What is Posterior Crossbite?
A crossbite is when your upper and lower teeth don’t align correctly, which is a common issue seen in orthodontic practice. This can be noticed when your lower teeth seem to jut out or lie closer to your cheek or lip compared to your upper teeth. This can happen on one side, both sides, or involving front or back teeth.
Normally, when your mouth is closed, the pointy parts (called “cusps”) of your upper back teeth (molars and premolars) should perfectly fit into the grooves (or “fossa”) of your lower back teeth. Also, your upper front teeth (incisors) should slightly overlap your lower front teeth from the front.
However, if you have a crossbite, the situation is reversed. The term ‘buccal crossbite’ refers to when the pointy parts of your lower teeth are more towards the cheek than those of your upper teeth. A ‘scissor bite’ means the pointy parts of the lower teeth are closer to the inside (or “lingual” side) of the upper teeth than they should be. A crossbite could be due to the positioning of your teeth (dental) or the alignment of your jawbones (skeletal), or a combination of both.
What Causes Posterior Crossbite?
A cross-bite is a kind of dental misalignment, and there are various reasons why it can develop:
- Hereditary influence: This means it can be passed down from parent to child through genes.
- Inadequate dental arch length: This is when your dental arch, which is the curved area where your teeth are located, isn’t long enough.
- Overretained deciduous teeth: These are baby teeth that stay in place after the adult teeth have started to grow in.
- Supernumerary teeth: This is a condition where you have more teeth than usual.
- Habits like digit sucking: Digit sucking is when a child sucks their thumb or fingers, which can affect the positioning of their teeth.
- Skeletal-anteroposterior discrepancy of arches: This complex term just means that the size or position of the dental arches don’t match up in the upper and lower jaw.
- Cleft lip and palate: This is when a baby’s lip or mouth doesn’t form properly during pregnancy, which can affect the teeth positioning.
It’s important to understand the cause because it helps the dentist to decide on the best way to treat the cross-bite.
Risk Factors and Frequency for Posterior Crossbite
Bell and Kiebach (2014) found that posterior crossbite is quite common in kids, particularly when their teeth are first coming in or changing from baby teeth to adult teeth. This condition affects 5% to 8% of children aged 3 to 12 years old. They also noted that a majority (90%) of functional crossbites come along with transverse discrepancies, which are differences in width. A study in Turkey conducted by Gungor and colleagues (2016) showed a high occurrence of bilateral crossbite (51%) and unilateral crossbite either on the right side (47.3%) or the left side (53.6%) in their adult teeth.
Signs and Symptoms of Posterior Crossbite
Crossbite is a condition that involves misalignment of teeth. There are two types of crossbites: anterior and posterior.
- Anterior crossbite – This occurs when one or more of the upper front teeth are positioned behind the lower teeth.
- Posterior crossbite – Here, the upper back teeth sit inside the lower back teeth when the mouth is closed. Posterior crossbite can further be categorized as:
- Unilateral buccal crossbite with displacement
- Unilateral buccal crossbite with no displacement
- Bilateral buccal crossbite
- Unilateral lingual crossbite
- Bilateral lingual crossbite-scissor bite
Anterior crossbites can come about during early childhood due to an imbalance in the child’s skeletal, functional, and dental framework. It’s characterized by one or more of the top front teeth closing behind the bottom front teeth.
There are three major kinds of anterior crossbite:
- Dental anterior crossbite – One or more teeth are involved. The teeth appear straight in natural closure and alignment, and it could be a result of abnormal tooth inclination.
- Functional anterior crossbite – This kind, also known as Pseudo Class III, arises from over-protrusion of the lower jaw, causing a change in tongue position and leading to alignment changes in the upper jaw. This situation can result in a straight or concave facial profile and a Class III molar relation when the mouth is normally closed.
- Skeletal anterior crossbite – Characterized by improper alignment of the molars and canines when the mouth is closed. The cause of the malocclusion and inclination of the affected teeth should be investigated. Treatment procedures usually involve expansion of the upper teeth arch and use of appliances like a Coffin spring, Quad helix appliance, surgically assisted rapid maxillary expansion, and Ni-Ti palatal expander. Affected individuals often display features like a receding upper lip, pronounced chin, and negative ANB angle.
