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

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

PURPOSE: 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.

MATERIAL AND METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.