This study included 113 patients diagnosed with ankylosing spondylitis and 110 healthy volunteers. Participants in both groups were evaluated using the 'Diagnostic Criteria for Temporomandibular Disorders (DC/TMD)' diagnostic criteria. In addition, the relationship between temporomandibular joint dysfunction and disease activity was investigated in patients with ankylosing spondylitis.

Ankylosing spondylitis (AS) is a chronic, inflammatory disease with an unknown etiology that primarily affects the axial spine, especially the sacroiliac joints, and can also involve peripheral joints and extra-articular clinical manifestations. Complaints related to temporomandibular joint pathologies are commonly observed in the general population but more frequent in the group of patients diagnosed with ankylosing spondylitis compared to the average population. Although the mechanism of temporomandibular joint involvement in ankylosing spondylitis is not fully understood, destruction of the joint capsule or disk, synovitis in the joint, and craniovertebral postural changes have been suggested as possible mechanisms. In addition, pain due to temporomandibular joint dysfunction can significantly affect daily life activities, quality of life, social participation, and the emotional status of the individual. Determining the level of relationship between quality of life and psychological status will support the development of new interventions and treatment approaches to improve patient's quality of life further.

The age, gender, body mass index, marital status, duration of ankylosing spondylitis (AS) diagnosis, symptom onset, treatment for AS, occupation, smoking status, and Human Leukocyte Antigen (HLA)-B27 positivity status were recorded for the patient. The 'Diagnostic Criteria for Temporomandibular Disorders (DC/TMD),' published in 2014 and translated into Turkish in 2016, was used to assess the presence of temporomandibular joint dysfunction in the patients. This evaluation system consists of two parts: the clinical evaluation and examination findings of the current pathology on Axis I, and the psychosocial status of the disease on Axis II. The questions in the Symptom Questionnaire on the first axis were directed to the patient, and then the results were recorded by performing the examinations indicated on the examination form. The diagnosis was determined according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) decision tree, and marked on the examination form. Two groups were created based on the decision tree: pain and joint disorders. Pain disorders were further subdivided into muscle pain, joint pain, and TMD-related headaches; muscle pain was further subdivided into local muscle pain, muscle-fascial pain, and referred muscle-fascial pain subgroups. Joint disorders were classified as disc displacement with reduction, disc displacement with reduction-intermittent locking, disc displacement without reduction-limited mouth opening, disc displacement without reduction-limited mouth opening, degenerative joint disease, and dislocation.

On Axis II, the patients were asked to mark the areas where they felt pain on the pain drawing form. The marked area was divided into categories according to its size. The level of experienced pain was evaluated with the Graded Chronic Pain Scale (GCPS), jaw function limitations were assessed with the Jaw Functional Limitation Scale-20 (JFLS-20), depression was evaluated with the Patient Health Questionnaire-9 (PHQ-9), anxiety was assessed with the General Anxiety Disorder 7 (GAD-7), physical symptoms were evaluated with the Patient Health Questionnaire-15 (PHQ-15), and parafunctional activities were evaluated with the Oral Behavior Checklist (OBC). Additionally, the relationship between the identified diagnosis and psychosocial factors, disease activity, and other disease-specific factors was investigated.

Inclusion Criteria:

• Patients diagnosed with Ankylosing Spondylitis according to the Modified New York Criteria between the ages of 18-75.
• Healthy volunteers between the ages of 18 and 75.

Exclusion Criteria:

• Changes in the treatment of ankylosing spondylitis within the last 6 months
• Patients with pathology related to the temporomandibular joint and associated structures prior to the diagnosis of ankylosing spondylitis
• Use of medication that affects bone metabolism
• Presence of neurological or cognitive deficits
• History of trauma, malignancy, infection, and surgery in the head and neck area
• Presence of dental or periodontal pain
• History of orthodontic treatment.

113 patients with ankylosing spondylitis were diagnosed and 110 healthy volunteers.