Comparison of marginal and internal fit of 3-unit zirconia frameworks fabricated with CAD-CAM technology using direct and indirect digital scans

Accurate marginal and internal fit of dental restorations are essential for their long-term success. The fit of zirconia restorations prepared using digital scan systems has not been fully evaluated. The purpose of this in vitro study was to compare the marginal and internal fit of 3-unit zirconia frameworks fabricated using direct and indirect digital scans. In a maxillary model, the left first premolar and first molar were prepared to receive 3-unit zirconia fixed dental prostheses. Conventional impressions were made using stock trays and 2-step putty/wash polyvinyl siloxane material and were scanned using laboratory scanner (Conventional Impression-Laboratory scanner [CIL] group). The impressions were then poured, and the stone casts were scanned (Dental Cast-Laboratory scanner [DCL] group). Digital scans were made using TRIOS (TRIOS Intraoral scanner [TRI] group) and CS3600 (CS3600 Intraoral scanner [CSI] group) scanners (n=10). Zirconia copings were designed and milled from presintered blocks and subsequently sintered. Marginal, mid-axial, axio-occlusal, and mid-occlusal discrepancies were measured using the silicone replica technique with stereomicroscopy at ×50 magnification. The data were analyzed using 1-way ANOVA (α=.01). The ANOVA revealed significant differences among the studied groups in terms of all studied characteristics (P≤.01). Marginal gap was significantly higher in the DCL group (106 ±45 μm) compared with all other groups (P≤.01). However, no significant differences were observed in marginal gap between the TRI (60 ±15 μm) and CSI (55 ±13 μm) groups (P>.01). Internal gap in the mid-occlusal and axio-occlusal regions were significantly higher in the CIL (238 ±92 μm and 227 ±95 μm) and DCL (248 ±71 μm and 216 ±68 μm) groups than those recorded in the TRI (104 ±27 μm and 126 ±31 μm) and CSI (128 ±16 μm and 147 ±28 μm) groups (P≤.01). Internal discrepancies in the mid-axial position were similar between the TRI (70 ±15 μm) and CSI (72 ±23 μm) groups (P>.01), but these values were significantly lower than those recorded in the CIL (88 ±31 μm) and DCL (85 ±30 μm) groups (P≤.01). Within the limitations of this study, zirconia frameworks in the TRI and CSI groups had lower marginal and internal gaps compared with those in the DCL and CIL groups. Marginal gap in all groups was within a clinically acceptable range.