It is widely accepted that the shape and structure of bone are closely related to the activity of attached muscle. Numerous clinical and animal experimental studies indicated the significant effects of masticatory muscle function on maxillofacial morphology.
Recently, the development of ultrasonography has spread throughout different fields of medicine. In the clinical examinations, ultrasonography is a convenient, inexpensive technique to apply with accurate and reliable results.
The aim of this study is to assess the thickness of the masseter muscle and its correlation to maxillofacial skeleton by examining 35 male and 15 female dental students at Kangnung National University. The masseter muscle thickness of the subjects were measured by ultrasonographic scanning with a 7.5M-1z linear probe, and their maxillofacial morphology were investigated by lateral cephalometric radiographs.
The relationship between the masseter muscle thickness and maxillofacial morphology of normal adult was statistically analyzed, and the following results were obtained.
1. The average thickness of male masseter muscle was 13.8±1.71mm in the relaxed state and 14.8±1.77mm at maximal clenching state, while that of female was 11.6±1.58mm and 12.4±1.47mm, respectively. Ethnic difference in thickness of the masseter muscle and maxillofacial skeleton was found when the results of many researchers were compared with those of this study. . .
2. The thickness of the masseter muscle in both sexes increased significantly at maximal clenching state than in relaxed state(P<0.05).
3. The masseter muscle thickness of male was greater than that of female both in the relaxed state and maximal clenching states(P<0.05).
4. In males, the thickness of the masseter muscle was negatively correlated with the mandibular plane angle and positively correlated with the mandibular ramus height and anterior cranial base length(P<0.05). It may suggest that the male with thicker masseter muscle has smaller facial divergence.
5. No significant correlation was found between the masseter muscle thickness and maxillofacial morphology in females(P<0.05).
Therefore, these data suggest that ultrasonography can add valuable information to the conventional examinations of masseter muscle function.
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