Calcium phosphate solutions at various concentrations and pH levels were used to obstruct the dentinal tubules. The effects were evaluated by measurements of permeability through dentin discs and by scanning electron microscopy. Precipitation kinetics were followed by pH changes in the solutions and products were determined by X-ray powder diffraction. The solutions were applied in two ways: (a) calcium and phosphate solutions were mixed before application and (b) one solution (calcium or phosphate) was applied first followed by the other solution. Three kinds of human dentin discs were used; one with smear layer and the other two with tubules exposed by sonication or etched by acid. The high concentration calcium phosphate solutions at pH=9.5 rapidly precipitated amorphous calcium phosphates that obstructed the dentinal tubules and decreased dentin permeability by 85% or more. At pH=5.6, the calcium phosphate solutions precipitated large crystals of dicalcium phosphate dihydrate. In this case, the effectiveness in obstructing dentinal tubules was found to be procedure sensitive.
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