Temporomandibular disorders (TMDs) are multifactorial clinical conditions affecting the masticatory muscles, the temporomandibular joint (TMJ), and the surrounding structures. The most common subtype is disc displacement, which is characterized by an abnormal position of the articular disc. Magnetic resonance imaging (MRI) is considered the gold standard for the diagnosis of disc displacement because it provides excellent soft tissue contrast, allows direct visualization of the disc, and enables dynamic evaluation. The parallel nature of mandibular and head-neck movements reflects the functional relationship between the temporomandibular and cervical neuromuscular systems. In addition, various craniofacial skeletal anomalies have been reported to be associated with disorders of the cervical vertebrae. TMD restricts mandibular movements and causes pain in the surrounding muscles, which may lead to referred pain in the neck, shoulder, and cervical muscles, thereby affecting head posture. Head and neck postural abnormalities are closely associated with cervical pain and dysfunction related to TMD. This relationship is thought to be bidirectional and can be explained through biomechanical, neurological, and pathophysiological mechanisms. In particular, upper cervical vertebral dysfunctions and changes in head position may influence the severity of TMD symptoms. For this purpose, lateral cephalometric radiography is frequently used to evaluate the hyoid position and the cervical spine in relation to the TMJ. Upper cervical vertebral anomalies and craniofacial morphological characteristics can be analyzed using these images.

A comprehensive medical history was obtained from all participants, including demographic characteristics (age, sex), systemic medical conditions (musculoskeletal, cardiovascular, and psychological diseases, and regular medication use), pain-related parameters (character, duration, and severity), TMD-related comorbidities (neck pain, headache, sleep disorders, and other pain syndromes), presence of bruxism, duration of mobile phone use, and body position during phone use (sitting or lying).

The temporomandibular joint region, masticatory muscles (masseter and temporalis), and cervical muscles (trapezius and sternocleidomastoid) were evaluated by palpation. Clinical TMJ parameters included limitation of mouth opening, presence of pain during opening, and joint sounds.

Patients included in the study were selected from individuals presenting to the clinic with TMJ-related symptoms. Patients with TMD and accompanying neck symptoms were evaluated using lateral cephalometric radiography, while the position of the articular disc was assessed using magnetic resonance imaging (MRI). MRI is routinely used for imaging the articular disc and surrounding soft tissues in patients with TMD and is considered the gold standard for the diagnosis of disc displacement. MRI images were independently evaluated by two maxillofacial radiologists (Melike Yurttaş and Emine Kübra Ceylan Altun), and only patients diagnosed with disc displacement were included in the study.

Morphological and morphometric measurements of the C2, C3, and C4 vertebral bodies were performed on lateral cephalometric radiographs of the included patients. Morphological assessment included the presence of osteophyte formation and generalized sclerosis of the vertebrae.

Morphometric measurements included vertebral body dimensions, craniovertebral posture parameters (NSL/OPT and OPT/HOR angles), hyoid triangle height, and intervertebral disc height. Vertebral dimensions were evaluated by measuring anterior height as the distance between the superior and inferior borders of the anterior vertebral margin, and posterior height as the distance between the superior and inferior borders of the posterior margin. Additionally, the anteroposterior diameter of the C2, C3, and C4 vertebrae was measured as vertebral depth, and the anterior height-to-depth ratio was calculated.

Intervertebral disc height between adjacent vertebrae was assessed using the inferior-anterior corner of the upper vertebra and the superior-anterior corner of the lower vertebra as reference points. An angle bisector was drawn between these points, and the perpendicular distances from both corners to the bisector were summed to obtain the anterior disc height. This value was divided by the depth of the lower vertebra to generate a dimensionless ratio unaffected by magnification differences.

Craniovertebral posture was evaluated using the NSL/OPT and OPT/HOR angles. For the NSL/OPT angle, the landmarks Nasion (N), Sella (S), cv2tg (the posterosuperior tangent point of the odontoid process of C2), and cv2ip (the posteroinferior point of the C2 vertebral body) were identified, and the angle between the NSL and OPT lines was measured. The OPT/HOR angle was defined as the angle between the true horizontal plane and the line tangent to the posterior surface of the odontoid process.

Hyoid triangle height was determined using a triangle formed by the most anterosuperior point of the hyoid bone (H), the anteroinferior point of the third cervical vertebra (C3ia), and retrognathion (RGN). All cephalometric measurements were performed using AudaxCeph software.

Statistical analyses were conducted to investigate the relationship between the obtained measurements and the presence of disc displacement.

Inclusion Criteria:

• Presence of TMJ symptoms on at least one side, including pain, abnormal mandibular movements, or joint noises.
• Parafunctional habits such as bruxism or clenching.
• Patients with disc displacement of TMJ.

Exclusion Criteria:

• Presence of malformations affecting the craniofacial region.
• History of trauma of the maxillofacial region.
• History of cervical surgery or any procedure involving the cervical region.
• Patients with tumors, cysts, hypoplasia, or hyperplasia in the TMJ region.
• Any condition related to a congenital anomaly or syndrome.
• Presence of contraindications to magnetic resonance imaging.
• Pregnancy.
• Women in the breastfeeding period.

Temporomandibular disorder