Al‐amad 2017.

Study characteristics
Methods	Trial design: RCT ‒ parallel arm Location: College of Dental Medicine, University of Sharjah, The University City, Sharjah, United Arab Emirates Setting: dental clinic Language: English Number of centres: 1 Study period: 2013 to 2014 Funding source: no funding received Protocol: not available
Participants	Age: not mentioned Total number of participants: 52 female dental students Inclusion criteria: female dental students in their 4th and 5th years, who would customarily wear headscarves To standardize the extent of the dental procedure, only dental cavity preparations on posterior teeth that were already planned for the patients were included. Exclusion criteria: not mentioned Number randomized: 52 (26 per group) Number evaluated (withdrawals/missing participants): 47 (5 dropouts: 4 from the rubber dam group and 1 from the non‐rubber dam group). 2 participants were excluded due to changes in the dental procedure type intraoperatively (from restorative cavity preparation to access opening and inlay preparation) and 3 students were excluded as they had to use a face shield. The final sample consisted of 47 students with 188 collection points (4 for each student). Of those collection points, 16 were outliers (more than 3 SDs from mean) and were excluded from statistical analysis. The majority of the outliers (13 collection points) belonged to the rubber dam group. The final number of collection points was 172 (188 minus 16 outliers).
Interventions	Comparison: rubber dam versus no rubber dam Intervention: Group name: with rubber dam Number of intervention groups: 1 Number randomized to intervention group: 26 but evaluated 22 Description of intervention: students who consented to participate (n = 52) were randomly assigned into 2 equal groups using computer‐generated random numbers and then assigned to a dental clinic where they performed a routine restorative dental procedure. A colleague from the same group was assigned to assist each student by holding the surgical suction tube throughout the clinical procedure. All students wore similar PPE, consisting of a disposable apron, mask, gloves and plastic goggles. Half the sample was asked to perform this procedure while a rubber dam was placed over the tooth that was being treated, while the other half performed similar procedures without a rubber dam. Any co‐interventions: none Comparator: Group name: without rubber dam Number of control groups: 1 Number randomized to control group: 26 but evaluated 25 Description of control: same as above. Control group underwent procedures without a rubber dam.
Outcomes	Outcome tested: reduction in the level of contamination in aerosols (measured at 4 sampling areas: the area overlaying the forehead (designated as point A), the area overlaying the left ear (point B), the area overlaying the submental triangle (point C), and the area overlaying the occiput (point D)) Outcome measurement: CFU Effect estimate: mean (SD not given) Key conclusions: "for each of the collection points, the average number of colony‐forming units (CFU) was higher in the rubber dam group than in the no rubber dam group. The difference between the two groups for each point was not statistically significant. However, when an adjustment was made for all collection points, the presence of a rubber dam was associated with significantly more bacteria‐containing aerosols based on the CFU counts (P = 0.009)"
Notes	Study author contacted for: allocation concealment, study protocol and SD. E‐mail sent on 26 July 2020. Received reply on 28 July 2020.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Method of randomization: computer‐generated random table Quote: “Students who consented to participate (n = 52) were randomly assigned into two equal groups using computer‐generated random numbers...”
Allocation concealment (selection bias)	High risk	No. No details given in the article; however in personal communication, the contact author reported that there was no allocation concealment.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Blinding is not possible. However, participants and personnel will not be able to alter their behaviour even if they know the received intervention.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	It is not clear if the CFU were manually counted or any automated colony counters were used ‐ there is subjectivity if manually counted.
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: “During the course of cavity preparation, 2 participants were excluded due to changes in the dental procedure type intra‐operatively (from restorative cavity preparation to access opening and inlay preparation) and 3 students had to use a face shield and were dropped out.” However, 16 observations were excluded because they were outliers. It is not clear what the effect estimate would be if those values were included.
Selective reporting (reporting bias)	Unclear risk	We are not sure of reporting selective outcomes as there is no protocol available. SDs for observations are not reported.
Other bias	Low risk	None