Scissor Bite (Brodie Bite): Orthodontic Treatment in the UK

What is a scissor bite?

A scissor bite (Brodie bite) is a type of posterior crossbite where the upper buccal teeth (premolars and molars) sit entirely outside and over the lower buccal teeth, rather than in the normal interdigitating relationship. In normal occlusion, the upper teeth overlap the lower teeth slightly at the buccal cusps, but the palatal cusps of upper teeth make contact with the central fossa of lower teeth. In a scissor bite, the lower buccal segment is positioned so far lingually that there is no contact at all between upper and lower buccal teeth — the teeth pass each other like the blades of scissors without meeting. This is distinct from a buccal crossbite (the more common posterior crossbite), where the lower teeth are outside the upper.

Causes of scissor bite

A scissor bite typically results from a discrepancy in the transverse width of the upper and lower arches: the upper arch is significantly wider than the lower, or the lower arch is significantly narrower than the upper, or both. Contributing factors include digit-sucking habits during development (which can narrow the lower arch while widening the upper), patterns of jaw growth, and skeletal discrepancies. Unilateral scissor bite may arise from asymmetric jaw growth, an early loss of deciduous teeth causing positional shift, or a single ectopic tooth. Bilateral scissor bite is less common and typically has a more significant skeletal component.

Unilateral vs bilateral presentation

Unilateral scissor bite affects one side of the arch and is more common. It may cause a functional shift of the mandible to one side on closure, with associated asymmetry of the midline. Left untreated, this shift can create adaptive changes in the TMJ and facial musculature over time. Bilateral scissor bite affects both sides, is rarer, and is more likely to have a significant skeletal aetiology. Treatment planning for bilateral scissor bite often requires more complex intervention, particularly in adults where growth modification is no longer possible.

Treatment: cross-arch elastics and buccalisation

The primary orthodontic approach to scissor bite is to buccalise the lower buccal teeth — moving them outward — while maintaining or reducing the upper arch width. Cross-arch elastics attached from the lingual aspect of lower premolar or molar brackets to the buccal aspect of the corresponding upper tooth apply a force couple that tips the lower tooth buccally and the upper tooth lingually. This can correct mild to moderate scissor bite, but the correction relies on tipping movement rather than bodily tooth movement, and relapse risk is significant without prolonged retention. Some cases also require lower arch expansion using a fixed lower expander or a lower lingual arch to create space for the lower buccal teeth to move buccally.

Temporary anchorage devices (TADs)

For more significant scissor bites, or where good anchorage is needed to achieve bodily movement rather than tipping, temporary anchorage devices (TADs / mini-screws) can be used. A TAD placed in the lower buccal alveolus can provide an anchorage point for elastic or spring force directed buccally on the lower buccal teeth, enabling more controlled movement. TADs allow forces to be applied more precisely and reduce the dependency on patient cooperation for elastic wear. They are placed under local anaesthetic as a minor chairside procedure and removed at the end of treatment.

Surgical treatment for severe cases

In adults with severe bilateral scissor bite driven by skeletal discrepancy — particularly a significantly narrow lower jaw — surgical correction may be required. Mandibular distraction osteogenesis can widen the lower jaw, and this can be combined with orthodontic treatment. For very severe asymmetric cases, orthognathic surgery may be needed. Surgical options are generally reserved for cases where orthodontic treatment alone cannot achieve a functional occlusion and stable result. The combination of orthodontic preparation, surgery, and post-surgical orthodontic finishing can provide a stable, functional correction.

Clear aligner treatment and scissor bite

Clear aligners face particular challenges in correcting scissor bite. The transverse movements required — buccalising lower buccal teeth while potentially narrowing the upper arch — are among the least predictable movements in aligner treatment. Aligner trays track poorly on teeth that are significantly out of arch form, and the tip corrections needed often require large overcorrections in the digital treatment plan. Many aligner companies acknowledge that posterior crossbites and scissor bites are better treated with fixed appliances, at least in part. If aligners are used, careful monitoring of tracking and the use of attachments to improve force delivery are essential.

NHS IOTN eligibility and treatment duration

A scissor bite may contribute to a higher IOTN score, particularly if it causes a functional mandibular shift (IOTN dental health component grade 4 or 5) or if it is causing trauma to soft tissues. However, each case is assessed individually, and scissor bite alone does not guarantee NHS eligibility. Private treatment for scissor bite typically takes 18 to 24 months depending on severity, whether TADs are used, and whether any skeletal component requires management. Relapse is a significant concern, and permanent retention — a fixed lower retainer and a upper retainer — is recommended indefinitely.

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.