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.Hunt NP. Why should the NHS continue to fund orthodontic treatment in the current financial climate? Royal College of Surgeons of England: Faculty Dental Journal 2013; 4: 16−19. 4.Burden DJ. Oral health-related benefits of orthodontic treatment. Semin Orthod 2007; 13: 76−80.
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 are twice as likely to suffer injury to their upper incisors.Nguyen QV et al. A systematic review of the relationship between overjet size and traumatic dental injuries. Eur J Orthod 1999; 21: 503−515.
Table showing the relationship between size of overjet and prevalence of traumatised anterior teethRoberts-Harry D & Sandy J. Orthodontics. Part 1: Who needs orthodontics? British Dental Journal 195. 433. (25 October 2003) {| class="wikitable" |- ! Overjet (mm) !! Incidence (%) |- | 5 || 22 |- | 9 || 24 |- | >9 || 44
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'.Thiruvenkatachari B et al. Orthodontic treatment for prominent upper front teeth (Class II malocclusion) in children. Cochrane Database Syst Revs 2013; 11: CD003452. 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.Rusanen J et al. Quality of life in patients with severe malocclusion before treatment. Eur J Orthod 2010; 32: 43−48. 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.Seehra J, Newton JT, Dibiase AT. Interceptive orthodontic treatment in bullied adolescents and its impact on self-esteem and oral-health-related quality of life. Eur J Orthod 2013; 35(5): 615−621.
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.
Causal propositions for orthodontic malocclusion and incisal crowding states 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:Barber, S.K., Forde, K.E. & Spencer, R.J. 2015, "Class II division 1: an evidence-based review of management and treatment timing in the growing patient", Dental Update, vol. 42, no. 7, pp. 632-642.
Skeletal factors − it is generally agreed that the majority of patients with a Class II malocclusion have some degree of skeletal imbalance with either a retrognathic mandible, protrusive maxilla or, most commonly, a combination Dental factors − crowding, spacing, proclined maxillary anterior teeth Soft tissue factors − incompetent lips, lower lip trap, tongue thrust Habits − digit-sucking, use of pacifiers
Diagnosis 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:Roberts-Harry D & Sandy J. 2003. Orthodontics. Part 2: Patient Assessment and Examination I. British Dental Journal 195, 489–493 (08 November 2003) Medical History Patient's Complaint History of Trauma Habits Extra-Oral Examination Intra-Oral Examination Radiograph Indication of Orthodontic Treatment Need Scoring Justification for Treatment Treatment Aims Treatment Plan
The Extra Oral Examination Should Include: Skeletal Pattern Anterior-Posterior Vertical Dimension Transverse Soft Tissues Temporomandibular Joint Examination
The Intra Oral Examination Should Include: Dental health Lower arch Upper arch Teeth in occlusion Radiographs
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 someone tries to move the teeth when there is active gingivitis and periodontal disease.Roberts-Harry D & Sandy J. 2003. Orthodontics. Part 3: Patient assessment and examination II. British Dental Journal 195, 563-565 (22 November 2003).
Overjet is measured from the labial surface of the most prominent incisor to the labial surface of the mandibular incisor. Normally, this measurement is . If the lower incisor is anterior to the upper incisors, the overjet is given a negative value.Mitchell, Laura. 2013. An Introduction to Orthodontics. 4th ed. Oxford: Oxford University Press. In the UK, an overjet is generally described as increased if it is >. The Index of Orthodontic Treatment Need rates overjet highly on its weighting system, second behind missing teeth. It then grades severity of overjet as:British Orthodontic Society. 2014. Quick Reference Guide to Orthodontic Assessment and Treatment. [Online Guide]. [viewed 7 January 2018] Available from https://www.bos.org.uk Grade 3, Borderline need for treatment = increased overjet < Grade 4, Need for treatment = increased overjet < Grade 5, Need for treatment = increased overjet > .