Class III malocclusion

Definition: according to british standards incisor classification, in class III malocclusion the lower incisor edges lie anterior to the cingulum plateau of the upper incisors. the overjet is reduced or reversed. According to Angls classification , in class III the mesiobuccal cusp of the lower first molar occluds mesial to the class I position.

Aetiology: 1- skeletal pattern 2- dental factors 3- soft tissue 4- specific conditions 5- familial tendency

Skeletal pattern: 1- mandbular prognathisim 2- maxillary retrognathisim 3- combination of both

Features of class III malocclusion 1- a concave facial profile 2- a retrusive nasomaxillary area 3- prominent lower third of the face 4- narrow upper arch 5- reduced or reversed overjet

Diagnosis: A successful treatment plan depends on an accurate diagnosis. For treating class III malocclusion a direct cause must be identified , that is true class III should be differentiated from pseudo class III malocclusion. pseudo class III malocclusion is a habitual established cross bite of all anterior teeth, without any skeletal discrepancy, resulting from functional forward positioning / shift of the mandible on closure. Causes include 1- occlusal prematurity 2- enlarged adenoids

Factors considered while treatment planning: 1- patient opinion 2- severity of skeletal pattern 3- amount of expected pattern of future growth 4- degree of crowding 5- if an edge to edge incisor contact can be achieved or not 6- amount of dento-alveolar compensation present

Treatment modalities 1- growth modification 2- orthodontic camouflage 3- orthgnathic surgery

Growth modification: In young patients who are still in their growing phase orthopedic and myofunctional appliances can be used in cases of skeletal class III malocclusion. Either there is deficient growth of maxilla or excess growth of mandible.

1- frankel III functional appliance: Used in mild skeletal problems. Causes downward and backward rotation of the mandible Has little or no effect on maxilla

2- reverse pull head gear (face mask) Indicated in patient with retrusive maxilla Obtain anchorage from forehead and chin Exerts force on maxilla via elastics that attach to maxillary splints Effects 1- forward and downward movement of maxilla 2- downward and backward rotation of mandible 3- lingual tipping of lower incisors Treatment given at the mixed dentition Requires great patient cooperation

3- chin cup therapy An effort to restrain mandibular growth Redirect mandibular growth in a more vertical direction Ideal in patients with: 1- mild skeletal problem 2- reduced lower anterior facial height 3- normal or proclined lower incisors Recommended force 300-500 gram/ side Patients are instructed to wear the appliance 14 hours / day

Orthodontic camouflage Proclination of upper labial segment: Correction of incisor relationship by proclination of the upper incisors can only be considered with the following features: 1- class I or mild class III skeletal pattern 2- the upper incisor are not already significantly proclined 3- adequate overbite will be present at the end of treatment to retain the corrected position of the upper incisors

Retroclination of lower labial segment In cases with mild to moderate class III skeletal pattern or in case of reduced overbite Space is required in the lower arch for retroclination of lower labial segment and extractions are required

Orthognathic surgery Indicated in sever skeletal problems Value of ANB is -4 Inclinationof lower incisors to mandibular plane is 83 degrees common surgical procedures 1- Lefort 1 maxillary advancement for retrognathic maxilla 2- bilateral sagittal split mandibular set back for prognathic mandible Surgically assisted R.P.E