CAD/CAM denture resins: in-vitro evaluation of mechanical and surface properties

Objectives: This study evaluated the mechanical properties and surface roughness of resins used for manufacturing CAD/CAM milled and rapidly-prototyped (3D-printed) complete dentures. This study further evaluated the influence of different printers and the printing orientation on the mechanical properties of these resins.
Methods: Six groups of resin samples were fabricated for mechanical testing, and surface roughness [Groups: n=6; 1:Milled Base (MB), 2:Milled Tooth-shade (MT), 3:Printed Tooth-shade (PT), 4:Printed Base with manufacturer-recommended 3D-printer (PB1), 5:Printed Base with third-party 3D-Printer (PB2), 6:Printed Base in a vertical orientation (PB2V)]. Three-point bending tests were performed using a universal testing machine (AG-X Plus, Shimadzu Corporation) to measure the ultimate strength, flexural elastic modulus, toughness, yield point, and strain at yield point. Surface roughness was evaluated using a high-resolution laser profilometer (CyberSCAN CT 100, Cyber technologies). ANOVA and post hoc tests were used for statistical analyses (alpha=0.05) using a statistical software package (IBM SPSS Statistics,IBM corporation).
Results: MB revealed a significantly higher ultimate strength (p=0.008), elastic modulus (p=0.002) and toughness (p=0.014), than PB1. MB demonstrated a higher elastic modulus than PT (p<0.001). MT had significantly higher elastic modulus than PT (p<0.001), higher ultimate strength (p=0.007) and elastic modulus (p=0.001) than PB1. Printing with the recommended 3D-printer demonstrated a higher ultimate strength (p=0.008), elastic modulus (p<0.001), hardness (p<0.001) and a reduced surface roughness (Ra: p=0.008; Rc: p=0.015; Rz: p=0.005). Printing in a vertical orientation revealed a significantly lower elastic modulus (p=0.011) but did not influence the ultimate strength and toughness. No differences were found in the other parameters.
Conclusions: CAD/CAM milled denture resins exhibit better material properties than the resins currently used for 3D-printed dentures. Rapid-prototyping of dentures with third-party 3D-printers may affect the resin strength and their surface properties.