Abstract: Objective: To quantify the changes of alveolar bone defects in adults crowding upon non-extraction clear aligner treatment. Materials& Methods: Cone beam computed tomography (CBCT) scans from adults who complete the first sequence treatment upon non-extraction Invisalign aligner were examined retrospectively in order to record the volume and the incidence of alveolar defects three-dimensionally before and after treatment (T0 &T1). The data were collected and analyzed using the computer programs Mimics 19.0 and Magics 21.0. Differences in alveolar defects between T0 and T1 were analyzed with SAS 8.02 using the Wilcoxon test and Chi-square test for paired samples. The significance level was set at α =0.05. Results: Thirty patients (30 women, average age: 24.9±3.8 years) were chosen for retrospective evaluation. A total of 840 teeth were evaluated, of which were mainly on the buccal root surfaces(99.64%). 219 (26.07%) teeth were involved before treatment and the incidence increased to 35.24% after the treatment, among which the dehiscence in maxillary molars and mandible premolars were significantly increased after treatment(P <0.05). The average volume of alveolar defects in patients before treatment was 83.67±63.33mm3, and after treatment was 97.16±73.79mm3(P <0.05). The Wilcoxon tests showed highly significant increases in the mandible incisors, while showed highly significant decreases in the maxillary canines(P<0.05). Conclusion: Alveolar defect is a common finding in adults crowding before orthodontic treatment, and showed an increased tendency upon non-extraction clear aligner treatment. It is suggested that the three-dimensional integrity of alveolar bone should be fully evaluated in clinical treatment when using clear aligners, and the treatment plan should be reasonably designed to reduce the aggravation of alveolar bone defects.

Key words: CBCT, Clear aligner, Dehiscence, Fenestration