**4. Probiotics**

274 Contemporary Approach to Dental Caries

of sugars in caries etiology and the importance of sugars as the principal dietary substrate

In a study, the ability of Mutans Streptococci to form biofilm measured in the presence of some sugars. The biofilm formation (percentage of strongely adherent strains in Fig. 3) in the presence of sucrose was higher than other carbohydrates significantly (p < 0.05). It is also revealed that the number of attached bacteria increased with the increase of sucrose concentration. The results corresponded to a non linear increase of attached bacteria (Tahmourespour et al., 2010). Therefore, among the various tested carbohydrates in this study and other different researches, sucrose is considered the most cariogenic dietary carbohydrate, because it is fermentable, and also serves as a best substrate for the synthesis of extracellular and intracellular polysaccharides and dental plaque formation (Brown et al., 2005; Bowen,

Evidences show that expression of required genes for glucan and fructan synthesis, such as gtfB, gtfC and ftf, is well-regulated after initial adhesion and results in forming dental

Fig. 3. The effect of different substrates in the adherence potential of streptococcal isolates. All isolates were classified into four groups. Data are expressed as means and standard

The ability of mutans Streptococci to adhere to teeth surfaces is vital for the progression of the disease. The bacterial adhesion mechanism is mediated by synthesis of both extracellular enzymes, glucosyltransferase (GTF) and fructosyltransferase (FTF). These extracellular enzymes identified in *Streptococcus mutans* are responsible for the synthesis of extracellular polysacharides such as glucans and fructans. These polymers are fundamental factors in dental biofilm formation. *α*-(1-3) - and *α*-(1-6)-linked glucan polymers through the concerted action of three secreted GTFs are encoded by the genes *gtfB*, *gtfC* and *gtfD.* In vitro studies have indicated that *gtfB* and *gtfC* are essential for the sucrose-dependent attachment of *S*. *mutans* cells to hard surfaces but *gtfD* is dispensable. The glucan polymers are involved in the colonization of cariogenic Streptococci and therefore have become a potential target for

The comparison between the mRNA level of *gtfB* in planktonic, biofilm and unattached cells of *S. mutans* by real time RT PCR also showed that, the level of *gtfB* gene expression in the

biofilm condition was significantly higher than the planktonic condition (Fig4).

that drives the caries process (Caglar et al., 2005; Touger et al., 2003; Loo et al., 2003).

2002; Cury et al., 2000; Pecharki et al., 2005; Ribeiro et al., 2005; Leme et al., 2006).

plaque, caries and other periodontal disease (Zero, 2004)

deviations of triplicate experiments (Tahmourespour et al., 2010)

protection against dental caries.

In general, a probiotic, is a live microorganism which beneficially affects the host animal by improving its intestinal microbial balance. The concept of probiotic evolved from Elie Metchnikoff's ideas that the bacteria in fermented products could compete with microbes that are harmful to host and are hence injurious to health. The term probiotic, meaning "for life," is derived from the Greek language. It is the antonym of the term antibiotics, was introduced in 1965 by Lilly and Stillwell as substances produced by microorganisms which promote the growth of other microorganisms. Since then several definitions for probiotics have been proposed (Table 1).


Table 1. Some definitions of probiotic bacteria.

The idea in the beneficial effects of probiotics is based on the knowledge that the intestinal flora can protect humans against infection and interruption of this flora can enhance

Probiotics and the Reduction of Dental Caries Risk 277

*Bacillus cereus*

*Clostridium butyricum Escherichia coli* 

*Saccheromyces boulardii Enterococcus faecalis Streptococcus thermophilus* 

*Proprionibacterium freundendsreichii* 

lactobacillus species Bifidobacterium species others

*B. longum B. breve B. infantis B. lactis B. adolescentis* 

Table 2. The most commonly used probiotics.

**4.1 Oral microbiota as a source of probiotics** 

in the oral cavity (Stamatova & Meurman, 2009).

selecting probiotics for the oral cavity.

**4.2 Probiotics and resistance to oral defense mechanisms** 

*L. acidophilus L. rhamnosus L. gasseri L. casei L. reuteri L. bulgaricus L. plantarum L. johnsonii L. lactis* 

*and B.longum*.

*B bifidum lanimalisl*

The oral cavity is a complex habitat of a great diversity of microbial species.

