The aim of this clinical trial is to evaluate anti-inflammatory effect of various intracanal medications:

1. Calcium Hydroxide Slurry mixed with 3% Sodium Hypochlorite
2. Calcium Silicate
3. Calcium Hydroxide

In retreatment cases in terms of:

1. Biological Evaluation: Biomarker (IL 1B)
2. Radiographic Evaluation: CBCT
3. Clinical Evaluation: Pain Score (VAS)

Sixty patients presenting with failed root canal treated lower first molars with periapical lesion were included in this randomized controlled single-center clinical superiority trial with two parallel arms and randomly allocated to 3 equal groups (n = 20) according to the type of ICM used. Patients were randomly allocated to receive either Ca(OH)2 slurry that was prepared from pure Ca(OH)2 powder mixed with 3% NaOCl, calcium-silicate (Bio-C Temp) or calcium hydroxide (CH) as ICM. Teeth were instrumented using a rotary file system (M3 pro Gold) and irrigated with 3% NaOCl. Subsequently, the root canals were dressed with a Ca(OH)2 + NaOCl or calcium silicate (test groups) or Ca(OH)2 (control group). Periapical fluid samples were collected after accessing the root canal in the first visit and after the root canal dressing removal in the second visit 2 weeks later using paper point. Samples were transferred to the microbiology lab immediately and levels of pro-inflammatory marker (IL1B) were measured using a specific enzyme-linked immunosorbent assay (ELISA) immediately after the second visit to test the reduction in inflammatory marker level after intracanal medication usage. Also, preoperative and 12 months-postoperative radiographic evaluation by CBCT were obtained to measure volumetric reduction in lesion size using segmentation technique. And patients rated their pain pre-operatively and then after 6, 12, 24, 48, 72 h and 7 days using the VAS score. Clinical and radiographic follow-up evaluations were scheduled for 1 week, 1 month, 6 months and 12 months by examining the patient clinically using palpation and percussion tests and pain questionnaire and periapical digital radiographs to compare reduction in lesion size.

Inclusion Criteria:

1. Age: 21-45 years.
2. Medically free patients. (ASA Class 1)
3. Gender: males and females
4. Patients who are cooperative at operation and in attendance at scheduled follow-up visits.
5. Restorable root canal treated permanent lower first molars with periapical lesions.
6. Small (<5 mm) or medium periapical lesion size (5-10 mm)

Exclusion Criteria:

1. Patients with a history of allergic reactions to any of the study materials.
2. Teeth that become non-restorable after complete caries excavation.
3. Teeth that have mobility or deep periodontal pockets.
4. Teeth with internal or external resorption.