24 AND #66

Appendix 3. MEDLINE Ovid search strategy

1 exp dentistry/
2 exp dental facilities/
3 infection control, dental/
4 exp dentists/
5 dental staff/
6 exp dental auxiliaries/
7 (dental or dentist$ or hygienist$).mp.
8 ((oral or maxillofacial) adj5 (care$ or procedure$ or surgery or surgical or medicine)).mp.
9 orthodonti$.mp.
10 periodont$.mp.
11 (tooth or teeth or gum$ or endodont$ or plaque$ or pulpotom$ or pulpectom$ or "cavity prep$" or molar$ or bicuspid$ or premolar$ or pre‐molar$ or incisor$ or canine$ or eyetooth or eyeteeth or cuspid$).mp.
12 ((scal$ adj2 polish$) or "root canal" or (root adj6 resect$) or (root$ adj3 planing) or apicectom$ or apicoectom$).mp.
13 ((root$ or periodont$ or dental or subgingiv$ or gingiv$ or supragingiv$) adj5 (scale or scaling or scaler$ or curettage)).mp.
14 Dental high speed equipment/
15 ("high speed air rotor$" or "low speed handpiece$" or "low speed hand piece$" or micromotor$ or "turbine handpiece$" or "electrosurgery unit" or "air polisher$" or "prophy angle$" or "air‐water syringe$" or "high speed hand piece$" or "high speed handpiece$" or "three‐way air syringe$" or "threeway air syringe$" or "ultrasonic scaler$" or "hard‐tissue laser$" or "dental drill$" or "piezo unit$" or "piezo hand piece$" or "piezo handpiece$" or "rotary instrument$" or "air abrasion" or "water spray$").mp.
16 or/1‐15
17 Air microbiology/
18 Air pollution, indoor/
19 Aerosols/
20 Inhalation exposure/
21 (aerosol$ or bioaerosol$).mp.
22 (droplet$ or splatter$ or spatter$ or microbe$ or bacillus or germ$ or microorganism$ or virus$ or viral or coronavirus$ or COVID$ or "middle east? respiratory syndrome$" or MERS or MERS‐CoV or "camel flu" or SARS or "sudden acute respiratory syndrome$" or "Wuhan virus$" or 2019‐nCoV or SARS‐CoV‐2 or SARS‐CoV or SARS‐CoV‐1 or SARS‐1).mp.
23 (air adj5 (pollut$ or quality or impur$)).mp.
24 or/17‐23
25 exp Mouthwashes/
26 (mouthwash$ or gargl$ or mouthrins$).ab,ti.
27 ((oral or mouth larynx$ or pharynx$ or intraoral) adj3 (irrigat$ or lavag$ or wash$ or rins$ or decontaminat$ or mist or clean$)).ab,ti.
28 exp Chlorhexidine/
29 exp Povidone‐Iodine/
30 exp Cetylpyridinium/
31 exp Hexetidine/
32 exp Anti‐Infective Agents, Local/
33 exp Hydrogen Peroxide/
34 exp Carbamide Peroxide/
35 exp Triclosan/
36 exp Oils, volatile/
37 exp Plant oils/
38 exp Plant extracts/
39 Menthol/
40 Lavandula/
41 Thymus plant/
42 Mentha piperita/
43 Eugenol/
44 Cinnamomum verum/
45 Muramidase/
46 Lactoferrin/
47 Glucose oxidase/
48 Lactoperoxidase/
49 Benzethonium/
50 Teas, herbal/
51 Cymbopogon/
52 Sesame oil/
53 (povidone or chlorhexidine or CHX or PVP or Polyvinylpyrrolidone or Betadine$ or Providine$ or Disadine$ or Isodine$ or Pharmadine$ or Alphadine$ or Betaisodona or Tubulicid or Novalsan or Sebidin or MK‐412A or MK412A).ab,ti.
54 (Chlorhexamed or Corsodyl or Curasept or Dyna‐Hex or Eludril or Gibitan or Hexidine or Hibiclens or Hibident or Hibiscrub or Hibisol or Hibitane or Peridex or avagard).ab,ti.
55 (Hexadecylpyridinium or Cetylpyridium or Biosept or Ceepryn or Cetamium or Catamium or Sterogenol or Dobendan or Merocets or Pristacin or Pyrisept or Angifonil or Cetylyre).ab,ti.
56 (Hexigel or Steri‐sol or "Steri sol" or Hextril or Oraldine or Oralspray or Hexoral or Bactidol or Elsix or Duranil or Doreperol or Hexetidine).ab,ti.
57 (Hydrogen Peroxide or H2O2 or Hydroperoxide or Superoxol or Oxydol or Perhydrol or Urea Peroxide or Perhydrol Urea).ab,ti.
58 (Methyl salicylate or methylsalicylate or Rheumabal or Metsal Liniment or Hewedolor or Linsal).ab,ti.
59 (Tricolsan or Hydroxydiphenyl or trichlorodiphenyl or Clearasil or Cliniclean or Irgasan or Trisan or Oxy Skin Wash or pHisoHex or Sapoderm or Tersaseptic or Aquasept or Ster‐Zac or Manusept or Microshield).ab,ti.
60 ((irrigat$ or rins$ or wash$ or lavag$ or intraoral$ or topical) adj3 (antimicrobial or anti‐ microbial or disinfect$ or antisept$ or anti‐infect$ or herbal)).ab,ti.
61 ("essential oil$" or "plant oil$" or menthol or menthyl or (mint adj2 oil$) or lavender or thyme or peppermint or "mentha piperita" or eugenol or eucalyptus or "blue gum$" or cajeput or clove or cinnamon).ab,ti.
62 (muramidase or lysozyme$ or leftose or lactoferrin or lactotransferrin or "glucose oxidase" or lactoperoxidase or "saliva substitute").ab,ti.
63 (Listerine or Biotene).ab,ti.
64 ("chlorine dioxide" or "Benzethonium chloride" or "Bencetonium Chloride" or "Formula Magic" or "Hyamine 1622" or "Orchid Fresh II" or Phemeride or Phemerol or Phemethryn or Puri‐Clens or Quatrachlor or Solamin or "Vital Oxide").ab,ti.
65 ("zinc salt$" or "green tea" or "lemon grass" or lemongrass or citronella or "Cymbopogon nardus" or "Andropogon nardus" or sesame or Triphala or Ela).ab,ti.
66 or/25‐65
67 16 and 24 and 66

The above subject search was linked with the highly sensitive search strategy designed by Cochrane for identifying randomised controlled trials and controlled clinical trials in MEDLINE (as described in Lefebvre 2020, box 3c). 

1. randomized controlled trial.pt.
2. controlled clinical trial.pt.
3. randomized.ab.
4. placebo.ab.
5. drug therapy.fs.
6. randomly.ab.
7. trial.ab.
8. groups.ab.
9. or/1‐8
10. exp animals/ not humans.sh.
11. 9 not 10

In addition, to identify non‐randomized studies, we linked the search to a study design filter designed by Waffenschmidt and colleagues (Waffenschmidt 2020):

1. exp cohort studies/or exp epidemiologic studies/or exp clinical trial/or exp evaluation studies as topic/or exp statistics as topic/
2. ((control and (group* or study)) or (time and factors) or program or survey* or ci or cohort or comparative stud* or evaluation studies or follow‐up*).mp.
3. or/1–2
4. (animals/not humans/) or comment/or editorial/or exp review/or meta analysis/or consensus/or exp guideline/
5. hi.fs. or case report.mp.
6. or/4–5
7. 3 not 6

Appendix 4. Embase Ovid search strategy

1.         exp dentistry/  
2.         dental facility/  
3.         exp dentist/
4.         exp dental personnel/
5.         (dental or dentist$ or hygienist$).mp. 
6.         ((oral or maxillofacial) adj5 (care$ or procedure$ or surgery or surgical or  medicine)).mp.
7.         orthodonti$.mp.
8.         periodont$.mp.
9.         (tooth or teeth or gum$ or endodont$ or plaque$ or pulpotom$ or pulpectom$       or "cavity prep$" or molar$ or bicuspid$ or premolar$ or pre‐molar$ or   incisor$ or canine$ or eyetooth or eyeteeth or cuspid$).mp.
10.       ((scal$ adj2 polish$) or "root canal" or (root adj6 resect$) or (root$ adj3      planing) or apicectom$ or apicoectom$).mp.
11.       ((root$ or periodont$ or dental or subgingiv$ or gingiv$ or supragingiv$) adj5         (scale or scaling or scaler$ or curettage)).mp.
12.       ("high speed air rotor$" or "low speed handpiece$" or "low speed hand      piece$" or micromotor$ or "turbine handpiece$" or "electrosurgery unit" or "air  polisher$" or "prophy angle$" or "air‐water syringe$" or "high speed hand        piece$" or "high speed handpiece$" or "three‐way air syringe$" or "threeway         air syringe$" or "ultrasonic scaler$" or "hard‐tissue laser$" or "dental drill$" or "piezo unit$" or "piezo hand piece$" or "piezo handpiece$" or "rotary       instrument$" or "air abrasion" or "water spray$").mp.           
13.       or/1‐12 
14.       Indoor air pollution/
15.       Aerosol/           
16.       exp Environmental exposure/ 
17.       (aerosol$ or bioaerosol$).mp. 
18.       (droplet$ or splatter$ or spatter$ or microbe$ or bacillus or germ$ or          microorganism$ or virus$ or viral or coronavirus$ or COVID$ or "middle east? respiratory syndrome$" or MERS or MERS‐CoV or "camel flu" or SARS or           "sudden acute respiratory syndrome$" or "Wuhan virus$" or 2019‐nCoV or            SARS‐CoV‐2 or SARS‐CoV or SARS‐CoV‐1 or SARS‐1).mp.         
19.       (air adj5 (pollut$ or quality or impur$)).mp.
20.       or/14‐19
21.       exp Mouthwash/
22.       (mouthwash$ or gargl$ or mouthrins$).ab,ti.
23.       ((oral or mouth larynx$ or pharynx$ or intraoral) adj3 (irrigat$ or lavag$ or  wash$ or rins$ or decontaminat$ or mist or clean$)).ab,ti.         
24.       Chlorhexidine/ 
25.       Povidone‐Iodine/         
26.       Cetylpyridinium salt/    
27.       Hexetidine/
28.       exp Anti‐Infective Agent/
29.       Hydrogen Peroxide/
30.       Carbamide Peroxide/
31.       Triclosan/
32.       exp Vegetable oil/
33.       exp Plant extract/
34.       Menthol/
35.       Eugenol/
36.       exp Isozyme/
37.       Lactoferrin/
38.       Glucose oxidase/
39.       Lactoperoxidase/
40.       Benzethonium chloride/
41.       Herbal tea/
42.       exp Cymbopogon/
43.       Sesame seed oil/
44.       (povidone or chlorhexidine or CHX or PVP or Polyvinylpyrrolidone or         Betadine$ or Providine$ or Disadine$ or Isodine$ or Pharmadine$ or     Alphadine$ or Betaisodona or Tubulicid or Novalsan or Sebidin or MK‐412A    or MK412A).ab,ti.        
45.       (Chlorhexamed or Corsodyl or Curasept or Dyna‐Hex or Eludril or Gibitan or         Hexidine or Hibiclens or Hibident or Hibiscrub or Hibisol or Hibitane or   Peridex or avagard).ab,ti.
46.       (Hexadecylpyridinium or Cetylpyridium or Biosept or Ceepryn or Cetamium or       Catamium or Sterogenol or Dobendan or Merocets or Pristacin or Pyrisept or      Angifonil or Cetylyre).ab,ti.
47.       (Hexigel or Steri‐sol or "Steri sol" or Hextril or Oraldine or Oralspray or       Hexoral or Bactidol or Elsix or Duranil or Doreperol or Hexetidine).ab,ti.
48.       (Hydrogen Peroxide or H2O2 or Hydroperoxide or Superoxol or Oxydol or Perhydrol or Urea Peroxide or Perhydrol Urea).ab,ti.
49.       (Methyl salicylate or methylsalicylate or Rheumabal or Metsal Liniment or  Hewedolor or Linsal).ab,ti.
50.       (Tricolsan or Hydroxydiphenyl or trichlorodiphenyl or Clearasil or Cliniclean or       Irgasan or Trisan or Oxy Skin Wash or pHisoHex or Sapoderm or Tersaseptic    or Aquasept or Ster‐Zac or Manusept or Microshield).ab,ti.        
51.       ((irrigat$ or rins$ or wash$ or lavag$ or intraoral$ or topical) adj3    (antimicrobial or anti‐microbial or disinfect$ or antisept$ or anti‐infect$ or         herbal)).ab,ti.
52.       ("essential oil$" or "plant oil$" or menthol or menthyl or (mint adj2 oil$) or   lavender or thyme or peppermint or "mentha piperita" or eugenol or          eucalyptus or "blue gum$" or cajeput or clove or cinnamon).ab,ti.          
53.       (muramidase or lysozyme$ or leftose or lactoferrin or lactotransferrin or     "glucose oxidase" or lactoperoxidase or "saliva substitute").ab,ti.   
54.       (Listerine or Biotene).ab,ti.
55.       ("chlorine dioxide" or "Benzethonium chloride" or "Bencetonium Chloride" or          "Formula Magic" or "Hyamine 1622" or "Orchid Fresh II" or Phemeride or           Phemerol or Phemethryn or Puri‐Clens or Quatrachlor or Solamin or "Vital         Oxide").ab,ti.   
56.       ("zinc salt$" or "green tea" or "lemon grass" or lemongrass or citronella or "Cymbopogon nardus" or "Andropogon nardus" or sesame or Triphala or         Ela).ab,ti.
57.       or/21‐56
58.       13 and 20 and 57

The above subject search was linked with the highly sensitive search strategy designed by Cochrane for identifying randomised controlled trials and controlled clinical trials in Embase (as described in Lefebvre 2020, box 3e). 

