Sköld 2005.

Methods	Design: 4‐arm RCT Location: Sweden (West coast) Study started: 1998
Participants	Number randomised: 854 Number analysed: 758 analysed at 3 years (present for all examinations) Age range: 13‐16 years (all subjects 13 years at start of 3‐year study) Background exposure to other fluoride: Water (in 1 of 3 trial sites only), toothpaste
Interventions	Comparison: FV (3 groups) + ptc** versus NT Group 1 (n = 190): NaF varnish (Duraphat® 22,600 ppm F), twice a year Group 2 (n = 186): NaF varnish (Duraphat® 22,600 ppm F), 3 times a year Group 3 (n = 201): NaF varnish (Duraphat® 22,600 ppm F), 8 times a year Group 4 (n = 181): No treatment Application in mobile units in schools, to all posterior approximal surfaces, with syringe, 0.3 mL (1 drop) applied, left to dry (duration NR) Post‐op instructions: Refrain from eating hard foods on that day; no brushing until next day **Toothbrushing with non‐fluoride paste carried out in FV groups only
Outcomes	3‐year DFS incidence ‐ (E) (DR/ER)xr (only) Reported at 3 years follow‐up: DS; FS; caries progression
Notes	Baseline characteristics (DS/FS) balanced X‐Ray caries assessment by 1 examiner; diagnostic threshold = DR and DE; state of tooth eruption included = E; for intra‐examiner reliability, 10% of the radiographs read twice with an interval of 2 months (Kappa 0.90 for all scores and 0.82 for carious surfaces)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "...the adolescents were randomly allocated within each school class into 4 groups" Comment: Not enough information given
Allocation concealment (selection bias)	Unclear risk	No information provided
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quotes: "Three trained dental nurses and one dental hygienist performed all the treatments..."; "...treated adolescents with fluoride....and no treatment (control)" Comment: No placebo described
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quotes: "...films were scored and analysed blindly by one of the authors"; "Three trained dental nurses and one dental hygienist performed all the treatments..." Comment: Blind outcome assessment
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Overall drop‐out for length of follow‐up: 11% in 3 years. Drop‐outs by group: Not reported. Reasons for losses: Moving away from the area, not attending all treatment sessions Comment: Numbers lost overall were reported, and not unduly high for length of follow‐up. Numbers randomised (at start) were not reported by group, thus drop‐outs by group not obtainable. It is unclear if reasons for the missing outcome data are acceptable and balanced. Caries data used in the analysis pertain to participants followed up for the entire study duration and attending all treatment sessions
Selective reporting (reporting bias)	Low risk	Outcomes reported: 1st and 2nd mpmDS/FS final prev and DFS incidence (CA/NCA) xr at 3 years follow‐up; drop‐outs 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: DS (approximal dentine): 0.15 (0.51) FV1, 0.12 (0.36) FV2, 0.13 (0.49) FV3, 0.07 (0.28) NT FS: 0.13 (0.48) FV1, 0.10 (0.43) FV2, 0.08 (0.46) FV3, 0.13 (0.45) NT DS (approximal enamel): 2.15 (3.37)FV1, 2.13 (3.30) FV2, 2.36 (3.86) FV3, 1.75 (2.43) NT Comment: Initial caries appears balanced between groups
Free of contamination/co‐intervention?	High risk	Quotes: "All participants in this study attended the dental clinics for regular check‐ups and were given prophylactic treatment according to their actual caries risk. The dentists who treated them had no knowledge to which group they belonged" "... 95% of the adolescents in all areas were treated with one F varnish at the yearly check‐up, ... all of them, independent of area and caries risk revealed they brushed their teeth twice a day using an F toothpaste" Comment: Although dentists treating the children in the yearly check‐ups were unaware of group assignment, 95% of all children were treated with 1 application of fluoride varnish, an apparent contamination