Effect of processing variables on texture development in a mica-based glass-ceramic

The purpose of this study was primarily to determine the feasibility of heat-pressing a mica-based glass-ceramic with the use of commercially available dental equipment, and secondly to evaluate the effect of various processing variables on the degree of crystal alignment in the pressed glass-ceramic. The hypotheses were that the mica-based glass-ceramic could be successfully heat-pressed and that some degree of crystal orientation would be obtained, depending on the processing variables. The glass composition was melted at 1400 degrees C for 2 h and cast into 12 x 60-mm rods. Ingots (10 x 12 mm) were cut from the glass rods, heat treated, and heat-pressed under various conditions. The microstructure of the pressed specimens was investigated by SEM and compared to that of heat-treated controls. The length of Vickers-induced cracks was measured on heat-pressed specimens and heat-treated controls. The results showed that mica-based glass-ceramics could be successfully pressed with the use of commercially available dental equipment. The resulting degree of crystal alignment (texture) along the direction of pressing varied between 35 +/- 6 and 79 +/- 6. There was a linear relationship between the degree of texture and the apparent aspect ratio of the mica platelets. A significant decrease in the length of the Vickers-induced cracks in the direction perpendicular to pressing was observed, associated with an increase in length in the direction of pressing.