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 (alpha=.05). RESULTS: The mean marginal discrepancies of CS3500 lithium disilicate crowns were 129.6 mum, 200.9 mum for Ceramill Map400, and 207.8 mum 176.1 mum for the heat-press technique; and the internal discrepancy volumes for CS3500 were 25.3 mm(3), 40.7 mm(3) for Trios, 29.1 mm(3) for Ceramill Map400, and 29.1 and 31.4 mm(3) 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.