AbstractThe effect of thermal coefficient of expansion (α) mismatch on porcelain‐metal bonding is frequently referred to in the dental literature. Thermally induced stresses may develop at metal‐porcelain system interfaces due to differences in the coefficients of thermal expansion of the porcelains, metals, and metal oxides. The objective of this research is to characterize alloy and porcelain expansion behavior as a first step in developing a more specific definition of thermal compatibility. It is clear from comparisons of porcelain data and alloy data that the porcelain has expansion characteristics which are quite different from those of the alloys. The overall differences in values between these alloys and porcelains constitute a mismatch. First run dilatometric heating measurements for porcelain yield large differences between ΔL/L and α values as compared to cooling measurements. For a comparison of alloy and porcelain expansion characteristics, data should be obtained at several temperatures up to the glass transition temperature (Tg) of the porcelain.