Treatment for Class III Malocclusion
Class III malocclusion is characterised by mandibular prognathism, maxillary retrognathia or both. Patients typically present with a concave profile because of a prominent mandible. Some common dental concerns associated with class III malocclusion are:
- narrow maxillary arch
- broad mandible
- posterior and anterior cross bite.
The soft tissue has minimal aetiological effect in class III patients. The degree of anteroposterior and vertical skeletal discrepancies determines the complexity of the necessary treatment. Unfavourable growth greatly affects the treatment outcome and highly increases the risk of relapse following treatment. A better prognosis is evident in patients who are able to achieve an edge‐to‐edge incisor relationship, which is also known as pseudo‐class III.
Treatment options for class III malocclusion vary, depending on the location of the excess or deficiency (Guyer et al., 1986). Mandibular prognathism or overgrowth with a normal maxilla is known as true mandibular prognathism. Hypoplastic maxilla results in an anterior cross bite in the absence of mandibular prognathism. A combination of maxillary retrusion and mandibular protrusion is one of the most commonly seen patterns in skeletal class III malocclusions.
Treatment in Mixed Dentition
The use of an acrylic splint expander (a bonded rapid maxillary expander) simultaneously together with a face mask (reverse pull headgear) is an effective treatment option for skeletal class III malocclusions during an active growth phase. This type of treatment was introduced by McNamara. The expansion of the maxilla aids in correction of the narrow upper arch and eliminates any posterior cross bite. The bonded rapid maxillary expander (RME) is designed with vestibular hooks to allow the attachment of the facemask for protraction of the maxilla (Figure 8.1). The facemask must be worn for a minimum of 14–16 hours for optimal results. For better patient comfort, this appliance is recommended to be worn outside of school hours. The degree of activation of the palatal expander is decided by the orthodontist. The treatment goal is to move the maxilla downwards and forwards using the face mask. Thus, when the face mask hooks are adjusted for elastic wear, it is critical to ensure that the elastics pull the maxilla downwards and forwards (Figure 8.2). This type of treatment is shown to be more effective in patients with mild to moderate skeletal class III malocclusions with a hyperdivergent growth pattern and a retrognathic maxilla.
Congenital class III malocclusions deteriorate after the growth spurt and surgery might be indicated. Thus, treatment might need to be delayed until growth has ceased to prevent relapse. Depending on the position of the maxilla in relation to the craniofacial reference points, the choice of the surgical procedure will vary (discussed further in Chapter 11).
Early intervention in some patients is advantageous for several reasons, although the timing and duration of the treatment is solely decided by the orthodontist. The objective of early treatment is:
- to reduce the severity of the problem, thus reducing the complexity of phase II treatment
- to enhance a functional occlusion
- to improve the psychosocial wellbeing of the patient
- to create favourable dentofacial development that accommodates future growth
- to reduce the need for future orthognathic surgery, although it is important to raise patient awareness that surgery may be indicated despite the success of the treatment. This possibility will depend on the type and degree of further growth.
The Frankel III regulator is not a popular appliance, although it has been used to treat some skeletal class III malocclusions. This functional appliance aids in forward development of the maxilla by using muscle force and redirects mandibular growth posteriorly. The labial pads distance the upper lip from the maxilla and allow the force to be transferred to the mandible as the appliance closely fits in the lower arch. This appliance is only effective with good patient compliance and full‐time wear of the appliance. Chin cup therapy was another effective treatment in patients with skeletal class III malocclusion who presented with a normal maxillary position. This early intervention inhibited mandibular growth in mild to moderate cases. This type of treatment is also no longer popular, particularly with the increased availability of treatments involving temporary anchorage devices and skeletal plates. Incorporation of temporary anchorage devices in skeletal class III treatment can be achieved in many ways and these devices have proven to be one of the most effective treatment options for class III malocclusions; for example, using lower skeletal plates in combination with an RME supported by a temporary anchorage device.