Open Bite: Causes, Diagnosis and Treatment Principles
An open bite is easy to see and hard to classify. The same gap can come from a thumb habit that resolves once it stops, or from a vertical growth pattern that orthodontics alone will not change; most cases sit in between. This guide covers the types of open bite, how to tell dental from skeletal forms, the usual causes, the cephalometric checks, treatment principles by age, and what the literature says about relapse, following the D.U. courses behind GS Ortho, Boileau, and systematic reviews.
What is an open bite?
An anterior open bite (incisal infraocclusion) is an insufficient vertical overlap of the incisors, with no contact between them. The normal overbite is about 2 mm (ideal 1 to 2 mm in the courses, 2 to 3 mm in classic norms). At 0 mm the incisors meet edge to edge; below that, the overbite is negative and the open bite is recorded in negative millimeters.
A few distinctions from the D.U. terminology course:
- a lip gap (lips apart at rest by more than 3 mm) is not an incisal open bite; write which one you mean;
- a posterior (lateral) open bite is the absence of contact over a group of posterior teeth;
- an open bite can be isolated or associated with any malocclusion except Class II division 2, which always has a deep bite.
The mechanism is simple. Incisors keep erupting until they meet a contact: edge to edge during protrusion and, to a lesser extent, the upper incisor resting on the lower lip. Anything placed between them (tongue, finger, object) blocks this eruption, and an open bite develops (Boileau).
Open bite is less frequent than deep bite: about 5% against 22% worldwide in a systematic review of 53 prevalence studies (Alhammadi et al., 2018, Dental Press J Orthod, PubMed).
Dental vs skeletal open bite
The two forms are often combined and hard to tell apart (D.U. courses). Several signs help.
| Criterion | Rather dentoalveolar (functional) | Rather skeletal |
|---|---|---|
| Extent | Incisors only | Extends to canines, premolars, sometimes molars |
| Incisors | Proclined, often with spacing (tongue thrust, sucking) | Often already overerupted (compensation) |
| Vertical pattern | Normodivergent, sometimes hypodivergent | Hyperdivergent (high FMA and SN-GoGn) |
| Face | Normal lower face height | Long lower face, lip incompetence, mentalis strain |
| Cause | An identifiable habit or dysfunction | Growth direction, weak musculature |
Extent is the first criterion in the courses: limited to the incisors, the open bite is rather functional; reaching the canines and premolars, it suggests a skeletal hyperdivergent component.
Two traps:
- an open bite in a hypodivergent patient is unusual and points to a tongue dysfunction or a sucking habit;
- a hyperdivergent patient without an open bite is not unaffected: mandibular alveolar compensation can mask the vertical excess, at the cost of a long alveolar process and a thin periodontium (Boileau).
Causes of open bite
Mouth breathing, low tongue posture, atypical swallowing and sucking habits often go together, with a narrow maxilla, an open bite and/or proclined incisors.
Sucking habits
Thumb sucking produces an open bite, proclined upper incisors and often a V-shaped maxilla; a pacifier usually produces an incisal open bite. The effect depends on the object, the intensity, the frequency and duration, and the point of pressure. The courses describe a sequence: the dentoalveolar region is affected first, the skeleton later, and the tooth displacement then encourages a tongue dysfunction.
The literature confirms the dose effect. In a meta-analysis of 33 studies, longer sucking habits carried a greater risk of anterior open bite than shorter ones, and daily pacifier use was strongly associated with it (odds ratio 10.22, from 3 studies) (Gao et al., 2025, BMC Oral Health, PubMed). Another meta-analysis of 12 studies found that both digit and pacifier sucking increased the risk of open bite, with no significant difference between them for this outcome (Faryad et al., 2026, Dent J, PubMed).
The tongue
Tongue interposition is the constant sign of atypical swallowing. Boileau distinguishes a primary tongue thrust (macroglossia, short lingual frenum, large tonsils), which can cause the open bite, from a secondary one, which is only an adaptation to a sucking or skeletal open bite. The causal role of the tongue remains debated, and its skeletal effect is considered small, rather aggravating.
Breathing
Open bite is often associated with mouth breathing and a low tongue. According to the EMC chapter on nasal obstruction cited in our knowledge base, a child who sucks a thumb often hides an unrecognized nasal obstruction, and a Class II with open bite relapses if the obstruction persists. An ENT opinion belongs in the workup.
Vertical growth pattern
Weak muscles go with excessive vertical growth and open bite; strong muscles with a short face and deep bite. A posterior (clockwise) growth rotation increases anterior face height and moves the chin back. Our article on the mandibular plane angle describes the high-angle patient in detail.
