Ultrasonic Cleaning and its Effects on Denture Biofilm: A Systematic Review

Abstract

Introduction and aims

Denture biofilm is associated with various oral and systemic diseases. Therefore, an effective denture-cleaning method should be adopted by denture wearers. This systematic review aimed to evaluate the efficacy of ultrasonic denture cleaning in reducing plaque quantity and microbial load and changing the microbial composition.

Methods

Clinical studies published in English with no restriction on the year of publication that compared ultrasonic denture cleaning with other cleaning methods were included. Literature was searched across 5 electronic databases (PubMed, Embase, Web of Science, Scopus, and Cochrane Central Register for Controlled Trials). An additional search via other methods was performed until June 2025. The Revised Cochrane Handbook risk-of-bias tools (RoB 2) for individually randomised and parallel-group trials, cluster-randomised trials, and crossover trials were employed for the risk of bias assessments. A narrative synthesis of the included studies was generated.

Results

A total of 2,811 articles were identified. Fifteen studies underwent full-text article screening, and an additional 4 articles were added through manual search. Ultimately, 10 randomised controlled clinical trials reporting the efficacy of ultrasonic denture cleaning contributed to this review. All included studies, assessed using the RoB 2, were considered to be of ‘some concerns’ to a ‘high risk’ of bias. The present review identified a diverse range of ultrasonic cleaning protocols. From the synthesis of the 10 included studies, positive outcomes were observed in reducing denture plaque quantity and microbial load, particularly when a chemical cleansing method was combined with ultrasonic cleaning.

Conclusion

There was consistent evidence from randomised clinical trials that supported ultrasonic cleaning reduced denture plaque quantity and modified microbial load, particularly when supplemented with an effervescent denture cleanser.

Clinical Relevance

Ultrasonic cleaning combined with chemical cleansing should be adopted by older adults to reduce denture plaque coverage and microbial loads.

Introduction

In general, removable dentures remain one of the most prevalent oral rehabilitation treatment options for patients with severe tooth loss. Most denture wearers belong to more disadvantaged patient groups, characterised by older age, complex medical histories, and lower socioeconomic status.¹ Cognitive impairment, poor vision, reduced manual dexterity, and a lack of awareness or knowledge with regards to oral and denture hygiene care among this group of patients may lead to suboptimal denture hygiene maintenance.2, 3, 4, 5 Additionally, the known high prevalence of pathogenic bacteria residing in denture biofilm^6,7 has been shown to be a threat to patients’ general oral and systemic health, causing denture stomatitis, bacterial endocarditis, gastrointestinal infection, aspiration pneumonia, and other respiratory infections.8, 9, 10, 11 Consequently, a growing demand for highly automated denture-cleaning methods, such as ultrasonic cleaning, can be foreseen.

Denture-cleaning methods are categorised into a mechanical approach, a chemical approach, and various combinations of these two.^12,13 As recommended by the Cochrane review, the combination of both mechanical and chemical cleaning provided a positive effect on denture cleanliness.¹² However, until now, most denture wearers still clean their dentures by simply brushing them with toothpaste, soap, detergent, or even water because this is the easiest, simplest, and inexpensive method.¹⁰ The effectiveness of this mechanical approach in reducing denture plaque remains uncertain, particularly when performed by older adults.¹⁴ The complex topography and unpolished denture fitting surface will further promote denture biofilm deposition and complicate the removal of microorganisms present on removable dentures.^15,16 To overcome this limitation, ultrasonic denture cleaning has been considered as a viable mechanical cleaning alternative.^17,18 Traditionally, ultrasonic cleaning devices are a mechanical aid used by dental practitioners in clinical settings. The mechanical mechanisms of action of these devices rely on ultrasound waves transferred to the immersion solution by generating vibration and causing the collapse of the formed bubbles, which subsequently detach the biofilm from denture surfaces.¹⁹

In the past, the Cochrane review reported a lack of randomised controlled trials to study the efficacy of ultrasonic cleaning to clean removable dentures.¹² Although there have been numerous clinical trials investigating the efficacy of ultrasonic denture cleaning, the efficacy of ultrasonic cleaning remains inconclusive because of variations and a lack of standardisation in ultrasonic cleaning protocols.^17,20,21 For example, previous studies often used ultrasonic devices shared among participants, varied the duration and frequency of cleaning, differed in using ultrasonic cleaning as a standalone approach or in combination with various chemical immersion solutions,²² and were operated either by researchers or by patients, all of which may have contributed to inconsistent findings and discouraged the use of this approach as a routine denture-cleaning method. It is therefore important to summarise the observed effects attributable to the mechanical action of the ultrasonic device in reducing the area of plaque coverage or affecting the microbial composition.

Changes in the area of plaque coverage, microbial load, and microbial composition are commonly used to assess denture hygiene interventions. Plaque coverage area was routinely evaluated using visual denture hygiene indices or computerised planimetric assessments.23, 24, 25 Microbial counts for certain fungi, including Candida albicans, Candida tropicalis, Candida krusei, Candida glabrata, and Candida parapsilosis, are also commonly measured.^14,26 Numerous bacterial species, such as Staphylococcus aureus and Streptococcus mutans, were also frequently assessed, given that they are important colonisers in denture biofilm and facilitate the adherence of Candida species.26, 27, 28 The high prevalence of respiratory pathogens residing on denture surfaces is receiving considerable attention and requires urgent solutions.^7,29 Although the findings of the effectiveness of ultrasonic cleaning, with or without an additional chemical cleanser, in reducing plaque coverage area are generally encouraging,¹⁷ their mechanical action of ultrasonication on microbial profile remains uncertain.

