Overjet | |
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Overjet or horizontal overlap. | |
Specialty | Dentistry |
Overjet is the extent of horizontal (anterior-posterior) overlap of the maxillary central incisors over the mandibular central incisors. In class II (division I) malocclusion the overjet is increased as the maxillary central incisors are protruded.
Class II Division I is an incisal classification of malocclusion where the incisal edge of the mandibular incisors lie posterior to the cingulum plateau of the maxillary incisors with normal or proclined maxillary incisors (British Standards Index, 1983). There is always an associated increase in overjet. In the Class II Division 2 incisal classification of malocclusion, the lower incisors occlude posterior to the cingulum plateau of the upper incisors and the upper central incisors are retroclined. The overjet is usually minimal but it may be increased.
Overjet (mm) | Incidence (%) |
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5 | 22 |
9 | 24 |
>9 | 44 |
In 1895 Edward Angle, a mid-North American dentist, published a book on the classification of bad bites - a term he latinised and popularised as malocclusion.
The modern discipline of orthodontics was begun by the establishment of the Angle classification of adult first molar relationship. This established that all forms of a bad bite were premised on a natural redundancy of premolar, and in particular third molar teeth (wisdom teeth). Eventually the dual dental specialties of orthodontic and oral surgery were popularised and came to work together in coordinating adolescent dental crowding by the treatment duopoly of extracting excessive teeth, and orthodontically straightening the remaining - especially front - teeth.
Once an assessment is made that there is dental crowding (a bad bite), the Angle classification of malocclusion is based only on an assessment of relative position of the upper and lower first adult molar.
Class I dental crowding is with a normal molar relationship. Class II dental crowding is with a molar relationship where the relative position of the lower molar is behind the Class I position. Class III is with the abnormal molar position being forward of the normal Class I position.
Classifying incisal relationship in the bad bite is made in profile and only of the relative positions upper and lower central incisors.
The terms used relate to visual or radiological (lateral cephalometric) measurements of dental overjet and dental overbite.
This describes the incisal relationship where there is both zero overjet and zero overbite, and where the incisal edge of both upper and lower central incisors are in direct edge to edge contact. It is considered a traumatic bite in that it accelerates wear and abnormal acquired incisal form, and unaesthetic smile development.
This is where there is no contact between the biting surfaces of the incisor teeth. This prevents both biting and incising. There is a negative incisal overbite, and is independent of overjet measurement.
This incisal relationship is usually where there is a long overjet and deep incisal overbite, and is always in company with a Class II first molar relationship.
Instances of long incisal overjet are also associated with Class I or Class III molar relationships.
This incisal relationship is where there is virtually no incisal overjet, and a very deep incisal overbite, and is always associated with a class II molar relationship.
In essence, Class II Div 2 malocclusion is a common description given to extreme crowding, or backward collapse of the anterior teeth and is a common presenting complaint by concerned parents of their child's tooth crookedness.
Class II malocclusion, either with prominent upper incisors (Class II division 1) or exceedingly crowded and collapsed upper incisors (Class II division 2) are the dominant presenting orthodontic malocclusion types that present to orthodontic offices works wide. They are also the dominant pattern of dental crowding leading to orthodontic premolar extractions, and later impacted wisdom teeth removal by oral surgeons.
The Angle classification is merely a means of describing common states or forms or patterns of adolescent dental crowding. These patterns emerge as baby (deciduous) teeth are lost, and a child's face and overall body are growing.
Thus the development of malocclusion and of dental crowding have come to be rationalised as distinct conditions defined by what was originally an arbitrary and simple 19th century classification. As the myth of the veracity of the classification system became entrenched more formally as orthodontic diagnoses, orthodontists attempted to apply epidemiological study as to why these patterns may exist or have become prevalent in modern society.
