Ringelberg 1979.

Methods	Stratified random allocation; double‐blind (A); placebo‐controlled; 37% drop out after 2.5 years (study duration = 2.5 years). Reasons for attrition not described; no differential group losses.
Participants	556 children analysed at 2.5 years (available at final examination). Average age at start: 11 years. Surfaces affected at start: 4.2 DMFS. Background exposure to fluoride: none reported. Year study began: 1973. Location: USA.
Interventions	FT (2 groups) versus PL(2 groups) (AmF group = 1250 ppm F, SnF2 group = 1000 ppm F). Home use/unsupervised, daily frequency assumed. Abrasive system: Ca pyrophosphate in SnF2 toothpaste and its placebo, NR for AmF and its placebo.
Outcomes	2.5yNetDMFS increment ‐ (CA)cl + (DR)xr. Reported at 2.5 years follow up. DMFT. Stain score.
Notes	Participants randomised (N = 888). Baseline characteristics (DMFS, DMFT) 'balanced'. Clinical (VT) caries assessment by two examiners, diagnostic threshold = CA. Radiographic assessment (5 BW) by two examiners; diagnostic threshold = DR. State of tooth eruption included NR. Reversal rate between 4 and 9% of observed caries increment in the groups.
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	Unclear risk	B ‐ Unclear