Although several systematic reviews have been published evaluating the effectiveness of denture-cleaning methods,^12,13 very few of the reviews have included the outcome measures such as changes of microbial profile, particularly using the ultrasonic cleaning method. Therefore, the efficacy of ultrasonic cleaning in reducing the plaque coverage area and changing the microbial profile has not been comprehensively summarized. There is a need to evaluate the clinical outcomes of this denture-cleaning approach via a systematic appraisal of the existing evidence. Hence, the present systematic review aimed to evaluate the efficacy of ultrasonic denture cleaning in changing the plaque quantity, microbial load, and microbial composition, compared with other cleaning approaches.

Methods

Registration and protocol

This systematic review was registered with PROSPERO, the International Prospective Register of Systematic Reviews (ID: CRD420250480059), and reported in compliance with the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Appendix 1).³⁰ However, there was no patient or public involvement in this systematic review.

Eligibility criteria

The eligibility criteria were designed based on the Population, Intervention, Comparison, Outcome, and Study schema. The search strategy was defined using a controlled vocabulary by incorporating Medical Subject Headings (MeSH) terms, Emtree terms, and keywords from selected journal articles, combined with Boolean logic. Included studies after searching were screened using the defined eligibility criteria:

Population (P): This review studied patients wearing removable complete and partial dentures.

Intervention (I): Denture cleaning using the ultrasonic cleaning method or ultrasonic denture cleaning was incorporated as part of the oral health education programme.

Comparison (C): Other denture-cleaning methods.

Outcome (O): The effects of denture cleaning, including changes in the quantity of plaque (visual indices or planimetric assessment) or changes in microbial load or composition.

Study (S): This review was limited to clinical studies, excluding literature and systematic reviews, protocols, in vitro studies, case reports, and case series. Studies had a mean observation period of more than 5 days.

Information sources and search strategy

Five electronic databases were initially searched, including PubMed, Embase, Web of Science, Scopus, and Cochrane Central Register for Controlled Trials, in December 2023. References cited in the excluded reviews that included full-text studies were also accessed to identify other potentially relevant studies that might have been unintentionally disregarded. A further grey literature search using Google Scholar was performed to update and capture studies published from January 2024 to June 2025 (Appendix 2). The search was restricted to articles published in English, but there was no restriction on the year of publication. All studies were compiled using EndNote X9 software.

The following search strategy for PubMed was adopted and further customised for Embase, Scopus, Web of Science, and Cochrane Central Register of Controlled Trials. It was verified by a medical librarian at the university: ("Dentures"[MeSH Major Topic:noexp] OR "Dental Prosthesis"[MeSH Major Topic:noexp] OR "denture, complete"[MeSH Terms] OR "denture, partial"[MeSH Terms:noexp] OR "denture, partial, removable"[MeSH Terms] OR "denture, overlay"[MeSH Terms] OR ((("Removable"[Title/Abstract] OR "complete"[Title/Abstract] OR "full"[Title/Abstract] OR "part*"[Title/Abstract]) AND "denture*"[Title/Abstract]) OR "RDP"[Title/Abstract] OR "RDPs"[Title/Abstract] OR ("Removable"[Title/Abstract] AND "dental"[Title/Abstract] AND ("prosthesis"[Title/Abstract] OR "prostheses"[Title/Abstract])) OR "removable prosthodontic*"[Title/Abstract] OR "overdenture*"[Title/Abstract] OR ("overlay"[Title/Abstract] AND "denture*"[Title/Abstract]))) AND ("Ultrasonics"[MeSH Terms] OR "Ultrasonic Therapy"[MeSH Major Topic:noexp] OR "Ultrasonic Waves"[MeSH Major Topic:noexp] OR (("ultrasonic*"[Title/Abstract] OR "ultrasound"[Title/Abstract]) AND ("clean*"[Title/Abstract] OR "hygiene"[Title/Abstract] OR "device*"[Title/Abstract] OR "cavitation"[Title/Abstract])) OR ("oral hygiene/methods"[MeSH Terms] OR "Toothbrushing"[MeSH Terms] OR "Dentifrices"[MeSH Terms] OR "Dental Disinfectants"[MeSH Terms:noexp] OR "sodium hypochlorite/therapeutic use"[MeSH Terms] OR "sodium hydroxide/therapeutic use"[MeSH Terms] OR "peroxides/therapeutic use"[MeSH Terms] OR "bicarbonates/therapeutic use"[MeSH Terms] OR "sulfates/therapeutic use"[MeSH Terms] OR "Mouthwashes"[MeSH Terms:noexp]) OR ("clean*"[Title/Abstract] OR ("hygiene"[Title/Abstract] AND "method*"[Title/Abstract]) OR ("clean*"[Title/Abstract] AND "method*"[Title/Abstract]) OR (("mechanical"[Title/Abstract] OR "chemical"[Title/Abstract]) AND "method*"[Title/Abstract]) OR ("sonic"[Title/Abstract] AND ("bath"[Title/Abstract] OR "clean*"[Title/Abstract])) OR "brush*"[Title/Abstract] OR "toothbrush*"[Title/Abstract] OR "tooth brush*"[Title/Abstract] OR "dentifrice*"[Title/Abstract] OR "toothpaste*"[Title/Abstract] OR "disinfect*"[Title/Abstract] OR "saniti*"[Title/Abstract] OR "decontaminat*"[Title/Abstract] OR "microwave"[Title/Abstract] OR "immers*"[Title/Abstract] OR "soak*"[Title/Abstract] OR "bleach*"[Title/Abstract] OR ("clean*"[Title/Abstract] AND "solution"[Title/Abstract]) OR ("clean*"[Title/Abstract] AND "tablet*"[Title/Abstract]) OR ("chemical"[Title/Abstract] AND ("cleaner*"[Title/Abstract] OR "product*"[Title/Abstract] OR "agent*"[Title/Abstract])) OR "Sodium hypochlorite"[Title/Abstract] OR "Sodium hydroxide"[Title/Abstract] OR "effervescent"[Title/Abstract] OR "carbon"[Title/Abstract] OR "peroxide*"[Title/Abstract] OR "Bicarbonate"[Title/Abstract] OR "Percarbonate"[Title/Abstract] OR "Persulphate"[Title/Abstract] OR "mineral acid*"[Title/Abstract] OR "enzyme*"[Title/Abstract] OR ("mouthrinse*"[Title/Abstract] OR "mouth rinse*"[Title/Abstract] OR "oral rinse*"[Title/Abstract] OR "mouthwash*"[Title/Abstract] OR "mouth wash*"[Title/Abstract]) OR ("flexible"[Title/Abstract] AND "denture"[Title/Abstract] AND "cleaner*"[Title/Abstract]))) AND ("Dental Plaque"[MeSH Terms] OR "Dental Plaque Index"[MeSH Terms] OR "Biofilms"[MeSH Terms] OR "colony count, microbial"[MeSH Terms] OR "Microbiology"[MeSH Terms:noexp] OR ("effectiveness"[Title/Abstract] OR "efficiency"[Title/Abstract] OR "efficac*"[Title/Abstract] OR ("dental"[Title/Abstract] AND "plaque"[Title/Abstract]) OR "biofilm*"[Title/Abstract] OR ("dental"[Title/Abstract] AND "plaque"[Title/Abstract] AND ("index*"[Title/Abstract] OR "indice*"[Title/Abstract])) OR "visual indice*"[Title/Abstract] OR "planimetric assessment*"[Title/Abstract] OR "microorganism*"[Title/Abstract] OR "Streptococcus mutans"[Title/Abstract] OR "Candida albicans"[Title/Abstract] OR "microbial"[Title/Abstract] OR "microbiolog*"[Title/Abstract] OR ("microbial"[Title/Abstract] AND "colony"[Title/Abstract] AND "count*"[Title/Abstract]) OR "CFU"[Title/Abstract] OR "colony forming unit*"[Title/Abstract] OR "dimensional change*"[Title/Abstract] OR "dimensional stability"[Title/Abstract] OR "color stability"[Title/Abstract])).

