In vitro methods for the study of plaque formation and carious lesions

Streptococci known to be caries-conducive in experimental animals formed heavy bacterial plaques on extracted teeth, artificial teeth, stainless-steel wires and other objects. This was accomplished by cyclic exposures to a growth medium for 3 hr, 5% sucrose solution for 1 hr, and synthetic saliva for 3 hr in that order, for a total of 2 weeks. Streptococci known to be caries-inactive in animal tests did not form plaque under these conditions. Sucrose was required for plaque production and could not be replaced by glucose, fructose, galactose, lactose, sorbitol, or a mixture of glucose and fructose. The mucin in the synthetic saliva was found to be essential for plaque production in this test system. Filament-forming actinomycetes isolated from animal periodontal disease also formed a heavy plaque. Plaques were grown on a glass probe electrode using the above mentioned methods in order to obtain an estimate of acidity levels which develop under such deposits. In 5% sucrose the pH dropped to a range where enamel would be decalcified (4.5–5.0). The low pH values persisted under the plaque for 3 hr after the electrode had been subsequently transferred to synthetic saliva. Extracted human teeth were placed in an apparatus in which the various media described above could be automatically metered to an incubation chamber in preselected sequences for varying the time periods. Extensive plaque formation and incipient carious lesions developed within a 3-week period. Les streptocoques, connus comme étant cariogènes chezl'animal d'expérience, forment d'importantes plaques bactériennes sur des dents extraites, des dents artificielles des tiges en acier inoxydable et d'autres objets. Cela est obtenue par expositions cycliques dans un milieu de culture pendant 3 heures, dans une solution de saccharose pendant 1 heure et dans une salive de synthèse pendant 3 heures, dans l'ordre indiqué, pendant 2 semaines au total. Des streptocoques, non cariogènes pour l'animal d'expérience, ne forment pas de plaques dans ces conditions. Le saccharose est nécessaire pour la production de plaque et ne peut être remplacé par le glucose, le fructose, le galactose, le lactose, le sorbitol, ou un mélange de glucose et de fructose. La mucine de la salive de synthèse est essentielle pour la production de plaque dans ce système test. Des actinomyces, formant des filaments, isolés sur des animaux présentant des lésions du parodonte, forment aussi des plaques importantes. Des plaques sont mises