[A study on the relationships between imbalance of stomatognathic function and asymmetry of craniofacial morphology, and the center of gravity of the upright posture].

Mastication is one of the most important functions of the stomatognathic system and it can be performed either on the left side or right side. However, some people have each habitual chewing side, so imbalance of stomatognathic function between left and right is observed. This imbalance is supposed to reflect the relationship between the left and right elements of the stomatognathic system. Therefore, the analysis of this imbalance is very useful for assessing the stomatognathic system. The purpose of this study was to reveal the relationship between imbalance of stomatognathic function between left and right and asymmetry of craniofacial morphology, and the relationship between imbalance of stomatognathic function between left and right and center of gravity of upright posture. Eighty subjects without stomatognathic dysfunction were selected for this study. Electromyograms of the left and right masseter, anterior temporal, posterior temporal and anterior belly of digastric muscles during clenching were recorded, and mandibular movements during chewing were recorded. Analysis of imbalance between left and right was performed using functional parameters. Cephalograms (P-A) were taken for an analysis of craniofacial symmetry. The center of gravity of the upright posture was recorded using stabilograph. Analyses were performed to study the relationships between the parameters of stomatognathic function and craniofacial asymmetry, and the center of gravity of the upright posture. The results were as follows: 1. The analysis of functional parameters revealed some subjects showed imbalance between left and right sides. 2. On the side with wider craniofacial morphology as determined by some parameters, the activity of the masseter muscle during clenching showed tendency to be higher than that of the opposite, while the activity of the anterior temporal muscle showed tendency to be lower. On the side with longer craniofacial morphology, the activity of the anterior temporal muscle showed tendency to be higher than that of the opposite. 3. On the side where the center of gravity was shifted during clenching, the activities of the masseter, anterior temporal and posterior temporal muscles showed tendency to be higher than those of the opposite, and the durations of chewing cycle and opening phase showed tendency to be shorter. These results suggest that there are close relationships between imbalance of stomatognathic function and craniofacial asymmetry, and between imbalance of stomatognathic function and the center of gravity of the upright posture.