The treatment of underbites (or anterior crossbites) in orthodontics is in a special category of its own, both in terms of jaw growth, and the challenge and difficulty in treating these cases. It is very important for patients and their parents to be educated as early as possible about the unique pattern of growth that is to be expected, and to set realistic expectations in treating this condition.
We are all familiar with the typical appearance of people with underbites (Jay Leno comes to mind for most). This appearance is often first seen at a very young age (often before the age of five), and is usually detected by parents or a dentist noticing that the child’s lower teeth are located ahead of, or even with, the upper teeth (the lower teeth should be located behind the upper teeth). ). In orthodontics we refer to this relationship of the teeth as a Class III relationship, which describes the lower teeth as being too far forward when compared to the upper teeth. The underlying cause of an underbite is most often skeletal in nature, and it is believed that genetics play a prominent role in causing the condition. Parents often recall a grandparent with an underbite, or may even have an underbite themselves. Recent research shows that about 68% of Class III patients have an upper jaw (maxilla) that is deficient, and 70% have a lower jaw (mandible) that is protrusive or growing too much. This means that many have both an upper jaw that is not growing enough, and a lower that is growing too much. The front teeth often, but not always, display a distinctive pattern in which the upper teeth are tipped excessively forward (proclined), while the lower teeth are tipped back (retroclined).
The first thing for parents to know is how this growth pattern will progress. All children undergo an adolescent growth spurt, where the body undergoes a rapid increase in the rate of growth, which includes the maxilla and mandible (upper and lower jaws). This spurt usually occurs earlier in girls (ages 9-12) than in boys (ages 10-14), with considerable individual variation. The intensity and duration of growth is on average greater in boys. After this growth spurt, most skeletal growth usually comes to an end in the mid-teens for females, and late teens to early 20’s for males.
When comparing children with Class III patterns with children with Class I (upper and lower jaws growing in harmony) patterns, research has shown that the maxilla (upper jaw) continues to grow less in Class III patients, while the mandible (lower jaw) continues to grow more in relation to the maxilla. What we have learned from the information in these last two paragraphs can be summarized as:
1) Class III patients will continue to be Class III patients as they develop.
2) The appearance of the underbite usually becomes worse with age into the teens, particularly during the growth spurt. This includes the underbite becoming larger, the lower jaw and chin appearing more protrusive, and the profile becoming more concave.
3) A relatively stable relationship occurs when growth stops, which is mid-teens for girls, and late teens to early 20’s for boys. This is why, in general, we treat girls at an earlier age than boys.
4) The earlier we detect an underbite or Class III, the earlier we can put together a plan to tackle this challenging growth pattern, as often there are considerable concerns regarding appearance, social issues, speech patterns, and proper functioning of the jaws.
In the next blog entry, I will discuss the treatment options for Class III patients, and the challenges and potential complications related to this treatment.
Dr. Dan Rejman is a Board Certified Orthodontist with a private practice in Castle Rock, Colorado. He has treated hundreds of Class III cases, ranging from relatively mild cases treated with braces, to severe surgical cases for teens and adults. He has a particular interest in underbites, as his youngest daughter has had a considerable underbite since her first baby teeth erupted!