Non-destructive stress analysis of porcelain-fused-to-metal crowns (1). X-ray stress measurement and X-ray diffraction of gold alloys used for porcelain fusing

Abstract

Porcelain-fused-to-metal crowns, though having a better aesthetic appearance, are admittedly inferior in fitness, as compared with full cast crowns. As compression stress is applied to porcelain after firing, porcelain is prepared with a slightly lower thermal expansion coefficient than is metal. This contributes to an increased strength of porcelain, but disturbs the fit due to tension stress, under conditions of an inadequate thickness of the metal.The X-ray stress measurement method is the only known means of a non-destructive measurement, and this method is used to assess the residual stresses of various metals.X-ray diffraction examinations were made to evaluate the possibility of X-ray stress measurement of precious metals.Precious metal strips 6mm widetimes;18mm long were then prepared to determine the change in the stress value during the porcelain firing process. The high compression stress after both the specimens had been polished was reduced by degassing.X-ray stress measurements of precious metals were successfully obtained.