Effects of fixed functional orthodontic treatment in hypo- and hyperdivergent Class II patients

Objective: To compare skeletal and dentoalveolar changes after orthodontic treatment of Class II malocclusion in patients with hypo- and hyperdivergent growth patterns through cast splint fixed functional appliances (FFA). Materials and Methods N = 42 patients with mandibular plane angles < 34° or ≥ 34° were divided into a hypo- (n = 24) and a hyperdivergent (n = 18) group. All patients received a single-step mandibular advancement protocol through an FFA. Lateral cephalograms were analysed after initial levelling and alignment (T1) and immediately after FFA removal (T2). The therapeutic effect was calculated through comparison with age-matched controls from a growth survey. Statistical significance was set at p < 0.05. Results Hypo- and hyperdivergent patients showed different treatment outcomes, but significant differences existed only for overbite and interincisal angle. Nearly all measurements suggested similar treatment related changes for both groups with exception for dentoalveolar parameters. Conclusion Treatment with FFA causes similar skeletal and dentoalveolar effects in hypo- and in hyperdivergent patients. The correction of overjet and molar relationship is mainly caused by dentoalveolar changes. Clinical relevance: Hyperdivergent patients do not respond unfavourably to FFA-treatment compared to hypodivergent patients. Lower incisor protrusion occurs more pronounced in hypodivergent patients. The growth pattern ought to be considered when choosing FFA for Class II treatment.