EFFECT OF PARTICLE SIZE ON THE FLEXURAL STRENGTH AND PHASE TRANSFORMATION OF AN AIRBORNE-PARTICLE ABRADED YTTRIA-STABILIZED TETRAGONAL ZIRCONIA POLYCRYSTAL CERAMIC

Abstract

Statement of problem. Because airborne-particle abrasion is an efficient method of improving the bond at the zirconiacement interface, understanding its effect on the strength of yttria-stabilized tetragonal zirconia polycrystal is important. Purpose. The purpose of this study was to evaluate the effect of the particle size used for airborne-particle abrasion on the flexural strength and phase transformation of a commercially available yttria-stabilized tetragonal zirconia polycrystal ceramic. Material and Methods. For both flexural strength (20.0 x 4.0 x 1.2 mm) (n=14) and phase transformation (14.0-mm diameter x 1.3-mm thickness) (n=4), the zirconia specimens were made from Lava, and their surfaces were treated in the following ways: as-sintered (control); with 50-mu m aluminum oxide (Al2O3) particles; with 120-mu m Al2O3 particles; with 250 gm Al2O3 particles; with 30-mu m silica-modified Al2O3 particles (Cojet Sand); with 120-mu m Al2O3 particles, followed by 110 gm silica-modified Al2O3 particles (Rocatec Plus); and with Rocatec Plus. The phase transformation (%) was assessed by x-ray diffraction analysis. The 3-point flexural strength test was conducted in artificial saliva at 37 degrees C in a mechanical testing machine. The data were analyzed by 1-way ANOVA and the Tukey honestly significant difference post hoc test (alpha=.05). Results. Except for the Cojet Sand group, which exhibited statistically similar flexural strength to that of the as-sintered group and for the group abraded with 250-mu m Al2O3 particles, which presented the lowest strength, airborne-particle abrasion with the other particle sizes provided the highest values, with no significant difference among them. The as-sintered specimens presented no monoclinic phase. The groups abraded with smaller particles (30 mu m and 50 mu m) and those treated with the larger ones (110 mu m and/or 120 mu m particles and 250 mu m) exhibited percentages of monoclinic phase that varied from 4% to 5% and from 8.7% to 10%. Conclusions. Except for abrasion with Cojet Sand, depending on the particle size, zirconia exhibited an increase or a decrease in its flexural strength. Airborne-particle abrasion promoted phase transformation (tetragonal to monoclinic), and the percentage of monoclinic phase varied according to the particle size.