Three-dimensional assessment of periodontal support of lower incisors for skeletal Class II malocclusion undergoing presurgical orthodontic treatment with different vertical skeletal patterns

Background The aim of the present study was to compare periodontal support changes during retraction of mandibular anterior teeth for skeletal Class II malocclusion with different facial divergence and to analyze relevant factors influencing bone remodeling by applying three-dimensional (3D) cone-beam computed tomography (CBCT) reconstruction technology.Methods Forty-eight patients with Class II malocclusion requiring surgical orthodontic treatment enrolled in the study were divided into the hyperdivergent group (n = 16), normodivergent group (n = 16) and hypodivergent group (n = 16) according to their vertical skeletal patterns. Cone-beam computed tomography (CBCT) scans were obtained before treatment (T1) and after presurgical orthodontic treatment (T2). The two-dimensional (2D) alveolar bone morphology, movement of mandibular central incisors and volume of the alveolar bone around incisors were measured on the labial and lingual sides by 3D CBCT reconstruction technology. Statistical analyses were performed with one-way ANOVA, paired t tests and multiple linear regression.Results During presurgical orthodontic treatment, the alveolar bone height on the labial side of the hyperdivergent group decreased significantly (P <= 0.05), but was maintained in the normodivergent and hypodivergent groups (P > 0.05). However, the alveolar bone volume, alveolar bone thickness at each level and alveolar bone height on the lingual side decreased significantly for all the groups. Apart from the initial morphometric measurements at T1, the morphology of lingual alveolar bone at T2 was significantly influenced by the direction and amount of tooth movement. Horizontal retraction and vertical protrusion of the root apex were negatively related to the alveolar bone on the lingual side after presurgical orthodontic treatment.Conclusion For Class II malocclusion patients undergoing presurgical orthodontic treatment, the changes in the periodontal support of the lower central incisors varied in different vertical skeletal patterns. There exists a great periodontal risk of alveolar bone resorption on the lingual side for various vertical types. To avoid alveolar bone deterioration, it is essential to investigate the bone remodeling of patients with different alveolar bone conditions and cautiously plan tooth movement prior to orthodontic treatment. Moreover, 3D measurements based on CBCT construction can provide complementary information to traditional 2D measurements.