1. Randomized controlled trial/

2. Controlled clinical study/

3. random$.ti,ab.

4. randomization/

5. intermethod comparison/

6. placebo.ti,ab.

7. (compare or compared or comparison).ti.

8. ((evaluated or evaluate or evaluating or assessed or assess) and (compare or compared or comparing or comparison)).ab.

9. (open adj label).ti,ab.

10. ((double or single or doubly or singly) adj (blind or blinded or blindly)).ti,ab.

11. double blind procedure/

12. parallel group$1.ti,ab.

13. (crossover or cross over).ti,ab.

14. ((assign$ or match or matched or allocation) adj5 (alternate or group$1 or intervention$1 or patient$1 or subject$1 or participant$1)).ti,ab.

15. (assigned  or allocated).ti,ab.

16. (controlled adj7 (study or design or trial)).ti,ab.

17. (volunteer or volunteers).ti,ab.

18. human experiment/

19. trial.ti.

20. or/1‐19

21. random$ adj sampl$ adj7 ("cross section$" or questionnaire$1 or survey$ or database$1)).ti,ab. not (comparative study/ or controlled study/ or randomi?ed controlled.ti,ab. or randomly assigned.ti,ab.)

22. Cross‐sectional study/ not (randomized controlled trial/ or controlled clinical study/ or controlled study/ or randomi?ed controlled.ti,ab. or control group$1.ti,ab.)

23. (((case adj control$) and random$) not randomi?ed controlled).ti,ab.

24. (Systematic review not (trial or study)).ti.

25. (nonrandom$ not random$).ti,ab.

26. "Random field$".ti,ab.

27. (random cluster adj3 sampl$).ti,ab.

28. (review.ab. and review.pt.) not trial.ti.

29. "we searched".ab. and (review.ti. or review.pt.)

30. "update review".ab.

31. (databases adj4 searched).ab.

32. (rat or rats or mouse or mice or swine or porcine or murine or sheep or lambs or pigs or piglets or rabbit or rabbits or cat or cats or dog or dogs or cattle or bovine or monkey or monkeys or trout or marmoset$1).ti. and animal experiment/

33. Animal experiment/ not (human experiment/ or human/)

34. or/21‐33

35. 20 not 34

Appendix 5. World Health Organization COVID‐19 Global Literature on Coronavirus Disease Database search strategy

(tw:(((mouthwash* or gargl* or mouthrins*)))) AND (tw:(((aerosol or bioaerosol))))

Appendix 6. Cochrane COVID‐19 Study Register search strategy

1          MESH DESCRIPTOR dentistry EXPLODE ALL        
2          MESH DESCRIPTOR dental facilities EXPLODE ALL 
3          MESH DESCRIPTOR infection control, dental 
4          MESH DESCRIPTOR dentists EXPLODE ALL 
5          MESH DESCRIPTOR dental staff 
6          MESH DESCRIPTOR Dental Auxiliaries EXPLODE ALL 
7          (dental or dentist* or hygienist*) 
8          ((oral or maxillofacial) and (care* or procedure* or surgery or surgical or medicine)) 9          orthodonti* 
10        periodont* 
11        (tooth or teeth or gum* or endodont* or plaque* or pulpotom* or pulpectom* or "cavity prep*" or molar* or bicuspid* or premolar* or pre‐molar* or incisor* or canine* or eyetooth or eyeteeth or cuspid*) 
12        ((scal* near2 polish*) or "root canal" or (root near6 resect*) or (root* near3 planing) or apicectom* or apicoectom*) 
13        ((root* or periodont* or dental or subgingiv* or gingiv* or supragingiv*) and (scale or scaling or scaler* or curettage)) 
14        MESH DESCRIPTOR Dental High‐Speed Equipment 
15        ("high speed air rotor*" or "low speed handpiece*" or "low speed hand piece*"  or micromotor* or "turbine handpiece*" or "electrosurgery unit" or "air  polisher*" or "prophy angle*" or "air‐water syringe*" or "high speed hand piece*" or "high speed handpiece*" or "three‐way air syringe*" or "threeway  air syringe*" or "ultrasonic scaler*" or "hard‐tissue laser*" or "dental drill*" or   "piezo unit*" or "piezo hand piece*" or "piezo handpiece*" or "rotary instrument*" or "air abrasion" or "water spray*") 
16        #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10 OR #11 OR #12 OR #13 OR #14 OR #15
17        MESH DESCRIPTOR Air microbiology 
18        MESH DESCRIPTOR Air Pollution, Indoor 
19        MESH DESCRIPTOR Aerosols 
20        MESH DESCRIPTOR Inhalation Exposure 
21        (aerosol* or bioaerosol*) 
22        (droplet* or splatter* or spatter* or microbe* or bacillus or germ* or microorganism* or virus* or viral or coronavirus* or COVID* or "middle east? respiratory syndrome*" or MERS or MERS‐CoV or "camel flu" or SARS or  "sudden acute respiratory syndrome*" or "Wuhan virus*" or 2019‐nCoV or SARS‐CoV‐2 or SARS‐CoV or SARS‐CoV‐1 or SARS‐1)
23        (air near5 (pollut* or quality or impur*)) 
24        #17 OR #18 OR #19 OR #20 OR #21 OR #22 OR #23
25        MESH DESCRIPTOR Mouthwashes EXPLODE ALL 
26        (mouthwash* or gargl* or mouthrins*)   
27        ((oral or mouth or larynx* or pharynx* or intraoral) and (irrigat* or lavag* or wash* or rins* or decontaminat* or mist or clean*)) 
28        MESH DESCRIPTOR Chlorhexidine EXPLODE ALL 
29        MESH DESCRIPTOR Povidone‐Iodine EXPLODE ALL 
30        MESH DESCRIPTOR Cetylpyridinium EXPLODE ALL 
31        MESH DESCRIPTOR Hexetidine EXPLODE ALL 
32        MESH DESCRIPTOR Anti‐Infective Agents, Local EXPLODE ALL 
33        MESH DESCRIPTOR Hydrogen Peroxide EXPLODE ALL 
34        MESH DESCRIPTOR Carbamide Peroxide EXPLODE ALL            
35        MESH DESCRIPTOR Triclosan EXPLODE ALL 
36        MESH DESCRIPTOR Oils, volatile EXPLODE ALL 
37        MESH DESCRIPTOR Plant oils EXPLODE ALL       
38        MESH DESCRIPTOR Plant extracts EXPLODE ALL 
39        MESH DESCRIPTOR Menthol EXPLODE ALL 
40        MESH DESCRIPTOR Lavandula EXPLODE ALL 
41        MESH DESCRIPTOR Thymus plant 
42        MESH DESCRIPTOR Mentha piperita 
43        MESH DESCRIPTOR Eugenol 
44        MESH DESCRIPTOR Cinnamomum verum 
45        MESH DESCRIPTOR Muramidase 
46        MESH DESCRIPTOR Lactoferrin 
47        MESH DESCRIPTOR Glucose oxidase 
48        MESH DESCRIPTOR Lactoperoxidase 
49        MESH DESCRIPTOR Benzethonium 
50        MESH DESCRIPTOR Teas, Herbal 
51        MESH DESCRIPTOR Cymbopogon 
52        MESH DESCRIPTOR Sesame oil 
53        (povidone or chlorhexidine or CHX or PVP or Polyvinylpyrrolidone or Betadine* or Providine* or Disadine* or Isodine* or Pharmadine* or       Alphadine* or Betaisodona or Tubulicid or Novalsan or Sebidin or MK‐412A or MK412A) 
54        (Chlorhexamed or Corsodyl or Curasept or Dyna‐Hex or Eludril or Gibitan or         Hexidine or Hibiclens or Hibident or Hibiscrub or Hibisol or Hibitane or   Peridex or avagard) 
55        (Hexadecylpyridinium or Cetylpyridium or Biosept or Ceepryn or Cetamium or       Catamium or Sterogenol or Dobendan or Merocets or Pristacin or Pyrisept or Angifonil or Cetylyre) 
56        (Hexigel or Steri‐sol or "Steri sol" or Hextril or Oraldine or Oralspray or Hexoral or Bactidol or Elsix or Duranil or Doreperol or Hexetidine) 
57        (Hydrogen Peroxide or H2O2 or Hydroperoxide or Superoxol or Oxydol or Perhydrol or Urea Peroxide or Perhydrol Urea) 
58        (Methyl salicylate or methylsalicylate or Rheumabal or Metsal Liniment or  Hewedolor or Linsal) 
59        (Tricolsan or Hydroxydiphenyl or trichlorodiphenyl or Clearasil or Cliniclean or       Irgasan or Trisan or Oxy Skin Wash or pHisoHex or Sapoderm or Tersaseptic or Aquasept or Ster‐Zac or Manusept or Microshield) 
60        ((irrigat* or rins* or wash* or lavag* or intraoral* or topical) and (antimicrobial or anti‐microbial or disinfect* or antisept* or anti‐infect* or herbal)) 
61        ("essential oil*" or "plant oil*" or menthol or menthyl or (mint near2 oil*) or  lavender or thyme or peppermint or "mentha piperita" or eugenol or eucalyptus or "blue gum*" or cajeput or clove or cinnamon) 
62        (muramidase or lysozyme* or leftose or lactoferrin or lactotransferrin or "glucose oxidase" or lactoperoxidase or "saliva substitute") 
63        (Listerine or Biotene) 
64        ("chlorine dioxide" or "Benzethonium chloride" or "Bencetonium Chloride" or          "Formula Magic" or "Hyamine 1622" or "Orchid Fresh II" or Phemeride or Phemerol or Phemethryn or   Puri‐Clens or Quatrachlor or Solamin or "Vital  Oxide") 
65        ("zinc salt*" or "green tea" or "lemon grass" or lemongrass or citronella or  "Cymbopogon nardus" or "Andropogon nardus" or sesame or Triphala or Ela) 
66        #25 OR #26 OR #27 OR #28 OR #29 OR #30 OR #31 OR #32 OR #33 OR  #34 OR #35 OR #36 OR #37 OR #38 OR #39 OR #40 OR #41 OR #42 OR #43 OR #44 OR #45 OR #46 OR #47 OR #48 OR #49 OR #50 OR #51 OR #52 OR #53 OR #54 OR #55 OR #56 OR #57 OR #58 OR #59 OR #60 OR #61 OR #62 OR #63 OR #64 OR #65
67        #16 AND #24 AND #66

Appendix 7. US National Institutes of Health Ongoing Trials Register (ClinicalTrials.gov) search strategy

Expert search: ((mouthrinse OR mouthrinses OR mouthrinsing OR mouthwash OR mouthwashes OR mouthwashing OR gargle OR gargles OR gargling) AND (aerosol OR aerosols OR bioaerosol OR bioaerosols))

