The aim of this study was to evaluate the effect of continuous rotation and reciprocation kinematics on post operative pain and difference in substance P levels in patients with irreversible pulpitis with symptomatic apical periodontitis. Twenty patients were randomly distributed into two groups; Continuous Rotation group(n=10): received mechanical preparation using EdgeEndo x7 rotary system (Albuquerque, New Mexico, USA), while Reciprocation group(n=10): received mechanical preparation using EdgeOne Fire reciprocating system (Albuquerque, New Mexico, USA). Apical fluid(AF) samples were collected, and substance P (SP) levels were measured using radioimmunoassay and postoperative pain was measured using Numerical Rating Scale (NRS) preoperatively, at 6h, 12h, 24h, 48h and 72h.

Inclusion Criteria:

• Single rooted mandibular second premolar teeth with complete root formation
• Pulpal diagnosis: Symptomatic irreversible pulpitis
• Periapical diagnosis: symptomatic apical periodontitis with no visible periapical radiolucent area
• Patients with pre-operative pain records above 4 on Numerical Rating Scale (NRS) to ensure standardization

Exclusion Criteria:

1. The presence of any systemic disease or allergic reactions
2. Pregnant and lactating females
3. Patients on antibiotic or anti-inflammatory medication
4. Use of analgesics a week prior to treatment
5. A radiographically untraceable canal or an excessively curved root
6. The presence of periapical radiolucency or sinus tract.
7. Teeth with open apices
8. Severe periodontal disease (generalized or localized to the tooth in question)
9. Absence of bleeding in the pulp chamber on access cavity preparation
10. Internal or external resorption