Lateral (posterior) open bite
Lateral open bites are rare. The courses attribute them mainly to a lateral tongue interposition or to ankylosis. One more cause must be kept in mind: primary failure of eruption (PFE), a rare genetic disorder that mostly affects the first and second molars and causes a unilateral or bilateral posterior open bite. Applying active orthodontic forces to these teeth is known to cause local ankylosis, which makes the correct diagnosis essential before any traction (Söz et al., 2025, Turk J Orthod, PubMed).
Diagnosis: what to examine
Clinical examination
Boileau lists the points to record:
- amount and extent of the open bite;
- incisor inclination: proclined incisors signal a tongue thrust and are a favorable factor, since retroclining them extrudes them relatively;
- curve of Spee, often exaggerated in the maxilla;
- upper incisor exposure at rest (about 2 mm normally), which reveals the compensation already present;
- height and thinness of the lower incisor alveolar process, which set the limit of what orthodontics can do;
- tongue and lips, at rest and in function.
Cephalometrics
The lateral cephalogram answers one question: is there a skeletal vertical excess behind the open bite? Read the indicators together.
| Indicator | Reference | Toward open bite |
|---|---|---|
| FMA (Tweed, Schudy) | 22° to 28° | Above 28°: hyperdivergent |
| SN-GoGn (Steiner) | 32° ± 5° | Above 37°: hyperdivergent |
| Facial height index (posterior / anterior) | 0.65 to 0.75 | Below 0.65: tendency to open bite |
The FMA cut-offs vary between sources (one course leaves 20-22° unclassified, Boileau does not). Three reading rules: never conclude on a single indicator; look at Björk’s structural signs (thin condylar neck directed backward, straight mandibular canal, antegonial notch, symphysis oblique downward and backward); and distinguish a state (hyperdivergence) from a change (posterior rotation between two cephalograms). Our cephalometric tracing guide covers the landmarks, and the free cephalometric analysis tool calculates FMA and SN-GoGn from the points you place.
Treatment principles by age
The courses sum it up in one sentence: during growth, functional rehabilitation and growth control; in adults, orthodontics for a dentoalveolar open bite, orthodontic-surgical treatment for a skeletal one.
| Stage | Key points from the knowledge base |
|---|---|
| Primary dentition | Look for functional factors; gentle approach to sucking habits; pacifier weaned gradually, around 3 years according to the EMC |
| Mixed dentition | Remove the habit or dysfunction; without skeletal excess, a functional open bite closes spontaneously in 75 to 80% of cases during the period of strong alveolar growth (up to 8-9 years) |
| Growing permanent dentition | Same logic; if fixed appliances are needed, vertical molar control (palatal bar, high-pull headgear, miniscrews) |
| Adult | Dentoalveolar: orthodontics; skeletal: orthodontic-surgical; palatal miniscrew with transpalatal arch for molar intrusion |
Stopping the habit
The courses insist on the method: dialogue, parental cooperation, rewards, a success calendar, and no scolding, punishment or guilt, which risk a substitute habit. The timing differs between sources: rarely before 6 to 7 years for the thumb according to the D.U., no fixed age for Boileau.
The evidence is thin. A Cochrane review of 6 trials (252 children), all at high risk of bias, found low-quality evidence that orthodontic appliances (palatal crib or arch) and psychological interventions help children stop digit sucking (Borrie et al., 2015, Cochrane Database Syst Rev, PubMed). For the open bite itself, crib therapy corrected about 3.1 mm of overbite in a meta-analysis, but most dental effects seemed to be lost over time (Feres et al., 2016, Eur J Orthod, PubMed). Another Cochrane review found only weak evidence for any early orthodontic or orthopedic treatment of open bite in children (Lentini-Oliveira et al., 2014, Cochrane Database Syst Rev, PubMed); a mixed-dentition review could not pool data at all (Pisani et al., 2016, Prog Orthod, PubMed).
Rehabilitation follows the removal of the obstacle: breathing first, then swallowing and tongue posture. Sources differ on "function before form": the courses make it a rule, while Boileau restricts it to small anomalies and considers myotherapy contraindicated in extreme vertical patterns. Our article on oral habits and dysfunctions (in French) goes further.
When the open bite does not close by itself
- Without skeletal excess: orthodontic extrusion on fixed appliances with anterior vertical elastics, after the root apices have closed, with light (about 25 g) continuous forces (Boileau).
- In the hyperdivergent patient: treating the hyperdivergence (controlling molar eruption) closes most of the open bite; additional incisor extrusion must stay very limited, bounded by the symphysis and alveolar bone below and by incisor exposure and the gingival smile above. No orthopedic appliance corrects hyperdivergence; the realistic aim is not to make it worse.
- Miniscrews (TADs) for molar intrusion: a 2025 meta-analysis of 12 studies found a pooled molar intrusion of 1.70 mm, with high heterogeneity (Burgos-Lancero et al., 2025, J Clin Med, PubMed).