Appendix 8. World Health Organization International Clinical Trials Registry Platform search strategy

mouthrinse AND aerosol OR mouthrinses AND aerosol OR mouthrinsing AND aerosol OR mouthrinse AND aerosols OR mouthrinses AND aerosols OR mouthrinsing AND aerosols

mouthrinse AND bioaerosol or mouthrinses AND bioaerosol OR mouthrinsing AND bioaerosol OR mouthrinse AND bioaerosols OR mouthrinses AND bioaerosols OR mouthrinsing AND bioaerosols

mouthwash AND aerosol OR mouthwashes AND aerosol OR mouthwashing AND aerosol OR mouthwash AND aerosols OR mouthwashes AND aerosols OR mouthwashing AND aerosols

mouthwash AND bioaerosol OR mouthwashes AND bioaerosol OR mouthwashing AND bioaerosol OR mouthwash AND bioaerosols OR mouthwashes AND bioaerosols OR mouthwashing AND bioaerosols  

Data and analyses

Comparison 1. Chlorhexidine versus no rinsing.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Reduction in the level of contamination at < 2 m	2		Mean Difference (IV, Random, 95% CI)	Totals not selected
1.1.1 Operator level	2		Mean Difference (IV, Random, 95% CI)	Totals not selected

Comparison 2. Chlorhexidine versus water.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
2.1 Reduction in the level of contamination at < 2 m	7		Mean Difference (IV, Random, 95% CI)	Subtotals only
2.1.1 Operator level	6	196	Mean Difference (IV, Random, 95% CI)	‐105.46 [‐146.70, ‐64.22]
2.1.2 Assistant level	4	136	Mean Difference (IV, Random, 95% CI)	‐38.19 [‐55.66, ‐20.72]
2.1.3 Combined levels	3	80	Mean Difference (IV, Random, 95% CI)	‐632.94 [‐1267.33, 1.45]
2.1.4 Tempered chlorhexidine versus water – combined levels	1	20	Mean Difference (IV, Random, 95% CI)	‐101.10 [‐107.01, ‐95.19]

Comparison 3. Chlorhexidine versus saline.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
3.1 Reduction in the level of contamination at < 2 m	2		Mean Difference (IV, Random, 95% CI)	Subtotals only
3.1.1 3 feet from patient's mouth	1	20	Mean Difference (IV, Random, 95% CI)	‐668.40 [‐1044.45, ‐292.35]
3.1.2 Operator level	1	12	Mean Difference (IV, Random, 95% CI)	‐21.33 [‐36.80, ‐5.86]

Comparison 4. Chlorhexidine versus essential oils or herbal mouthwash.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
4.1 Reduction in the level of contamination at < 2 m	4		Mean Difference (IV, Random, 95% CI)	Subtotals only
4.1.1 At operator level	3	76	Mean Difference (IV, Random, 95% CI)	‐23.09 [‐34.40, ‐11.78]
4.1.2 At assistant level	3	76	Mean Difference (IV, Random, 95% CI)	‐12.21 [‐15.58, ‐8.83]
4.1.3 At 15 cm from patient's mouth	1	20	Mean Difference (IV, Random, 95% CI)	‐44.10 [‐59.12, ‐29.08]

Comparison 5. Chlorhexidine versus povidone iodine.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
5.1 Reduction in the level of contamination at < 2 m	3		Mean Difference (IV, Random, 95% CI)	Subtotals only
5.1.1 Operator level – aerobic	2	52	Mean Difference (IV, Random, 95% CI)	‐10.75 [‐26.24, 4.74]
5.1.2 Operator level (aerobic and anaerobic combined)	1	30	Mean Difference (IV, Random, 95% CI)	‐4.70 [‐7.01, ‐2.39]
5.2 Reduction in level of contamination at ≥ 2 m	1		Mean Difference (IV, Random, 95% CI)	Totals not selected
5.2.1 Aerobic	1		Mean Difference (IV, Random, 95% CI)	Totals not selected
5.2.2 Anaerobic	1		Mean Difference (IV, Random, 95% CI)	Totals not selected

Comparison 6. Chlorhexidine versus cetylpyridinium chloride (CPC).

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
6.1 Reduction in the level of contamination at < 2 m	3	220	Mean Difference (IV, Random, 95% CI)	2.41 [‐4.52, 9.33]
6.1.1 Tempered chlorhexidine versus tempered CPC – operator	1	20	Mean Difference (IV, Random, 95% CI)	‐2.20 [‐9.07, 4.67]
6.1.2 Tempered chlorhexidine versus tempered CPC – assistant	1	20	Mean Difference (IV, Random, 95% CI)	‐0.20 [‐6.30, 5.90]
6.1.3 Cold chlorhexidine versus cold CPC – operator	2	50	Mean Difference (IV, Random, 95% CI)	4.43 [‐2.27, 11.13]
6.1.4 Cold chlorhexidine versus cold CPC – assistant	1	20	Mean Difference (IV, Random, 95% CI)	8.80 [2.70, 14.90]
6.1.5 Tempered chlorhexidine versus cold CPC – operator	1	20	Mean Difference (IV, Random, 95% CI)	‐11.50 [‐18.37, ‐4.63]
6.1.6 Tempered chlorhexidine versus cold CPC – assistant	1	20	Mean Difference (IV, Random, 95% CI)	‐8.80 [‐14.90, ‐2.70]
6.1.7 Cold chlorhexidine versus tempered CPC – operator	1	20	Mean Difference (IV, Random, 95% CI)	13.60 [6.73, 20.47]
6.1.8 Cold chlorhexidine versus tempered CPC – assistant	1	20	Mean Difference (IV, Random, 95% CI)	17.40 [11.30, 23.50]
6.1.9 Chlorhexidine versus CPC + zinc (Zn) + fluoride (F) – operator level	1	30	Mean Difference (IV, Random, 95% CI)	‐30.00 [‐85.86, 25.86]

Comparison 7. Tempered chlorhexidine versus non‐tempered chlorhexidine.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
7.1 Reduction in the level of contamination at < 2 m	2		Mean Difference (IV, Random, 95% CI)	Subtotals only
7.1.1 Operator level	1	20	Mean Difference (IV, Random, 95% CI)	‐15.80 [‐22.67, ‐8.93]
7.1.2 Assistant level	1	20	Mean Difference (IV, Random, 95% CI)	‐17.60 [‐23.70, ‐11.50]
7.1.3 Combined	1	20	Mean Difference (IV, Random, 95% CI)	‐10.80 [‐15.15, ‐6.45]

Comparison 8. Cetylpyridinium chloride (CPC) versus no rinsing.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
8.1 Reduction in level of contamination at < 2 m [CFUs]	4		Mean Difference (IV, Random, 95% CI)	Subtotals only
8.1.1 CPC versus no rinsing – operator level	1	30	Mean Difference (IV, Random, 95% CI)	‐34.80 [‐65.92, ‐3.68]
8.1.2 CPC + zinc + fluoride versus no rinsing – operator level	1	30	Mean Difference (IV, Random, 95% CI)	‐583.00 [‐958.36, ‐207.64]
8.1.3 CPC formulation versus no rinsing – combined	2	200	Mean Difference (IV, Random, 95% CI)	‐0.75 [‐1.32, ‐0.18]

Comparison 9. Cetylpyridinium chloride (CPC) versus water.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
9.1 Reduction in level of contamination at < 2 m [CFUs]	3		Mean Difference (IV, Random, 95% CI)	Subtotals only
9.1.1 CPC versus water – operator level	1	30	Mean Difference (IV, Random, 95% CI)	‐48.70 [‐67.82, ‐29.58]
9.1.2 CPC + zinc + fluoride versus water – operator level	1	30	Mean Difference (IV, Random, 95% CI)	‐246.00 [‐437.96, ‐54.04]
9.1.3 CPC formulation versus water – combined	1	105	Mean Difference (IV, Random, 95% CI)	‐0.78 [‐1.24, ‐0.31]

Comparison 10. Tempered cetylpyridinium chloride (CPC) versus cold CPC.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
10.1 Reduction in the level of contamination at < 2 m	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
10.1.1 Operator	1	20	Mean Difference (IV, Random, 95% CI)	‐9.30 [‐16.17, ‐2.43]
10.1.2 Assistant	1	20	Mean Difference (IV, Random, 95% CI)	‐8.60 [‐14.70, ‐2.50]

Comparison 11. Povidone iodine versus saline.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
11.1 Reduction in the level of contamination at < 2 m	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
11.1.1 Operator level	1	12	Mean Difference (IV, Random, 95% CI)	‐16.50 [‐32.65, ‐0.35]

Comparison 12. Essential oils/herbal mouthwash versus water.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
12.1 Reduction in the level of contamination at < 2 m	3		Mean Difference (IV, Random, 95% CI)	Totals not selected
12.1.1 At operator level	3		Mean Difference (IV, Random, 95% CI)	Totals not selected
12.1.2 At assistant level	3		Mean Difference (IV, Random, 95% CI)	Totals not selected

Comparison 13. Chlorhexidine versus ozonated water.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
13.1 Reduction in the level of contamination at < 2 m	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
13.1.1 Operator level aerobic	1	40	Mean Difference (IV, Random, 95% CI)	‐17.80 [‐33.70, ‐1.90]
13.2 Reduction in the level of contamination at ≥ 2 m	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
13.2.1 Aerobic	1	40	Mean Difference (IV, Random, 95% CI)	‐12.30 [‐27.12, 2.52]
13.2.2 Anaerobic	1	40	Mean Difference (IV, Random, 95% CI)	‐3.40 [‐14.66, 7.86]

Comparison 14. Povidone iodine versus ozonated water.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
14.1 Reduction in the level of contamination at < 2 m	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
14.1.1 Operator level aerobic	1	40	Mean Difference (IV, Random, 95% CI)	3.50 [‐17.10, 24.10]
14.2 Reduction in the level of contamination at ≥ 2 m	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
14.2.1 Aerobic	1	40	Mean Difference (IV, Random, 95% CI)	‐12.50 [‐26.33, 1.33]
14.2.2 Anaerobic	1	40	Mean Difference (IV, Random, 95% CI)	‐2.60 [‐9.54, 4.34]

Comparison 15. Chlorhexidine versus boric acid.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
15.1 Reduction in the level of contamination at < 2 m	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
15.1.1 Operator level	1	60	Mean Difference (IV, Random, 95% CI)	‐26.60 [‐28.24, ‐24.96]
15.1.2 Assistant level	1	60	Mean Difference (IV, Random, 95% CI)	‐8.03 [‐9.65, ‐6.41]

Comparison 16. Boric acid versus water.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
16.1 Reduction in the level of contamination at < 2 m	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
16.1.1 Operator level	1	60	Mean Difference (IV, Random, 95% CI)	‐29.30 [‐32.65, ‐25.95]
16.1.2 Assistant level	1	60	Mean Difference (IV, Random, 95% CI)	‐14.04 [‐16.47, ‐11.61]

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Bay 1993.

