Comparison of the fit accuracy of zirconia-based prostheses generated by two CAD/CAM systems

Abstract

Purpose: The purposes of this study are to evaluate the internal and marginal adaptation of two widely used CAD/CAM systems and to study the effect of porcelain press veneering process on the prosthesis adaptation.

Materials and methods: Molar of a lower jaw typodont resin model was prepared by adjusting a 1.0 mm circumferential chamfer, an occlusal reduction of 2.0 mm, and a 5° convergence angle and was duplicated as an abrasion-resistant master die. The monolithic crowns and copings were fabricated with two different CAD/CAM system-Ceramil and Zirkonzahn systems. Two kinds of non-destructive analysis methods are used in this study. First, weight technique was used to determine the overall fitting accuracy. And, to evaluate internal and marginal fit of specific part, replica technique procedures were performed.

Results: The silicone weight for the cement space of monolithic crowns and copings manufactured with Ceramil system was significantly higher than that from Zirkonzahn system. This gap might cause the differences in the silicone weight because the prostheses were manufactured according to the recommendation of each system. Marginal discrepancies of copings made with Ceramil system were between 106 and 117 µm and those from Zirkonzahn system were between 111 and 115 µm. Marginal discrepancies of copings made with Ceramil system were between 101 and 131 µm and those from Zirkonzahn system were between 116 and 131 µm.

Conclusion: Marginal discrepancy was relatively lower in Ceramil system and internal gap was smaller in Zirkonzahn system. There were significant differences in the internal gap of monolithic crown and coping among the 2 CAD/CAM systems. Marginal discrepancy produced from the 2 CAD/CAM systems were within a reported clinically acceptable range of marginal discrepancy.

Keywords: Fit accuracy; Press-over technique; Replica technique; Weight technique.

Fig. 1. Master die.

Fig. 2. (A) Scan of stone die, (B) Monolithic crown design, (C) Coping design, (D) Porcelain veneering form design, (E) Superposition of coping and porcelain veneering forms.

Fig. 3. (A) Silicone films representing the space between the abutment teeth and prosthesis, (B) Stabilized replica after segmentation in the bucco-lingual direction, (C) Measuring points of the cut silicone replica, (D) Microscopic crosssectional photograph of a replica showing the distances used to assess marginal accuracy.

Fig. 4. Silicone weights (mg). Initial: Before porcelain veneering, Final: After porcelain veneering.

Fig. 5. Internal and marginal gaps (µm) of monolithic crowns, simple copings and copings with porcelain veneering.