Malocclusion

A malocclusion is a misalignment or incorrect relation between the teeth of the two dental arches when they approach each other as the jaws close. The term was coined by Edward Angle, the "father of modern orthodontics",[1] as a derivative of occlusion. This refers to the manner in which opposing teeth meet (mal- + occlusion = "incorrect occlusion").

Malocclusion
Malocclusion in 10-year-old girl
SpecialtyOrthodontics 

Signs and symptoms

Malocclusion is a common finding,[2][3] although it is not usually serious enough to require treatment. Those who have more severe malocclusions, which present as a part of craniofacial anomalies, may require orthodontic and sometimes surgical treatment (orthognathic surgery) to correct the problem.

The ultimate goal of orthodontic treatment is to achieve a stable, functional and aesthetic alignment of teeth which serves to better the patients dental and total health. The symptoms which arise as a result of malocclusion derive from a deficiency in one or more of these categories.[4]

The symptoms are as follows:

  • Tooth decay (caries): misaligned teeth will make it more difficult to maintain oral hygiene. Children with poor oral hygiene and diet will be at an increased risk.
  • Periodontal disease: irregular teeth would hinder the ability to clean teeth meaning poor plaque control. Additionally, if teeth are crowded, some may be more buccally or lingually placed, there will be reduced bone and periodontal support. Furthermore, in Class III malocclusions, mandibular anterior teeth are pushed labially which contributes to gingival recession and weakens periodontal support.
  • Trauma to anterior teeth: Those with an increased overjet are at an increased risk of trauma. A systematic review found that an overjet of greater than 3mm will double the risk of trauma.
  • Masticatory function: people with anterior open bites, large increased & reverse overjet and hypodontia will find it more difficult to chew food.
  • Speech impairment: a lisp is when the incisors cannot make contact, orthodontics can treat this. However, other forms of misaligned teeth will have little impact on speech and orthodontic treatment has little effect on fixing any problems.  
  • Tooth impaction: these can cause resorption of adjacent teeth and other pathologies for example a dentigerous cyst formation.  
  • Psychosocial wellbeing: malocclusions of teeth with perceived poor aesthetics can have a significant effect on self-esteem. This is subjective in nature and will vary widely, being subject cultural and racial influences. [4][5]

Malocclusions may be coupled with skeletal disharmony of the face, where the relations between the upper and lower jaws are not appropriate. Such skeletal disharmonies often distort sufferer's face shape, severely affect aesthetics of the face, and may be coupled with mastication or speech problems. Most skeletal malocclusions can only be treated by orthognathic surgery.

Classification

Depending on the sagittal relations of teeth and jaws, malocclusions can be divided mainly into three types according to Angle's classification system published 1899. However, there are also other conditions, e.g. crowding of teeth, not directly fitting into this classification.

Many authors have tried to modify or replace Angle's classification. This has resulted in many subtypes and new systems (see section below: Review of Angle's system of classes).

A deep bite (also known as a Type II Malocclusion) is a condition in which the upper teeth overlap the lower teeth, which can result in hard and soft tissue trauma, in addition to an effect on appearance.[6] It has been found to occur in 15-20% of the US population.[7]

An open bite is a condition characterised by a complete lack of overlap and occlusion between the upper and lower incisors.[8] In children, open bite can be caused by prolonged thumb sucking.[9] Patients often present with impaired speech and mastication.[10]

Overbites

This is a vertical measurement of the degree of overlap between the maxillary incisors and the mandibular incisors. There are three features that are analysed in the classification of an overbite:

  • Degree of overlap: edge to edge, reduced, average, increased
  • Complete or incomplete: whether there is contact between the lower teeth the opposing teeth/tissue (hard palate or gingivae) or not.
  • Whether contact is traumatic or atraumatic

An average overbite is when the upper anterior teeth cover a third of the lower teeth. Covering less than this is described as ‘reduced’ and more than this is an ‘increased’ overbite. No overlap or contact is considered an ‘anterior open bite’. [4][5][11]

Crowding

Crowding is defined by the amount of space that would be required in order for the teeth to be in correct alignment. It is obtained in two ways. 1) by measuring the amount of space required and reducing this from calculating the space available via the width of the teeth. Or 2) by measuring the degree of overlap of the teeth.

