The Effect of Phosphate Structure on Dental Caries Development in Rats

¹ Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts

Five types of sodium phosphate compounds that differed only in their anion structure (ortho-, pyro-, tripoly-, trimeta-, and hexameta-) were added at the same phosphorus level to a cariogenic diet. These diets were fed to rats for 13 weeks beginning at 8 days of age.

In comparison with the control group, the reductions in caries development were: pyrophosphate, 29 percent; orthophosphate, 33 percent; tripolyphosphate, 46 percent; hexametaphosphate, 51 percent; and trimetaphosphate, 78 percent. All reductions were significant (<0.01 level, t test). The hexametaphosphate was more than twice as effective as a cariostatic agent than any of the other types.

The feeding of these phosphates (equivalent to 0.4 percent P) had no effect on weight gain, diet consumption, and the inorganic phosphorus content of serum or saliva.

An indirect correlation was observed between cariostatic activity and the buffer capacities of the phosphates. Since the cariostatic action of phosphates appears to be due primarily to a direct action on the tooth surface, this result indicates that a low pH in the oral environment may enhance the action of phosphates.

No correlation was observed between cariostasis and the chelating ability or the water solubility of the phosphates tested. Sodium trimetaphosphate has the highest cariostatic activity of the several phosphates tested in these laboratories to date and is currently the preferred compound for the control of dental caries in animals.