Adaptation, Marginal, and Occlusal Quality of Monolithic Zirconia Crowns: Effect of the CAD / CAM Milling Protocol

OBJECTIVES: Variables related to CAD/CAM processing can affect the final quality of all-ceramic crowns. This study aims to evaluate the effect of the milling protocol on the adaptation, marginal and occlusal quality of monolithic zirconia crowns. MATERIALS AND METHODS: Thirty-nine monolithic zirconia crowns were produced using three CAD/CAM milling protocols (n = 13): slow (S), normal (N), and fast (F). Adaptation (gap thickness) was evaluated using the replica technique, while marginal quality was assessed according to a severity scale. Occlusal quality was investigated qualitatively, using a stereomicroscope, and quantitatively, through an occlusal dimensional discrepancy analysis. Gap thickness and occlusal discrepancy data were analyzed with ANOVA and Tukey's test, and marginal quality with Kruskal-Wallis and Student-Newman-Keuls (α = 0.05). RESULTS: Gap thickness in the marginal, gingival-axial angle and axial regions was similar among groups. In the axio-occlusal angle and occlusal region, group N presented the smallest gap. For marginal quality, group F had higher scores in the severity scale than groups N and S for the mesial and buccal regions. Group F crowns showed less refined occlusal anatomy. Yet, when crowns produced with S and F protocols were compared with N, the total mean discrepancy was similar. CONCLUSION: The CAD/CAM milling protocol affected the adaptation, marginal, and occlusal quality of monolithic zirconia crowns.