Marginal Fit Evaluation of CAD/CAM All Ceramic Crowns Obtained by Two Digital Workflows: An In Vitro Study Using Micro-CT Technology

Purpose: To evaluate the marginal fit of CAD/CAM all ceramic crowns made from lithium disilicate and zirconia using two different fabrication protocols (model and model-less). Materials and Methods: Forty anterior all ceramic restorations (20 lithium disilicate, 20 zirconia) were fabricated from digital impressions using a CEREC Bluecam scanner. Two different digital workflows were used: a fully digital model-less approach and a printed model digital approach. The crowns were cemented on the respective prepared typodont teeth and marginal gap was evaluated using Micro-CT. Each specimen was analyzed in sagittal and trans-axial orientations, allowing evaluation of the marginal fit (vertical and horizontal) on each surface. Logarithmic transformation was used with a significance of 0.05. After that a reliability analysis was performed by re-measuring four randomized selected images for each specimen and performing intraclass correlations to determine any systematic bias in the measurements. Results: Vertical measurements in the lingual, distal and mesial views had an estimated marginal gap ranging from 101.9 to 133.9 µm for lithium disilicate crowns and 126.4 to 165.4 µm for zirconia. No significant differences were found between model and model-less techniques. Conclusions: Both workflows are valid protocols for the fabrication of monolithic ceramic restorations. The use of a printed model did not improve the marginal fit of lithium disilicate or zirconia crowns. Both materials are also clinically acceptable, no matter which workflow was used to obtain the restoration.