Marginal fit of alumina- and zirconia-based fixed partial dentures produced by a CAD/CAM system

Clinical long-term success of all-ceramic dental restorations can be signif icantly influenced by marginal discrepancies. As a result, this in vitro st udy evaluated the marginal fit of alumina and zirconia-based fixed partial dentures (FPDs) machined by the Precident DCS system. Different master stee l models of three-, four- and five-unit posterior FPDs with an 0.8 mm chamf er preparation were produced. FPDs made of DC-Zirkon and In-Ceram Zirconia core ceramics were machined by the Precident DCS system. The marginal fit o f the milled frameworks placed on the master steel models was determined by a replica technique using a light-body silicone to fill the discrepancies between crown and tooth and a heavy-body material to stabilize the light-bo dy impression material. The impressions were poured into an epoxy resin mat erial and each model was cross-sectioned with a low speed diamond saw to be tter visualize marginal discrepancies. The marginal fit of the FPDs was eva luated by scanning electron microscopy. The measurements of the marginal fi t exhibited mean marginal discrepancies in a range between 60.5 and 74.0 mu m, mean marginal gaps in a range from 42.9 to 46.3 mum, mean vertical discr epancies in a range from 20.9 to 48.0 mum and mean horizontal discrepancies in the range of 42.0 to 58.8 mum. Statistical data analysis was performed using the non-parametric test of Kruskal-Wallis and Mann-Whitney. The analy sis revealed no significant differences (p>0.05) between the mean marginal gaps and vertical and horizontal discrepancies. However, for some FPDs the mean values of the marginal discrepancies were significantly different (p l ess than or equal to0.05). The wide range of the measured values may be att ributed to the complex geometrical design of long span FPDs and difficultie s regarding the milling process of brittle ceramic materials. Based on the selection of 100 mum as the limit of clinical acceptability, the results of this study can conclude that the level of marginal fit for alumina- and zi rconia-based FPDs achieved with the Precident DCS system meet the clinical requirements.