Microscopic and Geometric Changes in the Mandibular Condylar Head in Response to Subtle Secondary Overload: In Search of a Mechanical Origin of Condylar Hyperplasia.

In condylar hyperplasia (CH), one of the condylar processes of the mandible (CPs) grows more than its counterpart, leading to facial asymmetry. Using a mouse model of asymmetric masticatory loading, we investigated a possible mechanical origin of CH by evaluating the association between morphometric parameters of CP cartilage and bone and the mandibular load regime. Thirty-nine adult male and female mouse hemimandibles that underwent different loading regimes were used: underloaded (UL), overloaded (OL), and symmetrically loaded (SL) controls. Micro-CTs were used to assess macroscopic shape and trabecular bone (TB) parameters, and articular cartilage features were studied histologically. Data were compared using multivariate and pairwise statistics. Principal component analysis showed that OL CPs exhibit a wide range of shape variation and show thicker cartilage but display TB features indicative of ongoing remodeling. Female OL tended to show more variable and larger parameters than males. However, differences in traits between sexes and load groups were not always statistically significant. We conclude that an asymmetric increase in mandibular loading may be associated with changes in the macro-/microscopic structure of the CP, affecting males and females differently. Signs of cartilage growth and bone remodeling are found in OL individuals, which are compatible with CH features.