Zirconia- and metal-based bridges – recommendations from prospective clinical trials

Advantages of all-ceramic materials over the traditional metal-ceramics include their tooth-resembling color and the enamel-like translucency. The high-strength ceramic zirconia has the potential to be applied as an alternative material to metal for the fabrication of frameworks for FDPs. Several clinical studies showed promising results of FDPs with zirconia frameworks after observation periods of 3 to 5 years. In these investigations low fracture rates of zirconia frameworks, ranging from 0% to 2.2%, were reported. The reasons for failures of FDPs were primarily biological complications like secondary caries or technical complications like fracture of the veneering ceramic. Interestingly, these are the same types of complications leading to the loss of metal-ceramic FDPs. Therefore, it may be assumed that reconstructions with zirconia frameworks may lead to a similar clinical outcome like the ones with metal framework. Results of a recent randomized controlled clinical trial of posterior FDPs with zirconia and metal frameworks indeed showed similar survival rates for both types of FDPs. Yet, differences of the technical outcomes were observed. Zirconia-ceramic FDPs tended to exhibit more chippings of the veneering ceramic, always associated with occlusal roughness of the ceramic. Furthermore, more problems with the fit were found at zirconia-ceramic FDPs. In order to reduce these clinical problems several factors need to be considered. Abutment tooth preparation, framework design, cementation, and occlusal adjustment need to be adapted to the new CAD/CAM- manufactured ceramic reconstructions.