The following criteria is used:

  • 0-4mm = Mild crowding
  • 4-8mm = Moderate crowding
  • >8mm = Severe crowding [5][4]

Angle's classification method
Class I with severe crowding and labially erupted canines
Class II molar relationship

Edward Angle, who is considered the father of modern orthodontics, was the first to classify malocclusion. He based his classifications on the relative position of the maxillary first molar.[12] According to Angle, the mesiobuccal cusp of the upper first molar should align with the buccal groove of the mandibular first molar. The teeth should all fit on a line of occlusion which, in the upper arch, is a smooth curve through the central fossae of the posterior teeth and cingulum of the canines and incisors, and in the lower arch, is a smooth curve through the buccal cusps of the posterior teeth and incisal edges of the anterior teeth. Any variations from this resulted in malocclusion types. It is also possible to have different classes of malocclusion on left and right sides.

  • Class I: Neutrocclusion Here the molar relationship of the occlusion is normal but the incorrect line of occlusion or as described for the maxillary first molar, but the other teeth have problems like spacing, crowding, over or under eruption, etc.
  • Class II: Distocclusion (retrognathism, overjet, overbite) In this situation, the mesiobuccal cusp of the upper first molar is not aligned with the mesiobuccal groove of the lower first molar. Instead it is anterior to it. Usually the mesiobuccal cusp rests in between the first mandibular molars and second premolars. There are two subtypes:
    • Class II Division 1: The molar relationships are like that of Class II and the anterior teeth are protruded.
    • Class II Division 2: The molar relationships are Class II but the central are retroclined and the lateral teeth are seen overlapping the centrals.
  • Class III: Mesiocclusion (prognathism, Anterior crossbite, negative overjet, underbite) In this case the upper molars are placed not in the mesiobuccal groove but posteriorly to it. The mesiobuccal cusp of the maxillary first molar lies posteriorly to the mesiobuccal groove of the mandibular first molar. Usually seen as when the lower front teeth are more prominent than the upper front teeth. In this case the patient very often has a large mandible or a short maxillary bone.

Review of Angle's system of classes and alternative systems

A major disadvantage of classifying malocclusions according to Angle's system is that it only takes into consideration the two-dimensional viewing along a spatial axis in the sagittal plane in the terminal occlusion, even though occlusion problems are, in principle, three-dimensional. Deviations in other spatial axes, asymmetric deviations, functional faults and other therapy-related features are not recognised. Another shortcoming is the lack of a theoretical basis of this purely descriptive classification system. Among the much discussed weaknesses of the system is the fact that it only considers the static occlusion, that it does not take into account the development and causes (aetiology) of occlusion problems and it disregards the proportions (or relationships in general) of teeth and face.[13] Thus, numerous attempts have been made to modify the Angle system or to replace it completely with a more efficient one,[14] but Angle's classification continues to prevail mainly because of its simplicity and clarity.

Well-known modifications to Angle's classification date back to Martin Dewey (1915) and Benno Lischer (1912, 1933). Alternative systems have been suggested by, among others, Simon (1930, the first three-dimensional classification system), Jacob A. Salzmann (1950, with a classification system based on skeletal structures) and James L. Ackerman and William R. Proffit (1969).[15]

Crowding of teeth

Crowding of teeth is where there is insufficient room for the normal complement of adult teeth.

