PHYSICAL CHEMISTRY OF ENAMEL DISSOLUTION 217 



Carious Lesion Formation 



Incipient carious lesions of enamel formed in the oral cavity com- 

 monly occur under a bacterial plaque. The metabolic products of 

 the bacteria that compose the plaque are almost certainly the de- 

 structive agents responsible for the attack on enamel. Unfortunately, 

 definition and characterization of plaque is too incomplete to permit 

 a chemical simulation of this system. In addition to establishing the 

 composition and morphology of the entire plaque, which consists 

 mostly of bacteria, it is necessary to define the composition of the 

 free aqueous phase. Furthermore, knowledge of the interfaces exist- 

 ing at the exposed plaque surface and the enamel-plaque junction 

 is needed for understanding the transport of the various chemical 

 species from one site to the other. At the moment, one of the most 

 deficient areas in caries research is this exact knowledge of the 

 plaque system, which can at best be described as a complicated mix- 

 ture of bacteria, enzymes, acids, other organic compounds, and in- 

 organic ions such as calcium and phosphate. This enamel-plaque 

 complex is the system of ultimate interest that needs to be described 

 by rational, scientific principles as well as simulated in the laboratory. 



The earliest attempts at producing carious lesions in the laboratory 

 (Magitot, 1878; xMiller, 1905; Pickerill, 1912) made use of mixtures 

 of saliva with foodstuffs such as sugar or bread, and, in some cases, 

 acidic solutions alone. These mixtures incubated with teeth for vary- 

 ing periods of time, but usually quite long, produced defects re- 

 sembling both the incipient stage and the fully developed lesion 

 with cavity formation. Such lesions covered the entire enamel sur- 

 face unless the area of exposure had been limited by protective 

 coatings. The importance of these experiments lay in the fact that 

 caries-like lesions could be produced outside the oral cavity. Com- 

 plicated as some of these systems were, they were more suitable 

 for experimental study than the oral situation. 



The next advances in the in vitro production of caries-like lesions 

 followed two directions. One consisted in studying known bacterial 

 cultures and nutrient systems, while the other involved elimination 

 of bacteria to use only chemical systems. The classical example of 

 the former is the "artificial mouth" devised by Pigman et al. ( 1952 ) . 



