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

A blended material composed of beta-tricalcium phosphate (β-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, 31P and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy, powder X-ray diffraction and calcium bioavailability. NMR studies showed that orthophosphate environments within β-TCP remain largely unaffected in the presence of FA during mechanochemical processing; alternately, 13C data indicated the carboxylic groups of FA are strongly affected during processing with β-TCP. X-ray results reveal β-TCP diffraction plane shifting with lattice contractions likely arising at the C3 symmetry site. While milled β-TCP (mTCP) produces a higher flux of bioavailable calcium relative to native β-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 β-TCP hexagonal crystal lattice, especially with the underbonded CaO3 cluster manifested within the C3 symmetry site of the β-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 β-TCP.