Slack 1967.

Methods	Trial design: 2‐armed, double‐blind, placebo‐controlled RCT Location: UK Number of centres: 11 secondary technical/grammar schools across Kent, UK Recruitment period: study began 1963
Participants	Inclusion criteria: not reported Exclusion criteria: not reported Baseline caries: 8.9 DFS (Gp A: 8.72 DFS (SE 0.281); Gp B: 9.13 DFS (SE 0.317)). Baseline characteristics (DFS, DFT, DMFS, DMFT, TAR) "balanced" Age at baseline (years): mean 11 years 11 months (Gp A: 11 years 11.5 months; Gp B: 11 years 11.4 months). Baseline characteristics (age, dental age) "balanced" Sex: 886 F:0 M Any other details of important prognostic factors: background exposure to fluoride: none reported Number randomised: 886 (Gp A: 443; Gp B: 443) Number evaluated: 696 at 3 years, all female (present for all examinations) (Gp A: 356; Gp B: 340) Attrition: 21% dropout rate after 3 years (study duration = 3 years). Reasons for dropout 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
Interventions	Comparison: FT versus PL Gp A (n = 443): SnF2 1000 ppm F; abrasive system: IMP; home use/unsupervised, daily frequency assumed Gp B (n = 443): placebo; abrasive system: dicalcium phosphate (dihydrate); home use/unsupervised, daily frequency assumed
Outcomes	Primary: 3‐year net DFS increment ‐ (E) (CA) cl; posterior MD‐DFS; DFT; DMFS; DMFT (at 1, 2, 3 years) Secondary: proportion of children with tooth staining (at 1, 2, 3 years) Assessments irrelevant to this review's scope: soft tissues; dental cleanliness Follow‐up duration: 3 years
Notes	Adverse effects: stains (all stains at 3 years: percentage of each group. Gp A: 39.2%; Gp B: 12.7%). Reasons for losses: staining: Gp A n = 6; Gp B n = 1 Funding source: Unilever Ltd Declarations/conflicts of interest: institutional affiliations only Data handling by review authors: n/a Other information of note: clinical (VT) caries assessment by 1 examiner, diagnostic threshold = CA; state of tooth eruption included = E/U. Radiographic assessment (2 postBW) by 1 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
Random sequence generation (selection bias)	Unclear risk	Quote: "As permission was received for participation, each child was randomly allocated within his own school, to the control and study groups" Comment: not enough information provided
Allocation concealment (selection bias)	Unclear risk	No information provided
Blinding (performance bias and detection bias) All outcomes	Low risk	Quotes: "This 3 year clinical trial..... was conducted double‐blind" and "The films from all 4 examinations were read at the end of the trial by one examiner, and charted seperate from the clinical examination data. The examiner did not know to which group the films belonged" and "The control dentrifice was essentially the insoluble metaphosphate silica paste as used for the study product" Comment: blind outcome assessment and use of placebo described
Incomplete outcome data (attrition bias) All outcomes	Low risk	Overall dropout for length of follow‐up: 21% in 3 years. Dropout by group: 87/443 FT, 103/443 PL. Reasons for losses: staining: 6 FT, 1 PL; moved away: 29 FT, 39 PL; changed school: 5 FT, 5 PL; parents' request: 5 FT, 6 PL; exclusion based on presence at all examinations: 42 FT, 52 PL Comment: numbers lost were not unduly high given length of follow‐up with no differential losses between groups. Reasons for the missing outcome data are acceptable and balanced, except for staining, which although related to the intervention, would not affect outcome due to very small loss (causing no obvious imbalance). Caries data used in the analysis pertain to participants present at all examinations
Selective reporting (reporting bias)	Low risk	Outcomes repoted: DFS increment ‐ (E) (CA) cl, reported at 1, 2 and 3 years follow‐ups DFT DMFS DMFT posterior MD‐DFS proportion of children with tooth staining Comment: trial protocol not available. All pre‐specified outcomes (in Methods) were reported and were reported in the pre‐specified way
Baseline characteristics balanced?	Low risk	Prognostic factors reported: DFS: 8.72 FT, 9.13 PL DFT: 6.21 FT, 6.06 PL DMFS: 12.36 FT, 12.25 PL DMFT: 6.82 FT, 6.86 PL age: 12 FT, 12 PL dental age: 24.80 FT, 24.33 PL TAR: 18.61 FT, 18.27 PL Comment: initial caries appears balanced
Free of contamination/co‐intervention?	Low risk	Quote: "The dentifrices were supplied by mail to the participants and their families.... One tube per person per month in each family was supplied..." Comment: there is sufficient indication overall of prevention of contamination/co‐intervention