Study characteristics
Methods	Title: effectiveness of antimicrobial mouth rinses on aerosols produced by air polisher Trial design: randomised 3‐arm parallel‐group design Trial registration: not reported Location: Kansas City, US Setting: university dental clinic Language: English Number of centres: 1 Study period: not reported, probably 1990–1992 Funding source: Procter and Gamble sponsored the Peridex mouth rinse Dental aerosol procedure tested: air‐abrasive polisher
Participants	Age: adults Total number of participants: 45 (30 women, 15 men) Inclusion criteria: ≥ 16 teeth; mean score of 2.5 on Turesky's modification of the Quigley‐Hein plaque index using Ramfjords teeth Exclusion criteria: use of anticoagulant or antibiotic medication; sodium restricted diet, heart murmur; rheumatic disease of valve replacement; gross caries; significant oral pathology; contagious disease; uncontrolled hypertension Number randomised: 45
Interventions	Intervention 1 Group name: essential oil Number randomised: 15 Description of intervention: 30 sec rinsing with 15 mL essential oil directly prior to treatment; Listerine (contained essential oils such as 0.042% menthol (mint), 0.064% thymol (thyme), 0.06% methyl salicylate (wintergreen) and 0.092% eucalyptol (eucalyptus); Warner‐Lambert, Morris Plains, NJ, US Any co‐interventions: no Intervention 2 Group name: CHX Number randomised: 15 Description of intervention: 30 sec rinsing with 15 mL 0.12% CHX rinse directly prior to treatment; Peridex, Procter Gamble, Cincinnati, OH, US Any co‐interventions: no Comparator Group name: water Number randomised: 15 Description of control: 30 sec rinsing with tap water directly prior to treatment
Outcomes	Outcome name: CFU per ft³ at 3 levels of inhalation and the total CFUs/ft³ across the levels Outcome measurement: Andersen air sampler, a cascade impactor system with 6 filters representing human respiratory tract of which 3 were used representing the pharynx (> 5.5 μm), secondary bronchi, (2–5.5 μm, alveoli (< 2 μm) with a constant air flow of 1 ft³ per min. Measurements taken at baseline (5 min), using the air abraser (3 min) and after treatment (2 min). Agar plates were incubated for 24 hours at 37 °C Effect estimate: mean difference in CFU Outcome name: total CFUs/ft³ across the levels Outcome measurement: see above Effect estimate: mean difference in CFU Adverse events: not reported
Notes	Key study conclusions Lack of effectiveness for all rinses. No difference between treatment groups in reducing bacterial aerosols. Neither mouth rinses nor water were consistently more effective in reducing bacterial aerosol. Contact information: Nina Louise Bay, Assistant Professor and Director, School of Dental Hygiene, Dental branch, University of Texas Health Science Centre, Houston, Texas, USA
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported.
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding of participants and personnel (performance bias) All outcomes	High risk	No blinding of participants or providers. There is a possibility of clinicians altering their behaviour.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "examiner‐blinded."  Comment: those who counted the CFUs were blind to the participant and the treatment conditions.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Not reported. We assumed no loss of data.
Selective reporting (reporting bias)	Unclear risk	Clinical trial registration details not available.
Other bias	Low risk	None detected.

Feres 2010.

Study characteristics
Methods	Title: the effectiveness of a preprocedural mouth rinse containing cetylpyridinium chloride in reducing bacteria in the dental office Trial design: randomised parallel‐group placebo‐controlled trial Trial registration: not reported Location: São Paulo, Brazil Setting: university clinic (periodontal clinic at Guarulhos University) Language: English Number of centres: 1 Study period: not reported, probably 2008–2010 Funding source: supported financially and through the donation of products by Colgate‐Palmolive, Sao Paulo. In addition, 2 authors are employees of this company. Dental aerosol procedure tested: full‐mouth oral prophylaxis using an ultrasonic scaler (Magnetostrictive)
Participants	Age: not reported (inclusion criteria range 30–70 years) Total number of participants: 60 Inclusion criteria: aged 30–70 years, available for duration of study, ≥ 20 natural teeth present, ≥ 80% of tooth surfaces had to have visible supragingival plaque, < 10% had to have visible supragingival calculus, and < 30% had to have PD and CAL of ≥ 5 mm Exclusion criteria: people with orthodontic bands, partial removable dentures, tumours of the soft or hard tissues of the oral cavity, advanced periodontal disease, ≥ 5 carious lesions requiring immediate restorative treatment, history of allergy to CPC or any of the personal care products used during the study, any medical condition that could compromise the participant's safety or the quality of the study results; people who had undergone a professional oral prophylaxis within 1 month of entering study and pregnant or breastfeeding women
Interventions	Intervention 1 Group name: test group (0.05% CPC) Number randomised: 15 Description of intervention: rinse for 1 min with 15 mL of 0.05% CPC and expectorate all remaining liquid Any co‐interventions: none Intervention 2 Group name: CHX Number randomised: 15 Description of intervention: rinse for 1 min with 15 mL of 0.12% CHX and expectorate all remaining liquid Any co‐interventions: no Intervention 3 Group name: water Number randomised: 15 Description of intervention: rinse for 1 min with 15 mL of water and expectorate all remaining liquid Any co‐interventions: no Comparator Group name: A (no rinsing) Number randomised: 15 Description of control: no rinsing performed (no intervention)
Outcomes	Outcome name: mean CFU Outcome measurement: plates containing 5% sheep blood agar supplemented with N‐acetyl muramic acid and menadione on a counter within the operatory for 30 min was used to collect and count CFU. Placed at 3 locations: patient's chest, examiner's forehead and support board attached to the chair tray. Effect estimate: data given in graph Outcome name: mean decrease in CFU Outcome measurement: as above Effect estimate: data given in graph Outcome name: specific microbes Outcome measurement: checkerboard DNA–DNA hybridisation Effect estimate: mean difference as percentage of the total DNA probe counts Adverse events: not reported
Notes	Key study conclusions CPC and CHX were equally effective in decreasing the total number of spatter micro‐organisms compared with no rinsing (P < 0.05, Kruskal‐Wallis and Mann‐Whitney U tests) for all locations. Contact information: Dr Feres, Universidade Guarulhos, Centro de Pós‐Graduação e Pesquisa–CEPPE, São Paulo, Brazil; e‐mail mferes@ung.br Comments: E‐mail sent on 30 March 2021 requesting the missing details and reply awaited.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported.
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "The examiner, study coordinator and investigator did not know which mouth rinse each participant used."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	The technician was blinded to which participants received which treatment solutions.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Not reported.
Selective reporting (reporting bias)	Unclear risk	Clinical trial registration details not available.
Other bias	Low risk	None detected.

Fine 1993a.

Study characteristics
Methods	Title: reducing bacteria in dental aerosols: pre procedural use of an antiseptic mouth rinse Trial design: randomised cross‐over trial Trial registration: not reported Location: New York, NY, USA Setting: university dental clinic Language: English Number of centres: 1 Study period: not reported, probably 1991–1992 Funding source: this study was supported by a grant from the Warner‐Lambert Co. Co‐authors Barnett, Vincent and Mr Olshan are employees of the Warner‐Lambert Company. Dental aerosol procedure tested: air sampled during ultrasonic scaling (Magnetostrictive) of random max quadrant for 5 min at baseline; after 40 min of treatment, air was resampled during the baseline scaling that was repeated for 5 min
Participants	Age: adults Total number of participants: 18 Inclusion criteria: ADA Periodontal Case Type I (gingivitis) or II (incipient periodontitis) as determined by clinical probing and radiographs; no history of diabetes, blood dyscrasia, hepatic or renal disease, or immunosuppression; no history of rheumatic fever, cardiac murmur or defect, or any other condition requiring prophylactic antibiotics before invasive dental procedures; no current antibiotic, anticoagulant or steroidal therapy; no periodontal therapy including scaling, root planing or dental prophylaxis during the previous 6 months; presence of ≥ 20 sound natural teeth with a mean plaque index > 1.5 and a mean gingival index > 1.5 Exclusion criteria: no details given Number randomised: 18 Number evaluated (withdrawals/missing participants): 17; 1 participant was excluded since they initiated antibiotic therapy during the study.
Interventions	Intervention 1 Group name: antiseptic mouth rinse (Listerine) Number randomised: 18 Description of intervention: rinsed with 20 mL of assigned rinse for 30 sec under supervision Any co‐interventions: no Washout period: 1 week Comparator Group name: coloured and flavoured 5% hydroalcohol Number randomised: no details given Description of control: rinsed with 20 mL of assigned rinse for 30 sec under supervision. Identical clinical procedures were repeated after 1 week with another 24‐hour no‐oral hygiene period. Washout period: 1 week
Outcomes	Outcome name: CFU expressed as log10 scores Outcome measurement: air sampling with a vacuum air sampling device (Mattson‐Garvin model 200) at 5 cm from patient's mouth at 55 ft³ per hour with a 0.45 μm filter. For each period, a filter was put on enriched trypticase soy agar incubated at 37 °C for 24–72 hours. CFU counted with dissecting microscope. Effect estimate: Listerine: before: mean 2.79 (SE 0.28), 17 participants; after: mean 1.60 (SE 0.30); hydroalcohol: before: mean 2.80 (SE 0.27); after: mean 2.63 (SE 0.32) Adverse events: not reported
Notes	Key study conclusions Preprocedural rinse reduced levels of bacteria in aerosols produced during routine dental procedures. Rinsing with an antiseptic at outset of a simulated dental visit can reduce level of viable bacteria in an aerosol produced by ultrasonic scaling 40 min later. Contact information: Dr Fine, Professor of Dentistry and Director, Division of Oral Infectious Diseases, Columbia University, School of Dental and Oral Surgery, New York, New York, USA
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomly assigned schedule with a computer‐generated random code.
Allocation concealment (selection bias)	Low risk	The personnel dispensing the test rinses did not otherwise participate in the study to avoid potential bias.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Participant, dentist and dental assistant were unaware of treatment code. Quote: "Double‐blinding was maintained by assigning the rinse schedule with a computer­ generated random code." Quote: "The control rinse was coloured and flavoured to resemble an actual product."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Participant, dentist and dental assistant were aware of the treatment code. Quote: "Double‐blinding was maintained by assigning the rinse schedule with a computer­ generated random code" Quote: "The control rinse was coloured and flavoured to resemble an actual product."
Incomplete outcome data (attrition bias) All outcomes	Low risk	1 dropout.
Selective reporting (reporting bias)	Unclear risk	Clinical trial registration details not available.
Other bias	Low risk	None detected.

Gupta 2014.

Study characteristics
Methods	Trial design: 3‐armed parallel‐group RCT Trial registration: not reported Location: Jodhpur, India Setting: dental school clinic Language: English Number of centres: 1 Study period: March 2012 to April 2012 (45 days) Funding source: not reported Dental aerosol procedure tested: piezoelectric ultrasonic scaling for 30 min
Participants	Age: mean 40 years, range 25–55 years Total number of participants: 24 (16 men, 8 women) Inclusion criteria: ≥ 20 permanent teeth; mean plaque score 2.0–3.0 on Plaque Index. ≥ 4 sites with pocket PD > 4 mm; non‐smokers; systemically healthy people Exclusion criteria: systemic or topical antibiotics; oral prophylaxis within last 3 months; ≥ 5 caries lesions requiring immediate restorative treatment; pregnant or breastfeeding Number randomised and evaluated: 24
Interventions	Intervention 1 Group name: group A: CHX mouth rinse Number randomised: 8 Description of intervention: rinse for 1 min with 10 mL of 0.2% CHX, 10 min before ultrasonic scaling Intervention 2 Group name: group B: herbal mouth rinse Number randomised: 8 Description of intervention: rinse for 1 min with 10 mL of herbal mouth rinse, 10 min before ultrasonic scaling; contained Terminilia bellirica, Piper betle, Salvadora persica, powders peppermint (Mentha spp) and Caraway, Wintergreen oil and cardamom Any co‐interventions: none Comparator Group name: group C: water Number randomised: 8 Description of control: rinse for 1 min with 10 mL of water, 10 min before ultrasonic scaling
Outcomes	Outcome name: total CFU at different locations Outcome measurement: blood agar plates at patients' chest; at doctor's chest and at the assistant's chest area; mean 30 cm from patient's mouth. Agar plates were open for 30 min during treatment and 30 min after treatment. Agar plates were incubated for 48 hours at 37 °C. CFUs were counted. Effect estimate: data given in graph Adverse events: not reported
Notes	Key study conclusions CHX mouth rinse for 1 min, 10 min before ultrasonic scaling resulted in consistently fewer CFUs than when herbal mouth rinse or water. Herbal mouth rinse was effective in reducing aerosol contamination produced by ultrasonic scaling, though less potent than 0.2% CHX. Contact information: Dr Gunjan Gupta, Vyas Dental College, Jodhpur, Rajasthan, India; E‐mail: drgunjan_arun@yahoo.co.in Comments: mail sent on 30 March 2021 requesting the missing details and reply awaited.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients were recruited in chronologic order, by systematic sampling."
Allocation concealment (selection bias)	Low risk	An independent examiner who was not involved in the study allotted the mouth rinse. Quote: "Treatment group was concealed from the patient, operator, and microbiologist."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Treatment group was concealed from the patient, operator and microbiologist. Quote: "double masked."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	The operator was not involved in any evaluations before or after. Treatment group was concealed from the patient, operator and microbiologist.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts.
Selective reporting (reporting bias)	Unclear risk	Clinical trial registration details not available.
Other bias	Low risk	None detected.

Joshi 2017.

