State-of-the-art dental restorative composite precursors are modified versions of BIS-GMA mixed with ceramic powder fillers developed 25 years ago. Revolutionary advances in restorative dental materials will not come from further modifications of this technology. It must come from completely different approaches to formulating composite precursors. To be revolutionary, the new materials must: (1) be easily processable, (2) be single phase (without filler), (3) offer exceptional adhesion to dentin and hydroxyapatite, (4) provide high toughness, (5) exhibit little or no shrinkage during curing, (6) offer equal or improved abrasion resistance and, (7) not degrade on exposure to saliva. Liquid crystalline (LC)/inorganic copolymers offer the opportunity for revolutionary changes in the field of dental restorative composite precursors. The LC component of these polymers provides toughness, processability (low viscosities), low shrinkage during polymerization, low CTE, excellent long term thermal, photochemical and oxidative stability. The inorganic component, silsesquioxane, -[RSiO1.5]x-, oligomers offer enhanced adhesion to many diverse surfaces, are oxidatively and thermally stable to temperatures exceeding 400 degree C and, when R - RO- they form silica particles upon exposure to moisture thus creating, in situ, the necessary abrasion resistance of new sites for adhesion. The proposed research program begins with the synthesis and characterization of LC[RSiO1.5] copolymers, proceeds to in-vitro evaluation of copolymer physical and chemical properties and then culminates in preliminary studies of these properties in more appropriate environments. The synthesis goal is to prepare a low viscosity LC/[RSiO1.5] co- macromonomer as a composite precursor. Synthesis studies will first focus on the preparation of simple monomer and dimer LC and silisesquioxane model compounds with alkenic caps. Baseline polymerization, adhesion and polymer composite characterization studies of these first round compounds will guide development of more sophisticated LC dimers, trimers and higher oligomers and silsesquioxane systems. Formation of LC/[RSiO1.5] co-macromonomers will begin in the second round. Efforts to escape the use of alkenic functionalities for composite crosslinking by use of silsesquioxane condensation reactions will begin. Third round studies will incorporate tethered-masked silica particles in some co-macromonomers. Mechanical behavior and long term stability studies will follow the development of the more sophisticated co-macromonomers. Iterative studies are planned in all phases of the research. Standard chemical, spectroscopic and physical characterization methods will be used where applicable.