Selection and data collection process

After the literature search, all identified articles were compiled into EndNote X9 software for reference management in order to deduplicate the results. Following this, 2 reviewers (J.L. and T.W.L.) conducted a thorough review of titles and abstracts of the remaining articles using Covidence software. Discussion was arranged if any discrepancies between the 2 reviewers happened during any stage of the review process, and a third reviewer (C.M.) was consulted if necessary. Articles deemed outside the scope of the present review based on the eligibility criteria were excluded. Data from the included studies were extracted and summarised in a standardised collection spreadsheet (Microsoft Excel 365) after the full-text screening, providing a narrative synthesis of the following parameters:

Publication details: Authors, publication year, and the country where the study was conducted.

General study characteristics: Inclusion period, study setting, study design (ie, type of randomised controlled clinical trial), sample size, number of dropouts, and study period.

Characteristics of study participants: Sex, mean and standard deviation (SD) or median and age range, community-dwelling or institutionalised, type of denture, and denture age.

Details about interventions: Frequency, duration, any add-on interventions, number of times per day, and who administered them.

Type of analysis: Intention-to-treat or per protocol.

Study risk of bias assessment

The risk of bias and quality of the included studies were assessed independently by 2 reviewers (T.W.L. and S.M.G) using the appropriate revised Cochrane handbook risk-of-bias tool (RoB 2) for individually randomised and parallel-group trials, cluster-randomised trials, and crossover trials.³¹ Excel tools containing macros for various designs of trial were downloaded to implement the RoB 2 assessment (https://www.riskofbias.info/welcome). Discrepancies in the risk of bias assessment were resolved through consensus between the 2 reviewers, with the involvement of a third senior reviewer (C.M.) if necessary. The RoB 2 comprises 5 domains for parallel-group design and 6 domains for crossover and cluster designs, to assess the bias that could be introduced. Following this algorithm, the risk of bias associated with each domain and the overall judgement could be assessed. In this review, the effects of assignment to the intervention (intention to treat) for outcomes are evaluated. Three categories of risk of bias, including ‘High’, ‘Some concerns’, and ‘Low’, were graded. A clinical trial was graded as having a ‘high risk of bias’ if any domain was rated as high risk. If at least 1 domain was graded as having ‘some concerns’, the trial was considered as having ‘some concerns’. The trial was graded as low risk of bias if all domains were low risk.

Results

Study selection

The initial search through 5 electronic databases resulted in 5,130 articles, and 2,319 articles were deduplicated using EndNote X9 software (Figure 1). Four articles were manually added to the search. After the title and abstract screening stage, 19 full-text articles were further screened using the inclusion and exclusion criteria. A total of 10 studies were included in the qualitative analysis.^17,18,20, 21, 22^,32, 33, 34, 35, 36 Nine excluded studies after full-text reading are presented with reasons in Appendix 3. The Cohen’s kappa coefficient (κ) for the full-text articles screened was 0.79, indicating substantial agreement between the 2 reviewers.

