In this study, the researchers will investigate the effect of single-file reciprocating versus single-file rotational file systems on the postoperative pain in adult patients who have necrotic pulp and apical periodontitis. The participants will be assigned by chance to separate groups that compare 2 different treatments, reciprocating single-file system (Reciproc Blue) and rotational single-file system (OneShape). As a reference, Mtwo multi-file (full-sequence) will be used.