Study characteristics
Methods	Title: efficacy of two pre‐procedural rinses at two different temperatures in reducing aerosol contamination produced during ultrasonic scaling in a dental set‐up – a microbiological study Trial design: 4‐arm randomised parallel‐group controlled trial Location: Mumbai, India Setting: dental school hospital Language: English Number of centres: 1 Study period: 60 days from September 2015 to October 2015 Funding source: not reported Dental aerosol procedure tested: ultrasonic scaling (piezoelectric)
Participants	Age (mean): group A1: 32.5 years; A2: 32.7 years; B1: 32.64 years; B2: 33.0 years Total number of participants: 40 Inclusion criteria: ≥ 20 natural teeth present excluding third molars; diagnosed with chronic gingivitis having PD ≤ 3 mm; modified Gingival Index ≥ 1 and Gingival Bleeding Index > 30% of the sites examined Exclusion criteria: allergies to constituents found in conventional mouth rinses; untreated/grossly carious teeth; having undergone non‐surgical or surgical periodontal therapy and antibiotic or anti‐inflammatory (or both) therapy within the past 6 months; systemically compromised; pregnant and breastfeeding women Number randomised: 40 Number evaluated (withdrawals/missing participants): all 40 evaluated
Interventions	4 groups with 10 participants in each Intervention 1 Group A1: 0.05% CPC at 47 °C Number randomised: 10 Description of intervention: rinsing for 60 sec with 10 mL of assigned mouth rinse 10 min prior to treatment Any co‐interventions: none Intervention 2 Group A2: 0.05% CPC at 18 °C Number randomised: 10 Description of intervention: rinsing for 60 sec with 10 mL of assigned mouth rinse 10 min prior to treatment Any co‐interventions: none Intervention 3 Group B1: 0.2% CHX at 47 °C Number randomised: 10 Description of intervention: rinsing for 60 sec with 10 mL of assigned mouth rinse 10 min prior to treatment Any co‐interventions: none Intervention 4 Group B2: 0.2% CHX at 18 °C Number randomised: 10 Description of intervention: rinsing for 60 sec with 10 mL of assigned mouth rinse 10 min prior to treatment Any co‐interventions: none
Outcomes	Exposure: oral prophylaxis for all participants was carried out in a standardised dental chair using distilled water with controlled frequency (30 KHz) and water pressure (0.3 MPa). Scaling for 30 min Outcome name: CFU count Outcome measurement: blood agar plates at the neck of the patient, the assistant and the operator 30 cm from patient's mouth. Labelled plates were exposed at start of scaling procedure performed for 30 min, and left uncovered on the operator's stool, assistant's stool and the back rest of the dental chair for additional 30 min. Incubated for 48 hours at 37 °C. CFUs counted using a colony counter Effect estimate: mean CFUs at patient, assistant or operator Adverse events: not reported
Notes	Key study conclusions Mouth rinses equally effective Groups A1 and B1 (47 °C) showed maximum reduction in bacterial counts in all 3 areas compared to their cold counterparts A2 and B2 at 18 °C Contact information: Amruta Arun Joshi, Department of Periodontics, MGM Dental College and Hospital, Maharashtra, India; E‐mail: amrutajoshi2611@gmail.com
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated random numbers. Quote: "Computer‐generated random numbers were used for randomization."
Allocation concealment (selection bias)	Unclear risk	Quote: mouth rinses "were procured from manufacturers and were transferred into identical opaque white bottles labelled as A1, B1, A2 and B2 for the purpose of blinding, by an investigator not involved in the study."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: mouth rinses "were procured from manufacturers and were transferred into identical opaque white bottles labelled as A1, B1, A2 and B2 for the purpose of blinding, by an investigator not involved in the study."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: mouth rinses "were procured from manufacturers and were transferred into identical opaque white bottles labelled as A1, B1, A2 and B2 for the purpose of blinding, by an investigator not involved in the study."
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "The non‐compliance rate for our study was zero and there were no dropouts."
Selective reporting (reporting bias)	Unclear risk	We are unsure if all planned outcomes were reported as the trial was registered retrospectively.
Other bias	Low risk	No other bias observed.

Kaur 2014.

Study characteristics
Methods	Title: effect of chlorhexidine, povidone iodine, and ozone on microorganisms in dental aerosols: randomized double‐blind clinical trial Trial design: randomised, parallel‐group trial Trial registration: not reported Location: Karnataka, India Setting: dental school hospital Language: English Number of centres: 1 Study period: October 2006 to March 2008 – personal communication Funding source: no funding received – personal communication Dental aerosol procedure tested: ultrasonic scaling (type of scaler not reported)
Participants	Age (range): 20–50 years Total number of participants: 60 Inclusion criteria: ≥ 20 permanent teeth present Exclusion criteria: presence of periodontitis, medical conditions or taking medications that would contraindicate treatment Number randomised: 60 Number evaluated (withdrawals/missing participants): 60 (no dropouts – personal communication)
Interventions	Intervention 1 Group name: 0.2% CHX Number randomised: 20 Description of intervention: 0.2% CHX rinse; volume unclear, for 1 min Any co‐interventions: none Intervention 2 Group name: 1% povidone iodine Number randomised: 20 Description of intervention: rinsing for 1 min Any co‐interventions: none Comparator Group name: ozonated water with 0.082 mg/hour ozone output Number randomised: 20 Description of intervention: rinsing for 1 min Any co‐interventions: none
Outcomes	Exposure: after baseline sampling for 30 min, prerinse scaling was performed for 10 min by operator, with universal tip attached to the ultrasonic scaler and prerinse sampling for 30 min; after this, patients rinsed and were again subjected to 10 min of scaling plus postrinse sampling for 30 min. Outcome name: CFUs aerobic Outcome measurement: 3 agar plates at chest of patient, mask of the operator and 9 ft behind patient at 3 measurement moments: baseline = 30 min before procedure; during prerinse scaling 10 min and postscaling 30 min; during postrinse scaling 10 min and postscaling 30 min. Agar plates incubated aerobically at 37 °C for 48 hours and anaerobically in an increased carbon dioxide chamber for 48 hours. CFU counted with a counter and examiner blind to treatment. Effect estimate: mean difference Outcome name: anaerobic CFU Outcome measurement: see above Effect estimate: mean difference Adverse events: no adverse effects seen – personal communication
Notes	Key study conclusions Significant reduction of bacterial CFU in all the 3 groups, showing the maximum reduction of up to 57%. At mask position, reduction in aerobic colonies from prerinse to postrinse was 57% for CHX group (57%), 54% for placebo group, and 47% for ozonated group. Highest anaerobic CFU reduction at chest position and 9 ft for CHX group followed by placebo and ozonated groups. Contact information: Dr Vandana KL, Departments of Oral and Maxillofacial Surgery, Christian Dental College, Ludhiana, Punjab, India; E‐mail: vanrajs@gmail.com Comments: mail sent on 30 March 2021 requesting missing details and reply received on 3 May 2021 via WhatsApp.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Used random number table. Quote: "randomization was done on an alternate basis."  Quote: "using a randomization table."
Allocation concealment (selection bias)	Low risk	Quote: "To maintain full blinding of the results, the randomization code was held by one of the authors remotely from all assessments and wasn't broken until all data had been collected and analyzed."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "To maintain full blinding of the results, the randomization code was held by one of the authors remotely from all assessments and wasn't broken until all data had been collected and analyzed." Quote: operator was "blinded of both, the mouth rinse and irrigation provided to the subjects."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Colonies were counted using the colony counter device by the examiner, who was blinded to the rinse provided. Quote: operator was "blinded of both, the mouth rinse and irrigation provided to the subjects."
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts.
Selective reporting (reporting bias)	High risk	Non‐significant results not reported.
Other bias	Low risk	None detected.

Mohammed 1964.

Study characteristics
Methods	Title: efficacy of preoperative oral rinsing to reduce air contamination during use of air turbine handpieces Trial design: 3‐arm randomised parallel‐group trial Trial registration: not reported Location: Puerto Rico, USA Setting: university dental clinic Language: English Number of centres: 1 Study period: no details given, 1963 assumed Funding source: not reported Dental aerosol procedure tested: high‐speed drilling for cavity preparation
Participants	Age: not reported but all were male or female students Total number of participants: 185 Inclusion criteria: all participants had moderate gingivitis and, for better control, all cavities were prepared in the lower molar region Exclusion criteria: not reported Number randomised: 185 Number evaluated (withdrawals/missing participants): 185
Interventions	Intervention Group name: group 2 (mouthwash) Number randomised: 80 Description of intervention: sampling done after rinsing with 20 mL of mouthwash formulation; CPC + domiphen bromide + quaternary ammonium compounds Any co‐interventions: none Comparator 1 Group name: group 1 (no rinse) Number randomised: 80 Description of control: no rinsing before cavity preparation Comparator 2 Group name: group 3 (distilled water) Number randomised: 25 Description of control: sampling performed after rinsing with 20 mL of distilled water
Outcomes	Outcome name: CFU Outcome measurement: mean bacterial counts. Used aerosol monitoring equipment made available by the Millipore Filter Corporation. Sterile impinger mounted rigidly in an upright position; top plug removed from the clinical field monitor, and adapter end of a sterile sampling tube inserted. 30 mL of sterile impingement fluid added to impinger. Vacuum source connected, and air sample was drawn into and through impinger. Effect estimate: mean difference
Notes	Key study conclusions Oral rinse before operative procedures with high‐speed drills was effective for the clearance of debris and the clearance of oral micro­organisms. Mouthwash formulation seemed superior to water (76% reduction). Contact information: Clive I Mohammed, University of Puerto Rico, School of Dentistry, San Juan, Puerto Rico
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method not reported. Quote: "allotted at random, divided as to sex and number."
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not reported.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts.
Selective reporting (reporting bias)	Unclear risk	No measure of variance reported and clinical trial registration details not available.
Other bias	Low risk	None detected.

Mohammed 1970.

Study characteristics
Methods	Title: preoperative oral rinsing as a means of reducing air contamination during use of air turbine handpieces Trial design: randomised controlled trial Trial registration: not reported Location: School of Dentistry, University of Puerto Rico Setting: university hospital Language: English Number of centres: 1 Study period: not reported Funding source: not reported Dental aerosol procedure tested: drilling tooth with air turbine handpiece
Participants	Age: not reported Total number of participants: 40 males Inclusion criteria: participants who needed class I cavity preparation in lower molar region Exclusion criteria: not reported Number randomised: 20 participants per group
Interventions	Intervention Group name: group II (preprocedural mouth rinse) Number randomised: 20 Description of intervention: CPC + domiphen bromide + quaternary ammonium antiseptics and cationic surfactants, alcohol Any co‐interventions: none Comparator Group name: group I (no preprocedural mouth rinse) Number randomised: 20 Description of control: none Any co‐interventions: none
Outcomes	Outcome name: contamination in aerosols Outcome measurement: mean colony count; used trypticase soy broth culture medium and sample collected after 1 min of the procedure using a sterile impinger from 10 inches in front of and above the patient's mouth Effect estimate: group I: 803.3 (total 16,066; 20 participants); group II: 348.3 (total 6967; 20 participants). SD not reported Adverse events: not reported
Notes	Key study conclusions Mouthwash formulation appeared to reduce contamination. Contact information: Victor Monserrate, Formerly Assistant Professor, Department of Histopathology, University of Puerto Rico School of Dentistry, Puerto Rico
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported.
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not reported.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts.
Selective reporting (reporting bias)	Unclear risk	No measure of variance reported and clinical trial registration details unavailable.
Other bias	Low risk	None detected.

Mohan 2016.

Study characteristics
Methods	Title: the efficacy of pre‐procedural mouth rinse on bacterial count in dental aerosol following oral prophylaxis. Trial design: randomised controlled trial Trial registration: not reported Location: Chennai, India Setting: university hospital Language: English Number of centres: 1 Study period: not reported Funding source: not reported Dental aerosol procedure tested: oral prophylaxis using ultrasonic scaler (type of scaler not reported)
Participants	Age (range): 25–40 years Total number of participants: 20 Inclusion criteria: ≥ 20 permanent teeth present; lack of any dental treatment for previous 8 months; Plaque Index 1–3 Exclusion criteria: people with systemic disorders such as hypertension, rheumatic disorders, pregnancy; receiving antibiotic or immunosuppressive treatment Number randomised: 10 per group Number evaluated (withdrawals/missing participants): 10 per group (0)
Interventions	Intervention Group name: group II Number randomised: 10 Description of intervention: 0.2% CHX mouth rinse for 1 min Any co‐interventions: none Comparator Group name: group I Number randomised: 10 Description of control: saline mouth rinse for 1 min Any co‐interventions: none
Outcomes	Outcome name: contamination in aerosols Outcome measurement: mean CFU; blood agar medium; 3 ft away from patient's mouth Effect estimate (mean CFU): group I: 891.1 (SD 595.19); group II: 222.7 (SD 117.8) Adverse events: not reported
Notes	Key study conclusions CHX had a significant effect as an antimicrobial preprocedural mouth rinse in reducing number of CFUs in the aerosol produced by the ultrasonic scaling units Contact information: Meenakshi Mohan, Saveetha Dental College, Chennai 77, India; E‐mail: drmeena.mohan23@gmail.com Comments: mail sent on 29 March 2021 requesting the missing details and reply awaited
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method not reported. Quote: "subjects were randomly distributed into two groups of ten subjects each."
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not reported.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts.
Selective reporting (reporting bias)	Unclear risk	Clinical trial registration details not available.
Other bias	Low risk	None detected.

