Adhesion of Denture Characterizing Composites to Heat-Cured, CAD/CAM and 3D Printed Denture Base Resins

Purpose To measure the adhesion of the denture characterizing composite to heat-cured, CAD/CAM and 3D printed denture base resins. Methods and Materials Two different denture characterizing composites with different viscosities (SR Nexco; high viscosity (SR) and Kulzer Cre-active; low viscosity (K)) and three denture base resins (Heat cure, CAD-milled and 3D printed) were investigated. 60 beams (25 x 4 x 3 mm) were fabricated for each denture base resin; 30 were bonded to SR and 30 to K to form a beam 50 x 4 x 3 mm. These were further divided (n = 10/group) to simulate the effects of 0, 6, and 12 months intraorally via thermocycling. The beams were subjected to a 4-point bend test using the chevron-notched beam method. Fracture toughness K-1C (MPa center dot m(1/2)) and flexural bond strength (MPa) were calculated. All specimens were analyzed for the mode of failure under the light microscope and selected specimens under scanning electron microscope. Results were statistically analyzed using ANOVA (SPSS Ver 25). Results The mean K-1C was highest for the SR composite bonded to the heat-cured denture resin group (0.28 +/- 0.11), followed by CAD/CAM (0.18 +/- 0.04) and 3D printed groups (0.23 +/- 0.16). Differences were not statistically significant (p = 0.268). Within each group, aging showed no statistical significance between the mean K-1C and flexural bond strength (p = 0.209). The mean K-1C for the K composites bonded to the three different denture bases were significantly lower compared to the SR group (p < 0.001). The mean K-1C for the heat-cured denture resin group was (0.21 +/- 0.1), followed by CAD/CAM (0.13 +/- 0.04) and 3D printed groups (0.03 +/- 0.02). Within each of the K group, aging showed a statistical significance for both the mean K-1C and flexural bond strength (p = 0.002). Conclusion The high viscosity SR showed significantly higher K1C and flexural bond strength to the lower viscosity K when bonded to heat-cured, CAD-milled and 3D printed denture base resins. Heat-cured denture base resins produced the highest K-1C and flexural bond strength when bonded to two different types of characterizing composites.