Basic Evaluations of the Effect of Anti-Acid Erosion of the Teeth by a Fluoride

Research publications concerning the prevention and control of an acid erosion of the teeth are relatively scarce. Among the efforts from a localized points of view, mention can be made of the use of alkali as a gargling agent, the gas-mask, the application of fluoride on the tooth surface, the use of anti-acid chewing gum, etc. Of the investigators of anti-acid gum, Baba alone offered his material for a follow-up by other researchers, others simply reporting the effectiveness of this kind of chewing gum in print. In the present study, the authors were concerned with a series of basic evaluations of the effect of a fluoride used for purpose of caries prevention from the standpoint of anti-acid erosion. With permanent teeth (extracted) as study material, Brudevold's fluoride phosphate acid solution was topically applied to their surfaces and three items were evaluated: i) change in the hardness of dental surfaces, ii) change in the thickness and weight of teeth, and iii) optical microscopical change in the tooth surfaces through immersion in the acid solution. As an experimental method, a scratch ardness tester developed by our Department was used to measure hardness of the tooth surface before and after the application of a fluoride. After 24 hours following the application of the fluoride solution, the teeth were again measured for surface hardness under identical conditions. The mechanism of dental erosion by an acid is generally thought to start with direct contact of acid fumes on the surface of teeth to resulting in an early stage of decalcification, which is aggravated by the lips and other mechanical action. Therefore, an acid solution was sprayed on the teeth for an hour, and replicas were taken of them after rinsing under tap water (See photographs). Subsequently, foam rubber containing water (5g load) was used to polish the surfaces and, after an hour of polishing, they were rinsed and replicase were taken of them again. These material subjected to observations of 100 hours. Change in the thickness and weight of teeth was respectively measured by the use of a micrometers and chemical scales after each 10-hour intervals of acid spray. The fluoride solution was applied at intervals of 1-hour or 10-hour sprays, according to Brudevold is first and second methods. Three solutions of HCl, H2SO4 and HNO3 at pH level of 4.0 were used for immersing the teeth. The teeth were immersed in these solutions for an hour and then rinsed for an hour, and then rins