Determination of Hardness and Fracture Toughness of Y-TZP Manufactured by Digital Light Processing through the Indentation Technique

Objective The purpose of the study was to determine the hardness and fracture toughness of dental yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) manufactured by digital light processing (DLP) technology to study its clinical prospects.Methods The experimental group was DLP-manufactured zirconia, and the control group was milled zirconia. The hardness was investigated under a range of test loads (0.49 N, 0.98 N, 1.96 N, 4.90 N, 9.81 N, 29.42 N, 49.03 N, 98.07 N, and 196.1 N). Meyer's law was applied to describe the indentation size effect (ISE). Meanwhile, the PSR model and MPSR model were utilized to generate true hardness values. The cracks were observed to be induced by indentation under loads above 49.03 N, while the cracks showed the radial-median type under the load of 196.1 N, under which the fracture toughness was calculated.Results The true hardness of DLP-manufactured zirconia was 1189 HV based on the PSR model and 1193 HV based on the MPSR model, a bit lower than that of milled zirconia. The fracture toughness was 3.43 ± 0.29 MPa√m, which showed no statistical difference with the milled zirconia.Conclusion The dental zirconia manufactured by the DLP 3D printing technique is similar to that manufactured by the conventional milling process in hardness and fracture toughness, thus having a promising future of clinical use.