Purpose The purpose of the present study was to compare marginal accuracy and internal fit of Co-Cr alloy crown-copings fabricated by casting, CAD/CAM milled, and 3-D laser sintered techniques and to investigate the degree of precision of manufacturing methods.
Materials and methods Thirty six Co-Cr alloy crown-copings were fabricated from a standard titanium implant abutment (TS system, Osstem, Seoul, Korea) for fit evaluation and divided into three groups according to the manufacturing methods; twelve copings for casting (n=12), twelve copings for milled technology (n=12), and twelve copings for laser sintered technology (n=12). Fit evaluation was performed using three different techniques; weighting the silicone material simulated a cement material, investigating the two-dimensional vertical marginal discrepancy, and measuring the internal gap widths in the cemented and sectioned specimens. One-way ANOVA followed by Scheffe’s and Bonferroni’s test were performed to determine the significant differences between the groups, and the level of significance was set at p = 0.05 and calculations were handled by the statistics software package (SPSS 19.0, IBM Co, NY, USA). The Pearson’s correlation analysis was used to assess the existence of the interrelation between the methods used for fit evaluation in this study.
Results Significantly low mean weight of silicone material (p<.001) were observed for the casting coping group, compared to the CAD/CAM milled and 3-D laser sintered groups. Mean two-dimensional vertical marginal gap widths were 38.229 ± 6.186 ㎛ in the casting group, 51.479 ± 6.986 ㎛ in the CAD/CAM milled group, and 72.458 ± 12.440 ㎛ in the laser sintered group, respectively. Significant differences were found among the all three groups as noted by the multiple comparison tests (p<.003). The mean average internal gap values was 61.528 ± 11.445 ㎛ in the casting group, 64.278 ± 9.145 ㎛ in the CAD/CAM milled group, and 95.806 ± 7.944 ㎛ in the laser sintered group, respectively. The 3-D laser sintered group showed the highest average internal gap value which was significantly different from those of the casting and the CAD/CAM milled copings (p< .0001).
Conclusion The different manufacturing methods influence the marginal accuracy and the internal fit of Co-Cr alloy crown-copings. The vertical marginal gap and the average internal gap of the casting group revealed the significantly smallest gap followed by the CAD/CAM milled and the laser sintered group. However, the Co-Cr alloy crown-copings fabricated with casting, CAD/CAM milled, and 3-D laser sintered technology in this in vitro study demonstrated acceptable range of marginal discrepancy and the internal gap widths referring to the literatures.