The effects of variations in the opposing dentition on changes in the partially edentulous mandible. Part II. Densitometric measurements.

Distal-extension lower removable partial dentures were used to study the effects of various types of opposing dentitions on the residual mandibular ridge. The opposing-dentition groups included complete upper dentures, removable partial upper dentures, and natural teeth. Changes in the bone of the lower residual ridge were measured by means of densitometry. A significant densitometric difference was found in the bone of the partially edentulous mandible between the group of subjects wearing complete upper dentures and the group with natural upper teeth. The reason for this difference is uncertain; however, several theories can be offered. These are (1) an inherent bone difference between the subjects in the two groups, implying a difference in the bone of the group that retained their natural upper teeth longer than did the complete denture group, (2) an increased frequency and/or duration of muscle pull on the mandible due to clenching of the teeth to stabilize the upper complete denture, and (3) the possibility of coincidence. None of the densitometric changes measured at +18 months was significant.