Harukazu Kanehira

Factors influencing Mandibular spatial Position Sense.

The purpose of this study was to investigate factors influencing mandibular position sense with four different jaw openings (5, 10, 15 and 20 mm from intercuspal position), Eight subjects memorized the reference positions with monitoring their spatial vertical jaw positions using a Mandibular Kinesiograph (M.K.G., K-5), Immidiately after memorizing one of those positions, they were required one of loaded conditions that were C1; clenching in I.C.P., C2; light teeth contact in I.C.P., C3; closing superior to memorized position (descending approach), C4: opening inferior to memorized position (ascending approach), C5; maximum widely open. Afterward, they were required the memorized position without monitoring again. Vertical distances from I.C.P. at lower incisal teeth were recorded by MKG and statistically analyzed.The results were as followed:1. Perceived mandibular positions in the descending approach (C1, C2, C3) were become significantly higher than in the ascending approach (C4, C5) on 10 to 20 mm reference positions (10 mm: P<0.05, 15 mm: P<0.01, 20 mm: P<0.01). On 5 mm reference position, however, it was no significant.2. On 5 mm reference position, variance of data was significantly lower than the others (P<0.01).3. In maximum open (C5) of five conditions, variance of data was significantly greater than the others (P<0.01).4. It was suggested that mandibular position sense was affected by mandibular spatical vertical position and that the muscle spindle plays an important role in neuronal mechanism of controlling mandibular position.

The Effect of Muscle Length of the Inferior Head of the Lateral Pterygoid Muscle on the Frequency of EMG Power Spectrum.

Six male subjects were studied to determine the effect on the EMG power spectra of shortening the inferior head of the lateral pterygoid muscle (ILPt) during isometric protrusive and lateral protrusive contraction at three different muscle lengths.Among all muscle lengths, no significant difference in mean frequency of EMG power spectra was seen on either side of the ILPt during isometric protrusive contraction, or on the contralateral side of the ILPt during isometric lateral protrusive contraction. This result is similar to that for the digastric muscle during isometric under opening at various jaw positions, but differs from those for the temporalis and masseter muscles at during isometric clenching at various jaw positions.It was speculated that this lack of significant mean frequency change at different muscle lengths is characteristic of the EMGs of jaw depressor muscles.

Electromyographic studies on continuous gum chewing and periodic clenching.

Eight healthy male subjects were asked to unilateral gum chewing continuously for 30min and other five subjects were asked to periodic clenching to the signals monitored on theoscilloscope for the same time. The signals were consisted of the three kinds of durations (500ms, 1s, 2s) and interval of 500ms. The force of clenching was as same as chewing. Surface EMG was picked up from a masseter muscle on the side of chewing.No significant changes were shown in EMG activity and mean frequency during gum chewingthrough the experiments. On periodic clenching, EMG activity strikingly decreaced in 5minand mean frequency was down significantly in 30min, of which tendency was clearer in long timedurations. These findings suggested that the fatigue was not appeared in gum chewing for 30min and it was appeared for a long time in periodic clenching as compared with gum chewing.

A Study on Image Analysis of distribution of Retentive Area on Abutment Teeth in Partial Denture

The purpose of this study was to propose the image analysis of the retentive area in removable partial denture by personal computer instead of surveyor.1. The image through CCD TV camera was processed on personal computer to recognized the shadow as the undercut area on the abutment teeth in removable partial denture. The binary processed image was reversed and added to the original one. The threshold level of digital processing was determined by density histogram of primary colors.2. The lines drawn by Laplacian emphasis corresponded to survey lines.3. The light was directed toward perpendicular to occlusal plane of the cast by the reflection of the mirror. The path of placement and removal was alternated by changing the inclination of the mirror. The distribution of undercut area on abutment teeth could be found repeatedly at different angles and the retentive areas in common to mesial and distal directions could be found by image calculating.