Causes

Extra teeth, lost teeth, impacted teeth, or abnormally shaped teeth have been cited as causes of malocclusion. A small underdeveloped jaw, caused by lack of masticatory stress during childhood, can cause tooth overcrowding.[16][17] Ill-fitting dental fillings, crowns, appliances, retainers, or braces as well as misalignment of jaw fractures after a severe injury are other causes. Tumors of the mouth and jaw, thumb sucking, tongue thrusting, pacifier use beyond age 3, and prolonged use of a bottle have also been identified as causes.[18]

In an experiment on two groups of rock hyraxes fed hardened or softened versions of the same foods, the animals fed softer food had significantly narrower and shorter faces and thinner and shorter mandibles than animals fed hard food.[16] Experiments have shown similar results in other animals, including primates, supporting the theory that masticatory stress during childhood affects jaw development. Several studies have shown this effect in humans.[19][20] Children chewed a hard resinous gum for two hours a day and showed increased facial growth.[17]

During the transition to agriculture, the shape of the human mandible went through a series of changes. The mandible underwent a complex series of shape changes not matched by the teeth, leading to incongruity between dental and mandibular form. These changes in human skulls may have been "driven by the decreasing bite forces required to chew the processed foods eaten once humans switched to growing different types of cereals, milking and herding animals about 10,000 years ago."[19][20]

Treatment

Crowding of the teeth is treated with orthodontics, often with tooth extraction, clear aligners, or dental braces, followed by growth modification in children or jaw surgery (orthognathic surgery) in adults. Surgery may be required on rare occasions. This may include surgical reshaping to lengthen or shorten the jaw (orthognathic surgery). Wires, plates, or screws may be used to secure the jaw bone, in a manner similar to the surgical stabilization of jaw fractures. Very few people have "perfect" alignment of their teeth. However, most problems are very minor and do not require treatment.[18]

Class II Division 1

Low- to moderate- quality evidence suggests that providing early orthodontic treatment for children with prominent upper front teeth (class II division 1 malocclusion) is more effective for reducing the incidence of incisal trauma than providing one course of orthodontic treatment in adolescence.[21] There do not appear to be any other advantages of providing early treatment when compared to late treatment.[21] Low-quality evidence suggests that, compared to no treatment, late treatment in adolescence with functional appliances is effective for reducing the prominence of upper front teeth.[21]

Class II Division 2

There is no evidence from clinical trials to recommend or discourage any type of orthodontic treatment to correct deep bite and retroclined upper front teeth (Class II division 2 malocclusion) in children.[6] A 2018 Cochrane systematic review anticipated that the evidence base supporting treatment approaches for Class II division 2 malocclusion is not likely to improve due to the low prevalence of the condition and the ethical difficulties in recruiting people to participate in a randomized controlled trials for treating this condition.[6]

Class III

The British Standard Institute (BSI) classify class 3 incisor relationship as the lower incisor edge lies anterior to the cingulum plateau of the upper incisors, with reduced or reversed over jet.[22] The skeletal facial deformity is characterised by mandibular prognathism, maxillary retrognathism or a combination of the two. This effects 3-8% of UK population with a higher incidence in Asia. [23]

One of the main reasons for correcting Class 3 malocclusion is aesthetics and function. This can have a psychological impact on the person with malocclusion resulting in speech and mastication problems as well. Saying this, with mild class 3 cases, the patient is quite accepting of the aesthetics and the situation is monitored to see the progression of skeletal growth.[24]

Studies have indicated similar maxillary and mandibular skeletal changes during prepubertal, pubertal and post pubertal stages showing that class 3 malocclusion is established before the prepubertal stage. One treatment option is the use of growth modification appliances such as the Chin Cap which has greatly improved the skeletal framework in the initial stages. However majority of cases are shown to relapse into inherited class 3 malocclusion during the pubertal growth stage and also when the appliance is removed after treatment.[25]

Another approach is to carry out orthognathic surgery; surgical correction of facial skeleton to restore proper anatomical and functional relationship. An example of this is bilateral sagittal split osteotomy (BSSO) which is indicated by horizontal mandibular excess. This involves surgically cutting through the mandible and moving the fragment forward or backwards for desired function and is supplemented with pre and post surgical orthodontics to ensure correct tooth relationship. Although the most common surgery of the mandible it comes with several complications including: bleeding from inferior alveolar artery, unfavourable splits, condylar resorption, avascular necrosis and worsening of temperomandibular joint.[26]

