β Scribed by Moustafa N. Aboushelib; Albert J. Feilzer; Niek de Jager; Cornelis J. Kleverlaan
No coin nor oath required. For personal study only.
Introduction: A general trend in all ceramic systems is to use veneering ceramics of slightly lower thermal expansion coefficients compared with that of the framework resulting in a positive mismatch in thermal expansion coefficient (+ΞTEC). The concept behind this TEC mismatch is to generate compressive stresses in the weaker veneering ceramic and thus enhance the overall strength of the restoration. This technique had excellent results with porcelain fused to metal restorations (PFM). However, there are concerns to apply this concept to allβceramic restorations. The aim of this research was to determine the stresses in bilayered allβceramic restorations due to the mismatch in TEC. Materials and methods: Two commercial veneering ceramics with a TEC lower than that of zirconia (+ΞTEC); NobelRondo zirconiaβ’ and Lava Ceramβ’, plus one experimental veneering ceramic with an identical TEC that matches that of zirconia (ΞTEC = 0) were used to veneer zirconia discs. The specimens were loaded in biaxial flexure test setup with the veneer ceramic in tension. The stresses due to load application and TEC mismatch were calculated using fractography, engineering mathematics, and finite element analysis (FEA). Results: In this study, the highest load at failure (64 N) was obtained with the experimental veneer where the thermal mismatch between zirconia and veneering ceramic was minimal. For the two commercial veneer ceramics the magnitude of the thermal mismatch localized at the zirconia veneer interface (42 MPa) exceeded the bond strength between the two materials and resulted in delamination failure during testing (ca. 50 MPa). Significance: For allβceramic zirconia veneered restorations it is recommended to minimize the thermal mismatch as much as possible. Β© 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008
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