THE AETIOLOGY OF CLASS II MALOCCLUSION

CLASS II MALOCCLUSION

• Class II malocclusion can be divided into two types:• Class II Div I

– the lower incisor edges lie posterior to the cingulum plateau of the upper incisors

– Increased overjet – upper central incisors are proclined

• Class II Div II– the lower incisor edges lie posterior to the cingulum plateau

of the upper incisors– Overjet is minimal but may be increased– upper central incisors are retroclined

AETIOLOGY OF MALOCCLUSION

• There are four major factors which contribute to the aetiology of any malocclusion :

• Skeletal factors• Soft Tissues• Dental factors• Local factors• Usually, a malocclusion is a result of the

combination of all four of the above factors.

AETIOLOGY OF CLASS II DIVISION I MALOCCLUSION

Skeletal pattern• A class II skeletal pattern is usually present in patients

with a class II division I malocclusion. This is most commonly due to a retrognathic mandible. It is also possible for patients to present with a protruded maxilla but this is less common. Size discrepancies between the mandible and maxilla may also be the cause of the class II malocclusion and would be due to decreased mandibular size and increased maxillary size. Vertical skeletal discrepancies are also common.

AETIOLOGY OF CLASS II DIVISION I MALOCCLUSION

Soft tissues• The soft tissues exert forces on the teeth and can contribute to the

malocclusion• Patients with class II division I malocclusion usually have incompetent

lips due to the prominence of the upper incisors. This can encourage upper incisor proclination and lower incisor retroclination as the lower lip is drawn behind the upper incisors and therefore worsening the incisor relationship. However, dentoalveolar compensation can occur to mask the skeletal problem if the patient postures the mandible forwards or uses their circumoral muscles to achieve an oral seal.

• A high lip line can cause protrusion of the upper incisors as it means the lip is no longer placing force over the upper incisors to prevent them splaying outwards

AETIOLOGY OF CLASS II DIVISION I MALOCCLUSION

Dental factors• Crowding in the upper arch can result in a lack

of space for the upper incisors, pushing them labially out of the arch and cause an increase in overjet.

AETIOLOGY OF CLASS II DIVISION I MALOCCLUSION

Local factors• Habits such as digit sucking can have a

significant effect on a patient’s malocclusion. Digit sucking causes proclination of the upper incisors and retroclination of the lower incisors. This will cause an increase in overjet and can exacerbate an existing class II malocclusion.

AETIOLOGY OF CLASS II DIVISION II MALOCCLUSION

Skeletal pattern• Class II division II malocclusion is usually

associated with a class II skeletal pattern. The vertical skeletal pattern is also typically reduced which results in the over eruption of the lower incisors and an increased overbite, due to an absence of an occlusal stop.

AETIOLOGY OF CLASS II DIVISION II MALOCCLUSION

Soft tissues• A high lower lip line is common in class II

division II and this causes retroclination of the upper incisors.

• A high lip line can also cause retroclination of the upper incisors due to forces being applied to the teeth.

AETIOLOGY OF CLASS II DIVISION II MALOCCLUSION

Dental factors• Crowding is common in patients with a class II div II

relationship. The retroclination of the upper incisors leads to a smaller arc circumference creating a lack of space. Lower arch crowding can also be seen as the retroclination of the upper incisors and increased overbite can cause the lower incisors to tilt lingually and thus cause crowding.

• In a few cases, the increased overbite can be traumatic and has been seen to cause ulceration of the palatal tissues and stripping of the lower labial gingival tissues.

Aetiology of Class III

Definition

• Angle’s Classification: mandibular first molar is anteriorly placed in relation to the maxillary first molar.

