Physicochemical and Mechanical Evaluation of Cation-Modified ACP Acrylic Resin Composites.

Our recent research of amorphous calcium phosphate (ACP)-based polymeric dental materials has resulted in biocompatible composites with a potential to arrest and/or reverse tooth mineral loss (1-4). However, less than optimal filler/matrix cohesion and the excessive water sorption may limit clinical applicability of ACP composites as currently formulated. The spontaneous, uncontrolled agglomeration of ACP fillers has been suggested as the major cause of ACP's uneven dispersion within polymerized resin matrices (5), resulting in diminished strength and durability of these composites. To improve the physical and chemical properties of ACP composites it is necessary to focus on (a) exploring structure/composition/property relationships of different ACP fillers and resin matrices, and (b) evaluating intra-composite filler/organic matrix interactions. In this study we assess the role of various cations, introduced during the synthesis of ACP as a means of controlling the particle size, compositional and structural properties of ACP fillers, with special emphasis on ACP's chemical stability (critical in preventing the premature intra-composite conversion to low-ion releasing crystalline apatite). The main hypothesis to be tested is that cations introduced ab initio during the synthesis may reduce the degree of spontaneous ACP agglomeration and lead to composites with improved properties because of more homogeneous dispersion of ACP in the resin matrices. These cations may also improve ACP's stability, i.e., lower its solubility by reducing the number of active dissolution sites via surface adsorption and/or structural incorporation. Relevant tasks are to validate the amorphous character of various cation-modified ACPs, evaluate their stability upon aqueous exposure and assess their effect on mechanical strength and degree of vinyl conversion of composites formulated with a photo-activated binary resin.