Influence of Chewing Side on Trajectory of Mandibular Movement

Purpose: Humans show laterality with a main chewing side showing a high frequency of use in the stomatognathic system. However, there have been few suggestions for prosthetic treatment in consideration of the chewing side. The present study therefore compared mandibular movement between chewing on the main chewing side and on the non-main chewing side, and also by age group and food texture. The objective was to obtain suggestions for prosthetic treatment. Methods: The subjects comprised 30 people with dentulous jaws. Evaluation of the main chewing side was performed on the side showing the higher frequency of 20 strokes after initiation of chewing. For measurement of mandibular movement during chewing, a jaw movement-measuring device with six degrees of freedom was used. Study items were chewing on the main chewing side and chewing on the non-main chewing side using beef jerky and gummy jellies, a type of candy. The jaw-closing angle of the lower incisors, length of condylar trajectory during activity of the jaw-closing muscles and maximum velocity of condylar movement were compared. Comparisons were also made by age group and by test foods. Results: With chewing on the main chewing side, the jaw-closing angle of the lower incisors was greater, length of condylar trajectory on the balancing side tended to be longer and maximum velocity of condylar movement tended to be greater than on the non-main chewing side. These tendencies were more marked in middle-aged subjects. No differences were found among test foods. Conclusion: Chewing on the main chewing side showed a marked tendency to be the grinding type, and the difference by age was assumed to be more marked because of occlusal wear centered on the main chewing side. Clinically, bilaterally symmetric prostheses are not necessarily optimal and it is suggested that prosthodontic treatment should consider functional morphology.