2 CLASS II MALOCCLUSIONClass II malocclusion can be divided into two types:Class II Div Ithe lower incisor edges lie posterior to the cingulum plateau of the upper incisorsIncreased overjetupper central incisors are proclinedClass II Div IIOverjet is minimal but may be increasedupper central incisors are retroclined
3 AETIOLOGY OF MALOCCLUSION There are four major factors which contribute to the aetiology of any malocclusion :Skeletal factorsSoft TissuesDental factorsLocal factorsUsually, a malocclusion is a result of the combination of all four of the above factors.
4 AETIOLOGY OF CLASS II DIVISION I MALOCCLUSION Skeletal patternA 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.
5 AETIOLOGY OF CLASS II DIVISION I MALOCCLUSION Soft tissuesThe soft tissues exert forces on the teeth and can contribute to the malocclusionPatients 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
6 AETIOLOGY OF CLASS II DIVISION I MALOCCLUSION Dental factorsCrowding 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.
7 AETIOLOGY OF CLASS II DIVISION I MALOCCLUSION Local factorsHabits 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.
8 AETIOLOGY OF CLASS II DIVISION II MALOCCLUSION Skeletal patternClass 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.
9 AETIOLOGY OF CLASS II DIVISION II MALOCCLUSION Soft tissuesA 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.
10 AETIOLOGY OF CLASS II DIVISION II MALOCCLUSION Dental factorsCrowding 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.
12 DefinitionAngle’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 incisorsAngle’s classification is a more useful definition due to incisal camouflage
13 The 4 Factors Skeletal pattern Dental factors The soft tissues Environmental issues
14 Skeletal pattern Increased mandibular length A more anteriorly placed glenoid fossa – leading to mandibular prognathismReduced maxillary lengthA more retruded position of the maxilla leading to maxillary retrusionA reduced cranial base angle (ANB <2o)Often a mixture of two or more of the aboveGrowth patterns are important in vertical discrepancies
15 DentalMaxillary incisors lie in a similar plane to a normal occlusion, however can be proclined due to soft tissue influencesMandibular incisors are often seen to be more anteriorly placed than in normal occlusionsA narrow maxillary arch coupled with a broad, anteriorly placed mandibular arch can cause a class III malocclusion
16 Soft Tissues Tend to mask the malocclusion, not cause e.g. dento-alveolar compensation
17 Environmental Enlarged tonsil Difficulty in nasal breathing Congenital anatomic defectsDisease of the pituitary glandHormonal disturbancesHabit of protruding the mandiblePostureTrauma and diseasePremature loss of 6Irregular eruption of permanent incisors or loss of deciduous incisors.
18 Twin StudiesConcluded that genetics are not solely responsible for a class III malocclusion – it is highly multi-factoral
19 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.
20 Subcategories of AOBDental 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.
21 Dental Open BiteDigit 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.
22 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.
23 Skeletal Open Bite Neurological Disturbances Muscular Dystrophy Muscle Weakness SyndromesCerebral 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.
24 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.
25 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 CrossbiteLocal 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.
26 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 eruptionShort-rooted or absent upper lateral incisorsCrowding Retention of primary deciduous canineGenetic factors- Evidence has been gathered supporting the genetic theory of canine displacement on the basis of 5 :The occurrence with other dental anomalies.Bilateral occurrence of palatally displaced canines.Sex differences with palatally displaced canines- affects females more often than males.Familial occurrence.Variations in different populations.
27 Summary Aetiology of malocclusions: Class II Class III AOB Crossbites Canine DisplacementFurther information can be found on uSpace:Group name: Ortho Wiki 09 Aetiology of MalocclusionLink: