Williams 1970.

Study characteristics
Methods	Trial design: CCT – split mouth (alternation) Location: University of Maryland School of Dentistry, Baltimore, Maryland, USA Setting: dental operatory Language: English Number of centres: 1 Study period: not mentioned Funding source: not mentioned Study protocol: not available
Participants	Age: not mentioned Total number of participants: 50 Inclusion criteria: patients who volunteered to receive prophylactic procedures, which involved cleaning and scaling of the maxillary and mandibular right or left sides of the dental arches on an alternating basis with an ultrasonic cleaning and scaling device Exclusion criteria: not mentioned Number alternated: 50 Method of randomization: alternation Method of allocation concealment: not mentioned Method of blinding: not mentioned Number evaluated (withdrawals/missing participants): 50 (nil)
Interventions	Comparison: laminar air flow and HEPA filter versus no air flow or filter Intervention: Group name: with laminar air flow and HEPA filter Number of intervention groups: 1 Number alternated to intervention site and control site: 50 Description of intervention: ceiling to floor laminar airflow that enters the room through a HEPA filter. In the dental procedure, the ultrasonic scaling device was used around all teeth supragingivally and subgingivally; dental tape was used interproximally and linen strips instituted where necessary. The teeth were polished with a mounted, webbed rubber cup and a flavoured prophylactic paste. At the completion of this procedure, the room was 'air washed' for 5 minutes, and then the other side of the mouth was given a dental prophylactic treatment while the environmental air in the room was washed with laminar air. Microbial samplings from dental aerosols were performed during the entire procedure. Any co‐interventions: no Comparator: Group name: without laminar air flow or filter Number of control groups: 1 Number alternated to control group: 50 Description of control: the other half of the mouth was given a complete prophylactic treatment without laminar air.
Outcomes	Outcome name: reduction in contaminated aerosols (measured as viable particle count = CFU) Outcome measurement: microbial samplings from airborne dental aerosols were taken throughout the room by Reyniers slit samplers at about 1.5 metres from the floor, and the Andersen sampler collected oral aerosol samples approximately 20 cm to 30cm from the patient's mouth measured as CFU per cubic feet per minute. Surface contamination by dental aerosols was also assayed both by gravimetric settling plates and Rodac contact plates. Effect estimate: total (SD not given). We converted this to an average per patient and used the SD from a similar study (Larato 1967). Key conclusions: through the use of laminar airflow in a dental operatory, dental aerosols containing micro‐organisms disseminated into the environmental air by an ultrasonic scaling device can be significantly reduced (99.67%); the risks of exposure to airborne infection are considerably minimized; and surface contamination can be controlled to near‐sterile conditions.
Notes	Study is 50 years old – missing data unlikely to be traceable. We could not contact the authors as their e‐mail details were not available.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Alternation
Allocation concealment (selection bias)	High risk	No details available
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Lack of blinding the participants and personnel will not have any effect on their behaviour
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No details available
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts
Selective reporting (reporting bias)	Unclear risk	Trial protocol not available and hence not possible to judge
Other bias	Low risk	None