Mechanical and microstructural characterization of monolithic zirconia and lithium disilicate and study of step stress accelerated life testing of crowns with different ceramic thickness

Abstract

Chipping of veneer porcelain is a recurrent problem in all-ceramic systems with yttria-stabilized tetragonal zirconia (Y-TZP). In order to eliminate the necessity of porcelain veneering, high translucency Y-TZP has been introduced, which as well as lithium disilicate, were developed for monolithic indication. However, the mechanical behavior of these new materials under fatigue and the minimum thickness recommended are still uncertain. Thus, the aim of this study is to assess two types of zirconia (Prettau and Prettau Anterior) and a lithium disilicate (IPS e.max CAD) through microstructural and mechanical analysis, and step stress accelerated life testing both in flat specimens and in crowns, varying the material thickness. To characterize the materials, biaxial flexural strength (n=15), scanning electron microscopy and x-ray diffraction will be performed. Flat specimens (discs) will be made at thickness of 1 mm and 1.5 mm to each material, which will be cemented on an epoxy resin substrate. Premolar crowns with different thickness will be designed in a specific software and milled by CAD/CAM technology, being cemented on the resin epoxy prototype of the prepared tooth. The flat specimens (n=24) and crowns (n=24) will be submitted to step stress accelerated life testing and after, the distribution of the failures and probability of survival will be compared by Weibull analysis. Fractography analysis will be performed to identify the type and origin of the fracture. (AU)