Evaluation of the ceramic liner bonding effect between zirconia and lithium disilicate

Little information is available for the strength of bonding between zirconia and lithium disilicate as affected by surface pretreatment methods.

The purpose of this in vitro study was to investigate the shear bond strength (SBS) between zirconia core and lithium disilicate (LS₂) veneered ceramic after surface pretreatments.

Fully sintered yttrium oxide partially stabilized tetragonal zirconia (Y-TZP) disk specimens were fabricated from zirconia ceramic materials. Specimens were divided into 4 groups with surface pretreatments applied (the as-received group, the liner group, the airborne-particle abrasion group, and the airborne-particle abrasion-plus-liner group). After pressing LS₂ on a zirconia disk, shear force was applied perpendicular to the zirconia-LS₂ interface. Data were analyzed using 2-way ANOVA and Tukey test (α=.05). For each group, the failure modes were measured by using optical microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction.

Airborne-particle abrasion induced significantly lower interfacial strength between zirconia and lithium disilicate (P<.05). After airborne-particle abrasion of the surface, the increased monoclinic volume fraction and reduced coefficient of thermal expansion of zirconia may weaken the interfacial strength between zirconia and LS₂. The liner treatment significantly improved the adhesion between zirconia core and veneering LS₂ (P<.05). The SBS values decreased in the following order: liner group > airborne-particle abrasion-plus-liner group > airborne-particle abrasion group. The interfacial image of zirconia and LS₂ showed a fusion of crystal structure between the 2 materials. Some components of the silica-containing glass-ceramic liner led to an increase in SBS as diffusion occurred on the zirconia surface.

The bond strength between zirconia and veneering LS₂ was significantly increased by application of silica-containing glass-ceramic liner but was decreased with airborne-particle abrasion.