Testing for Posterior Crossbite
Understanding the differences between a skeletal and dental crossbite becomes easier when you divide it into four key evaluations.
Firstly, a dental evaluation is necessary. This is where a dentist will look at the position of your incisors – the sharp, chiseled front teeth. If these teeth are in an edge-to-edge relationship and the bottom ones are tipped backward, it could indicate a Class III malocclusion. This complicated term just means that your teeth don’t align properly when you close your mouth. Alongside this, the dentist will also check the position of your back teeth and if your bite is correct.
The second step involves functional evaluation. In this stage, the connection between your upper jaw (maxilla) and the lower jaw (mandible) will be assessed. This is done to pinpoint any differences or inconsistencies when you open and close your mouth.
Thirdly, a profile evaluation comes into play. Here, the proportions of your face are observed, especially your chin and overall facial structure. This information helps to present a clear picture of any abnormalities present.
Lastly, a cephalometric analysis is done. This process involves creating a detailed radiographic image (like an X-ray) of the head. It’s used to figure out the positions of your upper and lower jaw relative to each other.
All these evaluations combined help a dental specialist to accurately tell apart a skeletal crossbite from a dental one. It’s been simplified here but if you’ve any questions about the process, don’t hesitate to ask your dentist.
Treatment Options for Posterior Crossbite
When dealing with an anterior crossbite, which is when your top teeth sit behind your lower front teeth when your mouth is closed, a few factors are taken into consideration before deciding on treatment. These include the type of movement needed to correct the crossbite, the final overbite at the end of treatment, deciding between extraction or non-extraction, and whether we need to move the opposing tooth.
The treatment will depend on whether we need to tip the tooth or move it entirely. For tip movements, we can use removable appliances. If we need to move the whole tooth, we use fixed appliances – similar to traditional braces. These appliances need to have secure front retention to counteract the effect of the active element. A bite plane or an active component helps move the teeth to free the occlusion – or the contact between teeth – with the teeth of the opposite jaw.
Open coil springs can be used in straight wire mechanics – a part of orthodontic treatment – to create enough arch length to position the teeth properly. Sometimes, a negative root torque might be needed for upper incisors placed at the roof of the mouth. An adequate overbite and a normal inclination of the tooth to be treated are important for the stability of the correction.
For younger patients, alternative methods, like the use of a tongue blade (a flat stick placed inside the mouth), can aid in correcting the development of a crossbite. Catalan’s appliance or a lower inclined plane can be used, which is constructed and cemented onto the lower incisors. The face masks and Rapid Maxillary Expansion method is for when there’s an issue with the width of the upper jaw. The Frankel III appliance is also used to correct a developing Class III skeletal malocclusion, a condition where the lower jaw is too far forward.
A Chin Cup Appliance can be used to redirect the growth of a lower jaw that’s too far forward. Adults and adolescents can use fixed appliances to correct a single or multiple-tooth crossbite. TADs, or temporary anchorage devices, can also be used.
For a posterior crossbite, which is when your top back teeth bite down inside your lower back teeth, we use different methods. This can include the coffin spring – an omega-shaped wire appliance for younger patients. Another option is the Quad Helix, a fixed appliance attached to the first molars. It can produce slow, controlled expansion.
The Rapid Maxillary Expansion method involves a type of appliance that can bring about skeletal changes in a short amount of time. The NiTi Expanders are nickel-titanium wire shapes that are attached to a lingual sheath welded to the molars. Various sizes are available and must be chosen based on the amount of expansion required and the pre-treatment width of the palate. Fixed orthodontic appliances can be used to correct posterior crossbites as they provide control over the tooth in three dimensions. The type of movement required will then be determined, and cross-elastics can be used to correct individual tooth crossbites in the posterior segment.
What else can Posterior Crossbite be?
Doctors may consider the following potential causes when diagnosing a condition known as posterior crossbite:
- Atypical swallowing patterns
- A combination of other factors
- Habits such as sucking on fingers or pacifiers
- Difficulty breathing through the nose
- Lower than normal position of the tongue
