Each year hundreds of millions of dental restorations are performed with esthetic polymeric composite materials now making up the majority of these treatments. While well received by patients and practitioners, the clinical performance and longevity of dental composites is not ideal. Because of the volumetric contraction and the accompanying stresses that develop during polymerization of these materials, defect-free bonding to tooth tissues can not be reliably attained. Since the polymer matrix is the source of the shrinkage-induced stress and also the component that limits the mechanical strength and toughness of composite materials, we propose an alternative approach to the monomers used. Instead of small molecule monomers that polymerize with considerable shrinkage, this application will demonstrate that high molecular weight, discrete particulate prepolymers known as nanogels, with appropriate functionality, can serve as dimensionally stable macromolecular monomers (or macromers) that can be combined in high proportions with conventional dimethacrylate monomers to dramatically decrease the stress that develops upon formation of the final polymer. To accomplish this, the following three aims will guide this project: (i) The basic science of nanogel particle synthesis and structural control will be examined. Nanogels with well defined size (~ 10 to >500 nm), controlled core/surface chemistries and predictable mechanical/physical properties will be produced and characterized. While preliminary data has shown these polymeric nanoparticles and their functionalized macromer analogs are readily obtainable from common monomers, we will extend the nanogel morphology to produce more complex core-shell and gradient structures. (ii) These nanogel-based macromers, representing a range of particle size, modulus, degree of functionality and structural complexity, will then be combined with conventional dental monomers to produce copolymers with designed heterogeneity introduced by the nanogel. For both unfilled and filled systems, properties including viscosity, reaction kinetics, shrinkage/stress and mechanical strength/toughness will be used to identify combinations that produce important performance advantages compared with conventional dimethacrylate resins and composites. Again, preliminary results have already demonstrated significant improvements in mechanical properties as well as reduced polymerization shrinkage and stress compared with a Bis-GMA/TEGDMA photopolymer control;however, with specific nanogel structural designs, further enhancements are expected. (iii) The use of nanogel macromers to model phase separated polymer structures will be explored in detail to better understand the creation and control of the interfacial regions as well as to exploit polymerization-induced phase separation as a means to achieve polymeric materials that exhibit extremely low shrinkage and stress. The expected outcome of this project is practical access to a diverse array of nanogel structures that can be used as macromers to substantially improve current deficiencies in dental composite materials.

R21DE018354

2007-03-01

2010-02-28