This is the second of a two part blog addressing the most current research and options for the treatment of underbites, or what orthodontists and dentists refer to as Class III relatioships. This facial type is one of the most difficult to treat in orthodontics, and the earlier it is identified and diagnosed, the higher the chance of arriving at a succesful outcome.
The first consideration is what age do we start treating anterior crossbites that are skeletal in nature (lower jaw growing too much, upper not enough, or a combination of both)? Most research continues to support treating at an early age for mild and moderate underbites, ideally prior to 8 years old. However, new research indicates that favorable changes can occur with treatment in older children, even well into the adolescent growth spurt. The positive changes appear not to be as dramatic compared to starting treatment earlier, but can still be significant.
In the early 1980’s a protocol for early treatment of underbites became the standard of care that has remained until this day (with some new modifications and options that I will discuss). Treatment usually consists of upper jaw expansion (using an “expander”), followed by facemask therapy. A facemask is a device that has rests on the patient’s forehead and chin, and elastics attach from this facemask to “arms” on the expander that place a forward directed force on the upper jaw. Studies have shown the correction comes from foreward movement of the upper jaw, usually accompanied by downward growth, which makes the lower jaw rotate downward (resulting in a chin position that is further back). This rotation of the lower jaw can also be a negative side effect, and must be monitored closely by the orthodontist.
It is imperative for parents and the child to understand that the success of treatment is dependent on the number of hours a day that the facemask is worn, and the number of months that it is worn. The highest success rates occur when it is worn all day and night, however, most orthodontists are understanding of the social issues of wearing a facemask to school. We ask that it be worn every hour that the child is not in school or sports, which usually is about 16 hours per day, including while they are sleeping. Studies have shown the greatest sucess rates occur when the facemask is worn upwars of 10-12 months, and an over correction is observed where the upper teeth are a ahead of the lower teeth by at least several millimeters.
A very important thing to keep in mind with the treatment of Class III cases is that after early treatment is stopped, the patient will continue to grow like a Class III patient until growth is complete. Since the growth of the lower jaw will continue to be more pronounced, a second phase of treatment is almost always needed, with full braces, rubber bands, and possibly more time with the facemask.
In the last several decades studies have increased our knowledge in treating underbites, and there have been several modifications to the basic protocol. First, the use of a palatal expander has been shown to be useful only if needed for other reasons such as gaining space or correcting a crossbite that exists along with the underbite. A large number of underbite patients have a hyposplastic maxilla (smaller upper jaw), so many continue to have an expander included with their treatment. Second, another viable option to the facemask has emerged that has demonstrated excellent, or even improved results. Skeletal anchorage in the form of surgically placed miniplates can now be placed, which allow the patient to wear elastics entirely within the mouth, and 24 hours a day. The downside is an increased cost due to two surgical proceedures needed to place and remove these miniplates after treatment. This option has been shown to be optimally successful between the ages of 10-12 years of age due to the need for higher bone density to hold these devices secure.
For more severe cases where a very pronounced underbite is detected early, and especially if there is a strong lower jaw component, it may be decided early on that jaw surgery will be needed to obtain a succesful result. These more severe cases cannot be corrected enough by orthodontics alone, but your orthodontist will continue to monitor facial growth, and work in conjunction with an oral surgeon to determine the optimal time to start preparing for a surgical correction. Jaw surgery to correct underbites are usually not performed until the patient’s jaws have completed growing. The best way to determine when this has occured is by taking a series of radiographs called serial lateral cephalograms, and measuring the size of the upper and lower jaws over time. Surgery performed prematurely while the jaws are still growingwill usually result in an unstable result with return of the underbite.
After treatment with full braces is completed, retainers are placed like any other case. However, I do monitor patients with Class III patterns for a longer period of time, as the underbite pattern sometimes returns to varying degrees due to small growth changes that occur throughout life. Yet another challenging aspect to this type of facial growth!
A summary of modern treatment for Class III cases (underbites):
1) Timing is important, with higher sucess rates occuring with early treatment prior to the age of eight. However, later treatment (just before or during puberty) has been shown to be more sucessful than previously believed.
2) Treatment with a facemask and elastics remain the most common forms of treatment. New advancements with surgically placed miniplates have provided another effective option.
3) Success with any treatment option is dependent on number of hours the device is activated, and how many months they are worn. Consistency is the key!
4) This facial growth pattern persists and is often accelerates during the adolescent growth spurt. This must be kept in mind regarding the length of treatment, and is the reason two phases of treatment are usually needed for this facial type.
5) Severe cases detected early usually will need a a surgical correction, usually done in the late teen/early 20’s, and no amount of orthodontic treatment alone can achieve an acceptable result. The earlier parents are informed of these cases, the earlier appropriate plans can be set in place to manage this issue.
Dr. Dan Rejman is the owner of Meadows Orthodontics in his hometown of Castle Rock, Colorado. Dr. Dan is a Board Certified Diplomate of the American Board of Orthodontics, and is the councilman representing both the Rocky Mountain and Southwest Orthodontic Societies for the College of Diplomates of the American Board of Orthodontics.