The overriding premises of the overwhelming majority of these studies are that 1. Malocclusion classifications of dental crowding are in fact diagnostic or disease states, and exist mostly and independently of any other medical condition 2. That malocclusion occurs as a feature or expression of childhood or adolescent growth, and that treatments can be directed at modifying growth and thus improve the abnormal development of malocclusion 3. That dental crowding is due to a redundant number of human teeth, and that this redundancy is due to a modern softer diet compared to a more primitive past, and is more conservatively managed by a combination of dental extractions and orthodontic treatments 4. That being a disease, and that malocclusion and dental crowding is a feature of tooth number redundancy, or oversize of permanent teeth, that epidemiological studies of the natural rates of the various classification states can be made. 5. That there are no other common associated features of malocclusion outside of the dental relationship. Malocclusion exists as a dental disease specific to itself; and that if there are other conditions or anatomical observations, they exist only to aggravate or impact upon the complexity of the malocclusion, or the orthodontic treatment of it.
In orthodontic studies, a number of genetic and environmental factors are postulated to contribute to a Class II division 1 malocclusion: [8]
Whenever orthodontic treatment is to be considered, it is essential to carry out a complete patient assessment to get a clear picture of the patient's medical and dental condition before any irreversible treatment (such as extractions) are carried out or the orthodontic treatment causes more harm than benefit. The assessment is also key in establishing the correct diagnosis and likely cause of the malocclusion.
This assessment should include the following: [9]
The Extra Oral Examination Should Include: [9]
The Intra Oral Examination Should Include:
The presence of dental disease precludes any active orthodontic treatment, even if the malocclusion is severe. This is because orthodontic appliances accumulate plaque and combining this with a high carbohydrate diet and poor oral hygiene can result in extensive decalcification of the teeth and accelerated bone loss if you try to move the teeth when there is active gingivitis and periodontal disease. [10]
Overjet is measured from the labial surface of the most prominent incisor to the labial surface of the mandibular incisor. Normally, this measurement is 2–4 mm (0.079–0.157 in). If the lower incisor is anterior to the upper incisors, the overjet is given a negative value. [11] In the UK, an overjet is generally described as increased if it is >3.5 mm (0.14 in). The Index of Orthodontic Treatment Need rates overjet highly on its weighting system, second behind missing teeth. It then grades severity of overjet as: [12]
Radiographs can aid your diagnosis. Any radiographs taken must be clinically justified in accordance with the IRMER Regulations 2000. Radiographs may help by giving you more information on: [11]
Untreated overjet can cause the following health complications:
The Twin Block appliance has been used in most studies evaluating functional appliance treatment as it is considered to be the 'gold standard' against which other appliances should be tested. When compared to other functional appliances, the Twin Block appliance was found to produce a statistically significant reduction in skeletal base discrepancy (ANB = -0.68 degrees; 95% CI -1.32 to -0.04) when compared to other functional appliances, although there was no significant effect from the type of appliance on the final overjet. [5] The Twin Block has also been shown to cause clinically significant beneficial changes to the soft tissues. [21]
There are problems associated with the Twin Block including excessive lower incisor proclination, a significant failure-to-complete rate of 25%, [22] and a breakage rate of up to 35%. Lower incisor proclination occurs with most functional appliances and this must be considered during treatment planning and monitored throughout treatment. Twin Block appliances can also cause an increase in vertical dimension, which may be desirable in some cases but may not be beneficial in patients with an increased lower anterior face height. In these patients, careful control of the vertical dimension should be planned. [23]
The success rate of the Herbst appliance, often considered to be a 'compliance-free' appliance, was found to be much higher than the Twin Block in one study, with a failure-to-complete rate of 12.9%. This is approximately half that of the Twin Block so may be considered in patients where compliance is predicted to be difficult. However, the Herbst is considerably more expensive and demonstrated a higher breakage rate so that the benefits of reduced compliance requirements must be balanced against this. [24]
Headgear exerts force to the dentition and basal bones via extra-oral traction attached directly to bands on the teeth or to a maxillary splint or functional appliance. The effects are mainly dento-alveolar with some skeletal effect through restriction of maxillary downward and forward growth. [25] Several studies found an additional small effect on mandibular growth when headgear is used in conjunction with an anterior bite plane. [26]
The effect of headgear treatment, as early treatment, was compared to one-phase treatment, carried out later, in a study of two trials. Both found a significant reduction in overjet and improvement in skeletal relationship after headgear treatment. [27] There was no difference in any outcomes that could be attributed to treatment timing, with the exception of risk of trauma where the later treatment group showed twice the risk of incisal trauma. [5] The Cochrane review summarizes that 'no significant differences, with respect to final overjet, ANB, or ANB change, were found between the effects of early treatment with headgear and the functional appliances'. However, headgear is highly reliant on good patient compliance, with 12−14 hours a day of wearing required to achieve the effects described.
