A Microbiological Study of Old Plaque in Occlusal Fissures of Human Teeth

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Abstract
As a part of our investigations on fissure plaque, the present study presents data on the microflora of ten natural occlusal fissures implanted for 200–270 days in lower molars of dental students. No carious lesions were revealed by clinical and microradiographic examination at the end of this period. Microscopy of fissure plaque suspensions showed predominantly gram-positive cocci and short rods, few gram-negative bacteria, few filaments and no fusiforms, spirils or spirochetes. Anaerobic viable counts (AnVC) were similar to our previous counts for 7-day-old samples. On selective media, no yeasts grew and lactobacilli, haemophili and veillonellae constituted minor and variable proportions of the cultivable flora. Streptococcal counts on mitis salivarius agar corresponded to 6–94% (median 23%) of the AnVC, and 23–10% (median 50%) of the colonies appeared to be Streptococcus mutans. Thus, even in the absence of caries, S. mutans constituted as large a proportion of the streptococcal flora in fissures as in caries-active smooth surface plaque. In an earlier study of 7-day-old fissures, S. mutans constituted less than 2% of the colonies on mitis salivarius agar. Apparently, S. mutans colonizes fissures rather slowly. It should be noted that even for 200- to 270-day-old fissures the counts of S. mutans on mitis salivarius agar and MSB agar constituted only minor proportions of the AnVC (median values 11 and 4%, respectively for the two media).