## 4 Discussion
### Probiotics in Periodontology
#### 4.2.1 Probiotics in Gingival Health and Gingivitis  
Fourteen randomized clinical trials related to the use of probiotics in gingivitis and gingival health were analyzed (Table S4). In a study by [PERSON] et al. [33], 4-week use of yogurt supplemented with _Bifidobacterium animals subsp. lactis_ DN-173010 had a positive effect on gingival inflammatory parameters after a 5-day non-brushing period. In a study by [PERSON] et al. [9], plaque index (PI) and gingival index (GI) scores were reduced in adolescents after two weeks administration of a probiotic combination containing _Bifidobacterium longum_, _Lactobacillus acidophilus_, _Bifidobacterium bifidum_, _Bifidobacterium lactis_ and acid lactic _bacillus_. [PERSON] and [PERSON] [11] showed a significant reduction of PI up to 4 weeks with the probiotic combination _Lactobacillus sporogenes_, _Streptococcus faecalis_ PC, _Clostridium butylrium_ TO-A, and _Bacillus mesentericus_ TO-A in patients with gingivitis. In studies by [PERSON] et al. [34] and [PERSON] et al. [7], individuals with gingival health and gingivitis were administered with a probiotic combination for two weeks. Control group used chlorhexidine. The probiotic combination reduced gingival inflammation and plaque accumulation in the same way as chlorhexidine in both studies suggesting it could serve as an adjuvant in plaque control. [PERSON] et al. [35] tested three modes of application of _Bacillus subtilis_, _Bacillus megaterium_, and _Bacillus pumulus_ in patients with gingivitis after mechanical therapy and no significant difference was observed between the probiotic and placebo groups. Similar negative results were obtained by [PERSON] et al. [36] when using _Lactobacillus rhamnus_ and _Lactobacillus curvatus_ tablets in patients with gingivitis. Contrasting results were obtained when using _Lactobacillus reuteri_ (DSM17938 and ATCC PTA 5289) probiotic for gingivitis. In a study by [PERSON] et al. [30], there were no clinical, microbiological, and immunological benefits in women with experimental gingivitis. In a study by [PERSON] et al. [37], there was a significant reduction in salivary counts of total anaerobes after 4 weeks of intervention, and _Prerotella intermedia_ counts after 4 and 8 weeks in patients with gingivitis relative to the placebo group. _Porphyromonas gingivalis_ counts also decreased significantly in a subgingival sample up to 4 weeks. However, there was no difference between PI and GI scores in the test and placebo groups. In contrast, [PERSON] et al. [4] showed a significant reduction in PI and GI scores in patients with controlled diabetes type II after 30 days on probiotic. Likewise, [PERSON] et al. [38] showed a significant reduction of clinical parameters and a complete resolution of sites with mild inflammation in pregnant women. The results suggest that \(L\). _reuteri_-based probiotics may help to manage gingivitis in individuals more susceptible to oral infections. [PERSON] et al. [39] evaluated the effects of _Lactobacillus brevis_ CD2 in experimental gingivitis. Significant differences at the bleeding on probing (BOP) level were found on day 10 in favor of the probiotic group but no longer on day 14 suggesting that this strain can delay the onset of gingivitis over a short period of time. Consistent with this, there was a progressive increase in nitric oxide (NO), an inflammatory mediator, in the gingival crevicular fluid (GCF) of the placebo group unlike the probiotic group in which there was no change. [PERSON] et al. [40] evaluated the 4-weeks administration of probiotic tablets containing _Lactobacillus rhamnus_, _Bifidobacterium lactis_ on adolescents with gingival health. There was a significant reduction in _Aggregatibacter actynomycetesamitans_ and _F. nucleatum_ counts in saliva and plaque, and _P. gingivalis_ count in plaque in the probiotic group. GI scores also improved in the probiotic group. In [PERSON] et al.