Olivier 1992.

Study characteristics
Methods	Study design: 2‐arm parallel‐group RCT; placebo controlled Study duration: 2 years
Participants	431 children analysed at 2 years (available at final examination) Participants randomised (N = 488) Age range 6‐7 years Surfaces affected: 0.68 DMFS Exposure to other fluoride: toothpaste Year study began: 1985 Location: Canada Setting of recruitment and treatment: school
Interventions	FG vs PL (APF group = 12,300 ppm F) Operator applied, with a foam tray, twice a year, applied for 4 min Prior to application = no tooth cleaning performed Postop instruction = excess saliva removed by saliva ejector, refrain from eating and drinking for 30 min
Outcomes	2‐year DMFS increment ‐ (CA) (by 2 levels of initial defs) Reported at 2 years follow‐up Dropout
Declaration of interest	No information provided.
Source of funding	Supported by a grant (66052247‐43) from the National Health Research and Development Program, Health and Welfare, Canada
Notes	Clinical (VT) caries assessment by 5 examiners; diagnostic threshold = CA; state of tooth eruption included NR; inter‐ and intra‐examiner reproducibility checks for DMFS in 10% sample (ICC over 0.96)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “...and were randomly assigned to experimental and control groups.” Quote from correspondence: “A research assistant who never met the subjects proceeded to their random assignation into one of two groups.” Comment: Not enough information provided.
Allocation concealment (selection bias)	Unclear risk	Quote from correspondence: “A research assistant who never met the subjects proceeded to their random assignation into one of two groups.” Comment: Not enough information provided.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quotes: “A double blind clinical field trial...” “...the control group received a placebo” “...each dentist, blinded to the exposure, examined the same number of subjects.” Comment: Blind outcome assessment and use of placebo described.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quotes: “A double blind clinical field trial ...” “... the control group received a placebo” “... each dentist, blinded to the exposure, examined the same number of subjects.” Comment: Blind outcome assessment and use of placebo described.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Overall dropout for length of follow‐up: 11.68% in 2 years. Dropout by group: 24/248 (9.7%) FG, 33/240 (13.8%) PL. Reasons for losses: Moved away, absent from school on day of final examination. Comment: Numbers lost not unduly high for length of follow‐up with no differential losses. Reasons for dropout are acceptable and balanced. Caries data used in analysis pertain to participants present at final examinations.
Selective reporting (reporting bias)	Low risk	Outcomes reported: DMFS increment ‐ (CA) (by 2 levels of initial defs), reported at 2 years follow‐up. Comment: Trial protocol not available. All pre‐specified outcomes (in Methods) were reported and were reported in the pre‐specified way.
Baseline characteristics balanced?	Low risk	Prognostic factor reported: DMFS: 0.59(1.44) FG, 0.74(1.68) PL defs: 21.75(12.43) FG, 22.31(13.30) PL Comment: Initial caries appears balanced between groups. Age, gender, daily sugar consumption, daily toothbrushing, exposure to other fluoride, etc. reported and balanced.
Free of contamination/co‐intervention?	Unclear risk	No information provided.