also affect the number of periodontopathogens in Furthermore, consumption of a mixture of seven plaque.49,50 Again, although encouraging results different Lactobacillus strains increased the num- have been observed, most studies have been fairly ber of salivary Lactobacillus counts, although the short. Furthermore, in some studies the observed identities of the strains in the saliva were not de- differences were quite small, though statistically termined.41 It seems feasible that probiotic bacte- significant. ria would colonize the oral cavity only when they were used in products in contact with the mouth. Oral candida Indeed, Maukonen et al8 did not detect any of the To the writer’s knowledge, only two studies probiotic bacteria administered in capsules in sa- have investigated the effects of probiotic bacte- liva samples. Surprisingly, consumption of cap- ria on oral Candida infection in humans.33,51 When sules containing a mixture of seven different Lac- a test group of elderly people consumed cheese tobacillus strains increased the number of salivary containing L. rhamnosus strains GG and LC705 and Lactobacillus counts.41 L. reuteri ATCC 55730 (= L. Propionibacterium freudenreichii ssp. shermanii JS reuteri SD2112) does not seem to influence the to- for 16 weeks, the number of high oral yeast counts tal number of salivary lactobacilli,36 but L. rhamno- decreased, but no changes were observed in mu- sus GG may increase it.33 cosal lesions.51 In a shorter study with younger Maybe because long-term colonization by pro- subjects, no significant difference was observed biotic bacteria is unlikely, albeit possible,58 poten- between effects of probiotic and those of control tial adverse effects of probiotic bacteria in the oral cheese on salivary Candida counts.33 cavity have not been a subject of much intensive research; however, probiotic products are used Halitosis widely; therefore, when dental health is consid- Halitosis is not a disease but a discomfort, al- ered, the acidogenicity of lactobacilli and bifido- though some oral diseases including periodontitis bacteria cannot be overlooked. For example, one may be the underlying cause; however, in approxi- L. salivarius strain is able to induce caries in an mately 90% of cases, the origin can be found in the animal model,62 and another is able to make a bio- oral cavity,52 and probiotics are marketed for the film model more cariogenic.63 treatment of both mouth- and gut-associated hali- tosis. Despite that, only a few clinical studies have FUTURE ASPECTS found different probiotic strains or products to Recently, oral lactic acid bacteria and bifido- be efficacious. The studied strains include E. coli bacteria have been isolated and characterized Nisle 1917, S. salivarius K12, three Weissella confusa for various oral health purposes, including car- isolates, and a lactic acid–forming bacterial mix- ies, periodontal diseases, and halitosis.10,56,64-68 ture, not specified by the authors of that work.53-56 In addition, dairy strains have been studied with the aim of characterizing potential new oral pro- COLONIZATION AND SAFETY OF biotics;69,70 thus, the new probiotic products tar- PROBIOTICS IN THE ORAL CAVITY geted for oral health purposes do not necessar- Some probiotic Lactobacillus and Streptococcus ily comprise the same species as products now strains seem able to colonize the oral cavity of in market. Furthermore, the species might not some people during the time that products con- necessarily belong only to genera Lactobacillus or taining them are in active use. However, both in Bifidobacteium. Indeed, S. salivarius K12 is used to vitro and in vivo evidence indicate that the differ- treat oral malodor,55 and preliminary results have ences between various probiotic strains, prod- been published on the safety and efficacy of a pro- ucts, and also host individuals are obvious.26,44,57,58 biotic mouthwash containing three different oral L. rhamnosus GG and two different L. reuteri strains streptococci for reducing the number of bacteria have been reported to colonize the oral cavity of associated with dental caries and periodontitis.71 48–100% of volunteers consuming products con- Genetically modified microbes bring a new taining them.44,58-60 In addition, S. salivarius K12, dimension to the concept of probiotics. One used for treating oral malodor, temporarily colo- approach is to reduce the harmful properties of nizes the oral cavity for a short time after use.61 pathogenic strains naturally colonizing the oral July 2010 - Vol.4 351 European Journal of Dentistry Haukioja