Effect of different tooth preparation designs on the marginal and internal fit discrepancies of cobalt-chromium crowns produced by computer-aided designing and selective laser melting processes

PURPOSE: To evaluate the impact of five different tooth preparation designs on the marginal and internal fit discrepancies of cobalt-chromium (CoCr) crowns produced by computer-aided designing (CAD) and selective laser melting (SLM) processes. MATERIALS AND METHODS: Five preparation data were constructed, after which design crowns were obtained. Actual crowns were fabricated using an SLM process. After the data of actual crowns were obtained with structural light scanning, intaglio surfaces of the design crown and actual crown were virtually superimposed on the preparation. The fit-discrepancies were displayed with colors, while the root means square was calculated and analyzed with one-way analysis of variance (ANOVA), Tukey’s test or Kruskal-Wallis test (α =.05). RESULTS: The marginal or internal color-coded images in the five design groups were not identical. The shoulder-lip and sharp line angle groups in the CAD or SLM process had larger marginal or internal fit discrepancies compared to other groups (P < .05). In the CAD process, the mean marginal and internal fit discrepancies were 10.0 to 24.2 µm and 29.6 to 31.4 µm, respectively. After the CAD and SLM processes, the mean marginal and internal fit discrepancies were 18.4 to 40.9 µm and 39.1 to 47.1 µm, respectively. The SLM process itself resulted in a positive increase of the marginal (6.0 – 16.7 µm) and internal (9.0 – 15.7 µm) fit discrepancies. CONCLUSION: The CAD and SLM processes affected the fit of CoCr crowns and varied based on the preparation designs. Typically, the shoulder-lip and sharp line angle designs had a more significant effect on crown fit. However, the differences between the design groups were relatively small, especially when compared to fit discrepancies observed clinically.