Probiotics are bacterial cultures or living microorganisms that, when ingested in certain numbers, exert health benefits beyond general nutrition and support a good and healthy intestinal bacterial flora. The efficacy of probiotics in the treatment of gastrointestinal diseases is well-established. Probiotic organisms are thought to act through a variety of mechanisms, including competition with potential pathogens for nutrients or enterocyte adhesion sites, degradation of toxins, production of antimicrobial substances, and local/systemic immunomodulation. Experimental studies and results from randomized controlled trials have shown that certain gut bacteria, particularly species of Lactobacillus and Bifidobacterium, may exert beneficial effects in the oral cavity by inhibiting cariogenic streptococci and Candida spp. The periodontal pathogens can be regulated by antagonistic interactions with the administration of probiotics. Recent studies have shown reduced gum bleeding and symptoms of gingivitis with the application of L. reuteri. The lactobacilli flora have been shown to inhibit the growth of Porphyromonas gingivalis and Prevotella intermedia. Probiotic strains included in periodontal dressings were shown to diminish the number of most frequently isolated periodontal pathogens, such as Bacteroides spp., Actinomyces spp., and S. intermedius. This article summarizes the application of probiotics in dentistry.