Sintering effect on zirconia manufactured by suspension enclosed projection stereolithography
Creators: name: Unnadkat, Amit
Publisher: name: University of Iowa
Year: 2025
Subjects: subject: 3D Printing
subject: Additive Manufacturing
subject: Dental
subject: DLP
subject: SLA
subject: Zirconia
subject: public abstract
subject: Biomedical Engineering
subject: FOS: Medical engineering

description: Objectives: To evaluate the suitability of using zirconia dental materials with a novel 3D printing process named suspension enclosed projection stereolithography (SEPS); and to investigate the effect of sintering time and temperature on the flexural strength and density of zirconia produced by SEPS.
description: Methods: Ceramic suspensions (slurries) were prepared using zirconia powders (Tosoh) and 3D printing resins, with varying percentages depending on the type of zirconia used. The 3Y (60wt%) slurries had a zirconia to resin ratio of 60:40 and used ANYCUBIC white 405nm UV resin and Formlabs Clear Resin at 20% each, while the 5Y (70wt%) slurries had a ratio of 70:30 and used the same resins at 15% each. The slurries were prepared with 1.5% Solsperse 20000 dispersant and 0.5% isopropyl alcohol, and were ball milled and degassed. 40 bar specimens (36.2mm x 4.9mm x 1.5mm) of each material were fabricated via SEPS manufacturing (Curing Time – 45 seconds/layer. 0.062mm layer thickness, 28 layers) and post-cured under UV light for 10min. Specimens were debinded at 600°C for 180min. Slurry viscosity was also measured. Samples were categorized into 4 groups (n=10 per group): A:1450°C for 120min, B:1530°C for 120min, C:1530°C for 30min, and D:1530°C for 10min, with a heating rate of 8°C/min using a Ceramill Therm 3 sintering furnace. Sintered specimens were measured with a digital micrometer. Flexural strength was tested in three-point bending at crosshead speed of 1 mm/min. Density was measured by the Archimedes method (n=10) and phase composition was determined by X-Ray diffraction.
description: Results: The viscosities of the 5Y and 3Y slurries at a shear rate of 1/100 were measured to be 2897.9 Pa·s and 2185.4 Pa·s, respectively One-way Welch ANOVA showed that there was no significant difference in mean flexural strength among 3Y groups (p=0.362), however there was a significant difference in mean flexural strength between 5Y sintered at 1450°C &amp; 120min compared to 5Y sintered at 1530°C &amp; 120min. Pairwise Welch t-tests with Holm adjustment revealed significant difference (p=0.002) between the Kruskal-Wallis followed by Dunn’s test indicated a significant difference for density between 3Y groups B and D (p=0.0326), but no significant differences between 5Y groups. 3Y samples sintered at 1450°C for 120 minutes showed significantly higher shrinkage in height compared to 3Y at 1530°C for 120 minutes. X-ray diffraction data confirmed the presence of predominantly tetragonal phase in both materials.
description: Conclusion: Zirconia printed via SEPS manufacturing can be sintered at a higher temperature with shorter dwell times compared to manufacturer recommendations for milled zirconia materials. X-ray diffraction and density data confirmed that different settings can be used to fully sinter 3D printed zirconia for potential dental applications.