The aim of this study is to evaluate the effect of different irrigation activation methods used during endodontic treatment on postoperative pain in teeth with periapical lesions, allowing us to clinically determine which agitation technique causes less postoperative pain.

Sample Size Determination and Patient Selection The sample size was calculated by reviewing relevant reference articles and pilot studies, using the G*Power 3 program. With a 95% confidence level, 80% power, and an effect size of 0.4, it was determined that at least 19 teeth per group were statistically required. To account for potential dropouts, it was decided to include 22 teeth per group, totaling 88 teeth in the study.

Patients were selected from individuals who met the inclusion and exclusion criteria listed below.

Inclusion criteria:

Healthy patients aged 18-65 years, Patients with chronic apical periodontitis, Teeth with PAI scores of 3-5, Mandibular canines and premolars, Teeth without root resorption, periodontal disease, previous endodontic treatment, or calcifications.

Exclusion criteria:

Patients with systemic diseases, Pregnant women, Teeth with acute pain, Teeth with crown or root fractures, Patients who used analgesics or anti-inflammatory drugs within the last 12 hours, Patients who used antibiotics in the past 2 weeks, Teeth with open apex or immature teeth, Patients with incomplete consent or follow-up forms. Treatment Protocol The study included patients treated at the Endodontics Clinic of the Faculty of Dentistry, Akdeniz University, following routine root canal treatment procedures. All treatments were performed by a single clinician. Data regarding patients' age, sex, systemic conditions, root canal anatomy, periapical status, irrigation activation method used during treatment, and postoperative pain intensity were obtained from patient records and follow-up forms.

Before the procedure, patients' medical and dental histories were recorded, and percussion and palpation sensitivities were assessed. Pulp vitality was evaluated using an electric pulp tester (Ai-Pex, Woodpecker, China) and a cold test (Cerkamed, Poland). Initial periapical radiographs were assessed, and teeth with PAI scores of 3, 4, or 5 were included, while teeth with scores of 1 or 2 were considered periapically healthy and excluded from the study.

Local anesthesia was administered using 1 ml of anesthetic solution containing 80 mg articaine hydrochloride and 0.024 mg epinephrine hydrochloride (Ultracain D-S forte, Sanofi, France) via a mental nerve block. Teeth were isolated using a rubber dam, and caries and existing restorations, if any, were removed using diamond burs to prepare a standard endodontic access cavity.

Working length was determined using #15 K-type hand files (Perfect, China) and an electronic apex locator (Woodpecker, Endo Radar Pro, China) and verified radiographically 0.5-1 mm short of the apex.

Root canal preparation was performed using an endodontic motor (Woodpecker, Endo Radar, China) and a nickel-titanium rotary file system (ProTaper Next; Dentsply-Sirona, Ballaigues, Switzerland) at 300 rpm and 2 N/cm torque. Apical preparation was completed with the X4 file. During shaping, files were removed when excessive apical resistance was encountered to prevent torsional overload, debris were cleaned from the files, and canals were irrigated.

Irrigation procedures were applied with different activation methods for four groups:

Group 1 (Control): During shaping, canals were irrigated with a total of 15 ml 2.5% NaOCl, 2 ml after each file change, using a 27G open-ended irrigation needle with 2-3 mm vertical movements, followed by recapitulation with a #15 K file. After preparation, canals were irrigated with 5 ml 17% EDTA (Endo-Solution, Cerkamed, Stalowa Wola, Poland) for 1 minute, followed by 5 ml distilled water to neutralize residual EDTA.

Group 2: Root canal preparation was performed as in Group 1. The EDDY tip was placed 2 mm short of the working length and activated in three cycles of 20 seconds each with 2-3 mm vertical movements. After each 20-second activation, 1 ml 2.5% NaOCl was applied to refresh the solution. Residual NaOCl was removed with 5 ml distilled water for 30 seconds. The canal was then irrigated with 2 ml 17% EDTA and activated in three 20-second cycles, adding 1 ml EDTA after each cycle. Residual EDTA was removed with 5 ml distilled water for 30 seconds.

Group 3: Root canal preparation and irrigation activation procedures were performed as in Group 2, but ultrasonic activation (DTE, Woodpecker, China) was used.

Group 4: Root canal preparation and irrigation activation procedures were performed as in Group 2, but XP-Finisher (FKG Dentaire, La Chaux-de-Fonds, Switzerland) was used.

Canals were dried with appropriate paper points (Meta Biomed, Korea) and obturated using gutta-percha (Diadent Group International, Canada) and an epoxy resin-based sealer (Dentac, Turkey) with lateral condensation technique. Temporary restorations were applied using chemically curing glass ionomer cement (Prime Dental Products, Prime Cem Restorative (Type 2), India) and occlusion was checked. Patients were prescribed 400 mg ibuprofen and advised to use it as needed. Permanent restorations were completed with light-cured composite (Coltene Whaledent Brilliant Ng, Switzerland) after one week, following collection of postoperative pain forms, and occlusion was checked.

Postoperative Pain Assessment Patients were provided with a postoperative pain assessment form including a Visual Analog Scale (VAS) and instructed to record their pain levels and analgesic use at 6, 24, 48, 72 hours, and on the 7th day. Patients returned for a follow-up visit after one week to submit the completed forms.

Inclusion Criteria:

• Healthy patients aged 18-65 years, Patients with chronic apical periodontitis, Patients with a PAI score of 3-5, Mandibular canine and premolar teeth, Teeth without root resorption, periodontal disease, previous endodontic treatment, or calcification.

Exclusion Criteria:

• Patients with systemic diseases, Pregnant patients, Teeth with acute pain, Teeth with crown or root fractures, Patients who have used analgesic or anti-inflammatory drugs within the last 12 hours, Patients who have used antibiotics within the last 2 weeks, Immature teeth with open apices, Patients with missing consent or follow-up forms.