Fig. 1.

PRISMA 2020 flow diagram for new systematic reviews which includes searches of databases, registers and other sources.

Study characteristics

Among the included studies, all were randomised controlled clinical trials with 4 individually randomised and parallel-group trials,^22,32, 33, 34 2 cluster-randomized trials^35,36 and 4 crossover randomised trials.^17,18,20,21 The included clinical trials were published between 1975 and 2025, 3 from Hong Kong SAR, 3 from Brazil, 2 from Germany, and 1 each from Belgium and the United States. The study period ranged from 5 days to 12 months, and one of the 12-month clinical trials experienced 73 participant dropouts.³⁶ Detailed study characteristics of the 10 included studies are summarised in Table 1.

Table 1.

A summary of the characteristics of the included studies.

No.	Study (Author; Year; Country)	Study Design; Study Setting; Study Period	Participant (Sex; Age; Type of Denture; Denture Age)	Sample Size; Dropout	Intervention	Outcome (Plaque Quantification Measures)	Outcome (Microbial Profile)	Conclusion
1.	Muenchinger 1975 United States	Randomized controlled clinical trial Dental school 4 wk	NR NR CD 5 wk	32 0	I: Sonac, an electrosonic energy waves (sonic) through a specially designed cleaning solution. II: Kleenite, a commercially available denture soaking agent *Self-administered	Plaque and calculus were scored as either present or absent on all teeth and adjacent flanges and on 3 selected tissue surfaces (Total score of 63) There was no statistically significant difference between the baseline and plaque and calculus scores after intervention for the 'Sonic' group (P > .05). In addition, there was no significant difference comparing sonic, soak, or the patient's usual cleaning method	-	All the intervention and control methods were equally effective in the prevention of plaque and calculus. However, none of the methods eliminated the formation of plaque or calculus.
2.	Cruz et al., 2011 Brazil	Randomized controlled clinical trial Dental school 21 d	47 F; 13 M 45-80 Acrylic CD 5-10 y	80 0	I: Brushing the dentures 3 times a day, after each meal for 2 min using tap water and specific brush for CD; b) Rinsing the oral cavity with running water after brushing; c) Soaking the denture in warm water and one effervescent tablet for 20 min after dinner; d) Rinsing the denture before insertion into oral cavity; e) keeping the CD immersed in water during sleep. II: Brushing the dentures 3 times a day, after each meal for 2 min using tap water and specific brush for CD; b) Rinsing the oral cavity with running water after brushing; c) keeping the CD immersed in water during sleep; d) on the 21st day, immersion the dentures in a sterile beaker containing 250 mL sterile water, and ultrasonic vibration for 15 min III: Combined Intervention I and II. IV: Brushing the dentures 3 times a day, after each meal for 2 min using tap water and specific brush for CD; b) Rinsing the oral cavity with running water after brushing; c) keeping the CD immersed in water during sleep. *Self-administered	Computerized planimetric assessment (Image Tool 2.02) The intervention I, II, and III achieve similar plaque coverage area after 21 d, there were significantly better than control group.	-	The use of peroxide (chemical approach), ultrasound (mechanical approach), and a combination of these two approaches, in addition to regular brushing, resulted in improved denture hygiene outcomes compared to brushing alone.
3.	de Andrade et al., 2011 Brazil	Randomized controlled clinical trial Dental school 21 d	87 F; 26 M 48-84 (mean = 64) Acrylic CD 5-10 y	77 0	I: Brushing the dentures 3 times a day, after each meal for 2 min using tap water and specific brush for CD; b) Rinsing the oral cavity with running water after brushing; c) Soaking the denture in warm water and one effervescent tablet for 20 min after dinner; d) Rinsing the denture before insertion into oral cavity; e) keeping the CD immersed in water during sleep. II: Brushing the dentures 3 times a day, after each meal for 2 min using tap water and specific brush for CD; b) Rinsing the oral cavity with running water after brushing; c) keeping the CD immersed in water during sleep; d) at the 21st day, immersion the dentures in a sterile beaker containing 250 mL sterile water, and ultrasonic vibration for 15 min III: Combined Intervention I and II. IV: Brushing the dentures 3 times a day, after each meal for 2 min using tap water and specific brush for CD; b) Rinsing the oral cavity with running water after brushing; c) keeping the CD immersed in water during sleep. *Self-administered	-	Culture technique Lower counts were found for Interventions I and III when compared with the other interventions against mutans streptococci (P < .001). Intervention I showed lower total aerobic counts than Control, whereas Interventions II and III showed intermediate results (P = .011). The yeast counts were not significantly influenced by the tested treatments (C. tropicalis: KW = 0.38, P = .944; C. glabrata: KW = 0.99, P = .803).	The effervescent tablets significantly decreased the microbial counts of mutans streptococci and total aerobes in denture biofilm. The impact of ultrasonic treatment was ambiguous, but it appeared to be more effective when used in conjunction with effervescent tablets.
4.	Duyck et al., 2016 Belgium	Crossover randomized controlled trial Long-term care facility 5 d + 2 d washout	NR NR Acrylic CD NR	13 1 (after the 3rd intervention)	I: brushing and overnight storage in water with a cleansing tablet II: ultrasonic cleaning and overnight storage in water without a cleansing tablet; 35 kHz for 15 min with tap water, denture placed in a glass container III: ultrasonic cleaning and overnight storage in water with a cleansing tablet; 35 kHz for 15 min with tap water, denture placed in a glass container IV: brushing and overnight storage in water without a cleansing tablet *Researcher-administered	Augsburger and Elahi method There were no statistically significant differences in visual plaque index scores between the interventions. However, the plaque score on the mucosal surfaces was significantly (P < .001) higher than the buccal surfaces of the mandibular dentures.	qPCR analysis for 20 selected oral bacteria and for Candida albicans. Overnight denture storage in water with a cleansing tablet significantly reduced the total microbial count compared to water without a cleansing tablet (P < .01), especially supplemented with ultrasonic approach. Besides, the abundance of Capnocytophaga species, Campylobacter concisus, Streptococcus milleri group, Actinomyces odontolyticus, and Veillonella parvula were significantly lower after a cleansing tablet was used.	The use of an effervescent tablet for denture overnight storage has significant effect on total microbial count and abundance of certain bacteria. Ultrasonic cleaning was found to be as effective as brushing in complete denture hygiene care.
