A preliminary randomized parallel controlled trial will be conducted. Forty teeth of 36 patients were randomly assigned into two groups: group PRF, treated with RET with PRF platelets rich fibrin (intervention), and group BC, treated with RET with induced blood clot(control). Upon clinical examination, the presence of pain on biting or percussion, swelling or sinus tract, or abnormal tooth mobility will be considered a failure. To monitor the changes in periapical radiolucency, a periapical index (PAI) will be used. The primary outcome of the current study will be to assess the effectiveness of RET using PRF platelets rich fibrin of mature permanent incisors with periapical radiolucency compared to RET using induced BC formation in the root canal space.~Eligibility criteria:~Healthy adolescents below the age of 18 years who need endodontic retreatment of previously obturated mature single-rooted incisors with gutta-percha will be recruited.~Patients with a positive history of allergic reactions, systemic diseases, and severe emotional or behavioral problems will be precluded. Only teeth diagnosed with asymptomatic apical periodontitis or chronic apical abscess (i.e. little discomfort with intermittent episodes of pus discharge through the sinus tract) were included. To confirm the clinical status, only teeth with a periapical index (PAI) score ≥3 based on Ørstavik et al classification were considered. Teeth with previous attempts for endodontic retreatment including pulpotomy or pulpectomy, non-restorable crowns or need post placement, or periodontal problems were excluded. A tooth must not be a candidate for endodontic surgery according to Glickman et al. indications and the updates of the European Society of Endodontology (e.g. obtaining biopsy, removal of intracanal broken files, persistent periapical lesions standing for a long period, radicular perforation, root fracture, or obstructed root canals, or the inability of complete removal of old gutta-percha or extruded material beyond the apex with persistent apical lesion for long duration).~Interventions:~According to the latest RET operating guidelines issued by the American Academy of Endodontics (AAE) and the European Society of Endodontics (ESE), the standardised operating procedure of RET requires two treatment visits. During the first appointment, infection is controlled and inflammation is relieved with complete removal of failed obturation material. Pulp regeneration and revascularization is accomplished during the second appointment.
Evalaution of clinical success of secondary treatment for total 40 permanent incisors with failed root canal treatment with apical radiolucency.~Twenty of of these permanent incisors will be treated with regenerative endodontic treatment(RET) with platelets rich fibrin PRF as intervention group vs. 20 incisors control group secondary treated with (RET) with induced blood clot (BC).