Overjet and Overbite: Definitions, Norms and Diagnosis

Overjet and overbite describe how the front teeth meet. They take seconds to measure, and they say a lot: a large overjet raises the risk of trauma to the upper incisors, a deep overbite can lock mandibular growth, a negative overjet points toward Class III. They are also easy to over-read, because the same value can come from the teeth, the jaws or a habit. This article covers definitions, measurement, normal values and the thresholds our team uses, what increased or negative values mean, their causes, and when a case should go to an orthodontist.

Overjet vs overbite: definitions

• Overjet is the horizontal overlap of the incisors: the distance, measured front to back, between the incisal edge of the upper incisor and the labial surface of the lower incisor. It is positive when the upper incisors are ahead of the lower ones, zero in an edge-to-edge bite, and negative in an anterior crossbite (reverse overjet).
• Overbite is the vertical overlap of the incisors: how far the upper incisors cover the lower ones. It is positive in a normal or deep bite, zero when the incisal edges just meet vertically, and negative when there is a gap between them, which is an anterior open bite.

In everyday English, "overbite" is often used for upper teeth that stick out. In orthodontics, protruding upper incisors are an increased overjet; an increased overbite is a deep bite.

How to measure overjet and overbite

With a ruler, in millimeters

Both measurements are taken in maximum intercuspation with a small millimeter ruler or a periodontal probe. Bassigny, an older French reference used in the D.U. courses, gives a simple recording rule:

• record both values in half-millimeters and with a sign: overjet positive when the upper incisors are ahead, negative when reversed; overbite positive when normal or excessive, negative in an open bite;
• measure on the most labially placed incisor, on the right and the left if the incisors are asymmetrical;
• state the level of the measurement (incisor or incisor-canine).

In a Class II, the D.U. course on semiology adds that overjet depends on the anterior compensations: compare it with the molar and canine relationships and with incisor inclination before interpreting it.

Overbite as a fraction of the crown

Overbite can also be expressed relative to the height of the lower incisor crown. Boileau gives a normal overbite of 2 to 2.5 mm, or about one third of the lower incisor crown (roughly 33% if you express it as a percentage). One Class III course describes a deep anterior guidance as an overbite of more than half the crown height.

Philippe’s functional test

Boileau also reports a functional definition of deep bite attributed to Philippe: ask the patient to bring the incisors edge to edge, and look at the molars. Normally 0 to 2 mm of space remains between them; molar contact indicates a reduced overbite, more than 2 mm indicates a deep bite.

Photos, casts and centric relation

Overjet and overbite should also be documented: the D.U. photo protocol includes high-angle and low-angle intraoral views for overjet and overbite, and casts allow you to quantify them along with molar and canine classes. In any anterior crossbite or edge-to-edge case, check the bite in centric relation as well: a forward functional shift can turn a mild discrepancy into an apparent reverse overjet. See our orthodontic photo protocol and clinical examination guide (both in French).

Normal values and thresholds

Norms are close across sources; the thresholds for "increased" differ.

Boileau notes that published millimeter thresholds for deep bite range from 2 to 4 mm depending on the author. He also distinguishes a descriptive norm from a treatment goal: in patients with a fragile temporomandibular joint, he aims for an overbite of 3 to 4 mm at the end of treatment, to secure anterior guidance.

The thresholds GS Ortho uses

The clinical exam of the GS Ortho diagnostic studio applies the rules our team adopted in its decision log (items 02-Q5a and 02-Q5b/07-Q7):

The overjet threshold of 2 mm follows the D.U. terminology course and Boileau; the decision log records a variant of 3 mm from the wider literature. The 3 mm deep-bite threshold follows the D.U. vertical course and Bassigny, with a normal value of about 2 mm. These flags are signs to examine, not diagnoses: an overjet of 3 mm in a patient with well-placed incisors and a Class I is not a treatment indication by itself.

