INTRODUCTION
Class III malocclusion is very easy to identify but difficult to treat.It represents a pre-normalcy where the mandible is in a mesial relation to the upper arch.
DEFINITION
According to Edward H. Angle, Class III malocclusion can be defined as:
“A condition where the mesiobuccal cusp of the upper first molar occludes between the mandibular first and second molars.”
FEATURES OF CLASS III MALOCCLUSION
- The patient has a Class III molar relationship.
- An edge-to-edge relationship or an anterior cross-bite may occur.
- Upper arch is narrow & short while the lower arch is broad.
- Posterior cross-bites are common.
- Upper teeth are crowded due to a narrow upper arch while the lower teeth have a spaced dentition due to broader lower arch. a
- Patient has a concave profile due to the presence of a prominent chin.
- Vertical growers exhibit an increased inter-maxillary height may have an anterior open-bite. In some patients a deep bite may develop.
A type of Class III malocclusion referred PSEUDO CLASS MALOCCLUSION characterized presence of by as is the occlusal prematurities resulting in a habitual forward positioning of the mandible. These patients may exhibit forward path of closure.
SKELETAL FEATURES OF CLASS MALOCCLUSION
Most Class III malocclusions are associated with underlying skeletal malrelationships. Commonly seen skeletal features are:
1. A short retrognathic maxilla. or
2. A long prognathic mandible. or
3. A combination of a maxilla retrognathic & prognathic mandible.
ETIOLOGY
True Class III malocclusion that exhibits underlying skeletal imbalance is usually inherited.
Environmental factors such as:
- Postural habits
- Mouth breathing
- Other cause: Habitual forward positioning of the mandible due to occlusal prematurities .
DIAGNOSIS
- Clinical examination should include observation of path of closure.
- Study models & radiographs should also be taken.
- A lateral cephalogram offers a valuable information on the skeletal nature of the malocclusion.
TREATMENT
Class III malocclusion should recognized & treated early due to the following reasons:
Early interception reduces the severity of the malocclusion. Developing Class III malocclusion characterized by anterior cross-bite often result in retarded maxillary growth due to locking of maxilla within the mandible.
The occlusal forces on the mandibular incisors exerted by the maxillary incisors in cross-bites encourage the continued forward growth of mandible worsening the pre-normalcy.
- MYOFUNCTIONAL APPLIANCES
Frankel III appliance can be used to intercept a malocclusion due to maxillary skeletal retrusion.
2. CHIN CUP THERAPY
Used in the treatment of Class III maloco with protrusive mandible & normal maxilla.
Two types:
Occipital pull chin cup
Vertical pull chin cup: Used in patients who exhibit a steep mandibular plane angle & excessive anterior facial height.
Effects of chin cup include:
Backward repositioning of the mandible.
Redirection of the mandibular growth remodeling of mandible with closure of the gonial angle.
Chin cups with headgears are indicated in primary & mixed dentition periods.
Force levels of 300-500gms per side are indicated for 12-14hours of wear everyday.
Treatment Using Fixed Appliances
◆ Best done in mixed dentition, before eruption of permanent canines.
◆ In patients with a mild to moderate class III skeletal pattern, a combination of retroclination of the lower incisors and proclination of the upper incisors may be required.
◆ Class III intermaxillary elastic traction from the lower labial segment to the upper molars can also be used to move the upper arch forwards & lower arch backwards. However, care is required to avoid extrusion of molars which will reduce overbite.
Treatment Of Anterior Crossbite
◆ Mild anterior cross-bite can be treated using lower anterior inclined planes or removable appliances incorporating screws designed for anterior expansion.
Treatment Of Posterior Crossbite
◆ Class III malocclusions are often accompanied by posterior crossbite.
◆ It can be treated by rapid maxillary expansion.
Role Of Extractions
◆ Class III malocclusion characterized by mild mandibular prognathism & lower arch crowding can be treated by extracting the lower first premolars followed by mechanotherapy.
This is an orthodontic camouflage of the underlying skeletal malocclusion.
Treatment Of Severe Class Malocclusion
◆ Severe class III malocclusion after growth completion is complete is treated by surgical & corrective procedures.
Class III due to maxillary deficiency is treated by maxillary advancement procedures such as leFort I osteotomy.
◆ Class III malocclusion that are a result of mandibular prognathism are treated by mandibular set back procedures.
Treatment of Pseudo Class III Malocclusion
◆ Pseudo class III malocclusion that occurs as a result of occlusal prematurity improves on the removal of cause.