Effect of photodynamic therapy on the morphological changes of periapical inflammation: An experimental study in rats

We aimed to explore the morphological changes with photodynamic therapy (PDT) in experimentally produced periapical lesions in rats, and to investigate if PDT used as an adjunct to conventional root canal debridement helps to enhance healing the inflammatory response around root apex of rats. Sixty adult Sprague-Dawley male rats (70–90 days/140–160 g) were experimented. Pulp was removed from the mesial root of the first maxillary molar and left open to oral environment to allow the formation of periapical lesion. The rats were numbered and randomly divided into two groups: (i) PDT group (n = 30) received a single session of PDT with conventional debridement and, (ii) Control group (n = 30) received conventional debridement but with no PDT. PDT application involved the use of methylene blue photosensitizer for 5 min inside the root canals and irradiated with diode laser of 805 nm and 20 W power output for 90 s and sealed. After 4 weeks, the experimental rats were sacrificed by cervical dislocation. The maxillary first molar was then collected along with the surrounding tissue for further processing. Hematoxylin and eosin and immunohistochemical staining were used to observe the morphological effects. Proliferating Cell Nuclear Antigen (PCNA), STRO-1 and CD-44 were used as the primary antibodies for the immunohistochemical study. A reduction in inflammatory cells, which were mainly composed of lymphocytes, was observed in the periapical lesions after PDT. The number of PCNA-positive cells increased to approximately twice in the PDT as compared to the control group. These PCNA-positive cells included STRO-1 and CD-44 positive cells, indicating enhancement of wound healing and reduction in inflammatory cells. The findings of the present experimental study indicate that PDT application induced proliferation of PCNA-positive cells, which included STRO-1 and CD44-positive cells. This suggests that PDT may help to enhance healing periapical lesion, indicating the potential of PDT in the treatment of periapical periodontitis.