Computer-analysed movements in three dimensions recorded by light-emitting diodes. A study of methodological errors and of evaluation of chewing behaviour in a group of young adults.

Mandibular movements recorded by means of intraorally placed light-emitting diodes (LEDs) were described and tested. By using a reference system attached to the test subject, the influence of head movements on the registration of the mandibular movements could be avoided. The errors of the method were tested. The stability of the reference system during function was found to be greater when the light impulses did not have to penetrate the lip. A limited clinical test was performed and the following observations were made: the mean cycle duration was, after the first cycles, stable through the whole chewing phase, 0.52 s when chewing crispbread; the duration of the occlusion phase appeared to be shorter than that of the opening and closing phases; the velocity of the mandible was greater in the opening phase than in the closing phase, with a mean velocity of 84 and 70 mm/s respectively; the clinical test showed that the method was easy to handle in the clinical situation, thereby creating an instrument for studies in larger groups of patients. By adding a simple computer program, the manual analysis could be reduced considerably and a number of variables could be measured with a high degree of precision.