What is malocclusion, and how does an orthodontist classify it?
Malocclusion means the teeth or the jaws are out of line with each other, so that the upper and lower teeth do not meet as they should. It can involve the teeth alone, for example when they are crowded, or the bones, when one jaw grows differently from the other.
Orthodontists use Angle’s classification, which describes how the first permanent molars meet. In Class I the molars meet correctly and the problem lies in the position of the teeth, for example crowding. In Class II the lower jaw sits back in relation to the upper jaw, which is colloquially called an overbite, and in Class III it sits forward, which is an underbite.
Angle’s class alone does not describe everything. The bite is assessed separately in the vertical plane (deep bite and open bite), across the arch (crossbite) and for the amount of space in the arch: crowding and gaps. These features often combine; for example, an overbite with protruding upper incisors usually goes hand in hand with a deep bite.
Types of malocclusion: what they look like and when they are treated
Each type has a different typical cause and a different right moment for treatment. The table brings together the most common ones, based on Cochrane reviews and the guidelines of the American Academy of Pediatric Dentistry (AAPD); the plan for a particular child is decided by the orthodontist after an examination and analysis of the X-rays.
| Type | What it looks like | Typical cause | When and how it is treated |
|---|---|---|---|
| Crowding | Teeth overlap or are rotated | Too little space in the arch, large teeth, early or late loss of milk teeth | Usually after the permanent teeth have come through, with fixed braces or aligners |
| Overbite (Class II) | Upper incisors stick out, lower jaw set back | Tooth position, a set-back lower jaw or a forward upper jaw | Usually in adolescence; earlier when the incisors are at risk of injury |
| Underbite (Class III) | Lower teeth in front of the upper ones, lower jaw pushed forward | Heredity and jaw growth, sometimes habits or injuries | Early, in the milk or mixed dentition; surgery in severe cases |
| Posterior crossbite | Upper back teeth bite inside the lower ones | A narrow upper jaw, prolonged dummy or thumb sucking | Widening the upper jaw, best studied at ages 7 to 11 |
| Anterior open bite | The incisors do not touch when the back teeth are clenched | Thumb or dummy sucking, tongue position | First stopping the habit; the evidence for appliances is weak |
| Deep bite | The upper incisors cover the lower ones too much | Differences in jaw growth, early loss of milk teeth | The plan depends on the cause; often occurs together with an overbite |
| Gaps between teeth | Spaces between the teeth, including between the central incisors | Missing or small teeth, habits, sometimes the frenulum | In children, usually monitored until the permanent canines come through |
How common is malocclusion in children in Poland?
Malocclusion is very common in Polish children, although there is no single figure for the whole country. In a study of 653 children aged 9 to 12 from Gdańsk and Sopot, malocclusion was found in 81.6%, most often Class II (36%) and crowding (38%). Worldwide, a meta-analysis of 77 studies estimates malocclusion in 56% of children and adolescents, and in Europe in 72%.
In a study of 738 adolescents aged 12 and 13 from West Pomerania, 22.1% had an overbite, 19.9% a deep bite, 19.5% crowding and 6.2% a crossbite. Underbite (2.3%) and anterior open bite (1.6%) were rare. Both Polish studies are regional and used different definitions, so their results should not be compared directly.
How common malocclusion is does not in itself mean that it needs treatment. In the Gdańsk study, half of the children wearing a removable appliance had no or only minimal need for treatment according to the Index of Orthodontic Treatment Need (IOTN), and the authors stress that not every diagnosed malocclusion requires braces.
What are the risks of untreated malocclusion?
The best-documented consequence of malocclusion is a higher risk of injury to protruding upper incisors. The AAPD states that the risk rises when the upper incisors stick out more than 3 mm in front of the lower ones, and that with protrusion of more than 8 mm, injury occurs in over 40% of children.
A posterior crossbite is often combined with the lower jaw shifting to one side when the mouth closes. According to the AAPD, early correction of such a crossbite clearly improves function and largely removes the asymmetry of the lower jaw, which is why this problem is usually not left until adolescence. Crowded teeth are also harder to clean thoroughly.
Malocclusion is not, however, a proven cause of temporomandibular joint pain. The US National Institute of Dental and Craniofacial Research (NIDCR) writes that research does not confirm that a bad bite or orthodontic braces cause these problems. The authors of the Gdańsk study point out, on the other hand, that the appearance of the smile can affect a child’s wellbeing and relationships with peers.
Why are some types treated during growth and others later?
Problems are treated early when bone growth can be put to use, or when a problem can be stopped before it becomes established; treatment of the others usually waits until the permanent teeth have come through. The British Orthodontic Society (BOS) states that most children start treatment at around the age of 12 or 13.
A posterior crossbite is an example of a problem treated early. A 2021 Cochrane review (31 studies) found that in children aged 7 to 11, appliances that widen the upper jaw, a fixed quad-helix and a removable plate, correct a crossbite considerably more often than monitoring alone, and that the Hyrax appliance is probably effective as well.
An underbite is also treated early. In a 2024 Cochrane review (29 studies, children aged 5 to 13), appliances such as the face mask clearly improved the bite immediately after treatment, but in the only long-term study the effect had not lasted after 6 years. Children treated with a face mask were, however, less often judged to need jaw surgery in the future (low-certainty evidence).
For an overbite, the case for early treatment is narrower. A 2018 Cochrane review (27 studies) found no difference in the final result between treatment started at ages 7 to 11 and a single course in adolescence, with one exception: an early functional appliance reduced the number of new incisor injuries (19% compared with 30%).
Malocclusion in adults: braces or surgery?
An adult can have malocclusion treated at any age, and the scope of treatment depends on whether the problem comes from the position of the teeth or from the position of the bones. When it mainly involves the teeth, fixed braces or aligners are usually enough; the article on aligners and fixed braces compares the two methods.
