Teruta Maeda

Influences of molar loss of rat on learning and memory

PURPOSE The maxillary unilateral or bilateral molars of rats were extracted, and the influences of the partial loss of occlusal support were evaluated using an 8-arm radial maze and a step-through type passive-avoidance apparatus. METHODS Rats were randomly allocated to three groups not undergoing molar extraction or undergoing extraction of the maxillary unilateral or bilateral molars. Each group was further divided into two groups for maze or passive-avoidance experiments. Thus, a total of six groups were established. The maze experiment was conducted once daily for 10 days. The number of correct choices, number of errors, and the trial time were recorded. The passive-avoidance experiment consisted of an acquisition trial and retention trial. In the acquisition trial, rats were placed in a light room, and the response latency until their entry into a dark room was measured. After 24h, a similar procedure was performed as a retention trial. RESULTS In the maze experiment, there was no significant difference by all the groups except on the day 1 in the number of correct choices. But bilateral molar loss group, the number of errors were significantly lower than no extraction group on days 1, 2, 3, 4, and 7. In the passive-avoidance experiment, though the response latency in the retention trial was longer than that in the acquisition trial in all three groups, according to the increase in the number of tooth extraction, it became significantly shorter between P1 and P3. CONCLUSION These results suggested that molar loss may be a cause of learning/memory impairment.

Mechanomyographic activity in the human lateral pterygoid muscle during mandibular movement

The activity of the lateral pterygoid muscle has been regarded to be related to the pathological condition of the temporomandibular joint (TMJ) in the craniomandibular disorders. Because the lateral pterygoid muscle is a deep muscle, a needle electrode is necessary for EMG recordings. The purpose of this study was to establish a non-invasive method for the evaluation of muscle activity of the lateral pterygoid muscle using mechanomyogram (MMG). In three male subjects, surface electromyogram (EMG) in the left masseter muscle, left anterior and posterior belly of the temporal muscle, left anterior belly of the digastric muscle and needle EMG of the inferior head of the lateral pterygoid were recorded during mandibular movement tasks simultaneously with the MMG derived from a condenser microphone in the external ear canal. There were significant positive correlations between the needle EMG signal of the lateral pterygoid muscle and the MMG signal for the tasks of static jaw opened position of 30 mm of interincisal distance (p=0.000, R(2)=0.725), static jaw opened position of 40 mm of interincisal distance (p=0.000, R(2)=0.753), 5mm protruded mandibular position (p=0.000, R(2)=0.653), the most protruded mandibular position (p=0.000, R(2)=0803). On the contrary, for the task of maximal clenching, there was no significant correlation between the EMG signal of the lateral pterygoid muscle and the MMG signal. These results suggest that the activity of the lateral pterygoid muscle could be evaluated by the MMG signals recorded in the external ear canal, unless jaw closing major muscles show active contraction.

Fluctuation of the Mandible during Intercuspation.

目的: 咬頭嵌合時に下顎は動いていることはこれまでの報告で明らかとなっている. しかしながらその詳細についてはいまだ不明である. 本研究は咬頭嵌合時の下顎の動揺を明らかにすることを目的として, 詳細に検討を行った.方法: 本研究において, 光スポット位置検出センサと赤外線発光ダイオードを利用して計測を行った. このセンサを用いて, 被験者は個性正常咬合を有する成人有歯顎者11名を対象に, 咬合器に装着した各被験者の上下顎模型の咬頭嵌合位 (on the model) と各被験者の生体における咬頭嵌合位 (in vivo) をそれぞれ観察した. 得られたデータよりそれぞれの水平面の二次元の変動を解析し, 分散分析法にて統計学的に検討を行った.結果: 分散分析の結果, 下顎の動揺範囲において, on the modelでは前後, 左右的に平均6μmであったのに対し, in vivoでは前後, 左右的には平均39.9μmの値をとり, 測定条件間にのみ有意な差を認めた. また下顎の動揺のばらつきを示す分散においても, 前後方向, 左右方向ともにon the modelに対してin vivoは大きな値を示し, 測定条件間にのみ有意な差を認めた.結論: 正常者において, 咬頭嵌合時に下顎は前後的, 左右的に約40μm範囲で常に動揺していることが明らかとなった. またこの動揺は, 咬頭嵌合位を一定に保持しようとするための生理的な動きであると推察された.

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.

The Study of Manual Forces of Prosthetic Practice. Influences of Postures on Maximum Exertable Forces and Consecutive Forces.

Eight operators (four males and four females) were tested for maximum exertable manual forces (MFs) and six male operators for the variations of consecutive manual forces (CFs) of 2 kgf during 3 minutes without monitoring them. Both forces were exerted on the simulation model with bilateral hands in six different postures of prosthetic practices.The results were as follows:1. Significant differences on MFs were found between sexes (p<0.05), between sides (p<0.005) and between postures (p<0.001).2. Significant factors on CFs were side (p<0.005), posture (p<0.001), time (p<0.001) and the side×time interaction (p<0.025).3. These findings indicated that the optimum posture for force application on maxilla was seating behind the model with index and middle fingers, and the one on mandible was standing in front of the model and on the right side with thumb fingers.

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.