Probiotics and oral health 352 cavity. The modified strain could then be used to replace the original pathogen. One ambitious and promising example is the generation of an S. mutans strain with a complete deletion of the open reading frame of lactate hydrogenase and thus significantly reduced cariogenicity.72 Another option could be to enhance the properties of a potentially beneficial strain. One example is the construction of an L. paracasei strain with a functional scFV (single-chain variable fragment) antibody binding to the surface of Porphyromonas gingivalis.73 Probiotics are by definition viable, and until re- cently the viability of probiotic bacteria was usu- ally ascertained by culture; however, both in the intestine and in the oral cavity, a significant pro- portion of bacteria are not yet cultivable. In ad- dition, bacteria in biofilms can enter a dormant state; therefore, it can be speculated that bacte- ria with the ability to influence the microbiota in these sites need not necessarily be culturable. There has also been debate on the definition of “vi- able,” and even whether the definition of probiotic should be changed. Indeed, heat-killed beneficial oral Streptococcus strains have been shown to ex- ert effects similar to those of a living bacterium.74 Furthermore, viable but nonculturable probiotic bacteria maintain properties of viable bacteria.75 SUMMARY AND CONCLUSIONS The interest in oral probiotics has been grow- ing during the last decades. Most of the stud- ies have been conducted with probiotic strains originally suggested for gut health; however, it is important to realize that each of the suggested health benefits should be studied for each bacte- rial strain individually. Thus, a probiotic bacterium in the mouth is not necessarily an oral probiotic. Furthermore, it is quite possible that the same species are not optimal for all oral health purpos- es; e.g., different properties might be desired in respect to dental and gingival health. At least some of the probiotic bacteria used in various probiotic products may colonize the oral cavity during the time they are in use; thus, the ef- fects of probiotic bacteria in the oral cavity are im- portant to understand. Probiotic bacteria seem to affect both oral microbiota and immune respons- es. On the other hand, the extent to which bacteria in food or in food ingredients can influence rela- European Journal of Dentistry tively stable oral microbiota is difficult to predict. Thus, both research to unravel the mechanisms of possible probiotic action and long-term clinical trials are needed if probiotics are to provide a new scientifically proven means of preventing or treat- ing oral diseases. Several health-promoting effects of probiotic bacteria are well documented,2,3 and there is no reason to restrict the use of probiotic products be- cause their effects on oral health are not yet well understood; however, their recommendation for dental health purposes is not yet justified. REFERENCES 1. Ashwell M. Concept of functional foods. 2002; ILSI (Inter- national Life Sciences Institute) Europe, B-1200 Brussels, Belgium ISBN 1-57881-145-7 2. de Vrese M, Schrezenmeir J. Probiotics, prebiotics, and synbiotics. Adv Biochem Eng Biotechnol 2008;111:1-66. 3. Saxelin M, Tynkkynen S, Mattila-Sandholm T, de Vos WM. Probiotic and other functional microbes: from markets to mechanisms. Curr Opin Biotechnol 2005;16:204-211. 4. Busscher HJ, van Hoogmoed CG, Geertsema-Doornbusch GI, van der Kuijl-Booij M, van der Mei HC. Streptococcus thermophilus and its biosurfactants inhibit adhesion by Candida spp. on silicone rubber. Appl Environ Microbiol 1997;63:3810-3817. 5. Rodrigues L, van der Mei H, Teixeira JA, Oliveira R. Bio- surfactant from Lactococcus lactis 53 inhibits microbial adhesion on silicone rubber. Appl Microbiol Biotechnol 2004;66:306-311. 6. Schwandt LQ, van Weissenbruch R, van der Mei HC, Buss- cher HJ, Albers FW. Effect of dairy products on the lifetime of Provox2 voice prostheses in vitro and in vivo. Head Neck 2005;27:471-477. 7. Ahrne S, Nobaek S, Jeppsson B, Adlerberth I, Wold AE, Molin G. The normal Lactobacillus flora of healthy human rectal and oral mucosa. J Appl Microbiol 1998;85:88-94. 8. Maukonen J, Mätto J, Suihko ML, Saarela M. Intra-individ- ual diversity and similarity of salivary and faecal microbio- ta. J Med Microbiol 2008;57(Pt 12):1560-1568. 9. Colloca ME, Ahumada MC, Lopez ME, Nader-Macias ME. Surface properties of lactobacilli isolated from healthy subjects. Oral Dis 2000;6:227-233. 10. Simark-Mattsson C, Emilson CG, Håkansson EG, Ja- cobsson C, Roos K, Holm S. Lactobacillus-mediated inter- ference of mutans streptococci in caries-free vs. caries- active subjects. Eur J Oral Sci 2007;115:308-314. 11. Rotimi VO, Duerden BI. The development of the bacterial flora in normal neonates. J Med Microbiol 1981;14:51-62.