- Surgery: in the knowledge base, posterior maxillary impaction with mandibular autorotation remains the reference procedure for a skeletal open bite, considered more stable than closure by mandibular sagittal split osteotomy. A meta-analysis of 16 cohort studies found the most favorable overbite change after bimaxillary surgery, a smaller positive change after maxillary surgery, and some relapse with mandibular surgery (Wang et al., 2022, Eur J Orthod, PubMed). See our article on orthognathic surgery indications (in French).
Mechanics that make an open bite worse
Extrusion is the easiest movement to obtain, especially with weak muscles, so any extrusive mechanics is suspect:
- maxillary expansion tends to open the mandibular angle; the effect is small and partly transient according to Boileau and Bassigny, but it calls for caution in hyperdivergent patients;
- Class II elastics have a vertical component that opens the angle;
- cervical headgear, distalization of the posterior segments and molar-anchored tip-back mechanics are to be avoided;
- an activator alone produces a parasitic clockwise rotation, hence its association with high-pull headgear; a Class III activator is contraindicated in open bite.
High-pull headgear, palatal bars and miniscrews, by contrast, restrain or intrude the molars.
Stability and relapse
Stability depends mainly on two factors: remaining growth and the removal of the cause (habit, tongue, breathing). Retention must therefore target function as well as the teeth.
- In a meta-analysis of 21 case series, a positive overbite was maintained at 12 months or more in about 75% of non-surgical and 82% of surgical patients (Greenlee et al., 2011, Am J Orthod Dentofacial Orthop, PubMed). Boileau cites this meta-analysis. The two groups came from different studies and populations, so they cannot be compared directly.
- After molar intrusion on miniscrews, the overbite relapsed by 1.23 mm on average after a mean follow-up of 2.5 years, with molar relapse of about 12% in the maxilla and 27.2% in the mandible; certainty was low to very low (González Espinosa et al., 2020, Prog Orthod, PubMed).
For a Class I open bite, often functional, Boileau recommends tongue and lip rehabilitation completed by appliance removal, with a possible nighttime tongue appliance. In finishing, for a hyperdivergent patient with an open bite, the courses aim for an overcorrected overbite (more than 2 mm) with fairly upright incisors.
Leaving an open bite untreated is not neutral either: in adults, severe hyperdivergence and open bite favor joint and periodontal problems in the long term, and the absence of anterior guidance is among the profiles at risk of temporomandibular dysfunction.
In practice
- Record the overbite in millimeters and the extent of the open bite (incisors, canines, premolars, molars).
- Note incisor inclination, incisor exposure at rest, the smile line and the thickness of the lower alveolar process.
- Look systematically for sucking habits, tongue interposition, a short frenum and mouth breathing; ask for an ENT opinion when needed.
- Read FMA, SN-GoGn and the facial height index together, then Björk’s signs; report any disagreement rather than concluding.
- In a lateral open bite, rule out primary failure of eruption before applying force.
- In the mixed dentition without skeletal excess, remove the cause and reassess before placing an appliance.
- In hyperdivergent patients, avoid extrusive mechanics and plan vertical molar control.
- Plan functional retention and compare FMA and the facial height index between cephalograms.
Frequently asked questions
What causes an open bite?
Usually a combination: sucking habits (thumb, pacifier), tongue interposition, mouth breathing, and a vertical (hyperdivergent) growth pattern. A long-lasting, daily habit carries the highest risk. An orthodontic examination is needed to tell which factor dominates in a given patient.
Does an open bite from thumb sucking close on its own?
Often, if the habit stops during the period of strong alveolar growth and there is no skeletal vertical excess: the courses report spontaneous closure in 75 to 80% of cases up to 8-9 years. Check that a secondary tongue thrust or mouth breathing does not take over.
How do you tell a dental open bite from a skeletal one?
By a set of signs: extent (incisors only or reaching the premolars), measured vertical pattern (FMA, SN-GoGn, facial height index), Björk’s signs, lower face height, incisor inclination and exposure. The two forms are often combined, and no single indicator decides.
Can an open bite be fixed without surgery?
Yes, when it is dentoalveolar, and in many growing patients. In adults with a skeletal open bite, molar intrusion on miniscrews is an option studied as an alternative, but the decision between orthodontics and surgery depends on the facial height index, the extent, the compensation already present and the periodontium.
Does an open bite come back after treatment?
It can. About three quarters of non-surgical and four fifths of surgical cases kept a positive overbite in a meta-analysis of case series (Greenlee et al., 2011). Relapse is more likely if the habit, tongue posture or breathing problem persists.
With GS Ortho
In GS Ortho, the 12-panel guided diagnostic studio has you record the overbite and the extent of the open bite in the clinical examination, then compares them with the vertical pattern measured on the cephalogram, where AI places 29 landmarks that you check and correct before validating. Functions and habits are examined in the same workflow, and the decision stays yours. For a case on the border between orthodontics and surgery, "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.