Polymer induced crystal organization of composite resins.

The elaboration of efficient dental resins requires a high degree of internal cohesion and a strong organization of the filler/matrix systems, and a good compatibility between the organic and inorganic constituents of the composite. Combining fractal aerosils and polymer constitutes an original way to realize promising dental composites. Determination of the combined roles of fractal fillers and polymers in the synthesis of composite resins, and the polymer dose in the crystal arrangement of the composite constituents, both being a requisite for the optimization of the filler/matrix compatibility. Poly(methyl methacrylate) was used to enhance the compatibility between the organic matrix composed of the (bisphenol A dimethacrylate+1,3-butanediol dimethacrylate) mixture, and the aerosil filler. The characteristics of the assemblage of the latter particles that was mediated by adsorbed polymer and resulted in the formation of dense sediments were determined. The macroscopic crystals that nucleated within the settled phases were analyzed in order to evidence their internal arrangement and cohesion by Differential Scanning Calorimetry. Atomic force microscopy was employed to reveal the surface texture. The association of fractal powders and polymer gives rise to agglomerated structures of high imbrications and cohesion. The polymer dose initially added to the aerosil particles suspended in the mixture was determined (i) to set the aerosil aggregation mechanism and, as a result, the aggregate size and porosity; (ii) to control the formation and characteristics of the settled phase; and (iii) to determine the crystal organization and the filler/matrix compatibility. The formation of hexagonal platelets incorporating the filler/polymer aggregates within the crystal organization demonstrates the high degree of compatibility of the different constituents of the composite that is mediated by the amount of polymer adsorbed at the aerosil/matrix interface.