In severe skeletal problems, especially an underbite, moving the teeth alone is not enough. The 2024 Cochrane review points out that in severe cases, or after unsuccessful treatment in childhood, jaw surgery (orthognathic surgery), carried out together with orthodontic treatment, is sometimes needed in adulthood. The AAPD adds that in people with an underbite, growth of the lower jaw lasts longer and is less predictable.
In adults, orthodontic treatment starts with healthy gums. The European Federation of Periodontology (EFP) recommends braces only once periodontitis (advanced gum disease) is under control, and after treatment, retention and lifelong periodontal care; the details are in the article on braces for adults.
Malocclusion on the NFZ: what is a child entitled to?
The NFZ funds treatment of malocclusion only with a removable appliance and only up to the 12th birthday; fixed braces are excluded from the list of services. Check-ups during retention are available to children treated under the NFZ up to the 13th birthday (legal position as of 18 October 2026).
Detecting malocclusion is also part of the free preventive check-ups for children and adolescents. The regulation provides for orthodontic prevention in young children (assessment of the incisors, breathing and sucking habits), an assessment of how the first permanent molars meet according to Angle’s principles in the 7th year of life, and an assessment of malocclusion using the IOTN in the 10th, 12th, 13th, 16th and 19th years of life.
It is worth planning the first orthodontic check-up by the age of 7 at the latest, as the American Association of Orthodontists (AAO) recommends; the signs that are a reason to come earlier are described in the article on when to take your child to an orthodontist. The legal basis is the Minister of Health’s regulation on guaranteed dental treatment services (consolidated text, Dz.U. 2025 poz. 615).
How does an orthodontist diagnose malocclusion, and what do diagnosis and an appliance cost?
An orthodontist diagnoses malocclusion on the basis of an examination, X-rays and measurements. A panoramic X-ray (pantomogram) shows all the teeth and tooth buds, and a side view of the skull, the cephalometric X-ray, makes it possible to measure the position of the jaws; according to a European Commission review, its dose is below 6 µSv.
The cost of treatment depends on the type of malocclusion, the type of appliance, the number of stages and visits, and on retention after treatment. In the clinic’s price list, an orthodontic consultation costs 300 zł, a cephalometric X-ray 120 zł and a treatment plan with cephalometric analysis 380 zł.
Appliances used during growth have separate items in the price list. A Twinblock, a functional appliance used for an overbite, costs 1 500 zł, a Hyrax appliance for widening the upper jaw also 1 500 zł, and a Hybrid Hyrax, which is anchored on the teeth and on mini-implants, 4 500 zł. The final scope and cost are set at the consultation, and prices may change.
How it works at DentalBlue
At DentalBlue in Białystok, malocclusion is treated by the orthodontic team, which plans treatment with fixed braces and Clear Aligner trays digitally, on the basis of cephalometric analysis. The cephalometric X-ray, the panoramic X-ray and, where needed, CBCT tomography are taken in the clinic’s own radiology unit, with no need to go elsewhere. For children, orthodontics is combined with paediatric dentistry and prevention, including fissure sealing and fluoride treatment. Patients can be seen in Polish, English, Ukrainian and Russian. An orthodontic consultation can be booked by phone.
Frequently asked questions
Can a child’s malocclusion correct itself?
Sometimes, yes. An open bite caused by thumb or dummy sucking often resolves if the habit stops before the permanent incisors come through, and gaps between the teeth usually get smaller with age. The AAPD recommends dealing early with a crossbite, which is unlikely to correct itself, so the choice between monitoring and treatment is made by the orthodontist.
Is malocclusion hereditary?
Partly. According to the AAPD, an underbite can have hereditary or environmental causes, or both at once, and the environmental ones include injuries, sucking habits and tooth decay. A review in the StatPearls database states that only about 8% of malocclusions have a known cause, and that the rest usually result from a combination of genes and environment.
Does malocclusion cause temporomandibular joint pain?
Research does not confirm this. The NIDCR writes that neither a bad bite nor orthodontic braces are a proven cause of temporomandibular disorders, and that procedures that change the bite have no evidence of effectiveness in treating them and may make the symptoms worse. Joint pain needs a separate diagnosis.
How long does treatment of malocclusion with braces take?
According to the BOS, treatment with braces takes 6 to 30 months, and in a meta-analysis of 22 studies the average length of treatment with fixed braces was about 20 months. Two-phase treatment, with an early appliance in childhood, takes longer in total. Once the braces come off, retention begins, which the BOS recommends keeping up long term.
Does an underbite in an adult always need surgery?
Not always. The AAPD distinguishes between an underbite caused by the position of the teeth and one caused by the position of the bones. Jaw surgery is needed above all in severe skeletal problems or in cases where treatment in childhood did not work; the operation is then planned together with orthodontic treatment, after an examination and cephalometric analysis.
Sources
- Cochrane: Batista KB et al., treatment of Class II malocclusion in children and adolescents (2018)
- Cochrane: Owens D et al., treatment of Class III malocclusion in children (2024)
- Cochrane: Ugolini A et al., treatment of posterior crossbite (2021)
- AAPD: Management of the Developing Dentition and Occlusion in Pediatric Dentistry (2024)
- Dent Med Probl: Kalinowska J et al., malocclusion in children aged 9 to 12 (2025)
- BMC Oral Health: Milona M et al., malocclusion in Polish adolescents (2025)
- NIDCR: TMD (Temporomandibular Disorders) (2026)
- ELI: Rozporządzenie MZ w sprawie świadczeń gwarantowanych z zakresu leczenia stomatologicznego, t.j. Dz.U. 2025 poz. 615
An informational article. It does not replace a consultation, and treatment decisions are made during a visit.
