Orthodontics

Class III

By Cezar Edward

contents

11.1 Aetiology 138

11.1.1 Skeletal pattern 138

11.1.2 Soft tissues 138

11.1.3 Dental factors 138

11.2 Occlusal features 139

11.3 Treatment planning in Class III

malocclusions 139

11.4 Treatment options 140

11.4.1 Accepting the incisor relationship 140

11.4.2 Early orthopaedic treatment 140

11.4.3 Orthodontic camoufl age 143

11.4.4 Surgery 145

Introduction

Class III incisor relationship includes those

malocclusions where the lower incisor edge

occludes anterior to the cingulum plateau of

the upper incisors.

-Increase vertical dimension

-Decrease overbite

-Decrease overjet

Aetiology

Skeletal pattern

Soft tissues

Dental factors

Skeletal pattern most important factor

Class III malocclusions exhibit the following:

• increased mandibular length;

• a more anteriorly placed glenoid fossa so that the condylar head is

positioned more anteriorly leading to mandibular prognathism;

• reduced maxillary length;

• a more retruded position of the maxilla leading to maxillary retrusion.

Patient with mandibular prognathism Patient with maxillary retrognathia

Soft tissues

*Do not play a major aetiological role.

*The dento-alveolar compensation occurs in Class III

malocclusions because an anterior oral seal can frequently

be achieved by upper to lower lip contact.

This has the effect of moulding the upper and lower labial

segments towards each other.

The main exception occurs in patients with increased

vertical skeletal

proportions where the lips are more likely to be

incompetent and an anterior oral seal is often

accomplished by tongue to lower lip contact.

Dental factors

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.

Occlusal features

Fig. 11.3 Diagram illustrating the path of

closure in a Class III

malocclusion from an edge-to-edge incisor

relationship into maximal

occlusion. Although the mandible is

displaced forwards from the initial

contact of the incisors to achieve maximal

interdigitation, the condylar

head is not displaced out of the glenoid

fossa.

Fig. 11.4 A Class III malocclusion with a

narrow crowded upper arch

and a broader less crowded lower arch

with associated buccal crossbite.

Class III malocclusions often exhibit

dentoalveolar compensation with the

upper incisors proclined and the lower

incisors retroclined, which reduces the

severity of the incisor relationship

Treatment planning in Class III

malocclusionsA number of factors should be considered before planning treatment.

1. Patient’s concerns and motivation towards treatment

2.The severity of the skeletal pattern, both anteroposteriorly and vertically,

should be assessed.

3.The amount and expected pattern of future growth -When evaluating the

likely direction and extent of facial growth, the patient’s age, sex, facial pattern and

family history of Class III malocclusions should be taken into consideration

4.If the patient can achieve an edge-to-edge incisor contact and then

displaces forwards into a reverse overjet, this increases the prognosis for

correction of the incisor relationship.

5.The degree of crowding in each arch

6.Amount of dento-alveolar compensation present

7.Overbite

Using headgear for distal movement of the upper buccal segments to

gain space for alignment is inadvisable in Class III malocclusions as this

will have the effect of restraining growth of the maxilla.

Functional appliances are less widely used in Class III malocclusions

because it is difficult for patients to posture posteriorly to

achieve an active working bite.

headgear can be used for children “to reduce the growth of the mandible

Treatment options

Accepting the incisor relationship

Early orthopaedic treatment

Orthodontic camouflage

Surgery

Accepting the incisor

relationship

Mild Class III case where it was decided to accept the incisor

relationship and direct treatment towards alignment of the

arches only

Early orthopaedic treatment

Protraction face-mask used to advance the maxilla. The forces

applied in this technique are in the region of 400 g per side and a co-

operative patient is necessary to achieve the 14 hours per day

wear required

A recent multi-centre randomized controlled trial in patients under the

age of 10 years showed a success rate of 70 per cent in terms of

achieving a positive overjet over a followup period of 15 months.

Bone anchored maxillary protraction (known as BAMP). Screws or

mini-plates are used in the posterior maxilla and anterior mandible

for Class III elastics. There is some evidence to show that a greater

degree of maxillary advancement is achieved than with face-mask

therapy alone.

A combination of these two techniques – elastics are run between

skeletal anchorage in the maxilla and a face mask.

Chin-cup – this has the eff ect of rotating the mandible downwards

and backwards with a reduction of overbite so is largely historic.

Orthodontic camouflageCorrection of an anterior crossbite in a Class I or mild Class III skeletal

pattern can be undertaken in the mixed dentition when the unerupted

permanent canines are high above the roots of the upper lateral incisors

.Extraction of the lower deciduous canines at the same time may

allow the lower labial segment to move lingually slightly.

Later in the mixed dentition when the developing canines drop

down into a buccal position relative to the lateral incisor root there may be

a risk of resorption if the incisors are moved labially. In this situation correction

is then best deferred until the permanent canines have erupted.

Fig. 11.10 Diagram to show how proclination of the

upper incisors results in a reduction of overbite.

Fig. 11.11 Diagram to show how retroclination of the

lower incisors results in an increase of overbite

Fig. 11.13 Class III intermaxillary traction.

Remember!!

In class III we need space in lower arch to

make retroclination

Surgery

It has been suggested that surgery is almost

always required if the value for the ANB angle is

below –4° and the inclination of the lower incisors

to the mandibular plane is less than 80°

planning and commencement of a combined

orthodontic and orthognathic approach is best

delayed until age 15 years in girls and age 16

years in boys.

Key points

• Growth is often unfavourable in Class III malocclusions

• If orthopaedic treatment might be an option then it is important

to refer the patient to a specialist before 10 years of age

Reference