Cobb 1980.

Study characteristics
Methods	Study design: 3‐arm parallel‐group RCT (only 2 relevant arms used); non‐placebo controlled Study duration: 2 years
Participants	193 children analysed at 2 years (available at final examination) Participants randomised (N = 237) Age range 11‐14 years Surfaces affected: 5.7 DMFS (data from original sample only) Exposure to other fluoride: toothpaste assumed Year study began: in/before 1977 Location: USA Setting of recruitment and treatment: school
Interventions	FG + ptc versus NT + ptc (APF group = 12,300 ppm F) Operator applied, with cotton‐paint tip, twice a year, applied for 4 min Prior to application = tooth cleaning of stained plaque (with disclosing solution) performed with brush and floss (no paste/toothpaste used) Postop instruction = refrain from eating and drinking for 30 min
Outcomes	2‐year DMFS increment ‐ (CA) Reported at 0.5, 1, 1.5, and 2 year follow‐ups Dropout
Declaration of interest	No information provided
Source of funding	The trial authors thank Pacemaker Corp for supplying the gel.
Notes	Clinical (VT) caries assessment by 1 examiner; diagnostic threshold = CA; state of tooth eruption included NR; diagnostic errors NR.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “... students were randomly assigned to one of three groups.” Comment: Not enough information provided.
Allocation concealment (selection bias)	Unclear risk	No information provided.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: “Subjects in group C also had plaque removed from their teeth but had no fluoride application.” Comment: No placebo described.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quote: “The protocol was designed so that the examiner did not know which group the subjects were assigned to until data collection was complete.” “Subjects in group C had plaque removed from their teeth but had no fluoride application.” Comment: Blind outcome assessment, but no placebo described.
Incomplete outcome data (attrition bias) All outcomes	High risk	Overall dropout for length of follow‐up: 18.56% in 2 years. Dropout by group: 15/130 (11.54%) FR, 29/107 (27.10%) NT. Reasons for losses: Not reported. Comment: Numbers lost not unduly high for length of follow‐up, with differential losses between groups (even though reported as NS difference). It is unclear if 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), reported at 0.5, 1, 1.5, and 2 year follow‐ups. 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: 6.01(5.24) FG, 5.38(4.76) NT Age, gender, ethnicity, regularity of dental care described as ’balanced’ (values not reported). Comment: Initial caries appears balanced between groups.
Free of contamination/co‐intervention?	Unclear risk	No information provided.