Recently, it has been estimated that over 1000 bacterial species are present in it. The most commonly used probiotic bacterial strains belong to the genera Lactobacillus and Bifidobacteria. So, there is of special interest to realize whether such microbes naturally inhabit the oral cavity. In the oral cavity, lactobacilli usually comprise 1% of the total cultivable bacteria; commonly isolated species include *L .paracaseie*, *L.plantarum, L.rhamnosus, L.salivarius*. Bifidobacterial species isolated from oral samples include *B.bifidum, B.dentium* 

A promising finding was that lactobacilli population differed in healthy and individuals with periodontal disease. In another study it is observed that healthy persons are populated by *L. gasseri*and *L. fermentum*, whereas the predominant species in periodontitis patients was *L. plantarum* while the first two were undetectable (Koll Kalis et al., 2005). Observations also showed that microorganisms with probiotic properties may really exist and inhabit in the oral cavity. Though, the complexity of biofilm development and interspecies interactions require more detailed investigations in order to state true probiotic candidates with activity

At first, ingested probiotics are exposed to saliva. During this first step of contact, survival and resistance to oral environmental factors are very important. Salivary proteins such as lysozyme, lactoferrine, salivary peroxidase, and secretory IgA can collectively affect viability or cell surface morphology of probiotic species. The adhesion and metabolic activity of them is then affected. Saliva role on microbial establishment can be contradictory. In one hand, saliva can inhibit colonization of probiotics (by growth inhibition, killing, or prevention of adherence to host tissues), and on the other hand, it can promote microbial colonization. It has been observed that, Lysozyme pretreatment could significantly reduce the adhesion of *L. rhamnosus* GG, *L. rhamnosus* Lc705 and *L. casei* Shirota. However, the adhesive properties of *L. johnsonii* La1 and *B. lactis* Bb12 remained unaffected. These results highlight the strainspecific response to proteolytic enzymes and this feature needs to be considered when

susceptibility to infection. The most important sources of probiotics for humans are the bacteria in yogurt and fermented milk products.

The valuable effects of probiotics may be mediated by direct antagonistic effect against specific groups of organisms, resulting in a decrease in numbers or by an effect on their metabolism or by stimulation of immunity (Ouwehand et al.,2001; Teugheles et al., 2008; Millette et al., 2008; Tahmourespour & Kermanshahi, 2011)*.* 

Probiotics have been suggested to have the following properties and functions:


Lactic Acid Bacteria or LAB, as the main probiotic species, are thought to be safe that have been ingested from foods without any problems for many years and are known as GRAS (Generally Recognized As Safe) bacteria that are important for animal health(Saito, 2004). The proposed mechanisms of the actions of probiotics are summarized in Fig. 5.

Fig. 5. Mechanisms of the actions of probiotics (Saito, 2004).

Promising probiotic strains include members of the genera Lactobacillus, Bifidobacterium and Enterococcus. The most commonly used probiotics mainly come from two genera Lactobacillus and Bifidobacterium (table2).

susceptibility to infection. The most important sources of probiotics for humans are the

The valuable effects of probiotics may be mediated by direct antagonistic effect against specific groups of organisms, resulting in a decrease in numbers or by an effect on their metabolism or by stimulation of immunity (Ouwehand et al.,2001; Teugheles et al., 2008;

• production of acids, hydrogen peroxide and bacteriocins antagonistic to pathogen

Lactic Acid Bacteria or LAB, as the main probiotic species, are thought to be safe that have been ingested from foods without any problems for many years and are known as GRAS (Generally Recognized As Safe) bacteria that are important for animal health(Saito, 2004).

Promising probiotic strains include members of the genera Lactobacillus, Bifidobacterium and Enterococcus. The most commonly used probiotics mainly come from two genera

Probiotics have been suggested to have the following properties and functions:

• Improvement of intestinal microflora (Kaur *et al*. 2002; Ouwehand *et al*. 2002).

The proposed mechanisms of the actions of probiotics are summarized in Fig. 5.

bacteria in yogurt and fermented milk products.

• adherence to host epithelial tissue, • acid resistance and bile tolerance,

growth,

Millette et al., 2008; Tahmourespour & Kermanshahi, 2011)*.* 

• safety, non-pathogenic and non-carcinogenic, and

Fig. 5. Mechanisms of the actions of probiotics (Saito, 2004).

Lactobacillus and Bifidobacterium (table2).

• elimination of pathogens or reduction in pathogenic adherence,


Table 2. The most commonly used probiotics.
