Investigation of thiol-ene and thiol-ene-methacrylate based resins as dental restorative materials

Abstract

Objectives: The objective of this work was to evaluate thiol-norbornene and thiol-ene-methacrylate systems as the resin phase of dental restorative materials and demonstrate their superior performance as compared to dimethacrylate materials.

Methods: Polymerization kinetics and overall functional group conversions were determined by Fourier transform infrared spectroscopy (FTIR). Flexural strength and modulus were determined with a 3-point flexural test. Polymerization-induced shrinkage stress was measured with a tensometer.

Results: Thiol-ene polymer systems were demonstrated to exhibit advantageous properties for dental restorative materials in regards to rapid curing kinetics, high conversion, and low shrinkage and stress. However, both the thiol-norbornene and thiol-allyl ether systems studied here exhibit significant reductions in flexural strength and modulus relative to BisGMA/TEGDMA. By utilizing the thiol-ene component as the reactive diluent in dimethacrylate systems, high flexural modulus and strength are achieved while dramatically reducing the polymerization shrinkage stress. The methacrylate-thiol-allyl ether and methacrylate-thiol-norbornene systems both exhibited equivalent flexural modulus (2.1+/-0.1 GPa) and slightly reduced flexural strength (95+/-1 and 101+/-3 MPa, respectively) relative to BisGMA/TEGDMA (flexural modulus; 2.2+0.1 GPa and flexural strength; 112+/-3 MPa). Both the methacrylate-thiol-allyl ether and methacrylate-thiol-norbornene systems exhibited dramatic reductions in shrinkage stress (1.1+/-0.1 and 1.1+/-0.2 MPa, respectively) relative to BisGMA/TEGDMA (2.6+/-0.2 MPa).

Significance: The improved polymerization kinetics and overall functional group conversion, coupled with reductions in shrinkage stress while maintaining equivalent flexural modulus, result in a superior overall dental restorative material as compared to traditional bulk dimethacrylate resins.

Figure 1

Chemical structures of monomers utilized in this study along with their abbreviations.

Figure 2

Average functional group conversion versus time for (a) BisGMA/TEGDMA, EBPADMA/TEGDMA, PETMP/TATATO, and PETMP/TMPTN and (b) BisGMA/TEGDMA, EBPADMA/PETMP:TATATO, and EBPADMA/PETMP:TMPTN. All samples are 70/30 wt% BisGMA/TEGDMA, EBPADMA/TEGDMA, or methacrylate/thiol-ene, contain 0.1 wt% DMPA and are irradiated for 300 seconds at 15 mW/cm² UV light.

Figure 3

Average polymerization shrinkage stress versus methacrylate conversion for 70/30 wt% mixtures of BisGMA/TEGDMA, EBPADMA/TEGDMA, EBPADMA/PETMP:TATATO, and EBPADMA/PETMP:TMPTN. Samples contain 0.1 wt% DMPA and are irradiated at 21 mW/cm² for 600 seconds.