Investigation of the effect of different laser applications on the phase change of zirconia based substructures and the bonding strength of superstructure porcelain

The high strength and fracture toughness of zirconia have supported its extensive application in dentistry. However, the fracturing of veneering porcelain remains one of the primary causes of failure. The aim of the study was to investigate the effect of different laser applications on the surface roughness, phase change and bond strength of veneering porcelain to zirconia. In the present study, 256 zirconia samples (8x8x3 mm) were obtained from zirconia blocks and and sinterization was performed. Samples were randomly divided into 8 subgroups (n = 32): Group 1, control (no treatment); Group 2, sandblasting (125 μm Al2O3); Group 3, Er,Cr: YsGG laser (3W); Group 4, Er,Cr: YsGG laser (4W); Group 5, Nd: YAG laser (2W); Group 6, Nd: YAG laser (3W); Group 7, ultrafast fiber laser (10W), Group 8, ultrafast fiber laser (20W). After the surface treatment, surface roughness was measured with a profilometer. In addition, X-ray diffraction analysis (XRD) was applied to a sample from each group and underwent Scanning Electron Microscopy (SEM) analysis. Then, surface treated specimens were divided into 2 subgroups according to metal primer application. Zirconia core specimens were then layered with veneering porcelain and specimens were thermocycled up to 5000 cycles. Shear bond strength was measured and samples were examined under a stereomicroscope. After the test, one representetive sample from each group was examined by SEM and Energy Dispersive x-ray Spectroscopy (EDS) analysis. Shear bond strength data were analyzed with two-way ANOVA and Benferroni post hoc tests, surface roughness data were analyzed with one-way ANOVA and Tukey's post hoc tests (p<0.05). According to the results, metal primer application increased bond strength in all groups. While the sandblasting (with or without metal primer) demonstrated significantly higher bond strength values than all the other surface treatment methods (p<0.05), the lowest value was observed in the control group without metal primer. Different types of lasers created different bond strength values. Ultrafast fiber laser applications (10W and 20W) with or without metal primer showed significantly higher bond strength than control (p<0.05). As a result, ultrafast fiber laser can be shown as an alternative to sandblasting to increase bonding values between zirconia and veneer ceramics. Keywords: Bonding, laser, porcelain, surface treatment, zirconia