The neutral or ortho-static head position (with horizontal Frankfurter plane) will allow healthy TMJ, craniovertebral, cervico-thoracic functions, and a stable occlusion (‘bite’). Rocabado further defined normal cervical lordosis and normal craniovertebral relationships based on cephalometric measurements. A line that connects the posterior nasal spine to the basi-occiput is called the McGregor’s plane or line. The odontoid plane (OP) is a line that extends from apex to the anterior inferior angle of the odontoid process. A normal measurement of the posterior-inferior angle (craniovertebral angle -CV) at the intersection of McGregor’s plane and OP is 101 degrees +/- 5 degrees (96-106 degrees). A distance between the basi-occiput to the posterior arch of the atlas is 4-9 mm (less than 4 mm indicates cranio-vertebral compression). When we lose this normal CV angle and assume a forward head posture, we also lose our normal or healthy cervical curve or lordosis, which can potentially lead to premature cervical spine joint degeneration and of course pain.
With forward head posture we increase the distance from chin to sternum stretching the hyoid muscles, which in turn will have the tendency to pull mandible back and down. This may also lead to the development of a retro-inclined profile (the chin posteriorly set) and mandibular malformation, as the mandible is being held posteriorly during growth and development. This can also be the start of creating a disc displacement issue with the temporomandibular joint as well as general myofascial pain of the muscles of mastication and the cervical spine.
By causing posterior cranial rotation and stretching of the infrahyoid muscles, forward head posture has the effect of increasing the activity of the masticatory muscles and cranial extensors, which often results in overuse, strain and pain. In this environment, the muscles of mastication pull on the mandible try to maintain a mouth closed position, while the infrahyoid muscles try to bring the mandible down and back. The constant fight between muscles that perform depression and elevation of the mandible is referred to as parafunction. Tension in these muscle groups will be reduced and balanced with proper therapy including restoring normal alignment of the craniovertebral angle and cervical lordosis on a stable shoulder girdle. Hence, the importance of finding a qualified physical therapist with appropriate certifications in the management of temporomandibular disorders (TMD).