Recording orthopedic jaw movements. Part IV: The rotational component during mastication

The recording and analysis of mastication provides information on neuromuscular engrams, and hence avoidance mechanisms. Avoidance mechanisms are pathologic movement patterns which are developed to avoid occlusal interferences during functional movements. Evaluation of hinge-axis rotation permits selective quantitative analysis of a complex movement pattern. The objective of this study was to determine the amount of hinge axis rotation in mastication using computerized axiography. Furthermore, the distance of the condyles from reference position (RP) at maximum rotation was evaluated and the chronological sequence of translation and rotation was investigated. The mean value for the rotational angle of the mandible (gamma) during mastication was 14.1 degrees in the volunteers and 13.44 degrees in the patients. The linear spatial distance from RP amounted to a mean of 6.57 mm on the right side and 6.21 mm on the left in the volunteers. In the patients, the measurements were 6.33 mm on the right side and 6.7 mm on the left. In most cases, maximum rotation did not correspond with maximum translation. The chronological sequence of maximum excursion was not constant.