Accuracy of marginal fit and axial wall contour for lithium disilicate crowns fabricated using three digital workflows

Statement of problem. Comparative assessment of the effectiveness of computer-aided design and computer-aided manufacturing (CAD-CAM) technologies used to fabricate complete-coverage restorations is needed. A quantitative assessment requires precise documentation of the marginal adaptation and external surface contour of fabricated restorations. Limited information is currently available regarding the effects of milling mode on marginal adaptation and reproduction of the external surface contour for CAD-CAM-fabricated restorations. Purpose. The purpose of this in vitro study was to evaluate the outcomes for 3 different digital workflows on the marginal gap and the external surface contour reproducibility of CAD-CAM-fabricated lithium disilicate complete-coverage restorations. Material and methods. Twelve Ivorine molars were prepared to receive lithium disilicate crowns. The preparations were digitally recorded using 2 intraoral scanners (TRIOS 3; 3Shape A/S and Planmeca PlanScan; E4D Technologies), and the restorations were designed using their associated design software with reference to the anatomy of an unprepared tooth. The designed restorations were then manufactured from lithium disilicate blocks using a 3-axis milling machine. Twelve restorations were manufactured using the detailed mode (Planmeca PlanScan detailed mode [PPD-D]), and 12 using the standard mode for the Planmeca system (Planmeca PlanScan standard mode [PPD-S]). Restorations from the 3Shape system were fabricated using the detailed mode (TRIOS 3Shape detailed mode [T35-D]). The restorations were secured on their associated preparation with an elastomeric material. The marginal gap of each restoration was then measured in the lmageJ software using images captured by a stereo microscope at x20 magnification. External surface reproducibility was evaluated by measuring undercut at 4-line angles using a dental surveyor. Differences in the marginal gaps of restorations fabricated using the 3 different workflows were compared by Brown-Forsythe robust ANOVA, followed by a post hoc test (alpha=.05). Chi-square analysis (alpha=.05) was used to evaluate differences in the contours of the external surface of the restorations, resistance form, and marginal integrity produced using the 3 workflows. Results. The mean marginal gap for restorations fabricated using the T3S-D workflow was 60 mu m, a distance significantly lower (P<.05) than that of PPD-D and PPD-S workflows, which yielded a marginal gap of 95 mu m for the detailed mode and 124 lim for the standard mode of milling. Restorations fabricated using PPD-D and PPD-S workflows produced a significantly more reproducible external surface contour than those fabricated using the T3S-D workflow. Conclusions. Restorations fabricated using the T3S-D workflow produced the smallest marginal gap. However, reproducibility of the external surface contour for this workflow was the worst of the three workflows analyzed.