Voluntary Bite Research Articles

Distribution of movement-related cortical potential upon jaw-biting in humans.

We examined the cerebral location of the readiness potential (hereinafter referred to as "RP") upon activation of the masseter muscle by voluntary and unilateral jaw-biting movement. Four normal adults served as subjects. Five scalp electrodes were placed according to the international 10-20 method at CZ, C3, C4, T3 and T4. In addition, in one of the subjects, RPs were recorded by 12 scalp electrodes in order to study changes occurring in the distribution of RPs with time. The maximum amplitude of the RP was located at T4 in the temporal area, which was involved in the biting movement as a negative slow potential occurring 1.4-0.8 s before the beginning of the discharge to the masseter muscle. The maximum amplitude of the RP on the contralateral side was located at T3. This meant that the amplitude of the RP tended to be higher on the same side as the biting movement than on the contralateral side in all subjects. From scalp topography, the maximum amplitude of the RP was shown to be confined to T4, and was especially marked immediately before the beginning of discharge to the masseter muscle. From these results it is thought that in the case of voluntary biting movement, the RP reflects activities of the pyramidal cells in the masticatory area of the cortex, and that strong descending impulses from both sides then reach the masseter muscles.

Long-term effect of intra-articular injections of sodium hyaluronate and corticosteriod on temporomandibular joint arthritis

The long-term effect of intra-articular injections of sodium hyaluronate and corticosteroid (betamethasone) was compared in a sample of 24 patients who had pain and tenderness to palpation in the temporomandibular joint (TMJ arthritis) of at least six months duration, and who had not responded to conservative treatment. The two drugs were randomly allocated to the patients. The drugs, 0.5 ml, were injected twice into the superior joint compartment of the TMJ with a two-week interval between injections. The effect on subjective symptoms, clinical signs, and bite force was assessed. At the one and two-year follow-ups both the hyaluronate-and the corticosteriod-group had significantly reduced subjective symptoms as well as clinical signs, and the maximum voluntary bite force was significantly increased. The differences in effect between treatments were not statistically significant. It was concluded that both drugs have a significant long-term effect on chronic arthritis of the TMJ and that either of the drugs can be helpful; however, sodium hyaluronate might be the best alternative due to the least risk for side effects.

The influence of jaw position and antagonistic tooth relations on the appearance of a short-latency excitatory reflex in the human masseter muscles following mechanical tooth stimulation

Post-stimulus electromyographic complexes (PSEC) were elicited by standardized tapping of a central upper incisor in 12 subjects during isometric voluntary biting in two positions, the incisor edge-to-edge (IEE) or the maximal occlusion (MO). In IEE a short latency excitatory peak (P wave) was present in the PSEC; this was absent in MO. By superimposing the rough EMG sweeps without full-wave rectification, it appeared that this P wave was brought about by synchronous masseter motor-unit firing.

Factors influencing the excitatory-masseteric reflex evoked by gingival electrical stimulation in man

An excitatory-masseteric reflex response was evoked by electrical gingival stimulation in five subjects; the reflex had an onset latency of 7.6 ms with a SD of 0.7 ms. The response occurred just prior to the silent or inhibitory period. There was consistent post-inhibitory synchronization of the EMG activity record in all subjects. Several methods were used to demonstrate this short-latency reflex. The first was to average non-rectified EMG activity. The second was to increase the number of receptors which are simultaneously activated by using multiple electrodes so that a greater area of gingiva could be stimulated. A third was to increase the level of excitability of the motoneurons in the masseteric pool by increasing voluntary bite force. Fourthly, the excitatory reflex was evoked during increased-excitatory drive to the pool, with the additional feature that the reflex appeared at a time when no ongoing EMG activity was present in the masseter muscle. Little doubt should now remain concerning the existence of a short latency excitatory reflex from intra-oral receptors to masseteric motoneurons in man.

Pyramidal tract activity associated with a conditioned hand movement in the monkey.

Pyramidal tract activity associated with a conditioned hand movement in the monkey.