Temporomandibular disorder (TMD) is a collective term for pain and dysfunction of the masticatory muscles and temporomandibular joint (TMJ). Typical signs and symptoms of TMD includes regional pain, noises from the TMJs and limitations in jaw movements. Altered jaw kinematics and muscle activity have also been reported. TMD may be related to neck problems. Over 50% of patients with TMD suffer from nonspecific neck pain. Patients with TMD often have symptoms over neck, including upper cervical spine movement impairment and reduced cervical muscles endurance. Conversely, TMD may also develop in patients with neck pain. Twenty to thirty-three percent of patients with neck pain also have TMD. Subjects with neck pain present with a twofold higher prevalence of TMD than those without neck pain. In patients with neck pain, the development or perpetuation of TMD may be due to the anatomical connection between TMJ and neck: neck posture affects the mandible position and sensory inputs from the cervical-mandibular region converge at the trigemino-cervical nucleus. Early identification of TMD is essential but to our knowledge, no study has investigated whether patients with neck pain demonstrate altered jaw movement and muscle activity, which is associated with TMD. The purposes of this proposal are to compare the jaw kinematics, muscle activity and muscle sensitivity in healthy individuals and patients with non-specific chronic neck pain (NCNP). This study also aimed to investigate the relationship between forward-head posture and the jaw kinematics, muscle activity as well as muscle sensitivity. With a cross-sectional exploratory study design, 30 healthy control subjects and 30 subjects with NCNP will be recruited. Clinical assessments will include cervical range of motion (CROM), pressure pain threshold (PPT) over the cervical-mandibular region and the cranial-cervical angle (CCA). Jaw kinematics will be measured by Ultrasonic Jaw Motion Analyzer (Zebris GmbH) during functional jaw movements. Muscle activities are record from bilateral anterior temporalis, masseter, sternocleidomastoid muscle and upper trapezius by surface electromyography during resting and clenching.

Inclusion Criteria (nonspecific chronic neck pain group):

• Aged between 20 to 65 years old
• Mechanical pain that provoked by sustained neck postures or specific neck movements without any identifiable diseases or structure anomalies
• Chronic or recurrent neck pain of at least 3 months duration
• Minimum of 3 points on the numerical pain rating scale (NPRS) over cervical region
• Without any pain, clicking or range of motion limitation over TMJ

Inclusion Criteria (healthy control group):

• Age (± 5 years) and gender match to NCNP group
• No pain or clinical pathology involving the masticatory system or cervical spine for at least one year prior to the start of the study

Exclusion Criteria (both groups):

• Serious injury, tumor, infection
• Recent cervical-cranial surgery
• Neurologic involvement
• Inflammatory rheumatic diseases
• Pregnancy
• Nonmechanical cause of neck pain (e.g. herniated disk, spinal fractures)
• Had been diagnosed with spinal conditions (e.g. spondylolisthesis)
• Shoulder pain within 1 years
• Loss of posterior tooth
• Dental pain or periodontal problems
• Orthodontic, orofacial myofunctional or TMD treatment within 3 months
• Use of analgesic or anti-inflammatory drugs within 3 days

Patients with nonspecific chronic neck pain for at least 3 months and the matched healthy control subjects