Changes in the alveolar bone thickness of maxillary incisors after orthodontic treatment involving extractions - A systematic review and meta-analysis.

Background: Orthodontic treatment involving en-masse retraction of incisors following premolar extractions, may induce morphological alterations of the alveolar bone surrounding the anterior teeth.

Objective: To assess changes in alveolar bone thickness around the incisors of extraction patients measured with CBCT.

Material and Methods: An electronic search was conducted in PubMed, Scopus, Embase and Cochrane Library, using search terms, with no limitation on publication date, up to April 2018. The articles selected for analysis included randomized controlled trials, case-control studies and cohort studies of patients treated with fixed appliances and premolar extractions, which had measured alveolar bone thickness with CBCT before and after treatment. Changes in bone thickness were calculated and the heterogeneity of the studies was assessed using the I2 and Cochran's Q tests.

Results: Of the 136 articles identified in the initial search, 19 were related to the review subject. After removing a further 14 that did not meet the inclusion criteria, 5 articles were selected for analysis. All five were retrospective studies of medium quality. The main changes in alveolar bone thickness were found in the labial cervical third of the central incisor, presenting increases of 0.4-0.64 mm. On the palatal side the results varied considerably.

Conclusions: A significant increase in alveolar bone thickness occurs in the labial cervical third of the central incisor. These changes may be influenced by incisor position and inclination, the orthodontic technique and mechanics employed, the timing of the final CBCT scan and the bone remodeling capacity during en-masse retraction. Key words: Cone-beam computed tomography, alveolar bone, orthodontics.