Ashley 1977.

Methods	Trial design: 4‐armed, double‐blind, placebo‐controlled and stratified RCT Location: UK Number of centres: 9 comprehensive high schools in London, UK Recruitment period: study commenced 1973
Participants	Inclusion criteria: first‐year high school students attending 1 of 9 selected schools Exclusion criteria: not reported Baseline caries: 9.1 DFS (Gp A: 8.44 DFS (SD 5.58); Gp B: 9.79 DFS (SD 7.28)). Baseline characteristics (DFS, DMFS, DMFT) "balanced" Age at baseline (years): mean 12 years (Gp A: 12.33; Gp B: 12.28). Baseline characteristic (age) "balanced" Sex: overall 279 F:210 M (Gp A: 138 F:108 M; Gp B: 141 F:102 M) Any other details of important prognostic factors: no background exposure to fluoride. Water supply fluoridated to 0.3 ppm F Number randomised: 1135 (numbers for relevant groups not reported) Number evaluated: overall: 1002 at 2 years; relevant groups to this review: 489 at 2 years (present at final assessment. Gp A: 246; Gp B: 243) Attrition: 12% dropout (for all study groups combined) after 2 years. Natural losses; any differential group losses not assessable
Interventions	Comparison: FT versus PL Gp A (n = not reported): SMFP 1000 ppm F; IMP (main abrasive) abrasive system; school use/supervised, daily, 1 g applied for 1 min, post‐brushing water rinse done (non‐fluoride toothpaste provided to all for home use) Gp B (n = not reported): placebo; IMP (main abrasive) abrasive system; school use/supervised, daily, 1 g applied for 1 min, post‐brushing water rinse done (non‐fluoride toothpaste provided to all for home use)
Outcomes	Primary: 2‐year net DFS increment ‐ (E + U) (NCA) cl + (ER) xr; DFS (U); PF‐DFS; MD‐BL‐DFS; MD‐DFS Secondary: none assessed Assessments irrelevant to this review's scope: compliance; inflamed gingival units/person; calculus sites/person Follow‐up duration: 2 years
Notes	Adverse effects: not reported Funding source: "support of the Warner‐Lambert Research Institute" (manufacturers of Listerine mouthwash and Dentyne chewing gum) Declarations/conflicts of interest: not reported Data handling by review authors: Gps C and D (fluoride mouthrinse and fluoride mouthrinse + fluoride toothpaste) irrelevant to this review Other information of note: clinical (V) caries assessment by 1 examiner (FOTI used), diagnostic threshold = NCA. Radiographic assessment (postBW) by 1 examiner, diagnostic threshold = ER. State of tooth eruption included = E/U. Intra‐examiner reproducibility checks for incremental caries data (ICC for clinical 0.95, for radiographic 0.8); reversal rate between 12% and 7% of observed DFS increment in study groups
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Using a table of random numbers, subjects were allocated within each school to one of four study groups"
Allocation concealment (selection bias)	Unclear risk	No information provided
Blinding (performance bias and detection bias) All outcomes	Low risk	Quotes: "The control dentifrice was identical, except that it did not contain sodium MFP..." "The study was organised on a double‐blind basis..." "Records of earlier examinations were not available at the subsequent examination sessions" 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: 12% in 2 years (133/1135, all 4 groups combined). Dropout by group: not reported. Reasons for losses: mainly due to moving from the area Comment: numbers lost were not unduly high given length of follow‐up; it is unclear if there were any differential losses, and if reasons for missing outcome data are acceptable and balanced. Caries data used in the analysis pertain to participants present at baseline and final exams
Selective reporting (reporting bias)	Low risk	Outcomes reported: DFS increment ‐ (E + U) (NCA) cl + (ER) xr, reported at 2 years follow‐up PF‐DFS MD‐BL‐DFS MD‐DFS 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 factors reported: DFS: 8.44 (5.58) FT, 9.79 (7.28) PL DMFT: 5.35 (3.03) FT, 6.06 (3.66) PL DMFS: 9.89 (6.94) FT, 11.05 (7.98) PL age: 12.33 FT, 12.28 PL Comment: initial caries appears balanced between groups
Free of contamination/co‐intervention?	Low risk	Quote: "...all subjects received ample supplies of the non‐fluoride control toothpaste and toothbrushes. This ensured that the exposure of the subjects to fluoride dentifrice or rinse was restricted to the experimental regime" Comment: there is sufficient indication overall of prevention of contamination/co‐intervention