Englander 1967.

Study characteristics
Methods	Study design: 3‐arm parallel‐group RCT, non‐placebo controlled Study duration: 1.8 years, + 1.9 years postintervention period
Participants	500 children analysed at 1.8 years (present for all examinations) Participants randomised (N = 574) Age range 11‐14 years (average = 12) Surfaces affected: 10.1 DMFS Exposure to other fluoride: no Year study began: 1964 Location: USA Setting of recruitment and treatment: school
Interventions	FG (2 groups) versus NT (APF group = 5000 ppm F, NaF group = 5000 ppm F) Self applied under supervision, with tray, 140 times a year (average), 1 mg ‐ 2 mg F (5‐10 drops) applied for 6 min* Prior to application = no tooth cleaning performed Postop instruction = no brushing after application
Outcomes	1.8‐year DMFS increment ‐ (CA) Reported at 1.8 years follow‐up (and 1.9 years post‐treatment) DMFT(CA) Dropout Etching of enamel; inadvertent swallowing, by total increase in fluoride urinary excretion
Declaration of interest	No information provided.
Source of funding	The trial authors thank Davies, Rose Hoyt Pharmaceutical Div, the Kendall Co, Needham, Mass, 02194 for supplying the gels.
Notes	Clinical (VT) caries assessment by 1 examiner; diagnostic threshold = CA; state of tooth eruption included NR; diagnostic errors NR *Gel application started 7 weeks after baseline examination.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “The children ... were stratified by age and sex and assigned at random ...” 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	Quotes: “The third group was the control group ... no NaF gels were applied.” Comment: No placebo described.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quotes: “The third group was the control group ... no NaF gels were applied.” “All clinical examinations were conducted by one of the authors .... He did not know to which group a child belonged at the time of the examination.” Comment: Blind outcome assessment, but no placebo described.
Incomplete outcome data (attrition bias) All outcomes	High risk	Overall dropout for length of follow‐up: 12.9% in 1.8 years. Dropout by group: 64/369 (17.3%) for both FG groups, 10/205 (4.9%) NT. Reasons for losses: Moved away or could not participate, exclusions based on presence in all follow‐up examinations. Comment: Numbers lost not unduly high for length of follow‐up, with differential losses between groups (17.34% FG (both groups), 4.89% NT). 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 1.8 years follow‐up (and 1.9 years post‐treatment) DMFT(CA) Etching of enamel; inadvertent swallowing, by total increase in fluoride urinary excretion 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: 10.23 FG1, 10.19 FG2, 10.00 NT DMFT: 6.05 FG1, 5.99 FG2, 5.95 NT Comment: Initial caries appears balanced between groups. Age and gender reported as balanced (values for age not reported).
Free of contamination/co‐intervention?	Low risk	Quote: “All children in the three groups were provided with a generous supply of fluoride‐free dentifrice for home use throughout the study.” Comment: There is sufficient indication overall of prevention of contamination/co‐intervention.