Morphometric evaluation of changes in the alveolar bone of adolescents with bimaxillary protrusion via cone beam computed tomography

This study aimed to evaluate the morphometric changes in the alveolar bone of the maxillary and mandibular anterior regions after retraction in adolescents.The sample size comprised 30 adolescent patients with class 1 bimaxillary protrusion (12 males and 18 females, age: 12-18 years old) and were treated by extracting four first pre-molars. Cone beam computed tomography (CBCT) was performed 1 month before and 1 month after the retraction. For each maxillary and mandibular anterior tooth, the labial and palatal alveolar plates at cervical 1/3, middle 1/3, and apical 1/3 levels for bone thickness changes during the retraction of the maxillary and mandibular anterior regions were checked. The movements of cervical 1/3, middle 1/3, and apical 1/3 levels of the maxillary central incisor were measured. Statistical analyses were performed with SPSS 16.0.For the adolescents, alveolar bone thickness increased on the labial side and decreased on the palatal side. The alveolar bone thicknesses of cervical 1/3 and middle 1/3 of maxillary central incisor, cervical 1/3 and apical 1/3 of maxillary lateral incisor, middle 1/3 of mandibular central incisor, apical 1/3 of mandibular lateral incisor, and middle 1/3 and apical 1/3 of mandibular canine all increased after retraction. By contrast, the alveolar bone thickness of the apical 1/3 of maxillary canine and the cervical 1/3 of mandibular canine decreased after retraction. No statistically significant difference was observed in other region.During retraction, a controlled tipping movement occur in adolescents. After retraction, the alveolar bone thickness of the labial side increase, whereas that of the palatal side decrease. Moreover, the thicknesses of major areas in the alveolar bone significantly increase.