Evaluation Fit of All-Ceramic Crowns According to Different Finishing Line

Objectives: The purpose of this study was to evaluate the marginal and internal fit of lithium disilicate and zirconia crowns, with horizontal and vertical finishing line, manufactured from different CAD/CAM materials.
Methods: Two natural maxillary central incisors were used as primary model and prepared according to the clinical rules: incisal 2 mm reduction, axial 1.2 mm reduction, and 6° to 10° convergence angle. Each tooth were prepared with a different finish line, horizontal (1 mm chamfer preparation) and vertical (0.3 mm feather-edge preparation). Both teeth were scanned and thirty dies from polymerized resin were printed. For each type of preparation, fifteen identical crowns were fabricated and divided in 3 groups (n=5): 1) CAD/CAM milled lithium disilicate; 2) CAD/CAM wax pattern followed by pressed lithium disilicate; and 3) CAD/CAM milled monolithic zirconia. The silicone replica-technique was applied to quantify the marginal and internal fit. The replicas were analyzed using a reflected light microscope at 50x magnification. Four-sectioned locations (buccal/mesial/distal/palatal) and four measurement areas (marginal opening/chamfer area/axial wall/incisal plateau) were evaluated. Means for every measurement location and area were calculated for all specimens. The data were analyzed by Mann-Whitney U test and Kruskal-Wallis followed by Sidak test (α=0.05).
Results: For marginal opening, the vertical preparation (83.2 μm) showed significantly lower mean values than the horizontal preparation (124.5 μm) (p<0.001). Only for the horizontal preparation significant differences were found between the groups (p<0.001): milled lithium disilicate crowns (65 μm) showed a better marginal opening than zirconia crowns (178 μm) (p<0.001). The finishing line influenced the fit only for pressed lithium disilicate crowns (p=0.009) with lower mean value for horizontal preparation.
Conclusions: All groups showed values in the clinical acceptance range, except for zirconia crowns with horizontal preparation. Marginal opening was higher for the horizontal than for vertical preparation. Milled lithium disilicate crowns showed better marginal opening values.