Jaw reflexes in subjects with temporomandibular disorders and bruxism
The overall aim of this study, was to investigate the jaw-opening reflexes in TMD patients and bruxists in order to get a better understanding of these disorders. At the beginning, it was decided to study the reflexes evoked in the masseter muscle by electrical stimulation across the lip in healthy subjects. The aim was to find the threshold at which each of the significant responses occurred and to investigate the effect of reversing the polarity of the stimulus electrode on the pattern of reflexes. A sequence of inhibitor, excitatory, inhibitory and excitatory responses could be produced in the muscle by both polarities of stimuli. It was found that stimulation of nerves supplying the skin outside the mouth evokes predominantly long-latency jaw reflexes whereas short-latency responses can be evoked by stimulating nerves supplying oral mucosa. Furthermore, long-latency excitatory reflexes seem to be the most easily evoked by stimulation of the lip. Another aim of the study was to investigate whether difference could be observed between bruxists and non-bruxists in response to electrical stimulation of the lip. In both groups, there were significant differences in the thresholds of the different responses. Also, there were differences between the two groups in the presence of the short-latency excitation and the long-latency inhibitory responses. These findings suggest that long-latency inhibitory responses evoked by electrical stimulation of the lip are weaker in bruxists than in non-bruxists. Finally, jaw reflexes in TMD patients were investigated to determine whether differences could be detected in electrically-evoked inhibitory and excitatory responses. Moreover, the occlusal splint is one of the most universally accepted forms of therapy in TMD patients and it was possible that these splints might have an effect on the pattern of jaw reflexes in view of their therapeutic effect.