Diagnostic group differences in temporomandibular joint energy densities

Objectives: Cartilage fatigue, due to mechanical work, may account for precocious development of degenerative joint disease in the temporomandibular joint (TMJ). This study compared energy densities (mJ/mm³) in TMJs of three diagnostic groups. Setting and Sample Population: Sixty-eight subjects (44 women, 24 men) gave informed consent. Diagnostic criteria for temporomandibular disorders (DC/TMD) and imaging were used to group subjects according to presence of jaw muscle or joint pain (+P) and bilateral disk displacement (+DD). Material and Methods: Subjects (+P+DD, n = 16; -P+DD, n = 16; and -P-DD, n = 36) provided cone-beam computed tomography and magnetic resonance images, and jaw-tracking data. Numerical modeling was used to determine TMJ loads (F_normal). Dynamic stereometry was used to characterize individual-specific data of stress-field dynamics during 10 symmetrical jaw-closing cycles. These data were used to estimate tractional forces (F_traction). Energy densities were then calculated as W/Q (W = work done or mechanical energy input=tractional force × distance of stress-field translation, Q = volume of cartilage). anova and Tukey-Kramer post hoc analyses tested for intergroup differences. Results: Mean ± standard error energy density for the +P+DD group was 12.7 ± 1.5 mJ/mm³ and significantly greater (all adjusted p < 0.04) when compared to -P+DD (7.4 ± 1.4 mJ/mm³) and -P-DD (5.8 ± 0.9 mJ/mm³) groups. Energy densities in -P+DD and -P-DD groups were not significantly different. Conclusion: Diagnostic group differences in energy densities suggest that mechanical work may be a unique mechanism, which contributes to cartilage fatigue in subjects with pain and disk displacement.