Maxillary third molars with horizontal impaction: A cross-sectional study using computed tomography in young Japanese patients

Objective To examine the anatomical characteristics of impacted maxillary third molars to help predict and prevent possible adverse events during extraction. Methods This retrospective study enrolled young Japanese patients that were assessed for third molar extraction. Patients with maxillary third molar impaction presenting with no space between the maxillary second molar and the occlusal surface of the maxillary third molar were analysed using computed tomography data. Results In this study, a total of 663 patients aged 20–29 years were examined for third molar extraction and 26 teeth in 23 patients were analysed. The mean ± SD angle between the second and third molar axes was 54.2° ± 7.5° and the mean ± SD length of the maxillary third molar was 16.1 ± 1.9 mm. The maxillary third molars showed close or extensive contact with the maxillary sinus and computed tomography did not show any bone from the maxillary sinus floor. Furthermore, in all patients, the crowns of the third molars were not completely covered by the alveolar bone. Conclusions Maxillary third molars with horizontal impaction showed close or extensive contact with the maxillary sinus and their crowns were not completely covered by the alveolar bone.