Clinically relevant approach to failure testing of all-ceramic restorations

Statement of problem. One common test of single-unit restorations involves applying loads to clinically realistic specimens through spherical indenter s, or equivalently, loading curved incisal edges against flat compression p latens. As knowledge has become available regarding clinical failure mechan isms and the behavior of in vitro tests, it is possible to constructively q uestion the clinical validity of such failure testing and to move toward de veloping more relevant test methods. Purpose. This article reviewed characteristics of the traditional load-to-f ailure test, contrasted these with characteristics of clinical failure for all-ceramic restorations, and sought to explain the discrepancies. Literatu re regarding intraoral conditions was reviewed to develop an understanding of how laboratory testing could be revised. Variables considered to be impo rtant in simulating clinical conditions were described, along with their re cent laboratory evaluation. Conclusions. Traditional fracture tests of single unit all-ceramic prosthes es are inappropriate, because they do not Create failure mechanisms seen in retrieved clinical specimens. Validated tests are needed to elucidate the role(s) that cement systems, bonding, occlusion, and even metal copings pla y in the success of fixed prostheses and to make meaningful comparisons pos sible among novel ceramic and metal substructures. Research over the past 6 years has shown that crack systems mimicking clinical failure can be produ ced in all-ceramic restorations under appropriate conditions.