The aim of this study is to evaluate the impact of anterior disc displacement with reduction (ADDR) on postoperative pain following root canal treatment in patients diagnosed with symptomatic apical periodontitis.

This prospective clinical study included individuals diagnosed with symptomatic apical periodontitis who had a vital mandibular molar tooth and were diagnosed with anterior disc displacement with reduction (ADDR) according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) (n = 45), as well as individuals without any temporomandibular joint pathology (n = 45). Following patient dropouts, a total of 70 patients with complete and eligible data were included in the final analysis, with 35 participants in each group.

All root canal treatments were performed by the same clinician using a standardized treatment protocol. Postoperative pain intensity was assessed using the Numeric Rating Scale at 6 and 12 hours and at 1, 2, 3, 5, and 7 days after treatment. In addition, joint sounds, joint pain, and maximum mouth opening were recorded in the preoperative period and at the 7-day postoperative follow-up, and their associations with postoperative pain were analyzed.

The findings of this study provide insight into the relationship between temporomandibular joint disorders and endodontic postoperative pain and may contribute to improved clinical understanding.

Inclusion Criteria:

• Individuals aged between 18 and 65 years with no systemic disease
• Patients diagnosed with symptomatic apical periodontitis
• Presence of a vital permanent mandibular first or second molar tooth requiring root canal treatment
• Teeth with no radiographic evidence of periapical changes or only slight widening of the periodontal ligament space
• Patients reporting preoperative spontaneous pain with a Numeric Rating Scale (NRS) score between 4 and 10 (moderate pain: 4-6; severe pain: 7-10)
• Patients reporting pain intensity of 4 or higher on the NRS during percussion testing
• Patients diagnosed with isolated anterior disc displacement with reduction according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) (experimental group) or patients without any temporomandibular joint disorder or pathology (control group)

Exclusion Criteria:

• Teeth found to have necrotic pulp tissue during access cavity preparation
• Patients in whom the study tooth was not located on the same side as the temporomandibular joint diagnosed with anterior disc displacement with reduction
• Occurrence of any endodontic complications during treatment
• Use of medications that could affect pain perception (e.g., analgesics or anti-inflammatory drugs) within at least 12 hours before treatment, or use of systemic antibiotics within one month prior to enrollment
• History of major jaw trauma, dentofacial deformities, or previous temporomandibular joint surgery
• Concurrent use of steroids, muscle relaxants, or narcotic medications
• History of diagnosed neuropathic pain, myofascial pain, neuralgic pain, or chronic headache disorders
• Presence of periodontal disease (probing depth > 5 mm or tooth mobility greater than Grade I) or teeth lacking adequate coronal structure
• Teeth without occlusal contact or with premature contacts, patients with bruxism or clenching habits, or patients with fewer than three teeth on one side of the mandible
• Inability to read, understand, or complete the pain assessment scale or to provide the required follow-up data
• Presence of significant cognitive impairment (e.g., communication deficits, intellectual disability) or diagnosed psychiatric disorders (e.g., depression, anxiety disorders)
• Presence of immature teeth or teeth with open apices
• Pregnant or breastfeeding women

Individual participant data will not be shared.

An oral diagnosis and radiology specialist with more than 10 years of clinical experience evaluated the patients' endodontic treatment needs and performed the temporomandibular joint examination. Patients diagnosed with anterior disc displacement with reduction according to the Diagnostic Criteria for Temporomandibular Disorders were assigned to the experimental group, while individuals without temporomandibular joint disorders constituted the control group.

At this stage, both the participants and the clinician performing the root canal treatments were blinded to the temporomandibular joint status of the patients (double-blind). Group allocation was concealed until completion of the data analysis, resulting in a triple-blind study design.