36 - Low Power Laser Debonding: Ceramic Thickness and Irradiation Time

Abstract

To evaluate the effect of irradiation time, for debonding purposes, on the shear bond strength of yttria-stabilized zirconia (YSZ) irradiated by an erbium-based laser at low power output under body temperature conditions. YSZ square-shaped slices of 0.5 mm, 2 mm, and 3 mm thicknesses were tribochemical silica-coated and cemented to resin composite cylinders with a resin-based cement. Five groups of specimens were tested, one served as the control group (non-irradiated) and the other four were submitted to laser irradiation for 30 s, 60 s, 90 s, and 120 s. After water storage for 24 h, the control and the irradiated group were subjected to shear bond strength (SBS) test. Both, the testing and the irradiation were performed at body temperature. For irradiation, an erbium, chromium: yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser was used with the following parameters: 1 W, 20 Hz, and 1% of air spray. Optical microscope and scanning electron microscope were used for failure analysis. SBS data were analyzed using two-way ANOVA and Tukey post hoc test to determine significant differences. Data for irradiated groups are shown in the table. The control group (9.22.4) showed only significant differences with the 0.5 mm group at 30 (p<0.001), 60 (p<0.001), 90 (p<0.001), and 120 s (p<0.001). No statistical differences were found between the 2 and 3 mm groups at any irradiation time. The 0.5 mm group presented significantly low bond strength in comparison with the other groups. For the 0.5 mm group, the SBS values were significantly different after 30 and 120 s of irradiation (p=0.018), while all the other irradiation times had similar values. All the failures were classified as mixed. Zirconia SBS in the thickest groups (2 and 3 mm) was not affected by any of the irradiation times tested. Longer irradiation times might reduce the SBS of thicker zirconia for debonding purposes. For the thin group, any irradiation time decreased the bond strength to the resin cement.