Background: The World Health Organization defines probiotics as ‘live microorganisms which, when administered in adequate amounts, confer a health benefit to the host’. Traditionally, probiotic microorganisms have been used to prevent or treat gastrointestinal tract diseases. In the last 15 years, there has been increasing interest of a possible probiotic impact on the oral microbiota and dental caries. Dental caries is a multifactorial disease, and the causative factor in the oral microbiota includes a shift from a balanced microflora to a microflora that includes more aciduric species such as mutans streptococci (MS), non-mutans streptococci, and Actinomyces. MS is considered an opportunistic pathogen although several other bacteria also contribute to the disease. Early acquisition of MS is associated with early development of caries; therefore a desirable complement to other prophylactic measures would be a MS colonization inhibitor. Objective: To better understand how selected strains of probiotic lactobacilli interact with MS in vitro and in vivo and to study the impact of probiotic lactobacilli on caries development during childhood. Material and methods: The in vitro properties of probiotic lactobacilli were studied with regard to (i) acid production from sugars and sugar alcohols, (ii) growth inhibition capacity on clinical isolates and reference strains of MS as well as Candida albicans and (iii) the capacity to co-aggregate with MS. A randomized controlled trial (RCT) tested the short-term effect of intervention with two Lactobacillus reuteri strains on MS, which was evaluated after treatment with chlorhexidine. The re-growth patterns of MS and 19 other selected strains were also evaluated. In the second clinical study  we investigated the long-term effect on MS prevalence and dental caries after an intervention with Lactobacillus paracasei ssp. paracasei F19 (LF19) between 4 and 13 months of age. Results: The results from the in vitro testing showed that strains of probiotic lactobacilli differed in their fermentation patterns, inhibition capacity and their capacity to co-aggregate, which should be kept in mind in the translation to clinical research. The clinical study on short-term effects of two L. reuteri strains on MS and other oral strains showed no effect on re-growth patterns after intervention. The clinical study on long-term effects of LF19 showed no effect on the prevalence of MS. Furthermore, the clinical follow-up at 9 years of age showed no differences in either decayed, missing, and filled surface (dmfs) or DMFS between the probiotic and placebo groups. Evaluation of saliva samples showed no signs of oral colonization with LF19 in the study group. Conclusion: The in vitro testing showed potentials of the selected probiotic Lactobacillus strains for interference with MS and C. albicans. The results from the clinical studies showed no such effect on MS or dental caries. Evidence regarding the effectiveness of specific probiotic applications in the prevention of dental caries is limited and does not allow for conclusions concerning the use of probiotic bacteria as a preventive measure.

Background: Probiotic products are used to improve health, cure disease and in a prophylactic aim. However, there is limited research about its general effects on health in children, especially on oral health.  Aim: This study aimed to evaluate potential effects on oral health and otitis in 3-year- old children consuming probiotic Lactobacillus reuteri 17938 and Lactobacillus reuteri 5289.  Methods: This was a quantitative cross-sectional study where questionnaires concerning health and lifestyle of children (n=169) participating in the longitudinal study NorthPop Child, at the age of 4, 9, 18 and 36 months old, were compared to clinical parameters from a visit at the Public Dental Health Care at 3 years of age. Saliva samples from 142 children were analyzed by PCR. Results: This study showed that children consuming Lactobacillus reuteri 17938, had prevalence of the bacteria in saliva. Prevalence of Lactobacillus reuteri 5289 in saliva was not indicated. The prevalence of caries disease tended to be lower in probiotic- consuming children, though not statistically significant. Children consuming probiotics showed a higher prevalence of otitis and consumption of antibiotics compared to non- eaters.  Conclusion: Any conclusions about consumption and frequency required to gain and maintain the bacteria in the oral microbiome could not be made. Contradictory to other studies, this study found that children who consumed probiotics had more occasions of otitis media and antibiotic use. Future studies with a higher number of participants would be of interest to confirm these potential findings.