## 4 Discussion
salivarius_ strain K12 in the treatment of DS. Inclusion/exclusion criteria were designed to minimize the influence of factors other than microbial dysbiosis due to inadequate oral hygiene on the presence of clinical signs and symptoms of DS. Subjects wearing not-well-fitting dentures were excluded, as well as subjects affected by diseases altering immunity and oral homeostasis. In the selection of patients, attention was paid to minimize the possible interference of potential confounders. Consequently, in addition to the rigid application of inclusion/exclusion criteria, attention was dedicated to include only patients in apparent good conditions: diabetic patients with high glycemic levels, patients with arterial hypertension not well controlled by drugs (i.e., pressure levels > 140/90 mmHg)and patients smoking >10 cigarettes/day were excluded from the study. Nevertheless diabetes, arterial hypertension and smoking were not included as variables in the statistical analysis. Due to the preliminarily nature of this study, the CTR group was not designed to receive a placebo; this could have influenced perception of subjective symptoms between the two groups of patients. As expected, our experimental data confirm that, in the absence of repeated trauma due to inadequacy of the denture base or too prolonged denture wearing, improvement of the oral and denture hygiene procedure reduces clinical signs and symptoms of DS and reduces oral colonization by _C. albicans_[13; 14]. Moreover, data show that the effectiveness of oral and denture hygiene alone is limited in time. In fact, when (after T30) patients of the CTR group were invited to resume their previous habits with the dentures, their clinical conditions worsened significantly. Although microbiological samples were not analyzed at T60, it can be considered plausible, in accordance with data from the literature [25], that clinical relapse was paralleled by an increase in oral _C. albicans_ counts. Experimental data show that when improved oral and denture hygiene procedures were flanked by the administration of a preparation of the probiotic strain _S. salivarius_ K12, a significantly greater improvement of clinical conditions and a higher reduction of oral _C. albicans_ counts were obtained in the EXP group at T30. Interestingly and unexpectedly, clinical evaluations performed at T60, when patients of the EXP group had discontinued treatment for 30 days and had resumed previous oral and denture hygiene habits, revealed a further improvement of clinical conditions, as opposed to the partial relapse observed in the CTR group. These data suggest that _S. salivarius_ K12 could be able to colonize oral mucosa at least for some weeks after discontinuation of treatment and consequently exhibit a prolonged anti-_Candida_ action. Unfortunately, microbiological sampling was not planned for T60 and consequently this aspect will deserve future further investigations. A prolonged presence of the probiotic strain would be in accordance with the well-known role of _S. salivarius_ as a pioneer colonizer of the human oral cavity [29]. The effective duration of oral colonization by _S. salivarius_ K12 after 30 days of treatment and the consequent duration of its anti-_Candida_ activity will be the object of future investigations using specific molecular methods that were recently made available [34]. Future studies will also be necessary to elucidate the cellular and molecular mechanisms underlying the clinical and microbiological effects of _S. salivarius_ K12 on DS described in this paper.