Malocclusion — Types, Causes and Treatment

What is malocclusion?

Malocclusion is the clinical term for misalignment between upper and lower teeth when the jaws are closed. Normal — or Class I — occlusion involves specific molar and incisor relationships where the teeth fit together in a balanced, functional way. Any deviation from this in any direction constitutes a malocclusion. Fewer than 30% of people have a clinically perfect occlusion; the remainder have some degree of malocclusion, ranging from mild crowding with no functional impact to severe skeletal discrepancies affecting eating, speech, and facial appearance.

Angle's Classification

The most widely used classification system was developed by Edward Angle in the late 19th century and remains the clinical standard. Class I describes a normal molar relationship where the upper and lower first molars align correctly, but crowding, spacing, or rotations may still be present — the most common finding. Class II Division 1 describes upper front teeth that protrude forward with an increased overjet, often associated with an underdeveloped lower jaw — commonly called buck teeth. Class II Division 2 describes upper incisors that are retroclined (tipped backwards) producing a deep overbite; this subtype has an association with TMJ problems. Class III describes a lower jaw that protrudes ahead of the upper, or an underdeveloped upper jaw, resulting in an underbite or anterior crossbite.

Causes of malocclusion

Genetics account for the majority of malocclusion — jaw size, tooth size, and their relationship are largely inherited traits. Developmental factors also play a role: early loss of baby teeth allows adjacent teeth to drift, and impacted permanent teeth can cause crowding or displacement. Habits during childhood — prolonged thumb sucking, dummy use beyond age 3 to 4, and mouth breathing — can influence jaw development and tooth position. Jaw injuries during growth can alter development. Missing teeth cause adjacent teeth to drift over time. Bolton discrepancy — a mismatch between the combined size of upper and lower teeth — can cause crowding or spacing that cannot be fully resolved without additional treatment.

Does malocclusion always need treatment?

No. Many people have mild malocclusion that causes no functional problems and requires no treatment. Treatment is typically recommended when there is difficulty eating or speaking, risk of tooth damage such as lower incisors biting into the gum behind the upper front teeth, a significant aesthetic concern affecting quality of life, or where the IOTN score meets the threshold for NHS treatment for eligible under-18s. Mild crowding that does not affect function, bite, or oral hygiene does not need to be treated unless the patient wishes it for cosmetic reasons.

Treatment options by malocclusion type

Class I crowding or spacing is typically treated with fixed braces or clear aligners, with extractions where crowding is severe. Class II Division 1 in growing patients responds well to functional appliances such as twin blocks or Herbst appliances that guide jaw growth, followed by fixed braces. In non-growing adults with a skeletal component, orthognathic (jaw) surgery combined with orthodontics may be required for the best outcome. Class II Division 2 requires fixed braces to correct the deep overbite and retroclination. Class III malocclusion with a dental cause can often be treated with braces alone; skeletal Class III in adults who have stopped growing usually requires orthognathic surgery combined with orthodontic preparation and finishing.

Useful related pages

This guide is for general information only. It is not a diagnosis, treatment plan, or substitute for advice from a registered dentist or orthodontist.