Comparison and evaluation of marginal and internal gaps in cobalt–chromium alloy copings fabricated using subtractive and additive manufacturing

Purpose To evaluate the marginal and internal gaps of cobalt–chromium (Co–Cr) alloy copings fabricated using subtractive and additive manufacturing. Methods A study model of an abutment tooth 46 was prepared by a 2-step silicone impression with dental stone. Fifteen stereolithography files for Co–Cr alloy copings were compiled using a model scanner and dental CAD software. Using the lost wax (LW), wax block (WB), soft metal block (SMB), microstereolithography (μ-SLA), and selected laser melting (SLM) techniques, 15 Co–Cr alloy copings were fabricated per group. The marginal and internal gaps of these Co–Cr alloy copings were measured using a digital microscope (160×), and the data obtained were analyzed using the non-parametric Kruskal–Wallis H-test and post-hoc Mann–Whitney U-test with Bonferroni correction. Results The mean values of the marginal, axial wall, and occlusal gaps were 91.8, 83.4, and 163 μm in the LW group; 94.2, 77.5, and 122 μm in the WB group; 60.0, 79.4, and 90.8 μm in the SMB group; 154, 72.4, and 258 μm in the μ-SLA group; and 239, 73.6, and 384 μm in the SLM group, respectively. The differences in the marginal and occlusal gaps between the 5 groups were statistically significant (P <.05). Conclusions The marginal gaps of the LW, WB, and SMB groups were within the clinically acceptable limit, but further improvements in the μ-SLA and SLM approaches may be required prior to clinical implementation.