5.	Klotz et al., 2017 Germany	Randomized controlled clinical trial (Cluster) Long-term care facility 12 mo	150 F; 69 M 83.1 ± 9 RPD + CD NR	Total 219 (Denture - 163) 52	I: 2-d oral health programme (Dental education, instruction in standardized assessment of oral health for nondentists, and introduction of ultrasonic baths for denture cleaning) II: No oral health programme *Self-administered	Denture Hygiene Index (DHI) The logistic regression model for all participants revealed an odds ratio of 2.1 for mortality in the control group (Intervention II), P = .043. However, the results could not be reproduced for participants wearing denture, P = .106	-	The multivariate logistic regression model for participants wearing dentures (n = 163) revealed a significant association between mortality and the Revised Oral Assessment Guide (P = .033), and there may be an association between mortality and age (P = .075).
6.	Schwindling et al., 2017 Germany	Randomized controlled clinical trial (Cluster) Long-term care facility 12 mo	189 F; 80 M Intervention (82.6 ± 9.2); Control (84.1 ± 8.3) NR NR	14 nursing homes (269 residents) 73	I: Oral health education for caregivers and use of ultrasonic devices for denture cleaning. II: No oral health programme *Caregiver-administered	Denture Hygiene Index (DHI) Significantly different changes in the DHI were observed in the intervention group at the 6-mo and 12-mo reviews compared to baseline. In the mixed-model analysis, participants with greater care dependence benefited more in terms of DHI changes than less-dependent participants (P < .001).	-	Oral health education showed positive effects on oral health over a 12-mo period of observation. Ultrasonic cleaning appeared as a promising approach to improve removable denture hygiene, especially in severe care-dependent nursing home older adults.
7.	Sponchiado et al., 2021 Brazil	Crossover randomized controlled trial Long term care facility 5 d + 7 d washout	13 F; 4 M 72.5 Maxillary CD At least 1 y	17 0	I: Ultrasonic bath (160 watts once daily, at a fixed time, for 15 min) with neutral liquid soap solution (glass jars containing 100 mL of tap water and one drop of dishwashing soap). II: Manual brushing (soft brush, once daily for 2 min) with neutral dishwashing soap. *Caregiver-administered	Ultrasonic cleaning showed a significantly higher percentage change of biofilm biomass using MTT reduction assay compared to manual brushing (P < .05)	Culture technique The microbial load of Streptococcus spp. was significantly reduced in both cleaning methods. However, only ultrasonic cleaning showed significant reduction in the percentage of Staphylococcus spp. and Candida spp.	The ultrasonic cleaning demonstrated a favourable outcome for mechanical cleaning of complete dentures in long-term care facilities.
8.	Chan et al., 2023 Hong Kong SAR	Randomized controlled clinical trial Dental hospital 1 mo	48 F; 18 M 66.97 ± 6.91 CoCr RPD 19.05 ± 5.63	66 2	I: Clean with a soft toothbrush and liquid detergent, ultrasonic cleaning [42 kHz] for 7 min and 30 s with 0.07% cetylpyridinium chloride (CPC) mouthrinse, once daily II: Clean with a soft toothbrush and liquid detergent and ultrasonic cleaning [42 kHz] for 7 min and 30 s with distilled water, once daily III: Clean with a soft toothbrush and liquid detergent, once daily *Self-administered	Denture Cleanliness Index (DCI) - CoCr (review and change) I [1.14 (0.56)] and [1.45 (0.86)]; II [1.15 (0.37)] and 1[1.00 (0.86)]; III [2.09 (0.75)] and [0.23 (0.68)] - Acrylic (review and change) I [1.09 (0.53)] and [1.68 (0.95)]; II [1.15 (0.59)] and [1.20 (1.01)]; III [1.95 (0.72)] and [0.37 (0.79)] Computerized Planimetric Assessment (Adobe Photoshop) - CoCr (review and change) I [17.89 (12.96)] and [28.70 (16.59)]; II [16.22 (9.22)] and [22.79 (17.88)]; III [39.60 (20.68)] and [8.35 (11.39)] - Acrylic (review and change) – I [19.33 (12.34)] and [34.98 (24.11)]; II [17.82 (10.09)] and [28.40 (22.58)]; III [38.83 (17.96)] and [5.21 (11.23)]	Culture technique Median microbial viable counts (CFU/mL) - Intrarm CoCr interventions I and II - significant difference; No significant difference between groups; Intervention I demonstrated significantly lower mean yeast viable counts (CFU/mL) at 1-mo review compared to baseline (P = .004). Median microbial viable counts (CFU/mL) - Intrarm Acrylic Intervention I and II - significant difference; No significant difference between groups; Reductions in microbial viable counts were significantly greater in Intervention II compared to Intervention III (P = .047).	The ultrasonic denture cleaning was effective in the reduction of plaque coverage, DCI, and microbial viable counts on both CoCr and acrylic denture surfaces after 1 mo. However, the use of CPC as the denture immersion solution unable to provide additional advantages over distilled water.
9.	Lim et al., 2024 Hong Kong SAR	Crossover randomized controlled trial Dental hospital 3 mo + 2 wk washout	34 F; 22 M 69.8 ± 5.59 Acrylic CD and EPD 25.29 ± 19.72 mo	56 7	I: Ultrasonic cleaner (45 kHz for 15 min) and enzymatic peroxide-based denture cleanser tablets to use daily. II: Brush with a commercially available denture brush and the same denture cleanser tablets (15 min) to use daily, followed by standardised brushing using the same cleanser solution for 30 s. *Self-administered	Semiautomated planimetric assessment Both the I and II methods showed a significant improvement in denture plaque coverage. The intervention approach showed a significant reduction in plaque coverage compared to the control method by using Generalized Estimating Equations model.	-	Denture plaque coverage, denture stomatitis, and patient satisfaction were significantly improved after ultrasonic cleaning with denture cleanser tablet solution.
10.	Lim et al., 2025 Hong Kong SAR	Crossover randomized controlled trial Dental hospital 3 mo + 2 wk washout	34 F; 22 M 69.8 ± 5.59 Acrylic CD and EPD 25.29±19.72 mo	56 7	I: Ultrasonic cleaner (45 kHz for 15 min) and enzymatic peroxide-based denture cleanser tablets to use daily. II: Brush with a commercially available denture brush and the same denture cleanser tablets (15 min) to use daily, followed by standardised brushing using the same cleanser solution for 30 s. *Self-administered	-	2bRAD-M sequencing The microbial community structures between the I and II arms were significantly different as assessed by the Jaccard qualitative distance matrix (P = .034). However, the Chao 1 index in both arms was not significantly different (P = .343).	The microbial communities in denture biofilms changed after interventions using both Test and Control arms. Very few opportunistic pathogens remained in the denture biofilms, suggesting that both arms were equally effective in reducing the presence of pathogenic bacteria

