the aim of the study is to evaluate the effect of cryotherapy on postoperative pain in molar teeth with irreversible pulpitis and apical periodontitis

the purpose of the study was to evaluate the effect of 2.5c cold saline irrigation as a final irrigant on postoperative pain after single visit root canal treatment of teeth with vital pulp and apical periodontitis .thirty patients will be included in the study .the teeth will be divided into 2 groups (i.e the control group and the cryotherapy group ) in the cryotherapy group ,final irrigation with 2.5c cold saline solution for 5 mins will be performed following completion of biomechanical preparation whereas in control group same solution stored at room temperature will be used . treatment will be done in a single visit then participants will be asked to rate the intensity of postoperative pain using numerical rating scale at 6,12,24,48 hrs

Inclusion Criteria:

• Age between 20-40 years old.
• Systemically healthy patient (ASA I or II).
• mandibular first molar teeth with:
• Preoperative sharp pain and Symptomatic apical periodontitis .absence or slight widening in the periodontal ligament (PDL). .Vital response of pulp tissue to cold pulp tester (ethyl chloride spray).
• Ability for isolation with rubberdam.
• Restorable teeth
• Ability to fill the root canals in single visit treatment.

Exclusion Criteria:

• Teeth without good apical constriction, such as wide or open apex
• Use of any type of analgesics or antibiotic medications within 3 days .Pregnant or nursing females.
• Patients having significant systemic disorder (ASA III or IV).
• Teeth that have :

Non vital pulp tissues. Association with swelling or fistulous tract Acute or chronic periapical abscess Greater than grade I mobility Pocket depth greater than 5 mm No possible restorability

After determining the eligibility of the patient, the assistant supervisor will be contacted to assign the participant to either the intervention (cryotherapy) or the control (normal saline) groups according to the random sequence generated.