**3. Dental plaque biofilm management**

For therapeutic purposes, it is necessary to attack the formed biofilm. For prophylactic purposes, it seems reasonable to target processes involved in the actual biofilm formation of single- or mixed-bacterial communities that have the potential to cause or support disease, without disturbing the balance of the normal flora. It is known that the mature oral biofilm is the result of a well regulated series of processes, which begins by adhesion of planktonic cells to the surfaces and could represent potential targets for biofilm control.

The shift in the treatment paradigm incorporates the ecological plaque hypothesis, which states that prevention of disease should not only focus on the putative pathogens inhibition, but also on interference with environmental factors that drive selection and enrichment for these bacteria as reported by Marsh(2005). One of the key characteristics of biofilm that could be targets for dental plaque management includes its behavior as an adhesive mass.

The environmental key factors in concerned with biofilm formation are the fermentable dietary carbohydrates and Streptococci, as pioneer strains, depend on them as an energy source (Tahmourespour et al., 2010). The cariogenicity of sugar-containing foods can be modified by many factors including the amount and type of carbohydrates, protective components (proteins, fats, calcium, phosphate, fluoride) and physical and chemical properties (liquid vs. solid retentiveness, solubility, pH, buffering capacity). The fact that sugars are readily metabolized by oral bacteria, leading to the production of organic acids and extra cellular polysaccharides such as glucan and fructan was shown repeatedly in clinical studies (Zero, 2004; Touger et al., 2003). Numerous studies have established the role

Probiotics and the Reduction of Dental Caries Risk 275

Fig. 4. The comparison of *gtfB* gene expression level in different condition (planktonic cells in the absence of sucrose, attached cells in the present of 1% sucrose and unattached or detached cells from biofilm in the presence of 1% sucrose) (Tahmourespour et al., 2010).

So, despite the fact that, the relationship between sugar consumption and caries is so strong; sugar consumption restriction still has an important role in prevention of caries going along

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

growth of other microorganisms

health effects in this host

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

microflora (by implantation or colonization)

amounts, confer a health benefit on the host

Substances produced by microorganisms that promote the

A preparation of, or a product containing, viable, defined microorganisms in sufficient numbers, which alter the

in a compartment of the host and as such exert beneficial

Live microorganisms that, when administered in adequate

a live microbial food ingredient that, when ingested in sufficient quantities, exerts health benefits on the consumer

with other new strategies.

have been proposed (Table 1).

Year with reference Definition

Table 1. Some definitions of probiotic bacteria.

**4. Probiotics** 

1965

2001

2001

Lilly & Stillwell

Schrezemeir & de Vrese

International Life Science Institute (ILSI) Europe

WHO/FAO report

of sugars in caries etiology and the importance of sugars as the principal dietary substrate that drives the caries process (Caglar et al., 2005; Touger et al., 2003; Loo et al., 2003).

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

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

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

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 protection against dental caries.

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).

Fig. 4. The comparison of *gtfB* gene expression level in different condition (planktonic cells in the absence of sucrose, attached cells in the present of 1% sucrose and unattached or detached cells from biofilm in the presence of 1% sucrose) (Tahmourespour et al., 2010).

So, despite the fact that, the relationship between sugar consumption and caries is so strong; sugar consumption restriction still has an important role in prevention of caries going along with other new strategies.
