Load-bearing capacity and the recommended thickness of dental monolithic zirconia single crowns

Purpose: The aim of this study was to evaluate the load bearing capacity and a reasonable thicknesss of dental monolithic zirconia crowns. Materials and methods: Polymethyl methacrylate (PMMA) abutment tooth specimens were made by CAD/CAM technic. Monolithic zirconia crowns (MZC), monolithic lithium disilicate crowns (MLC), layered zirconia crowns (LZC) and metal ceramic crowns(MCC), of which the occlusal thickness was 1.5 mm were thereafter fabricated and cemented on the abutment tooth specimens. MCC with occlusal thicknesses of 0.6 mm, 0.8 mm, 1.00 mm, 1.2 mm were also made. All specimens underwent load-to-fracture test. Weibull parameters (sigma 0) and (m) were calculated. Fracture modes were also evaluated. Results: The mean fracture load was 1863.16 +/- 116.81 for MLC, 2284.77 +/- 355.60 for MCC, 2308.0 +/- 510.94 for LZC, 4109.93 +/- 610.18 for MZC (1.5 mm), 3068.31 +/- 233.88 for MZC (1.2 mm), 2429.88 +/- 315.03 for MZC (1.0 mm), 1814.60 +/- 68.21 for MZC (0.8 mm) and 1308.38 +/- 111.38 for MZC (0.6 mm). The fracture load of MZC was significantly higher than MCC, LZC and MLC (P<0.05). The fracture loads for MCC with different thickness were significantly different (P<0.05). Similar trend was observed for the characteristic strength (sigma 0) and Weibull modulus (m). For MZC and MLC, the fracture mode was catastrophic failure. The predominant fracture mode for LZC was catastrophic fracture. The fracture loads of MZC(1.0 mm) and MCC were not statistically different (P >0.05). Conclusions: Monolithic zirconia crowns exhibit higher fracture loads than monolithic lithium disilicate crowns, layered zirconia crowns and metal ceramic crowns. The fracture resistance of monolithic zirconia crowns with a thickness of 1.0 mm can be equal to metal ceramic crowns. Doubling the monolithic zirconia core from 0.6 mm to 1.5 mm increases the fracture resistance of this restorative system threefold. (C) 2014 Elsevier Ltd. All rights reserved.