The size of occlusal rest seats prepared for removable partial dentures

OBJECTIVE: The aim of this study was to test whether rest seats cut by a group of general dental practitioners for a removable partial denture differed in size and shape from those prepared by either a group of postgraduate students or their academic teachers. METHOD: The occlusal surfaces of a number of plastic teeth were scanned by a laser profilometer. Each tooth was then placed in a set of articulated phantom head dental arches. 30 dental practitioners, 16 postgraduates and 11 dental academics were asked to cut a rest seat preparation in the mesial marginal ridge suitable for the construction of a removable chromium cobalt partial denture. The tooth was removed from the models, rescanned, and this data converted to grey level images for measurement of the width, length and area of each rest seat. Depth was calculated as the difference between the pre and post preparation scanned profiles. RESULTS: There was a wide variation in the size of the individual rest seat preparations. There was no significant difference between the measured parameters from the images of the preparations made by academic staff and postgraduate students. The two sets of data were therefore combined. The length, width and area of the rest seats prepared by the staff and postgraduate group were significantly greater than those cut by the dental practitioner group. However, there was no significant difference in the depths measured. The outline form of the rests prepared by the dental practitioners was often round with sharply defined margins contrasting with the smooth triangular preparation the staff and postgraduates prepared. CONCLUSION: A 'refresher' in tooth modification for GDPs designing partial dentures would improve the long term success of the prosthesis.