Relationship and spatial differences between mandibular movement and complementary mandibular movement

We elucidated the relationships and differences between mandibular movement (MM) and complementary mandibular movement (cMM), defined as the relative motion of the maxilla with respect to the mandible, by analyzing their spatial characteristics, symmetry, and associated rotational axes.

Twenty-seven healthy participants (mean age, 53.0 years) were examined. Jaw movements, including sagittal border (SAG), lateral excursion-incursion (LAT), and protrusion-retrusion (PRO), were recorded using a six-degree-of-freedom electromagnetic jaw-tracking device. The cMM data were obtained as the inverse matrices of the MM data. The kinematic (KA) and complementary kinematic axes (cKA) were calculated using Shigemoto's method. The symmetry between the MM and cMM was evaluated at the incisal point, kinematic axis point (KAP), and complementary kinematic axis point (cKAP). Furthermore, the spatial relationship between KA and cKA was analyzed.

The MM and cMM displayed partial symmetry near the intercuspal position (ICP); however, none of the movements exhibited complete correspondence. The PRO, which consists of translational motion, demonstrated significantly greater symmetry than the SAG and LAT. The cKA was located 14.14 mm antero-superior to the KA. The maximum displacement at the cKAP (22.68 mm) was significantly larger than that at the KAP (17.85 mm), whereas no significant difference was observed in path thickness (KA: 0.47 mm; cKA: 0.50 mm).

The MM and cMM were not strictly point-symmetric, and their rotational axes (KA and cKA) did not coincide. The accurate recognition of both MM and cMM is essential when applying jaw movement data to CAD-CAM workflows for prosthetic designs.