Selection criteria for base metal alloys for use with porcelains

Today's chromium alloys constitute a distinct alloy group that, because of favorable physical and chemical properties, is widely used for porcelain fused to metal restorations. In making a selection from within this alloy group, the individual should first be aware of how to modify casting techniques in order to produce complete and well-fitting castings. Differences in important mechanical characteristics, such as modulus of elasticity, hardness, and an alloy's formability, do exist between various Ni-Cr and Co-Cr alloys, and one needs to be cognizant of these differences if an optimal restoration design is to result. Because chromium alloys do not represent a homogeneous group, gross differences in castability and porcelain bonding behavior will be encountered between alloys with nominally similar compositions and mechanical properties. No universally accepted test for alloy-porcelain compatibility or bond strength exists, but the interested individual can perform some preliminary tests on new or untried alloy-porcelain combinations prior to fabrication of actual restorations. Although soldering the chromium alloys continues to be technique-sensitive, optimal results can be achieved by proper selection of high- and low-fusing solders for specific alloys.