81.In restoring a mandibular first molar, lingual cusps are important for which movement?

A. Centric occlusion B. Protrusive
C. Retrusive D. Working E. Nonworking

ANS. D. To answer this question, place your own teeth in centric occlusion(maximum intercuspation). Notice that the occlusion is held in place by the lingual cusps of maxillary teeth and the buccal cusps of mandibular teeth. Mandibular lingual cusps are not in contact. In protrusion, the anterior teeth act to separate the maxilla and mandible as the mandible moves forward. The anterior teeth act as guides in retrusion as well (try it). So far the mandibular lingual cusps are not involved. If you make a left working movement (slide your mandible left), notice that the mandibular lingual cusps on the left, drag against the lingual side of the maxillary lingual cusps. In the nonworking side (in this case, the right side), the mandibular lingual cusps move AWAY from contact.


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