In this study, a novel set of materials, EXOTHANE™ Elastomers, have been investigated through mechanical testing alongside traditional polymeric matrix resins; urethane dimethacrylate (UDMA) and a blend of bis[p-(3-methacryloxy-2-hydroxypropoxy)phenyl]propane( BisGMA ) and triethylene glycol dimethacrylate (TEGDMA).
Mechanical testing data was obtained by photo-initiating and curing the "neat" materials under a UVA light. Stress/strain curves for these materials were obtained using a universal tester with a 5 kN load cell and a crosshead speed of 10 mm/min. The shrinkage stress was determined using a tensometer. Volumetric shrinkage was measured using a linometer (ACTA). Conversion and real-time monitoring of the polymerization kinetics was carried out using the near-infrared (NIR) spectrum in a Fourier transform spectrophotometer (FTIR).
Results of mechanical testing indicate that Exothanes have superior toughness at max strength compared to the BisGMA/TEGDMA blend. Exothanes 8, 9 and 10 also had toughness values greater than UDMA. The percent elongation of Exothane 8 and Exothane 10, 79% and 64% respectively, far exceeds the traditional resins. The Shore D hardness of Exothane 24 is unique as it exceeds that of UDMA and the blend of BisGMA and TEGDMA typically used in dental composites. Collectively, Exothanes cured faster and displayed higher conversion than traditional resins. The volumetric shrinkage of the new materials were all lower than the UDMA and the BisGMA/TEGDMA blend. Shrinkage stress of the Exothanesshowed an 80% improvement over traditional resins.
Conclusions: The enhanced properties of the EXOTHANE Elastomers, specifically the high percent elongation and hardness, suggest that these novel materials could be used as functional additives to increase the toughness and durability of traditional dental composite restorations. The combination of high conversion, low volumetric shrinkage and low shrinkage stress has applications in dental composites where de-bonding from surrounding dentin is a problem.
Keywords: Composites, Dental materials, Elasticity, Polymers and Stress
See more of: Dental Materials 6: Polymer-based Materials-Chemistry and Composition