Comparison of the flexural and surface properties of milled, 3D-printed, and heat polymerized PMMA resins for denture bases: An in vitro study

Purpose: To compare the flexural properties and the adhesion of Lactobacillus salivarius (LS), Streptococcus mutans (SM), and Candida albicans (CA) on heat-polymerized (CV), CAD-CAM milled (CAD), or 3D- printed (3D) Poly (methylmethacrylate) (PMMA). Methods: Ultimate Flexural Strength (UFS), Flexural Strain (FS) (%) at Flexural Strength, and Flexural Modulus (FM) of specimens (65.0x10.0x3.3 mm) from each PMMA group (n=6) were calculated by using the 3-point bending test. The surface roughness profiles (R) were measured before and after polishing with a contact profilometer. LS, SM, and CA adhesion on PMMA specimens (n=18) (10 mm in diameter, 3 mm in height) was assessed after 90 minutes and 16 hours by using scanning electron microscopy. The Kruskal-Wallis test with post hoc analysis was performed to compare the groups (alpha=0.05). Results: Mean UFS values were 80.79 +/- 7.64 MPa for CV, 110.23 +/- 5.03 MPa for CAD, and 87.34 +/- 6.39 MPa for 3D. Mean FS values were 4.37 +/- 1.04% for CV, 4.71 +/- 0.62% for CAD, and 6.19 +/- 0.13 % for 3D. Mean FM values were 2542 +/- 301 MPa for CV, 3435 +/- 346 MPa for CAD, and 2371 +/- 197 MPa for 3D. CAD had the lowest average R value (0.29 +/- 0.16 mu m) before polishing, and bacterial adhesion after 90 minutes of incubation. R value and microbial adhesion were not different amongst groups after polishing and 16 hours of incubation, respectively. Conclusion: The CAD group displayed the best flexural properties, except for FS, the lowest roughness before polishing and bacterial adhesion after 90 minutes of incubation. All tested PMMAs had similar surface roughness after polishing, and microbial adhesion after 16 hours of incubation.