Relationship between head position and the muscle hardness of the masseter and trapezius muscles: a pilot study.

The purpose of this study was to examine the hardness of the masseter and trapezius muscles at various head positions and to explore the relationship of these two muscles to each other in terms of their respective levels of muscle hardness at different head positions. Twenty-two asymptomatic male subjects participated in this study. Using a hand-held hardness meter, muscle hardness was first measured in a relaxed position as a baseline. The subjects were then asked to assume five deviated head positions, and the muscle hardness was measured again. The data obtained at each deviated head position were compared to those at baseline. In addition, the subjects were asked to maintain a five minute sustained anterior flexion of the head, and muscle hardness was also measured and compared to the baseline. As a result, there was a significant increase in muscle hardness at the point of the whole trapezius with 30-degree anterior flexion, while there was a significant decrease at the point of the right masseter. A significant increase in hardness was seen in the upper trapezius muscle in conjunction with right side bending and in the right upper trapezius muscle on left side bending. Also, a significant decrease in hardness was observed in the right masseter with right side bending. With reference to the axial rotation, there was a significant increase in hardness in the upper right trapezius muscle upon right axial rotation. Moreover, there was a significant increase in the muscle hardness in the whole trapezius after the five minute anteriorly sustained head task. This study provides evidence that deviated head positions lead to an increase in hardness of the trapezius muscle. The data also revealed the simultaneous occurrence of the elevation of muscle hardness in the upper trapezius muscle and the decrease in muscle hardness in the masseter muscle associated with right side bending and anterior flexion.

Effect of short-term use of a centric occlusion stabilization oral appliance on sensory and pain perception thresholds in the cervically innervated area: a pilot study.

This preliminary study was done to determine the effect of short-term use of a centric occlusion stabilization oral appliance with regard to noxious and sensory perception in the upper extremities. The subjects consisted of 22 asymptomatic females, and the experiments were performed on two separate days within the same week, with the days randomly assigned as either appliance-wearing or nonappliance-wearing days. For each experimental day, cool sensation, warm sensation, cold-induced pain and heat-induced pain were measured using a computer-based quantitative testing device, and these thresholds were compared between the experimental days with or without the oral appliance. We found that during the experimental day wearing an oral appliance, subjects had significantly higher thresholds for warm sensation and heat-induced pain. There was no statistical difference between the testing days in cool sensation or cold-induced pain thresholds. These findings indicate that short-term wearing of a centric occlusion stabilization oral appliance may inhibit some noxious and sensory inputs from cervically innervated structures, which are primarily served by unmyelinated C fibers, and that oral appliances may be appropriate for the treatment of painful cervical disorders.