The Instantaneous Center of Rotation of the Mandible in Nonhuman Primates

Kinematic analyses of mandibular movement in humans demonstrate that the mandibular instantaneous center of rotation (ICoR) is commonly located near the level of the occlusal plane and varies in its position during a chewing sequence. Few data are available regarding the location of the ICoR in nonhuman primates and it remains unclear how the position of the ICoR varies in association with mastication and/or gape behaviors. ICoR was quantified throughout the gape cycle in five species of nonhuman primates (Macaca mulatta, Cebus apella, Chlorocebus aethiops, Eulemur fulvus, and Varecia variegata). The ICoR is commonly located below the mandibular condyle close to the occlusal plane and varies considerably both superoinferiorly and anteroposteriorly through the gape cycle. The path of the ICoR, and by inference condylar movement, in Macaca and Chlorocebus differs from humans whereas movement in Cebus resembles that of humans. Similarities between humans and Cebus in articular eminence and occlusal morphology may explain these resemblances. Food material properties had little influence on ICoR movement parameters.