Effects of Fluoride on the Calcium Phosphate Precipitation Method for Dentinal Tubule Occlusion

Abstract

Use of the calcium phosphate precipitation (CPP) method makes possible the occlusion of dentinal tubules to approximately 10 to 15 pn from the dentinal surface, and thus shows good potential for the treatment of dentin hypersensitivity. The precipitate formed in the dentinal tubules by the CPP method is, however, not apatite [HAP; Ca10(PO4)6(OH)2], a component of tooth and bone, but dicaldum phosphate dihydrate (DCPD; CaHPO 4·2H2O). Since fluoride enhances the conversion of DCPD to HAP, we evaluated the effects of fluoride on the texture of the precipitate formed by the CPP method and on its capacity to occlude dentinal tubules in this in vitro study. CPP solution (1.0 mol/L CaHPO4·2H 2O dissolved in 2.0 mol/L H3PO4) was applied to a dentin disk and was subsequently neutralized with a post-treatment solution (1 mol/L NaOH, from 0 to 0.1 mol/L NaF). Scanning electron microscopy revealed that the precipitate occluded dentinal tubules to a depth of approximately 10 to 15 μm from the dentinal surface, regardless of the NaF concentration (from 0 to 0.1 mol/L) in the post-treatment solution. Also, dentin permeability was reduced to 15% by the CPP treatment regardless of the NaF concentration. The Ca/P molar ratio of the precipitate, measured by x-ray micro-analysis, was higher (1.25 ± 0.04) in the presence of NaF than in its absence (1.03 ± 0.01). For further identification of the precipitate formed in the dentinal tubules, the same procedure was used in glass tubes (diameter, 1 mm), so that a larger amount of precipitate would be obtained. Powder x-ray diffraction analysis and Fourier transform infrared (FT-IR) measurement revealed that the precipitate formed by the CPP method gradually changed from DCPD to apatitic as the NaF concentration increased. We concluded that the addition of NaF to the post-treatment solution with the CPP method was desirable, since it led to more apatitic precipitate formation and did not lessen the occluding capacity of the precipitate.