Quantitative X‐ray Diffraction Determination of Leucite Thermal instability in Dental Porcelain

Alterations in the leucite content of dental porcelain during thermal treatments required for fabrication of dental restorations produce proportional changes in the thermal expansion coefficient. Such thermal expansion changes can create a thermal expansion mismatch with the metal to which it is fused and can result in the fracture of the porcelain during fabrication. The purpose of this study was to determine whether changes in the leucite content of a dental porcelain resulting from thermal treatments could be detected via quantitative X‐ray diffraction. The thermal treatments investigated were isothermal soaks for 0, 4, 8, and 16 min at 500° and 750°C, or multiple firings of 1, 2, 4, 8, and 16 times. Quantitative X‐ray diffraction was performed on the heat‐treated porcelain specimens, and the data were subjected to linear regression analysis. A significant negative correlation (r=−0.92, p < 0.001) was found between leucite volume fraction and the number of firings. A significant positive correlation (r= 0.88, p < 0.001) was obtained between leucite volume fraction and duration of heat soak at 750°C. No relationship was found (r= 0.40, p= 0.127) between the leucite content and the duration of the heat soak at 500°C. Such leucite variations could be responsible for changes in porcelain—metal thermal compatibility.