Slack 1967a.

Methods	Random allocation; double‐blind (A); placebo‐controlled; 21% drop‐out rate after 3 years (study duration = 3 years). Reasons for drop out described with numbers: left school, moved away, staining of teeth, on parents request; exclusions based on presence in all follow‐up examinations; no differential group losses.
Participants	757 children analysed at 3 years, all female (present for all examinations). Age range at start: 11‐12 years. Surfaces affected at start: 7 DFS. Background exposure to fluoride: none reported. Year study began: 1962. Location: UK.
Interventions	FT versus PL (SnF2 group = 1000 ppm F). Home use/unsupervised, daily frequency assumed. Abrasive system: dicalcium pyrophosphate.
Outcomes	3yDFS increment ‐ (E) (CA)cl. Reported at 3 years follow up. DFT. DMFS. DMFT. postMD‐DFS. Proportion of children with tooth staining.
Notes	Participants randomised (N = 961). Baseline characteristics (age, dental age, DFS, DFT, DMFS, DMFT, TAR) 'balanced'. Clinical (VT) caries assessment by one examiner; diagnostic threshold = CA; state of tooth eruption included = E/U. Radiographic assessment (2 postBW) by one examiner; diagnostic threshold = ER. Consistency of clinical diagnosis maintained by re‐examination of 10% sample and calibration checks made against reserve examiner.
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	Unclear risk	B ‐ Unclear