CORRELATION OF MONSON’S SPHERE AND SOME OTHER DENTOFACIAL VARIABLES TO TEMPOROMANDIBULAR JOINTS (TMJs) IN THE CHINESE POPULATION

Abstract

Purpose: The purpose of this study was to investigate the correlation of Monson’s Sphere along with several dentofacial variables to the morphologic changes of condyles (condylar height in this case), as well as the possible mechanism that may govern this correlation. These variables are: the discrepancy of the mandibular and maxillary spheres, ANB (anterior-posterior relationship of the maxilla with the mandible), Bonwill’s Angle, Overbite, Overjet, the angle of mediolateral axes of two condyles and the distance between the two condyles.

Materials and methods: CT (Computed Tomography) DICOM (Digital Imaging and Communications in Medicine) data of 54 Chinese patients were collected, including 43 females and 11 males aged from 11 to 49 years old. The coordinates of the dental, craniofacial and temporomandibular landmarks were measured through a DICOM viewer. A linear regression model was used to fit the sphere to the coordinates of the dental and temporomandibular landmarks. As well, condylar height and other variables were calculated from the coordinates of the landmarks. Pearson Correlation was performed to illustrate the bivariate correlation of the variables in couples. The difference among the groups categorized by the fixed factors including gender, age, ANB and so on, was tested by ANOVA, and the influence of multiple independent variables on dependent variables was examined.

Results: From the data analysis, the mean radius of Monson’s Sphere in the maxilla is 92.42 mm and the mean radius in the mandible is 85.69 mm. Condylar height is correlated to the angle of the mediolateral axes of two condyles positively, and to Overjet, ANB and Bonwill’s angle in a negative way. The discrepancy of the two Monson’s spheres seems to have a linear correlation with both Overjet and Overbite, and the group with the lower values of condylar height are more likely to obtain a portfolio of the greater values of Overjet, Overbite and the discrepancy of the two spheres.

Conclusion: The average radius of the mandible Monson’s Sphere is less than 100mm and the radii of only 3 out of 54 subjects are around 100 mm; however, the average distance between two submits of condyles is 100.87 mm. The group of Angle Classification Class II Division I seem to be the high-risk population with the feature of lower condylar height. This finding may pave the way for further research on the relationship between occlusion and temporomandibular joints. Note that since all the results and conclusions herein come from a specific set of populations (Chinese in particular), generalization to other populations may need to be applied with careful and informed consideration.