Abstract
[Purpose] The effect of temporomandibular disorder (TMD) symptoms on mouth opening in two head positions was examined. [Subjects] The subjects were 22 adults who were not receiving dental treatment. [Method] In upright sitting (UP) and in forward head posture (FHP), in maximal mouth opening, range of mouth opening and left and right mandibular head movement distance were compared between TMD and no TMD subjects. [Results] For the two groups of subjects, there were no significant differences in range of mouth opening, and left and right mandibular head movement distance between head positions. For the no TMD group, in the UP position, significant positive correlations were seen between left and right mandibular head movement distance, and between range of mouth opening and both left and right mandibular head movement distance; and in the FHP position, significant positive correlations were found between left and right mandibular head movement distance, and between range of mouth opening and left mandibular head movement distance. For the TMD group the same relationships were found only in the UP position; no significant relationships were found in the FHP position. [Conclusion] The results suggest the possibility that coordinated movements of the jaw are easily disturbed by head position in subjects having TMD symptoms.
