Gisselsson 1999.

Study characteristics
Methods	Study design: 3‐arm parallel‐group quasi RCT, placebo controlled Study duration: 3 years, + 1.9 years postintervention period
Participants	280 children analysed at 3 years (available at final examination) Participants randomised (N = 317) Average age 13 years Surfaces affected: 0.24 DFS* ‐ 39% caries‐free Exposure to other fluoride: toothpaste Year study began: 1993 Location: Sweden Setting of recruitment and treatment: school and public dental clinic, respectively
Interventions	FG (2 groups) vs PL (NaF group = 4500 ppm F, SnF2 group = 2425 ppm F) Operator applied, with syringe + floss, 1 ml applied to approximal surfaces of all teeth, in 10 min, 4 times a year Prior to application = no tooth cleaning performed Postop instruction = no information provided
Outcomes	3‐year MD‐DFS increment ‐ (CA/NCA)CL+ (DR/ER)XR Reported at 3 years follow‐up DS FS Proportion of children remaining caries‐free, proportion with 1 or more new DFS (at NCA/ER level) Dropout
Declaration of interest	No information provided.
Source of funding	The study was supported by Patentmedelsfonden for odontologisk prophylaxforskning, Malmohus County Council, and the Faculty of Odontology, Goteborg University. Apoteksbolaget for manufacturing the gels used.
Notes	Clinical caries assessment by 11 examiners; diagnostic threshold = CA and NCA; state of tooth eruption included NR. Radiographic assessment (postBW) by 1 examiner; diagnostic threshold = DR and ER. Diagnostic errors NR. *Gel application started 12 weeks before (2nd) baseline examination.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Quote from correspondence: “The children were ranked at 12 years of age to the numeric values of caries prevalence ... from this list, from top to bottom, the children were distributed in respective group ... first name distributed to a group, second to B, third C, fourth A and so on ...” Comment: Non‐random method used.
Allocation concealment (selection bias)	High risk	The non‐random method used for sequence generation would not allow for allocation concealment.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: “The gels were marked 1, 2, 3, and the study was carried out double‐blind. All gels were manufactured and packed in identical bottles ... The code was not broken until all caries data had been analysed.” Comment: Use of placebo described.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: “The gels were marked 1, 2, 3, and the study was carried out double‐blind. All gels were manufactured and packed in identical bottles ... The code was not broken until all caries data had been analysed.” Comment: Use of placebo and blind outcome assessment described.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Overall dropout for length of follow‐up: 11.67% in 3 years. Dropout by group: 10/107 FG1, 16/101 FG2, 11/109 PL. Reasons for losses: Refused to participate (8), moved away or preferred to visit a private dentist (29). Comment: Numbers lost were not unduly high given length of follow‐up, almost no differential losses between groups 9.35% FG1, 15.84% FG2, 10.09% PL. It is unclear if reasons for the dropout 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: MD‐DFS increment ‐ (CA/NCA)CL + (DR/ER)XR, reported at 3 years follow‐up DS FS Proportion of children remaining caries‐free, proportion with 1 or more new DFS (at NCA/ER level) 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 (CA)(from correspondence): 0.25(0.91) FR1, 0.18(0.56) FR2, 0.28(1.00) PL DS (CA)(from correspondence): 0.11(0.50) FR1, 0.09(0.33) FR2, 0.16(0.68) PL Comment: Initial caries (FS and % caries‐free also reported) with some imbalance (reported as NS difference).
Free of contamination/co‐intervention?	Unclear risk	No information provided.