Load-bearing properties of minimal-invasive monolithic lithium disilicate and zirconia occlusal onlays: Finite element and theoretical analyses

AbstractObjective m of this study was to test the hypothesis that monolithic lithium disilicate glass-ceramic occlusal onlay can exhibit a load-bearing capacity that approaches monolithic zirconia, due to a smaller elastic modulus mismatch between the lithium disilicate and its supporting tooth structure relative to zirconia. s c occlusal onlays of various thicknesses cemented to either enamel or dentin were considered. Occlusal load was applied through an enamel-like deformable indenter or a control rigid indenter. Flexural tensile stress at the ceramic intaglio (cementation) surface—a cause for bulk fracture of occlusal onlays—was rigorously analyzed using finite element analysis and classical plate-on-foundation theory. s onded to enamel (supported by dentin), the load-bearing capacity of lithium disilicate can approach 75% of that of zirconia, despite the flexural strength of lithium disilicate (400 MPa) being merely 40% of zirconia (1000 MPa). When bonded to dentin (with the enamel completely removed), the load-bearing capacity of lithium disilicate is about 57% of zirconia, still significantly higher than the anticipated value based on its strength. Both ceramics show slightly higher load-bearing capacity when loaded with a deformable indenter (enamel, glass-ceramic, or porcelain) rather than a rigid indenter. icance upported by enamel, the load-bearing property of minimally invasive lithium disilicate occlusal onlays (0.6–1.4 mm thick) can exceed 70% of that of zirconia. Additionally, a relatively weak dependence of fracture load on restoration thickness indicates that a 1.2 mm thin lithium disilicate onlay can be as fracture resistant as its 1.6 mm counterpart.