Determination of Sex-dependent Temporomandibular Joint Anatomy Using Statistical Shape Modeling

Objectives: The objective of this study was to elucidate sex differences in the anatomy of human temporomandibular joint mandibular condyles using statistical shape modeling (SSM).
Methods: Mandibles were obtained from 16 human cadavers (9 males, 7 females, 79±13 years). The condyles were dissected at the point of the sigmoid notch concavity and scanned using micro-computed tomography with 27 micron resolution. An image processing algorithm was used to segment the bone and determine the border of the entire mandibular condyle and trabecular bone compartments. Triangulated meshes of the compartments were created. One subject was chosen as the template and was registered to the other individuals using a coherence point drift algorithm. This process positioned all vertices at corresponding anatomic locations. For the trabecular bone region, around each vertex position, the average bone image intensity, which is proportional to bone density, and microstructural traits, including trabecular bone volume fraction, thickness, number, separation, and connectivity density were calculated. For the entire mandibular condyle mesh, the surface vertices were extracted to represent the overall anatomy of the condyle. Using SSM, the shape and trait information was reduced to a small set of independent and uncorrelated variables for each individual. Wilcoxon rank sum tests were used to test for differences in the variables between sexes.
Results: Male condyles were on average larger than female condyles, and the microstructural traits were not qualitatively different between sexes. Two out of 15 shape variables were statistically different between males and females (p<0.1). These shape modes described overall enlargement of the condyle with larger differences seen in the right and left ends of the condyle.
Conclusions: SSM was able to determine sex-dependent differences in the shape of the mandibular condyle. These differences may alter the biomechanics of the joint and contribute to the development of temporomandibular joint disease.