The relative movements of the chin and the mandible during chewing

The suitability of the soft tissue over the chin as a reference point in studies of mandibular performance during chewing was investigated. The movements of reference diodes (LEDs), one on the chin and the other attached to the lower front tooth, were registered simultaneously using the Selspot system and analysed in relation to the reference system in this method. With respect to chewing rhythm, the conformity of the behaviour of the two diodes-or the two tissue locations-was good, thus allowing the conclusion that the chin reference point is suitable for analysing chewing rhythm. Vertical displacement and velocity were less marked with the chin reference than with the tooth reference, however, indicating that the skeletal part of the mandible moves within the tissues envelope. The difference in movement at maximal opening was significant, the magnitude of the difference being between 12 and 20%. Lateral displacement seemed to be of similar magnitude, although a tendency towards larger movements of the chin point than of the tooth was found.