CBCT Study of Mandibular, Vertical Facial and Airway Adaptation Related to the Temporomandibular Joint

Background and Objective: The vertical skeletal pattern, temporomandibular joint (TMJ) and the airway size of individuals are important factors to consider during orthodontic diagnosis and treatment planning. There is a tendency for both a reduction in airway dimensions and adaptation of mandibular structures secondary to TMJ degenerative disorders, inflammatory disorders and fracture. The purpose of this study was to evaluate the association between these selected TMJ disorders and facial type, to correlate facial types with airway dimensions and to evaluate the association between selected TMJ disorders and airway dimensions.Materials and Methods: This was a two-component study: the first component was a case-control study, 22 cases and 242 controls, determining the association between facial type and TMJ degenerative disorders, inflammatory disorders and fracture with the outcome being TMJ degenerative, inflammatory disorder or fracture and the predictor being facial types. The second component was a cross-sectional study, 22 cases and 66 controls divided equally in three groups of low, normal and high mandibular plane angles, determining the association between airway dimensions and mandibular phenotypic characteristics. CBCT scans of adults (female 16 years of age or older and male 18 years of age and older) that included the entire mandible as well the cephalometric landmark nasion. The 3D CBCT scan of the individuals were evaluated and measurements were done using Invivo Anatomage, Dolphin Imaging and Vultus 3DMD programs. Odds ratio were calculated based on facial type and gender. ANOVA was used to compare the airway volume and cross section and mandibular measurements between the groups.Results: The odds of having a long face subject within the case group was significantly higher compared to having a long-face subject in control group. 81% of the case subjects with TMJ involvement had a long vertical facial dimension versus 11% of the control group that had a normal TMJ indicating a highly statistically significant difference. The condylar, ramus, and mandibular heights were significantly smaller in the case group with the TMJ pathology compared to the control group. Ramus height and mandibular alveolar housing for central incisors were significantly smaller in the long face subjects in the control group. The smallest cross sectional area of the airway of the cases was significantly narrower compared to the controls, however, there was no differences in airway volume. There was a considerable trend, not statistically significant, in reduction of the airway smallest cross sectional area and volume, as the facial type got longer within the control group. Conclusions: The results of this study suggest that a long facial type is strongly associated with previous TMJ inflammatory disorders and degenerative disorders or a fracture of the condyle. There are certain skeletal and dentofacial adaptations that follow resulting in vertical dimension changes, more specifically, smaller condylar process, ramus and body of the mandible height, thinner alveolar housing at the lower incisor region and smaller cross-sectional area of the airway. The results from this study suggest that clinician should carefully monitor the TMJ status in adult individuals with hyperdivergent facial type