EFFECT OF LOW-POWER LASER IRRADIATION ON THE SHEAR BOND STRENGTH AND THERMAL CHANGES ACROSS DIFFERENT ZIRCONIA THICKNESSES USING DIFFERENT IRRADIATION TIMES.

Purpose: To investigate the effect of irradiation time and zirconia thickness using low power Er,Cr:YSGG laser irradia)on (for debonding purposes) on the thermal changes and shear bond strength (SBS) of resin-bonded 3% mol yIrium oxide stabilized tetragonal zirconia polycrystal (3YTZP) specimens.

Materials and methods: 3Y-TZP slices of 0.5-, 2-, and 3- mm thick were used. The temperatures during laser irradiation using single spot irradiation at different times (30 seconds, 60 seconds, 90 seconds, and 120 seconds) and line scanning irradiation from one spot to another at three different distances (2, 4, and 6 mm) were recorded. Single spot and line scanning irradiation data were analyzed using three-way ANOVA (α = .05) and generalized linear mixed model, respectively. Nonirradiated (control) and irradiated resin-bonded 3Y-TZP specimens were shear tested, and the data were analyzed using two-way ANOVA (α = .05).

Results: Under single spot irradiation, the laser-induced temperature was higher through thin 3Y-TZP at any time compared to thick 3Y-TZP. For the line scanning method, short distances (2 and 4 mm) resulted in a significant increase in temperature for 0.5-mm thick specimens. Laser irradiation significantly decreased the SBS of the 0.5-mm group compared to the nonirradiated group. After irradiation, the bond strength of the 2- and 3-mm thick 3Y-TZP was similar to the nonirradiated group.

Conclusions: The temperature and bond strength of low-power laser irradiated 3Y-TZP specimens was affected by the specimen thickness but not by the irradiation time tested. Low-power laser irradiation is an effective debonding method for thin Y-TZP restorations.