A Fundamental Study on Lanthanum as a Preventive of Dental Caries

Abstract

Lanthanum inhibits dental caries in experimental animals. The question of how lanthanum is absorbed by the enamel surface still leaves much to be studied.
The items of this study were as follows:
1) the relation between the concentration and the time of action of lanthanum when it is absorbed by the enamel surface;
2) the concentration of lanthanum in experimental caries control and its distribution in internal organs when it is prescribed;
3) quantitative analysis of the three elements La, Ca, and P by electron probe X-ray microanalyser and X-ray fluoressent spectrometer;
4) various lanthanum phosphates in enamel surface seen by X-ray diffractometory.
An exchange reaction of Ca and La in enamel surface occurred when an extracted human tooth was dipped in lanthanum solution and the surface become coated with lanthanum phosphate (LaPO₄).
After 3 days of immersion of a tooth in 2-8% of lanthanum solution, about 65% of the Ca was replaced and an equilibrium was reached. But in lanthanum solution of less than 1% replacement was slow, and in solution of 0.001% no reaction was detected.
The lanthanum compounds in the enamel surface were aciduric.
When lanthanum solution was given to a hamster, caries decreased clearly and 0.1%-0.01% of lanthanum solution (La: 312-31.2μg/ml) was most effective in preventing dental caries.
In an acute toxicity test, La was accumulated in all the internal organs when solution of more than 1.5% were used.
From this study I conclude that lanthanum fortifies the acid resistance of the teeth, that it is only slightly toxic, and that it is only slightly accumlated in internal organs.