There is a descending relationship between the skull, the jaw and the underlying structures (cervical area, hyoid bone, shoulder blades, rib cage, and the muscles that connect these areas).
Thus it is evident that an asymmetrical boney structure in the craniomandibular area that alters the plane of occlusion generates asymmetry also in the underlying areas and then in the rest of the body. With a skeletal asymmetry, the muscles adopt such an asymmetry as well, generating compensatory mechanisms. Thus the musculature plays a very important role in this process.
The muscles that connect the hyoid with the other structures involved in this process are:
– hyoid and tongue through the glossus muscle
– hyoid and jaw through the mylohyloid, geniohyoid and anterior digastric (anterior belly) muscles
– hyoid and skull through the posterior digastric (posterior belly) and stylohyoid muscles
These three components listed above make up parts of the same functional unit: the craniocervical mandibular system.
Closing the mouth can be carried out voluntarily or involuntarily during every act of swallowing. This is an important event from a biomechanical point of view as it permits the jaw to take part actively in the stabilization of the skull on the spine.
For the stabilization of the jaw in static or dynamic situations the muscular system which intervenes can be simplified into three subgroups: the levator muscles, the depressor muscles and the cervical (neck) muscles. These all have different functions, in fact, in jaw posture we distinguish between two different positions: that during repose and that during occlusion.
The muscles used during a position of repose are principally the hyoid muscles: the suprahyoid and the infrahyoid, and the muscles related to the clavicle, with the rachis cervical muscles, pharynx and tongue; all these use the hyhoid bone like a caruncle to determine their positions, which results in tension in all the muscles connected to it.
The muscles principally used in the closed position are the levator muscles: the temporal, masseter, and internal pterigoid muscles. When, in swallowing, for a brief moment, all these muscles work together synergistically they make the jaw into a solid base which always maintains the same inclination.
The work that these muscle groups do together synergistically ensures that during swallowing the jaw can make large movements, thanks to the elevation of the hyoid bone and its ability to move.