Influence of Tooth Preparation Design on Fitting Accuracy of CAD-CAM Based Restorations.

Abstract

The purpose of this study was to evaluate the marginal fit of different zirconia and metal frameworks and compare them with each other on different finish line configurations. 20 stainless steel dies 10 with shoulder and 10 with chamfer finish line including 6 mm preparation height and 3 degree axial angle simulating a 6 degree total occlusal covergence of the prepared tooth were produced. After embedding the each group of die into the arch-shaped acrylic resin blocks, impressions were made using silicone based impression material and 120 casts were prepared subsequently. The dies were divided into six groups each having 20 specimens (10 with shoulder, 10 with chamfer finish line). Group CM consisted of Co-Cr produced by conventional casting procedure, group MM of Co-Cr prepared by metal milling, group LM of Co-Cr prepared by direct laser metal sinterization (DLMS), group ZZ of Zirkonzahn (Zirkonzahn GmbH, Gais, Italy), group LZ of Lava Zirconia (3 M ESPE Dental AG, Seefeld, Germany) and group DZ of DC-Zirkon (DCS Dental AG, Allschwil, Switzerland). Stereomicroscope were used to evaluate the marginal fit of frameworks and marginal gap values obtained from the images were analyzed using Mann-Whitney U Test and Kruskal-Wallis H Test with Bonferroni correction. The lowest value of marginal gap was identified in the samples from the LZ group and the highest value was identified in those from ZZ in both finish lines. The effect of finish lines was not significant for most groups but CM frameworks with chamfer finish lines and the DZ frameworks with shoulder finish lines showed significantly lower marginal gap values. The marginal gaps of the various tested zirconia and metal framework were within the range of clinical acceptability (120 µm). The results of this in vitro study suggest that margin preparation design and type of zirconia and metal framework materials for various CAD-CAM systems have a significant effect on marginal fit of the resulting restorations. (J Esthet Restor Dent 28:238-246, 2016).