Preparation, characterization and in vitro efficacy of an acid-modified β-TCP material for dental hard-tissue remineralization

Abstract

A blended material composed of beta-tricalcium phosphate (beta-TCP) and fumaric acid (FA) was prepared using a mechanochemical process. The structure and properties of the TCP-FA material was probed using particle size analysis, infrared, (31)P and (13)C solid-state nuclear magnetic resonance (NMR) spectroscopy, powder X-ray diffraction and calcium bioavailability. NMR studies showed that orthophosphate environments within beta-TCP remain largely unaffected in the presence of FA during mechanochemical processing; alternately, (13)C data indicated the carboxylic groups of FA are strongly affected during processing with beta-TCP. X-ray results reveal beta-TCP diffraction plane shifting with lattice contractions likely arising at the C(3) symmetry site. While milled beta-TCP (mTCP) produces a higher flux of bioavailable calcium relative to native beta-TCP, the mechanochemical conditioning of TCP-FA generates more than seven times the level of ionic calcium relative to mTCP. Collectively, the results from these studies indicate FA interfaces with calcium oxide polyhedra of the beta-TCP hexagonal crystal lattice, especially with the underbonded CaO(3) cluster manifested within the C(3) symmetry site of the beta-TCP motif. An in vitro remineralization/demineralization pH cycling dental model was then used to assess the potential of the TCP-FA material in reversing early stage non-cavitated enamel lesions. Characterization of the remineralization via surface and longitudinal microhardness measurements demonstrated that the TCP-FA material provides statistically superior remineralization relative to milled and native beta-TCP.