Atsushi Uchida

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.

Relationship between reaction time for mandibular movement and the level of muscular discharge of the masticatory muscles in a reaction time task in patients with cerebral palsy

Abstract We hypothesized that patients with Cerebral Palsy (CP) are affected by the preparatory process in the central nervous system for initiating a jaw movement. We tested this hypothesis on 13 in patients with CP (average: 36.9 years old) and 13 in healthy adults (average: 34.7 years old) as subjects. We recorded the muscular discharge of the masticatory muscles from the time a warning stimulus was presented to the time an instruction stimulus was presented during the reaction time (RT) with the open mouth movements in patients with CP. The following results were obtained. The RT for executing the open mouth movements is significantly longer in the CP subjects than in the healthy subjects. In the CP subjects during the movement task, the level of muscular discharge of the masticatory muscles in the 1-s period before presentation of a warning stimulus was significantly lower than that in the 1-s period or in the period from 1s to 2s after the presentation of the warning stimulus. The other side, In the healthy subjects, no change in the muscular discharge of the masticatory muscles was observed. However, In the CP subjects and in the healthy subjects during the nonmovement task, no change in the level of muscular discharge of the masticatory muscles in each period was observed. A significant correlation was observed between the percent change of the level of muscular discharge of the masseter muscle (or the digastric muscle) and RT for the open mouth movement. From the results of this study, as one of the reasons for the difficulty in executing smooth voluntary movements in the oromandibular region in individuals with CP, we consider that the movement is delayed because the period of preparation of the movement is significantly prolonged in individuals with CP although they started the preparation of the movement at an earlier period than in individuals who do not have CP.

Characteristics of sensing lower-jaw-position in patients with cerebral palsy during laughing gas-induced sedation

Abstract To clarify the effects of the applied during sedation with nitrous oxide (hereafter referred to as laughing gas) on the ability of muscles attached to the lower jaw to sense lower-jaw-position and on the sensation of muscle spindles attached to the lower jaw in patients with cerebral palsy (CP) using healthy adult subjects without functional abnormalities of the jaws and oral cavities as control subjects (hereafter referred to as healthy subjects). Experiments were performed under the following conditions: for each subject, before the inhalation of laughing gas (LG) and oxygen (air-inhalation condition: referred to as without LG inhalation) and during the inhalation of LG and oxygen (inhalation condition of LG and oxygen under LG-induced sedation: referred to as during LG inhalation). Subjects in the experiments were eight CP patients and eight healthy people as controls. The ability to discriminate lowerjaw- position was estimated by asking the subjects to determine whether the diameter of a test stick was larger or smaller than that of a reference stick after performing the following tasks: a) holding a reference stick between the central teeth of their upper and lower jaws for 5s, and b) replacing the reference stick with a test stick and holding it at the same position for 5s, and the test stick was then removed. The following findings were obtained. 1)In comparing discrimination ability in the absence of LG-induced sedation and that during LG-induced sedation of healthy control subjects, the rate of mis-estimation (RME) was significantly larger during LG-induced sedation than in the absence of LG-induced sedation for a test stick diameter (10.5mm or 11.0mm) larger than the reference stick diameter (10.0mm) (P 0.05). 2)In comparing discrimination ability in the absence of LG-induced sedation and that during LG-induced sedation of CP patients, RME was significantly smaller during LG-induced sedation than in the absence of LG-induced sedation, when the test stick diameter (9.5mm) was smaller than the reference stick diameter (P 0.05). These results indicate that neural functions are inhibited at the upper level of the central nervous system in CP patients, leading to the attenuation of sustained increase in muscle tonus that is characteristic of CP patients. In summary, it seems that the LG has some inhibitory effect on the activity of γ-motor neurons innervating muscle spindles attached to the lower jaw via the upper level of the central nervous system and that this inhibitory effect contributes to an improvement in the discrimination ability.

Study on the relationship between sensation of the mandibular position and the oral dysfunctions in the cerebral palsy patients

Abstract The ability to discriminate the sensation of the mandibular position in the cerebral palsy (CP) patients was studied and the relationship between this ability to discriminate the sensation of the mandibular position and the oral dysfunctions was evaluated. Interdental dimension discrimination tests (IDD test) were performed in order to evaluate the ability to discriminate the sensation of the mandibular position in 18 CP patients and in 15 healthy individuals. Using the test result, points of subjective equality (PSE) and difference limen (DL) were obtained. In addition, the oral dysfunction index was used to evaluate the oral dysfunctions of the CP patients. The results obtained are as follows 1) PSE in the CP patients was significantly lower than that in the healthy individuals. 2) No significant difference was observed in DL between the CP patients and healthy individuals. 3) A significant correlation was observed between PSE and ODI in the CP patients.

