In this article we will talk about the relationship between probiotics and oral health .
Second only to the colon , the mouth is also home to a large population of microorganisms . Some of these have beneficial effects, others are considered pathogenic, still others can wear the loaves of one or the other according to the circumstances.
We will go into more detail below, trying to understand if taking probiotics can be considered a valid way to improve the health of the mouth.
However, let’s start with a short but important paragraph on the relationship between the host microbiota and the host tissue.
Relationship between microbiota and health: useful considerations
In the common imagination, the presence of these elements is considered potentially harmful to health. In reality this is not always the case; in fact, it depends on the type of microorganism and its “behavior”.
In reality, there is a rather important link between the physiological microbiota and the health of the organism on which it thrives; this because it represents the first “defensive barrier” against the spread of pathogens.
Physiological microorganisms inhabit all body surfaces. Hair , skin , nose , eyes , ears , mouth, oesophagus , nails , bronchi , lungs and colon host a dense population of microorganisms .
There is a mutually collaborative relationship between the host microorganisms and the host tissue. Certain bacteria and yeasts are free to:
- nourish ourselves by releasing molecules that are useful for us;
- multiply but only within certain limits (therefore self-regulating);
thus preventing the proliferation of further more aggressive species and strains.
Even the differentiation between physiological and pathological is often difficult to establish; sometimes this distinction even varies according to the general conditions.
What is usually normal, therefore positive, in some situations can become anomalous and potentially negative; after all, you know, compromises aren’t always easy to maintain.
If one side doesn’t make the right contribution or lets its guard down, the balance can be upset to the detriment of both – in the long run.
What is the oral cavity and functions
The mouth , also known as oral cavity , buccal cavity or cavum oris in Latin, in animal anatomy is the opening through which different species take food,start digestion, communicate, ventilate, disperse heat, fight.
Note : in biology, the oral cavity is one of the hallmarks of a “complete”digestive system.
The mouth forms the upper end of the food canal ordigestive tractand is made up of two regions, the vestibule and the oral cavity proper.
The oral cavity is bounded on the outside by thelipsand on the inside by thepharynx; in higher vertebrates, it contains a tongue andteeth.
The oralmucosais the epithelium that lines the inside of the mouth; it performs various functions, such as the absorbent and secretory one, and is populated by a vast but physiological microbiota.
The role of the buccalbacterial florais above all to avoid the proliferation of bacteria and fungi that could attack the mucosa or descend (from the pharynx to thelarynxand beyond).
However, the excessive presence of food residues can – especially in the presence of an unfavorable pH – facilitate the attack of the microbiota on the teeth, generating tartar , plaque and caries.
Potential beneficial mechanisms of probiotics in the oral cavity
Probiotic supplementation is predominantly associated with intestinal health; this is because, historically, clinical interest has focused more on the prevention and treatment of infections and diseases of this portion of the digestive system.
The use of probiotics to improve oral health has significantly increased in the last decade. This is because the metabolic activity of certain bacteria, particularlylactobacilliand bifidobacteria , may have proven benefits for the mouth.
The mechanisms of action of probiotics takenorallyare basically three:
- Normalization of the intestinal microbiota;
- Modulation of the immune response;
- metabolic effects.
The impact of probiotics on the oral cavity could be similar to that described for theintestine.
Ways probiotics might affect oral health include:
- Competition for membership sites;
- Competition for nutrient substrate and growth factors;
- Production of antimicrobial compounds such as certain acids;
- Improving the immune response eg and improving the production of IgAand defesins;
- Inhibition of the synthesis of pro-inflammatory cytokines;
- Reduction of MMP production.
- Steps 1 and 2 inhibit adhesion and improve clearance;
- All points participate in inhibiting the growth of pathogens and other effects related to the ecology of dental plaque*;
- Points 5, 6 and 7 affect the local and systemic immune response.
Ecological theory of plaque
The ecological theory of plaque is a hypothesis according to which the buccal mucosal surface is lined with a biofilm of both commensal (physiological) and pathogenic bacteria . In conditions of balance, no disease is generated; otherwise it happens if the compromise fails.
- The three effects just mentioned constitute a complete effect of antagonismtowards pathogens;
- This antagonism, also associated with the influenceof the local and systemic immune response as an independent factor, is responsible for the reduction of inflammation and tissue destruction.
Until now, oral colonization by probiotic bacteria has often been considered essential to exert localized effects.
However, the presence of systemic effects cannot be excluded, although the total IgA levels in saliva do not appear to be influenced by the use of probiotics.
Interestingly, the use of some probiotic strains by lactating women appears to affect the composition of breast milk .
Regarding commensal oral microbes, several aspects support the idea that there are different bacterial strains potentially useful in the prevention or treatment of oral diseases.
The ecological plaque theory suggests that environmental selection can change the balance between oral health and disease occurrence.
The bacteria themselves are capable of influencing their surroundings, with both synergistic and antagonistic interactions between groups.
However, it is well known that the physiological microbiota protects the oral cavity from infections.
However, just as various bacterial species associated with oral cavity diseases are recognised, species associated with perfect health are also observed.
The efficacy of orally administered bacteria to influence the oral microbiota, which overall is relatively stable, particularly in adults, remains questionable.
It should also be noted that all mechanisms described in this section are based on in vitro findings and that the clinical evidence is established in short pilot clinical studies.
Effects observed on oral health intake of probiotics
Tooth decay and associated microbes
Several studies suggest that consuming products containing probiotic lactobacilli or bifidobacteria could reduce the number of Streptococcus mutans in saliva.
