Planning for corrective jaw surgery for underbite deformity

Underbite deformity in Singapore is the most commonly correct dentofacial deformity. With advances in understanding of the healing process and orthodontic movement of teeth, it is usually treated in a surgery-first approach today. This is in contrast with the old practice of going through a year or two of pre-surgical orthodontics to prepare the teeth for surgery. The use of CT scans and 3D modeling software enable both surgeon and patient to visualize the facial aesthetic treatment outcome that is desired. Let’s take a look at a typical case of surgical correction of an underbite deformity.

A 25 year old male complained of a long protruding lower jaw and requested for orthognathic surgery to correct it. Physical examination showed that the face was long both vertically and horizontally. In addition, the midface was flat, giving the face a concave profile. Intraorally, the teeth were crowded and poorly aligned.

A CT scan was done and analysis of the facial skeletal structures and proportions was done. Using a specialized software, the CT data was used to generate a 3D model of his facial bones, separating the upper jaw, the lower and the rest of the skull. A soft tissue model was also generated.

Based on the diagnosis of a long face with protruding lower jaw and depressed midface, a treatment plan was formulated. This consisted of a Le Fort I osteotomy to advance the upper jaw and a bilateral sagittal split to set the lower jaw back. To determine the amount of movement of each jaw, the surgery was simulated on the computer using the software. Within the program, the jaws was moved by different distances and in different directions and the resultant changes in facial appearance would be simulated.

Other than being a useful planning tool, this simulation process is a very important communication tool between the surgeon and the patient. While the functional aspects of corrective jaw surgery is based on certain well established principles of how the teeth should meet, the aesthetic aspect is very subjective. Sometimes, what the patient has in mind may not be the same as the surgeon and both are none the wiser about it. Having a simulation tool enables calibration of the aesthetic demands and preferences between surgeon and patient.

Once the plan was finalized, the surgical plan was simulated once more on stone models of the jaws before actually doing the surgery itself. This patient underwent a four hour operation and stayed in the hospital for three days postoperatively. One month after the surgery, orthodontic treatment was started.