• British Standards Incisor classification: lower incisor edge occludes anterior to the cingulum plateau of the upper incisors

• Angle’s classification is a more useful definition due to incisal camouflage

The 4 Factors

• Skeletal pattern

• Dental factors

• The soft tissues

• Environmental issues

Skeletal pattern• Increased mandibular length• A more anteriorly placed glenoid fossa – leading to

mandibular prognathism• Reduced maxillary length• A more retruded position of the maxilla leading to maxillary

retrusion• A reduced cranial base angle (ANB <2o)

• Often a mixture of two or more of the above

• Growth patterns are important in vertical discrepancies

Dental

• Maxillary incisors lie in a similar plane to a normal occlusion, however can be proclined due to soft tissue influences

• Mandibular incisors are often seen to be more anteriorly placed than in normal occlusions

• A narrow maxillary arch coupled with a broad, anteriorly placed mandibular arch can cause a class III malocclusion

Soft Tissues

• Tend to mask the malocclusion, not cause• e.g. dento-alveolar compensation

Environmental• Enlarged tonsil• Difficulty in nasal breathing• Congenital anatomic defects• Disease of the pituitary gland• Hormonal disturbances• Habit of protruding the mandible• Posture• Trauma and disease• Premature loss of 6• Irregular eruption of permanent incisors or loss of deciduous

incisors.

Twin Studies

• Concluded that genetics are not solely responsible for a class III malocclusion – it is highly multi-factoral

Aetiology of Anterior Openbite

Definition; the anterior teeth in the maxilla do not occlude with the opposing teeth in the mandible in any mandibular position.

Subcategories of AOB

• DENTAL OPEN BITE; Cases of AOB in which the vertical skeletal pattern is not contributory.

• SKELETAL OPEN BITE; The open bite is at least partly due to the vertical facial form, usually the AOB develops due to excessive vertical growth. These are usually more severe than dental open bites, often with only the most distal molars in contact.

Dental Open Bite

• Digit Sucking; Open bite caused by digit sucking is characterised by an asymmetrical open bite, the greater extent being on the side the digit is most commonly placed, and upper incisal proclination (effects on the lower incisors are more variable), and often over eruption of posterior teeth as a result of the digit acting as a barrier to eruption of the anteriors.

Dental Open Bite (continued)• Abnormal Tongue Function; abnormal tongue thrusts are

often noted in patients with AOB however it is believed that these are often a result of the AOB or other factors, and Proffit suggests tongue thrusts are not likely to be the causative factors in an AOB, more likely abnormal tongue resting positions may have an effect as the durations involved in thrusts, whether endogenous or adaptive is too short to cause any displacement but the durations involved when the tongue is at rest are much greater. Often an abnormally large tongue can result in unusual tongue resting positions resulting in AOB, such cases will require tongue reduction as part of their treatment.

Skeletal Open Bite

• Neurological Disturbances• Muscular Dystrophy• Muscle Weakness Syndromes• Cerebral Palsy (certain forms)

Lengthening of the lower face and accompanying anterior open bite in a 15 year old patient resulting from muscle weakness due to muscular dystrophy.

Other Causes of Open Bite

• IATROGENIC OPEN BITE; Failure to prevent over eruption of posterior teeth when biteplanes and functional appliances are used may also give rise to AOB, as may extrusion of the molar teeth during fixed appliance treatment.

• PATHOLOGICAL OPEN BITE; Trauma to the facial skeleton, acromegaly and cleft palate are all associated with localised AOB.

Aetiology of crossbites

Crossbite: one or more teeth have a more buccal or lingual position in relation to its opposing tooth or teeth.

Figure 1: Anterior Crossbite Figure 2: Posterior Crossbite

Local causes: crowding, retention, trauma.

Skeletal causes: mismatch in the widths of the dental arches and/or an anteroposterior skeletal discrepancy.

Soft tissues/habits: digit-sucking.

Rarer causes: TMJ disorders, cleft palate.

Canine DisplacementDisplacement of canines can be classed into palatal and buccal displacements.

• Displacement of the crypts – this is thought to be the cause of the rarer forms of canine displacement e.g. Horizontal displacement.

• Long path of eruption• Short-rooted or absent upper lateral incisors• Crowding• Retention of primary deciduous canine • Genetic factors- Evidence has been gathered supporting the genetic theory of canine

displacement on the basis of 5 :1) The occurrence with other dental anomalies.2) Bilateral occurrence of palatally displaced canines.3) Sex differences with palatally displaced canines- affects females more often than males.4) Familial occurrence.5) Variations in different populations.

SummaryAetiology of malocclusions:• Class II• Class III• AOB• Crossbites• Canine Displacement

Further information can be found on uSpace:

Group name: Ortho Wiki 09 Aetiology of Malocclusion Link: http://

uspace.shef.ac.uk/clearspace/groups/ortho-wiki-09-aetiology-of-malocclusion