Patient compliance with Twin Block appliance during treatment of Class II malocclusion: a randomized controlled trial on two check-up prescriptions

BACKGROUND: Compliance is crucial for the treatment outcome with removable appliances. Previous studies on treatment with the Twin Block appliance have focused on effectiveness in relation to other treatment methods or wear-time. Studies on different check-up intervals to improve compliance seem to be lacking. OBJECTIVES: To compare the impact of two different check-up prescriptions on patient compliance and treatment outcome during treatment with Twin Block. TRIAL DESIGN: Two-arm parallel group, single-centre, randomized controlled trial. MATERIALS AND METHODS: Seventy-three patients, 38 boys, and 35 girls, mean age 11.2 years, were included and block-randomized into two groups treated with a Twin Block appliance. Group 1 was called for check-up visit every sixth week and group 2 every fourth week. Compliance was evaluated with a TheraMon® microsensor, moulded into the appliance, measuring wear-time. Overjet, overbite, and molar relationships were assessed on study casts before and after treatment. The treatment outcomes were analysed on an intention-to-treat basis. RESULTS: In group 1, the reduction of overjet was 5.2 mm and the mean wear-time was 6.9 hours. In group 2, the reduction was 4.7 mm and the wear-time was 6.1 hours. Seventy-four per cent of the patients presented an overjet of 4 mm or less. Wear-time did not correlate to age, gender, or severity of malocclusion. HARMS: No harm was observed in any patient. Lateral open bites were registered during treatment but were normalized at the end of the treatment. LIMITATIONS: The trial was a single-centre study and long-term effects were not evaluated. CONCLUSIONS: During treatment with the Twin Block appliance, a 4-week check-up interval did not improve treatment outcome or increase wear-time, compared to a 6-week check-up interval. The mean wear-time was 6.5 hours per day, even if the recommendation was 12 hours. CLINICAL TRIAL REGISTRATION: NCT05155774