Another approach is to carry out orthodontic camouflage in patients with mild skeletal discrepancies. This is a less invasive approach that uses orthodontic brackets to correct malocclusion and try to hide the skeletal discrepancy. Due to limitations of orthodontics, this option is more viable for patients who are not as concerned about the aesthetics of their facial appearance and are happy to address the malocclusion only, as well as avoiding the risks which come with orthognathic surgery.[27]

Deep bite
The most common corrective treatments available are fixed or removal appliances (such as dental braces), which may or may not require surgical intervention.[6]
Open bite
An open bite malocclusion is when the upper teeth don’t overlap the lower teeth. When this malocclusion occurs at the front teeth it is known as anterior open bite. An open bite is a difficult malocclusion to treat due to the multifactorial causes and relapse being a major concern particularly for an anterior open bite.[28] Therefore it is important to carry out a thorough initial assessment in order to obtain a diagnosis where a suitable treatment plan can be tailored to.[28] It is important to take into consideration any habitual risk factors as this is crucial for a successful outcome without relapse. Treatment approach defers for adults and children/ adolescents. These methods include behaviour changes, appliances and surgery. Treatment for adults include a combination of extractions, fixed appliances, intermaxillary elastics and orthonagthic surgery.[29] For children, orthodontics is usually used as they are still growing. However, if the children is with mixed dentition, the malocclusion may resolve on its own as the permanent teeth erupt. Furthermore, should the malocclusion be caused by childhood habits such as thumb or pacifier sucking, it may result in resolution as the habit is stopped. Some of the treatment options for patients who are still growing include posterior bite blocks and headgear appliances.

Tooth size discrepancy

To establish appropriate alignment and occlusion, the sizes of upper and lower front teeth, or upper and lower teeth in general, need to be proportional. Inter-arch tooth size discrepancy (TSD) is defined as a disproportion in the mesio-distal dimensions of teeth of opposing dental arches, which can be seen in 17% to 30% of orthodontic patients.[30][31]

Other conditions
Further information: Open bite malocclusion
Open bite treatment after eight months of braces.

Other kinds of malocclusions can be due to tooth size or horizontal, vertical, or transverse skeletal discrepancies, including skeletal asymmetries. Long faces may lead to open bite malocclusion, while short faces can be coupled to a Deep bite malocclusion. However, there are many other more common causes for open bites (such as tongue thrusting and thumb sucking), and likewise for deep bites. The upper or lower jaw can be overgrown or undergrown, leading to Class II or Class III malocclusions that may need corrective jaw surgery or orthognathic surgery as a part of overall treatment, which can be seen in about 5% of the general population.[32][33][34]

Cause

There are 3 general causative factors of malocclusion. These are skeletal factors, muscle factors and dental factors.

  1. Skeletal factors: size, shape and relative positions of the upper and lower jaws. These variations are caused by genetic and environmental factors. Some environmental factors include masticatory muscles, mouth breathing and head posture.
  2. Muscle factors: form and function of the muscles that surround the teeth such as lips, cheeks and tongue
  3. Dental factors: size of the teeth in relation to the size of the jaws

Oral habits and pressure on teeth or the maxilla and mandible may also cause malocclusion.[35][36]

In the active skeletal growth,[37] mouthbreathing, finger sucking, thumb sucking, pacifier sucking, onychophagia (nail biting), dermatophagia, pen biting, pencil biting, abnormal posture, deglutition disorders and other habits greatly influence the development of the face and dental arches.[38][39][40][41][42]

Pacifier sucking habits are also correlated with otitis media.[43][44]

Dental caries, periapical inflammation and tooth loss in the deciduous teeth alter the correct permanent teeth eruptions.

Malocclusion can occur in primary and secondary dentition. In primary dentition malocclusion is caused by:

  • Underdevelopment of the dentoalvelor tissue.
  • Over development of bones around the mouth.
  • Cleft lip and palate.
  • Overcrowding of teeth.
  • Abnormal development and growth of teeth.

In secondary dentition malocclusion is caused by:

  • Periodontal disease.
  • Overeruption of teeth.[45]
  • Premature and congenital loss of missing teeth

See also

References
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Classification
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