Three-Point Bending Tests of Zirconia Core/Veneer Ceramics for Dental Restorations

Introduction. The mechanical strength and the surface hardness of commercially available yttrium-doped zirconia were investigated. Furthermore, a comparative study of eight different ceramic veneers, to be used for the production of two-layered all-ceramic restorative systems, was carried out. Materials and Methods. Four types of zirconia specimens were analyzed, according to a standard ISO procedure (ISO 6872). Besides, two-layered zirconia-veneer specimens were prepared for three-point bending tests. Results. A strong effect of the surface roughness on the mechanical strength of zirconia specimens was observed. Finally, a comparative study of eight commercially available veneering ceramics shows different modes of failure between the selected veneers. Conclusion. The results indicate that close attention should be paid to the preparation of zirconia-based crowns and bridges by CAD/CAM process, because surface roughness has an important effect on the mechanical strength of the material. Finally, the results of the mechanical tests on two-layered specimens represent an important support to the choice of the veneering ceramic. 1. Introduction The use of advanced ceramics as restorative dental materials is strongly increasing, owing to the introduction of Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) milling techniques which allow the fabrication of large and complex restorations with very high-dimensional accuracy [1, 2]. The most promising production method consists in a soft machining of presintered blocks, which are subsequently sintered at high temperature [3]. As a final step, sintered structures are usually coated using veneering ceramics, in order to obtain two-layered all-ceramic restorative systems with very attractive mechanical properties, good biocompatibility, and excellent esthetic results [4]. Among the ceramic materials for dental applications, the zirconia-based ones are very widespread, because of their transformation toughening capabilities [5, 6]. The aim of the present study is to analyze the mechanical behavior of commercially available Y-TZP ceramics for dental applications and to estimate the effects of different processing conditions, which usually occur during production by CAD/CAM techniques. In addition to this, eight commercially available ceramic veneers, to be used for the production of all-ceramic restorations in combination with Y-TZP structures, were analyzed by using three-point bending tests on two-layered specimens. Finally, a systematic comparative analysis of the eight selected ceramic veneers was