Fracture toughness of veneering ceramics for fused to metal (PFM) and zirconia dental restorative materials

Abstract

Veneering ceramics designed to be used with modern zirconia framework restorations have been reported to fracture occasionally in vivo. The fracture toughness of such veneering ceramics was measured and compared to that of conventional feldspathic porcelain veneering ceramics for metal framework restorations. The fracture toughness of the leucite free veneer was measured to be 0.73 MPa m ± 0.02 MPa m, which is less than that for the porcelain fused to metal (PFM) veneering ceramic: 1.10 MPa ± 0.2 MPa. (Uncertainties are one standard deviation unless otherwise noted.) The surface crack in flexure (SCF) method was suitable for both materials, but precrack identification was difficult for the leucite containing feldspathic porcelain PFM veneer.

A fractographic study of clinically retrieved zirconia–ceramic and metal–ceramic fixed dental prostheses

“…Two mechanical properties, strength and fracture toughness, are pertinent to crack evolution in ceramics. Even though the strength of the two tested porcelain veneering ceramics are similar (~70 MPa) [48], the fracture toughness of the overlay porcelain for metal (1.10 MPa √m ± 0.13 MPa √m) is significantly greater than that of the veneering porcelain for zirconia (0.73 MPa √m ± 0.02 MPa √m) [49]. The lower fracture toughness leads to decreased resistance to crack propagation in porcelain fused to zirconia, suggesting that zirconia–ceramic FDPs have higher chipping rate and larger chipping size relative to metal–ceramic FDPs.…”

“…Typically the CTE of veneer is slightly smaller than that of metal coping, but the difference is no greater than 1 ppm K− 1 . Although the CTE mismatch in the current metal–ceramic and zirconia–ceramic systems are similar, which is only 0.5 ppm K− 1 [47,50], the low thermal diffusivity property of zirconia framework could alter the distribution of thermal stresses in porcelain veneer [49,51]. Baldassarri et al used the Vicker indentation method to estimate the magnitude and orientation of residual stresses in hand build-up zirconia–ceramic FDPs [52].…”

Finite Element Analysis of the Influence of Geometry and Design of Zirconia Crowns on Stress Distribution

“…Despite the known advantages of the bilaminate systems composed of Y‐TZP and porcelain, these systems still experience failures. These failures can be associated with diverse factors: low fracture toughness and thickness of the porcelain, inconsistency or differences in thermal expansion between materials, inadequate cooling rate, processing techniques, phase transformation, low thermal diffusivity of Y‐TZP, and insufficient support of the porcelain by the infrastructure . The present study focused on the thickness, shape, and support of the ceramics.…”

“…Investigators have studied several factors in an attempt to better understand these failures . In the study of restorative materials by in vitro tests, the results with specimens having simplified formats were reported to be constant .…”

Effect of the Cooling Rate on the Properties of Veneer Porcelain for Zirconia Dental Prosthesis

“…Nevertheless, some authors have pointed that porcelain with a higher content of leucite has higher fracture toughness 20,27,32 . According to Mackert Jr. et al 33 , the quantity, average size and structure of the crystalline phase can directly affect the mechanical properties of the final product.…”