Objectives: The aim of this review is to examine the potential mechanisms of probiotic bacteria in the oral cavity and to summarize the observed effects of probiotics with regard to oral health. Additionally, safety concerns and future aspects are briefly considered. Data sources: Studies suggest that probiotics may function not only by direct inhibition of—or enhanced competition with—pathogenic micro-organisms, but also by more subtle mechanisms including modulation of the mucosal immune system. Clinical studies reporting the anticariogenic effects of probiotics and their use in the treatment of periodontal disease and in the treatment of halitosis and Candida albicans have been identified. Study selection: The studies focus on probiotic Lactobacilli and Bifidobacteria genera that are most used in various probiotic products. Conclusions: Although direct recommendations for the use of oral probiotics cannot yet be given, scientific evidence so far indicates that probiotic therapy may be a reality in dentistry in the future.