In 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.
Signs and symptoms
Class II Div I Benefits associated with orthodontic treatment include a reduction in the susceptibility to caries, periodontal disease and temporomandibular joint dysfunction, whilst also improving speech and masticatory function. However, the supporting evidence is equivocal. It may be assumed that correction of an increased overjet will potentially reduce the risk of trauma, as it has been shown that individuals with an overjet greater than 3 mm (0.12 in) are twice as likely to suffer injury to their upper incisors. Table showing the relationship between size of overjet and prevalence of traumatised anterior teeth
The meta-analysis undertaken in a recent Cochrane review found that 'early orthodontic treatment for children with prominent upper front teeth is more effective in reducing the incidence of incisal trauma than providing one course of orthodontic treatment when the child is in early adolescence'. A number of studies have found that the presence of malocclusion can have a significant impact on an individual’s quality of life and result in reduced self-esteem. Prominent upper incisors may be a target for teasing and bullying and it is now accepted that one reason for undertaking treatment of malocclusion is the psychosocial benefit that it accrues.
Classification of the bad bite
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.
Incisal Edge-to-Edge 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.
Incisal Anterior Open Bite 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.
Incisal Class II Div I 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.
Incisal Class II Div 2 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.
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