TMJ Disc Energy Densities in Healthy Females and Males

Objectives: Cartilage fatigue, due to input of work (mechanical energy density, MED), may account for early degenerative joint disease (DJD) in the TMJ and why females are 3-times more likely to be afflicted than males. This study tested if there were sex differences in MEDs of healthy TMJs.
Methods: Eighteen adult females and eighteen adult males gave informed consent. Diagnostic Criteria for Temporomandibular Disorders and imaging (magnetic resounance, cone-beam computed tomography) were used to to ensure that subjects’ TMJs were normal, without disc displacement or signs of DJD. Numerical modeling determined TMJ-specific loads (F_normal) during jaw-loading functions. TMJ-specific data of dynamic stress-field mechanics during 10 symmetrical jaw closing cycles were characterized by jaw tracking and 3D dynamic stereometry. These data were used to estimate tractional forces (F_traction=μ_traction/ F_normal where μ_traction was determined from experiments as previously described (Nickel et al. 2009)), and to calculate MED=W/Q (mJ/mm³), where: W=input of mechanical work=F_traction●distance of stress-field translation and Q=cartilage volume, for each TMJ. ANOVA and Tukey Honest Significant Difference post-hoc analyses tested for sex differences in mean MEDs for ipsilateral and contralateral TMJs.
Results: Mean ± standard deviation of MED in females (contralateral and ipsilateral TMJs: 8.4 ± 5.5 and 9.0 ± 9.7 mJ/mm³, respectively) were significantly higher (P≤0.004) compared to males (contralateral and ipsilateral TMJs: 6.3 ± 4.2 and 5.6 ± 4.2 mJ/mm³, respectively).
Conclusions: Higher mechanical energy densities for the same jaw function in females compared to males may be a predisposing mechanism for sex differences in the mechanical fatigue of TMJ cartilage.