Overview of Mandible Reconstruction
The mandible, or our jawbone, plays an important role in our daily activities, such as eating, speaking, swallowing, and maintaining the balance of our facial features. If there’s serious damage to the mandible, it can negatively affect these basic functions. It might also impact our emotional and social health. This article discusses various strategies to repair major damage to the jawbone. The most important thing for successful reconstructive surgery is to have a team of different healthcare professionals working together to provide the best possible care for the patient.
Anatomy and Physiology of Mandible Reconstruction
The mandible, or the lower jawbone, starts to form from something called Meckel cartilage while we are still in the womb. Once fully formed, the mandible has different regions, each with their own names. The condyle is the highest and most posterior part of the mandible. This part connects with the temporomandibular joint, which is unique as it is the only joint in our body that works as a hinge and can slide. This is what allows our jaw to move. The condyle connects to a narrow, neck-like structure known as the subcondyle.
There is a triangle-shaped bony protrusion known as the coronoid process, found in front of the condyle. The tendon of a muscle in our temple, the temporalis muscle, connects to this process. The condyle and coronoid form the highest part of the mandible’s upward section, called the ramus. The angle of the jaw sits just below this.
The body of the mandible extends from the angle towards the front of the jaw on each side. The two bodies of the mandible meet in the middle at the front in an area known as the symphysis and parasymphyseal regions. Certain muscles, specifically the lateral pterygoid and masseter muscles, connect along the outer side of the ramus and work with the temporalis muscle to open the jaw and project it forwards.
On the other hand, the medial pterygoid muscle connects along the inside surface of the ramus and works to close the jaw and retract it. The inferior alveolar nerve, which is a branch of the mandibular nerve (itself a branch of the fifth cranial nerve or trigeminal nerve), travels through the lower third of the mandible in a bony conduit known as the mandibular canal. It then exits via a hole known as the mental foramen to provide feeling to the lower lip and chin.
This foramen is usually located below the first pre-molar tooth on each side. Certain muscles, specifically the digastric and mylohyoid muscles, connect to the inner surface of the mandible. The mandible supports 16 adult teeth, which ideally align perfectly with 16 upper jaw teeth.
The mandible gets its main blood supply from a branch of the maxillary artery called the inferior alveolar artery, which also runs through the mandibular canal.
Why do People Need Mandible Reconstruction
If there is considerable damage or loss of a section of the jaw bone (mandible), it often requires reconstruction with bone taken from another part of the body, a process known as free or vascularized bone grafting. In some cases, a reconstructive titanium plate can be used to stabilize the bone fragments on either side of the damaged area.
However, if the damaged area isn’t filled with new bone, there’s a higher risk that the surrounding soft tissue could shrink and contract. This might lead to the exposure of the titanium plate and potential infection. In severe cases, this could mean having to go through more surgery.
In situations where the surrounding tissue is healthy and has good blood supply, smaller missing or damaged portions of the jaw bone can be repaired using non-vascularized bone grafts. This means that small pieces of bone are packed into the damaged area to promote bone healing and improve strength. These grafts have been used successfully to rebuild parts of the jaw of varying lengths when the area has not been previously exposed to radiation.
The radius bone in the forearm is usually too thin to hold dental implants. However, it’s crucial that defects in the front area of the jaw (mandibular symphysis) be reconstructed with bone. Otherwise, a patient could develop a severe deformation where the skin and soft tissues of the chin and lower lip retract, causing issues like the exposure of the titanium plate, difficulty in oral control, and chronic drooling. This condition, known as the “Andy Gump” deformity, can be difficult to correct and significantly impact a patient’s quality of life.
When a Person Should Avoid Mandible Reconstruction
If there’s an ongoing infection in the wound, it’s best to wait a little before going ahead with the reconstruction. This is because an active infection could potentially damage the graft (tissue used for transplant).
If there are defects in the condyle (the round part of the bone), there’s no need for bone reconstruction. A synthetic condylar head prosthetic plate, which is essentially a man-made substitute, usually works best.
For people who are soon to go through radiotherapy as part of cancer treatment, a non-vascularized graft (transplant that does not have its own blood supply) reconstruction is a no-go. As radiotherapy lessens the blood supply of the tissue around it, this could lead to graft necrosis or the death of the graft.
Bone reconstruction should also be postponed until after radiotherapy, especially if surgical delay would affect the efficiency of cancer treatment. If there’s a plan for a vascularized bone reconstruction (transplant that has its own blood supply), the patient should have a thorough heart check-up before the procedure. This check-up is crucial as this type of surgery takes considerable time and it’s important to ensure that the patient’s heart and lungs are in a healthy condition.
Moreover, free tissue transfer often needs a blood transfusion either during or after the procedure. Therefore, the need for blood transfusion should be accessed and arranged before surgery.
