White spot lesions demineralization

White spot lesions are the earliest macroscopic evidence of enamel caries [37], The lesions are caused by acids formed by bacterial fermentation of dietary sugars. This leads to a fall in plaque pH and dissolution of the mineral component of the tooth enamel. Under normal conditions, the demineralization process is balanced by remineralization due to diffusion of ions (Ca, P and hydroxyl) from saliva into the enamel when plaque pH returns to neutrality. However, if demineralization extent exceeds that of remineralization, then an incipient lesion is formed. 

The unusual and important characteristic of a white spot lesion is that the majority of the demineralization occurs in the subsurface region. Typical lesions possess a surface layer which appears relatively unaffected by the acid attack. If lesion progression is left unchecked, then eventually the surface layer collapses to yield a cavity. 

White spot lesions vary from person to person, from tooth to tooth and from surface to surface, as well as with age of the lesion. Their nonstandard nature makes analysis of the lesion incredibly difficult. In order to increase the level of control over experiments with lesions, a standard method of producing in vitro lesions has been used in this study. Many of the features of white spot lesions can be mimicked by in vitro lesions, though no method completely replicates the development of the natural lesion. The lesions produced are usually referred to as caries-like lesions indicating that they are not a natural white spot lesion, but an artificially produced lesion for experimental analysis. These artificial lesions provide invaluable information about the formation, the processes of demineralization and remineralization, and the composition of the lesion at different stages, in addition to being the basis for the understanding of possible treatments of the lesion. 

To make the white spot lesions, human premolars were coated with nail polish except for a 5-mm square on their buccal surfaces. This ensured that demineralization always occurred at a specific location. The samples were then immersed in 200 ml methyl cellulose gel with 200 ml lactic acid solution (pH 4.6) poured on top, but separated by a sheet of filter paper. The teeth were stored in this solution at 3 7°C for 14 days to allow the lesions to develop. After removal from the gel, the teeth were washed and sectioned through the center of the lesions to enable the cross-section of each lesion to be viewed. The two cross-sections created for each lesion were then mounted in a low temperature cure epoxy and polished to an optical finish using 1/4-micron grit (diamond paste). 

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