PHYSICAL CHEMISTRY OF ENAMEL DISSOLUTION 219 



This system permitted the production of lesions in all the various 

 stages and demonstrated the wide variety of defects obtainable with 

 different l)acterial strains. Several other methods have been devel- 

 oped for producing incipient caries-like lesions using a nutrient 

 solution mixed with saliva or bacteria (Gore, 1940; Darling, 1956; 

 Newbrun et ciL, 1959; Soni and Bibb\-, 1961). Francis and Meckel 

 ( 1963 ) devised such a method using an agar liase containing the 

 nutrient and salix a that produced lesions in a matter of days and 

 was sufficiently well controlled for use as a routine test method. A 

 bacterial medium inoculated with Lactobacillus casei and sterilized 

 after a suitable incubation time was used to show that the products 

 of bacterial metabolism, such as acids, were responsible for produc- 

 ing the caries-like lesions rather than the l:)acterial enz\mes or the 

 bacteria per se (Briner, 1963). Teetli that were immersed in such a 

 medium developed the same defects as those found in a medium 

 containing viable organisms. The production of such lesions in en- 

 amel has been achiexed using onlv acid mixed with a viscous or gel 

 base, omitting entireh both the organisms and the nutrients (von 

 Bartheld, 1958; Miihlemann, 1960; Opdyke, 1962). 



One of the more extensive studies of a chemical svstem for pro- 

 ducing incipient caries-like lesions in enamel was done using acidic 

 solutions containing calcium and phosphate (Coolidge et al., 1955). 

 A definite relationship among the hydrogen, calcium, and phosphate 

 ion concentrations was found to be necessarv in order to obtain char- 

 acteristic incipient lesions. Similar observations were made using a 

 novel technique whereby the progress of the lesion could be ob- 

 served on a section of a tooth (Wachtel and Brown, 1963). A de- 

 tailed study was also made of lesions produced bv lactic acid alone 

 (Hals et al., 1955), and the various combinations of subsurface dis- 

 solution and surface dissolution were descril:)ed. Another investiga- 

 tion was made using acetic acid alone, where the lesions were 

 examined with polarized light and microradiography (Soni and 

 Brudevold, I960). 



In a stud\' of the dissolution of enamel in acidic bufi^ers, the im- 

 portant factors afi^ecting the reaction between acid and hvdroxy- 

 apatite were isolated (Gray, 1962). The rate of dissolution was 

 found to be primarily dependent on and proportional to the undis- 



