Genetic polymorphisms are differences in the sequence of human DNA that can alter gene expression and influence the organism's susceptibility to disease as well as its responses to the environment. Thus, in addition to microbial and mechanical factors related to the root canal itself, factors intrinsic to the host may interfere with the success of endodontic treatment and the need for reintervention. This study will investigate molecular aspects involved in the persistence of post-treatment periapical lesions by collecting saliva samples to compose a DNA bank, extracting genomic material, clinical and radiographic evaluation, and genotyping by PCR allelic discrimination analysis in real-time. Clinical and radiographic examinations will be used as phenotypic parameters to understand the molecular aspects involved in the etiology of persistent endodontic infection. Patients diagnosed with pulpal necrosis who still present persistent periapical lesion (n = 200) and patients with repair of the lesion (control group n = 200) will be included in the study 12 months after endodontic treatment. Saliva samples recently collected, as well as those that are already stored in the bank will be used as a source of genomic DNA. After sample processing, genotyping for the soluble tumor necrosis factor-alpha (TNF) and TNF-± receptor 1 and 2 (TNFRSF1A and TNFRSF1B, respectively) mediators will be performed by real-time PCR. Chi-square, Fisher's exact and Odds Ratio calculations will be used to assess whether any genotype or allele is associated with the persistent periapical lesion. The significance level established will be 5%.
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