Anterior Open Bite (AOB)
11th January 2021
Categories: Orthodontic Problems
This is a condition where the upper & lower posterior teeth are touching when the patient bites down, but the anterior teeth are not in occlusion.
ie the front teeth don’t meet when the back teeth are together and there is no overlap between upper incisor teeth and lower incisor teeth.
Thumb or digit sucking
Abnormal tongue function
Jaw joint pathology (trauma/fractures, arthritis, growth disturbances)
Hereditary/genetic jaw growth pattern
Poorly made mouth guards for tooth grinding
For all cases of AOB it is essential to determine what is the cause of the malocclusion.
In order to make this assessment a full medical history is taken before clinical examination and xrays or scans.
Anterior openbite (AOB) malocclusion is considered one of the most demanding challenges for the orthognathic team as occlusal correction is difficult, facial aesthetics may be unsatisfactory and the incidence of relapse is high.
There are a number of ways of manging an AOB.
In some cases an orthodontic only approach can be used and this can include upward intrusion of the maxillary molar teeth using temporary orthodontic anchorage screws.
These screws are generally placed under a local anaesthetic and act as a secure point to help intrude the upper molar teeth using orthodontic braces and elastics.
Commonly AOB are treated by a combination of presurgical orthodontics and surgery. The most common procedure would be a maxillary posterior impaction where the upper jaw is surgical repositioned with the posterior teeth moved up more than the anterior teeth (differential impaction). This allows the lower jaw to then rotate up and close the AOB.
If there is a gummy smile (vertical maxillary excess) present then this can be addressed at the same time by impacting the whole of the upper jaw to reduce the amount of incisor tooth and gum visible but by impacting the posterior part of the upper jaw more than the front (differential impaction) to allow for the AOB to be closed.
Often the closure of an AOB will require a bimaxillary procedure (upper and lower jaw surgery) as there is frequently an underlying jaw size discrepancy that needs to be corrected.
Some teams advocate the closure of an AOB with a mandible only procedure but there are concerns that the relapse rate is higher than in those having maxilla only or bimaxillary surgery.
When the open bite is in a very localised position then segmental jaw surgery is sometimes helpful. Segmental surgery means instead of the whole jaw being moved then either only part of the jaw is surgically repositioned or if the whole jaw is being moved then the jaw is segmented into more than one piece.
In a number of cases it is best not not to embark on any corrective treatment whatsoever as the risks of treatment far exceed the potential benefits.
These risks in AOB treatment are mainly for two reasons:
Relapse is defined as the failure to maintain the position of the skeleton and associated dental structures over time after treatment.
It is well documented that relapse rates in AOB correction are higher than in many other areas of orthognathic surgery. This is mainly related to the influence of the soft tissues on the “new” position of the teeth and jaws when the AOB has been closed. This is particularly the case where the cause of the AOB is related to a habitual tongue thrust habit.
The pre-treatment assessment of AOB cases in relation to the aetiology of the AOB and in particular the soft tissue component is an essential step in stratifying the risk in each individual case.
Very often in AOB cases the primary concern from the patient is the gap between the teeth and unless there is a significant underlying jaw size discrepancy there is little concern regarding general facial appearance.
In most AOB cases, surgery will involve impaction of the maxilla. Maxillary impaction surgery often cause nasal changes which include widening of the nasal base and upturn of the nasal tip.
Whilst in other jaw discrepancy cases the nasal changes caused by maxillary repositioning are often advantageous to facial aesthetics, these changes in many AOB cases are seen to detrimental.