The restoration of carious portions of otherwise sound teeth will continue to be a central focus of Dentistry into the foreseeable future. In spite of the significant improvements in composites over the last few decades, the projected service life of composite materials remains considerably less than that of Dental amalgams. Critical composite materials limitations are associated with shrinkage stress development during resin matrix formation and the establishment and long-term durability of the attachment between resin and filler. While many of the advances in composites have come from the selection of filler composition and particle size, the coupling agent interface between the resin and filler has received remarkably little attention. This proposed investigation will develop and evaluate the potential of an interfacial region that is dramatically different from that available with the conventional gamma-methacryloxypropyltrimethoxysilane used in Dental composites.
In Specific Aim 1 : controlled concentrations of functionalized silanes lacking polymerizable methacrylate groups will be applied to yield efficient surface coverage of small particle filler and microfiller. The silanization process will be studied in detail since significantly different application procedures can be used in the absence of methacrylate groups.
In Specific Aim 2 : the appended functionality will be used to covalently attach preformed oligomeric/polymeric chains. The surface-tethered chains can be significantly varied in terms of hydrophobicity, flexibility and length.
In Specific Aim 3 : the polymer brush surface-modified fillers will be formulated with traditional methacrylate-based Dental resins and the resulting composites will be evaluated with the reasonable expectation that the alternative coupling agents developed here will provide efficient and stable resin-filler attachment through both physical entanglements and direct copolymerization. Significant improvements are posited in composite materials based on higher filler loading, greater hydrolytic stability, increased wear resistance, improved fracture toughness and reduced polymerization shrinkage stress; all without compromise to mechanical strength properties. While the coupling agent makes up only a smell fraction of the Dental composite formulation, there appears to be substantial, clinically relevant benefits in composite performance that can potentially be obtained by changes in this interfacial region. Positive preliminary data offer encouragement that this nanotechnology approach to the resin-filler interface can provide broadly applicable enhancements in function and longevity of widely used Dental restoratives.