Properties of Printed Zirconia Using Suspension Enclosing Projection Stereolithography

To evaluate the feasibility of using suspension enclosing projection stereolithography (SEPS) in printing zirconia dental restorations. Different from most AM processes, this technique is capable of printing overhanging shapes without the need of support structures. A zirconia material (3 M Lava Esthetic, 5%mol zirconia), commonly used to mill zirconia dental restorations, and two experimental printed zirconia groups were analyzed regarding flexural strength, hardness, and microstructure. Thirty-two bar-shaped (n=16) specimens were printed using SEPS from 5% mol yttria zirconia powder (Zpex-Tosoh, Japan) and a photopolymerizable resin from an STL file, at a 70:30, and at a 75:25 ratio. Specimens were cured for 10 minutes, then debinded and sintered. Sixteen specimens were sectioned from zirconia pucks (control) and sintered using a heating, holding, and cooling cycle. Three-point bending test was performed for all 48 specimens using a universal testing machine at 0.5mmm/min cross-head speed. Knoop hardness measurements were performed, using a load of 200 g for 15 s for both groups (n=8). The average of two measurements was recorded. An Independent-Samples Kruskal-Wallis Test was performed to test the flexural strength among the groups. A statistically significant difference was observed for the milled group(p<0.003). The microhardness was not significantly different among groups (p= 0.29, One-way ANOVA). SEPS showed to be a feasible technique to produce zirconia specimens. SEPS produced zirconia showed favorable microhardness properties for dental application. However, SEPS specimens had significantly reduced flexural strength when compared to the control, in particular for the 75% group. Further research is necessary to optimize the debinding and sintering settings when using SESP to print zirconia structures.