The purpose of this study is to assess the effect of preoperative a single-dose of 50 mg diclofenac potassium on postoperative endodontic pain in mandibular molars with symptomatic irreversible pulpitis.

Patients with moderate-to-severe preoperative pain are selected. Patients receive either a single-dose of 50 mg diclofenac potassium (group A) or a placebo tablet as a control (group B). All patients receive the assigned premedication one hour before single-visit root canal treatment. Postoperative endodontic pain is measured at the following time points: 6 , 12,24,48 h after treatment. The incidence of analgesic intake is also recorded.

Inclusion Criteria:

• Patients with active pain (moderate-to-severe) in mandibular molars.
• Patients with prolonged response to cold testing and electric pulp tester.
• Patient with the ability to understand and use pain scales.
• Patient with vital coronal pulp tissue on access.
• Patient who accept to enroll to the study.

Exclusion Criteria:

• Patients' allergies or any other contraindication to diclofenac potassium or articaine.
• Pregnant and lactating females.
• Patients having pain medication in the last 6 hours.
• Patient has more than one symptomatic mandibular tooth in the same quadrant.
• Patients with periradicular pathosis and/or radiolucency other than widened periodontal ligaments.
• Patients with active peptic ulcer and gastrointestinal disorders.
• Patients with history of bleeding problems or anticoagulant use within the last month.