Marginal accuracy of titanium copings fabricated by casting and CAD/CAM techniques

Abstract

Statement of problem: Advances in computer-aided design/computer-assisted manufacturing (CAD/CAM) technology purportedly enhance the marginal fit of dental restorations. However, little information is available on the marginal accuracy of restorations manufactured with various CAD/CAM systems.

Purpose: The purpose of this study was to evaluate and compare the marginal accuracy and refinement time of titanium copings fabricated by 3 different CAD/CAM systems relative to standard casting techniques.

Material and methods: Sixty-four stone die duplicates of a human maxillary central incisor, prepared for a metal-ceramic crown, with a uniform chamfer design, were divided into 4 groups (n=16). The specimens were restored with titanium copings using CAD/CAM systems Pro 50 (PRO), DCS (DCS), and Everest (EVE). A conventional titanium casting technique, Biotan (BIO), served as a control. Vertical and horizontal discrepancies between restoration margins and the preparations were each measured before and after manual refinement. This refinement was completed using a disclosing agent and by removing the internal positive defects of the copings. The marginal discrepancies of the copings were evaluated at 4 standard areas using 10 measurements, for a total of 160 measurements of each margin. Repeated-measures ANOVA was used for analyzing marginal accuracy. The coping refinement time was analyzed with the Kruskal-Wallis and post hoc Wilcoxon rank sum tests (alpha=.05).

Results: The marginal discrepancies (microm) ranged from 32.9 to 127.8 before and from 3.4 to 58.4 after the manual refinement of copings. Manual refinement significantly improved the marginal accuracy (P<.0001) when compared with the initial fabrication. The relative (%) gain of marginal accuracy was PRO, 74.1%; DCS, 69.7%; EVE, 68.7%; and the control, BIO, 69.2%. The median duration of manual refinement time in minutes was 6.0 for PRO, 9.5 for DCS, 4.0 for EVE, and 4.0 for BIO (Kruskal-Wallis-test: P<.0001).

Conclusion: Manual adjustment significantly improves the marginal accuracy of CAD/CAM system-fabricated titanium copings. The highest marginal accuracy was achieved with the DCS system, using a longer refinement time.