The goal of this prospective cohort study is to evaluate the effectiveness of combined arthrocentesis and occlusal stabilization splint therapy in patients diagnosed with disc displacement without reduction of temporomandibular joint-induced closed locks. The main questions it aims to answer are:

• Is there a difference in the treatment response between chronic and acute closed-lock conditions?
• On which dimensions of pain did the treatment have positive effects? Participants will be preoperatively examined and assigned to one of the two study groups.
• All participants undergo a single session of TMJ arthrocentesis.
• Following the arthrocentesis session, all participants will use preoperatively fabricated occlusal splints.
• Participants will be recalled in one week to evaluate the outcomes. Researchers will compare acute and chronic closed-lock groups to see if there are differences between pain intensities and mouth-opening amounts postoperatively.

The study sample constituted patients diagnosed with DDWoR with limited opening according to the Turkish version of the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD Axis 1 questionnaire and examination form). The included patients with DDWoR-induced complaints persisting for more than three months were considered chronic (Group 1), and those with a shorter duration were considered acute (Group 2). For clinical diagnosis of DDWoR, Significant limitation of mouth opening, less than 35 mm assisted mouth opening, less than 4 mm increase in mouth opening with passive stretching, less than 7 mm contralateral movement of the mandible, and deviation of the mandible to the affected side during mouth opening was considered sufficient. The DC/TMD questionnaire and clinical examination diagnoses were confirmed by magnetic resonance images (MRI).

Preoperative and postoperative clinical examinations consisted of recording demographic information, amount of maximum mouth opening (MMO), and determination of McGill Pain Questionnaire (MPQ) and Visual Analog Scale (VAS) scores. MMO values were determined as the distance between the incisal edges of upper and lower central teeth and recorded in millimeters. MPQ scores were obtained with the questionnaire form consisting of four subsections. In the first subsection of the questionnaire, besides the patient's demographic data, the location of the current pain and whether it comes from superficial or deep tissues are questioned. In the second subsection, there are 20-word groups containing 78 words that ask the Sensory (groups 1-10), Affective (groups 11-15), Evaluative (group 16), and Miscellaneous (groups 17-20) components of current pain. In the third subsection, the relationship of pain with time is questioned. There are word groups to determine the continuity of pain, its frequency, and factors that increase or reduce pain. In the fourth subsection, five-word groups ranging from "mild" pain to "unbearable" pain to determine the severity of the pain; There are also six questions to assess the severity of pain that the patient can accept or experience without discomfort, which is also defined as "experienceable=target pain." The obtainable MPQ scores range from 0 to 78. The higher the scores, the greater the pain. Also, preoperative and postoperative VAS scores were obtained by marking a point on a 10 cm line. The score was calculated as the distance in centimeters between the zero and the marked points.

Inclusion Criteria:

• individuals over the age of 18
• completion of the arthrocentesis treatment without any complications;
• the presence of preoperative information and postoperative follow-up data;
• persistent complaints despite conservative methods (behavioral modification, diet restrictions, non-steroid anti-inflammatory drugs, and physical therapy) for at least three months.

Exclusion Criteria: The patients;

• diagnosed with any connective tissue, neurological, dermatological, inflammatory diseases, and TMD other than DDWoR,
• who underwent TMJ surgeries, arthrocentesis procedures, TMJ ankylosis surgery,
• previously used occlusal splints,
• who developed complications in the application of arthrocentesis in the current study (low-volume lavage, extravasation, inability to reach the upper joint space, e.g.),
• with lack of teeth to affect the fabrication of the occlusal stabilization splint,
• with a history of radiotherapy of the head and neck.

The data regarding participants were made available in the manuscript