Computerized simulation of jaw surgery for jaw asymmetry in Singapore

A 24 year old Chinese male was referred by his orthodontist for surgical correction of his facial and jaw asymmetry. He had noticed that his face was twisted to one side and wanted to correct that. Corrective jaw surgery for facial asymmetry is always a bit tricky because nobody is perfectly asymmetrical to start with. The left side of the face is always slightly different from the right. Furthermore, orthognathic surgery involves cutting jaw bones and repositioning them and the degree of accuracy in the order of millimeters. If the discrepancy is too small, corrective jaw surgery will not be able to achieve that degree of symmetry that the patient is looking for. As such, we need to look at the magnitude of the asymmetry before deciding that jaw surgery is the way to go.

In this particular case, there was an obvious deviation of the chin point to the left. While the deviated chin point was obvious, the “canting” of the upper jaw was not immediately apparent. The upper jaw was longer vertically on the right side compared to the left. This discrepancy pushed the lower jaw further down vertically compared with the left and was an important contributor to the asymmetrical appearance.

Asymmetry of the lower jaw is also due asymmetrically increased activity of the growth centre of one side. In this case, there was a general enlargement of the the right side of the jaw which not only pushed the chin to the left, but also created an underbite by pushing jaw forward, further than the upper jaw.

To adequately address these problems, a double jaw surgery was needed. The upper jaw needed to be “de-canted” i.e. leveled horizontally so that the vertical dimensions on the right and left were the same when measured from the eyes. Once the upper jaw position was centred, the lower jaw can be re-positioned to fit into the symmetrical upper jaw. In some cases, a separate chin surgery may be needed to bring the chin point to the centre but was not necessary in this case.

This plan was simulated on a computer using the Simplant OMS software. The bone cuts were made on the virtual model of the skull and moved to a achieve a symmetrical position. A soft tissue model was then generated to simulate the facial appearance that would be achieved based on the new position of the jaw segments. This process was repeated until a good symmetrical soft tissue model was achieved and the degree and direction of movement of the various jaw segments noted. 

For this case, the surgery was a Le Fort I osteotomy for the upper jaw and a bilateral sagittal splint osteotomy for the lower jaw. These procedures freed up the jaws and allow repositioning into a symmetrical and proportional structure.

The plan was then discussed with the patient and feedback of preferences in aesthetics was taken onboard and the necessary changes were made. Once the virtual plan was finalized, there surgery was further simulated in the laboratory using plaster models of the teeth mounted on an articulator. Surgical guides were made from these models in the corrected position to ensure that the plan was accurately done according to plan in the patient. 

The actual surgery took about 5 hours and the patient needed 2 days of rest in the hospital and thereafter, two weeks of recovery at home. Computerized simulation enable the patient and surgeont to have a clear communication of treamtent goals and objectives and helps in producing an aesthetic outcome that closely resembles what the patient has in mind.