**4.6 Safty aspects of probiotics**

Although probiotics can affect most important caries pathogens, lactobacilli may correlate with caries development. Some strains of *Lactobacillus* spp., together with *S. mutans*, play a key role in development of dental caries. The production of organic acids from dietary carbohydrates is also a main factor in dental caries progression. If lactobacilli taken orally are able to adhere or temporarily establish themselves in the oral environment, their metabolism and acid production should not support caries induction. Studies addressing sugar fermentation has shown a strain dependent

pH drop and the decrease was the fastest with glucose for all tested strains, thus highlighting the acidogenic potential of probiotics. The diversity of *in vitro* results does not allow clear conclusions about which probiotics may add benefit to the oral cavity. More large scale, multicenter clinical investigations are required to support the true effectiveness of probiotics in the prevention of oral and dental diseases.

It has been also observed that caries free subjects are colonized by lactobacilli that possess a significantly increased potential to suppress the growth of mutans streptococci compared with caries active or arrested subjects (Stamatova & Meurman, 2009*)*. Finally, it can be concluded that the lactobacilli effect on caries prevention seems favorable when probiotic strains are well selected.

Furthure more, it should be mentioned that, orally lactobacillus species are well tolerated by about every one. Flatulence or gas is the most common side effect of Lactobacilli supplementation. It is usually very mild and goes away after 2 or 4 days. Immunocompromised people should be careful with the probiotics use as there have been reports of entering the blood stream (sepsis) in these individuals.

Bifidobacteria, is not associated with any side effects. It can occasionally cause mild diarrhea in children.
