Failure of All-ceramic Fixed Partial Dentures in vitro and in vivo: Analysis and Modeling

Abstract

Hertzian cone cracks visible at the loading site of 20 all-ceramic fixed partial dentures (FPDs), tested in vitro, led to the hypotheses that failure was due to the propagation of localized contact damage crack systems (Hertzian stress state) and that such damage was an unlikely clinical failure mode. Fractographic analysis of the 20 laboratory-failed and nine clinically-failed all-ceramic FPDs allowed for definitive testing of these hypotheses and a comparison between in vitro and in vivo failure behavior. In all cases, failure occurred in the FPD connectors (none from contact damage), with approximately 70 to 78% originating from the interface between the core and veneer ceramics. The coincidence between failure origins provides strong evidence that the in vitro test modeled aspects of structural behavior having clinical importance. The fractographic observations, coupled with the in vitro failure load data, furnished very specific boundary conditions which were applied to constrain mathematical models of FPD connector failure. Finite element analysis (FEA) of the laboratory FPDs found that maximum principal tensile stresses would occur at locations consistent with the fractographic observations only if: (1) there were appropriate elastic moduli differences between the ceramics; and (2) a small amount of abutment rotation was allowed. Weibull failure probability (Pf) calculations, incorporating FEA stress profiles, very closely replicated the laboratory failure distribution only when: (1) the veneer ceramic was much weaker than the core ceramic; and (2) the Weibull modulus of the core-veneer interface was much lower than that for the free veneer surface (i.e., the interface is of lower quality with regard to defects).(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical performance and wear characteristics of veneered lithia-disilicate-based ceramic crowns

“…It is uncertain whether data obtained from the in vitro studies are clinically relevant [16,17]. Wear is a progressive phenomenon associated with several factors [18].…”

Bond Strength, Microhardness, and Core/Veneer Interface Quality of an All-Ceramic System

“…[5][6][7] Core ceramics are generally high elastic modulus, high strength materials compared with veneering ceramics. Stress distributions and failure behavior are different in laminate structures, comprised of materials with different elastic properties, than in homogenous structures.…”

“…3 In addition, studies testing the porcelain-to-metal bond strength suggest that shear bond strength (SBS) equal to the shear strength of the veneering porcelain provided an adequate bond. 4 In a study by Kelly et al 5 on the failure behavior of In-Ceram fixed partial dentures, it was reported that failure occurred in the connectors, none from contact damage, with approximately 70% to 78% originating from the core/veneer interface, indicating that the interface was a location of high tensile stress, in part due to the elastic modulus mismatch across the interface and the presence of structural flaws. The survival of multimaterial clinical structures is also influenced by material thickness ratios, geometric design factors, processing variables, thermal properties, and mechanical and elastic properties of component materials.…”

“…Many authors agree that the core/veneer interface is one of the weakest links of layered all-ceramic restorations and has a significant effect on the restoration success. [5][6][7][11][12][13] Hardness is one of the most frequently measured properties of a ceramic. Its value helps to characterize resistance to deformation, densification, and fracture.…”

“…[5][6][7] Three veneering materials have been developed for In-Ceram cores, and no authors have compared them. This study was designed to evaluate three core/veneer combinations in terms of bond strength, microhardness, and interface quality, as the veneering material can greatly influence the longevity, wear, and esthetics of all-ceramic systems.…”