August 24, 2005
Fixed partial dentures, or FPDs, used to be mixed blessing for most people. While they permanently filled in for missing teeth to ensure a firm bite, the prostheses typically were fabricated from metals that left a lot to be desired aesthetically. But the aesthetics of these devices took a giant leap forward a few decades ago with the arrival of all-ceramic FPDs that had an imperfect but more tooth-colored appearance. As dental researchers have sought both to improve upon the look of FPDs and make them more affordable to more patients, they have turned increasingly to zirconia, a well-known pure oxide processed in various forms from the minerals baddeleyite and zircon. A major sticking point has been existing technologies cannot make zirconia frameworks, or cores, as translucent as natural teeth, nor can they characterize or customize tooth shading. These shortfalls have led to the development of FPDs with zirconia cores overlaid with an enamel-like porcelain veneer. In the August issue of The Journal of Prosthetic Dentistry, NIDCR grantees evaluated a wide variety of these zirconia-porcelain FPD models, determining for each their tensile strength, elasticity, and failure modes, stresses, and loads. Interestingly, they found a substantially higher modulus of rupture than previously reported for other layered all-ceramic restoratives. The authors noted that their results highlight the critical importance of core thickness to the durability of these devices. They also said their data show the need to use an unveneered core in areas of high tensile stress.