Three-dimensional changes in patients with Class II malocclusion treated with the Twin-block functional appliance: A case-control study

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INTRODUCTION: This study aimed to visualize and quantify the 3-dimensional skeletal and dental changes in patients with Class II malocclusion after treatment with the Twin-block (TB) and fixed appliances compared with controls treated with Class II elastics. METHODS: Cone-beam computed tomography (CBCT) records of 22 patients treated with the TB appliance were analyzed before treatment, upon completion of the TB phase, and after fixed appliance treatment. Records of 22 matched patients treated with Class II elastics and who had CBCT scans taken before and after treatment were used as controls. The images were oriented and registered on the anterior cranial base and the mandibular corpus. Treatment outcomes were quantified using point-to-point measurements and compared using linear mixed-effects models. RESULTS: After adjusting for baseline characteristics (sex, skeletal maturation, vertical facial pattern, age at the first CBCT, and total treatment time), on average, the TB group exhibited more anterior displacement of the anterior fossa (1.38 mm/y), pogonion (1.39 mm/y), and B-point (1.79 mm/y) and more superior condylar growth (1.35 mm/y) compared with the control group. Within the TB group, more posterior condylar growth occurred during the TB phase, with minimal growth in the subsequent orthodontic phase. The TB group displayed greater extrusion of the mandibular incisors and molars, 2.99 and 2.07 mm more per year, respectively. CONCLUSIONS: The TB group had additional superior and posterior condylar growth, resulting in greater anterior repositioning of pogonion and B-point compared with the control group. Moreover, greater mandibular incisor and molar extrusion was induced in the TB group.

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