Do Zirconia-based Restorations Chip more often than Metal-based Restorations – Perception versus Evidence Zirconia- and metal-based bridges – recommendations from prospective clinical trials
I. SAILER, University of Zürich, Center for Oral and Dental Medicine, Zürich, Switzerland
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.
What can failed clinical restorations tell us?
S.S. SCHERRER, Universite de Geneve, Geneva, Switzerland This presentation will outline the application of descriptive (qualitative) fractography for clinical failure analysis of ceramic restorations to understand the failure event and assessing design or processing inadequacies. The fracture surface topography of clinically failed ceramic restorations including core materials (alumina, zirconia, lithium disilicate), and veneering ceramic chips for alumina, alumina-zirconia glass-infiltrated and PFM will be presented. Based on the recognition of fractographic features via microscopic means, maps of the crack path are generated reconstructing the sequence of the fracture event with identification of the location of the crack initiation site. Interesting findings with clinically relevant information as well as design and processing issues will be discussed.
How can zirconia-based restorations be improved? – Results from laboratory studies
M.V. SWAIN, University of Otago, Dunedin, New Zealand
Objective: This investigation sought to identify the basis of chipping of porcelain veneering materials on zirconia based restorations, which have opened up novel opportunities for clinicians involved in major crown and bridge cases, because of their excellent mechanical, aesthetic and biocompatibility properties. However over the past few years there have been increasing reports of chipping problems of the veneering porcelain, far in excess of traditional porcelain fused to metal systems. Methods: The thermo-elastic basis for residual stresses and the influence of cooling rate and specimen size will be considered. Zirconia and alumina plates 10 by 20 mm and 0.6 mm thick veneered with appropriate porcelains (e.max Ceram, IvoclarVivadent) and (VM7, Vita Zahnfabrik) of various thicknesses (0.5 to 2.5 mm) and subjected to different cooling rates were investigated. Vickers indentations from 5 to 30 N were placed on the surface of veneering porcelain and the size of the cracks measured. Results: Length of radial cracks were smaller for rapidly cooled specimens for the porcelain on both alumina and zirconia copings indicative of surface compressive residual stresses. Only for the porcelain fused to the rapidly cooled zirconia coping samples was unstable cracking within the veneering porcelain observed. Conclusion: The results are interpreted in terms of the thermo-elastic analysis developed. Suggestions to improve processing of zirconia based restorations by technicians and adjustment procedures by clinicians to minimise chipping are also considered.
Survival of Zircona- and Metal-supported bridges – A Systematic Review
S. HEINTZE, Ivoclar Vivadent, Schaan, Liechtenstein
Several clinical studies with data up to 5 years reported on a high prevalence of chipping of the ceramic veneer material of zirconia-supported fixed partial dentures (FPD) which is higher when the data are compared to metal-supported FPDs. On the other hand the fracture of the framework was a rare event to date. The question are: (1) Do zirconia-supported FPDs really chip more often than metal-supported FPDs or (2) If this is true may the higher chipping rate be due to the fact that the investigators are more attentive and register every small chip which in fact does not hamper function and aesthetics of the restoration ? It seems overdue to systematically analyse clinical studies related to zirconia-supported FPDs and compare the data with clinical studies on metal-supported restorations. For that purpose the medical/dental database provided by PubMed as well as published abstracts of scientific meetings will be searched for clinical studies on zirconia- and metal supported FPDs. The inclusion criteria are: (1) prospective clinical trial of at least 2 years, (2) report on technical failures like fracture of the framework and/or chipping of the veneer material and its extent, (3) replacement of FPD due to fracture/chipping.
