I see many young patients who have what is called a posterior crossbite, and it is important for parents to understand why certain crossbites should be corrected at an early age. Basically, a posterior crossbite means that the back teeth are located on the wrong side of one another. As an orthodontist, I determine what the cause of this problem is, if the crossbite is causing the lower jaw to shift to one side, and if this issue needs early correction before they are ready for a full set of braces. Usually a crossbite that is causing a shift should be corrected as early as it is detected (when the permanent teeth start to erupt), and I like parents to know why.
A common cause of crossbite is an upper jaw (maxilla) that is narrow in contrast to the lower jaw (mandible). As the lower jaw and it’s teeth close in a straight path, it contacts the upper teeth and they do not “fit” correctly. This is an uncomfortable feeling, and the child shifts their jaw to one side to find a comfortable place to bite. We call this a “unilateral posterior crossbite with a functional mandibular shift.” Several issues to note about this shifting:
- The shift to one side becomes habitual, and the child’s neuromusculature becomes adapted to the new position.
- This new shifted position causes the condyle (the uppermost portion that is apart of the TMJ) of the lower jaw to push upward and backwards on the side of the crossbite, whereas the condyle on the other side is pushed forward and downwards.
- This change of position causes compression (pressure) on the crosbite side, and tension (pulling) on the non-crossbite side.
- If left long enough in this position, remodeling of the condyle (upper portion of the lower jaw) and glenoid fossa (the “socket” portion of the skull and TMJ) can occur. Specifically, less bone grows on the crossbite side, and more bone grows on the other side.
- This asymmetric mandibular growth can cause facial disharmony and functional changes in the masticatory (chewing) muscles. Other than the obvious aesthetic and facial symmetry issues, the effects on TMJ disorder are still being researched.
It is interesting to note that the correction of the lower jaw’s asymmetric response to the narrow upper jaw is to symmetrically widen the upper jaw. If treated young enough (before the upper jaw’s mid-palatal suture fuses), the lower jaw will go back to biting in line with the middle of the upper. Unfortunately, I see older patients in their mid to late teens and adults who no longer can be corrected with orthodontics alone, and jaw surgery is the only way to correct the skeletal imbalance that has occurred. If there is any question at all about your child’s bite, give me a call an I will be glad to take a look and discuss if early treatment is indicated.
Dr. Dan Rejman lives and practices as a Board Certified Orthodontic Specialist in Castle Rock, Colorado. He is a proponent of treating children with braces at the proper age (some younger, some later!), dependent on their unique facial and dental relationships.