## 4 Discussion  
This interventional split-mouth prospective study aimed to evaluate the potential benefits of using instillations with _L. reuteri_ in periodontal pockets in patients with severe periodontitis. Our results demonstrated that both SRP alone and SRP supplemented with _L. reuteri_ treatment generated favorable results in terms of clinical parameters (probing depth, clinical attachment loss, bleeding on probing index) at three months after _L. reuteri_ treatment completion. More important, the attachment gain and the inflammation resolution (measured by BOP) were more significative for those sites that were subjected to _L. reuteri_ supplementation. These results are in accordance with other studies involving probiotics as an adjunct to clinical periodontal treatment which reported a marked improvement in patients' clinical condition compared to clinical therapy alone [16; 17; 18; 19]. [PERSON] et al. [17] investigated the effect of _L. reuteri_ probiotic lozenges, taken two times per day for 12 weeks, as an adjunct therapy to SRP. The authors observed significantly higher reductions in PD, especially in deep pockets. Significant improvements were observed in our study, especially in terms of probing depth and clinical attachment loss, after the local instillation of _L. reuteri_ solution. This aspect is of particular importance, since severe periodontal attachment loss poses a great risk for negative outcomes, e.g., tooth loss among other local and loco-regional complications [20; 21]. Deep periodontal pockets are also main candidates for surgical therapies [22], therapies which assume greater treatment costs, discomfort, and potential complications [23]. Nevertheless, except [PERSON] et al. [19], who investigated the effects of mouthwash with _L. reuteri_ and _L. salivarius_, all studies used chewing tablets as a base for probiotic intake. Local application in periodontal pockets of _L. reuteri_ could offer higher benefits due to a delivery system in the particular area of interest, at a higher concentration. At the same time, local administration of the probiotic eliminates a number of concerns about potential unwanted systemic side effects related to the administration of probiotic strains to individuals with systemic pathologies involving mild to moderate immune suppression. Different strains of _Lactobacillus_ proved efficient in decreasing probing depth in moderate periodontal pockets (4-6 mm) compared to placebo + SRP [19; 24; 25]. Contrary to these data, using _Streptococcus_ spp. as a probiotic did not generate the same benefits [26]. This may translate into the fact that not all probiotic strains exhibit the same efficacy. In our study, local delivery of _L. reuteri_ DSM 17938 exhibited a probing depth reduction of 0.91 \(\pm\) 0.23 mm, more significant than SRP alone (0.51 \(\pm\) 0.15 mm). Moreover, the clinical attachment gain for _L. reuteri_ sites when compared to the SRP alone sites was of 0.99 \(\pm\) 0.24 mm versus 0.37 \(\pm\) 0.11 mm. Data regarding BOP reduction after probiotic therapy are contradictory. [PERSON] et al. [25] found no significant differences in gingival bleeding between the probiotic and SRP alone groups (reduction of 3.70 and 0.7% for the control and study groups, respectively). Still,  
Figure 4: Comparaison between (**a**) difference in probing depth at 3 months and baseline for control group (Delta PDc) and study group (Delta PDs); (**b**) difference in clinical attachment loss at 3 months and baseline for control group (Delta CALc) and study group (Delta CALs); (**c**) difference in bleeding on probing at 3 months and baseline for control group (Delta BOPc) and study group (Delta BOPs). their subjects followed periodontal maintenance sessions throughout the study period, a fact that could interfere with the clear impact of probiotics. In our study, BOP reduction in _L. reuteri_ sites after five sessions of local delivery was of 65.98% versus 55.27% in control sites, with no proper maintenance program. [PERSON] et al. [24] and [PERSON] et al.