Computerized simulation of underbite corrective surgery in Singapore

A 19 year old male Chinese patient was referred by his orthodontist for surgical correction of underbite deformity. It is commonly believed by most patients looking for underbite corrective surgery that their problem lies with the lower jaw being too long. However, it is rarely a problem of just the lower jaw. In most cases, it is also a case of the upper jaw being underdeveloped.

This young man had a flat midface that contributed to the concave profile that he did not like. In order to obtain a good aesthetic result, the upper jaw needed to be brought forward and the lower jaw backward. The next question that is commonly asked by patients at this point is whether we can leave the upper jaw alone. Again, in the majority of cases, the answer is no. In fact, I have advised many young patients not to do jaw surgery at all if they do not want to do the full plan because we will simply be trading one type of deformity for another. In this case, looking at the profile view, if the correction of the bite was done by moving only the lower jaw, not only would the midface depression be uncorrected, the lower jaw would have been set back by an excessive amount, resulting in the chin almost touching the Adam’s apple, thereby obliterating the separation of the head from the neck.

This was confirmed when we examined the intraoral condition. Intraorally, there was an open bite of about 8mm at the incisors which were highly compensated, meaning tilted backwards. Pre-surgical orthodontics to prepare the teeth for surgery would tilt the teeth forward, thereby opening up the bite further. To achieve a proper biting position, if only the lower jaw was operated on, it would have to move about 14mm backwards. While the bite would have been corrected the chin would have moved so far back that it would be appear to be merged with the neck. That would have been an aesthetic disaster.

Nevertheless, a computerized simulation was done to determine the ideal surgical plan, taking the patient’s aesthetic preference into consideration. A CT scan was done and the data imported into the Simplant software for the planning. The bony surgery was simulated on the virtual 3D facial skeletal model.

Once that was done, a virtual 3D soft tissue model was generated and the software simulated the changes in facial appearance created by the repositioning of the segmentalizes facial bones.

The plan was shown to the patient and he made suggestions as to which part of the plan he liked and which he did not. Changes can be made with regard to the degree and direction of movement that the patient liked and a simulated soft tissue model generated.

 When a desired facial appearance was achieved, the preparation for the surgery proper could commence. Sometimes, some patients were unable to decide in one or two visits. Several plans may need to be simulated on the software on different days so as to ensure an outcome that is as close as possible to what the patient has in mind. Corrective jaw surgery is not just putting the jaw together in a position that the patient can bite. If it is purely for a better bite, a bit of compromised camouflage orthodontic treatment will probably achieve 80% of the result. In Singapore, while orthognathic surgery is not considered cosmetic surgery, I believe that the aesthetic outcome is as important as the functional occlusion of the teeth and as such, planning must start with the final facial appearance in mind.