Brief Summary: This prospective randomized controlled clinical trial aims to evaluate the effects of different irrigation solutions (NaOCl, HEDP) and activation methods (conventional syringe irrigation, EDDY, diode laser) on postoperative pain and oral health-related quality of life in single-visit root canal treatment of asymptomatic mandibular molars.

The primary aim of this prospective randomized controlled clinical trial is to evaluate the effects of two different irrigation solutions (2.5% NaOCl and HEDP) and three different activation methods (conventional syringe, EDDY, diode laser) on postoperative pain and oral health-related quality of life in single-visit root canal treatment of asymptomatic mandibular molars, aiming to overcome the limitations of conventional irrigation. Additionally, the study will compare patients' oral health-related quality of life before treatment and one week after treatment. While no significant difference in postoperative pain is expected, an improvement in quality of life is anticipated.Eligible participants will be adult patients requiring endodontic treatment of asymptomatic mandibular molars. After meeting inclusion criteria and providing informed consent, participants will be randomly assigned to six different groups. Randomization will be performed using a computer-generated random number sequence and the codes will be kept in sealed opaque envelopes to prevent bias between groups.The irrigation protocols and activation methods to be applied in the study are as follows:Irrigation Solutions: 2.5% NaOCl and HEDP (HEDP; Dual Rinse, Medcem GmbH, Weinfelden,Switzerland)Activation Techniques: Conventional syringe, EDDY (Micron, Tokyo, Japonya), diode laser Dentsply Sirona Sirolaser Advance; Sirona Dental Systems, Bensheim, Germany)Anesthesia: Regional mandibular block using Articaine-containing MaxicainAll procedures will be performed under rubber dam isolation. Root canal working length will be determined using a #10 K-type file and apex locator, and canals will be shaped using a nickel-titanium rotary system. Each canal will be irrigated according to the assigned protocol, and root canals will be obturated using gutta-percha and an epoxy resin-based sealer with a single-cone technique. Postoperative radiographs will be taken to confirm obturation, and definitive restorations will be completed with composite resin materials.Postoperative pain will be assessed using the Visual Analog Scale (VAS) at 6, 12, 24, 36, 48, 72 hours, and one week after treatment. Quality of life will be measured using the OHIP-14 questionnaire before treatment and one week postoperatively.The study sample size is 90 participants, with 15 volunteers per group. All treatments will be performed by a single operator, and the materials and devices used in the study are standard products routinely used in clinical practice. The expected benefit of the study is to determine the effects of different irrigation solutions and activation methods on postoperative pain and patient quality of life, providing insights for clinical practice.

Inclusion Criteria:

• Systemic Inclusion Criteria1. Volunteers must not have any systemic symptoms or be pregnant.2. According to the ASA classification, individuals with: • ASA I (Healthy (without acute and/or chronic diseases)• ASA II (with mild systemic diseases) (asymptomatic congenital heart disease, well-controlled dysrhythmias, non-exacerbated asthma, well-controlled epilepsy, non-insulin-dependent diabetes mellitus, oncological conditions in remission) will be included in our study.3. Must be between 18 and 65 years of age.4. Must not have used analgesic anti-inflammatory drugs in the last two weeks or cortisone in the last 6 months.5. Volunteers must be able to contact us again 6, 12, 24, 48, or 72 hours after completing their treatment and must be mentally fit enough to express pain scores and answer the questionnaire.6. Volunteers must not have bruxism.Local inclusion criteria 1. Mandibular molars must be present.2. Teeth must be asymptomatic preoperatively.There must be no palpation, percussion, or radiographic findings.3. Rubber dams must be attached to the teeth to be treated.4. The teeth must be in its normal position within the mouth.5. The volunteer must be able to open their mouth sufficiently.

Exclusion Criteria:

• 1. Volunteers who have used analgesics, anti-inflammatory drugs, antibiotics, etc. that could alter pain and infection control in the last 12 hours.2. Subjects with a history of sensitivity or adverse reactions to any medication or material used in this study3. Teeth with calcified canals or severe periodontal disease4. Subjects with missing opposing or adjacent teeth5. Pregnant or breastfeeding female subjects6. Teeth requiring additional anesthesia methods (e.g., intrapulpal, intraligamentary, second block anesthesia, or additional local anesthetic agent) will be excluded from the study if anesthesia is insufficient.7. Teeth with apical lesions will not be included in the study.8. Teeth with root resorption will not be included in the study.9. Teeth requiring restorations such as endocrowns, onlays, overlays, or full crowns due to excessive material loss after root canal treatment will not be included in the study.Teeth with structural loss sufficient to require post-core application will be excluded.10. Teeth with untreated periodontitis and teeth or sites that have undergone surgical treatment within the last 6 months will not be included in the study.

the bioistatician performing the data analysis will be blinded to group allocation. the cinician performing th treatments will not be blinded.