The overall goal is to generate rationally designed expanding monomers and coreactants for a low stress, low shrinkage high performance resin system with optimal cure characteristics, structural integrity, and biocompatibility that has the potential of long term clinical success as a stable adhesive/matrix resin for dental composites. The successful development of these material would greatly increase the longevity of dental composite/adhesive systems and substantially improve dental patient care. In order to achieve these goals the following specific aims will be addressed: (1) To synthesize the most promising expandable monomer and polymer structures as specified by the Molecular Modeling and Rational Biomaterials Design (MMRBD) project. (2) To formulate and polymerize matrix resin systems containing expandable monomers designed for optimum physicochemical compatibility, reactivity, and expandability; (3) To evaluate and test the physicochemical mechanical, and structural properties of the expandable monomer/epoxy-based matrix resin formulations and (4) To generate bond strength data for Quantitative Structure Activity Relationships so that specific and quantifiable relationships between molecular structure of cationic cure promoters and bonding to tooth structure can be established. This project has four phases of effort corresponding to the four specific aims. The first phase will focus on synthesis and characterization of recommended structures designed and screened using functional group reactivity principles, molecular and computational modeling of reaction energetic nd solubility parameter theory, as suitable monomers for incorporation into cationic matrix resins. The second phase will focus on the formulation and polymerization of matrix resin systems containing these new compounds, and will include studies to determine the effects of water and/or impurities on photocationic cure. The third phase will involve physicochemical characterization and testing of promising matrix resin systems and will include studies to establish polymerizate structure and confirm polymerization pathways of expandable monomer/oxirane comonomer system. The fourth phase will focus on generating data to establish and expand a QSAR data base relating structural features of cationic cure promoters to cure and bonding of cationically cured oxirane based adhesives. Close interaction and sharing between this projects in the program, as guided by the Principal Investigators and coordinated through the Administrative Core, will result in superior, efficacious materials for the next generation of epoxy-based cationic dental adhesive/composite restoratives.