Nayak 2020.

Study characteristics
Methods	Title: comparative evaluation of efficacy of chlorhexidine and herbal mouthwash as a preprocedural rinse in reducing dental aerosols: a microbiological study Trial design: blinded, placebo‐controlled, randomised, 3‐group parallel design Trial registration: CTRI/2019/01/017038 Location: Mangalore, India Setting: university hospital Language: English Number of centres: 1 Study period: not reported Funding source: Warren, a division of Indoco remedies, India, and Sagar Pharmaceuticals, BPRL PVT Ltd., India, provided free Rexidin (CHX mouthwash) and Befresh (herbal mouthwash containing Cinnamomum zeylanicum, Mentha spicata, Syzygium aromaticum, and Eucalyptus globulus) samples Dental aerosol procedure tested: ultrasonic scaling (piezoelectric)
Participants	Age (mean): group A (CHX): 42.43 (SD 6.3) years; group B (Herbal mouthwash): 43.73 (SD 5.5) years and group C (control): 44 (SD 6) years Total number of participants: 30 (10 per group) Inclusion criteria: systemically healthy people; aged > 18 years; ≥ 20 teeth; diagnosed with mild–moderate form of chronic periodontitis Exclusion criteria: smokers, pregnant and breastfeeding women, underwent any periodontal treatment in last 6 months or received antibiotics or non‐steroidal anti‐inflammatory drugs in past 8 weeks and people using mouthwash or known allergy to CHX mouthwash Number randomised: 30 Number evaluated (withdrawals/missing participants): 30 (0)
Interventions	Intervention 1 Group name: group A Number randomised: 10 Description of intervention: 0.2% CHX herbal mouthwash (10 mL for 1 min as a preprocedural rinse 30 min before procedure) Any co‐interventions: none Intervention 2 Group name: group B Number randomised: 10 Description of intervention: Befresh herbal mouthwash (10 mL for 1 min as a preprocedural rinse 30 min before procedure; contained Cinnamomum zeylanicum, Mentha spicata, Syzygium aromaticum and Eucalyptus globulus Any co‐interventions: none Comparator Group name: group C Number randomised: 10 Description of control: preprocedural rinse with water (10 mL for 1 min as a preprocedural rinse 30 min before procedure) Any co‐interventions: none
Outcomes	Outcome name: contamination in aerosols Outcome measurement: mean CFUs/plate at 30 cm from patient's mouth, at assistant chest area, operator chest area and patient chest area (postscaling for 10 min; blood agar plates used to collect samples) Effect estimate: mean (SD) Adverse events: not reported
Notes	Key study conclusions Reduction in bacteria present in aerosol during ultrasonic scaling found with herbal rinse (Befresh) and it was as effective as CHX. Contact information: Sangeeta Umesh Nayak, Department of Periodontology, Manipal College of Dental Sciences, Mangalore; Manipal Academy of Higher Education, Manipal, Karnataka, India; E‐mail: sangeeta.nayak@manipal.edu
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Used computer‐generated table.
Allocation concealment (selection bias)	Low risk	Quote: "The enrollment and allocation were done by a masked examiner."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	All assigned mouthwashes were colourless. Assigned mouthwash was dispensed in a similar opaque bottle and by a blinded operator. Operator who performed scaling was also blinded.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Blinded researchers performed the microbial analysis.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts.
Selective reporting (reporting bias)	Low risk	All outcomes mentioned in the trial registration document were reported in the article.
Other bias	Low risk	None detected.

Nisha 2021.

Study characteristics
Methods	Title: efficacy of preprocedural boric acid mouth rinse in reducing viable bacteria in dental aerosols produced during ultrasonic scaling Trial design: 3‐arm parallel‐group randomised controlled trial Trial registration: CTRI/2017/10/010189 (registered retrospectively) Location: Mysuru, India Setting: university hospital Language: English Number of centres: 1 Study period: March 2016 to August 2016 Funding source: JSS Academy of higher education and Research University, Mysuru, Karnataka (No.REG/DIR(R)/URG/5 4/2011‐12/7279/9) Dental aerosol procedure tested: ultrasonic scaling (type of scaler not reported)
Participants	Age (mean): 37 years Total number of participants: 96 (32 in each group) Inclusion criteria: systemically healthy men or women aged 25–55 years; diagnosed with moderate chronic periodontitis having ≥ 20 natural teeth with a mean Plaque Index of 2–3, probing pocket depth ≥ 4 mm in ≥ 4 sites (probing pocket depth criteria not mentioned in the trial register) Exclusion criteria: people with respiratory infection, smokers, pregnant/breastfeeding women, administration of any mouth rinses or oral irrigation, any systemic or topical antimicrobial drug intake in last 6 months, hypersensitivity to CHX gluconate or boric acid and other formula ingredients Number randomised: 96 Number evaluated (withdrawals/missing participants): 30 in each group (2 dropouts from each group)
Interventions	Intervention 1 Group name: group A: CHX Number randomised: 32 Description of intervention: 0.12% CHX (Periogard, Colgate‐Palmolive) Any co‐intervention: none Intervention 2 Group name: group B: boric acid Number randomised: 32 Description of intervention: boric acid 0.75% Any co‐intervention: none Comparator Group name: group C (control group): water Number randomised: 32 Description of intervention: water Any co‐intervention: none Participants rinsed for 1 min with 15 mL of 0.12% CHX, 10 mL boric acid or 10 mL water 15 min prior to procedure.
Outcomes	Outcome name: contamination of aerosols at 30 cm from patient's mouth on patient's chest, operator's chest and dental assistant's chest. Blood agar plates used for culture. Outcome measurement: mean CFUs Effect estimate: mean (SD) Adverse events: not reported
Notes	Key study conclusion Study recommends routine use of preprocedural mouth rinse to reduce bacterial aerosols generated during ultrasonic scaling and that 0.12% CHX gluconate is more effective than 0.75% BA mouthwash in reducing CFUs count. Contact information: Dr Avinash Bettahalli Shivamallu, Department of Periodontology, J.S.S Dental College and Hospital, JSS Academy of Higher Education and Research, Mysuru, Karnataka, India; E‐mail: avinashbs@gmail.com Comments: type of scaler, method of allocation concealment, reason for dropout, any adverse events were not reported. Trial registration document mentions the method as cross‐over trial and sample size as 10 per group. The trial was registered retrospectively.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The patients were randomly allotted using computer‐generated random sequence table (GraphPad) to one of the three groups by one examiner."
Allocation concealment (selection bias)	Unclear risk	Not reported in main publication. Trial registration document quote: "an open list of random numbers."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "the treatment was performed by another examiner (S Nisha) unknown of the pre rinse used before scaling." Quote: "Since the study protocol involved triple masking, the operator, microbiologist, and the patients were unaware of allocated groups."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "Since the study protocol involved triple masking, the operator, microbiologist, and the patients were unaware of allocated groups."
Incomplete outcome data (attrition bias) All outcomes	Low risk	2 dropouts from each group; reason for dropout not reported, but intention‐to‐treat analysis appears to have been used.
Selective reporting (reporting bias)	Unclear risk	All outcomes mentioned in trial registration document were reported in the article; however, the trial registration was done retrospectively and for a sample of 10 participants.
Other bias	Low risk	None observed.

Reddy 2012.

Study characteristics
Methods	Title: efficacy of 0.2% tempered chlorhexidine as a pre‐procedural mouth rinse: a clinical study Trial design: 3‐arm parallel‐group randomised controlled trial Trial registration: not reported Location: Bengaluru, India Setting: university hospital Language: English Number of centres: 1 Study period: not reported Funding source: none declared Dental aerosol procedure tested: ultrasonic scaling (type of scaler not reported)
Participants	Age: not reported Total number of participants: 30 Inclusion criteria: not reported Exclusion criteria: history of treatment for moderate‐to‐severe periodontitis in past 6 months, having systemic disease, receiving systemic antibiotics Number randomised: 30 Number evaluated (withdrawals/missing participants): 30 (0)
Interventions	Intervention 1 Group name: group II: 0.2% non‐tempered CHX Number randomised: 10 Description of intervention: 0.2% non‐tempered CHX Any co‐interventions: none Intervention 2 Group name: group III: 0.2% tempered CHX mouthwash Number randomised: 10 Description of intervention: 0.2% tempered CHX mouthwash rinsing for 60 sec (tempering = warming to 47 °C) Any co‐interventions: none Comparator Group name: group I Number randomised: 10 Description of control: rinse with sterile water for 60 sec Any co‐interventions: none
Outcomes	Outcome name: contamination of aerosols at a distance of 4 ft at 3, 6 and 12 o'clock positions from patient's mouth. Blood agar plates used for culture Outcome measurement: mean CFUs Effect estimate: mean (SD) Adverse events: not reported
Notes	Key study conclusions CHX had a significant effect as an antimicrobial preprocedural mouth rinse in reducing number of CFUs in aerosol produced by ultrasonic scaling units. Both tempered and non‐tempered forms of 0.2% were effective in reducing the bacterial load in aerosol, but tempered CHX was slightly better. Contact information: Dr MGS Prasad, Department of Periodontics, Dr Syamala Reddy Dental College, Karnataka, India; E‐mail: prasadmgs@indiatimes.com Comments: we mailed the contact author for missing details on 29 March 2021 and the mail was returned as unavailable.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method not reported. Quote: "divided randomly into 3 groups."
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not reported.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropout.
Selective reporting (reporting bias)	Unclear risk	Clinical trial registration details not available.
Other bias	Low risk	None detected.

Retamal‐Valdes 2017.

Study characteristics
Methods	Title: effectiveness of a pre‐procedural mouthwash in reducing bacteria in dental aerosols: randomized clinical trial Trial design: 4‐arm single‐blind randomised controlled trial Trial registration: NCT02875769 Location: Sao Paulo, Brazil Setting: university hospital Language: English Number of centres: 1 Study period: February to April 2015 Funding source: supported by Colgate Palmolive Company (Piscataway, NJ, USA) and Latin America Oral Health Association (LAOHA) Dental aerosol procedure tested: dental prophylaxis using ultrasonic scaler (Magnetostrictive)
Participants	Age (mean): no rinsing group: 46.27 (SD 6.63) years; water group: 36.13 (SD 8.71); CPC+Zn+F: 45.47 (SD 11.79) years; CHX group: 41.40 (SD 10.93) years Total number of participants: 60 Inclusion criteria: men or women aged 18–70 years, ≥ 20 natural teeth, ≥ 80% of the sites with visible supragingival plaque, < 10% of sites with visible supragingival calculus, < 30% of sites with PD ≥ 5 mm Exclusion criteria: presence of orthodontic bands; partial removable dentures; lesions of the soft or hard tissues of the oral cavity; carious lesions requiring immediate restorative treatment; history of allergy to CHX, CPC, zinc lactate or sodium fluoride; participation in any other clinical study within 1 month period prior to entering study; professional tooth cleaning procedure (oral prophylaxis) during 1 month prior to entering study; pregnant or breastfeeding women; antibiotic therapy in previous 6 months; continuous use of oral mouthwashes and any systemic condition that may require prophylactic medication for dental treatment (e.g. mitral valve prolapse) Number randomised: 60 Number evaluated (withdrawals/missing participants): 60 (0)
Interventions	Intervention Group name: test: CPC+Zn+F (0.075% CPC + 0.28% zinc + 0.05% sodium fluoride) mouth rinse Number randomised: 15 per group Description of intervention: 20 mL CPC+Zn+F solution dispensed in opaque bottles Any co‐interventions: none Comparator 1 Group name: A (no rinsing) Number randomised: 15 per group Description of control: group A volunteers did not rinse their mouth before the dental prophylaxis. Any co‐interventions: none Comparator 2 Group name: B (water) Number randomised: 15 per group Description of control: group B volunteers rinsed their mouth with 20 mL water Any co‐interventions: none Comparator 3 Group name: CHX digluconate 0.12% Number randomised: 15 per group Description of control: volunteers rinsed their mouth with 20 mL of CHX, dispensed in an opaque bottle Any co‐interventions: none
Outcomes	Outcome name: contamination of aerosols at the support board, volunteer's chest (immediately in front of the volunteer's mouth) and on the clinician's forehead. HNK agar (tryptic soy agar with yeast extract enriched with 5% menadione, 5% sheep blood and 1% N‐acetylmuramic acid) plates were used for the sample collection and incubated under anaerobic conditions. Outcome measurement: mean CFUs Effect estimate: mean (SD) Adverse events: none of the participants reported any adverse events.
Notes	Key study conclusions CPC+Zn+F was effective in reducing viable bacteria in oral aerosol after a dental prophylaxis with ultrasonic scaler. Contact information: Magda Feres, Universidade de Guarulhos, Department of Periodontology, Dental Research Division, São Paulo, Brazil; E‐mail: mferes@ung.br
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Used computer‐generated random numbers table.
Allocation concealment (selection bias)	Low risk	Centralised allocation performed by a researcher who was not involved in any other phases of the trial.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Opaque bottles used for test and CHX mouth rinses. No rinse and rinse with water group were not blinded. However, the outcome measurement was objective (colony count) and was not influenced by the blinding of participants.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Clinician and the laboratory technician who counted the colonies were blinded to test or comparator.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropout.
Selective reporting (reporting bias)	Low risk	In the results section, CHX group showed fewer number of microbial CFUs compared to CPC+Zn+F group. However, the conclusion of the report highlights the reduction in only the CPC+Zn+F group.
Other bias	Low risk	None detected.

