Brudevold 1966.

Methods	Stratified random allocation; double‐blind ('A'); placebo‐controlled; 25% drop out (for all study groups combined) after 2 years (study duration = 2 years). Reasons for attrition NR; any differential group losses not assessable.
Participants	1278 children analysed at 2 years (present for the entire trial period). Average age at start: 7‐16 years (average = 12). Surfaces affected at start: 15.7 DFS. Background exposure to fluoride: data not available for fluoridation status of site. Year study began: 1961. Location: USA.
Interventions	FT (3 groups)** versus 'PL' (both SnF2 groups = 1000 ppm F, APF group = 1000 ppm F). Home use/unsupervised, daily frequency assumed. Abrasive system: Ca pyrophosphate in one SnF2 toothpaste, IMP in the other SnF2 and in the APF toothpaste, control toothpaste abrasive NR.
Outcomes	2yDFS increment ‐ cl+xr. Reported at 2 years follow up. DMFS. DMFT. DFT.
Notes	Participants randomised (numbers for relevant groups NR). Baseline characteristics (dental age, DFS, DFT, DMFS, DMFT, gender) 'balanced'. Clinical (VT) caries assessment by two examiners; diagnostic threshold = CA. Radiographic assessment (10 BW) by one examiner; diagnostic threshold NR. State of tooth eruption included NR. Diagnostic errors NR. **NaF‐secondary Ca phosphate toothpaste group not considered (abrasive system known to be incompatible with NaF).
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	Unclear risk	B ‐ Unclear