Structural and in vitro adhesion analysis of a novel covalently coupled bioactive composite

The interfacial adhesion between a restorative composite and tooth is one of the major factors that determine the ultimate performance of composite restoration. A novel polyurethane (PU) composite material was prepared by chemically binding the nano-hydroxyapatite (nHA) to the diisocyanate component in the PU backbone by utilizing solvent polymerization. The procedure involved stepwise addition of monomeric units of the PU and optimizing the reagent concentrations. The resultant materials were characterized structurally (Raman Spectroscopy) and in vitro bioactive analysis was conducted in modified-simulated body fluid for periodical time intervals. The in vitro study evaluated the push-out bond strength of existing obturating material and novel covalently linked PU/nHA composites to dentin after long-term storage in deionized water and artificial saliva. Human extracted molar roots were filled with experimental samples and analyzed at predetermined time intervals. The shear bond strength of samples was measured and surface morphologies were evaluated. Covalent bond formation was achieved between PU and nHA without intermediate coupling agent. With the increase in concentration of nHA, the composite showed more bioactivity and adhesion toward tooth structure. Bond strength of this new composite were in accordance with obutrating material, therefore, the material can be used as an obturating material because of its direct adhesion with tooth structure.