THE MICROBIOLOGY AND HISTOPATHOLOGY OF HUMAN ROOT CARIES

Based on numerous microbiological studies performed over the past seve ral decades, it is clear that mutans streptococci can cause human root caries. S. mutans fulfills the criteria for implicating bacteria in t he etiology of a mixed infection. For example, S. mutans is found in h igh numbers in lesion sites, higher than on sound root surfaces in the same subject. Subjects make elevated antibody levels to S. mutans ant igens. The organism produces a number of virulence factors including m etabolic acid from dietary sucrose and extracellular polysaccharides w hich facilitate bacterial colonization of tooth surfaces. Eliminating or reducing the number of S. mutans reduces the number of root caries lesions and can even result in ''healing'' of incipient lesions. There is also data demonstrating the cariogenic potential of S. mutans in a nimal models. Clearly, S. mutans fulfills the aforementioned requireme nts. Further, there is also evidence to implicate Lactobacillus as bei ng important in the pathogenesis of root caries by virtue of its assoc iation with S. mutans in these lesions. There is less recent evidence regarding the importance of Actinomyces in this disease. While this mi croorganism is present in root caries and while animal studies clearly point to their cariogenic potential, more recent studies with few exc eptions fail to find much association between Actinomyces and root car ies. There is an important caveat, however. The Actinomyces may have s ubspecies groups which are more highly virulent and more closely invol ved in the etiology of root caries than other groups. For example, A. viscosus serovar 2 is associated with root caries. This and other subs pecies groups may produce certain virulence factors not found within A ctinomyces species as a whole. For this group of microorganisms and fo r other potential pathogens, techniques in molecular biology such as 1 6S ribosomal RNA sequencing offers the hope of more precisely defining species and unraveling what may be largely problems in bacterial taxo nomy. Ribosomal RNA sequencing may reveal taxonomic relationships not apparent with classical phenotypic or serologic analyses. Other molecu lar methods, such as DNA or RNA probes to specific virulence factors m ay also reveal relationships between clinical lesions and microorganis ms possessing these virulence factors. Finally, there are clearly a nu mber of additional species which may have importance in root surface c aries as shown in some studies. These techniques can be used to identi fy the distribution of novel, even uncultivable bacteria in root carie s lesions and in this way establish their role in this important disea se.