Morito Akasaka

Cortical potentials associated with voluntary biting movement in humans

We compared the distribution of Bereitschaftspotentials (BPs) on both sides of the scalp preceding jaw biting movements in order to identify the relationship between the cortical regions and the activation of the masseter muscle in 10 healthy subjects. The BPs were recorded from the midline-central, central and temporal areas of the scalp according to the international 10-20 system, preceding self-paced biting on one side. The cortical negative potentials began 1.0 approximately 1.5 s before the EMG onset of the masseter muscle. All of these negative potentials could be considered to be BPs, and the additional negative slope component (NS) occurred 70 approximately 80 ms before the EMG onset of the masseter muscle. The BPs were detected from all the recorded regions of the scalp, while the NS was observed only from the bilateral temporal area. The amplitudes of BPs and NSs were largest in the temporal areas (T3 and T4) that were ipsilateral to the biting. The rates of occurrence of NS at T3 and T4 ipsilateral temporal areas were 80% and 60%, respectively. These results suggest that unilateral biting movements may be controlled mainly from the ipsilateral hemisphere.

Contingent Negative Variations Associated with Jaw Opening in Humans

We examined the relationship between contingent negative variation (CNV) amplitude and digastric muscle activity in jaw-opening motor task. Subjects were instructed to open their jaws in response to a sound stimulus following a visual warning stimulus. Electroencephalograms were averaged by using the visual stimulus pulse as a trigger. Bilateral CNVs were clearly recorded at several cortical locations, with a tendency for larger amplitudes at temporal placements.

Characteristics of lower-jaw-position sensation with respect to oral-jaw functions in patients with cerebral palsy

Abstract In order to investigate the effects of desensitization which is induced by the application of a vibration stimulus simulating massage to patients with cerebral palsy (CP) on the lower-jaw-position sensation, we compared the masticatory-muscle sensation of patients with CP with that of healthy adults without functional abnormalities of the jaw and oral cavity who were used as control subjects, using a lower-jaw-position sensation discrimination test. The subjects of the study were eight patients with CP and eight healthy adults as control subjects. The following findings were obtained. 1)When the discrimination ability in healthy adults was compared between before and after the stimulus application, it was significantly higher after the stimulus application when the interincisal distance was smaller (9.5mm) than that with the reference stick. 2)When the discrimination ability of patients with CP was compared between before and after the stimulus application, it was significantly lower after the stimulus application when the interincisal distance was smaller (9.5mm) than that with the reference stick. Thus, results for the patients with CP are contrary to those for healthy adults; this is because of the appearance of the tonic vibration reflex in CP patients, which results in a decrease in the activity of γ-motor neurons. The threshold value of muscle sensation was increased by the application of vibration stimulus. Consequently, the discrimination ability of the patients with CP increased.

Development of six degree of freedom tracking device of mandibular movement in which magnetism is used. About the error of measurement value in clinical use.

顎口腔系の形態や機能の研究に3次元測定装置が開発・応用され, これを用いた多くの報告がある.特に下顎運動の解析には3次元的な軌跡の記録が不可欠であり, このような測定を目的とした下顎運動記録装置が用いられてきた.しかし, 小児を被験者とした際, 満足のいく装置は少ない.著者らは小児にも応用可能である磁気を利用した下顎運動6自由度測定装置の開発を行っているが, 本装置の臨床上の性能を検討するため, 咬合器上で実際の測定状態および各種下顎運動を再現し, 精度を求めたところ, 以下のような結論を得た.1.本装置による寸法における最大誤差は, 被験者に中心咬合位から最大開口運動をさせた際の切歯点移動量における3.3mmであった.2.本装置による角度における最大誤差は, 被験者に中心咬合位から最大開口運動をさせた際の矢状面における2.13°であった.3.本研究により, 本装置が実際の臨床の場で下顎運動の6自由度測定に使用できる見通しが得られた.

A Study on Minor Anomalies in the Oral Region

In children with congenital anomalies, minor anomalies may often occur in their oral regions. This is more so in children with Down’s syndrome. But tooth anomalies in children with Down’s syndrome at their deciduous tooth stage have been little known. In this study, the authors examined the incidence of tooth anomalies in a group of 108 children with Down’s syndrome at their deciduous tooth stage, compared it with that in the group of 16,233 twoyear-old children dealt with in our previous report and obtained the following results : 1) In the incidence of tooth anomalies at the deciduous tooth stage, a marked difference was noted between children with Down’s syndrome at 61.1 1 % and normal children at 6.22%. 2) In terms of the form of anomaly, fused teeth were seen at the highest rate of incidence in normal children, whereas the incidence of missing teeth was the highest in children with Down’s syndrome.