Evaluation of the fit of zirconia copings fabricated by direct and indirect digital scanning procedures

Statement of problem Intraoral scanners are effective for direct digital impression when dental restorations are fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM); however, if the abutment tooth cannot be dried completely or the prepared margin is placed subgingivally, accurate digital images cannot always be guaranteed. Purpose The purpose of this in vitro study was to compare the internal and marginal discrepancies of zirconia copings fabricated directly using an intraoral scanner with those fabricated indirectly with impression scanning. Material and methods Forty-five resin dies fabricated with a 3-dimensional (3D) printer were divided into 3 groups: direct scanning (DS), impression scanning (IMP), and lost-wax casting (LW). For the DS group, a resin die was scanned with an intraoral scanner (Trios; 3Shape), whereas for the IMP group, impressions made with polyether were scanned with a cast scanner (D700; 3Shape). The zirconia copings were fabricated in the same way in the DS and IMP groups. For the LW group, impressions were made in the same way as in the IMP group, and Ni-Cr alloy copings were fabricated using LW. The marginal and internal discrepancies of the copings were measured by cementing them onto resin dies, embedding them in acrylic resin, and sectioning them in a buccolingual direction. The cement layer was measured, and the Kruskal-Wallis test was used to detect significant differences (α=.05). A nonparametric Friedman test was also performed to compare the measurements of each group by location (α=.05). Results The mean marginal discrepancies in the DS, IMP, and LW groups were 18.1 ±9.8, 23.2 ±17.2, and 32.3 ±18.6 μm (mean ±standard deviation), respectively. The mean internal discrepancies of the DS, IMP, and LW groups in the axial area were 38.0 ±9.1, 47.0 ±16.3, and 36.5 ±15.8 μm, and those in the occlusal area were 36.7 ±16.9, 33.4 ±21.6, and 44.5 ±31.9 μm, respectively. No statistically significant differences were found in marginal or internal discrepancies among groups ( P >.05). Conclusions Within the limitations of this study, the zirconia copings fabricated with CAD-CAM using different digitization methods and Ni-Cr copings fabricated using the lost-wax technique and casting produced clinically acceptable marginal and internal discrepancies. No significant differences were found among the DS, IMP, and LW groups.