CNP is affected by the chewing strength —Pattern of the appearance of masticatory masseter electric discharge—

To determine whether cortical negative potential (hereafter referred to as CNP), which was recorded from the scalp (sites: T3, CZ and T4), preceding the right-side chewing, is affected by the pattern of the appearance of masseter electric discharge, difference of strong and weak chewing with CNP appearance were compared. In the case of strong chewing, CNP appeared early, and its amplitude increased as compared with the results in the case of weak chewing. From this result, we related that CNP amplitude is related to the chewing output.

Changes in cortical negative potential associated with local anesthetization of apex of tooth root

Abstract To determine whether cortical negative potential (hereafter referred to as CNP), which was recorded from the scalp (sites: T3, CZ and T4), preceding the right-side chewing is affected by input from the periodontal membrane, the CNP and pattern of the appearance of masseter electric discharge before the anesthetization of the apex of the tooth root and those after the anesthetization were compared. 1)CNP preceding the right-side chewing appeared at T4 early both before and after the anesthetization and showed a maximum amplitude immediately before masseter electric discharge. CNP duration and amplitude increased after the anesthetization as compared with those before the anesthetization. 2)The initial increase in electromyogram associated with chewing became sharper after the anesthetization than before the anesthetization. From these findings, that the cerebral cortex is in a preparatory state at an early stage when the sensation in the periodontal membrane on the chewing side is blocked, and that, as a consequence, strong chewing is produced.

Effects of vibration stimulus on lower-jaw-position sensation in patients with cerebral palsy during inhalation of laughing gas

Abstract To clarify the effects of a vibration stimulus applied during sedation with nitrous oxide (hereafter referred to as laughing gas) on the ability of muscles attached to the lower jaw to sense lower-jaw position and on the sensation of muscle spindles attached to the lower jaw in patients with cerebral palsy (CP) using healthy adult subjects without functional abnormalities of the jaws and oral cavities as control subjects (hereafter referred to as healthy subjects). Experiments were performed under the following conditions: for each subject, before the application of the vibration stimulus (referred to as S pre ) and after the application of the vibration stimulus (S post ); before the inhalation of laughing gas (LG) and oxygen (air-inhalation condition: referred to as without LG inhalation) and during the inhalation of LG and oxygen (inhalation condition of LG and oxygen under LG-induced sedation: referred to as during LG inhalation). Subjects in the experiments were eight CP patients and eight healthy people as controls. The ability to discriminate lower-jaw position was estimated by asking the subjects to determine whether the diameter of a test stick was larger or smaller than that of a reference stick after performing the following tasks: a) holding a reference stick between the central teeth of their upper and lower jaws for 5s, and b) replacing the reference stick with a test stick and holding it at the same position for 5s, and the test stick was then removed. The following findings were obtained. 1)In comparing the ability of healthy subjects to discriminate between S pre and S post during LG inhalation using different test sticks, when the test stick diameter was 9.5mm (smaller than the reference stick diameter), the rate of mis-estimation (RME) for Spost was significantly larger than that for Spre (P 2)In comparing the ability of CP patients to discriminate between S pre and S post during LG inhalation using different test sticks, when the test stick diameter was 9.5mm (smaller than the reference stick diameter), the RME for S post was significantly smaller than that for S pre (P These results suggest the following: the combination of LG for sedation with vibration stimulus further inhibits neuronal functions at the upper level of the central nervous system in CP patients, compared with cases in which each variable is applied separately, and the combination also inhibits the sustained increase in muscle tonus, which is characteristic of CP patients. LG reduces the activity of γ-motor neurons via the upper level of the central nervous system. In addition, tonic vibration reflex (TVR) develops due to the vibration stimulus, which increases the threshold value of sensitive muscle sensation and decreases the activity of γ-motor neurons, and furthermore decreases the activity of muscle spindles attached to the lower jaw. Consequently, a tendency toward increased ability to discriminate lower-jaw position is observed.