Effect of digital scans on marginal and internal discrepancies of zirconia crowns.

STATEMENT OF PROBLEM: A few studies have compared the accuracy of newly introduced intraoral scanners (IOSs); however, limited evidence is available concerning which system provides the best marginal and internal adaptation of zirconia crowns. PURPOSE: The purpose of this in vitro study was to compare the marginal and internal discrepancies of zirconia crowns fabricated with 4 digital scanners by a silicone replica technique. MATERIAL AND METHODS: A maxillary central incisor was prepared for a ceramic crown and duplicated to form 10 metal abutments. Four groups of zirconia crowns with different scanning methods were produced for each die: 1 laboratory scanner, L (Ceramill Map 400), and 3 different IOSs, CS (CS3600), TR (TRIOS3), and CE (CEREC Omnicam). The marginal and internal discrepancies were measured by a silicone replica technique under a static load of 50 N. The replica specimens were sectioned buccolingually and mesiodistally and then examined by using a stereomicroscope (JTZ-7XT) at ×200 magnification. Fifteen reference points were measured on each specimen. One-way ANOVAs with the Duncan multiple range tests were used for statistical analysis of the data (α=.05). RESULTS: The mean marginal discrepancies of zirconia crowns were 12.7 µm for group L, 12.6 µm for group CS, 14.8 µm for group TR, and 15.8 µm for group CE. No significant differences were found in marginal and incisal discrepancies among 4 groups. However, groups CS and L showed significantly better cervical and axial discrepancies than groups TR and CE. Group TR showed significantly better axial discrepancy than group CE. CONCLUSIONS: Zirconia crowns made by using the CS3600 and the laboratory scanner with a conventional impression showed significantly better internal discrepancies than those made by using TRIOS3 and CEREC Omnicam.

Fit of lithium disilicate crowns fabricated from conventional and digital impressions assessed with micro-CT.

STATEMENT OF PROBLEM: Although the number of lithium disilicate crowns fabricated with computer-aided design and computer-aided manufacturing (CAD-CAM) technology has increased, the accuracy of the prostheses produced by using digital pathways remains unknown. PURPOSE: The purpose of this in vitro study was to compare marginal and internal discrepancies of lithium disilicate crowns fabricated from digital and conventional impressions. MATERIAL AND METHODS: A typodont mandibular first molar was prepared for a lithium disilicate crown, and 20 duplicate dies were fabricated by milling poly(methyl methacrylate) resin blocks from laboratory scans. Four groups of 5 lithium disilicate crowns each were created by using a CS3500 (Carestream Dental) intraoral digital impression; Trios (3shape) intraoral digital impression; Ceramill Map400 (Amann Girrbach) extraoral digital impression; and a heat-press technique as a control group. All of the IPS e.max CAD (Ivoclar Vivadent AG) crowns were produced using a 5-axis milling engine (Ceramill Motion2). The lithium disilicate crowns were cemented with zinc phosphate cement under finger pressure. Marginal and internal discrepancies were measured using micro-computed tomography (SkyScan1172). One-way ANOVAs with the Tukey honest significant differences test were used for statistical analysis of the data (α=.05). RESULTS: The mean marginal discrepancies of CS3500 lithium disilicate crowns were 129.6 µm, 200.9 µm for Ceramill Map400, and 207.8 µm 176.1 µm for the heat-press technique; and the internal discrepancy volumes for CS3500 were 25.3 mm3, 40.7 mm3 for Trios, 29.1 mm3 for Ceramill Map400, and 29.1 and 31.4 mm3 for the heat-press technique. The CS3500 group showed a significantly better marginal discrepancy than the other 3 groups and a smaller internal discrepancy volume than the Trios group (P<.05). CONCLUSIONS: Significant differences were found between IPS e.max CAD crowns produced using 2 intraoral digital impressions, whereas no differences were found between IPS e.max CAD crowns produced from an extraoral digital impression and IPS e.max Press crowns produced using a heat-press technique.