Promicrobial strategies to combat oral biofilm disease

A healthy mouth makes for a confident laugh and ensures us that we can enjoy that tasty steak or juicy apple. However, oral diseases can have consequences even beyond the mouth. Lately, there is a growing interest for the link between gum health and several systemic diseases. However, despite its far-reaching effects and a focus on prevention, oral health problems are still affecting the majority of the population worldwide. There is thus a need for alternative and/or complementary therapies in addition to the current preventive and therapeutic strategies.

In a healthy mouth, there is a symbiotic relationship, a dynamic balance between the oral microbiome, the host and the environment. A disturbance of this homeostasis can lead to an overgrowth of pathogenic bacteria. Traditional therapies focus on the reduction and elimination of the bacterial load. More recently, in line with previous gastrointestinal research, it was suggested that administering live, "beneficial" microorganisms (probiotics) could be an alternative for restoring this homeostasis.

At the start of this PhD, the interest in using probiotics for a healthier mouth was already growing. Although the research was limited at that moment, the available results were promising (Chapter 1). However, there were still many unanswered questions concerning the ideal probiotics for oral health, uninvestigated applications, etc.

The most studied probiotic for oral health is, to the best of our knowledge, a dual strain lactobacilli probiotic containing Lactobacillus reuteri DSM 17938 and Lactobacillus reuteri ATCC PTA 5289. Research showed the added value of this product in the prevention of caries and as a complementary therapy in the non-surgical therapy of periodontitis. We demonstrated for the first time the additional effect of this product to re-instrumentation of residual pockets in chronic periodontitis patients. However, we failed to show an added effect after the administration of this product compared to a placebo as complementary treatment to the non-surgical debridement of initial peri-implantitis sites (Chapter 2).

Lactobacilli are of course only one example of microorganisms to which probiotic capacities are attributed. The third chapter of this thesis investigated the use of a streptococci probiotic and the clinical effects of oral health products containing Bacillus species. However, both studies could not show any added effects of these probiotics for the examined indications. The first trial failed to show better treatment results of a Streptococcus oralis KJ3, Streptococcus uberis KJ2 and Streptococcus rattus JH145 probiotic compared to a placebo used for 3 months after scaling and root planing in chronic periodontitis patients. In addition, the second study did not demonstrate improved clinical parameters of the usage of Bacillus species based probiotics compared to a placebo in gingivitis patients.

Combining the studies in this thesis and the current literature, one can conclude that probiotics can be an interesting, alternative strategy for improving oral health. However, it is important to note that probiotic effects depend on strain, concentration, mode of delivery and, moreover, are indication-specific. However, it is not clear what the underlying mechanisms of the seen clinical benefits of certain probiotics are.

In conclusion, there appear to be different applications for probiotics in dentistry, but more fundamental research is needed to use them in a targeted way, which in turn will lead to more effective usage of time and resources in clinical research