Vertical marginal fit of zirconia copings fabricated with one direct and three indirect digital scanning techniques

Statement of problem. Direct digitization of the impression by using an intraoral scanner is a newly introduced technique, but studies comparing the method with other digitization techniques are lacking. Purpose. The purpose of this in vitro study was to compare the marginal accuracy of zirconia copings fabricated with 4 different scanning methods. Material and methods. Scans (n=10) of a brass master die were made with a direct method (ISD) in which the die was directly digitized by using an intraoral scanner (IOS) and 3 indirect scanning methods, a conventional impression with polyvinyl siloxane material digitized with either the same IOS (ISI) or with a laboratory extraoral scanner (ESI), or a cast from the impression was scanned by using a laboratory extraoral scanner (ESC). Forty zirconia copings were milled from presintered zirconia blanks and sintered. The vertical marginal gap was measured at 12 points on the master die by using a digital microscope. One-way ANOVA was used to compare the mean differences among the 4 groups, and post hoc analysis was used for pairwise comparison of the groups (a=.05). Results. The mean +/- standard deviation of the vertical marginal gap was 73 +/- 7 mm in the ISD group, 109 +/- 36 mm in the ISI group, 42 +/- 4 mm in the ESI group, and 97 +/- 5 mm in the ESC group. The lowest marginal gap was seen in the ESI group, which was significantly different from the 3 other groups (P<.001). The copings in the ISD group had a significantly lower marginal gap than those in the ISI (P=.04) and ESC (P<.001) groups. However, the ISI and ESC groups were not significantly different (P=.69). Conclusions. Marginal adaptation of all zirconia copings fabricated with these 4 scanning techniques was within a clinically acceptable range. However, ESI was the best method of digitization and yielded copings with minimum vertical marginal gap.