Patterns of mandibular movements in subjects with craniomandibular disorders

Mandibular movements were evaluated for border and functional movements in 24 adult normal subjects and 26 adult patients with muscle pain associated with a craniomandibular disorder. The mandibular incisor position was tracked with an electromagnetic system in three planes by use of either a Myotronic Kinesiograph or a Siemens Sirognathograph instrument while the subject sat in an upright position. In the normal subjects, the maximum movements of the mandible in lateral, protrusive, and vertical directions were compared with the envelope of movement during speech and mastication. The range of the rest position was 1 to 5 mm in relation to the intercuspal position; the range of maximum excursion during speech was 30% to 36% of maximum opening; the vertical extent of excursion during mastication was 18% to 90% of the maximum vertical opening dependent on the bolus. Protrusive movements were straight forward, dividing the angle evenly between left and right laterotrusion. Laterotrusive movements were of equal length and similar to the length of protrusion. Twenty-six patients with muscle pain, in many instances, demonstrated asymmetry in the length of laterotrusive movements. Different pathways for moving the mandible away from the intercuspal position and returning to this position could be seen during laterotrusion. Unequal laterotrusive excursions and asymmetrical, nonparallel movement patterns for mandibular protrusion and retrusion were often observed. In contrast, the extent of the speech envelope and the envelope of mastication were similar to that of the controls.