CD, complete denture; CoCr, cobalt chromium; EPD, extensive partial denture; F, female; M, male; NA, not available; RPD, removable partial denture

Participants

Most of the studies focused on older adults, predominantly females and aged 65 years and older, wearing removable complete or partial dentures. Some included studies recruited slightly younger populations,^32,33 but the emphasis remained on older adults because of the higher prevalence of removable denture wearing in this population. Among them, 6 studies recruited community-dwelling participants while 4 studies enrolled institutionalised older adults.^20,21,35,36 The total number of participants involved in this review ranged from 13 to 269. Notably, Cruz et al.,³² de Andrade et al.,³³ Lim et al.,^17,18 might have derived subjects from the same patient population, but each focused on different outcome measures.

Interventions

The included studies compared ultrasonic cleaning protocols with a diverse range of denture-cleaning interventions. Overall the present review included the following ultrasonic intervention protocols: (1) clean with a soft toothbrush and liquid detergent followed by ultrasonic cleaning (42 kHz) for 7 minutes and 30 seconds with 0.07% cetylpyridinium chloride mouthrinse or distilled water²²; (2) brush with a specific brush 3 times a day for 2 minutes using tap water with or without soaking the denture in warm water with 1 effervescent tablet for 20 minutes after evening meal, and on the 21st day immerse the dentures in a sterile beaker containing 250 mL sterile water and ultrasonic vibration for 15 mins^32,33; (3) ultrasonic cleaning (35 kHz for 15 minutes with tap water, by placing the denture in a glass container) and overnight storage in water with or without a cleansing tablet²¹; (4) 2-day oral health programme including dental education, instruction in standardised assessment of oral health for nondentists and introduction of ultrasonic baths for denture cleaning³⁵; (5) sonic cleaning using electrosonic energy waves through a specially designed cleaning solution³⁴; (6) ultrasonic cleaning (45 kHz for 15 minutes) and enzymatic peroxide-based denture cleanser tablets to use daily^17,18; (7) oral health education for caregivers and use of ultrasonic devices for denture cleaning³⁶; (8) ultrasonic cleaning (160 watts once daily for 15 minutes) with neutral liquid soap solution (glass jars containing 100 mL of tap water and 1 drop of dishwashing liquid).²⁰ The interventions were administered by the participants in 7 clinical trials; whereas in the remaining 3 clinical trials, the ultrasonic cleaning was carried out by researchers or caregivers. ^20,21,36

Outcomes

All included studies presented quantitative data on the comparisons between interventions using intention-to-treat analysis. In summary, 5 clinical trials reported changes in denture plaque coverage area using either visual indices or planimetric assessment, 2 trials assessed the changes in microbial profile (either microbial load or composition), and the remaining 3 trials showed outcomes on both plaque coverage area and microbial profile (Table 1).

