Howat 1978.

Methods	Trial design: 2‐armed, double‐blind, placebo‐controlled RCT Location: UK Number of centres: single mobile dental unit visiting 2 secondary comprehensive schools in North‐West England, UK Recruitment period: study commenced in/before 1974
Participants	Inclusion criteria: not reported Exclusion criteria: not reported Baseline caries: 7.4 DMFS (Gp A: 7.42 DMFS (SD 5.92)/4.63 DMFT (SD 3.32); Gp B: 7.37 DMFS (SD 5.59)/4.65 DMFT (SD 3.17)) (evaluated participants only). Baseline characteristics (DMFS, DMFT, SAR) "balanced" Age at baseline (years): range 11 to 12 years (group distribution not reported) Sex: distribution not reported Any other details of important prognostic factors: no background exposure to fluoride reported (community water supply suboptimally fluoridated (0.15 ppm F)) Number randomised: 560 (Gp A: 279; Gp B: 281) Number evaluated: 495 at 3 years (present at final assessment. Gp A: 253; Gp B: 242) Attrition: 12% dropout after 3 years (study duration = 3 years). Reasons for attrition described with respective total numbers (56 left school, 7 withdrawn by own choice, 2 lack of co‐operation); no differential dropout ‐ 65 failed to complete the trial, 39 in placebo group and 26 in fluoride group
Interventions	Comparison: FT versus PL Gp A (n = 279): SMFP 1000 ppm F; abrasive system: silica zerogel; school use/supervised, daily, for 1 min (appropriate toothpastes also provided for home use) Gp B (n = 281): placebo; abrasive system: silica zerogel; school use/supervised, daily, for 1 min (appropriate toothpastes also provided for home use)
Outcomes	Primary: 3‐year net DMFS increment ‐ (E) (CA) cl + (DR) xr; anterior DMFS; posterior DMFS; PF‐DMFS; MD‐DMFS; MD‐BL‐DMFS; DMFT (at 8 months, 2 years, 3 years) Secondary: none assessed Assessments irrelevant to this review's scope: compliance Follow‐up duration: 3 years
Notes	Adverse effects: not reported Funding source: Colgate‐Palmolive Ltd Declarations/conflicts of interest: not reported 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 = DR. Reproducibility checks done in 10% sample clinically and radiographically (ICC of incremental data between 0.96 and 0.99)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The subjects were randomly allocated to test and control 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	Quote: "The trial was double‐blind with neither the subjects nor the examiner being aware who was receiving test or control products..... dentifrices were indistinguishable in taste and appearance and their composition varied only in their fluoride content"  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: 11.6% (in 3 years). Dropout by group: 26/279 FT, 39/281 PL. Reasons for losses: changing school (56), withdrawal from study by choice (7), exclusion due to lack of co‐operation (2) Comment: numbers lost were not unduly high for the length of follow‐up, with no differential losses 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: DMFS increment ‐ (E) (CA) cl + (DR) xr, reported at 3 years follow‐up anterior DMFS posterior DMFS PF‐DMFS MD‐DMFS MD‐BL‐DMFS 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: 7.42 (5.92) FT, 7.37 (5.59) PL DMFT: 4.63 (3.32) FT, 4.65 (3.17) PL SAR: 93.48 (19.74) FT, 92.81 (21.52) PL Comment: initial caries appears balanced
Free of contamination/co‐intervention?	Low risk	Quote: "Active and control dentifrices were used daily at school ... under the care of brushing supervisors... subjects were also given liberal supplies of the same dentifrice for home use.... and independent checks of the dispensed dentifrices were carried out at regular intervals to assess the accuracy of the trial supervisors" Comment: there is sufficient indication overall of prevention of contamination/co‐intervention