[Experimental study of the influence of removal of the zygomatic arch on craniofacial growth and development].

To observe effects of the procedure on craniofacial growth and development, the author removed 10mm of the right zygomatic arch from rats. The subjects (128 rats) were divided into 3 groups: operation group, sham-operation group, and control group. Surgical removal of the right side of the zygomatic arch was performed on 51 rats; sham operations were performed on 42 rats, and 35 rats served as controls. Operations were performed 30 days after the animals' births. The rats were sacrificed 60 to 120 days after birth. Lateral and parietal cephalograms of the crania were projected by means of a profile projector, model V-16, and enlarged 5 times. Because they reveal craniofacial-facial morphology most clearly, 15 lateral and 7 parietal points were selected. Coordinates of these points were plotted by means of an X--Y plotter system Tracings were composed as follows: For lateral cephalograms, the intersphenoid synchondrosis(S)was the zero point, and the line between S and the basion (Ba) was the abscissa. For parietal cephalograms, the occipital bone was the zero point; and the line between (0) and the upper central (Ui) was the abscissa. The masseter muscles were microsectioned for observation of changes in muscle fibers. Results 1. There were no significant differences among the body weights of the 3 groups (control, operation, and sham operation). 2. There were no significant differences in ulnar length among the 3 groups 3. Facial asymmetry and changes in occlusion were noted in the group observed 120 days after surgery. 4. Lateral cephalographic examination showed that the zygomatic arch has almost no influence on craniofacial growth and development in terms of relations among the points examined. 5. Parietal cephalographic examination showed that removal of the zygomatic arch promoted depth development and suppressed width development in the zygomatic-arch region of the side on which surgery was performed. This may indicate that the zygomatic arch acts to suppress anterior and posterior craniofacial growth and development while promoting growth and development in the lateral dimension. 6. Horizontal cytology of the masseter muscle showed atrophied masseteric tissue at the resected site of the zygomatic arch. But, because this was a partial resection, influence of muscular function is slight. And data obtained from this experiment must be considered the outcome of the removal of the zygomatic arch itself.