Abrams 1980.

Methods	Trial design: 3‐armed, double‐blind, placebo‐controlled and stratified RCT Location: USA Number of centres: 14 schools in San Francisco Bay area Recruitment period: study commenced in/before 1976
Participants	Inclusion criteria: not reported Exclusion criteria: not reported Baseline caries: 3.2 DFS (Gp A: 3.34 DFS; Gp B: 3.06 DFS; Gp C: 3.13 DFS; "balanced") Age at baseline (years): range 5 to 12 years. Mean not reported Sex: not reported Any other details of important prognostic factors: background exposure to fluoride not reported. Natural fluoride level of community water supply ranged from 0.015 to 0.093 ppm F Number randomised: 2210 (Gp A: 740; Gp B: 721; Gp C: 749) Number evaluated: 1141 at 3 years (present at final assessment: Gp A: 383; Gp B: 378; Gp C: 380) Attrition: 48% dropout after 3 years. Reasons for high dropout described: change of residence, absenteeism, non‐adherence to study protocol; no differential group losses
Interventions	Comparison: FT (2 groups) versus PL Gp A (n = 740): SnF2 1000 ppm F; silica gel abrasive system; home use/unsupervised, daily frequency assumed Gp B (n = 721): SnF2 1000 ppm F; Ca pyrophosphate abrasive system; home use/unsupervised, daily frequency assumed Gp C (n = 749): placebo; silica gel abrasive system; home use/unsupervised, daily frequency assumed
Outcomes	Primary: 3‐year net DFS increment ‐ (E + U) (CA) cl + (ER) xr; MD‐DFS; DFS rate; DFT; DFT rate; DMFS; DMFT (at 1, 2 and 3 years follow‐up) Secondary: none assessed Assessments irrelevant to this review's scope: none assessed Follow‐up duration: 3 years
Notes	Adverse effects: not reported Funding source: "grant from the Lever Brothers Company", Lever manufacture Aim (Gps A, and C ‐ without fluoride) Declarations/conflicts of interest: not reported Data handling by review authors: combined 2 SnF2 1000 groups with different abrasive systems Other information of note: clinical (VT) caries assessment by 2 examiners, diagnostic threshold = CA. Radiographic assessment (postBW) by 2 examiners, diagnostic threshold = ER. State of tooth eruption included = E/U. Intra‐ and inter‐examiner reproducibility of clinical caries diagnosis (DFS) assessed annually by duplicate examination of 10% random sample (percentage of times diagnosis replicated in all 3 examinations ranged 42% to 97% and 77% to 92% for both examiners and for each respectively)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Children were randomly assigned to one of 3 treatment groups. A stratified sequential sampling technique was used within each school to balance the sample size with respect to sex and grade level for each dentifrice" 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: "A 3 year double‐blind study of a dentifrice containing 0.4% stannous fluoride and a placebo..." "The examiners at all times were unaware of the children's dentifrice assignment" 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: 48% in 3 years. Dropout by group: 357/740 FT1, 343/721 FT2, 369/749 PL. Reasons for losses: change of residence, absenteeism, exclusion due to non‐adherence to study requirements Comment: numbers lost were high for the length of follow‐up. No differential loss between groups. It is unclear if reasons for missing outcome data are acceptable and balanced. Caries data used in analysis pertain to participants present at final examination
Selective reporting (reporting bias)	Low risk	Outcomes reported: DFS increment ‐ (E + U) (CA) cl + (ER) xr, reported at 1, 2 and 3 years follow‐ups DMFT DMFS DFT MD‐DFS DFT rate DFS rate 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: 2.90 FT1, 3.28 FT2, 2.94 PL Comment: initial caries appears balanced
Free of contamination/co‐intervention?	Low risk	Quotes: "Provisions were made ensuring the randomization process to assure that only one dentifrice code would be available in each household.... A letter to parents was attached, giving brushing instructions and urging use of only the assigned dentifrice" Comment: there is sufficient indication overall of prevention of contamination/co‐intervention