Segal 1967.

Methods	Trial design: 2‐armed, double‐blind, placebo‐controlled, stratified RCT Location: USA Number of centres: single school district (number of schools not reported), in rural Western Pennsylvania Recruitment period: study began in/before 1964
Participants	Inclusion criteria: not reported Exclusion criteria: not reported Baseline caries: not reported Baseline characteristics (SAR) "balanced" Age at baseline (years): range 7 to 12 years (group distribution not reported) Sex: not reported Any other details of important prognostic factors: background exposure to fluoride: none reported. Community water supply which did not contain significant levels of the fluoride ion (F level not reported) Number randomised: 845 (Gp A: 425; Gp B: 420) Number evaluated: 648 at 2 years (available at final examination) (Gp A: 338; Gp B: 310) Attrition: 23% dropout after 2 years (study duration = 2 years). Reasons for attrition not reported; slight differential group losses
Interventions	Comparison: FT versus PL Gp A (n = 425): SnF2 1000 ppm F; abrasive system: IMP (mainly); school use/supervised, daily (appropriate toothpaste also provided for home use) Gp B (n = 420): placebo; abrasive system: IMP (mainly); school use/supervised, daily (appropriate toothpaste also provided for home use)
Outcomes	Primary: 2‐year DFS increment ‐ (CA) cl + xr; DFS (U) (at 1, 2 years) Secondary: none assessed Assessments irrelevant to this review's scope: n/a Follow‐up duration: 2 years
Notes	Adverse effects: not reported Funding source: partially funded by Lever Brothers Company. Other partial source of funding not reported Declarations/conflicts of interest: 1 (A Picozzi) of 4 authors employed by Lever Brothers. Remaining authors declare institutional affiliations Data handling by review authors: n/a Other information of note: clinical (VT) caries assessment by 2 examiners, diagnostic threshold = CA. Radiographic assessment as a supplementary aid, diagnostic threshold not reported. State of tooth eruption included E/U. Inter‐ and intra‐examiner reproducibility checks done
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "In order to achieve adequate balance between test and control groups in terms of previous caries experience, all the children were classified in blocks according to school, age, sex...... Within each block the subjects were assigned at random to one of four subgroups..." 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: "... No reference to the findings of previous examinations was permitted at any time. The study was conducted as a double blind investigation. At the time of the initial exam, preassigned coded dentifrices were distributed to the children" and "Control dentifrice contained no stannous fluoride" Comment: blind outcome assessment and use of placebo described
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Overall dropout for length of follow‐up: 23% in 2 years. Dropout by group: 87/425 FT, 110/420 PL. Reasons for losses: not reported Comment: numbers lost were not unduly high given length of follow‐up, but with some differential losses between groups (20% FT, 26% PL). It is unclear if reasons for the missing outcome data are acceptable and balanced. Caries data used in the analysis pertain to participants present at final examination
Selective reporting (reporting bias)	Low risk	Outcomes reported: DFS increment ‐ (CA) cl + xr, reported at 1 and 2 years follow‐ups DFS (U) 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 factor reported: SAR: 77.34 FT, 76.49 PL Comment: initial caries appears balanced
Free of contamination/co‐intervention?	Low risk	Quote: "Sufficient dentifrice was distributed to the panelists for family use" Comment: there is sufficient indication overall of prevention of contamination/co‐intervention