Babaahmadyi, Kaboutar Gholam; (1996) Variations in the microflora of dental plaque at defined sub-sites on approximal tooth surfaces. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Dental caries is most prevalent in sites which retain plaque. Environmental conditions vary markedly over such caries-prone sites (e.g. fissures and approximal surfaces), and this may influence the distribution and levels of the predominant bacteria. The primary aim of this study was to compare the microflora of plaque from discrete, small sub-sites around the, contact area on approximal surfaces of clinically sound teeth extracted for orthodontic reasons. The study was divided into three main sections: 1) Investigation of the distribution and composition of the microflora in approximal surface gingival margin plaque. Small plaque samples were removed from three sub-sites, away from (A), to the side of (S), and below (B) the contact area of clinically sound approximal surfaces. An average of 7–9 species were cultured from each plaque sample, but the species recovered varied between the sub-sites. The isolation frequency and proportions of S. mutans and Veillonella spp. were significantly higher at sub-site B. 2) A comparison of culture and immunofluorescence methods of bacterial detection. The use of immunofluorescence for identification proved to be a more rapid alternative to culture techniques. Both S. mutans 'c' and S. sobrinus 'd' showed a site preference in the order of B>S>A. An overall positive association was found between the presence of S. mutans 'c' and S. sobrinus 'd', and between mutans streptococci and lactobacilli. The results of the culture study were compared with those of immunofluorescence from the same samples, and the latter proved to be a more feasible method than conventional culture techniques. 3) Comparative analysis by restriction fragment length polymorphism (RFLP) of S. mutans 'c' and S. sobrinus 'd', and between S. oralis, S. mitis I and S. mitis II in order to improve discriminations among these species. Type strains and representative clinical isolates were compared for heterogeneity. 16s RNA genes from these species were amplified by the polymerase chain reaction and digested with restriction enzymes and the fragments separated by agarose gel electrophoresis. The restriction patterns obtained for S. mutans could be used to differentiate this species from other streptococci in human dental plaque. For other streptococci tested, the restriction profiles were similar with the exception of S. mitis I and II.

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