James J. Rae

The Effect of Sodium Fluoride on the Solubility of Calcium Phosphate, Tooth Enamel and Whole Teeth in Lactic Acid

When whole teeth were suspended in 1% lactic acid solutions, buffered with potassium hydrogen phthalate and adjusted to a pH of about 3.6, marked decalcification occurred in 24 hours at 37°. No decalcification was apparent, however, when sodium fluoride was added under the same conditions in concentrations varying from 0.2 to 0.5%. Tooth enamel was prepared according to the method of Manly and Hodge (2) and this material was used in an attempt to overcome individual variations in teeth. On shaking purified powdered tooth enamel with: (a) 1% buffered lactic acid and (b) 1% buffered lactic acid to which 0.5% sodium fluoride had been added, both at pH 3.5, a marked difference in the weights of residue left in the tubes after 24 hours was observed and these weights showed no appreciable difference after an additional 24 hours shaking. The addition of a similar amount of sodium chloride had only a very slight-effect on the decrease in the weight of the residue. Determinations of inorganic phosphate on the supernatant liquids were made calorimetrically by means of Kings method (3). The results of this experiment are shown in Table I. These phosphate values would indicate that even though the sodium fluoride decreases the apparent solubility of tooth enamel (as shown by the differences in decrease in weight of residue) the enamel is being dissolved, as indicated by the phosphate values, to the same or to even a greater extent in the tubes containing fluoride. This experiment was repeated, substituting pure tri-calcium phosphate in place of the tooth enamel, in view of the fact that powdered tooth enamel is a very complex substance. The results obtained (Table II) were entirely analogous to those described above, viz., the addition of sodium fluoride decreased the apparent solubility of calcium phosphate to about one-third of its solubility in 1% lactic acid; while at the same time the inorganic phosphate in the supernatants of all tubes rose to approximately the same values. The wide differences in calcium values would indicate that the decrease in the weight of the residue

Ammonia Production and Urease Activity in Saliva

A IMONIA concentration in saliva has been suggested as one of the controlling factors in natural immunity to dental caries. Although the am-, monia concentration has been thoroughly investigated,1-4 in no case has it been reported as high as the 50 mg. per cent claimed by Kesel5 to be necessary for the inhibition of the growth of lactobacillus acidophilus. Ludwick and Fosdick6 investigated the ammonia content of dental brushings to determine whether the ammonia concentration on the tooth itself was related to dental caries. No difference was found in the ammonia concentration on the tooth surfaces of caries-active or caries-immune persons. Kesel5 measured the ammonia produced by broth cultures of caries-immune salivas over an 8 day period and found that the caries-immune broths had an inhibitory effect on the growth of lactobacillus acidophilus which he attributed to the high ammonia content. In a previous report7 we found the ammonia producing ability of saliva reached a maximum in 24 to 48 hours and in no case did the amount produced equal 50 mg. per cent. As the salivas of a limited number of individuals formed the basis of this observation, it was decided to extend the investigation to a larger group and to include a study of the relation of the amount of salivary urease to the lactobacillus count and the effect of glucose on the activity of salivary urease.

Estimation of Salivary Phosphatase

The close relationship between bone formation and phosphatase was first indicated by Robison (1) in 1923. Since then he and his coworkers have shed much light on the problem of ossification and decalcification in the human body. They have shown that the enzyme phosphatase is one of the prime factors in controlling these processes. Phosphatases occur in most mammalian tissues and their importance and distribution has been reviewed by Folley and Kay (2). Their presence in saliva was demonstrated by Demuth (3). The methods for their estimation in saliva in use at present require too much time, often as long as 24 hours (4). For this reason the following rapid method is proposed. Native saliva is a mechanical mixture consisting of microorganisms, epithelial cells, food particles, calculi and a more or less viscid opalescent fluid. For an accurate analysis of this mixture it should be centrifuged and the centrifugate and precipitate analysed separately. Some workers have reported that centrifuged saliva contains no phosphatase (5), others are of the opinion that the mouth organisms are largely responsible for salivary phosphatase (6). Many have attempted to find a relationship between salivary phosphatase and dental caries. As an aid in arriving at a definite conclusion on any of these questions a rapid accurate method for the quantitative determination of salivary phosphatase would be valuable. The usual method for the determination of phosphatase is to hydrolyse a phosphoric ester, such as sodium glycerophosphate, by means of the phosphatase in the saliva and measure the inorganic phosphate liberated after 24 hours at 37°C. In the method proposed a phenolic ester of phosphoric acid, disodium phenyl phosphate, is used as sug-