[Difference of body movements accompanying mandibular movements in standing and sitting positions]

To assess whether body movement accompanying jaw movement exists even in sitting position, and, if so, to investigate differences of body movements in the sitting and standing positions.

The subjects were six men (age, 25-29 years, mean, 27.0 years) without stomatognathic problems. During the measurements, their Camper's planes were kept horizontal. One measurement sequence consisted of 20 s of tapping preceded and followed by 10 s of intercuspation. Mandibular movements (lower incisor point) were measured by referring to a coordinate system located on the maxilla, and head movements (upper incisor, condyle, etc) with TRIMETII (Tokyo Sizaisya) and body movements (sternum point) in sagittal plane were measured by referring to a coordinate system located on the floor with Proreflex (Qualisys).

Body movements accompanying jaw movements were detected even in sitting position. The ratio of body movements to jaw movements was significantly larger in standing position than in sitting position using Wilcoxon matched-pairs signed-rank test. Peak power of body movement at corresponding frequency to the open-close movement was significantly larger in standing position than in sitting position using Wilcoxon matched-pairs signed-rank test. On the other hand, there was no difference between sitting and standing position in probability of body movement detection by the original wave analysis using Wilcoxon matched-pairs signedrank test.

Body movements accompanying jaw movements were detected even in sitting position, and were smaller than in standing position. However, the probability of movements detected in original wave had no difference between the positions. Thus we concluded that we can analyze body movements during mastication in natural sitting position.