Overshot mouth
Professor Meningaud - Maxillofacial Surgery at Paris Est Créteil
Overshot mouth
Overshot mouth is an anomaly characterised by a malformation of the jaw: ‘the bony bases of the mandible (the lower jawbone) are too developed in relation to the maxillae (the upper jawbones),’ describes Professor Jean-Paul Meningaud, head of the plastic, reconstructive and maxillofacial surgery department at the Henri-Mondor University Hospital (Créteil). In other words, the mandible is too far forward in relation to the upper jaw’. Overshot mouths often develop without any identifiable cause. It evolves during childhood and adolescence, until growth is complete.
What are the symptoms of prognathism?
First and foremost, they are visual,’ says Professor Meningaud. The discrepancy between the two parts of the jaw results in a particular morphology of the face, with a protruding chin and a smile that does not allow the upper teeth to be seen. In fact, the diagnosis is obvious. It is then clarified by looking to see whether the malformation is the result of an overdeveloped mandible or underdeveloped maxillae. As a general rule, these two anomalies occur simultaneously’. In addition to the aesthetic aspect, prognathism has functional consequences. As the teeth do not fit together perfectly, it can be difficult to chew food. There is also a risk of tooth wear and even tooth loss,’ adds Jean-Paul Meningaud. Temporomandibular joint problems are also likely to occur, leading to pain on the edge of the cheek, in front of the ear’.
What are the causes?
Prognathism is sometimes the consequence of other pathologies. This is the case with certain genetic anomalies, such as Down’s syndrome or Crouzon syndrome. Acrodysostosis and basal cell nevomatosis can also lead to the development of prognathism,’ adds the specialist. The same goes for acromegaly, a disease resulting from a pituitary problem’. While there are many potential causes, each of them remains extremely rare. Often, prognathism is simply the result of a family influence – which is the only identified risk factor – without any specific gene being involved. ‘In most cases, there is no clear explanation for this malformation, which is therefore a matter of chance,’ notes Prof Meningaud.
What are the treatments for prognathism?
If prognathism is detected during childhood, ‘it is important to consult a specialist without waiting for the milk teeth to fall out’, recommends Prof Meningaud. It is already possible to introduce interceptive treatments, such as aligners or orthodontic equipment, to avoid the need for surgery in the future’.
When growth is complete, surgery is not always necessary if there is only a slight discrepancy between the bone bases of the upper and lower jaws. Here again, orthodontic treatment is an option. It can modify the position of the teeth so that they fit together correctly,’ explains Professor Meningaud. However, you need to be careful not to overcompensate in order to avoid surgery at all costs. This exposes the teeth to stresses that make them suffer. There is also a risk that they will return to their natural position after treatment. In all cases, it is preferable to consult a maxillo-facial surgeon before making any decision, to find out which strategy to adopt.
When there is a significant shift in the position of the bony bases, surgery is essential. But beforehand, orthodontic treatment must be carried out to prepare the teeth, in particular by seeking the ideal inclination of the teeth. ‘This takes the form of dental arches with brackets bonded to the teeth (the famous braces) or transparent aligners that have to be changed every month. Between 10 and 50 aligners, each gradually changing shape, are fitted one after the other until the desired result is achieved. At the end of this stage, and after a simulation of the surgery on a plaster model, the patient is admitted to hospital for the operation. At the latest the day before, surgical orthodontic arches are fitted. The operation itself involves cutting into the bone to move the lower jaw backwards and the upper jaw forwards,’ explains Professor Meningaud. The presence of the dental nerve requires great caution: it gives sensitivity to the lower teeth and the lower lip.
Once the bone cuts have been made, the teeth of the upper and lower jaws are fixed in the correct position using elastics. ‘We can then fit custom-made titanium osteosynthesis plates that anticipate the exact movements of the maxilla and mandible to within a quarter of a millimetre. When everything is fixed, we check that the assembly is solid and that the components fit together correctly. If everything is perfect, the operation can be stopped at this stage and the teeth released. But if there is the slightest doubt, the blockage remains in place for 4 weeks. All in all, the operation takes between 3 and 5 hours, depending on the difficulty of the case.
What happens after the surgery?
After the operation, the patient remains in hospital for 2 or 3 days. There is still a lot of swelling – ‘more than after the removal of wisdom teeth,’ explains Jean-Paul Meningaud – but the pain is moderate and well relieved by painkillers. ‘A follow-up scan is carried out before the patient returns home. If it shows that the assembly is not correct, the patient goes back to the operating theatre. Fortunately, this is very rare. If all goes well, the patient is discharged. He will follow a very mixed or fluid diet for a few weeks. It is important to know how to eat in order to limit weight loss, which could compromise bone consolidation. To this end, dieticians visit the wards to give advice and explanations.
Follow-up consultations are scheduled one week later, and then one month later when bone consolidation is complete. Then it’s time to see an orthodontist again to make any final adjustments to any small residual defects. If the balance is impeccable, no treatment is necessary,’ stresses Pr Meningaud. If it is slightly unstable, an archwire is simply bonded to the back of the teeth to keep them in the correct position. It will remain in place for life and should be checked regularly.
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