Applicability of Calcium Phosphate Based Paste as a Tooth Care Material

Abstract

 Purpose: The purpose of the present study was to clarify the mechanism and applicability of calcium phosphate based paste as a tooth care material (hereafter, “AP paste”) that was designed on the principle of calcium phosphate cement. The study examined: 1) percolate modality of the elements derived from AP paste, 2) identification of the precipitated apatite crystals in dentin, and 3) crystal growth of apatite in dentin.
 Methods: Extracted human permanent teeth were used in this study. (1) Element analysis: The analysis evaluated the distribution and percolate modality of elements derived from AP paste to dentin. Dentin samples having experimental windows were demineralized with 50 mmol/l acetic acid for three days. AP paste was then applied to the windows three times a day for two weeks. The samples were embedded in epoxy resin and sectioned. The highly polished sections were observed with secondary electron images and back-scattered electron images. Semi-quantitative analysis was also performed for Ca, P and F elements using an electron probe micro analyzer (EPMA). (2) Transmission electron microscopy (TEM) : The samples were evaluated for crystal morphological observation and crystal identification using TEM and electron diffraction pattern, respectively, with references of HAp, tetra-calcium phosphate (TTCP) and calcium hydrogen phosphate anhydrous (DCPA).
 Results: 1) EPMA analysis confirmed that Ca, P and F elements obviously percolated to and accumulated in dentin; 2) Newly formed crystals were precipitated in the dentin surface and dentinal tubules. The electron diffraction pattern confirmed that those crystals were apatites; 3) The application of AP paste caused the mineral contents in demineralized dentin to regain the normal level of mineral contents in intra- and inter-tubular dentin. Distinct crystal growth and remineralization were exhibited by comparing the a- and c-axis of the crystals.
 Conclusion: TTCP and DCPA in the paste released calcium and phosphate ions, and the ions clearly promoted crystal growth in demineralized dentin. Thus, it is considered that the AP paste would promote dentin calcification to a higher degree as a biocompatible material.