Bimaxillary Proclination: When Both Upper and Lower Teeth Stick Out

What is bimaxillary proclination?

Bimaxillary proclination — sometimes called bimaxillary protrusion — occurs when both the upper and lower incisors are labially inclined beyond the accepted cephalometric norms for the individual's skeletal pattern and ethnic background. The upper incisor to maxillary plane angle and the lower incisor to mandibular plane angle are both increased. Unlike a straightforward Class II overjet, where only the upper teeth protrude relative to a retruded lower jaw, bimaxillary proclination involves both arches equally — the overall jaw relationship (skeletal pattern) is typically Class I, but the dental bases are both tipped forward.

How does it differ from a simple overjet?

In a Class II Division 1 malocclusion with increased overjet, the upper incisors protrude but the lower incisors are often upright or retroclined, and the underlying jaw relationship is typically Class II — meaning the lower jaw sits further back than ideal. In bimaxillary proclination the overjet may be relatively normal because upper and lower incisors are both proclined by a similar degree. The profile shows lip protrusion — a convex soft-tissue profile with the lips often sitting in front of the E-line (Ricketts' aesthetic plane). This is a key distinction: both the bony and dental components are positioned anteriorly as a unit.

Ethnic variation and the question of normalcy

Cephalometric norms developed historically from white European populations and do not apply universally. Research consistently shows that people of Afro-Caribbean, South-East Asian, and South Asian descent have significantly higher incisor inclinations and more anteriorly positioned lips that are completely normal within their ethnic group. Applying Caucasian norms to these patients risks over-treating a natural variation. Orthodontists use ethnicity-specific cephalometric standards and individualised norm tables to distinguish genuine proclination requiring treatment from natural variation. Patients referred for treatment should ask whether the assessment accounts for their ethnic background.

Clinical assessment — cephalometrics and lip competence

Assessment involves a lateral cephalometric radiograph to measure upper and lower incisor inclinations, the inter-incisal angle, and the relationship of the dentition to the facial skeleton. Key measurements include the upper incisor to maxillary plane angle (norm approximately 109 degrees), the lower incisor to mandibular plane angle (norm approximately 92 degrees), and the lower incisor to A-Pog line. Lip competence — whether the lips meet at rest without muscular strain — is assessed clinically. Incompetent lips that require effort to close, or lips resting between the teeth (lip trap), suggest significant proclination. Soft-tissue profile analysis assesses lip position relative to the E-line and S-line. Profile photographs and standardised records are taken before any treatment planning.

Treatment planning considerations

Treatment is indicated where proclination is outside ethnic norms, where lip incompetence causes dryness and speech effects, where the profile is a significant concern to the patient, or where a lip trap is causing damage to the periodontal tissues. Where proclination is mild and within ethnic norms, no treatment is needed. A frank discussion about the trade-off between treatment duration, the need for extractions, and the likely improvement in profile should precede any commitment to treatment. Orthognathic surgery is not typically required for bimaxillary proclination unless there is also a significant underlying skeletal Class II or Class III component.

The premolar extraction approach

The standard treatment for genuine bimaxillary proclination involves the extraction of four premolars — typically the first premolars from each quadrant — to create space for retracting both the upper and lower incisor segments. Fixed appliances are used to close extraction spaces and tip or bodily retract the incisors back into a more upright position. The treatment aims to reduce incisor inclination, decrease lip protrusion, and achieve lip competence. Extraction decisions depend on the degree of proclination, the crowding present, and how much retraction is realistically achievable with the available anchorage.

TAD-assisted retraction

Skeletal anchorage using temporary anchorage devices (TADs) or miniscrews allows greater and more controlled incisor retraction than conventional anchorage provided by the molars alone. In cases requiring maximum anchorage — where significant retraction is needed without losing posterior tooth position — TADs are inserted into the interradicular bone and used to provide absolute anchorage for retraction mechanics. This approach is particularly valuable in bimaxillary proclination where both arches need substantial retraction. TADs typically remain in place for 6 to 18 months and are removed at the end of treatment under local anaesthetic.

Lip trap consequences

A lip trap occurs when the lower lip habitually rests behind the upper incisors, applying pressure that forces the upper teeth further forward while restraining the lower incisors. This is both a cause and a consequence of increased overjet and proclination. Untreated, a lip trap perpetuates and worsens the proclination over time. Correcting the incisor position typically resolves the lip trap. In children, early interception of habits and myofunctional appliances may reduce the severity of proclination before comprehensive orthodontic treatment is undertaken.

Stability and retention

Bimaxillary proclination cases require careful retention planning. The retracted incisors are under pressure from the lips and tongue, and without adequate retention there is a tendency for teeth to drift back towards their original positions. Permanent bonded retainers on both upper and lower incisors are strongly recommended following treatment, supplemented by removable retainers worn at night. Patients should be counselled from the outset that retention is lifelong — removing retainers after a few years increases the likelihood of relapse.

NHS vs private treatment in the UK

NHS orthodontic treatment for bimaxillary proclination is available to eligible under-18s where the IOTN score meets the threshold (grade 4 or 5). Incisor proclination contributing to increased overjet, lip incompetence, or soft-tissue injury can contribute to a high IOTN score. Adults and those with borderline IOTN scores are typically treated privately. Private treatment costs for extraction cases with fixed appliances range from approximately £3,000 to £6,000 depending on the practice and complexity. Cases requiring TADs add to this cost.

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.