Abstract: Objective： To evaluate the difference of features of alveolar bone support under lower anterior teeth between high-angle adults with skeletal class Ⅱ malocclusions and high-angle adults presenting skeletal class Ⅲ malocclusions by using cone-beam computed tomography (CBCT). Methods: Patients who had taken the images of CBCT were selected from the Peking University School and Hospital of Stomatology between October 2015 and August 2017. The CBCT archives from 62 high-angle adult cases without orthodontic treatment were divided into two groups based on their sagittal jaw relationships: skeletal class Ⅱ and skeletal class Ⅲ. vertical bone level (VBL), alveolar bone area (ABA), and the width of alveolar bone were measured respectively at the 2 mm, 4 mm, 6 mm below the cemento-enamel junction (CEJ) level and at the apical level. After that, independent samples t-tests were conducted for statistical comparisons. Results: The ABA of the mandibular alveolar bone in the area of lower anterior teeth was significantly thinner in the patients of skeletal class Ⅲ than those of skeletal class Ⅱ, especially in terms of the apical ABA, total ABA on the labial and lingual sides and the ABA at 6 mm below CEJ level on the lingual side (P<0.05). The thickness of the alveolar bone of mandibular anterior teeth was significantly thinner in the subjects of skeletal class Ⅲ than those of skeletal class Ⅱ, especially regar-ding the apical level on the labial and lingual side and at the level of 4 mm, 6 mm below CEJ level on the lingual side (P<0.05). Conclusion: The ABA and the thickness of the alveolar bone of mandibular anterior teeth were significantly thinner in the group of skeletal class Ⅲ adult patients with highangle when compared with the sample of high-angle skeletal class Ⅱ adult cases. We recommend orthodontists to be more cautious in treatment of highangle skeletal class Ⅲ patients, especially pay attention to control the torque of lower anterior teeth during forward and backward movement, in case that the apical root might be absorbed or fenestration happen in the area of lower anterior teeth.

Key words: Malocclusion, Alveolar bone, Cone-beam computed tomography