Overjet


Overjet is the extent of horizontal overlap of the maxillary central incisors over the mandibular central incisors. In class II 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. 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

Cause

Class II Div I

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 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:
The Extra Oral Examination Should Include:
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.
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. In the UK, an overjet is generally described as increased if it is >. The Index of Orthodontic Treament Need rates overjet highly on its weighting system, second behind missing teeth. It then grades severity of overjet as:
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:
Untreated overjet can cause the following health complications:

Class II div 1

Early intervention

Functional appliances

Twin block appliances
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 when compared to other functional appliances, although there was no significant effect from the type of appliance on the final overjet. The Twin Block has also been shown to cause clinically significant beneficial changes to the soft tissues.
There are problems associated with the Twin Block including excessive lower incisor proclination, a significant failure-to-complete rate of 25%, 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.
Herbst appliance
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.
Headgear
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. Several studies found an additional small effect on mandibular growth when headgear is used in conjunction with an anterior bite plane.
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. 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. 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

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.

Late intervention

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. 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'.

Epidemiology

Class II Div I

History

Class II div 1

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.