Threshold strength ceramic dental crowns by direct ink writing

Abstract

A functionally graded threshold strength dental ceramic consisting of a ZrO2 core coated with Al2O3 strengthened ZrO2 (ASZ) is produced by direct ink writing (DIW). The two materials are printed as a core-shell disk and co-sintered to induce a threshold stress caused by a mismatch in coefficient of thermal expansion (CTE). Biaxial flexure testing with a piston-on-3-ball procedure outlined in ISO 6872/2008 is used to assess the flexural strength of the composite disks alongside monolithic samples of the three constituent materials (ZrO2, Al2O3, and ASZ). The threshold strength ceramic possesses the greatest average flexural strength (670.22 ± 69.74 MPa) of the four materials tested, and possesses significantly greater flexural strength than several ceramics commonly used as crown materials. Additionally, Weibull analysis is used to provide a quantifiable metric for failure reliability, where the composite samples outperform the other tested materials in both Weibull modulus (m = 8.60) and characteristic strength (sigma0 = 737.15 MPa). In light of these results, functionally graded threshold strength ceramics produced via robocasting show great promise as potential dental ceramics.