The aim of the present thesis was to find a test for prediction of caries activity which would be useful in routine clinical work.Correlations between oral health, general health, food habits and socioeconomic conditions were investigated in 4- and 8-year-old children. It was found that the salivary secretion rate and the prevalence of oral lactobacilli were factors which might be useful in caries prediction.In 5- and 8-year-old children negative correlations between caries frequency and secretion rate, pH and buffer effect of saliva were demonstrated. However, these parameters showed a wide range of variation.A dip-slide test (Dentocult®), for determination of the number of lactobacilli in saliva, were investigated. The test proved to be reliable for determining of the number of lactobacilli in saliva.The clinical use of information on salivary secretion rate and number of lactobacilli in saliva in prediction of caries activity was examined in 115 14-year-old children over a period of 64 weeks. The number of lactobacilli in saliva, but not the salivary secretion rate, was correlated to caries activity. The number of lactobacilli in saliva seems to reflect the frequency of ingested fermentable carbohydrates and indirectly the risk for initiation of carious lesions. However, when the lactobacillus test is used it is important that there are no such areas of microbial retention on the teeth, as open cavities, poorly executed conservations, dentures or orthodontic bands. The lactobacillus test would make it possible to individualize prophylactic caries treatment. / <p>Annan ISSN på omslaget och titelblad (ISSN 0934-7532).</p><p>Härtill 5 delarbeten.</p> / digitalisering@umu