POTENTIAL INTERFERENCE OF LEUCITE CRYSTALLIZATION DURING PORCELAIN THERMAL-EXPANSION MEASUREMENT

Objectives. The elevated temperatures and slow heating and cooling rat es associated with a thermal expansion run provide a thermal treatment comparable to those previously shown to produce leucite crystallizati on in dental PFM porcelains. The purpose of this study was to determin e whether the exposure of dental porcelains to the time-temperature pr ofile of a thermal expansion run could result in leucite crystallizati on, a potential interference with the accurate determination of the th ermal expansion coefficient. Methods. A total of 112 thermal expansion specimens were prepared, 16 each of six commercially available body p orcelains, as well as the ''Component No. 1'' (leucite-containing) fri t of the Weinstein et al. (1962) patent. In a randomized design, the l eucite contents of specimens subjected to a 3 degrees C/min thermal ex pansion run were compared to those of untreated controls. The leucite content of each specimen was determined via quantitative X-ray powder diffraction using an Al2O3 internal standard. One-tailed t-tests were applied to determine whether the dilatometer thermal treatment produce d a statistically significant increase in leucite content. Results. Th e heat treatment afforded by a 3 degrees C/min dilatometer run was not sufficient to induce measurable leucite crystallization in any of the porcelains examined in this study. Significance. The crystallization of leucite during a dilatometer heating run can be ruled out as a poss ible interference with the determination of the coefficient of thermal expansion of dental porcelain.