Effects of surface pre-treatment on shear bond strength between zirconia and lithium disilicate

Objectives: The purpose of this study was to investigate the shear bond strength (SBS) between zirconia core and lithium disilicate (LS₂) veneered ceramic after surface pre-treatments.
Methods: Fully-sintered yttrium oxide partially stabilized tetragonal zirconia (Y-TZP) disc specimens were fabricated from zirconia ceramic materials. Specimens were randomly divided into 4 groups with surface pre-treatments applied (as received group, sandblasting group, liner group, and sandblasting + liner group). After pressing of LS₂ on zirconia disc, shear force was applied perpendicular to the zirconia-LS₂ interface. For each group, the failure modes were measured by optical microscopy, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD), respectively.
Results: Sandblasting induced significantly lower interfacial strength between zirconia and lithium disilicate (P < .05). After sandblasting the surface, the increased monoclinic volume fraction and reduced coefficient of thermal expansion (CTE) of zirconia may weaken the interfacial strength between zirconia and LS₂. Liner treatment significantly improved the adhesion between zirconia core and veneering LS₂ (P < .05). The SBS values decreased in the order: “liner” group > “sandblasting + liner” group> “sandblasting” group. The interfacial image of zirconia and LS₂ showed a fusion of crystal structure between the two materials. Some components of the LS₂ glass ceramic-based liner are considered to be an increase in SBS as diffusion occurs on the zirconia surface.

Conclusions: The bond strength between zirconia and veneering LS₂ was significantly increased by application of LS₂ glass–ceramic based liner, but decreased by sandblasting.