The casting accuracy of nickel--chromium alloys for fixed prostheses.

The casting accuracy of four nickel--chromium alloys (Ultratek, Omega, Microbond N/P2, and Nobil-Ceram) was compared to that of a precious alloy, Jelenko "O". The experiment consisted of fabricating and fitting cast copings to a cobalt--chromium test preparation of a maxillary central incisor and measuring the marginal discrepancy in eight selected points. The experiment indicated that Jelenko "O" had the greatest casting accuracy, followed successively by Ultratek, Nobil-Ceram, Microbond N/P2, and Omega. Statistical analysis of the data revealed no significant difference between Jelenko "O" and Ultratek alloys in fit of five of eight test points, but Jelenko "O" was significantly better in fit than Nobil-Ceram, Microbond N/P2, and Omega alloys. The following conclusions may be drawn from this experiment: 1. The nickel--chromium alloys tested did not cast as consistently or as accurately as precious alloy Jelenko "O". 2. The casting accuracy may be related to the amount of casting shrinkage that occurs in each alloy type, and further research is necessary to determine if expansion compensation of the selected phosphate-bonded investment recommended by the alloy manufacturers is adequate for the casting shrinkage of the test alloys. 3. Alloy composition and technique parameters may also influence the accuracy of the casting, but further research is necessary to determine their singular effects.