Thomas 1966.

Methods	Stratified random allocation; double‐blind (A); placebo‐controlled; 32% drop out after 2 years (study duration = 2 years). Reasons for attrition NR; no differential group losses.
Participants	464 children analysed at 2 years (present for the entire study period). Average age at start: 7‐16 years (average = 12). Surfaces affected at start: 10.7 DFS. Background exposure to fluoride: none reported. Year study began: 1961. Location: USA.
Interventions	FT (2 groups) versus PL (Both SnF2 groups = 1000 ppm F). Institution use/supervised, twice a day. Abrasive system: IMP in one SnF2 and placebo toothpaste, Ca pyrophosphate in another SnF2 toothpaste.
Outcomes	2yDFS increment ‐ cl+xr. Reported at 6m, 1, 1.5 and 2 years follow ups. DFT.
Notes	Participants randomised (N = 679). Baseline characteristics (DFS, DFT, TAR) 'balanced'. Clinical (VT) caries assessment by one examiner, diagnostic threshold = NR. Radiographic assessment (10 BW) by one examiner; diagnostic threshold = NR. State of tooth eruption included = NR. Check of diagnostic errors done.
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	Low risk	A ‐ Adequate