Impact of posterior occlusal support on the condylar position

The purpose of this study was to investigate condylar displacement related to the loss of posterior occlusal support. Each of 23 subjects received one occlusal adjusted splint that covered all teeth from the right to the left second mandibular molar. None of the subjects had a third molar and none of them had a missing tooth or showed tooth mobility. The splint was inserted and vertical and horizontal condylar position was measured by an ultrasonic motion analyser. The splint was then unilateraly shortened tooth-by-tooth up to the canine tooth and the measurement was repeated after each shortening. Cutting off the splint's second molar on one side lead to a slight ipsilateral cranial motion of the condyle if subjects clenched with maximum voluntary force. If the second and first molar were cut off, a noticeable cranial condylar movement of about 0.3 mm was observed even when teeth occluded with low force. These results suggest that loss of posterior occlusal support as it happens in routine oral rehabilitation leads to a noticeable cranial condyle movement during registration, even if the clenching force is low.