Comparison of the accuracy of working casts made by the direct and transfer coping procedures

Abstract

A working cast with dies that accurately record the prepared abutments, surrounding soft tissues, and adjacent and opposing teeth is necessary. This study compared the accuracy of the direct and transfer coping methods in recording the vertical and horizontal dimensional relationship of a pair of removable dies in a working cast before and after separation from the stone base. Among the procedures used for making impressions of abutments for fixed partial dentures, the transfer coping procedure has specific advantages. In particular, where there are multiple abutments, this procedure, in which individual impressions are made of the abutments, transfer copings are made, and a transfer impression of the copings is used for seating the dies and fabrication of a dental stone base, is useful. Two groups of working casts were fabricated from a stone master cast containing 2 ivorine teeth to simulate abutments. The first group of working casts was fabricated directly from the elastomeric impression of the abutments using a 2-pour procedure. The second group of working casts was made using the transfer coping procedure. When the interdie dimensions in each group were compared with that of the master cast, after separation and replacement of the dies in the stone base, the differences were less than 100 microm and similar for both the direct and transfer coping techniques. These findings show that either procedure is equally effective in positioning the dies in the working casts.