Habitual mastication in dysfunction: a computer-based analysis.

To study the different parameters of habitual mastication in stomatognathic dysfunction, mandibular movements and electromyographic activity of the elevator muscles were recorded during three chewing sequences in 86 dysfunctional subjects. The Dysfunction Index system was used to treat two subgroups, patients with severe temporomandibular joint impairment and patients with severe muscle dysfunction. Data on the different parameters of mastication from the single patients, the whole group, and the two subgroups were statistically assessed and compared with those from 12 normal individuals. The following conclusions were drawn. (1) In dysfunctional patients the normal symmetrical and balanced distribution of the chewing cycles is lost and movements are more restricted. (2) The electromyographic data show marked alterations with a tendency to reduce or suppress the isometric phase of contraction during closing in the temporomandibular joint patients. This can be viewed as a defensive mechanism of the impaired system. (3) The data at hand are helpful in explaining some of the mechanisms that lead to muscle pain in dysfunctional patients.