Merck Manual

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Bernard J. Hennessy

, DDS, Texas A&M University, College of Dentistry

Reviewed/Revised Feb 2022 | Modified Sep 2022
Topic Resources

Malocclusion is abnormal contact between the maxillary and mandibular teeth.

Normally, each dental arch consists of teeth in side-by-side contact, forming a smooth curve, with the maxillary anterior teeth overlying the upper third of the mandibular anterior teeth (see figure Identifying the teeth Identifying the teeth Identifying the teeth ). The buccal (outer) cusps of the maxillary posterior teeth are external to the corresponding cusps of the mandibular posterior teeth. In most cases, the anterior buccal cusp of the maxillary 1st permanent molar fits into the anterior buccal groove of the mandibular 1st molar. Because the outer parts of all maxillary teeth are normally external to the mandibular teeth, the lips and cheeks are displaced from between the teeth so that they are not bitten. The lingual (inner) surfaces of the lower teeth form a smaller arch than those of the upper teeth, confining the tongue and minimizing the likelihood of its being bitten. All the maxillary teeth should contact the corresponding mandibular teeth, so that the masticatory forces (which may be > 150 pounds [> 1000 kilopascals] in the molar region and 250 pounds [> 1700 kilopascals] when clenching during sleep) are widely distributed. If these forces are applied to only a few teeth, those teeth may eventually become mobile or show abnormal wear.

Identifying the teeth

The numbering system shown is the one most commonly used in the United States.

Identifying the teeth

Etiology of Malocclusion

Causes of malocclusion include

  • Size mismatch between jaw and teeth

  • Certain oral habits (eg, thumb-sucking, tongue thrusting)

  • Missing teeth

  • Certain congenital defects

Malocclusion most often results from jaw and tooth size discrepancies (ie, the jaw is too small or the teeth are too large for the jaw to accommodate them in proper alignment). People who habitually suck their thumb or push their tongue up against their front teeth may cause gradual protrusion of the upper incisors. When permanent teeth are lost, adjacent teeth may shift and opposing teeth may extrude, causing malocclusion unless a bridge, implant, or partial denture (see Dental Appliances Dental Appliances Teeth may be lost to dental caries, periodontal disease, or trauma or may be removed when treatment fails. Missing teeth may cause cosmetic, phonation, and occlusal problems and may allow movement... read more ) is worn to prevent these movements. When children lose deciduous teeth prematurely, the teeth more posterior in the arch or the permanent 1st molars often drift forward, leaving insufficient space for other permanent teeth to erupt. Malocclusion after facial trauma Fractures of the Mandible and Midface Blunt facial trauma can fracture the jaw and other bones of the midface. Symptoms depend on the location of the fracture. A dental x-ray or CT is diagnostic. Treatment may include surgery and/or... read more Fractures of the Mandible and Midface may indicate tooth displacement and/or alveolar bone or jaw fractures. In ectodermal dysplasia, cleft palate Cleft Lip and Cleft Palate An oral-facial cleft is a birth defect in which the lip, the roof of the mouth, or both do not close in the midline and remain open, creating a cleft lip and/or cleft palate. These defects are... read more Cleft Lip and Cleft Palate , or Down syndrome Down Syndrome (Trisomy 21) Down syndrome is an abnormality of chromosome 21 that can cause intellectual disability, microcephaly, short stature, and characteristic facies. Diagnosis is suggested by physical anomalies... read more Down Syndrome (Trisomy 21) , malocclusions may result from having too few teeth.

Evaluation of Malocclusion

  • Physical examination

Occlusion is checked on both sides of the mouth by retracting each cheek with a tongue depressor while telling the patient to close on the back teeth; telling patients to bite may mistakenly cause them to close on their incisors (as in biting a piece of fruit), which gives the false appearance of malocclusion of the back teeth. Malocclusion sometimes is identified as early as the first dental visit (age 1 year). Early identification may make later treatment easier and more effective.

Treatment of Malocclusion

  • Dental modification

  • Orthodontic appliances (braces or aligners)

  • Sometimes surgery

Malocclusions are corrected primarily for aesthetic and psychologic reasons. However, in some cases, treatment may increase resistance to caries (by improving ability to clean realigned teeth), to anterior tooth fracture Fractured and Avulsed Teeth Fractured and avulsed teeth are dental emergencies that require immediate treatment. Fractures are divided by depth into those that Affect only the enamel Expose the dentin Expose the pulp read more , and, possibly, to periodontal disease Periodontitis Periodontitis is a chronic inflammatory oral disease that progressively destroys the tooth-supporting apparatus. It usually manifests as a worsening of gingivitis and then, if untreated, with... read more Periodontitis or stripping of the gingiva on the palate. Treatment may improve speech and mastication as well. Occlusion can be improved by aligning teeth properly, by selectively grinding teeth and restorations that contact prematurely, and by inserting crowns or onlays to build up tooth surfaces that are below the plane of occlusion.

Braces (metal orthodontic appliances) apply a continuous mild force to teeth to gradually remodel the surrounding alveolar bone. Extraction of one or more permanent teeth (usually a 1st premolar) may be needed to allow other teeth to be repositioned or to erupt into a stable alignment. After the teeth are properly aligned, the patient wears either a fixed retainer (wire bonded to the back of the teeth) or a removable retainer. Removable retainers are made from plastic-and-wire or vacuum-formed plastic and are worn 24 hours a day initially, then only at night for 2 to 3 years.

Tooth aligners are a set of clear plastic appliances (similar to retainers) that are used in a specific order to gradually move teeth (up to 0.3 mm per aligner). Each aligner is worn for about 2 weeks and then changed for a new one until the misalignment is corrected. As with traditional braces, a retainer is used to keep the teeth from shifting back.

When orthodontic treatment alone is insufficient, surgical correction of jaw abnormalities contributing to malocclusion (orthognathic surgery) may be indicated.

NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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