抄録
Bite force decreases as bite points change posteroanteriorly along the dentition; this raises questions about how the efficiency of the jaw elevator muscles is affected. The objective of this study was to determine the relation between bite force and the EMG/Force characteristics of the jaw elevator muscles as the bite point is changed posteroanteriorly during maximal (MVBF) and submaximal (30%MVBF) isometric clenching efforts. Seven fully dentate subjects without any history of craniomandibular dysfunction, mean age 30.8±2.4 volunteered for this study. Bilateral surface bipolar EMG activity from the superficial masseter (SM) and anterior temporal (AT) muscles was recorded simultaneously to alternate antagonistic vertical bite force measurements from the right and left first molar, first premolar, canine and anterior incisor teeth. The subjects clenched three times for 2 seconds each time to a requested level (MVC; 30%MVBF) on a force transducer. EMG/Force ratio (E/F) values for working (W) and balancing (B) muscles were calculated and normalized for each task. Statistical differences among unilateral bite points were analyzed with Two-way ANOVA. The magnitude of bite forces were similar to those proposed by other authors. Changing posteroanteriorly the bite point induced a gradual and significant (MVBF: p<0.01; 30%MVBF: p<0.001) increase of the corresponding working and balancing SM E/F values, with the latter being either the same or higher than the working ones. The E/F registered at the MVBF and 30%MVBF molar and anterior bite points were different in a proportion of 1: 2 in all subjects. At MVBF the AT's E/Fs also increased corresponding to the anteroposterior shift of the bite point (p<0.01) ; however, the 1: 2 proportion of the molar vs the anterior bite point was not observed; at 30%MVBF there was not any evident pattern, and the E/F were not significantly different among bite points. From these results it can be concluded that the EMG/Force ratio of the working and balancing superficial masseter and anterior temporal muscles is a posteroanterior increasing function and therefore has an inverse relationship with bite force, condition which may induce a negative effect in the electrical efficiency of the jaw elevator muscles.
The results of this study have been previously presented at the following meetings:
74th General Session of the International Association for Dental Research.
20th Annual Conference of the European Prosthodontic Society.
96th Meeting of the Japan Prosthodontic Society.
44th Annual Meeting of the Japanese Association for Dental Research.
75th General Session of the International Association for Dental Research.
Annual Meeting of the Niigata Dental Association, July 1997.
