Overjet

Overjet is the horizontal distance between the labial surface of the most prominent maxillary incisor and that of the mandibular incisor, measured in millimetres, with a normal value of about 2 to 4 mm and values above 3.5 mm regarded as increased in most orthodontic indices.

It is common, with an increased overjet of 3.5 mm or more present in roughly 15 to 20 per cent of children in European and North American surveys, and it is a major risk factor for incisal trauma, especially when the overjet exceeds 5 mm.

Terminology and classification

• Overjet is the horizontal anterior-posterior overlap of the maxillary central incisors over the mandibular central incisors, measured in millimetres from the labial surface of the most prominent upper incisor to the labial surface of the lower incisor.
• The normal value is about 2 to 4 mm, and a negative value is recorded when the lower incisors lie anterior to the upper incisors.
• Overjet is distinct from overbite, which is the vertical overlap, and the two measurements are recorded separately in every orthodontic assessment.
• The Angle classification of 1899 divides malocclusion into three classes on the basis of the first molar relationship, and an increased overjet usually accompanies Class II division 1.
• The Index of Orthodontic Treatment Need, published by Brook and Shaw in 1989, grades overjet as grade 3 for 3.5 to 6 mm, grade 4 for 6 to 9 mm and grade 5 above 9 mm.
• ICD-10 codes the anomaly within K07.2 for anomalies of dental arch relationship, and the Wikidata identifier Q7113715 provides a cross-database anchor while Orphanet does not list it.
• The term is sometimes confused with bimaxillary protrusion, which describes a facial pattern of protrusive upper and lower jaws rather than a single dental measurement.

History

• Edward Angle published his classification of malocclusion in 1899, establishing the first molar relationship as the basis for describing dental arch discrepancies.
• Cephalometric radiography, introduced in the 1930s, allowed overjet and the underlying skeletal pattern to be measured objectively rather than estimated from plaster casts.
• The Index of Orthodontic Treatment Need was developed in the United Kingdom in 1989 to prioritise access to publicly funded orthodontic care.
• The Twin Block functional appliance, introduced by William Clark in 1982, became the reference appliance in randomised trials of Class II correction.
• A multicentre randomised trial published by O'Brien and colleagues in 2009 showed that early functional treatment gave no lasting skeletal advantage over a single phase of treatment in adolescence.
• A Cochrane review by Thiruvenkatachari and colleagues, updated in 2013, synthesised trials of early treatment for prominent upper front teeth.
• Digital intraoral scanning and three-dimensional cephalometry have largely replaced plaster study models in contemporary practice since the 2010s.

Epidemiology

• Increased overjet is one of the most frequent orthodontic findings, and Class II division 1 malocclusion accounts for about one third of orthodontic cases in European and North American clinics.
• A systematic review published in 1999 found that children with an overjet greater than 3 mm were about twice as likely to sustain trauma to the upper incisors.
• The same review reported traumatised anterior teeth in 22 percent of children with a 5 mm overjet, 24 percent with a 9 mm overjet and 44 percent with an overjet above 9 mm.
• Increased overjet is more frequent in children with digit-sucking habits, in those with incompetent lips and in some syndromic conditions such as Pierre Robin sequence.
• Grade 5 overjet above 9 mm is uncommon, and the Index of Orthodontic Treatment Need places it in the highest treatment-need category.
• The Global Burden of Disease study counts severe malocclusion within the burden of oral disorders, and the 2019 analysis estimated that oral disorders affect about 3.5 billion people worldwide.
• Data sources include the UK Child Dental Health Survey, the United States National Health and Nutrition Examination Survey and national orthodontic commissioning audits.

• Trauma to the upper incisors affects about 15 to 20 per cent of children and adolescents, and a large overjet is the strongest single risk factor, with relative risks of about 2 to 3 compared with children who have a normal overjet.

