Effect of Nd:YAG laser energy density on bond strength and phase transformation of zirconia

Objectives: This study sought to assess the effect of energy density of neodymiumdoped yttrium aluminium garnet (Nd:YAG) laser on morphological characteristics and phase transformation of zirconia ceramic and its microshear bond strength to resin cement. Materials and Methods: Sixty zirconia discs (7 × 2 × 10 mm) were divided into four groups (n=15). Group C received no surface treatment (control). Group S samples underwent sandblasting with 50 μ aluminum oxide particles. Group L9 was subjected to laser irradiation with an energy density of 9 J/cm2 and group L5 was subjected to laser irradiation with an energy density of 5 J/cm2. One disc of each group underwent atomic-force microscopy (AFM) and scanning electron microscopy (SEM) analyses for evaluation of surface morphology. Phase transformations were evaluated by X-ray diffraction (XRD). Small cylinders of Panavia F2.0 resin cement were fabricated and placed on treated surfaces; samples were incubated at 37°C for 24 hours and were then subjected to microtensile tester for measurement of microshear bond strength. The Welch test and Games-Howell test were used for data analysis (P<0.05). Results: Surface-treated groups were not significantly different in terms of bond strength but had significant differences with the control group (P<0.05). The highest surface roughness and the highest frequency of cohesive failure were noted in groups S and L9. In all samples, tetragonal phase decreased after surface treatment and no tetragonal to monoclinic phase transformation occurred in any group. Conclusion: Nd:YAG laser irradiation changes the morphological properties of zirconia ceramic and increases its surface roughness. It can also increase the microshear bond strength of zirconia to resin cement. Increase in Nd:YAG laser energy results in higher surface roughness but cannot cause a significant change in microshear bond strength of zirconia to resin cement. Laser irradiation with the parameters employed in our study does not cause any phase transformation.