Variation of approximal tooth contact tightness with postural change.

In order to investigate the role played by posture in determining posterior dental contact tightness, we measured contact tightness of maxillary and mandibular posterior teeth in ten adult subjects, while each was initially seated upright, after each had assumed a supine posture for two h, and finally after each had returned to an upright posture for two h. The technique used for measurement of contact tightness was based on frictional force concepts and consisted of the recording of the force required to withdraw a 0.038-mm-thick stainless-steel strip that had been slipped into each contact. A decreased mean tightness of all maxillary and mandibular contacts followed the change from an upright to a supine posture. The most significant decrease (-32%) occurred at the mandibular first molar-second premolar contact, and the smallest decrease (-10%) occurred at the mandibular first premolar-canine contact. An increased mean tightness of all maxillary and mandibular contacts followed a return to an upright posture. The most significant increase (20%) occurred at the maxillary first molar-second premolar contact, and the smallest increase (8%) occurred at the maxillary first premolar-canine contact. We conclude that posterior dental contact tightness, generally regarded by dentists as a static feature of occlusion, varies significantly as a function of posture.