Perioral and dental perception of mechanical stimulus among subjects with and without awareness of bruxism.

We studied whether perioral and dental sensitivity to mechanical stimulation is changed in subjects with awareness of bruxism. Tactile detection threshold in the vermilion border of the lower lip and in the upper incisor was determined using calibrated monofilaments (von Frey hairs) and spatial resolution threshold of the lip was determined using a grating orientation task. The tactile detection threshold and the spatial resolution threshold in the perioral region were not significantly different between bruxers (n = 7) and asymptomatic control subjects (n = 13). Neither was the detection threshold for mechanical stimulation of the tooth different between bruxers (n = 6) and asymptomatic controls (n = 6). It is concluded that the tactile sensitivity of perioral region or the tooth is not significantly changed in subjects with awareness of bruxism.

Altered control of submaximal bite force during bruxism in humans.

The control of bite force during varying submaximal loads was examined in patients suffering from bruxism compared to healthy humans not showing these symptoms. The subjects raised a bar (preload) with their incisor teeth and held it between their upper and lower incisors using the minimal bite force required to keep the bar in a horizontal position. Further loading was added during the preload phase. A sham load was also used. Depending on the session, the teeth were loaded by the experimenter or the subject and in one session the subject did not see the load (no visual feedback). The bite force was measured continuously using a calibrated force transducer. In all the subjects, the bite force increased with increasing load. Following the addition of the load, the level of the tonic bite force was reached rapidly with no marked overshoot. The patients with bruxism used significantly higher bite forces to hold the submaximal loads compared to the control subjects. In the control subjects, the holding forces for each submaximal load were identical in the men and the women and were independent of subject maximal bite force. Sham loading evoked no marked responses in biting force. Whether the subject or the experimenter added the load or whether the subject had visual feedback or not were not significant factors in determining the level of bite force. The results indicated that the patients with bruxism used excessively large biting forces for each given submaximal load. This study showed no evidence that the inappropriate control of bite force by patients with bruxism was due to an abnormality in the higher cortical circuits that regulates the function of trigeminal motoneurons in the brainstem. This was shown by a lack of abnormality in coordination of voluntary hand movement with biting force, a lack of abnormal anticipation response to a sham load and a lack of any effect of visual feedback. The results were in line with the hypothesis that afferent input from oral (periodontal or masticatory muscle) tissues does not provide an appropriate control of motor command in bruxism.