Occlusion of Dentinal Tubules with Calcium Phosphate Using Acidic Calcium Phosphate Solution Followed by Neutralization

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Abstract
The occlusion of dentinal tubules with calcium phosphate, by a calcium phosphate precipitation method (CPP method), was investigated in vitro for evaluation of the potential value of this method for the treatment of dentin hypersensitivity.The method consists of treating the dentinal surface with a CPP solution, i.e., an acidic solution that contains both calcium and phosphate, followed by neutralization with basic post-treatment solution. The CPP solutions used in this study ([Ca] = 0.2 - 1.0 mol/L, [PO 4] = 0.2 - 4.0 mol/L) were prepared by dissolving Ca(OH)2 or CaHPO 4·2H2O in H3PO4 or HCl, and 1 mol/L NaOH solution was used for the post-treatment solution. Sections of human dentin disks treated by the CPP method were observed by scanning electron microscopy, and the precipitate in the dentinal tubules was subjected to x-ray micro-analysis. After treatment by the CPP method, dentinal tubules were occluded to a distance of approximately 15 μm from the surface, and the precipitate showed a Ca/P molar ratio of 1.03 ± 0.01. To obtain a larger amount of precipitated mineral for further analysis, we used the same procedure with glass tubes (inside diameter, 1 mm). Powder x-ray diffraction analysis and FT-IR measurement revealed that the precipitate was dicalcium phosphate dihydrate (CaHPO4·2H2O). The instant precipitation of calcium phosphate mineral in the dentinal tubules demonstrated the potential value of the CPP method for the occlusion of dentinal tubules; this occlusion may be useful for the treatment of dentin hypersensitivity.