13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- carried out in the attempt to explain the fragility of the porcelain. 2. Experimental procedure Two samples (designated “prosthesis #1 and #2”) of porcelain-veneered sintered zirconia restorations were supplied for analytical examination as examples of clinical failure. Fig.1 illustrates the failure mode primarily confined to the porcelain veneer and commonly referred to as “chipping”. Fig.1(a) shows the image of prosthesis #1 taken with the fractured unit when still mounted in the oral cavity (9, left maxillary central incisor), whilst Fig.1(b) shows a similar chipping failure in the veneering porcelain on the upper 1st molar. (a) (b) Figure 1 Porcelain-veneered sintered zirconia restoration. (a) fractured unit mounted in the oral cavity; (b) chipping failure on the upper 1st molar. Energy-Dispersive X-ray (EDX) analysis is a technique for surface examination conducted within the Environmental Scanning Electron Microscopy (ESEM) vacuum chamber and allows the determination of specific elemental composition at high spatial resolution. ESEM with EDX analysis was firstly carried out on the prosthesis samples (Fig. 1) to investigate the nature of interfacial bonding and fracture features in order to identify the crack initiation sites and propagation directions. To investigate further the fracture mechanism and material properties, nine cylindrical porcelain-veneered zirconia bars were fabricated, three of which (designated “bar #1-#3”) were fractured by three-point bending. The fractured surfaces were studied by ESEM, while the other six bar samples (designated “Vickers #1-#6”) were indented by Vickers hardness testing machine. The corresponding Vickers hardness and toughness values were evaluated with the aid of ESEM imaging. 3. ESEM characterization of prosthesis samples 3.1. Interfacial bonding EDX is useful in determining elemental distribution of materials, and thus the mutual elemental diffusion can be identified. In the present study, EDX analysis was conducted on the broken surfaces within the region shown in Fig. 2(a). The results indicate that the porcelain region contains a high overall concentration of O and silicon (Si), due to the high silica (SiO2) content. Notably, there is evidence of not only Si diffusing into the Zr-rich domain (Si map), but also zirconium (Zr) diffusing into the Si-rich porcelain domain (Zr map). This evidence of mutual elemental diffusion of Zr and Si reveals the origins of the good mechanical bonding observed between zirconia ceramic copings and porcelain veneers [11-13]. It is also worth noting that the studies of fracture surfaces of the sample supplied failed to identify prominent cases of adhesive fracture localized along the
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