Trubman 1973.

Study characteristics
Methods	Study design: 4‐arm parallel‐group RCT (only 2 relevant arms used), placebo controlled Study duration: 3 years
Participants	311 children analysed at 3 years (present for all examinations) Participants randomised (N = 575) Average age 8.1 years Surfaces affected: 2.1 DMFS Exposure to other fluoride: water Year study began: in/before 1969 Location: USA Setting of recruitment and treatment: school
Interventions	FG + ptc vs PL + ptc (APF group = 12,300 ppm F) Self applied under supervision, with tray, 4 times a year, applied for 4 min (children could expectorate during application if needed) Prior to application = tooth cleaning (supervised toothbrushing) performed with with non‐F prophy paste Postop instruction = no information provided
Outcomes	3‐year net DMFS increment ‐ (CA) Reported at 2 and 3 year follow‐ups NetDMFT(CA) Dropout
Declaration of interest	No information provided.
Source of funding	US Public Health Service Grants DH00122‐01 through ‐04 [The authors thank Davies, Rose Hoyt Pharmaceutical Div, the Kendall Co, Needham, Mass, 02194 for supplying the gels]
Notes	Clinical (VT) caries assessment by 2 examiners; diagnostic threshold = CA; state of tooth eruption included NR; reversal rate 18.4% and 9.2% of observed DMFT increment in FG and PL groups, respectively.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “After baseline examinations, children were randomly assigned to one of four groups ...” Comment: Not enough information provided.
Allocation concealment (selection bias)	Unclear risk	No information provided.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quotes: “The examiners had no knowledge of group assignments of children or of results of previous examinations.” “Children in group 1 applied a non fluoride gel.” Comment: Blind outcome assessment and use of placebo described.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quotes: “The examiners had no knowledge of group assignments of children or of results of previous examinations.” “Children in group 1 brushed with non fluoride prophylaxis paste and applied a non fluoride gel.” Comment: Blind outcome assessment and use of placebo described.
Incomplete outcome data (attrition bias) All outcomes	High risk	Overall dropout for length of follow‐up: 45.9% in 3 years. Dropout by group: 141/286 FG, 123/289 PL. Reasons for losses: Exclusions based on presence at all follow‐up examinations. Comment: Numbers lost unduly high for length of follow‐up with no differential group losses (49.30% FG, 42.56% PL). It is unclear if reasons for dropout are acceptable and balanced. Caries data used in analysis pertain to participants present at all examinations.
Selective reporting (reporting bias)	Low risk	Outcomes reported: DMFS increment ‐ (CA), reported at 2 and 3 year follow‐ups. DMFT(CA) 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 factors reported: DMFS: 2.36 FG, 1.92 PL DMFT: 1.51 FG, 1.17 PL Comment: Initial caries with some imbalance between groups (stats adjustment had trivial effect). Age also reported, and balanced.
Free of contamination/co‐intervention?	Unclear risk	No information provided.