Powell 1981.

Methods	Stratified random allocation; double‐blind (A); placebo‐controlled; drop‐out rate NR nor obtainable (study duration = 4 years). Reasons for attrition NR; any differential group losses not assessable.
Participants	125 children analysed at 4 years (subjects who developed caries). Age range at start: 12‐14 years. Surfaces affected at start: 21.4 DMFS (from sample above). Background exposure to fluoride: none reported. Year study began: 1963. Location: Australia.
Interventions	FT (pp/Plsol) versus PL(pp/Plsol)** (SnF2 group = 1000 ppm F). Home use/unsupervised, daily frequency assumed. Abrasive system: Ca pyrophosphate.
Outcomes	Caries increment data NR (not obtainable). Progression rate of initial carious lesions in MD surfaces of permanent posterior teeth at annual intervals (for 4 years).
Notes	Participants randomised (numbers NR). Baseline characteristics (age, gender, DMFS) 'balanced'. Radiographic (post BW) enamel caries progression assessment by one examiner; state of tooth eruption included = E. High reproducibility of radiographic diagnosis (icc = 0.91). **Prior prophylaxis with lava pumice followed by professional application of placebo solution performed every six months for 2 years in both relevant groups compared.
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	Unclear risk	B ‐ Unclear