Shear bond strength of resin luting material to zirconia using a pre-sintered coating approach

PURPOSE: The effect of a feldspathic porcelain coating applied before or after zirconia sintering on the shear bond strength between a resin luting agent and zirconia was evaluated. METHODS: Pre-sintered and fully sintered zirconia specimens were coated with feldspathic porcelain and divided into three surface treatment groups: no treatment, airborne-particle abrasion, and hydrofluoric acid etching. The specimens were bonded using a dual-polymerizing resin luting agent and subjected to 0 or 5,000 thermocycles. The shear bond strength was measured. The fracture modes were analyzed microscopically. The surface morphology and composition were examined by scanning electron microscopy (SEM) and X-ray diffraction. RESULTS: Before thermocycling, both airborne-particle abrasion and hydrofluoric acid etching significantly increased the bond strength compared with no treatment. After thermocycling, airborne-particle abrasion maintained the highest bond durability, while hydrofluoric acid etching showed a marked decrease. SEM revealed that airborne-particle abrasion produced a rough surface favorable for micromechanical retention, whereas hydrofluoric acid etching resulted in smoother morphology. CONCLUSION: Airborne-particle abrasion effectively enhanced and preserved the bond strength between the resin luting agent and feldspathic porcelain-coated zirconia, regardless of the coating sequence. Hydrofluoric acid etching was ineffective after thermocycling, likely due to surface precipitation that occurred during firing.