<h4>Aim</h4>To evaluate the impact of polymorphisms in SOCS-1, TNF-α and RANKL on gene expression of RANK, RANKL, TNFRSF1, SOCS-1, IL-10, IL-1β and TNF-α, and to evaluate the histopathological, immunohistochemical and microbiological aspects of persistent apical periodontitis (PAP) after root canal treatment (RCT) in Brazilian individuals.<h4>Methodology</h4>Patients with pulp necrosis and apical periodontitis at the time of the non-surgical RCT (NSRCT) were followed up for at least 1 year after NSRCT. This evidence concerns the gene TNF and periapical periodontitis.