The lower jaw
The lower jaw consists of a U-shaped bone, whose thighs bend upwards at the angle of the lower jaw and merge into an ascending branch. These two branches each carry two extensions, a rear one, which forms the joint head of the temporomandibular joint, and a front one, to which parts of the chewing muscles are attached. The strongest chewing muscle of the human being, the masseter muscle, starts at the angle of the lower jaw, coming from the zygomatic arch.
At the inner sides of the “U”, the muscles of the mouth floor stretch and connect the lower jaw with pharynx and hyoid bone. The upper edge of the lower jaw is notched like the upper jaw and carries the periodontium of the lower dental arch. The temporomandibular joint consists of the posterior extension of the lower jaw branch as the joint head and a notch between two cusps on the temporal bone as the joint socket.
Between the two joint surfaces is a joint disc, which compensates for differences in curvature. The cylindrical structure of the joint head on the lower jaw allows rotation, sliding and grinding movements in the temporomandibular joint. Although the temporomandibular joint is surrounded by a capsule and is also surrounded by ligamentous structures, it can dislocate as a result of an accident, a blow, and in some people even when the mouth is particularly wide open (e.g. when yawning).
The joint head of the lower jaw slides in front of the front hump of the joint socket – the mouth can no longer be closed (“jaw lock”). In most cases, it is easy to bring the dislocated joint back into position, but there are people who are prone to repeated dislocations of the temporomandibular joint (“habitual dislocation”). Pain in the temporomandibular joint can also be caused by uneven loading, for example, by toothache, tooth damage or missing teeth, poorly fitting crowns or fillings – in this case, a visit to the dentist and the taking of bite impressions can provide an indication of the cause of the discomfort.
Even in the case of increased teeth grinding, which can also happen at night and unconsciously, there is pain in the chewing muscles and temporomandibular joints due to overstrain. The reasons for teeth grinding are not completely clear, so the causal treatment is not always easy. As stress factors are suspected to be the trigger, relaxation techniques are considered, but the success varies from patient to patient.The possible effects of teeth grinding, damage to the teeth themselves, tension in the jaw muscles and overstressing of the jaw joints can usually be alleviated by a specially adapted bite splint.
The best results for building up the jawbone are achieved with the body’s own (autologous) bone. The bone graft is either taken from the rising branch of the lower jaw in the wisdom tooth region or, if more bone is required, from the hip bone. However, bone substitutes are also available for building up the jawbone.
These are materials of mostly synthetic origin. Here it is mainly hydroxyapatite ceramic, which is offered in granular form and in sterile packaging. But also materials of animal (beef or pork) and plant (algae) origin can be used to build up new jawbone.
A mixture of own bone and bone substitute is also possible. Possible complications are rejection reactions, allergic reactions as well as infections due to the penetration of bacteria. When lifting the sinus floor, a perforation of the mucous membrane or penetration of the replacement material can lead to an inflammation of the maxillary sinus (sinusitis). Complications are rare, however.