Fixed appliances can be used alone or in combination with extractions or temporary anchorage devices to retract the maxillary teeth to correct a Class II division 1 malocclusion by dental means only. Class II intermaxillary elastics are used to retract the maxillary teeth against the mandibular teeth, with reciprocal mesialization and proclination of the mandibular teeth.
Cochrane review showed that, at the end of all treatment, no significant differences were found in overjet, skeletal relationship or PAR score between the children who had a course of early treatment, with either headgear or functional appliances, and those who had not received early treatment. The only outcome to be affected by treatment timing was the incidence of new incisal trauma, which was significantly reduced by early treatment with either functional appliance or headgear (odds ratio 0.59 and 0.47, respectively). The Cochrane review concludes 'the evidence suggests that providing early orthodontic treatment for children with prominent upper front teeth is more effective in reducing the incidence of incisal trauma than providing one course in early adolescence. There appears to be no other advantage for providing early treatment'. [5]
Functional appliances: The first reported use of a mandibular positioning device was the 'Monobloc' by Dr Robin, in France in 1902, for neonates with under-developed mandibles. This was followed by the first functional device for growth modification, the Andresen Activator, in Norway in 1908. A number of German appliances, such as the Herbst appliance in 1934, the Bionator appliance in the 1950s and the Functional Regulator in 1966 followed on. The table below summarizes the various types of functional appliance that are currently in use. The Twin Block, first described by Clark in 1982, consists of two blocks with interlocking 70° bite planes, which cause forward posturing of the mandible.
Orthodontics is a dentistry specialty that addresses the diagnosis, prevention, management, and correction of mal-positioned teeth and jaws, as well as misaligned bite patterns. It may also address the modification of facial growth, known as dentofacial orthopedics.
Dental braces are devices used in orthodontics that align and straighten teeth and help position them with regard to a person's bite, while also aiming to improve dental health. They are often used to correct underbites, as well as malocclusions, overbites, open bites, gaps, deep bites, cross bites, crooked teeth, and various other flaws of the teeth and jaw. Braces can be either cosmetic or structural. Dental braces are often used in conjunction with other orthodontic appliances to help widen the palate or jaws and to otherwise assist in shaping the teeth and jaws.
Hypodontia is defined as the developmental absence of one or more teeth excluding the third molars. It is one of the most common dental anomalies, and can have a negative impact on function, and also appearance. It rarely occurs in primary teeth and the most commonly affected are the adult second premolars and the upper lateral incisors. It usually occurs as part of a syndrome that involves other abnormalities and requires multidisciplinary treatment.
Prognathism is a positional relationship of the mandible or maxilla to the skeletal base where either of the jaws protrudes beyond a predetermined imaginary line in the coronal plane of the skull.
In orthodontics, a malocclusion is a misalignment or incorrect relation between the teeth of the upper and lower dental arches when they approach each other as the jaws close. The English-language term dates from 1864; Edward Angle (1855–1930), the "father of modern orthodontics", popularised it. The word "malocclusion" derives from occlusion, and refers to the manner in which opposing teeth meet.
Orthodontic technology is a specialty of dental technology that is concerned with the design and fabrication of dental appliances for the treatment of malocclusions, which may be a result of tooth irregularity, disproportionate jaw relationships, or both.
Occlusion, in a dental context, means simply the contact between teeth. More technically, it is the relationship between the maxillary (upper) and mandibular (lower) teeth when they approach each other, as occurs during chewing or at rest.
Crossbite is a form of malocclusion where a tooth has a more buccal or lingual position than its corresponding antagonist tooth in the upper or lower dental arch. In other words, crossbite is a lateral misalignment of the dental arches.
Overbite is the extent of vertical (superior-inferior) overlap of the maxillary central incisors over the mandibular central incisors, measured relative to the incisal ridges.
Serial extraction is the planned extraction of certain deciduous teeth and specific permanent teeth in an orderly sequence and predetermined pattern to guide the erupting permanent teeth into a more favorable position.