Increased overjet

Class II division 1

A large overjet is the hallmark of Class II division 1. In the D.U. courses, division 1 combines proclined upper incisors with an overjet at least equal to the amount of Class II at the molars. Overjet alone does not tell you whether the cause is a forward maxilla, a retruded mandible or proclined incisors; SNA, SNB and ANB do, and our article on Class II diagnosis (in French) details the reasoning.

Boileau gives a useful reading clue: a large overjet without anterior alveolar compensation points to a functional cause, with a hypotonic upper lip, an overactive lower lip that retroclines the lower incisors, and a high, forward tongue. A lower lip trapped behind the upper incisors maintains the overjet; a thumb habit pushes the upper incisors forward and the mandible back.

The trauma risk

The most solid argument for acting early on a large overjet is the risk of incisor trauma.

• In a 1999 meta-analysis of 11 studies, children with an overjet greater than 3 mm were about twice as likely to injure their anterior teeth as children with a smaller overjet, and the risk tended to rise with overjet size (Nguyen et al., 1999, Eur J Orthod, PubMed). Boileau cites this meta-analysis.
• A meta-analysis of 54 studies found pooled odds ratios of about 2 for both a 3-4 mm and a 6 ± 1 mm threshold in the permanent dentition, and estimated that 21.8% of traumatic dental injuries worldwide are attributable to a large overjet (Petti, 2014, Dent Traumatol, PubMed).
• A 2019 review proposed age-specific thresholds: an overjet of 3 mm or more in the primary dentition (odds ratio 3.37), and above 5 mm in the mixed and early permanent dentition (odds ratio 2.43) (Arraj et al., 2019, Dent Traumatol, PubMed).

These are observational associations, and inadequate lip coverage is a risk factor of its own: they argue for discussing early treatment, not for a fixed threshold.

Reduced, edge-to-edge and negative overjet

• Class II division 2: the upper central incisors are retroclined, the overjet is normal or 1 mm or less, and a deep bite is always present according to the D.U. vertical course. Our article on Class II division 2 (in French) covers it.
• Edge-to-edge bite (overjet 0): it can be a compensated Class III, a Class I with retroclined upper incisors, or a functional shift. Check centric relation.
• Negative overjet (anterior crossbite): one or more upper incisors behind the lower ones. In a Class III, the incisors can be in crossbite, edge to edge or even in normal overlap, depending on dentoalveolar compensation. Bassigny’s grid lists a negative overjet with incisor contact and an edge-to-edge relationship in centric relation among the factors favorable to orthopedics or orthodontics, and a negative overjet without contact, identical in centric relation and maximum intercuspation, among the factors pointing toward surgery. Timing matters: the D.U. courses place Class III orthopedics as early as possible, from 4 to 5 years, with a facemask before 10 years. See our article on Class III diagnosis (in French).

Deep bite: increased overbite

A deep bite (French supraclusion) is an excessive vertical overlap, a term reserved for the anterior region. The D.U. courses describe its origin as:

• anterior: overeruption of the upper and/or lower incisors;
• posterior: infraocclusion of the molars, for example from a lateral tongue interposition;
• mixed.

It is almost constant in hypodivergent (low-angle) patients, always present in Class II division 2, and can exist without any skeletal anomaly. The incisors erupt until they meet a contact; without one, they overerupt. In a child, a deep bite can lock mandibular growth; it also carries joint and periodontal risks, and Boileau adds that it prevents a Class I canine relationship once the incisors are aligned and complicates some anterior prosthetic work. In low-angle patients, the D.U. vertical course also notes palatal impingement by the lower incisors.

Corrections are notoriously prone to partial relapse, especially in Class II. Our article on deep bite (in French) details the options. Worldwide, deep overbite affected about 22% of individuals in a systematic review of 53 prevalence studies, against about 5% for open bite (Alhammadi et al., 2018, Dental Press J Orthod, PubMed).

