Andresen activator (AA) is a functional appliance used to correct Class II malocclusion in growing patients. It corrects the malocclusion stimulating mandibular growth and determining a palatoversion of the upper incisors and a vestibularization of the lower incisors. The aim of this study was to analyze the treatment efficacy of class II malocclusion due to mandibular hypodevelopment before peak growth. Fourteen subjects with class II relationship of the skeletal bases and cervical vertebrae maturation stage 1 or 2 were enrolled in the study. Cephalometric analyses were carried out using landmarks derived from the analyses of Pancherz, Ricketts, Tweed and Steiner. A significant decrease (P less than 0.05) in ANB angle was found (-2.29±3.05°) after treatment, which was expression of an improvement in maxillo-mandibular sagittal skeletal relationships. There was also a significant reduction of OJ after treatment (-4.44±2.36 mm; P less than 0.001), indicating a vestibularization of the mandibular incisors and a palatoversion of the maxillary incisors, and a correction of the molar relationship. The favorable effects of the Andresen activator for the correction of the mandibular defect can be found even prior to peak growth; the achieved class I relationship maintains a correct mandible position in time, ensuring a proper skeletal growth.
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