Anatomical changes in alveolar bone structure following the extraction of the mandibular second molar using CBCT measurements

This study seeks to investigate the changes in the anatomical structure of the alveolar bone after the extraction of the mandibular second molar at 3, 6, and 12 months using cone-beam computed tomography (CBCT). This study analyzed CBCT images from 87 cases following the extraction of mandibular second molars. The anatomical structures of the alveolar bone were measured immediately after extraction, as well as at 3 months, 6 months, and 12 months post-operation. The changes in the anatomical structures of the alveolar bone corresponding to different types of alveolar bone after the extraction of mandibular second molars were also assessed. The inverted fossa type of alveolar bone was the most common, accounting for 66.6%, followed by the parallel type at 11.5% and the confluent type at 21.9%. The available buccal bone width decreased in the order of inverted fossa type, confluent type, and parallel type. The lingual mandibular fossa of the inverted fossa type was classified into three categories: Type I (48.3%), Type II (41.4%), and Type III (10.3%). Within 12 months after the extraction of the mandibular second molar, the width of the inverted fossa type and the distance between the crest and the canal had the least absorption. The lingual inclination of the alveolar bone increased. In Type I, L2, L3, and L4 were all greater than 2 mm. In Type II, L2 was less than 2 mm, while L3 and L4 were greater than 2 mm. In Type III, L2 and L3 were less than 2 mm, and L4 was greater than 2 mm. Within 12 months after the extraction of the mandibular second molar, both the height and horizontal width of the alveolar bone decreased, and the degree of decrease is correlated with the type of alveolar bone. The deeper the lingual depression, the higher the risk of mandibular nerve injury and lingual perforation. The increase in lingual inclination of the alveolar bone after extraction is a contributing factor to the risk of lingual perforation.