Microorganisms in the oral cavity play an active role in maintaining oral health. They form an important biofilm that has evolved through evolution in parallel with human development. Health therefore depends on a delicate balance between bacteria that are constantly present in the oral cavity and “harmful” bacteria that enter this environment and, if they become dominant, lead to disease. The most common disease in the oral cavity (caries) is therefore associated with the presence of carbohydrates, which serve as food for bacteria that live in an acidic environment (Streptococcus mutans and Lactobacillus). These bacteria cause an imbalance in the bacterial biofilm and consequently the dissolution of hard dental tissues.
Based on this, the idea arose of manipulating the bacteria within the “resident” biofilm in order to achieve greater stability of the biofilm and thus reduce the likelihood of pathogenic bacteria developing. By bacterial therapy we therefore mean a procedure in which a harmless and active factor is introduced into the patient's microflora and, through its action, positively affects “good” bacteria and negatively affects pathological or “bad” bacteria. Bacteria thought to have this ability are called probiotics. The WHO, or World Health Organization, defines them as living microorganisms that, in sufficiently large quantities, can help saprophytic or “good, resident” bacteria. They are indigestible components of certain foods that, through selective stimulation of bacteria in the biofilm, provide a benefit to the host organism (human).
Many studies have already demonstrated positive effects of probiotics in cases of diarrhea, asthma, eczema… The question of their effect on oral health remains open, although clear guidelines are emerging regarding what may be beneficial and what may not.
As early as 1900, Nobel Prize winner Mtschnikow proposed that certain harmless microorganisms have a positive effect on health. These were bacteria, fungi or molds that were called probiotics (pro bios; Greek for life) and are found in yogurt, sour milk and cheese, and can also be found in humans. Probiotic bacteria belong to lactobacilli and bifidobacteria, which are also components of the normal human microflora. The mechanism of action of probiotics is not well understood, but they have both local and systemic effects. They inhibit the growth of pathogens, produce bacteriocin and hydrogen peroxide, which also has a bactericidal effect, stimulate and modulate the natural immune system, and compete with pathogenic bacteria for living space. Modes of action differ among different types of probiotics, while on the other hand the same types can have different effects in different people. Some modes of action in the oral cavity are shown in the table below.
Based on this, the idea arose of manipulating the bacteria within the “resident” biofilm in order to achieve greater stability of the biofilm and thus reduce the likelihood of pathogenic bacteria developing. By bacterial therapy we therefore mean a procedure in which a harmless and active factor is introduced into the patient's microflora and, through its action, positively affects “good” bacteria and negatively affects pathological or “bad” bacteria. Bacteria thought to have this ability are called probiotics. The WHO, or World Health Organization, defines them as living microorganisms that, in sufficiently large quantities, can help saprophytic or “good, resident” bacteria. They are indigestible components of certain foods that, through selective stimulation of bacteria in the biofilm, provide a benefit to the host organism (human).
Many studies have already demonstrated positive effects of probiotics in cases of diarrhea, asthma, eczema… The question of their effect on oral health remains open, although clear guidelines are emerging regarding what may be beneficial and what may not.
As early as 1900, Nobel Prize winner Mtschnikow proposed that certain harmless microorganisms have a positive effect on health. These were bacteria, fungi or molds that were called probiotics (pro bios; Greek for life) and are found in yogurt, sour milk and cheese, and can also be found in humans. Probiotic bacteria belong to lactobacilli and bifidobacteria, which are also components of the normal human microflora. The mechanism of action of probiotics is not well understood, but they have both local and systemic effects. They inhibit the growth of pathogens, produce bacteriocin and hydrogen peroxide, which also has a bactericidal effect, stimulate and modulate the natural immune system, and compete with pathogenic bacteria for living space. Modes of action differ among different types of probiotics, while on the other hand the same types can have different effects in different people. Some modes of action in the oral cavity are shown in the table below.
| Lactobacillus rhamnosus | Milk, yogurt, cheese | Blocks S. mutans, reduction of caries |
| Lactobacillus reuteri | Candy, chewing gum | Plaque reduction, anti-inflammatory effect |
| Lactobacillus paracasei | Dietary supplements | Blocks S. mutans |
| Lactobacillus plantarum | Fruit juices | Inhibits cariogenic bacteria |
| Lactobacillus salivarius | Tablets | Reduces gingival inflammation |
| Bifidobacterium lactis | Yogurt | Blocks S. mutans in saliva |
| Streptococcus salivarius | Candy | Reduces bad breath |
| Weisella cibaria | Mouthwashes | Reduces bad breath and plaque levels |
Probiotic bacteria are not permanently present in the human body and can only be found for about one week after consuming food that contains them, which means that permanent colonization is not necessary for their action.
Over the last twenty years, several studies have mainly examined the effect of probiotic bacteria on the amount of Streptococcus mutans in saliva, the incidence of gingivitis (inflammation of the gums) and the amount of plaque in participants (younger adults and children). Studies have also compared the action of chlorhexidine, the most commonly used agent in mouthwashes, with that of probiotic bacteria on the incidence of plaque and gingival inflammation. Positive effects of probiotic bacteria were found in all studies; the most interesting finding was that the effects were even greater than those of chlorhexidine. The table shows the results of some studies.
| Age of participants | Food consumed | Study duration | Type of probiotic | Effect |
| 12–16 years | Yogurt | 2 weeks | Bifidobacteria | Reduction of S. mutans |
| 12–15 years | Milk | 2 weeks | L. rhamnosus | Unchanged level of S. mutans |
| 6–8 years | Solution | 2 weeks | Bifido/ L. acidophilus | Less plaque and gingivitis compared with the effect of chlorhexidine |
| 12–14 years | Ice cream | 10 days | Bifido/ L. acidophilus | Reduction of S. mutans |
| 7–14 years | Powder | 14 days | L. rhamnosus/ bifido | Reduction of S. mutans |
| 4–12 years | Drops | 25 days | L. reuteri | Reduction of S. mutans |
Studies investigating the effect of probiotics on the occurrence or reduction of dental caries in children also reported positive effects of probiotics. The first study was published in Finland, where 594 children aged one to six years were given probiotic milk (L. rhamnosus) four times a week for seven months. The results showed a significant reduction in caries activity compared with the control group, which received regular milk. The reduction was approximately 21%, and even 56% when the group of children aged three to four years was analyzed separately. Another similar study was conducted in Sweden, included a considerably larger number of children, and further confirmed the conclusions of the first study.