The relationship between ultrasonographically measured muscle thickness and craniofacial morphology

SUMMARY The Relationship between Ultrasonographically Measured Muscle Thickness and Craniofacial Morphology It is widely accepted that an interaction exists between the size of facial muscles and craniofacial morphology. In related literature, mostly the size and function of masseter muscle was shown to be related to facial morphology. Besides masseter muscle, the thicknesses of temporal, digastric, medial pterygoid and lateral pterygoid muscles were reported to be in relation with craniofacial morphology. The aim of this study was to determine the thicknesses of masseter, levator labii superioris and zygomaticus major muscles of individuals with different vertical growth patterns and to compare the thicknesses of these muscles among groups. Our study included 47 voluntarily-participated healthy dental students between the ages of 20-33 years. After determination of the vertical facial morphology of each subject by the evaluation of 11 angular, 6 linear measurements on lateral cephalometric radiographs, all individuals were divided into normal, high angle and low angle groups. The thicknesses of masseter, levator labii superioris and zygomaticus major muscles were measured on each side of the face by ultrasonographic imaging technique. For the three measured muscles, our results did not show any significant difference between the thicknesses measured on the left and right sides of the face. The thickness of masseter muscle in low angle group both under relaxed and contracted conditions was higher than the high angle and normal groups. Among the compared groups, there were no significant differences between the thicknesses of levator labii superioris and zygomaticus major muscles. We have found that the thickness of masseter muscle measured both under relaxed and contracted conditions was higher in men compared to IVwomen and there was a positive correlation between body mass index and masseter muscle thickness measured under both conditions. Although it was not statistically significant, our findings revealed that the thickness of zygomaticus major muscle was related to body mass index. Summarizing, the findings of this study showed that the size of masseter muscle was significantly related to craniofacial morphology. Meanwhile, there was no relation between the vertical growth of the face and the thicknesses of the investigated mimical muscles. Our study revealed that ultrasonography can be used for the investigation of superfacial muscles and it has reproducible results. Our study did not include other muscles of mastication that might also contribute to the interaction between muscle and facial morphology due to the limitations of the ultrasonographic imaging technique. New researches done by different imaging techniques might be necessary. Key Words: Ultrasonography, masseter muscle, levator labii superioris muscle, zygomaticus major muscle. V