The aim of this study is to evaluate the effect of intracanal cryotreated (2-3°C) 2.5% sodium hypochlorite and Saline used throughout the procedure, compared with a room-temperature irrigation protocol with a final cryotreated saline flush or an entirely room temperature irrigation protocol, on postoperative pain in patients with symptomatic irreversible pulpitis and symptomatic apical periodontitis in mandibular molars.

Inclusion Criteria:

1. Age between 20-40 years old.

2. Systemically healthy patients (ASA I or II).

3. Mature Mandibular molar teeth with :

   • Preoperative sharp pain and symptomatic apical periodontitis marked on NRS scale by reading not less than 6.
   • Absence or slight widening in the periodontal ligament (PDL).
   • Vital response of pulp tissue to cold pulp tester and (ethyl chloride spray).
   • Positive response to percussion test.

4. Restorable teeth.

5. Ability to complete the endodontic treatment in a single visit.

6. Positive patient acceptance for participation in the trial. -----------------------------------------------------------------

Exclusion Criteria:

1. Medically compromised patients (ASA III or IV)

2. Patients who used NSAIDs in the 24 hours before treatment.

3. Patients with two or more adjacent teeth requiring endodontic treatment.

4. Pregnant women.

5. Patients reporting bruxism or clenching.

6. Teeth associated with :

   • Acute periapical abscess and/or swelling.
   • Greater than grade I mobility or pocket depth greater than 5mm.
   • Non-restorable teeth.
   • Immature Apex.

7. Radiographic evidence of external or internal root resorption, vertical root fracture, perforation, calcification.