Zacherl 1970a.

Methods	Stratified random allocation; double‐blind (A); placebo‐controlled; 35% drop out after 2.5 years (study duration = 2.5 years). Reasons for attrition NR; no differential group losses.
Participants	528 children analysed at 2.5 years (available at final examination). Age range at start: 13‐14 years. Surfaces affected at start: 23.5 DMFS. Background exposure to fluoride: none reported. Year study began: in/before 1963. Location: USA.
Interventions	FT versus PL (SnF2 group = 1000 ppm F). Home use/unsupervised, daily frequency assumed. Abrasive system: Ca pyrophosphate.
Outcomes	2.5yDMFS increment ‐ cl+xr. Reported at 10 m, 1.5 and 2.5 years follow ups. DMFT.
Notes	Participants randomised (N = 811). Baseline characteristics (dental age, gender, DMFS, DMFT, oral hygiene) 'balanced'. Clinical (VT) caries assessment by one examiner, diagnostic threshold = NR. Radiographic assessment (5‐10 BW) by one examiner; diagnostic threshold = NR. State of tooth eruption included = NR. Diagnostic errors NR.
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	High risk	C ‐ Inadequate