Length-tension relations of the masticatory elevator muscles in normal subjects and pain dysfunction patients.

Myofascial pain and dysfunction is the primary diagnosis in a large proportion of facial pain complaints. Myofascial disease can present in the form of trigger points, fibromyositis, myositis, muscle spasm, and muscle weakness. The purpose of this study is to research for quantifiable physiological differences between groups of normal subjects and myofascial pain dysfunction (MPD) patients. The first specific aim was to determine the opening of the jaw at which maximal isometric tension can be produced by the jaw closing muscles, with the hypothesis that this opening of maximal tension would be less for a group of MPD patients than for a group of normal subjects being tested. The second aim was to test the hypothesis that the maximal isometric bite forces for the two groups would differ. Patients with mandibular dysfunction are reported to have a lower maximal bite than normal subjects. Bite force was measured with the T-Scan system. An 80 micron horseshoe-shaped sensor connected to a dedicated IBM XT computer recorded the data. A self-contained printer produced the hard copy for later analysis. Vertical dimension or jaw opening was increased in 0.5-mm increments using double flat plane appliances standardized by the Relator. A MANOVA was used for statistical analysis of the data. MPD patients had significantly higher bite forces at 8.0, 8.5, 9, and 9.5 mm. Normal subjects had higher force values at 5.0 mm. There was no significant difference in mean maximal bite force between groups.