DePaola 1980.

Study characteristics
Methods	Study design: 4‐arm parallel‐group RCT (only 2 relevant arms used), placebo controlled Study duration: 2 years, + 1‐year postintervention period (but only 1‐year results used)
Participants	270 children analysed at 1* year (after exclusions, present for both examinations) Participants randomised (numbers NR) Age range 12‐14 years (average = 13) Surfaces affected: NR Exposure to other fluoride: toothpaste assumed Year study began: in/before 1977 Location: USA Setting of recruitment and treatment: school
Interventions	FG versus PL (APF group = 12,300 ppm F) Self applied under supervision, with tray, 10 consecutive applications (days) in 1st year, applied for 5 min Prior to application = no tooth cleaning performed Postop instruction = no information provided
Outcomes	1‐year* net DFS increment ‐ (CA) CL + XR Reported at 1 and 2 year follow‐ups (and 1 year post‐treatment)
Declaration of interest	No information provided.
Source of funding	The study was supported by National Institute of Dental Research contract No NOI‐DE42445.
Notes	Clinical (VT) caries assessment by 2 examiners; diagnostic threshold = CA; state of tooth eruption included NR. Radiographic assessment (2 postBW) by 2 examiners (diagnostic threshold NR); diagnostic errors NR. *Intervention applied during 1st year of study only (final 2 years results not considered).
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “Subjects were randomly assigned to 1 examiner and 1 of 4 treatment groups at the time of the clinical examination” Comment: Not enough information provided.
Allocation concealment (selection bias)	Unclear risk	No information provided.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quotes: “A strict double‐blind routine was maintained throughout the course of the investigation.” “The same procedure as group 1 except that placebo gel was used ...” Comment: Use of placebo described.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quotes: “A strict double‐blind routine was maintained throughout the course of the investigation.” “The same procedure as group 1 except that placebo gel was used ...” Comment: Blind outcome assessment and use of placebo described.
Incomplete outcome data (attrition bias) All outcomes	High risk	Overall dropout for length of follow‐up: Not reported. Dropout by group: Not reported. Reasons for losses: Exclusions based on compliance and presence at all exams.
Selective reporting (reporting bias)	Low risk	Outcomes reported: DFS increment ‐ (CA) CL + XR, reported at 1 and 2 year follow‐ups (and 1 year post‐treatment). Comment: Trial protocol not available. All pre‐specified outcomes (in Methods) were reported and were reported in the pre‐specified way.
Baseline characteristics balanced?	Unclear risk	Prognostic factors reported: DFS, dental age and age reported as balanced (values not reported).
Free of contamination/co‐intervention?	Low risk	Quote: “Special care was taken to be sure that each subject received the proper agent ...” Comment: There is sufficient indication overall of prevention of contamination/co‐intervention.