Reed 1975.

Methods	Trial design: 2‐armed, double‐blind, placebo‐controlled, stratified RCT Location: USA Number of centres: not reported ("several elementary schools") Kansas City, Missouri, USA Recruitment period: study began in/before 1968
Participants	Inclusion criteria: not reported Exclusion criteria: not reported Baseline caries: 5 DMFS (Gp A: 4.83 DMFS (SE 0.256); Gp B: 5.19 DMFS (SE 0.273)). Baseline characteristics (DMFS, DMFT) with some imbalance Age at baseline (years): range 8 to 13 years, mean 9.7 years (Gp A: 9.7 years; Gp B: 9.7 years). Baseline characteristic (age) with some imbalance Sex: 272 F:295 M (Gp A: 136 F:143 M; Gp B: 136 F:152 M). Baseline characteristic (sex) with some imbalance Any other details of important prognostic factors: background exposure to fluoride: none reported. Community water supply not fluoridated Number randomised: 567 (Gp A: 279; Gp B: 288) Number evaluated: 344 at 2 years (available at final examination) (Gp A: 168; Gp B: 176) Attrition: 39% dropout after 2 years (study duration = 2 years). Reasons for high dropout not described; no differential group losses
Interventions	Comparison: FT versus PL Gp A (n = 279): NaF 1000 ppm F; abrasive system: Ca pyrophosphate; home use/unsupervised, daily frequency assumed Gp B (n = 288): placebo; abrasive system: Ca pyrophosphate; home use/unsupervised, daily frequency assumed
Outcomes	Primary: 2‐year DMFS increment ‐ cl + xr; DMFT (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: not reported Declarations/conflicts of interest: not reported, institutional affiliation only Data handling by review authors: n/a Other information of note: clinical (VT) caries assessment by 1 examiner, diagnostic threshold not reported; state of tooth eruption included not reported. Radiographic assessment (up to 7 BW) by 1 examiner, diagnostic threshold not reported. Diagnostic errors not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Following the initial clinical caries examinations, the subjects were stratified by age, sex, visual DMFS and assigned at random to one of the following 2 dentifrices.." 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: "... to one of the following 2 dentifrices: control dentifrice.... or test dentifrice.... Both products were similar in colour, flavour, and other consumer properties" and "A double blind study...." 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: 39% in 2 years. Dropout by group: 111/279 FT, 112/288 PL. Reasons for losses: not reported Comment: numbers lost were high given length of follow‐up. No differential losses between groups. 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: DMFS increment ‐ cl + xr, reported at 1 and 2 years follow‐ups DMFT 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: DMFS: 4.83 FT, 5.19 PL DMFT: 3.00 FT, 3.24 PL age: 9.73 FT, 9.70 PL gender: 143 M, 136 F FT; 152 M, 136 F PL Comment: initial caries appears balanced
Free of contamination/co‐intervention?	Low risk	Quote: "A family supply of the appropriate toothpaste (in coded tubes) and toothbrushes were distributed every 2 months..." Comment: there is sufficient indication overall of prevention of contamination/co‐intervention