Fit of unit-cast fixed partial dentures related to casting ring size and shape.

Four types of casting rings were tested for producing accurate-fitting fixed partial dentures. None of the casting rings tested produced ideal results, but the larger oval and round rings produced fixed partial dentures cast as a single unit with more complete seating than those produced in smaller round casting rings when phosphate bonded investment and Type III gold were used. Fixed partial denture seating was affected by the casting ring size but not because of its shape. While distortion of the wax and dimensional change in the gold alloy do affect the seating qualities of castings, this was not statistically significant in this study.