The causes can be either dental or skeletal. In dental underbite, the usual cause is a crossbite. Crossbite is a condition, wherein one or more lower teeth are present ahead of the upper teeth when the two jaws are in occlusion. In this condition, the tooth/teeth are slightly forwardly placed. Thus, the problem appears to be so due to the placement of these few teeth. Furthermore, sometimes, false underbite may be observed in children. In such cases, due to the incomplete eruption of some teeth, the person may seem to have a bad bite, but it is not actually so.
A skeletal underbite is the one, wherein the lower jaw itself is forwardly placed when compared to the upper jaw. This can be due to many reasons. It may be hereditary, or it may even be due to either a retruded maxilla and/or a prognathic mandible. If the condition does not lead to any problems, then it does not need any active treatment since it is a case of class III malocclusion.
If a child has only a dental underbite, then this can be corrected with the help of orthodontic braces. In this treatment, with the help of brackets and wires, the lower teeth are made to occlude behind the upper teeth. In case of a non-skeletal bad bite, orthodontic treatment is the best way to deal with the case.
Initially, if the child has a skeletal underbite, then luckily, since the child is still in his growing years, the mandible can be made to grow into its proper and desired position. This is done with the help of appliances like a headgear. These appliances help bring the mandible into its desired position by applying the right kind of forces. However, if the child has reached an age where the bone has stopped growing, then the only way of achieving bad bite correction is with the help of surgical intervention.
If a person has a severe skeletal underbite to the extent that he has a severe crossbite, then an underbite or crossbite surgery will need to be performed. In this surgery, if it is the mandible that is slightly prognathic, then it is taken and pushed back, and secured in this position. However, if the mandible is retruded, then it is taken and pushed further, and brought ahead of the mandible. Sometimes, when the growth is complete, then instead of moving the entire mandible, only a part of it is cut and pushed back, which is a jaw surgery known as bilateral sagittal split osteotomy.
However, you need to understand that even if your child is showing symptoms of bad bite, he may not necessarily need treatment for it just yet. This is because, it could be a case where the child may simply appear to have a bad bite because the teeth haven’t fully erupted yet. So, you need to visit an orthodontist and get your child’s condition diagnosed to check whether it is truly a case of underbite, and if it is, then appropriate treatment should be started out accordingly.