Lec: Treatment of class III malocclusion
..........The British Standards definition of Class III incisor relationship includes those malocclusions where the lower incisor edge occludes anterior to the cingulum plateau of the upper incisors (The overjet is reduced or reversed).
According to Angle classification, he stated that class III malocclusion is the advancement of the lower permanent 1st molar a half or complete cusp unit to the upper corresponding one. (the mesiobuccal cusp of the lower 1st molar occludes mesial to the Class I position).
Class III is the least common type of occlusal relationship in many communities as it affecting around 3-5 percent of population, therefore it is seen relatively less frequently in orthodontic practice.
? The main variants in class III malocclusion are:
1..The degree of class III sagittal relationship of the dental arches.
2..The degree of horizontal discrepancy in the upper and lower arch size.
3..The degree of crowding of teeth.
3..The dgree of incisal overbite or anterior openbite.
The source of these variations is found in the main etiological features:
((Skeletal factors; oral musculature; the size of the dentition)).
? Skeletal factors ; which have three important aspects:
? Antero-posterior skeletal relation: The skeletal relationship is the most important factor in the aetiology of most Class III malocclusions, and the majority of Class III incisor relationships are associated with an underlying Class III skeletal relationship which is also largely responsible for the reverse overjet and buccal crossbite in many cases.
? The relative width of the upper and lower jaws: Unilateral or bilateral crossbite may be caused by discrepancy in the width of the jaws, similarly since the buccal segments diverge backwards, discrepancy in the sagittal relation may produce ...... .
? Vertical dimension of the face: Class III malocclusions occur in association with a range of vertical skeletal proportions, ranging from increased to reduced. A backward opening rotation pattern of facial growth will tend to result in a reduction of overbite; however, a forward rotating pattern will lead to an increase in the prominence of the chin. It is also influenced by the gonial angle of the mandible... .
? The oral musculature: In the majority of Class III malocclusions the soft tissues do not play a major aetiological role. In fact the reverse is often the case, with the soft tissues tending to tilt the upper and lower incisors towards each other so that the incisor relationship is often less severe than the underlying skeletal pattern.
? Dental factors: Class III malocclusions are often associated with a narrow upper arch and a broad lower arch, with the result that crowding is seen more commonly, and to a greater degree, in the upper arch than in the lower. Frequently, the lower arch is well aligned or even spaced.
Treatment objectives and limitations:
? Reduction of crowding.
? Correction of reversed overjet.
? Correction of incisal overbite.
? Correction of buccal segment relation.
1* Reduction of crowding: In the upper arch, it is necessary to create a space for crowding by expansion and proclination of upper incisors, while extraction of teeth may be needed and retroclination of the lower incisors, in the lower arch.
2**Correction of the reversed OJ: In very mild cases, it can be treated by proclination and retroclination of the upper and lower incisors, respectively; by using fixed or removable appliances.
3***Correction of incisal OB: This could be a deepbite or anterior openbite, the correction of the former is largely depend on the correction of the reversed OJ. Whereas correction of the latter is better to be limited for minor cases by fixed appliance for extrusion of incisors.
4****Correction of crossbite: Unilateral crossbite associated with mandibular shifting on closure (premature contact), can be corrected by maxillary expansion. In case of bilateral type is better to accept it unless there is a very narrow upper arch with crowding, so it is possible to expand the arch either by rapid maxillary expansion or by expansion screws.
Treatment planning of Class III malocclusion:
A number of factors should be considered before planning treatment:
• Patient’s concerns and motivation towards treatment
• Severity of skeletal pattern
• Amount and direction of any future growth
• Can patient achieve edge-to-edge incisor contact
• Overbite
• Amount of dento-alveolar compensation present
• Degree of crowding
Treatment of postural and very mild cases of class III:
These cases associated either with anterior crossbite or due to postural position of the lower jaw in cases of inadequate nasal breathing in which the patient tries to push the mandible forwards to break the posterior oral seal facilitating oral breathing, in case for example in adenoid patient or chronic tonsillitis, they have edge to edge relationship in centric, then displace the mandible anteriorly into occlusion to produce typical appearance of class III or reversed OJ & OB.
o For treatment of such cases is brought about by proclination of upper incisors by removable appliances.
o We dont need a retainer after treatment as the ..... .
Treatment of mild to moderate cases of class III:
This is the most common type of class III and it is mostly confused with the previous type as the patient can easily achieve edge to edge incisor relation. In this type the upper incisors are not retroclined as in the previous type, i.e. the upper incisal long axis form with the maxillary plane a normal inclination of about 110°. While the lower incisors are retroclined and the skeletal pattern is marked class III.
o Early orthopaedic treatment: Orthopaedic correction of Class III malocclusions aims to enhance or encourage maxillary growth and/or restrain or re-direct mandibular growth.
o Treatment by fixed appliances.
........Clinical experience suggests that during growth the mandible tends to become more prognathic than maxilla, we can alter the direction of growth by using an external forces applied at an early stage through chin- cap from occipital traction head-gear...
Sever skeletal discrepancy:
In this type the skeletal pattern is very obvious and the patient can not close in edge to edge relationship and the facial appearance is not acceptable. The overjet is reversed and this could be associated with deep overbite or with crossbite.
Orthognathic surgery: For those patients where orthodontic treatment will be challenging owing to the severity of the skeletal pattern and/or a lack of overbite, a surgical approach should be considered before any permanent extractions are carried out, and preferably before any appliance treatment. The reason for this is that management of Class III malocclusions by orthodontics alone involves dento-alveolar compensation for the underlying skeletal pattern. However, in order to achieve a satisfactory occlusal and facial result with a surgical approach, any dento-alveolar compensation must first be removed or reduced.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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