## 5 aPDT Performance in Clinical Studies
The microbiological results revealed that both interventions were effective in eliminating the bacterial biofilms [52]. The results suggested the benefit of aPDT in minimizing the number of endodontic treatment visits. However, long-term evaluation to monitor the periapical infections around the apex may provide more critical information. The combinatory effect of aPDT and Ca(OH)\({}_{2}\) was investigated to illustrate if a synergetic effect was evident [53]. Following the chemo-mechanical debridement, teeth were either treated in a single visit using aPDT or in two visits, using Ca(OH)\({}_{2}\) medication for 14 days followed by aPDT treatment. The aPDT protocol involved the use of 0.1 mg/mL of MB incubated inside the canal for 1 min and then irradiated for 2 min, using a light intensity of 60 mW and an energy density of 129 J/cm\({}^{2}\). In the one-visit group, bacterial samples were isolated before and after the chemo-mechanical preparation and after the aPDT treatment. In the two-visit group, bacterial samples were isolated at four time points: (i) before the treatment, (ii) after the chemo-mechanical preparation, (iii) after the Ca(OH)\({}_{2}\) medication, and (v) after the aPDT treatment. Both approaches significantly reduced the bacterial load following the chemo- mechanical debridement. It worth noting that the bacterial reduction obtained with aPDT treatment in the one-visit group was equivalent to that found after Ca(OH)\({}_{2}\) application. The supplementary aPDT following the Ca(OH)\({}_{2}\) application did not increase the bacterial reduction or endotoxins' content. These results may emphasize the ability of aPDT to minimize the number of endodontic visits. The adjunctive use of aPDT following the Ca(OH)\({}_{2}\) medication was found significant in reducing the counts of _E. faecalis_, compared to the use of Ca(OH)\({}_{2}\) alone [54]. In this study, MB 100 mg/mL was incubated for 5 min and then activated via an indium-, gallium-, and aluminum-phosphide laser (InGaAlP) for a total of 70 s with a total energy density of 7 J/cm\({}^{2}\). In another investigation, endodontic treated teeth were observed six months after the intervention [55]. Teeth diagnosed with pulp necrosis and periapical periodontitis were treated with either Ca(OH)\({}_{2}\) medications, kept for 7-10 days with or without supplemental aPDT. The aPDT protocol involved the use of 0.5 mL of MB 25 mg/mL, incubated inside the canal for 5 min followed by 5 min of irradiation time via diode laser. Using radiographic evaluation by observing the tissues around the treated teeth apex, aPDT was significantly associated with improved healing than the conventional endodontic therapy using the Ca(OH)\({}_{2}\) medication. No significant difference in the microbial sampling was found between the two groups. This study was unique for being the first study to perform long-term evaluation following aPDT [55]. Our search also reveals contradicting outcomes. To date, only two investigations have focused on post-operative pain as an outcome after aPDT endodontic disinfection. While one clinical report concluded that no additional benefit is associated with using aPDT to reduce post-operative pain [56], the other showed that using aPDT was effectively significant [57]. Both studies used MB as a PS; however, variation in the parameters may suggest a divergent outcome. From the perspective of bacterial reduction, five of the seven clinical studies, found in Table 1, reported a positive outcome for aPDT against endodontic pathogens. Four of the five used MB as a PS with different concentrations ranged between 0.025 and 50 mg/mL [51; 53; 54; 55], and one study used TBO at a concentration of 0.1 mg/mL [52]. The study that used the highest methylene blue concentration (50 mg/mL) reported that no additional effect could be obtained from using aPDT for disinfection [51]. It is critical to observe here that the irradiation time was low (10 s), which may affect the dosimetry of the aPDT.