VARIATIONS IN THE PREDOMINANT CULTIVABLE MICROFLORA OF DENTAL PLAQUE AT DEFINED SUBSITES ON APPROXIMAL TOOTH SURFACES IN CHILDREN

The distribution and composition of the resident microflora were deter mined in approximal gingival margin plaque from 21 premolars extracted from schoolchildren (mean age 12.0+/-1.8 yr). Indigo carmine (5% w/v) was used to visualize plaque to facilitate sampling. About 1 mm(2) of plaque was removed from sites away from (A), to the side of (S), and below (B) the contact area. Plaque samples were dispersed, serially di luted, and cultured on selective and non-selective agar media. An aver age of seven to nine species was found at each subsite. Streptococcus and Actinomyces were subdivided on the basis of a range of biochemical tests. The predominant Actinomyces and streptococcal species at most subsites were A. naeslundii and Strep. mitis biovar I. A naeslundii an d A. odontolyticus were isolated more often at subsite B (90.5 and 57. 1%, respectively), and A. israelii at subsite S (66.7%). Strep. mitis I ans Strep. sanguis were found more frequently at subsite S (76.2 and 66.7%, respectively), whereas Strep. mutans, Strep. sobrinus, Strep, gordonii and Veillonella spp. were recovered most commonly from subsit e B (85.7, 33.3, 38.1 and 76.2%, respectively). The isolation frequenc ies of Strep. mutans and Strep. sobrinus were significantly higher at subsite B (A<B, p<0.01 and p<0.05, respectively), Veillonella spp. wer e significantly higher at subsites B and S (A<B, P>0.01; B>S, P<0.05), while Neisseria spp. were most common at subsite A (A>B, P<0.03). IgA 1 protease-producing species were found at each subsite, but they form ed only a small proportion of the total Streptococcus population. This study has shown that local variations were evident at different subsi tes, both with respect to species prevalence and to proportions of eac h species within each subsite. The population shifts in gingival margi n plaque appear to relate to the location of plaque in relation to the most caries-prone site below the contact area B. (C) 1997 Elsevier Sc ience Ltd.