Shetty 2013.

Study characteristics
Methods	Title: compare the efficacy of two commercially available mouth rinses in reducing viable bacterial count in dental aerosol produced during ultrasonic scaling when used as a preprocedural rinse. Trial design: randomised single‐blind, placebo‐controlled parallel‐group study Trial registration: not reported Location: Mangalore, India Setting: university hospital Language: English Number of centres: 1 Study period: not reported Funding source: none declared Dental aerosol procedure tested: ultrasonic scaling (type of scaler not reported)
Participants	Age (range): 25–45 years Total number of participants: 60 Inclusion criteria: ≥ 20 permanent teeth, an oral hygiene score (Green and Vermillion 1960) 1.3–3, Plaque Index (Silness and Loe 1964) 1–2, gingival index score (Loe and Silness 1963) 1–2 Exclusion criteria: cardiac pacemakers, resin restorations, conditions requiring prophylactic antibiotics, prior to dental procedures or currently using antibiotics or history of antibiotic usage in past 6 months and with any history of systemic diseases Number randomised: 60 Number evaluated (withdrawals/missing participants): not reported
Interventions	Intervention 1 Group name: group II Number randomised: 20 per group Description of intervention: 0.2% CHX digluconate (Rexidine) Any co‐interventions: none Intervention 2 Group name: group III Number randomised: 20 per group Description of intervention: group III: tea tree oil (Emoform) Any co‐interventions: none Comparator Group name: group I Number randomised: 20 Description of control: rinse with distilled water Any co‐interventions: none
Outcomes	Outcome name: contamination of aerosols at 15 cm from operator's nose level, 15 cm from dental assistant's nose level and 30 cm from patient's chest level. Trypticase soy agar plates used for aerobic culture Outcome measurement: mean CFUs Effect estimate: mean (SD) Adverse events: not reported
Notes	Key study conclusions Antiseptic mouthwashes reduced bacterial CFUs in aerosol samples. CHX rinses were superior to tea tree rinses when used preprocedurally in reducing aerosolised bacteria. Contact information: Shamila K Shetty, Assistant Professor, Department of Periodontics, AB Shetty Memorial Institute of Dental Sciences, Nitte University, Mangalore, Karnataka India; telephone: +919901121270; e‐mail: shetty.shamila@gmail.com Comments: mail sent on 29 March 2021 requesting the missing details and reply awaited
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Used random number table.
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not reported.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Not reported.
Selective reporting (reporting bias)	Unclear risk	Clinical trial registration details not available.
Other bias	Low risk	None detected.

Suresh 2011.

Study characteristics
Methods	Title: comparison of efficacy of preprocedural rinsing with chlorhexidine and essential oil mouthwash in reducing viable bacteria in dental aerosols – a microbiological study Trial design: 2‐arm, parallel‐group randomised controlled trial Trial registration: not reported Location: Chennai, India Setting: dental school hospital Language: English Number of centres: 1 Study period: not reported Funding source: none reported Dental aerosol procedure tested: oral prophylaxis (piezoelectric scaler)
Participants	Age (range): 20–45 years Total number of participants: 20 Inclusion criteria: ≥ 20 permanent teeth; mean Oral Hygiene Index – simplified and Gingival Index score 2.0–3.0 Exclusion criteria: medical conditions contradicting the use of ultrasonic scalers and those on systemic or topical antibiotics and antiseptic mouth rinses for the past 6 months Number randomised: 20 Number evaluated (withdrawals/missing participants): all 20 participants evaluated
Interventions	Intervention Group name: group 1 CHX Number randomised: 10 Description of intervention: 0.2% mouth rinse CHX – 10 mL with 1‐min rinsing time Any co‐intervention: none Comparator Group name: group 2 (essential oil mouth rinse) Number randomised: 10 Description of intervention: 20 mL with 1 min rinsing time; mouth rinse contained eucalyptol, thymol, methyl salicylate and menthol essential oil Any co‐intervention: none
Outcomes	Exposure: oral prophylaxis with a piezoelectric scaler Outcome name: CFU number Outcome measurement: blood agar plates placed at patient's chest area (location A) and at the dental chair's tray 15 cm from the patient's mouth (location B). Used 5% sheep blood agar plates; plates incubated at 37 °C in an increased carbon dioxide chamber for 48 hours Effect estimate: data given in graph Outcome name: mean CFU Outcome measurement: as above Effect estimate: data given in graph
Notes	Key study conclusions When CHX was used as a prerinse before ultrasonic scaling there were consistently fewer CFUs in the 2 standard locations than when an essential oil‐containing mouth rinse was used. Contact information: Dr Snophia Suresh MDS, Reader, Department of Periodontics, Thaimoogambigai Dental College & Hospital, Chennai, India; E‐mail: Suresh_sno@yahoo.com Comments: mail sent on 29 March 2021 requesting missing details and reply awaited
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported.
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not reported.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "laboratory technician was not aware which plate was exposed during the two test procedures."
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts.
Selective reporting (reporting bias)	Unclear risk	Clinical trial registration details not available.
Other bias	Low risk	None detected.

Tasneem 2017.

Study characteristics
Methods	Title: effectiveness of preprocedural rinse with chlorhexidine and povidone iodine in preventing bioaerosol contamination during ultrasonic scaling – a clinical and microbiological study Trial design: double‐blind parallel‐group randomised controlled trial Trial registration: not reported Location: Srikakulam, India Setting: university hospital Language: English Number of centres: 1 Study period: June to December 2016 (personal communication) Funding source: no funding received (personal communication) Dental aerosol procedure tested: ultrasonic scaling (type of scaler not reported)
Participants	Age (range): 20–50 years Total number of participants: 30 Inclusion criteria: ≥ 20 permanent teeth Exclusion criteria: presence of periodontitis, medical conditions or taking medications that would contraindicate treatment Number randomised: 30 Number evaluated (withdrawals/missing participants): 30 (0)
Interventions	Intervention Group name: group I Number randomised: 15 Description of intervention: 0.2% CHX mouth rinse Any co‐interventions: none Comparator Group name: group II Number randomised: 15 Description of intervention: povidone iodine mouth rinse (concentration not reported) Any co‐interventions: none
Outcomes	Outcome name: contamination of aerosols at patient's chest level (15 cm) and on the mask of the operator (45 cm). Blood agar plates used for aerobic and anaerobic culture. Outcome measurement: mean CFUs Effect estimate: mean (SD) Adverse events: no adverse events (personal communication)
Notes	Key study conclusions CHX was superior to povidone iodine in reducing the number of viable bacteria confirmed by decreased number of CFUs. Contact information: Dr Sheema Tasneem (PG Student), Department of Periodontics and Oral Implantology, SreeSai Dental College and Research Institute, Chapuram, Srikakulam, India; E‐mail: sheema.tasneem@gmail.com Comments: mail sent on 29 March 2021 requesting missing details and reply received on 7 April 2021.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Used random numbers table.
Allocation concealment (selection bias)	Unclear risk	Quote: "Allocation of patients for either of the groups was done by flip coin method of randomization." (personal communication)
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Operator who performed the scaling was blinded for the mouth rinse used. Participants were not blinded. However, participant blinding would have not influenced the study outcomes.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Laboratory technician was blinded for the agar plates from group I or II.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts.
Selective reporting (reporting bias)	Unclear risk	Clinical trial registration details not available.
Other bias	Low risk	None detected.

Verma 2017.

Study characteristics
Methods	Title: evaluation of aerosol contamination during ultrasonic procedures Trial design: 3‐arm parallel‐group randomised controlled trial Trial registration: not reported Location: Udaipur, India Setting: university hospital Language: English Number of centres: 1 Study period: not reported Funding source: not funded Dental aerosol procedure tested: ultrasonic scaling (piezoelectric)
Participants	Age: not reported Total number of participants: 18 Inclusion criteria: presence of full complement of maxillary and mandibular anterior teeth; absence of any dental treatment for past 1 year; people with plaque and gingival score 1–2 Exclusion criteria: history of systemic disease, cardiac pacemakers or respiratory complication; pregnancy; conditions requiring prophylactic antibiotics, prior to dental procedure and those currently on medication Number randomised: 18 Number evaluated (withdrawals/missing participants): 18 (0)
Interventions	Intervention 1 Group name: group II Number randomised: 6 Description of intervention: 0.2% CHX mouth rinse for 2 min Any co‐interventions: none Intervention 2 Group name: group III Number randomised: 6 Description of intervention: 5% povidone iodine mouth rinse for 2 min Any co‐interventions: none Comparator Group name: group I Number randomised: 6 Description of control: 0.9% saline used as mouth rinse for 2 min
Outcomes	Outcome name: contamination in aerosols Outcome measurement: mean CFUs measured at 3 locations; operator's eye level, participant's eye level and participant's chest level. Blood agar plates used for aerobic culture. Effect estimate: mean (SD) Adverse events: none reported
Notes	Key study conclusions Antiseptic mouth rinses reduce the bacterial CFU in the aerosol. Povidone iodine was superior to CHX when used preprocedurally. Contact information: Dr Neha Verma, Department of Periodontics, Pacific Dental College and Hospital, Udaipur, India; E‐mail: nehavarma_0731@yahoo.com Comments: mail sent on 29 March 2021 requesting the missing details and reply received on 4 May 2021.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computerised selection (from personal communication).
Allocation concealment (selection bias)	High risk	Quote: "All the procedure was carried by a single examiner. This was done to avoid inter‐examination bias." (from personal communication)
Blinding of participants and personnel (performance bias) All outcomes	High risk	Blinding not performed (from personal communication). There is a possibility of clinicians altering their behaviour.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Blinding not done (from personal communication).
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts.
Selective reporting (reporting bias)	High risk	Povidone iodine showed no difference in the mean CFUs compared to the CHX group on plate 3 (participant's eye level). However, the results section stated, "The present study also demonstrates maximum reduction of aerobic colonies using Povidone Iodine at subject's eye." The conclusion section mentioned it as, "Povidone iodine was found to be superior to chlorhexidine when used pre‐procedurally."
Other bias	Low risk	None detected.

ADA: American Dental Association; CAL: clinical attachment level; CFU: colony‐forming units; CHX: chlorhexidine; CPC: cetylpyridinium chloride; ft: feet; min: minutes PD: probing depth; RCT: randomised controlled trial; SD: standard deviation; SE: standard error; sec: second.

