Mechanical Property of Resin Composite Fabricated by vat Photopolymerization

Objectives: Dental CAD/CAM has been mainly used for final restorations by subtractive machining, however additive manufacturing (AM) remains to clarify use. Recently, resin and resin composite fabricated by vat photopolymerization (VPP) in AM are developed. Therefore, the purpose of this study was to clarify the relationship between water absorption and flexural strength of resin-based materials fabricated in processed in VPP.
Methods: Acryl type of resin (PDT; dima Print Denture Teeth, Kulzer Japan) and two resin-based composite materials (TAT; Teeth & Temp, Kulzer Japan and CMG; 3D Ceramage; Shofu) in VPP were used in this study. The specimens were prepared as 2 x 2 x 25 mm rods and 1.2 x 4 x 14 mm plates. These specimens were polished with waterproof abrasive paper up to 2000 grits. Each specimen was immersed in 37 degree C distilled water for 1, 7 and 14 days. The water adsorption and flexural strength were measured. Flexural tests were performed using a three-point bending test with a distance of 20 mm and 12 mm between the supports for rods and plate, respectively. Statistical analysis was performed using the Steel-Dwass method after the Kruskal-Wallis test for water absorption and the Tukey-Kramer multiple comparison test after two-way ANOVA for flexural strength (α=0.05).
Results: Water absorption increased significantly (P<0.05) up to 7 days immersion for all the specimens, but remained the similar at 7-day and 14-day immersion. The flexural strength had more than 100 MPa before immersion, and the strength decreased to ca. 80 MPa with 14-days immersion in water (P<0.05). No significant difference in flexural strength was observed between rod and plate specimen types, while PDT plate specimens exhibited greater flexural strength.
Conclusions: The resin and resin composite fabricated using VPP in AM could be useful for crown restorations, although their flexural strength decreased due to water adsorption.