Earlier, it was believed that successful regeneration cannot be achieved once tooth has become infected. However, recent studies suggest that regenerative endodontics may in fact be possible in teeth with pulpal necrosis and periapical pathology.

The primary goal in regenerative procedure is to eliminate clinical symptoms and resolve apical periodontitis. The blood clot acts as a scaffold, and the growth factors inside recruit stem cells, most likely from periapical papilla. But unfortunately, the erythrocytes in the clot of the blood column undergo necrosis, affecting its properties so the blood column is augmented by the use of different types of scaffolds.

Platelet-rich fibrin is classified into four types (Standard PRF, Injectable PRF, Advanced PRF and Concentrated Growth Factor CGF) according to speed and time of centrifuge with the overall aim to increase the number of platelets and leucocytes

Inclusion Criteria:

• Medically free patients who accept to participate in the study.
• Age between 18-35 years old with no sex predilection.
• Patients with good oral hygiene.
• Patients with necrotic pulp in mandibular & maxillary single rooted permanent teeth with mature apex that Symptomatic or Asymptomatic , Doesn't respond positively with the electric pulp tester ,Associated with or without swelling /sinus tract, Has radiographic evidence of periapical radiolucency, Has a straight, non-curved root, Teeth with normal occlusal contact with the opposing teeth.

Exclusion Criteria:

• Illiterate patient because they can't estimate the pain level on the pain scale (NRS).
• Patients with systemic diseases or on systemic corticosteroids therapy because they have impaired healing and higher incidence of pain.
• Pregnant women to avoid radiation exposure during the treatment which may be hazardous to the fetus and breasts from dental X-ray examinations shields.
• Patients that have allergy to ciprofloxacin or metronidazole to avoid any allergic reaction after placement of bi-antibiotic paste as intra-canal medication.
• Patients reporting bruxism or clenching because this induce more pressure on teeth and may initiate the post-operative pain in the treated tooth which is already have peri-apical inflammation
• Teeth that, Have vertical root fracture, coronal perforation, and calcification, Are indicated for retreatment because they have lower success rate , Have pocket depth greater than 5mm,Need periodontal therapy , Non restorable , Hopeless tooth, patients that have T.M.J disorder

double blinded