Characteristics of excluded studies [ordered by study ID]

Study	Reason for exclusion
Altonen 1976	Not an RCT.
Ciancio 1994	Not an RCT.
CTRI/2017/10/010189	Unable to access.
CTRI/2018/05/013935	Unable to access.
Dawson 2016	Not an RCT.
Devker 2012	Split‐mouth design.
Fine 1992	Split‐mouth design.
Fine 1993b	Split‐mouth design.
Klyn 2001	Split‐mouth design
Litsky 1970	Not an RCT.
Logothetis 1995	High‐velocity suction used with the preprocedural rinse.
Narayana 2016	Split‐mouth design.
NCT02319668	Mouthwash was compared with toothpaste.
NCT04659928	High‐volume evacuation used with the preprocedural rinse.
Paul 2020	Not an RCT.
Rajachandrasekaran 2019	Not an RCT.
Ramesh 2015	High‐volume suction used with the preprocedural rinse.
Santos 2014	Cross‐over sequence not randomised.
Sawhney 2015	Split‐mouth design.
Swaminathan 2014	High‐speed evacuator used with the preprocedural rinse.
Toroglu 2001	Not an RCT.
Worrall 1987	Not an RCT.
Young 2002	Bacterial contamination was checked in the bone debris collected from the osteotomy site.

RCT: randomised controlled trial.

Characteristics of ongoing studies [ordered by study ID]

CTRI/2021/03/031653.

Study name	Efficiency of a herbal mouthwash in decreasing infection from splatter production during dental treatment procedures
Methods	Type of study: randomised, parallel‐group, placebo‐controlled trial Method of generating random sequence: coin toss, lottery, toss of dice, shuffling cards, etc. Method of concealment: open list of random numbers Blinding: participant blinded
Participants	Age (range): 18–60 years Gender: both Sample size: 30 Inclusion criteria: age 18–60 years; with minimum of 20 permanent teeth; Plaque Index Score 2–3; probing pocket depth ≥ 4 mm for > 2 sites; People who were systemically healthy Exclusion criteria: history of systemic or topical antibiotics use within last 3 months; smokers and people dependent on alcohol; pregnant and lactating women; history of oral prophylaxis or mouthwash use within last 3 months
Interventions	Intervention: turmix mouth rinse. Participant will be asked to rinse mouth using turmix mouthwash and then have ultrasonic scaling performed to check the efficacy of turmix mouthwash in reducing the aerosol contamination Comparator 1: chlorhexidine mouthwash. Participants will be asked to rinse mouth using chlorhexidine mouthwash and then have ultrasonic scaling performed to check the efficacy of chlorhexidine in reducing the aerosol contamination Comparator 2: placebo. Participants will be asked to rinse mouth using water and then have ultrasonic scaling performed
Outcomes	Aim: to determine the effectiveness of turmix mouthwash as preprocedural rinse in reducing aerosol contamination during ultrasonic scaling in people with chronic periodontitis. Extent of aerosol contamination during ultrasonic scaling and root planing Efficacy of intervention during ultrasonic scaling and root planing
Starting date	4 March 2021
Contact information	Nidhi Pandey, PG Student, Institute of Dental Sciences Bareilly, Department of Periodontology and Implantology Institute of Dental Sciences, Rohilkhand Medical College, Bareilly, UTTAR PRADESH, 243006, India; telephone: 8218251306; E‐mail: docpandey.n19@gmail.com
Notes	Open for recruitment

CTRI/2021/10/037528.

Study name	Comparison of providone iodine and chlorhexidine as a mouth rinse before cleaning treatment to reduce the bacterial count during treatment
Methods	Study design: randomised, parallel‐group trial Method of random sequence generation: computer‐generated randomisation Allocation: on‐site computer system Blinding: not applicable
Participants	Age (range): 17–54 years Gender: male and female Sample size: 42 Inclusion criteria: systemically healthy people; with ≥ 20 permanent teeth present; give informed consent to participate in the study Exclusion criteria: people who are asthmatic, have infectious disease or are immunocompromised; pregnant and lactate women
Interventions	Comparator: povidone iodine Intervention: chlorhexidine gluconate There was some inconsistency in the descriptions of the concentration used in each intervention.
Outcomes	Efficacy as a preprocedural mouth rinse in reducing aerosol contamination and bacterial count during ultrasonic scaling
Starting date	5 November 2021
Contact information	Naskath Sabana, PG student, Yenepoya Dental College, Department of Periodontology, Yenepoya University Deralakatte, Karnataka, India; telephone 9003493961; E‐mail: naskathsabana651@gmail.com
Notes	Not yet recruiting

NCT03839719.

Study name	Efficacy of ocimum sanctum as a pre‐procedural mouth rinse in reducing aerosol contamination produced by ultrasonic scaler: a clinical and microbiological study
Methods	Allocation: randomised Intervention model: cross‐over assignment Intervention model description: ultrasonic scaling done in 1st and 4th quadrant without any mouth rinse and fall out samples were collected in the blood agar plates kept at a distance of 0.5 m and 1 m from the oral cavity. After ultrasonic scaling of the 1st and 4th quadrant minimum 30‐min interval maintained. After 30 min rinsing the mouth with the ocimum sanctum mouth rinse, chlorhexidine gluconate mouth rinse or placebo for 60 seconds. Ultrasonic scaling was repeated in 2nd and 3rd quadrant and fall out samples were collected in the newly placed blood agar plates kept at 0.5 m and 1 m away from the patient. Treatment was carried out by placing 3 sterile agar plates uncovered at predesignated sites to collect samples of aerosolised bacteria. Single‐centre, double‐blind, placebo‐controlled study conducted over 2 months. Blinding: triple (participant, investigator, outcomes assessor) Blinding description: participants and investigator are blinded about mouth rinse use and assigned quadrant Primary purpose: prevention
Participants	Age (range): 18–40 years Gender: men and women Inclusion criteria: people with generalised chronic gingivitis or mild generalised chronic periodontitis of either sex; systemically healthy people, have ≥ 20 teeth; aged 18–40 years; who abide by approved protocol guidelines and willing to give written informed consent Exclusion criteria: any known systemic disease that affects periodontium, such as diabetes, cardiovascular disease, cancer, etc.; receiving anti‐inflammatory, perioceutics, antibiotics, steroids, cytotoxic and drugs for 3 months; known allergy to the material used; pregnant and breastfeeding women; have undergone any type of non‐surgical or surgical periodontal therapy (or both) earlier, in the past 6 months; tobacco users (smoke and smokeless) and people dependent on alcohol
Interventions	Placebo; before rinsing with the mouth rinse, ultrasonic scaling was performed in the 1st and 4th quadrant without any mouth rinse (placebo mouth rinse) and fall out samples were collected in the blood agar plates kept at a distance of 0.5 m and 1 m from the oral cavity. Ocimum sanctum mouth rinse. After ultrasonic scaling of the 1st and 4th quadrant minimum 30‐min interval maintained. After 30 min rinsing the mouth with ocimum sanctum mouth rinse for 60 seconds, ultrasonic scaling was repeated in 2nd and 3rd quadrant and fall out samples were collected in the newly placed blood agar plates kept at 0.5 m and 1 m from the patient. Chlorhexidine gluconate mouth rinse. After ultrasonic scaling of the 1st and 4th quadrant minimum 30 min interval maintained. After 30 min rinsing the mouth with chlorhexidine gluconate mouth rinse for 60 seconds. Ultrasonic scaling was repeated in the 2nd and 3rd quadrant and fall out samples were collected in the newly placed blood agar plates kept at 0.5 m and 1 m from the patient.
Outcomes	Counting of CFU up to 48 hours Preformed 10% blood agar plates were incubated at 37 °C for 48 hour after collecting the sample. Counting of CFUs was performed by a microbiologist who was blinded regarding the time of exposure and location of agar plate. The microbial counting was performed afterwards.
Starting date	9 January 2019
Contact information	Dr Pratik Kumar Ashok Bhai Chaudhari, Government College of Dentistry, Indore, India
Notes	Study completed 26 April 2019

NCT04717063.

Study name	Clinical efficacy of single‐use of peroxyl mouthwash for reducing bacteria saliva and bioaerosol contamination phase 2
Methods	Allocation: randomised Intervention model: parallel assignment Intervention model description: each participants will be randomised to receive 1 of 2 possible study products Blinding: triple (participant, investigator, outcomes assessor) Blinding description: triple (participant, investigator, outcome assessor) Primary purpose: treatment
Participants	Gender: men and women Sample size: 100 Inclusion criteria: ALL of the following criteria: ages 18–70 years inclusive; availability for the duration of the study; good general health; ≥ 20 natural teeth; Gingivitis Index 1.0 (Loe and Silness); signed informed consent form Exclusion criteria: must NOT HAVE ANY of the following conditions: symptoms consistent with COVID‐19 or have tested positive; presence of orthodontic bands; tumour(s) of the soft or hard tissues of the oral cavity; advanced periodontal disease (purulent exudate, tooth mobility, extensive loss of periodontal attachment or alveolar bone, or a combination) or peri‐implantitis; ≥ 5 carious lesions requiring immediate restorative treatment; use of antibiotic 1 month prior to entry into the study; participation in any other clinical study or test panel within 1 month prior to entry into study; dental prophylaxis during the past 2 weeks prior to baseline examinations; history of allergies to oral care/personal care consumer products or their ingredients; receiving any prescription medicines that might interfere with the study outcome; an existing medical condition that prohibits not eating or drinking for periods up to 4 hours; history of alcohol or drug abuse; pregnant or breastfeeding women
Interventions	Drug: peroxyl mouth wash 1.5% Placebo: placebo mouth wash
Outcomes	Antibacterial efficacy of mouthwash in reducing the levels of bacteria in bioaerosols generated by dental prophylaxis at 30 min
Starting date	16 November 2020
Contact information	Yiming Li, Loma Linda University
Notes	Recruitment completed

CFU: colony‐forming unit; min: minute.

Differences between protocol and review

We performed sensitivity analysis in those meta‐analyses that had imputed data to check for differences between the results of these analyses.

We asked 11 dental surgeons to prioritise the comparisons for presentation in the summary of findings tables, as we had not planned this in our protocol. We used purposive sampling to select these dental surgeons based on geographic locations and their experience in using rinses before performing AGPs. We shared a Google form with all the comparisons and the dental surgeons ranked the comparisons (from rank 1 for the most important comparison to rank 10 for the least important comparison). One dental surgeon was unable to complete the prioritisation exercise within the given deadline and the other 10 dental surgeons prioritised the comparisons. We calculated the total of these Likert scales for each comparison from the 10 dental surgeons and identified the seven lowest scored comparisons as the most important ones.

Contributions of authors

SKN: obtaining full‐text articles, data extraction, GRADE and final review draft preparation, and review update.

PE: data analysis, GRADE and final review draft preparation.

MP: screening of titles and abstracts, screening full texts and final review draft preparation.

MN: arbiter, data extraction, analysis and final review draft preparation.

GS: screening of titles and abstracts, screening full texts and final review draft preparation.

TF: screening of titles and abstracts, data extraction and final review draft preparation.

JHV: data extraction and analysis, writing results and discussion.

Sources of support

Internal sources

• Division of Dentistry, School of Medical Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, UK

  Support to Cochrane Oral Health

• Manchester Academic Health Sciences Centre (MAHSC) and the NIHR Manchester Biomedical Research Centre, UK

  Support to Cochrane Oral Health

External sources

• Cochrane Oral Health Global Alliance, Other

  The production of Cochrane Oral Health reviews has been supported financially by our Global Alliance since 2011 (oralhealth.cochrane.org/partnerships-alliances). Contributors in recent years have been the American Association of Public Health Dentistry, USA; AS‐Akademie, Germany; the British Association for the Study of Community Dentistry, UK; the British Society of Paediatric Dentistry, UK; the Canadian Dental Hygienists Association, Canada; the Centre for Dental Education and Research at All India Institute of Medical Sciences, India; the National Center for Dental Hygiene Research & Practice, USA; New York University College of Dentistry, USA; and Swiss Society of Endodontology, Switzerland.

• NIHR, Other

  This project was supported by the National Institute for Health and Care Research (NIHR), via Cochrane Infrastructure funding to Cochrane Oral Health. The views and opinions expressed herein are those of the review authors and do not necessarily reflect those of the Evidence Synthesis Programme, the NIHR, the National Health Service or the Department of Health and Social Care.

Declarations of interest

SKN: none.

PE: none.

MP: none.

MN: none.

GS: none.

TF: none.

JHV: none.

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