After collecting the biological material, the periapical lesions obtained were subjected to analysis of gene expression levels for RANK, RANKL, TNFRSF1, SOCS-1, IL-10, IL-1β and TNF-α, and histopathological evaluation for characterisation and differentiation into periapical granulomas and cysts; immunohistochemical evaluation for SOCS-1 and IL-1β protein labeling; and microbiological analysis to identify the microorganisms involved in persistent periapical infection. The gene discussed is TNF; the disease is periapical granuloma.