I just returned from the College of Diplomates of the American Board of Orthodontics annual summer meeting. I attended four days of speakers presenting research related to how genetics influences the treatment of our orthodontic patients.  Topics included the genetic influence on temporomandibular disorder (TMD), obstructive sleep apnea (OSA), missing and malformed teeth, external apical root resorption (roots of teeth becoming shorter during braces), and the latest research on a possible connection between missing upper lateral incisor teeth and an increased risk of ovarian and colorectal cancer. I will write a separate blog about several of these topics individually, but below are some interesting points about genetics.

• The human genome contains 3.2 billion (!!) base pairs, or chemical nucleotides.
• There are approximately 25,000-30,000 human genes, which are the smallest units of “instructions”.
• 99.9% of the human genome sequence is the same!
• Genetic variation can often arises from what is called a SNP (“snip”), a single nucleotide polymorphism. One nucleotide change within a gene can result in no discernible change, or can result in a change in phenotype (an observable trait, characteristic, shape, etc…)
• Tooth development, or odontogenesis, involves over 300 genes.
• Sporadic changes, or snips, in the genome can cause dental agenisis (failure to develop, or missing teeth), or a change in the size or number of teeth.
• About 2-9% of the U.S. population has hypodontia, or teeth that are developmentally missing.
• Genes such as AXIN2 and PAX9 have been identified as genes that can contribute to a family history of teeth that are missing.

I will follow up with an article on the genetic influence on obstructive sleep apnea, and its ramifications on orthodontic treatment.

Dr, Dan Rejman is a Board Certified Orthodontic Specialist. He practices in Castle Rock, Colorado, and treats children and adults with braces, clear braces, and Invislaign.

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.