Movement of the Condyle Point and Incisal Point during Exercise

Purpose: During exercise, the lower jaw is unlikely to be in a relaxed position, such as the mandibular rest position, and may be fixed in a position suitable for exercise.

In this study, we examined movement of the condylar point and incisal point during exercise.

Methods: Six healthy dentulous subjects performed extension/flexion movement of the body trunk using a multipurpose muscle function training system. After a start signal, subjects stood upright within the predetermined range of motion (extension), and then returned to the initial bent position (flexion). The condylar and incisal point movement patterns were measured using a jaw movement analyzer and 3D ultrasonic navigator. The movement was performed 3 times, and the mean displacement caused by each movement in 4 directions, i.e., anterior, posterior, superior, and inferior, was calculated. The maximal mean displacement in each direction was defined as the maximal displacement in the movement direction. The relative percentage of the condylar and the incisal displacement to its maximum value was calculated. Differences in displacement were compared between anterior and posterior, superior and inferior by the Mann-Whitney U-test.

Results: The mean relative percentages of the right condylar point displacements in the 6 subjects were 8.1%, 30.1%, 73.2%, and 10.7% in the anterior, posterior, superior, and inferior directions, respectively, those of the left condylar point were 5.8%, 31.3%, 61.8%, and 13.0%, respectively, and that of the incisal point was 7.1%.

On statistical analysis, the relative condylar displacements during extension/flexion movement of the body trunk were significantly greater in the posterior and superior directions than in the anterior and inferior directions (p<0.01, p<0.05). The incisal point showed slight mouth openeing during extension/flexion movement of the body trunk.

Conclusion: These findings suggest that the mandibular position sways in each direction and the possibility of an-settled jaw position during strong trunk muscle exertion.