Pathophysiology

• Overjet results from a mismatch between the skeletal bases, the dental positions or both, and most patients with a large overjet have some degree of mandibular retrognathia.
• Maxillary prognathism, a short mandibular body, a steep mandibular plane and a reduced gonial angle all increase the horizontal discrepancy.
• Dental factors include proclined maxillary incisors, retroclined mandibular incisors and premature loss of primary molars with loss of arch length.
• Soft tissue factors such as incompetent lips, a lower lip trap and tongue thrust perpetuate the incisor discrepancy and favour relapse.
• Non-nutritive sucking and pacifier use beyond about three years of age are established environmental risk factors for anterior open bite and increased overjet.
• Genetic influences are strong, and sibling and twin studies show high heritability for skeletal Class II patterns.
• Severe overjet predisposes to incisal trauma because the upper incisors are unprotected by the lower lip during falls and collisions.

Clinical features

• The main sign is visible prominence of the upper incisors, often with a convex profile and a retrusive chin.
• Patients may report difficulty incising food, speech sounds that require lip contact, mouth breathing and dry lips.
• Incompetent lip closure, mentalis strain and a deep labiomental fold are common findings on examination.
• Trauma to the upper incisors, including crown fractures, luxation and avulsion, is the most important complication.
• Other complications include caries, gingivitis, temporomandibular joint pain, obstructive sleep apnoea in severe retrognathia and psychosocial distress from teasing.
• Children with a large overjet are more likely to be bullied, and quality of life studies show reduced oral health-related quality of life before treatment.
• Severe skeletal Class II with a small mandible can be associated with sleep-disordered breathing, particularly in syndromic children.

Diagnosis

• Diagnosis requires a full orthodontic assessment including medical history, extraoral and intraoral examination, study models or intraoral scans and radiographs.
• Overjet is measured with a millimetre ruler or digital caliper from the labial surface of the most prominent upper incisor to the labial surface of the lower incisor.
• Lateral cephalometric radiography quantifies the skeletal contribution through the ANB angle, the Wits appraisal and upper and lower incisor inclination.
• The Index of Orthodontic Treatment Need and the Peer Assessment Rating provide objective measures of severity and of treatment outcome respectively.
• Differential diagnosis includes bimaxillary protrusion, Class III malocclusion with reversed overjet, anterior open bite, retained primary incisors and supernumerary teeth.
• Dental disease must be treated before appliance therapy, because appliances increase plaque accumulation and risk decalcification and periodontal breakdown.
• Undiagnosed habits, airway obstruction and skeletal discrepancies are common reasons for relapse when they are not addressed before treatment.

Management

• Treatment aims to reduce the overjet, establish a functional occlusion, protect the incisors and improve facial and dental aesthetics.
• Removable or functional appliances such as the Twin Block advance the mandible and reduce overjet largely through dental rather than skeletal change.
• Fixed appliances with premolar extraction or distalisation correct moderate overjet, while skeletal anchorage with miniscrews allows en masse retraction.
• Orthognathic surgery with mandibular advancement or maxillary impaction is reserved for severe skeletal discrepancies that cannot be camouflaged.
• Early treatment at 7 to 9 years reduces incisal trauma and bullying but does not improve the final skeletal result, and a single phase in early adolescence is usually preferred.
• Retention with fixed lingual retainers or removable retainers is required because relapse of overjet is common in the first two years.
• The Cochrane review of 2013 concluded that early treatment for prominent upper front teeth reduces incisal trauma compared with one course of treatment in adolescence.

• In growing children a functional appliance such as the Twin Block reduces overjet by about 4 to 5 mm within 12 months, whereas a skeletal discrepancy in adults may require orthognathic surgery in addition to orthodontic treatment.

Research and controversies

• Clear aligner therapy is being compared with fixed appliances in randomised trials, and evidence for severe overjet remains limited.
• Skeletal anchorage with mini-implants has expanded the range of non-surgical correction, and long-term stability data are still accumulating.
• The relative contribution of genetics and environment to Class II malocclusion remains debated, and twin studies give heritability estimates that vary widely.
• Whether early treatment prevents temporomandibular disorders is contested, and systematic reviews find no consistent evidence of benefit.
• Three-dimensional imaging and automated landmark detection are being evaluated for measuring overjet, with the aim of replacing manual cephalometric tracing.
• Access to publicly funded orthodontic care differs between countries, and the Index of Orthodontic Treatment Need remains the most widely used prioritisation tool.
• Patient-reported outcome measures are increasingly used, because severity grading alone does not capture the psychosocial impact of a prominent overjet.