To compare the effect of 1% melatonin gel versus calcium hydroxide as intra canal medication in necrotic mandibular premolars on:

• Intensity of postoperative pain.
• Bacterial load reduction.
• Periapical (MMP-9) level.

Inclusion Criteria:

1. Age between 18-50 years old.
2. Males and females.
3. Healthy patients categorized as I or II according to The American Society of Anesthesiologists. (ASA I or II), with no underlying allergies.
4. Single-rooted mandibular premolar teeth, having single root canal: diagnosed clinically with pulp necrosis.
5. Patients accepting to participate in the trial.
6. Patients who can understand pain scale (Appendix I) and can sign the informed consent (Appendix II).

Exclusion Criteria:

1. Medically compromised patients having significant systemic disorders (ASA III or IV).
2. Pregnant females.
3. If analgesics or antibiotics have been administrated by the patient during the past 24 hours preoperatively as it might alter their pain perception.
4. Teeth with multiple canals.
5. Teeth that show association with acute periapical abscess or swelling.
6. Teeth with vital pulp.
7. Non-restorable teeth or teeth that could not be adequately isolated with a rubber dam.
8. Immature teeth.
9. Teeth with greater than grade I mobility or pocket depth greater than 4 mm.
10. Teeth showing radiographic evidence of external or internal root resorption, vertical root fracture, perforation or calcification.
11. Patients with two or more adjacent teeth requiring endodontic treatment.
12. Patients reporting bruxism, clenching or TMJ problems.
13. Teeth with previous endodontic treatment.
14. Inability to perceive the given instructions.