For fibular free tissue transfer (use of fibula or calf bone for transplant), a person’s foot blood supply should be checked. Normally, the blood flow to the foot is carried by the peroneal, anterior tibial, and posterior tibial arteries. However, these arteries may be compromised due to peripheral vascular disease, prior leg surgery or other medical conditions. So, if a fibula is used for transplant along with its peroneal artery, it poses a risk of foot necrosis (death of foot tissue due to lack of blood supply). People with compromised foot blood supply should not go through a fibula harvest.
In such cases, using scapula (shoulder blade) and iliac crest (upper part of the hip bone) flaps are viable alternatives.
Equipment used for Mandible Reconstruction
When reconstructing the jawbone – also known as a ‘mandibular reconstruction’ – it’s common to use a special toolkit. This can be supplied by various companies and is generally useful for the procedure. The process may involve using either a ‘vascularized graft’ (a piece of tissue that has its blood supply) or a ‘non-vascularized graft’ (a piece of tissue without its blood supply).
Regardless of the type of graft used, a titanium plate is necessary to hold the bone pieces together. In some instances, a plate specifically designed for the patient is prepared before the surgery. This is done to save time during the operation and to ensure the bone pieces position accurately. Although these customized plates can be expensive, a standard bar of 2.0 mm thickness usually works just fine for everyone. The bar is then shaped during the surgery to fit the patient’s jawbone shape.
Often, screws sized 10 mm to 18 mm go through both layers of the bone (what’s called ‘bicortical’) are used to secure the titanium bar. If a vascularized graft is used, 8 mm screws that only go through one layer of the bone (‘monocortical’) are used to prevent cutting off the graft’s blood supply, which could lead to tissue death (or ‘necrosis’). If a non-vascularized bone graft is used, a titanium tray is placed to hold the ‘bone chips’ – small fragments of bone – in place while they combine and heal. Some companies also provide a synthetic bone structure that can be used alone or along with a ‘autologous transfer’, where the patient’s own bone is used.
A bone mill can be useful to grind a solid piece of bone into these smaller ‘chips’. In some cases, if the surgical site is infected, it may be advisable not to place a titanium bar, as it could harbor bacteria and lead to continued infection. For these patients, the jaw can be held in place with an ‘external fixator’, a device made of steel bars that attaches to the bone through the skin.
An external fixator provides solid support to the jawbone, adds minimal foreign materials to the wound, and allows the infection to clear up before the definite fixation and bone graft are placed. When placing bars and screws, a drill is typically used to make pilot holes for the screws. In addition, mechanical saws and clippers (rongeurs) are used to shape and size the natural ends of the jawbone and the transferred bone.
Who is needed to perform Mandible Reconstruction?
Mandible reconstruction, or rebuilding of the jawbone, is a procedure that is carried out in an operation room while the patient is under general anesthesia – a state of unconsciousness brought about by certain medications to prevent pain during surgery. This surgery requires at least a team of four healthcare professionals:
* A surgeon who is in charge of the operation. A surgeon is a doctor who is specially trained to perform surgeries.
* An anesthetist or anesthesiologist, who is a doctor that gives you the medication to put you to sleep and prevent you from feeling any pain while the surgery is happening.
* A circulating nurse who assists the surgeon and anesthesiologist by providing tools, supplies, and other necessary equipment during the surgery.
* A scrub tech, also known as a surgical technologist, is a person who prepares surgical tools and assists during surgery.
Often, the surgical team also includes a retractor holder or first-assist. This is a person who helps the surgeon by holding back your tissues or organs so the surgeon can clearly see the area they are working on. Having a retractor holder enables the scrub tech to focus more on passing instruments efficiently to the surgeon during the operation.
Preparing for Mandible Reconstruction
Before a patient has surgery involving the lower jaw, the doctor uses imaging tools to get a clear picture of the exact location and degree of the problem. One of these tools might be a computed tomography (CT) scan. This is a special kind of X-ray that can give a detailed view of the body’s internals. Rapid, 1mm images are taken, and they can be used to assist the surgeon during the operation. In some cases, these images are used to make patient-specific plates and instruments which will be used during the operation.
In cases where a type of bone graft from the lower leg (called a free fibula transfer) is planned, doctors make sure to take detailed images of the arteries in the leg. This is to check on their position and condition to prepare for the surgery. To get these images, they may use a Doppler sonogram, which uses sound waves to image blood vessels, or another type of CT scan, called an angiogram. If a CT scan with fine cuts is performed, it helps the doctor plan for the procedure and shape the bone graft to fill the area they’re repairing.
Lastly, they may also use an electrocardiogram (EKG) or an echocardiogram. These are tests that help the doctor understand how the patient’s heart is working, as it’s important to know this before a major operation. By doing these tests beforehand, doctors can plan the surgery better, helping to make the operation as safe and effective as possible.