The trend towards a decrease in the number of streptococci in saliva appears to be independent of the product or strain used; however, this effect was not observed in all studies.
The discrepancies between the results cannot be explained by the use of different probiotic strains alone, as different results were also obtained using the same strains.
Salivary lactobacilli levels were also measured in most of these studies . An increase in the number of salivary Lactobacillus was observed with three products.
Unfortunately, with regard to dental caries , the groups have been relatively small and the studies quite short.
Also, it is important to realize that the salivary level of caries-associated microbes is not directly related todental cariesitself. The saliva microbiota resembles that of the tongue more than that of plaque. Therefore, no conclusive statement can be made regarding the effects of probiotic bacteria on dental caries.
The first studies on the use of probiotics to improve oral health involved the treatment of periodontalinflammation .
Patients suffering from various periodontal diseases, gingivitis, periodontitis and gravidarian gingivitis were treated locally with a strain ofL. acidophilus . Significant improvement was reported in nearly all cases.
Interest in the use of probiotics in the treatment ofperiodontal diseasehas also recently increased. The probiotic strains used in these studies include L. reuteri , L. brevis (CD2), L. casei Shirota , L. salivarius WB21 and Bacillus subtilis . L. reuteri and L. brevis improved gingival health, as measured by the reduction ingingival bleeding.
The use of probiotic chewing gum containing L.reuteriATCC 55730 and ATCC PTA 5289 also reduced the levels of pro-inflammatory cytokines in GCF, and the use of L. brevis reduced MMP ( collagenase ) activity and other inflammatory markers in saliva.
No difference in gingival bleeding or measured plaque index was observed with L. casei Shirota and Bacillus subtilis for the test and control groups, but the use of L. casei Shirota reduced PMN elastase activities and of MMP-3 in GCF, and gingival inflammation was lower in the group consuming the probiotic product, as measured by MPO activity after a four-day period of gingivitis.
- subtilisappeared to reduce the number of periodontal pathogens. The use of tablets containing L. salivarius WB21 has been shown to reduce the depth of the gingival pocket, particularly in high-risk groups such assmokers, and also affect the number of periodontopathogens in plaque.
Again, although encouraging results were observed, the duration of most of the studies was quite short. Furthermore, in some the observed differences were quite modest, although statistically significant.
Only two studies have investigated the effects of probiotic bacteria on oralCandidainfection in humans.
A test group of elderly people who consumed a cheese containing the L. rhamnosus strains GG and LC705 and Propionibacterium freudenreichii ssp. shermanii JS for 16 weeks, found a reduction in the density of the pathogenic yeast . However, no changes in mucosal lesions were observed.
In a shorter study with younger subjects, no significant difference was observed between the effects of the probiotic and those of the control cheese on salivary Candida .
Bad breath is not a disease but a discomfort, although some oral diseases, including periodontitis, may be the dominant cause; however, in about 90% of cases, the origin is to be found in the oral cavity and therefore probiotics are marketed for the treatment of bad breath associated with the mouth and intestines.
Despite this, only a few clinical studies have found efficacy. Strains studied include E. coli Nisle 1917, S. salivarius K12, three isolates of Weissella confusa and a lactic bacterial mixture, not specified by the authors of that work.
Safety of using oral probiotic supplements
Only certain probiotic strains of Lactobacillus and Streptococcus appear capable of colonizing the oral cavity of some people during use.
However, both in vitro and in vivo tests indicate substantial differences between various probiotic strains, between products and even between individuals.
- rhamnosusGG and two different strains of L. reuteri effectively colonize the oral cavity of 48-100% of volunteers.
- salivariusK12, used for the treatment of halitosis, only temporarily colonizes the oral cavity for a short time after use.
Consumption of a mixture of seven different Lactobacillus strains increased the number of salivary Lactobacillus counts , although the identity of the strains in saliva was not determined.
It seems possible that probiotic bacteria can only colonize the oral cavity when used in mouth – contact products. In fact, Maukonen et al. they did not detect any probiotic bacteria administered in capsules in saliva samples. Surprisingly though, consuming capsules containing a blend of seven different Lactobacillus strains increased the number of salivary Lactobacillus counts.
- reuteriATCC 55730 (= L. reuteri SD2112) does not appear to influence the total number of salivary lactobacilli, unlike L. rhamnosus GG.
The potential adverse effects of probiotic bacteria in the oral cavity have not been the subject of much research – perhaps because long-term colonization by probiotic bacteria is unlikely, although possible.
However, probiotics remain widely used; therefore, when considering dental health, the acidogenicity of lactobacilli and bifidobacteria cannot be overlooked. For example, one strain of L. salivarius has been shown to induce caries in animals, and another to create a more cariogenic biofilm model.
Importantly, each of the suggested health benefits should be studied individually for each bacterial strain. Therefore, a bacterium present in the oral cavity is not necessarily to be considered a probiotic.
Furthermore, it is possible that the species themselves are not optimal for all oral health purposes; for example, the therapeutic properties could be distinguished with respect to dental and gingival health.
Probiotic bacteria appear to influence both the oral microbiota and immune responses. On the other hand, it is difficult to predict to what extentbacteria in foodsordietary supplementsmay affect the oral microbiota, which appears to be relatively stable.
Several therapeutic effects of probiotic bacteria are documented and there is no reason to limit their use; however, their use in dental health is not yet well justified.