Comparative Evaluation of the Shear Bond Strength of Different Core-Veneer Restorative Systems: An In Vitro Study

Introduction: Porcelain-fused-to-metal (PFM) systems have long been the gold standard for fixing partial dentures (FPDs).The bond between the ceramic and the core depends on various factors, such as the oxide layer, the thermal expansion coefficients, and the alloy's microstructure.The longevity of any bilayer restoration depends critically on the bond strength between the aesthetic porcelain and the underlying core material.Given that the interfacial bond strength dictates the clinical survival of bilayer restorations, this study evaluated and compared the nominal shear bond strength across four distinct core-veneer restorative systems.Methodology: A total of 40 standardised rectangular specimens (25 mm × 3 mm × 0.5 mm) of different alloy combinations were fabricated and equally divided into four groups.Group 1 is conventional cast Ni-Cr alloy, Group 2 is conventional cast Co-Cr alloy, Group 3 is direct metal laser sintered (DMLS) Co-Cr alloy, and Group 4 is CAD/CAM milled zirconia.Conventional Ni-Cr (Group 1) and Co-Cr (Group 2) core alloy specimens were fabricated using rectangular wax patterns obtained from smooth casting wax sheets of 0.5 mm thickness.Porcelain buildup was applied to all specimens in the central 8 mm, leaving 8.5 mm on either side, to a uniform thickness of 1 mm, followed by a ceramic firing cycle as recommended by the manufacturer.Each prepared specimen of veneered porcelain with core structure was subjected to shear force at a crosshead speed of 1mm/min on a universal testing machine (UTM).Loading was done till fracture occurred.The shear bond strength was calculated in megapascals (MPa).Results: Maximum shear bond strength of 25.67 MPa was observed in Group 1, while a minimum of 2.54 MPa was observed in Group 2. To compare all groups, a one-way ANOVA was performed, which revealed a highly significant difference (p < 0.001) among the study groups.To make individual pairwise comparisons, Tukey's HSD post-hoc test was applied.This test revealed a highly significant difference in the mean shear bond strength between Group 1 and all other study groups.However, the comparison among all remaining study groups was not statistically significant.Conclusion: Within the limitations of this in vitro study, the conventional Ni-Cr/IPS classic system had higher baseline nominal shear bond strength compared to the other core-veneer systems under immediate loading conditions.Because each restorative group utilised material-specific interfacial bonding protocols and distinct veneering ceramics, these findings reflect integrated system-level performance rather than isolated intrinsic core properties.Furthermore, the reported bond values represent nominal, unaged baseline values obtained without failure-mode classification.Long-term studies incorporating artificial ageing, cyclic fatigue loading, and fractographic analysis are essential before clinical recommendations can be drawn.