Study Of Anterior Alveolar Morphology In Patients With Skeletal Class Ⅲ Malocclusion Based CBCT Data

Objective:To obtain the relationship between vertical facial type and anterior alveolar morphology in adult patients with skeletal class III malocclusion, this study focused specifically on CBCT measurement of anterior alveolar bone and central incisors in adult patients with skeletal class III malocclusion. It offers the theory support for the clinic treatment of skeletal class III malocclusion.Methods:Fifty-sevenadult skeletal class III malocclusion patients were included in t his study.The subjects were divided into three groups of hypodivergent group,normodi vergent group and hyperdivergent group according to the lateralcephalograms of patie nts. All the subjects were taken corn beam tomography (CBCT) scans and after that the CBCT scans were transferred to Mimics10.01software (Materialism’s interactive medical image control system, Materialise, Belgium), measurements were taken on mid-sagittal sections of both the upper and lower central incisors. Parameters respectively defining the alveolar thickness of incisor, the labio-lingual inclination of incisor and alveoli, the distance from the root apex to the cortex were measured. One way analysis of variance and Student-Newman-Keuls tests were performed to check the differences among the three facial types, and pearson correlation and linear regression analysis were performed to study relationship between the inclination of the incisors and the inclination of the bone plate at the same time.Results:1. At the maxillary central incisors, the hyperdivergent subjects showed significantly shortest distance from root apex to lingual cortex (P<0.01), the hypodivergent subjects showed significantly farthest distance from root apex to lingual cortex.Normodivergent and hypodivergent also showed significant difference concerning the distance from root apex to lingual cortex. At the mandibular central incisors, the distance from root apex to labial cortex was found to be the shortest in the hyperdivergent group (P<0.01). No significant differences were found among the normodivergent and the hypodivergent groups concerning the distance from root apex to labial cortex, and the distance from root apex to lingual cortex was also found to be the shortest in the hyperdivergent group, Normodivergent and hypodivergent also showed significant difference concerning the distance from mandibular root apex to lingual cortex.2. The lingual alveolar thickness of the central incisors was found to be thinnest in the hyperdivergent group (P<0.01). TLi2(figurel) of normodivergent and the hypodivergent groups was found to have no significant differences, butTLi4and TLi6and TLi8(figurel) had significant differences. The labial alveolar thickness of the mandibular central incisors was found to be the shortest in the hyperdivergent group (P<0.01), but no significant differences were found among the normodivergent and the hypodivergent groups.3. The lingual alveolar thickness of the central incisors was found to be thicker than the labial alveolar thickness among the hyperdivergent, normodivergent and the hypodivergent groups, and especially at the level of root apex.4. No significant differences were found among the hyperdivergent, normodivergent and the hypodivergent groups concerning the distance from the maxillary root apex to labial cortex, to palatal plane and the inclination of the central incisor. The distance from the mandibular root apex to the mandibular plane had also no significant differences.5. The labio-lingual inclinations of the alveoli at the upper and lower central incisors and the inclination of the incisors were positively correlated (P<0.01). there were negative correlation between the distance from the maxillary root apex to lingual cortex, the lingual alveolar thickness of the maxillary central incisors and the inclination of the incisors(P<0.05). the labial alveolar thickness of the mandibular central incisors and the distance from the mandibular root apex to lingual cortex were found to be smaller, while the inclination of the incisors was found to be greater. Conclusion:There is significant correlation between vertical facial type and anterior alveolar morphology in adult patients with skeletal class III malocclusio. As the Frankfort-mandibular angle becomes larger, or the labio-lingual inclination of the central incisor becomes greater, the associated alveolar bone becomes thinner. The lingual alveolar thickness of the central incisors was found to be thicker than the labial alveolar thickness among the hyperdivergent, normodivergent and the hypodivergent groups.