## 4 Discussion  
This text is a systematic review that aims to evaluate the clinical and microbiological effects of probiotics as an adjunct to mechanical debridement alone through RCTs. Nine studies were included, and all of them reported clinical parameters' results, while three reported microbiological results. Therefore, it was possible to perform a meta-analysis of the clinical parameters, but not the microbiological parameters, due to the limited number of studies and the heterogeneity of microbiological techniques for identifying pathogenic bacteria. The meta-analysis was conducted on studies with follow-ups at 3 and 6 months. It demonstrated that adjunctive probiotic therapy to scaling and root planning (SRP) was more effective in reducing clinical parameters (BOP, PI, and PPD). One of the mechanisms of action of probiotics is the modulation of the immune system, helping to control inflammation and prevent infection [28; 29]. The main characteristic of mucositis is inflammation and bleeding on probing [2]. Thus, the studies included in the meta-analysis have shown that probiotics can attenuate inflammation by reducing bleeding upon probing. Three studies monitored the immune response by measuring levels of im-munomarkers in the gingival crevicular fluid. Two studies [11; 18] showed a greater reduction in the inflammatory markers interleukin (IL)-1\(\beta\), IL-6, IL-8, and tumor necrosis factor-alpha (TNF-\(\alpha\)) in favor of the probioticic group compared to the control group without the use of probiotics after 6 months. One study indicated [23] a significant reduction in pro-inflammatory markers IL-1\(\beta\), IL-8, and CCL5 in the probioticic group, but without statistical differences between the groups after 26 weeks. Studies indicate [30; 31] that probiotics promote a potential immunomodulatory effect by reducing pro-inflammatory cytokines associated with the destruction of peri-implant tissues. In this systematic review, seven studies [8; 11; 19; 20; 21; 22; 23] used the probiotic bacterium _Lactobacillus_ spp. (_L. reuteri_) at concentrations ranging from 1 \(\times\) 10\({}^{8}\) to 2 \(\times\) 10\({}^{8}\) colony-forming units (CFU), and one study [18] combined strains of _B. lactis_, _L. rhamnus_, and _L. paramcasei_ at a dosage of 1 \(\times\) 10\({}^{9}\) CFU, and the treatment duration ranged from 2 weeksto 3 months. The _Lactobacillus_ species were the most commonly used strain in the studies. Bacteria of the genus _Lactobacillus_ spp. comprise a large group of facultatively anaerobic, Gram-positive, non-spore-forming bacteria. Among these, the most studied strain is _L. reuteri_ (_Lr_), and there is evidence that this strain is capable of producing lactic acid, which can help maintain a lower pH in the mouth, making it less favorable for the growth of pathogenic bacteria [32]. In addition, a systematic review [33] showed that especially the strain _Lactobacillus reuteri_, without combination with other strains, offered a greater reduction of pathogenic bacteria and deep periodontal pockets. Another study indicates that _Lactobacillus reuteri_ (intestinal strain/species) is capable of producing various antimicrobial substances, such as reuterin, reuteran, and reutericyclin, which can inhibit the growth of pathogenic bacteria [34]. This explains why the authors of the included studies preferred to use the _Lactobacillus reuteri_ strain. It was also observed that probiotic strains were used in adequate amounts greater than \(1\times 10^{7}\), which is important since inadequate dosages can influence results [33]. However, there was heterogeneity in the duration of probiotic treatment, requiring more studies with more homogeneous times. Regarding the microbiological results, two studies [21; 23] showed no major changes in the total bacterial load of pathogenic species, and there was no difference in time and between groups. Meanwhile, one study [22] showed statistically significant results in favor of the probiotic group in reducing the count of Pg species between baseline and 90 days.