Lower Jaw Surgery: Bilateral Sagittal Split Osteotomy

Why is lower jaw surgery done?

The lower jaw can be lengthened to correct a retrusive lower jaw and correct an excessive overbite or “bucked teeth”. The lower jaw can also be shortened to correct a protrusive or enlarged lower jaw. The lower jaw can also be rotated (lengthened on one side, shortened on the other side) correct facial asymmetry.  Sometimes, the lower jaw surgery is done simultaneously with upper jaw surgery or chin surgery.

 

How is lower jaw surgery done?

An incision is made in the gums at the back of the lower jaw near the wisdom teeth region and extending down to the first molar region.  There are no skin incisions and no scarring.  The bone in lower jaw is cut around the molar teeth region. The bone is cut in a special way , it is cut long ways (sagittally)  in order to allow a “sliding” of each segment of the jaw bone and protect the integrity of the nerve that runs the length of the lower jaw to supply sensation to the lower lip. The bone segments are carefully split using specialized instrumentation to allow controlled separation of the bone segments and nerve protection. The lower jaw can then be moved to the new planned position. If the jaw is lengthened, there is a small gap, but due to the sagittal split sliding design, bone will grow predictably and there is no need for a bone graft.  The movements have been done in the laboratory prior to surgery and surgical splints created to reproduce the movements. The surgical splint is placed between the teeth to establish the position and the jaws temporarily wired together using the surgical hooks placed on the braces into the new planned position and new bite. We now have the new position and the lower jaw is then fixated to this position using titanium mini-plates and mini-screws. There is usually 1 or 2 miniplates with 4 holes per plate per side. Each plate is precisely bent and shaped to fit over the bone to hold the jaw into the new position. The wires are then released and the jaws are no longer wired together as the plates/screws are now maintaining the new position.

 

How much pain and length of recovery?

Most patients worry about the pain after surgery however, the pain and discomfort is quite manageable. During surgery, a long-acting local anaesthetic is given so that patients do not wake up with much pain. Patients are connected to a drip attached to an automatic pain medication dispenser which they can activate by pressing a button. This is removed once patients no longer are using it usually in 48 hrs after which pain tablets such as Nurofen or Panadeine Forte are sufficient.

 

What are the risks and complications?

The main risk of lower jaw surgery (BSSO) is the risk of nerve injury. There is a nerve that runs the length of the lower jaw and exits near the front of the jaw to supply sensation to the lower lip and chin. This nerve is invariably involved in the surgery and either stretched or compressed. Most people have a degree of numbness which is usually a partial numbness immediately after surgery, and can last 3 to 6 months. Usually, there is a gradual recovery of sensation after 6 months. Dr Lim is highly experienced in performing this operation, however, there is still a risk of nerve injury resulting in permanent loss of sensation to the lower lip which after 12 months is less than 5%.  The other risks include the risk of relapse of the bite position.