Abstract: Objective：To evaluate the distinction of basal bone width and dental arch width before and after orthognathic surgery in patients with skeletal class Ⅲ malocclusion, and to provide empirical reference and theoretical basis for clinical treatment. Methods：A retrospective analysis was performed on patients with skeletal class Ⅲ malocclusion treated in the department of stomatology of Xuzhou Central Hospital from June 2017 to June 2021. Among them, 32 patients received orthodontic and orthognathic surgery, and 26 patients were screened out for preoperative orthodontic and maxillary arch expansion. CBCT image data were collected to establish three-dimensional images. The base bone discrepancies and dental arch widths of maxillomandibular were measured at initial diagnosis, after orthodontic arch expansion and after orthodontic surgery respectively. Paired samples t test was used to analyze the variances of base bone widths and dental arch widths after orthodontic arch expansion and after orthodontic surgery. Results：After maxillary arch enlargement, the width of basal bone and dental arch was wider than that at initial diagnosis, with statistical significance (P<0.05). The widths of maxillary base bone and dental arch which patients were operated on were less 2~5 mm than themselves when the first time they were treated with arch expansion by orthodontic appliances, the difference was statistically significant (P<0.05), while the widths of mandibular base bone widths and dental arch was not significantly narrowed compared with preopration, and the change was within 1mm in width, and the difference was not statistically significant (P＞0.05). Conclusions：Patients with skeletal class Ⅲ malformation usually require preoperative maxillary orthodontic arch expansion. After orthodontic arch expansion and orthodontic surgery, the maxillary base bone width and dental arch width of patients with skeletal class Ⅲ malocclusion were narrowed compared with that before the surgery. And further arch expansion was required after orthodontic surgery, while there was no significant change in mandible.

Key words: Bony Angle's third class malocclusion, orthodontics, orthognathic treatment, CBCT