Changes in denture plaque quantification

Three clinical trials found that ultrasonic denture cleaning with denture cleanser solution, mouthrinse, liquid soap solution, or distilled water was more effective in the reduction of plaque coverage and biomass than brushing with denture cleanser solution or detergent alone.^17,20,22 Even a single application of ultrasonic cleaning at the end of the study period resulted in reduced plaque coverage area compared to brushing alone.³² Another clinical trial assessing an oral health education programme using ultrasonic denture cleaning significantly reduced the Denture Hygiene Index (DHI) in the intervention group after 6 months and 12 months compared to the baseline.³⁶ In contrast, 2 studies found no significant differences in visual plaque index scores between interventions.^21,34 Klotz et al. also reported that the oral health programme, which involved denture cleaning using ultrasonic devices, did not reduce the risk of 1-year mortality among institutionalized older adults wearing dentures.³⁵

Changes in microbial profile

In a clinical trial conducted in Hong Kong, ultrasonic cleaning for cobalt chromium partial dentures resulted in a significant reduction in both microbial and yeast counts after 1 month.²² However, there was no significant difference between the ultrasonic cleaning and brushing approaches. de Andrade et al. reported significantly lower microbial counts for denture cleaning using denture cleanser tablets, with or without ultrasonic devices, compared to other interventions.³³ However, yeast counts were not significantly influenced by any of the interventions. Duyck et al. demonstrated similar findings.²¹ On the contrary, a clinical trial in a nursing home showed that ultrasonic cleaning significantly reduced the percentage of Streptococcus spp., Staphylococcus spp., and Candida spp.²⁰ The only clinical trial that performed the microbiome analysis using a high-throughput next-generation sequencing method (2bRAD-M) reported significant differences in the microbial community structures between ultrasonic cleaning and brushing.¹⁸

Risk of bias in studies

Risk of bias assessments for all included clinical trials using RoB 2, including domain judgements and summary plots for each domain, are presented in Appendix 4. There were 2 recent clinical trials graded ‘high risk’ for overall bias.^33,36 The remaining included studies were considered ‘some concerns’ for overall bias. The summary plots for all 3 assessments reported that all studies were judged as ‘some concerns’ in the ‘deviation from intended interventions’ domain because the participants or carers delivered the interventions without blinding during the trial. In addition, the ‘randomization process’ domain was graded ‘high risk’ in 2 studies because of discrepancies at baseline that indicated issues with the randomisation process.

Discussion

This systematic review aimed to assess the efficacy of ultrasonic denture cleaning in changing plaque quantification measures, microbial load, microbial composition, and other clinical parameters compared to other cleaning approaches. Ultrasonication helps to detach bacterial cells and plaque from denture surfaces using acoustic energy, or sound waves, with a frequency range beginning at 20 kHz and a power of 0.1 to 2 W/cm².^19,37 The mechanisms are related to the rapid expansion and shrinkage of the cavitation bubbles, which can cause fluid shear forces that can dislodge denture plaque from the surface. Additionally, collapse cavitation events may lyse the bacterial cells or increase the permeability of their membranes, subsequently killing them. Therefore, ultrasonic cleaning is suggested for denture plaque removal.

In this review, a total of 8 ultrasonic cleaning protocols were adopted in the controlled trials, resulting in high variability. Among them, ultrasonic cleaning devices were shared among participants by placing glass containers into the devices for infection control purposes.^20,21,32,33 This practice was likely adopted because of the superior cleaning performance of the in-office ultrasonic cleaning devices. However, this practice may not be generalisable for routine use because of its size and cost. More recently, several studies conducted in Hong Kong SAR investigated homecare portable ultrasonic baths to clean removable dentures.^17,18,22 This inexpensive solution was adopted to overcome occupational infection among caregivers and avoid possible cross-contamination among participants. Additionally, other ultrasonic denture-cleaning parameters were explored, including the immersion solution, duration or frequency of cleaning, and ultrasonic frequency and intensity. Within the scope of this review, an enzymatic peroxide-based denture cleanser solution, tap water with liquid soap, sterile water, distilled water, and 0.07% cetylpyridinium chloride mouthrinse were used as denture immersion solutions. Notably, very few studies used a chemical solution during ultrasonic immersion, but many used it as a separate step in addition to ultrasonic cleaning. Most of the included studies implemented ultrasonic denture cleaning once per day for at least 15 minutes to achieve the most effective method of denture plaque removal. The frequency of ultrasonic devices used in clinical trials ranged from 35 kHz to 45 kHz, except 1 study, which adopted an electrosonic energy wave technology that had a frequency lower than 20 kHz.³⁴ Notably, there were a few included trials that did not provide any additional information about the ultrasonic cleaning method,34, 35, 36 reflecting the inconsistency of the reported methods in published studies and making it such that it may not be generalisable for routine use.

In general, for the plaque quantity measurements, the use of ultrasonic cleaning devices as a mechanical denture-cleaning method provided superior performance in reducing the plaque coverage area. There were 2 clinical trials that could not demonstrate any additional advantages when comparing ultrasonic cleaning with other conventional cleaning methods, possibly because of the use of low-frequency electrosonic wave technology (<20 kHz) that is not commonly used nowadays,³⁴ and the use of a visual index²¹ that was not sensitive enough to detect changes. As suggested by a systematic review, computerised planimetric assessment should be a highly accurate assessment of denture plaque quantification in clinical studies.³⁸ This finding is in agreement with Lim et al.²³ who emphasised the importance of incorporation of chemical cleaning as part of the ultrasonic cleaning protocol. Notably, the use of an enzymatic peroxide-based denture cleanser solution,¹⁷ tap water with dishwashing liquid,²⁰ and 0.07% cetylpyridinium chloride mouthrinse²² as denture immersion solutions during the ultrasonic cleaning resulted in the highest changes in denture plaque reduction. The importance of incorporating chemical cleaning is evident, with the enzymatic peroxide-based effervescent denture cleanser standing out as superior and being more commonly tested, as it will decompose and release oxygen bubbles or increase fluid shear forces that can assist with the mechanical detachment of denture plaque from the denture surface.³⁹ However, the effectiveness of other immersion solutions remains unclear, and further investigations are needed.

