3D printing and milling accuracy influence full-contour zirconia crown adaptation

Objectives: To correlate trueness and cement-space characteristics of crowns milled chairside and in the laboratory with those of inkjet 3D-printed crowns, and to assess whether 3D-printing accuracy meets the clinical standard.Methods: Thirty crowns were either (1) milled using a chairside Cerec MCXL unit from Cerec Zirconia Mono L (Dentsply Sirona), (2) milled using a LX-O 5-axis (Matsuura Machinery) industrial machine from Initial Zirconia HT (GC), or (3) 3D-printed using an inkjet Carmel 1400 (Xjet) printer (n = 10). Crown trueness determined by comparing the original CAD with each visible-light digitized crown was correlated with the 3D cementspace characteristics recorded by micro-CT. Statistics involved Kruskal-Wallis testing and Spearman correlation. Results: Crown trueness at the intaglio marginal area positively correlated with the marginal and axial cement-space characteristics. 3D-printing revealed data in-between those of the two milling systems with undercut values being not statistically different from those recorded for chairside milling and a low overcut level that was statistically similar to that obtained by laboratory milling. Laboratory milling revealed a significantly better marginal accuracy with a consequently lower cement-space thickness. A higher overcut level was recorded for the chairside-milled crowns in the marginal/occlusal thirds, resulting in the significantly highest occlusal cement-space thickness and cement-volume percentage with a cement thickness above 120 mu m (limit considered as clinically acceptable). No statistical difference in trueness was found for the external crown dimensions. Significance: The 3D-printed zirconia crowns provided sufficient manufacturing accuracy for clinical use. Accurate milling and printing of the crown's intaglio marginal area is primordial. (c) 2022 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.

Automated summary

This study compared the trueness and cement-space characteristics of crowns milled chairside, in the laboratory, and 3D-printed using inkjet technology. The results showed that 3D-printed zirconia crowns provide sufficient manufacturing accuracy for clinical use, and accurate milling and printing of the crown's intaglio marginal area are crucial.