The participants were divided into two groups: Group I (cryotherapy) (n =10) after the completion of the mechanical preparation intra oral cryotherapy was applied. Group II (control) (n =10) received standard root canal treatment without the application of any type of cryotherapy.

1-Patients selection: 20 patients with symptomatic apical peridontitis related to mandibular premolars were selected . After proper anestehsia, Access cavity preparation was performed. The working length measured using apex locator. chemicomechanical preparation was done. for cryotherapy group: cold pack (ice gel enveloped by a sealed plastic cover) measuring 2.5 x 5 centimetres was placed intraorally on the vestibular surface of the treated tooth for a total time of 30 minutes. apical fluid sample was collected by paper point and the root canal was then filled using gutta percha and resin-based sealer.The access cavity was sealed using glass ionomer restoration. for the control group normal treatment was done and apical fluid was collested also before obturation.

Inclusion criteria:

• clinical diagnosis of symptomatic apical periodontitis related to ving a mandibular single-rooted premolars
• radigraphically: absence of periapical radiolucency on x ray.

Exclusion criteria:

• The presence of any systemic disease or allergic reactions
• Vulnerable population: prisoners, pregnant women, mentally ill people, etc.
• Use of analgesic or antibiotic medication within three days
• A radiographically untraceable canal

detailed Statistical Analysis Plan

2025 ,available for a year

review the purpose of request

A) Sequence generation;was done using a random sequence number generated by computer software.

B) Allocation Concealment Mechanism: Folded, numbered papers were placed in tightly sealed envelopes containing the patient's coding