title: The relevance of microbiological tests in the prediction of caries in adolescents
Creators: name: Russell, Joyce Irene
Publisher: name: University of Glasgow
Year: 1987
Subjects: subject: Microbiology, dentistry.

description: Although many investigators have attempted to associate dental caries rates with levels of oral micro-organisms, it has not yet proved possible to predict caries development reliably on an Individual basis using a single predictive test. Surprisingly, few studies have investigated the effects of combining the results of a number of different microbiological tests. This thesis reports the investigation of a range of different methods for the estimation of salivary levels of micro-organisms identified by other investigators as being related to subsequent dental caries development. The organisms studied were Lactobacillus spp., Streptococcus mutans, and Candida spp.. Additionally, Veillonella spp. were investigated because, although they had not previously been identified as predictors of caries, it is believed that these micro-organisms metabolise the lactate produced by other oral bacteria, and may thus modify the caries process. It was therefore thought possible that knowledge relating to salivary levels of Veillonella spp. might be of additional benefit in caries prediction. Both pure cultures of the micro-organisms described, and mixed salivary samples, were used in the selection of media for use in subsequent caries prediction. The media chosen were Rogosa SL agar, Dentocult dip-slides and Snyder tests for Lactobacillus spp.; Mitis Salivarius Bacitracin agar and a mannitol-containing colorimetric broth for Strep, mutans; Sabouraud dextrose agar for Candida spp.; and Rogosa vancomycin agar for Veillonella spp. The magnitude of variation in counts of oral micro-organisms on Rogosa SL agar, mitis salivarius bacitracin agar, Sabouraud dextrose agar and Rogosa vancomycin agar was then studied: within repeated estimations of counts from mixed salivary samples; using salivary samples obtained from the same children at different times of the day; in samples obtained on different days; and in sampling at monthly intervals over 2.5 years. Additionally, the effects of sample storage at different temperatures and for increasing periods of time were investigated, and the effects of subjects eating or drinking two snack foods prior to sample donation were also studied. It was concluded that the standard deviation of counts within single salivary specimens was of the order of 0.1 logarithmic units, with increasing variation on daily and monthly sampling, with the standard deviation of such counts usually being within 0.5 logarithmic units. Additionally, storage of samples for up to 24 hours at room temperature was found to effect sample counts little, and the ingestion of potato crisps or cola, either five minutes or one hour before sample donation, were not found to affect microbiological counts significantly. The Lanarkshire clinical dentifrice trial, involving 3000 children who were examined clinically and radiographically at annual intervals over a three year period, provided the opportunity to investigate the relevance of the selected microbiological caries predictive tests in a large subgroup, initially of over 500 adolescents. The dentifrice trial itself showed that a significant dose-relationship existed between dental caries increments and sodium monofluorophosphate in toothpastes, at concentrations over 1000 ppm. When the levels of the micro-organisms studied were compared with caries prevalence and caries incremental data, associations were found between the caries indices and counts of Lactobacillus spp., Strep, mutans and Candida spp.. Levels of Veillonella spp. were not found to correlate consistently with either caries prevalence or incidence. However, the magnitude of these significant correlations was insufficient to allow single microbiological counts to be used as diagnostic or prognostic tests at an individual level. Indeed, correlations between caries prevalence data and subsequent caries increments were greater than those between any of the microbiological estimations and the caries increments, although using stepwise regression analysis the prediction of future caries increment was improved using combinations of clinical and microbiological data. However, by combining microbiological tests alone, or even using combinations of clinical and microbiological tests, diagnosis or prediction of caries groups (low, medium, or high) proved possible in less than 50% of individuals. Microbiological predictive tests were also compared with some salivary and dietary predictors, and were generally found to be superior to these other predictive methods. The possibility that microbiological tests might provide more accurate predictions in a group of younger children was also investigated. Although some of the correlations found appeared higher than those found for the adolescents, the differences were nonsignificant. It was concluded that caries prediction at an individual level is not yet possible using either single or combined microbiological tests, and that clinical examination of adolescents was a quicker, less expensive and more accurate predictor of caries increment. However, these tests provide additional information about caries incidence, which might possibly be of benefit in monitoring selected groups of individuals, such as those with previous high caries experience for whom advanced dental techniques are considered, or those with medical problems in whom it is essential that caries is prevented.