Anchorage in orthodontics is defined as a way of resisting movement of a tooth or number of teeth by using different techniques. Anchorage is an important consideration in the field of orthodontics as this is a concept that is used frequently when correcting malocclusions. Unplanned or unwanted tooth movement can have dire consequences in a treatment plan, and therefore using anchorage stop a certain tooth movement becomes important. Anchorage can be used from many different sources such as teeth, bone, implants or extra-orally.
Elastics are rubber bands frequently used in the field of orthodontics to correct different types of malocclusions. The elastic wear is prescribed by an orthodontist or a dentist in an orthodontic treatment. The longevity of the elastic wear may vary from two weeks to several months. The elastic wear can be worn from 12 to 23 hours a day, either during the night or throughout the day depending on the requirements for each malocclusion. The many different types of elastics may produce different forces on teeth. Therefore, using elastics with specific forces is critical in achieving a good orthodontic occlusion.
Activator Appliance is an Orthodontics appliance that was developed by Viggo Andresen in 1908. This was one of the first functional appliances that was developed to correct functional jaw in the early 1900s. Activator appliance became the universal appliance that was used widely throughout Europe in the earlier part of the 20th century.
Frankel appliance or Frankel Functional Regulator is an orthodontic functional appliance which was developed by Rolf Fränkel in 1950s for treatment to patients of all ages. This appliance primarily focused on the modulation of neuromuscular activity in order to produce changes in jaw and teeth. The appliance was opposite to the Bionator appliance and Activator appliance.
Molar distalization is a process in the field of Orthodontics which is used to move molar teeth, especially permanent first molars, distally (backwards) in an arch. This procedure is often used in treatment of patients who have Class 2 malocclusion. The cause is often the result of loss of E space in an arch due to early loss of primary molar teeth and mesial (forward) migration of the molar teeth. Sometimes molars are distalized to make space for other impacted teeth, such as premolars or canines, in the mouth.
ACCO or Acrylic Cervical Occipital Anchorage is an appliance in field of orthodontics which is used for distalization of maxillary molars. This appliance is a removable type of appliance which was developed by Herbert I. Margolis. This appliance is intended to be worn 24 hours a day except during meals. It is one of the few removable appliances made for distalization of molars and thus require patient compliance for the treatment to be successful.
Open bite is a type of orthodontic malocclusion which has been estimated to occur in 0.6% of the people in the United States. This type of malocclusion has no vertical overlap or contact between the anterior incisors. The term "open bite" was coined by Carevelli in 1842 as a distinct classification of malocclusion. Different authors have described the open bite in a variety of ways. Some authors have suggested that open bite often arises when overbite is less than the usual amount. Additionally, others have contended that open bite is identified by end-on incisal relationships. Lastly, some researchers have stated that a lack of incisal contact must be present to diagnose an open bite.
An ectopic maxillary canine is a canine which is following abnormal path of eruption in the maxilla. An impacted tooth is one which is blocked from erupting by a physical barrier in the path of eruption. Ectopic eruption may lead to impaction. Previously, it was assumed that 85% of ectopic canines are displaced palatally, however a recent study suggests the true occurrence is closer to 50%. While maxillary canines can also be displaced buccally, it is thought this arises as a result of a lack of space. Most of these cases resolve themselves with the permanent canine erupting without intervention.
Orthodontic indices are one of the tools that are available for orthodontists to grade and assess malocclusion. Orthodontic indices can be useful for an epidemiologist to analyse prevalence and severity of malocclusion in any population.
The Herbst appliance is an orthodontic appliance used by orthodontists to correct class 2 retrognathic mandible in a growing patient, meaning that the lower jaw is too far back. This is also called bitejumping. Herbst appliance parts include stainless steel surgical frameworks that are secured onto the teeth by bands or acrylic bites. These are connected by sets of telescoping mechanisms that apply gentle upward and backward force on the upper jaw, and forward force on the lower jaw. The original bite-jumping appliance was designed by Dr. Emil Herbst and reintroduced by Dr. Hans Pancherz using maxillary and mandibular first molars and first bicuspids. The bands were connected with heavy wire soldered to each band and carried a tube and piston assembly that allowed mandibular movement but permanently postured the mandible forward. The appliance not only corrected a dental Class II to a dental Class I but also offered a marked improvement of the classic Class II facial profile.