A theoretical analysis of longitudinal temporomandibular joint compressive stresses and mandibular growth

Objectives: To determine if temporomandibular joint (TMJ) compressive stresses during incisor biting (1) differed between growing children over time, and (2) were correlated with Frankfort Horizontal-mandibular plane angle (FHMPA, degrees) and ramus length (Condylion-Gonion (Co-Go), mm). Materials and Methods: Three-dimensional anatomical geometries, FHMPA and Co-Go, were measured longitudinally from lateral and posteroanterior cephalographs' of children aged 6 (T1), 12 (T2), and 18 (T3) years. Geometries were used in numerical models to estimate subject-specific TMJ eminence shape and forces for incisor bite-forces of 3, 5, and 8 Newtons at T1, T2, and T3, respectively. TMJ compressive stresses were estimated via two steps: First, TMJ force divided by age-dependent mandibular condylar dimensions, and second, modified by loading surfaces' congruency. Analysis of variance and Tukey honest significant difference post-hoc tests, plus repeated measures and mixed effects model analyses were used to evaluate differences in variables between facial groups. Regression analyses tested for correlation between age-dependent compressive stresses, FHMPA, and Co-Go. Results: Sixty-five of 842 potential subjects had T1-T3 cephalographs and were grouped by FHMPA at T3. Dolichofacial (FHMPA >= 27 degrees, n = 36) compared to meso-brachyfacial (FHMPA< 27 degrees, n = 29) subjects had significantly larger FHMPA at T1-T3, shorter Co-Go at T2 and T3 (all P < .01), and larger increases in TMJ compressive stresses with age (P < .0001). Higher compressive stresses were correlated with larger FHMPA (all R-2 >= 0.41) and shorter Co-Go (all R-2 >= 0.49). Conclusions: Estimated TMJ compressive stress increases from ages 6 to 18 years were significantly larger in dolichofacial compared to meso-brachyfacial subjects and correlated to FHMPA and Co-Go.