How is Mandible Reconstruction performed
The jawbone, or mandible, can be reached by making a cut inside the mouth in the area between the gum and the cheek, or through a cut on the skin of the neck. If the cut is made inside the mouth, care is taken not to harm a nerve, called the mental nerve, that exits at a hole on the jawbone, unless it has already been removed. If the cut is made on the skin, the surgeon has to be careful not to harm a main nerve on the face called the facial nerve, as this could lead to facial weakness or paralysis.
The jawbone may need to be supported by a reconstruction bar, ideally with four screws on either side of the missing or damaged part of the jaw for maximum support. This reconstruction bar should be fitted along the bottom edge of the jawbone and should not interfere with any tooth roots.
Before fitting the reconstruction bar, the jaw should be brought back to its original position to ensure any remaining teeth align properly. If parts of the bone are missing, the remaining bone edges should be trimmed to create a fresh, bleeding edge to encourage healing.
To rebuild the missing or damaged part of the jaw, non-vascularized bone grafts (pieces of bone from other parts of the body) may be used. These grafts are typically taken from the hip or the front of the lower leg. The harvested bone can be used as a single piece or ground into smaller pieces and packed into a tray to fill the missing or damaged area of the jaw. In some instances, harvested bone can be mixed with donor bone to make up for any lack of volume.
For more complex reconstruction involving bone and skin grafts, a cut is made in the neck and appropriate blood vessels are identified for reconnecting the blood supply to the graft. The bone graft is then secured to the reconstruction plate with screws, ensuring not to overuse screws, which can risk cutting off the new blood supply and causing the graft to fail.
After the reconstruction, it is ideal for the bone graft to have good contact with the patient’s own jawbone to encourage healing. If there is a gap, it can be filled with extra autologous (from the patient’s own body) or allograft (donor) bone chips.
Following the reconstruction of the jaw, patients need to stick to a no-chew diet for about six weeks to allow the bone to heal. If patients chew or put pressure on the reconstruction plate before healing is complete, there’s a risk the reconstruction could fail. If there were cuts made inside the mouth, patients may need to be fed through a tube for a few days to allow the inside of the mouth to heal. After any major tissue transfer, patients are usually kept in the hospital for a few days for regular check-ups to make sure the graft is healthy.
Possible Complications of Mandible Reconstruction
Rebuilding the jawbone comes with risks. The most dreaded outcome is failure of the graft (the part used to fix the bone), which would mean another surgery is necessary. Certain conditions like early movement of the jaw (maybe due to chewing soon after surgery), infection or poor nutrition supplied by the blood vessels can all raise the likelihood of the reconstruction not succeeding. People with certain conditions like previous radiotherapy to the jaw, underactive thyroid, protein deficiency, poorly controlled diabetes, smokers, among others, are more likely to have problems with their wounds healing. It’s important to try to manage these conditions as much as possible before the surgery.
In a type of reconstruction surgery known as osseous free tissue transfer, usually over 95% are successful. Nonetheless, the most frequently seen issue is a blockage in the blood supply which could lead to partial or full failure of the graft. A blockage in the veins is more common than in the arteries. The first three days after the graft receives its new blood supply are the most crucial, as this is when the blood vessels adapt to their new situation. However, a blockage could happen anytime in the first 2 to 3 weeks until the graft has grown enough new blood vessels to maintain itself independently.
Even after the reconstruction is fully healed, some problems may arise. If the graft or the plate used to fix it is not correctly sized, positioned, or shaped, it may lead to unequal teeth alignment, an asymmetric face, and chronic pain in the jaw joint. Also, factors like radiotherapy, severe infection, or further surgery (like getting dental implants installed) after everything has healed can restrict blood supply to the area and put the graft at risk of failure.
What Else Should I Know About Mandible Reconstruction?
The mandible, also known as the lower jaw, plays a vital role in our day-to-day life. It helps us with essential activities like chewing and swallowing food, contributes to our facial appearance, and can impact our overall comfort. Therefore, if there’s damage to this bone, accurately reconstructing it is crucial for maintaining our life’s quality.
There are a few key stages involved in reconstructing the mandible. Firstly, a thorough examination is done before surgery to tailor the procedure to the patient’s needs. During the operation, meticulous care must be taken with the jaw to restore its function and appearance. Finally, after the surgery, careful monitoring and follow-up care are necessary to ensure the patient’s swift recovery.
Rewards of successful reconstruction include restoring the patient’s natural facial look, relieving pain, and getting back to everyday activities, which can improve confidence and independence. On the other hand, if the reconstruction is not done correctly, it can have serious consequences, potentially leading to lifelong disabilities.
