What is an underbite?
In this condition, called “Class III” in orthodontics, the lower teeth and often the lower jaw are forward of the upper jaw. The lower jaw may look prominent and the facial profile concave. Not every underbite is caused by a genuinely oversized lower jaw; in some people the real problem is that the upper jaw is set back, and in others it is a combination of both.
Dental or skeletal?
- Dental (pseudo) Class III: The jaws actually match, but because of the position of the front teeth the lower jaw slides forward when closing. It usually responds well to early treatment.
- Skeletal Class III: The lower jaw may be large or forward, and the upper jaw small or set back. It can become more pronounced with growth.
The distinction is made with an examination and a cephalometric X-ray.
Why is early assessment important?
Methods that support the development of the upper jaw (such as a face mask and palatal expansion) are most effective at a young age. That is why orthodontic assessment should not be delayed in children whose lower front teeth are seen to close in front of the upper front teeth. Because growth of the lower jaw can continue until after puberty, monitoring is needed after treatment until growth is complete.
Treatment options
In children
- If the upper jaw is also set back, a face mask and palatal expansion
- Removable appliances or clear aligners to correct an anterior crossbite
- Correcting habits and the forward shift that occurs when closing
In adults
- Orthodontic camouflage: In mild and moderate cases, the bite can be improved by changing the inclination of the teeth, using clear aligners or brackets.
- Orthognathic surgery: In marked skeletal cases, jaw surgery is planned after orthodontic preparation. For details, see the skeletal jaw problems page.