Slack 1964.

Methods	Random allocation; double‐blind (A); placebo‐controlled; 32% drop‐out rate after 2 years (study duration = 2 years). Natural losses and other reasons; exclusions based on presence in all follow‐up examinations; no differential group losses.
Participants	719 children analysed at 2 years (present for all examinations). Age range at start: 11‐13 years. Surfaces affected at start: NR. Background exposure to fluoride: none reported. Year study began: 1962. Location: UK.
Interventions	FT versus PL (SnF2 group = 1000 ppm F). Home use/unsupervised, 3 times/day instructed but daily frequency assumed. Abrasive system: IMP in fluoride toothpaste, dicalcium phosphate (dihydrate) in placebo toothpaste.
Outcomes	Caries increment data NR (not obtainable). Proportion of carious teeth/surfaces (by tooth type) reported at 1 and 2 years follow ups. Proportion of caries‐free teeth/surfaces (by tooth type) which developed caries after each year. Proportion of children with tooth staining.
Notes	Participants randomised (N =1059). Baseline characteristics 'balanced'. Clinical (VT) caries assessment by one examiner; diagnostic threshold = CA; state of tooth eruption included NR. Diagnostic errors NR.
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	Unclear risk	B ‐ Unclear