Actinomycosis is not Frequent in the Periapex But is a Persistent Lesion

Periapical actinomycosis caused by a gram-positive anaerobic pathogen characterizes a typical extra-radicular infection. This study determined the frequency and correlated the content of bacteria colonies with the of periapical actinomycosis size. The study comprised a total of 218 periapical lesions (PL) (cysts, granulomas or abscess). The specimens embedded in paraffin were sliced into 4-µm sections and stained with hematoxylin-eosin, Gram, Periodic Acid-Schiff (PAS) and Grocott's stain. The presence of bacterial colonies composed of filamentous structures labeled with the histochemical stains were described as Actinomyces, and for each case, the bacterial colonies were counted and measured. The correlation between the number and size of bacterial colonies and the size of PL was tested using Pearson's adjusted correlation coefficient. From 218 PL, bacterial colonies were identified in 64 biopsies. Seven cases (0.3%) fulfill the criteria for diagnosis of periapical actinomycosis. All of cases were therapy-resistant and did not showed periapical repair after 12 months of follow-up. Periapical surgery or dental extraction was performed. The correlation test indicated no correlation between the number of bacterial colonies and the lesion size (p=0.752, r=-0.148). However, a larger bacterial colony size generally resulted in a larger periapical lesion (P=0.000, r=0.657). The frequency of periapical actinomycosis was low, and this lesion should be included in the differential diagnosis of PL. The size of the Actinomyces colonies seemed to contribute to increase the size of the periapical lesion.