As the human face is never symmetrical, most patients with facial asymmetry can accept a fair degree of asymmetry. In fact, many patients with fairly obvious asymmetry are quite willing to accept status quo. What often prompts these patients to seek professional advice is the fear of a continuing worsening of the asymmetry. How do we tell whether the asymmetry is getting worse or predict whether it is likely to worsen?
corrective First point to consider is the age of the patient. In a growing patient, the asymmetry is likely to continue to develop. This is often due to an overactive growth centre in the lower jaw situation in the condyle, i.e. the part of the lower jaw that forms the jaw joint. When there is a differential growth rate between the right and left side of the jaw, the more active side grows longer, making that side of the face larger and pushing the chin point to the opposite side. This is often accompanied by corresponding downward development of the upper jaw on that side, thereby giving rise to a slanting occlusal plane known as canting. This hyperactivity is developmental in nature and is unpredictable. As such, in a growing patient, corrective jaw surgery is delayed till the excessive growth activity levels off.
Monitoring this kind of growth is done by several tests. A Technetium bone scan is a good single test to check for presence of differential growth rates. A radioactive isotope of Technetium is injected into the blood vessel and allowed to circulate through the body. The active growth areas will have more uptake of the Technetium. The protocol involves comparing the uptake of the condyles against the uptake of the lumbar vertebrae expressed as a ratio. If there is a significant difference between the left and right sides, it is indicative of continuing growth which will likely result in worsening of the asymmetry. For this group of patients, it is best to delay any surgical treatment for a couple of years. A repeat bone scan can be done again prior to surgery to confirm cessation of growth activity.
However, intravenous injection of a radioactive isotope is an invasive procedure that is not without risk. In recent years, the risk of such a diagnostic test is being questioned against the perceive benefits. Alternative means of tracking continuing growth can be done by means of serial skull radiographs, photographs and dental plaster casts. These can be recorded annually and measured and compared in series to determine if there are significant changes from year to year. This method does not allow a snapshot diagnosis unlike a bone scan but is less invasive and risky. When two sets of records taken one year apart shows no major difference, growth can be deemed to have stopped and treatment can commenced.
For adults, especially those beyond the typical orthognathic surgical age group of late teens and early twenties, the concern is usually about whether the asymmetry will worsen as they grow older. This group of patients typically has already accepted their facial asymmetry and it does not bother them very much. The possibility for further deteriorating is often the driving factor behind them seeking treatment. Just like for the younger group, bone scans, serial radiographs and dental plaster cast can be used to monitor development. In some cases, asymmetry can result from not just hyperactive growth of one condyle but from condylar resorption of one side. Idiopathic condylar resorption, a process whereby the condyle shrinks in size, can cause shortening on one side of the lower jaw. Because such changes are gradual, the opposing jaw often grows correspondingly to maintain the teeth contact, creating a cant in the process. As the name suggests, the cause of the condition is unknown. Surgery in this group should be approached with caution not just to prevent relapse but to minimize the risk of worsening the condylar resorption.
Facial asymmetry, being a dentofacial deformity with more aesthetic challenges than functional deficits, is often tolerated well by patients, so long as it is not progressively worsening. Monitoring with bone scans, serial radiographs, photographs and dental plaster cast is critical to determining the developmental status.