Milsom 2011.

Methods	Design: 2‐arm cluster RCT Location: Lancashire, UK Study started: 2006
Participants	Number randomised and eligible: 2967 (1473, 1494) Number analysed: 2604 at 3 years Age range: 7‐8 average age 8.1 years Backgound exposure to fluoride: Toothpaste + rinse
Interventions	Comparison: FV versus NT Group 1 (n = 1473): 5% NaF varnish (Duraphat® 22,600 ppm F), applied 3 times a year over 3 years in school, with small brush, 0.1 ml applied per child Group 2 (n = 1494): No treatment Post‐op instructions: No other fluoride treatments for 2 days
Outcomes	3‐year DFS, DFT increment (1stm), number with caries (DFS, DFT) CA
Notes	Baseline characteristics (DFS) 'balanced' Clinical caries assessment by 8 examiners
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "...using computer‐generated random numbers, stratified by the locality of the school and the size of the school"
Allocation concealment (selection bias)	Low risk	Quote: "An ordered list of random group codes for all schools was produced, and only the study statistician and the trial manager had access to these codes"
Blinding of participants and personnel (performance bias) All outcomes	High risk	No blinding of participants mentioned and no placebo used
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "Examiners and their assistants were given a sealed envelope containing the allocation code for the school; this was opened after all the baseline examinations had been completed and the dentist made another appointment for application of the fluoride varnish in the test schools. This system ensured allocation concealment and facilitated efficient delivery of the intervention"
Incomplete outcome data (attrition bias) All outcomes	Low risk	Overall drop‐out for length of follow‐up (reported for individuals within clusters only): 12% in 3 years. Drop‐outs by group: 197/1473 FV, 166/1494 NT (13%, 11%). Reasons for losses (FV/NT): Not explained Comment: Numbers lost were not unduly high for the length of follow ‐up, and showed no differential losses between groups. Losses are acceptable and balanced between groups. Caries data used in the analysis pertain to participants present for at follow‐up exam (and analysis done taking clustering into account)
Selective reporting (reporting bias)	Low risk	Outcomes reported: DMFS/T increment (CA)cl at 3 years follow‐up; caries progression/prevalence. Drop‐outs
Baseline characteristics balanced?	Low risk	Prognostic factors reported: initial DFS: 3 FV, 3 NT Toothbrushing frequency, toothpaste use, participation in rinsing programme, SES are not tabulated but reported as balanced between groups
Free of contamination/co‐intervention?	Low risk	Quote: "Participants were advised not to have fluoride treatment administered by their dentist for 2 days after application of the varnish"