Vertical Marginal Discrepancy Performance of a CAD-CAM System with Multiple Users

The purpose of this evaluation was to evaluate the vertical marginal discrepancies of a computer-aided design-computer-aided manufacture (CAD-CAM) system used by different providers at separate time intervals.

Lithium disilicate monolithic crowns on mandibular third molars were fabricated by three different providers inexperienced in digital dentistry. Using a precision rotary stage mounted on a digital recording microscope, the crown vertical marginal discrepancy was assessed using 160× magnification at 5-degree intervals around the crown marginal circumference for a total of 72 measurements per specimen. In addition to mean vertical marginal discrepancy, the maximum vertical marginal discrepancy, and its location as well as the percent of closed marginal assessments, were assessed. Mean data was analyzed using Kruskal-Wallis and Dunn post hoc testing at a 95% level of confidence (α=0.05).

The mean marginal vertical discrepancy for all specimens was 21.1 ± 5.5 μm and a significant difference (p=0.0016) existed between groups but with noted wide similarity overlap. No difference (p=0.65) was observed with the mean closed margin percentage, but a significant difference (p=0.0012) existed in the observed maximum marginal discrepancy between groups. The 2-mm axial wall height (AWH), 20-degree total occlusal convergence (TOC) had significantly less (p<0.017) mean vertical marginal discrepancies than the 4-mm AWH, 20-degree TOC, and the 3-mm AWH, 16-degree TOC groups with the remaining groups similar (p>0.147). The plotted location of the specimen's maximum vertical discrepancy suggests a potential pattern amid the 360-degree margin circumference.

Under the conditions of this study, CAD-CAM-derived monolithic lithium disilicate ceramic crowns fabricated by different clinicians demonstrated mean vertical marginal discrepancy results that were less than the suggested maximum clinically acceptable values. A potential for patterns of marginal discrepancy results was identified and deserves further evaluation. Results should be interpreted with caution as in vitro methodologies vary and do not directly correlate with clinical conditions.