Several authors have suggested that probiotic bacteria could also be beneficial to oral health. Species of Lactobacillus and Bifidobacteria may exert beneficial effects in the oral cavity by inhibiting cariogenic Streptococci and Candida spp (Bhardwaj, 2010).
The mechanisms of probiotic action in the oral cavity could be similar to those described for the intestine. The mechanisms by which probiotics exert their effects are largely unknown, but may involve modifying pH, antagonizing pathogens through production of antimicrobial compounds, competing for pathogen binding and receptor sites, stimulating immune modulatory cells and producing lactase. It is also showed that they have influence to the immune system through several molecular mechanisms (Bhushan & Chachra, 2010).
To have a beneficial effect in oral cavity, a probiotic should have a tendency to form a biofilm that acts as a protective lining for oral tissues against oral diseases. Probiotics strains have been shown to vary broadly in their adhesiveness to saliva-coated HA and so in biofilm formation ability. Among probiotics strains L. rhamnosus GG exhibited the maximum values of adhesion, comparable to those of the early tooth colonizer S. sanguinis. Dairy starter L. bulgaricus strains adhered poorly to sHA.
Probiotic bacteria adhesion to oral soft tissues is another aspect that promotes their health effect to the host. Cell adhesion is a complex process involving contact between the bacterial cell and interaction with surfaces. The epithelial lining of the oral cavity despite its function as a physical barrier, actively participates in immune response. It has been shown that probiotic bacteria can stimulate local immunity and modulate the inflammatory response. Lactobacilli as well as other gram positive bacteria express ligands for toll-like receptors (TLRs) which initiate immune responses enabling detection of both pathogens and indigenous microbiota by epithelial cells. Recognition of commensal bacteria by these receptors (TLRs) is necessary for homeostasis, epithelial cells protection from injury and repair stimulation (Stamatova & Meurman, 2009).
Production of antimicrobial substances
• Organic acids
• Hydrogen peroxide
• carbon peroxide,
Binding in Oral Cavity
• Compete with pathogens for adhesion sites
• Involvement in metabolism of substrates
(competing with oral micro organisms for substrates available)
• Stimulate non specific immunity
• Modulate humoral and cellular immune response
Modify oral conditions
• Modification of oxidation reduction potential
• Modulating pH
Table 3. Possible mechanisms of a probiotic in oral health 4.4 Probiotics and dental caries
From a view point, probiotics (lactobacilli) could hydrolyse proteins, stimulate growth of streptococci: the streptococci are acidogenic bacteria and produce low pH conditions in the oral environment (Robinson and Tamine, 1981). Also untreated caries cavities should also be questioned at this point. On the other hand, in recent studies, it was stated that probiotic might decrease the risk of the highest level of Streptococcus mutans (Ahola et al, 2002) or might increases salivary counts of lactobacilli while S. mutans levels were not modified (Montalto et al, 2004).
To have a beneficial effect in limiting or preventing dental caries, a probiotic must be able to adhere to dental surfaces and integrate into the bacterial communities making up the dental biofilm. Such a biofilm holds pathogens off oral tissues by filling a space which in future, could have served as a niche for pathogens, and it should also compete with and antagonize the cariogenic bacteria and thus prevent their proliferation (Caglar et al., 2005; Sheikh et al., 2011). According to our researches, it is cleared that the presence of Lactobacillus Sp. Such as L. acidophilus DSM 20079, L. fermentum ATCC 9338 and L.rhamnosus ATCC 7469 can cause reduction in the adherence of Streptococcal strains that it is probably related to interaction between bacteria. The mutans streptococci adherence reduction was significantly stronger in the case of L. acidophilus and L. rhamnosus while in the other study showed that L. fermentum reduced the adherence of non mutans Streptococci more than mutans Streptococci (figure 6).
In general, Inoculation of probiotic strain before Streptoccocal isolates to in vitro system showed more effect on adherence reduction (about 25% reduction in adherence) with significant difference (Pvalue< 0.05) especially in the case of L. rhamnosus. It is thought that adhesion reduction is likely due to bacterial interactions and colonization of adhesion sites with probiotic strain before the presence of streptococci. Also, the probiotic strains were able to modify the proportion of the oral species within the biofilm (Tahmourespour & Kermanshahi, 2011).
Nikawa et al. (2004) also reported that consumption of yoghurt containing lactobacillus reuteri (L. reuteri) over a period of 2 weeks reduced the concentration of S. mutans in the saliva by up to 80%. Comparable results were obtained by incorporating probiotics into chewing gum or lozenges. Comelli et al (2002) reported that inoculation of dairy strains before adding the oral bacteria did not increase their colonization. They also found that dairy strains and particularly L. lactis NCC2211 were able to modify the extent of oral species within the biofilm and also able to reduce cariogenic bacteria levels. They suggest that the reduction of these strains can be explained either by competition for adhesion sites or growth factors. Miller et al., in their study about the effect of microbial interaction on In Vitro plaque formation by Streptococcus mutans found that microbial interaction may have the potential to affect the amount and type of plaque formed, depending upon the kinds of organisms involved. They also reported that the addition of the lactobacilli to cultures of S. sanguis resulted in more inhibition of plaque formation when compared with pure cultures of S. sanguis. A 34% inhibition of plaque formation was observed when L. casei interacted with S. mutans NCTC 10449. Furthermore Simark-Mattsson et al. (2007) have shown the interference capacities of lactobacilli against strains of Streptococcus mutans and Streptococcus sobrinus. Meurman (2005) showed the inhibitory activity of Lactobacillus rhamnosus GG against Streptococcus mutans in low pH and it can be useful for preventing the cariogenic effects of oral streptococci. In vivo studies have also confirmed the effects of probiotic bacteria consumption on decreasing the risk of dental caries and mutans Streptococcus counts. Nase et al., (2001) reported long term consumption of milk containing the probiotic Lactobacillus rhamnosus CG strain reduced caries in kindergarten children. In one of the earlier studies, Marquis et al, demonstrated a potential probiotic approach for reducing dental caries by using oral Streptococci that are able to metabolize arginine or urea to ammonia. Cagler et al have showed a reduced S. mutans level in patients receiving fluid or tablet probiotic forms. In another study by Cagler et al a significantly reduced level was observed for S.mutans not for Lactobacillus in an ice-cream containing Bifidobacterium lactis (Caglar et al., 2005; Kargul et al., 2003). Lactobacilli have been used to deliver vaccine components for active immunization in vivo. In this way, the vectors, with the ability of the streptococcal antigen I/ II (S. mutans adhesion molecules) recognition were constructed and expressed in a strain of Lactobacilli. After the administration of such Lactobacilli to a rat model of dental caries development, S. mutans counts and caries scores were reduced obviously (Kruger et al., 2002). The above studies also suggest that consumption of products containing probiotic Lactobacilli or Bifidobacteria could reduce the number of mutans Streptococci in saliva. Oral probiotics may help fight tooth decay, since acid production from sugar is detrimental to teeth, care must be taken not to select strains with high fermentation capacity.
However, according to the researches, it is cleared that, there are some attractive vehicles for probiotic intake such as using fermented dairy products containing probiotic bacteria (milk, cheese, yogurt and ice cream) and also chewing gum, candies, tablets and water containing probiotics.
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