The goal of this clinical trial is to evaluate the effect of cold saline (2.5 degrees Celsius) irrigation on postoperative pain in patients who require root canal treatment in molar teeth because of dead dental pulp and infection around the apex of the root of the involved teeth. This cold saline irrigation will be done after standard irrigation of the canal using a 5.25% sodium hypochlorite solution. The main questions it aims to answer are:

• Is there any difference in postoperative pain when final irrigation is performed using a cold saline solution compared to the irrigation using the saline solution at room temperature in patients who require dental root canal treatment of molar teeth?
• Because of cold saline irrigation, what type of adverse event/s may result?

Participants will be asked to fill out a questionnaire before the start of the root canal treatment and record the preoperative pain using the visual analog scale (VAS). Root canal treatment will be completed in one visit. The standard procedure of root canal treatment will be followed, including irrigation of the canal using 5.25% sodium hypochlorite. As a final irrigation, either cold saline solution or a normal saline solution at room temperature will be used. The participants will be asked to fill out another questionnaire and record the presence, duration, and intensity of postoperative pain, and if painkiller medicine was taken immediately after completion of root canal treatment and at 6 hours, 12 hours, 72 hours, and 1-week intervals.

The researcher will compare the effect of the final irrigation of a cold saline solution with that of a normal saline solution at room temperature on postoperative pain.

Postoperative pain in root canal therapy is multifactorial in nature, including changes in periapical pressure, microbial factors, inflammatory mediators, and psychological factors. Postoperative pain in endodontics between visits or after completion of the treatment is a major concern to both patients and operators. Teeth presented with preoperative pain, irreversible pulpitis, pulp necrosis, and apical periodontitis are the most susceptible to postoperative pain The pharmacological management of pain using medications such as nonsteroidal anti-inflammatory drugs, paracetamol, or corticosteroids, despite being relatively safe, can have side effects such as gastrointestinal intolerance and renal, hepatic, and respiratory disorders such as asthma which have been reported in the literature. To avoid these secondary effects, intracanal medications, laser, and cryotherapy have been suggested in the literature.

Physical and clinical evidence suggests that the application of cold may decrease pain through the mechanism of decreasing the conduction velocity of nerve signals, hemorrhage, edema, and local inflammation. An in vitro study showed that intracanal irrigation with cold saline at 2.5 degrees Celsius reduced the external root surface temperature by more than 10 degrees Celsius, which would be enough to produce the anti-inflammatory effect in peri-radicular tissues.

There are very few studies done to evaluate the effect of intracanal cryotherapy on postoperative pain in root canal therapy.

This clinical trial aims to assess if final irrigation using cold saline solution after standard chemo-mechanical preparation (root canal instrumentation and irrigation using 5.25% sodium hypochlorite) procedures results in any difference in the incidence and intensity of postoperative pain in patients presenting with molar teeth with necrosis of pulp and symptomatic apical periodontitis. This clinical trial will also assess the incidence of any adverse event as a result of cold saline irrigation.

Inclusion Criteria:

• Healthy patients
• Patients with maxillary or mandibular molar teeth that require root canal treatment
• The diagnosis of pulp necrosis
• The presence of symptomatic apical periodontitis
• The presence of normal occlusion

Exclusion Criteria:

• Previously done root canal treatment
• Pregnancy
• Presence of any systemic disease or allergic reactions
• Use of any analgesic or antibiotic medications within the past three days
• Sinus tract or local gingival swelling around the affected tooth
• Periodontal pocket greater than 3 mm around the affected tooth
• Severe periodontal disease
• Internal or external root resorption
• Broken files
• Over instrumentation
• Incomplete filling of the root canal
• Overfilling of the root canal