Some Factors Affecting the Interaction of Hydroxyapatite with Sodium Monofluorophosphate

The reaction between hydroxyapatite and sodium monofluorophosphate has been studied under conditions pertinent to the use of a sodium monofluorophosphate dentifrice. Salivary o-phosphate and bicarbonate both inhibit the reaction. As the flow of saliva is stimulated the bicarbonate level rises and the inhibition becomes more marked. The reaction between monofluorophosphate and hydroxyapatite is favoured by a decrease in pH and the inhibition caused by saliva can be partially overcome by raising the concentration of sodium monofluorophosphate in the dentifrice. The results of these experiments indicate that the content of sodium monofluorophosphate in a dentifrice should be increased from 0.8 to 2.0%. It is preferable that the dentifrice gives a pH of below 7.0 in the mouth and that the other components of the dentifrice be chosen so that they do not add to the soluble o-phosphate in the saliva.