## 7 Discussion  
Periodontal therapy is successful when it provides the decrease of the periodontal bacteria in the subgingival area [54]. _Porphylomonas gingivalis, Treponema denticola,_ and _Tannerella forystthia_, included in the red complex bacteria, represent the main periodontal pathogens, which can induce periodontal disease progression: Significant periodontal tissue destruction, increasing depth of periodontal pockets and bleeding [31; 55]. The literature reported that subgingival debridement (scaling and root planning) leads to a temporary change in the composition of subgingival microorganisms, including species like the microflora found in healthy periodontal sites [56; 57]. However, recolonization of the periodontal sites by spirochetes and motile rods one to two months after the end of the therapy, together with the persistence of red and orange complexes bacteria in the deepest part of the periodontal pockets, make it clear that non-surgical periodontal treatment (SRP) is not sufficient in contrasting chronic periodontitis [58; 59; 60]. Data obtained in our study demonstrated that the non-invasive procedure of PDT, in association with non-surgical therapy, is effective in the treatment of periodontitis, obtaining the deactivation and detoxification of periodontal pathogens, the decrease of probing depth and clinical attachment loss [61; 62]. Microorganism photoinactivation can be obtained by direct or indirect mechanisms. The direct method involves high-energy photons directly damaging vital parts of bacterial cells, while the indirect antimicrobial PDT can be described as an oxygen-dependent photochemical reaction generated by the activation of a PS through a light source. The combination of a non-toxic PS, visible light with appropriate wavelength and oxygen leads to the production of highly reactive and cytotoxic ROS (singlet oxygen), consequently destroying cells [63; 64; 65; 66; 67; 68]. The randomized controlled split-mouth clinical trial by [PERSON] et al. [69] evaluated the role of adjunctive PDT in patients suffering from chronic periodontitis, highlighting significant short-term improvements (three months follow-up) in terms of bacterial count, CAL, and PD. Positive long-term clinical effects of PDT were demonstrated in the randomized clinical trial by [PERSON] et al. [70], in which improvement in periodontal clinical indicators (CAL, PD, BOP) of 136 sites was recorded for at least one year. Thirty-three patients were selected in the research by [PERSON] et al. [71] and divided in three groups, treated with SRP alone, PDT alone, and SRP associated with PDT: The data proved that periodontal sites, which received the combined therapy (scaling and root planning + PDT) showed a higher reduction of clinical attachment loss, probing pocket depth decrease, and BOP decrease in comparison with those treated with SRP alone. Our in-vivo analysis evaluated the effectiveness of photodynamic therapy, performed by the concurrent use of a novel product containing aminolaevulinic acid (ALA) and red led irradiation against different types of bacteria involved in oral infections. Support periodontal therapy alone is widely used, but data obtained in our research reported a greater decrease of bacterial load when SRP is associated with the administration of ALADENT, which is the sole medical device using a PS applied topically. ALADENT is easy to use and causes no discomfort for the patient. It is administered directly into the periodontal  
Figure 6: PBI of the selected sites after treatment with SRP alone and SRP plus ALADENT. pocket, drastically reducing the adverse effects that could occur during a systemic therapy. ALADENT presents a bactericidal activity, reducing gingival inflammation and thus representing an effective procedure in the treatment of periodontitis.