Reduced overbite and open bite

When the overbite falls to zero, the incisors meet edge to edge vertically; when it becomes negative, there is an anterior open bite (incisal infraocclusion). The D.U. courses insist on precise wording: a lip gap (lips apart at rest by more than 3 mm) is not an incisal open bite. An open bite limited to the incisors is more often functional (thumb, pacifier, tongue), while one extending to the canines and premolars suggests a skeletal, hyperdivergent component. Our article on anterior open bite (in French) covers its diagnosis and management.

Causes: skeletal, dental, functional

Habits deserve a systematic search: our article on oral habits and dysfunctions (in French) describes how to look for them.

How overjet and overbite guide diagnosis

The courses repeat one rule: an occlusal sign is not a diagnosis.

1. Sagittal: compare overjet with the molar and canine classes, then with ANB, SNA and SNB. A skeletal Class II can hide behind a normal overjet when the lower incisors are proclined.
2. Vertical: relate overbite to the typology. An open bite in a hypodivergent patient, or a deep bite in a hyperdivergent one, is unusual and calls for checking whether the problem is alveolar or skeletal. The mandibular plane angle and the facial height index answer that question.
3. Function: look for the habit, the tongue posture or the breathing pattern that maintains the sign.
4. Centric relation: in any edge-to-edge or reverse bite, compare centric relation and maximum intercuspation.

When to refer

For a general dentist, these signs justify an orthodontic opinion:

• a large overjet in a child, especially with lips that do not cover the upper incisors (trauma risk);
• any anterior crossbite or edge-to-edge bite in a growing child, whatever the age;
• a deep bite with palatal or gingival impingement, or an incisor contact that blocks the mandible;
• an open bite that persists after the habit has stopped, or that extends beyond the canines;
• in an adult, any planned prosthetic or restorative work on the incisors when overjet or overbite is outside the norm.

In practice

1. Measure overjet and overbite in millimeters, signed, to the nearest half millimeter, on the most labial incisor.
2. Note the level (incisor or incisor-canine) and the right and left values if they differ.
3. For overbite, also estimate the fraction of the lower incisor crown covered.
4. In an edge-to-edge or reverse bite, check centric relation.
5. Relate overjet to the molar and canine classes and to ANB; relate overbite to the vertical pattern.
6. Search for habits, tongue posture and mouth breathing.
7. State which threshold you used (2 or 3 mm for overjet, 3 mm for deep bite) when you call a value increased.

Frequently asked questions

What is the difference between overjet and overbite?

Overjet is the horizontal distance between the upper and lower incisors; overbite is their vertical overlap. Protruding upper teeth are an increased overjet; upper teeth covering too much of the lower ones are an increased overbite, or deep bite.

What is a normal overjet?

About 2 mm in the D.U. courses and in Boileau, with an ideal range of 1 to 2 mm; the wider literature often gives 2 to 3 mm. GS Ortho flags an overjet above 2 mm as increased. A larger overjet is associated with a higher risk of incisor trauma.

What is a normal overbite?

About 2 to 2.5 mm, or roughly one third of the lower incisor crown (Boileau). An overbite above 3 mm is a deep bite in the D.U. courses; a negative overbite is an open bite.

Can an overjet or overbite correct itself?

Some can, once the cause disappears: an open bite maintained by a habit can close spontaneously in the mixed dentition if there is no skeletal excess. Skeletal overjets and deep bites do not correct themselves. Only an orthodontic examination can tell which situation applies to a given patient.

Is a large overjet dangerous?

It is associated with about twice the risk of trauma to the upper incisors in children (Nguyen et al., 1999), and more when the lips do not cover the teeth. That is a reason for an early orthodontic opinion, not necessarily for immediate treatment.

With GS Ortho

In GS Ortho, the 12-panel guided diagnostic studio records overjet and overbite during the clinical examination, then puts them side by side with the photos and the cephalometric analysis of the same patient, where AI places 29 landmarks that you check and correct before validating. The platform also includes teaching guides and fictitious training cases. When a value sits on a boundary, "Request an opinion" sends the question, with the panel attached, to a colleague or supervisor you choose; the answer stays in the record. The GS Ortho interface is currently available in French.

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