The seating of one-piece and soldered fixed partial dentures.

This laboratory study compared the seating of one-piece castings with that of soldered fixed partial dentures. Two investments were investigated, five American Dental Association type III and five metal ceramic alloy fixed partial dentures were made by using the conventional indirect technique. The investing and casting protocol was designed to produce an ideal fit of the individual complete crown abutments, not the fixed partial denture. Independent seating of each retainer provided a baseline measurement for complete seating and was compared with fixed partial denture seating. Fixed partial dentures were then sectioned and reassembled by soldering twice, using a low- and high-expansion investment. Statistical evaluation identified significant differences between the metals and the techniques. Marginal discrepancies with one-piece casting and lower (0.6%) thermal-expansion soldering were clinically unacceptable. A clinically acceptable fit was obtained with the higher (1%) thermal-expansion soldering investment.