Getting treatment for prognathia and disto-occlusion

Your specialists at the Center for Oral, Maxillofacial and Facial Surgery in Frankfurt am Main

After growth has ended the upper or lower jaw can each be either too small (micrognathia) or too large (macrognathia). Not only the discrepancy in size but also the position of upper and lower jaw in relationship to each other is very important so that we must distinguish between retrognathia (the jaw is too far back) and prognathia (the jaw is too far in front). The bite shows which situation we have – it may be a progenie (reversed overbite of the incisors, mesio-occlusion, angle class III or prognathism, respectively) or a disto-occlusion (lower jaw too far back, major overbite, distal bite, angle class II).

The surgical goal is moving the upper or lower jaw, respectively, sufficiently for compensating the discrepancy and getting the teeth to meet perfectly. In doing this we pay extraordinary attention to facial esthetics and the functioning of the temporomandibular joints.

The surgical goal will be to move either maxillary or mandible far enough to even out the maladjustment, so that the teeth fit accurately against each other. Special attention is paid to facial esthetics and joint function.

Progenie

Formally, we distinguish between real progenie and spurious progenie. Most often, however, we find a combination of both forms of this malocclusion where the too long lower jaw comes with a too large chin and a too small upper jaw. But the patients and the people around them usually see only the characteristic long lower jaw or the large lower lip. In addition the middle face is flattened. It is also called a dish face or a concave facial profile. Nasolabial folds are pronounced so that the nose appears large and long (large nose profile). Altogether the face appears angular and hard.

The malpositioning of the jaws can be clarified only after careful cephalometric analysis (cephalometry). For this the jaws are surveyed by means of computer-aided cephalometric imaging  and their positions are determined.

Biting shows the characteristic reversed overbite of the incisors (progenie, frontal crossbite, orthodontic: mesal bite or angle class III tooth system). If the posterior teeth are involved, it is called a circular crossbite. The reason for these malpositionings  is either an upper jaw that is too narrow or a lower jaw that is too wide (vide: crossbite). The cause can only be determined after analysis by means of a dental cast model and evaluation of X-ray images (incl. 3-D images).

The most obvious problems with prognathia are difficulties in biting off and chewing. In addition there is a malfunctioning of the tongue with restricted nasal and increased oral breathing. But the correlation between this and a malocclusion is rarely thought of. Every once in a while there are also problems with the mandibular joints, mainly temporomandibular joint click (crackling jaw) due to repositioning of the discs.

Disto-occlusion (enlarged overbite)

This malpositioning of the jaws is a very widespread cause for malocclusion. Usually the incisors in the upper jaw prop themselves against the anterior teeth in the lower jaw at a certain physiological angle and that requires that both jaws are positioned in a correct relationship to each other. If there occurs a growth inhibition during the growth of the lower jaw, it leads to a so-called mandibular retrognathia. This becomes noticeable by an enlarged overbite (orthodontic: distal bite, angle class II tooth system) and adds to reduced support of the anterior teeth for each other.

The anterior teeth in the lower jaw are often noticed for having tipped forward and interlocking. If the overbite is pronounced, the lower lip may settle between the incisors in the upper jaw and the anterior teeth in the lower jaw so that in extreme cases the incisors are pushed far forward. If there is also a weak chin, the distal position of the lower jaw becomes very obvious. So, we have a combination of a distal mandible and a not very prominent chin (weak chin). In especially severe cases of malocclusion a narrow maxilla may further aggravate the condition.

Depending on the enlarged overbite a patient can bite off successfully only, if the lower jaw is pushed far to the front. The patients do that unconsciously and put a lot of strain on the temporomandibular joints, so that their capsule and band structures are greatly overstretched and irritated.  In consequence, there is a risk that the disc in the joint may slip. This is called a disc luxation. Depending on the degree we talk of a partial or total disc luxation with or without repositioning of the disc.

The permanent malfunctioning of the temporomandibular joints may result in structural changes of the joints and, in the long run, in a joint arthrosis. This may lead to a number of variously severe problems with the temporomandibular joints, such as clicking, scraping, pain while chewing, impaired opening of the mouth and is generally called a temporomandibular dysfunction. Because of the above, thorough radiological and functional diagnostics of the temporomandibular joints should always be performed prior to starting treatment of a malocclusion. Depending on the diagnosis a fitting occlusal splint therapy can then be chosen for a preliminary treatment in order to relieve the temporomandibular joints.