## 1 Introduction  
Periodontitis is a multifactorial chronic disease induced by the result of a dysbiotic microbiota that involves a cascade of inflammatory reactions and is characterized by the destruction of periodontal tissue, which leads to the resorption of alveolar bone and tooth loss [1].  
It has a high worldwide prevalence, and its management aims to reduce the level of microbiome charge, reach a homeostatic balance between the host and microbial communities, and promote the healing of damaged periodontal tissue [2].  
Recent microbiological studies support a new pathogenesis model based on a polymicrobial synergy and dysbiosis, according to which this disorder starts from a disbalance between the host and the microflora, in which some key species form part of _The Orange and Red Complex_ by Socransky (_Porphyromonas Gingivalis, Tannerella Forsythia_ and _Treponema Denticola_[3]) capable of compromising host immune surveillance and increasing the pathogenicity of the microbiota by selecting an inflammatory microbiota that supports periodontal inflammation [4; 5; 6].  
The first step of the periodontal disease therapy involves the mechanical destruction of oral biofilm and the elimination of retentive factors by the application of the non-surgical periodontal therapy (NSPT), which is considered the \"gold standard\" of periodontal treatment [7; 8].  
Despite the effectiveness of the NSPT therapy in reducing the depth of the gingival pocket (PPD) and improving the clinical attachment level (CAL), it has limitations due to anatomical access, very deep pockets and functions, as well as microbiological reasons, including the frequent recolonization of pathogenic bacteria [9]. Therefore, to enhance the periodontal results, adjuvant therapies to the mechanical treatment have been proposed, such as antibiotics, ozone, photobiomodulation and probiotics [10; 11].  
Probiotics are microorganisms that can bring benefits to the health of the host when given in adequate and sufficient quantities [12]. Their administration serves to restore the balance of the oral microbiota by increasing the population of beneficial bacteria through the competitive inhibition of periodontal pathogens, thus modulating the host response [13].  
Moreover, probiotics are able to produce antimicrobials and bacterioxins that are opposed to the pathogenic action of the bacterial biofilm [14; 15; 16].  
Therefore, the use of probiotics could have a potential benefit in the management of periodontal disease; several clinical studies have investigated their effects in addition to NSPT, but there are few data concerning the clinical impact and long-term microbiological and immunological outcomes.  
Studies on gastrointestinal probiotics present strong scientific evidence, but several heterogeneous sources have been recognized in empirical therapy with probiotics [17] and it has been shown that the host-microbiome interface exhibits variable resistance to colonization in different individuals [18], resulting in the need for personalized approaches.  
It is therefore essential to understand which factors can influence the efficacy of probiotics in periodontal therapy and how long a potentially beneficial effect persists, allowing to know the methods of application in addition to NSPT.  
This systematic review seeks to assess the efficacy of the effects of probiotics in addition to NSPT compared to controls with follow-up of clinical, microbiological and immunological outcomes.