This article discusses crossbites, the causes, their impact, whether you always need to correct them or if you should sometimes leave them alone, and how to decide what to correct.
What is a crossbite?
The American Association of Orthodontists states that a crossbite is a type of malocclusion where the upper teeth occlude behind the lower teeth. It can affect a single tooth or a group of teeth, the anterior teeth, posterior teeth, or a combination of both. A posterior crossbite is when the upper posterior teeth are occluding inside the lower teeth and an anterior crossbite is where the upper anterior teeth sit behind the lower teeth.
The condition can be described to a patient like an old shoe box, where the lid (upper teeth) does not fit squarely on the bottom. This helps them understand how teeth should occlude or should close together.
What causes a crossbite?
Crossbites may be caused by numerous factors. These factors could include a genetic disposition, delayed loss of baby teeth, abnormal eruption of permanent teeth, abnormal habits such as thumb sucking, tongue thrusting, or a combination of all the above.
Does it need to be fixed?
Whether a crossbite needs to be fixed depends on the age of the patient, the condition of the teeth in crossbite (wear patterns/tooth mobility) and aesthetics. This will be decided in the diagnosis and treatment planning, but there are conditions where you should certainly correct the crossbite and where you may prefer to leave the occlusion as it is.
A crossbite may reveal an underlying jaw problem and this is best addressed at a young age where an expansion appliance may be used while the face and jaws are still developing. If we don't correct crossbites at the younger age, asymmetry can develop where the jaw may shift to one side, or lopsided jaw growth develops, or unusual toothwear patterns can be observed.
While it is optimal to treat young patients for crossbites, there are additional factors contributing to whether you may decide to make a correction or to leave it like it is.
It is important to note that crossbites do not always have an impact on oral health, which is backed by a paper published in the American Journal of Orthodontics and Dentofacial Orthopaedics, in 2020, “Do malocclusion and orthodontic treatment impact oral health?"
If the patient is older in age (over 30 years for example) and the teeth that are in crossbite and the adjacent teeth are not showing signs of wear and the patient is not concerned about the aesthetics of the crossbite (if in the anterior region), it may be acceptable to maintain the crossbite and monitor the patient. Attempting to correct posterior crossbites using aligners unless well experienced in aligner use can be difficult and lead to adverse outcomes as discussed later in this article.
How to evaluate cases and what to look for?
Consider the patient’s teeth position and their occlusion prior to treatment, and how the biomechanics of clear aligners will affect their final occlusion.
As the forces applied to a tooth are on its crown and the centre of resistance is somewhere along the root of the tooth, almost inevitably a moment of force is created and perfect translation may be impossible to achieve. Clear aligners are good at providing tipping forces and this may cause an undesirable occlusion, such as an edge-on-edge cuspal finish which can lead to accelerated toothwear and/or cuspal fracture.
Clear aligners have a distinct advantage in correcting crossbites where upper teeth are proclined and as a result occlude behind their lower counterpart tooth/teeth. As clear aligners disclude the teeth when they are worn and are good at providing tilting forces, crossbites of this origin can be successfully corrected with clear aligner therapy.
Comments