EXPERIMENTAL STUDIES ON THE CHANGES OF FORM OF DENTAL PORCELAINS DURING FIRING

Abstract

The purpose of this study was to clarify the changes of the forms during firing on the dental porcelain. Specimens were two types of feldspathic porcelains and three types of aluminous porcelains. The properties investigated here were the particle distribution, the changes of the forms during firing in continuous observations (Heating Microscope), the internal structure (Microradiography), and the dimensional changes during fring on the metal die (Heating Microscope). The following conclusions were obtained;1. The particle distribution in each porcelain was almost similar. Therefore, it seemed that the particle size distribution had almost no relation to the firing shrinkage.2. Each grade of low bisque firing, medium bisque firing and high bisque firing was observed in all the porcelains in the changes of the forms during firing and in the internal structure.3. In the changes of the forms during firing, the feldspathic porcelains tended to be in globular shape, while the aluminous porclains showed reduction of the size in the similar figures in the state of high bisque firing.4. The dimensional changes in the transverse direction of the dental porcelain on the metal die were larger than those in the vertical direction. The firing shrinkage in the transverse direction on the axial wall of the die was the largest.