Sex differences in mandibular movements during opening and closing

This study evaluated the sex differences in maximum 3-dimensional opening and closing movements. The sample included 29 men (ages, 23-39 years) and 27 women (ages, 23-35 years), who were selected for normal Class I occlusion, temporomandibular function, and skeletal patterns. Condylar (hinge axis) translation and mandibular incisor movements, were recorded with an optoelectric jaw-tracking system; each participant performed 4 maximum opening/closing cycles. The results showed significant (P <.05) sex differences for incisor opening and closing movements, with most of the differences in the vertical component. Male incisor straight-line distances and curvilinear pathways averaged 52.1 mm and 54.8 mm, respectively. Female straight-line distances and curvilinear pathways averaged 46.0 mm and 48.1 mm, respectively. There were significant (P <.05) sex differences for condylar translation, with most of the differences in the anteroposterior component. Male condyles translated 15.4 to 17.6 mm (straight-line distances) and 20.5 to 20.7 mm (curvilinear pathways); female condyles translated 12.4 to 12.7 mm (straight-line distances) and 16.2 to 17.9 mm (curvilinear pathways). Mandibular length accounted for some of the sex difference in interincisal opening and for most of the sex differences in condylar translation. Closing movements showed the same pattern of sex differences as opening movements. Mandibular opening rotation was approximately 4 degrees larger in men than in women. The shapes of the condylar opening and closing pathways also differed significantly between men and women. For both sexes, condylar translation did not correlate with incisor opening or closing movements. It was concluded that (1) significant sex differences exist in incisor opening movements that are independent of mandibular size, (2) sex differences in condylar translation are dependent on mandibular size, (3) incisor opening movements should not be used as an indicator of condylar translation, and (4) sex differences in the shapes of the condylar pathways indicate sex differences in articular eminence morphologic features.