Fracture toughness mode mixity at the connectors of monolithic 3Y-TZP and LS2 dental bridge constructs

Most dental ceramics are produced from partially crystallized glass. Even though these materials are hard, they are extremely susceptible to damage, especially due to the glass phase content. A strategy for strengthening these materials makes use of their microstructure to form reinforcing sites within the structural design. Such approach has potential for application with lithium disilicate (LS2) glass–ceramics, which contain needle-form Li2Si2O5 crystals that deflect oncoming cracks. By press injection of the glass melt through specifically oriented injection channels, crystals are aligned in patterns that lead to high mechanical anisotropy. Here we apply this approach in the context of monolithic dental bridges simulated by beams under 3-point bending. Notches at different distances from the midspan play the role of connectors, and the mixed-mode fracture toughness is measured at varying positions for a LS2 and a 3Y-TZP material. A strong anisotropic fracture behavior is obtained with the LS2 glass–ceramic through local crystal alignment, leading to fracture energies higher than for the isotropic 3Y-TZP ceramic. Further, the anisotropic nature of the LS2 microstructure is successfully reproduced in dental bridge geometries, validating the use of bending beams for the study of the mechanical behavior of ceramic dental bridges.