Incidence and Risk Factors of Alveolar Bone Dehiscences and Fenestrations after Clear Aligner Therapy with Class II Elastics: A Retrospective Study

Background In clear aligner therapy (CAT), Class II elastics are widely used to reinforce the anchorage during the distalization of upper molars, however, their association with alveolar bone dehiscences (ABDs) and fenestrations (ABFs) in the anterior region remains unclear. The aim of this research is to assess the incidence of ABDs/ABFs in adult patients undergoing non-extraction CAT with Class II elastics, and to explore risk factors associated with the occurrence of ABDs/ABFs. Methods Thirty adult patients with Class II malocclusion who underwent non-extraction CAT with Class II intermaxillary elastics were enrolled in this study. Cone-beam computed tomography (CBCT) images were obtained before (T0) and immediately after (T1) CAT to assess the occurrence of ABDs/ABFs on the labial and lingual sides of anterior teeth. Chi-square tests were used to compare the incidence of ABDs/ABFs at T0 and T1, meanwhile, binary logistic regression was utilized to analyze the risk factors associated with ABDs/ABFs at T1. Results On the labial side, the incidence of ABDs increased significantly in the mandibular central incisors (from 36.7–62.8%, P  < 0.05), mandibular lateral incisors (from 36.7–70.0%, P  < 0.05), mandibular canines (from 31.7–53.3%, P  < 0.05) and maxillary canines (from 30.0–55.0%, P  < 0.05). While on the lingual side, it increased significantly in the maxillary central incisors (from 1.7–23.3%, P  < 0.05), lateral incisors (from 6.7–38.3%, P  < 0.05), and canines (from 21.7–46.7%, P  < 0.05). The incidence of ABFs only increased on the labial side of the maxillary canines and mandibular central incisors. The occurrence of maxillary ABDs was strongly associated with the crowding ( OR  = 1.318, P  = 0.007), while the occurrence of the mandibular ABDs was significantly associated with root surface (labial vs. lingual, OR  = 1.836, P  = 0.008). Conclusions The incidence of ABDs/ABFs significantly increased after non-extraction CAT with Class II elastics in adults, especially on the labial root surface of the mandibular anterior teeth. Orthodontists should be well aware of the periodontal risks of CAT with Class II elastics.