A Denture Base Resin Developed Using Hyperbranched Polyurethane Acrylate, Tricyclodecane Dimethanol Diacrylate, and Liquid Crystal Display-Based Three-Dimensional Printing

Abstract

Poly-(methyl methacrylate) (PMMA) is the most widely used denture base material. However, because of PMMA's insufficient mechanical strength, fracture is a frequent problem after long-term denture use for chewing. In this study, hyperbranched polyurethane acrylate (HBPUA) was synthesized using trimethylolpropane, isophorone diisocyanate, and hydroxyethyl acrylate in a molar ratio of 1:3.1:3.2. Gel permeation chromatography revealed that the number- and weight-average weights of the synthesized HBPUA were approximately 1325 and 1797, respectively. For blended resins comprising different HBPUA and tricyclodecane dimethanol diacrylate (TCDDMDA) weight ratios, viscosity increased with increasing HBPUA content. A composition of 10 and 90 wt % HBPUA and TCDDMDA (TC10), respectively, was optimal for developing a denture base resin using liquid crystal display-based three-dimensional (3D) printing. Resins exposed to light for 5, 15, and 30 s and containing photoinitiator concentrations of 1 and 2 mol % were fabricated for comparison with a commercial resin, Denture 3D+. Attenuated total reflectance Fourier-transform infrared spectroscopy revealed that Denture 3D+ possessed a higher double bond conversion rate than those of the TC10 materials. Three-point bending tests revealed that Group 4 (TC10-0.01, 15 s) possessed the highest flexural strengths after both 50 h and 28 d of water immersion and that this group's flexural modulus also exceeded that of Denture 3D+, although the group's toughness and elongation were lower than those of Denture 3D+. In addition, the water sorption and solubility, surface roughness, and volumetric shrinkage of TC10 materials were lower than those of Denture 3D+. Furthermore, the impact strength, microhardness, and biocompatibility of Group 4 were comparable to those of Denture 3D+. These results indicate that Group 4 not only satisfied the ISO 20795-1 requirements but also possessed some properties superior to those of Denture 3D+, implying strong potential for practical application as a denture base material.

1

Chemical structures of HBPUA, TMP, IPDI, HEA, and TCDDMDA.

2

Printed specimen (64 mm in length × 12.7 mm in width × 3.2 mm in thickness), featuring a V-shaped notch (tip radius of 0.25 mm, depth of 2 mm, and an angle of 45°) was used for the Izod impact strength measurement, with the notch created in the middle of the specimen.

3

FT-IR spectra of (a) reactants at T0, (b) HBPUA, (c) TMP, (d) IPDI, and (e) HEA. T0 was defined as all the reactants being completely dissolved in acetone and homogeneously mixed for 1 min.

4

GPC chromatograms of (a) polystyrene standard, (b) HBPUA, (c) urethane diacrylate, (d) IPDI, and (e) HEA.

5

Schematic for urethane diacrylate synthesis.

6

(a) Representative FTIR spectra of Denture 3D+ resin before and after polymerization, showing a weakened CC stretching peak (at 1636 cm^–1). (b) CC DBC rates (%) of Denture 3D+ and TC10 resins exposed to light for various lengths of time. Significant differences are labeled as * (p < 0.05).

7

Representative stress–strain curves of Groups 2, 4, and 7 after water storage for (a) 50 h or (b) 28 d. Comparison of (c) flexural strengths and (d) moduli, (e) toughness values, and (f) elongations of different resin groups after short- and long-term water immersions (50 h and 28 d), respectively. All the tests were conducted according to the ISO 20795-1 standard. Values are expressed as means ± standard deviations. Asterisks (*) indicate statistically significant differences between 50 h and 28 d water immersions within the same group (*p < 0.05, **p < 0.01, ***p < 0.001).

8

(a) Impact strength (kJ/mm²) and (b) microhardness (VHN) of Denture 3D+ and TC10 resins. Significant differences are labeled as *p < 0.05, **p < 0.01, ***p < 0.001.

9

(a) Surface roughness (Ra, μm) and (b) shrinkage (%, determined by volume displacement according to Archimedes’ principle). Significant differences are labeled as *p < 0.05, ***p < 0.001.

10

(a–h) Photographs of representative printouts of Groups 1–8, respectively. (i) Water sorption values (Wsp, mg mm^–3) of Denture 3D+ and TC10 resins, as determined according to the ISO 20795-1 standard. Significant differences are labeled as * (p < 0.05).

11

HGF-1 cell viabilities for Denture 3D+, TC10-0.01, and TC10-0.02, as determined using a CCK-8 assay.