EVALUATION OF SHEAR BOND OF TWO PRESSABLE GLASS CERAMICS TO THEIR VENEERING MATERIALS (IN VITRO STUDY)

INTRODUCTION: The bond between the veneering ceramic and the substructure is important for the long-term survival of the restorations. However, the shear bond strength (SBS) of heat-pressed ceramic substructures to veneering ceramic materials remains unclear. AIM OF STUDY: This study aimed to evaluate the SBS and mode of failure of two heat-pressed glass ceramic substructures (lithium disilicate (LDS) and zirconia-reinforced lithium silicate (ZLS)) with their corresponding veneering ceramics. MATERIAL AND METHODS. Thirty glass ceramic disk-shaped specimens were fabricated from heat-pressed LDS and ZLS (n = 15) with a diameter of 10mm and a thickness of 3mm. LDS and ZLS specimens were veneered with fluorapatite glass ceramic (FLGC) and leucite-reinforced feldspathic porcelain (LFP), respectively. The veneering material was condensed in a mold and fired on the glass ceramic materials to form a disk with a diameter of 3mm and a thickness of 2mm. Specimens were subjected to shear force in a universal testing machine at a crosshead speed of 0.5 mm/minute until failure of the specimens. The failed specimens were examined under an optical microscope and a scanning electron microscope to analyze the mode of failure. Data were analyzed using independent t-test. RESULTS. LDS (29.75 MPa) showed a statistically significant higher shear bond strength than that ZLS (21.96 MPa) ( P value<.05). LDS group showed predominantly cohesive failure, while ZLS group showed mixed adhesive/cohesive failure. CONCLUSIONS. Zirconia-reinforced lithium silicate complex failed at lower load levels compared to the lithium disilicate complex. The predominantly cohesive failure mode in LDS specimens reflects the higher bond strength that surpassed the cohesive strength of the heat-pressed ceramic and the veneering material