Denture-related oral and systemic diseases will develop in the absence of optimal hygiene care because of the presence of pathogenic bacteria in denture biofilm.^8,40,41 Dentures favour the growth of microbial biofilms with the majority being bacteria,⁶ but most of the existing microbiological studies in removable dentures focused on fungi, particularly Candida albicans. However, ultrasonication was unable to completely remove all of the microorganisms in other fields, with approximately 80% to 95% of the bacteria eliminated.42, 43, 44 Therefore, the evidence of efficacy of ultrasonic cleaning in mitigation of microbial load or changing microbial composition should be systematically appraised. de Andrade et al.³³ reported the importance of denture cleanser tablets in reducing S. mutans and total aerobic bacteria counts, but not of ultrasonic cleaning. This can be explained by the use of ultrasonic cleaning only once at the end, rather than consistently, so the effect of ultrasonication was not fully implemented.³³ On the contrary, a clinical trial conducted in a nursing home found that ultrasonic denture cleaning with dishwashing liquid significantly reduced Streptococcus spp., Staphylococcus spp. and Candida spp., suggesting a favourable effect of ultrasonication in removing bacteria and fungi. However, most included studies emphasised the importance of combining ultrasonic cleaning with chemical cleansing methods. This finding is consistent with Nishi et al., who concluded that ultrasonic cleaning combined with immersion in a peroxide-based cleanser solution significantly reduced the total microbial counts including Candida spp.²⁷ In addition, as highlighted by a systematic review, microbial colonisation on denture surfaces should be managed by antimicrobial denture materials or effective cleaning protocols.⁴⁵ To date, studies examining denture biofilm using high-throughput whole metagenomic sequencing are limited⁴⁶; the only clinical trial assessing efficacy of denture cleaning using 2bRAD-M sequencing showed changes in the microbiome after interventions, particularly the good control of pathogenic bacteria.¹⁸ This study provided a more accurate and comprehensive overall picture of the microbial composition in denture biofilms and was not restricted to certain bacteria or fungi.

Given high heterogeneity in methodologies, particularly the outcome measurements and individualised ultrasonic protocols, meta-analysis was not feasible in this systematic review, and mutual comparison of the findings was challenging. Furthermore, there were limited studies recruiting participants from the younger age populations,^32,33 and none of them discussed the impact of age on outcomes, which might limit the generalisability of the present findings. Even though denture wearers are predominantly older adults, 2 studies reported that age was not a significant factor affecting changes in denture plaque coverage after using ultrasonic cleaning.^17,36 Notably, older adults with greater care dependence or compromised manual dexterity were more likely to experience inadequate denture cleanliness because they require more assistance from caregivers to maintain optimal denture hygiene.³⁶ Therefore, a more equitable oral health care system should be adopted to address social inequalities in oral health.⁴⁷ For example, the adoption of ultrasonic cleaning protocol in a nursing home was found to be effective for residents who are more care dependent.³⁶ Notably, maintenance of oral health, including prevention of various oral diseases, tooth loss, and oral functional decline through preventive care, oral health education and treatment is crucial to reduce noncommunicable diseases and frailty.⁴⁸ Future studies with bigger sample sizes, longer follow-up periods, reduced confounding factors, standardised ultrasonic cleaning protocol and better-designed controlled clinical trials investigating the efficacy of denture cleaning using ultrasonic devices are strongly recommended to overcome the limitations of the current evidence. Although all clinical trials included in this review were graded as having ‘some concerns’ and up to ‘high risk’ of bias, it should be acknowledged that the studies employed a randomised controlled design. One of the limitations in this systematic review was the application of language restriction. Studies published in other languages should be considered in future reviews to increase the number of included studies and reduce the potential risk of bias.

Based on the outcomes of the randomised controlled clinical trials in this systematic review, there was clear evidence to substantiate the notion that ultrasonic cleaning reduced the area of denture plaque coverage and microbial loads if supplemented with an effervescent denture cleanser. Notably, it is still important to note that the high variability in ultrasonic cleaning protocols among the included studies may affect the generalisability of the finding. All included studies, assessed using the RoB 2 tool, were considered to have ‘some concerns’ or even a ‘high risk’ of bias. Therefore, future clinical studies, particularly with a standardised ultrasonic cleaning protocol, are recommended to investigate the efficacy of denture cleaning to overcome the limitations of the existing evidence.

Author contributions

Conceptualisation: Burrow, Lim, McGrath

Methodology: Burrow, Ghani, Lee, Lim, McGrath

Validation: Ghani, Lee, Lim, McGrath

Investigation: Ghani, Lee, Lim

Resources: Burrow, Ghani, Lee, Lim, McGrath

Data curation: Burrow, Ghani, Lee, Lim, McGrath

Formal analysis: Burrow, Ghani, Lee, Lim, McGrath

Visualisation: Lim

Writing—original draft: Lim

Writing—review and editing: Burrow, Lim, McGrath

Project administration: Lim

Funding acquisition: Lim

Supervision: Burrow, Lim, McGrath

Funding

This study was supported by funding from the RGC General Research Fund 2024/25 (Project Number: 17122724).

Conflict of interest

Tong Wah Lim reports financial support from The University of Hong Kong Faculty of Dentistry. All other authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.