220 J. A. GRAY AND M. D. FRANCIS 



sociated acid concentration. The rate was also inhibited by the 

 presence of cations and selected anions. Although this study dealt 

 only with surface decalcification, and the white spots typical of 

 incipient carious lesions were not produced, the relationships de- 

 termined also apply to some stages of incipient carious lesion forma- 

 tion. On this basis, an elementary mechanism was proposed for 

 incipient carious lesion formation (Gray et ah, 1962) founded on 

 the diffusion of undissociated acid into enamel to cause subsurface 

 decalcification. In addition, it was suggested that this system was 

 influenced by the presence of an organic coating to protect the en- 

 amel surface, as will be discussed subsequently. 



More recently, the rate of growth of incipient carious lesions was 

 measured (Kapur et ah, 1962) using a technique similar to that of 

 Wachtel and Brown ( 1963 ) . The lesions were produced with aque- 

 ous solutions of either lactic acid or acetic acid, and the formation 

 rate was determined by measuring the depth of the lesion as a func- 

 tion of exposure time. The rates of formation were then measured 

 as a function of pH and buffer concentration. The significant con- 

 clusion reached in this study was that the rate of formation was 

 proportional to the concentration of undissociated acid following, in 

 essence, the mechanism proposed by Gray et ah ( 1962 ) . 



Study of Incipient Carious Lesion Formation 

 Using Chemical Systems 



Cardinal Factors Affecting Decalcification Systems 



The study of the physical chemistry of incipient carious lesion 

 formation required the development of a system that would imitate 

 the in vivo circumstances and would be suitable for a quantitative 

 evaluation of the variables of the system. Acid or acidic buffer con- 

 stituted the fundamental element of the dissolution or decalcification 

 medium. Lactic acid was chosen on the basis of its being one of 

 the important acid products of bacterial metabolism. The organic 

 coating protecting the enamel surface, mentioned previously, was 

 considered essential, and a material to provide such a coating con- 

 stituted another fundamental element of the decalcification medium. 



