Bond strength enhancement of zirconia-porcelain interfaces via Nd:YAG laser surface structuring

Objectives: The aim of this study was to evaluate the effect of laser surface structuring on the bond strength of feldspar-based porcelain to zirconia, as compared to conventional sandblasting treatment. Materials and methods: Thirty cylindrical zirconia substrates, previously sintered, were divided in three groups according to the type of surface conditioning: 1) sandblasting with 50 mu m Al2O3; 2) laser structuring (phi 25 mu m holes); and 3) laser structuring (phi 50 mu m holes). Porcelain was injected onto the zirconia substrates. X-ray diffractometry (XRD) was used to evaluate the influence of the laser treatment on zirconia crystallographic phases. Shear bond strength test was performed. Micrographs using SEM were used to evaluate the zirconia surface after each surface treatment and to evaluate the fracture surface after the shear test. Results: The laser-structured groups presented the highest shear bond strength (65 +/- 16 MPa and 65 +/- 11 MPa, for the 25 mu m and 50 mu m holes, respectively). The sandblasting samples presented shear bond strength of 37 +/- 16 MPa. XRD analysis showed that there was no phase transformation on the thermally affected surface due to laser action. Microcracks were created at some holes due to the high temperature gradient generated by laser. Significance: Laser structuring significantly increased (up to 75%) the shear bond strength of zirconia to veneering porcelain as compared to conventional sandblasting treatment. Therefore, laser structuring arises as a surface conditioning method for producing stronger and long lasting zirconia-porcelain interfaces.