Diagnosis
The diagnosis can be a dental Class III (dental displacement), skeletal Class III (skeletal displacement) or a combination of both.
A dental or skeletal Class III will have different subtypes and their diagnosis is usually derived by history taking and a clinical examination supported by radiographs and dental models.
Dental Class III
- A dental Class III occurs if a patient has Class III buccal segments (canines and molars) and/or Class III incisor relationships. See the intra-oral appearance of a dental Class III here.
- It is important to diagnose the position of the lower and upper incisors within the alveolar bone to determine the level of dental compensation present on a Class III skeletal base.
- A pseudo Class III relationship can exist due to a forward functional shift.
- Asymmetries of left and right side dental relationships, called subdivisions, often exist.
- The aetiology can be multiple factors including early loss of deciduous teeth/leeway space leading to mesial drifting of teeth, tooth-arch size discrepancy, malformed teeth, supernumerary teeth, retained deciduous teeth or ectopic teeth.
Skeletal Class III
- A skeletal Class III jaw relationship can occur with or without a Class III dental malocclusion.
- It occurs when the mandible is more posterior to its normal position relative to the maxilla. See the extra-oral appearance of a skeletal Class III here.
- According to the Steiner’s analysis, a skeletal Class III is an ANB < 1 degree for caucasians.
- According to the Wits analysis, a skeletal Class III is a Wits value more negative than -1mm.
- There are several types:
- Maxilla retrognathia (most common)
- Mandibular prognathism
- A combination of the above
- Asymmetries may exist.
- The aetiology of mild to moderate cases are often unknown and can be considered part of the normal genetic variation and environmental influences of size and position of the jaws.
- The aetiology of severe cases can be several factors including in-utero developmental disturbances (e.g. Treacher Collins syndrome, Crouzon syndrome), in-utero growth disturbances (e.g. intra-uterine moulding), childhood and adolescent growth disturbances (e.g. condylar hyperplasia) and adult growth disturbances (e.g. pituitary gland tumors causing acromegaly).
Clinical Considerations
Determine the aetiology of the dental and/or skeletal Class III
- Treatment should be targeted to diagnosis and aetiology. The relevant mechanics, appliances and possible need for surgery can be planned accordingly.
- Multiple diagnoses are often present. For example, a patient with a skeletal Class III hypoplastic maxilla may have Class I molars and Class III canines and incisors, with mid-arch dental crowding.
What is the growth status?
- The growth status of the patient will influence the possibility if the Class III pattern will worsen or remain consistent with growth.
- The growth status will also influence if early treatment, growth modification or surgical treatment options are available to the patient at their current age.
Should the Class III be corrected?
- Class III occlusion is the least common sagittal malocclusion (5% Todd and Lader 1988), however it has great variability depending on the race and geographical regions (Hardy et al. 2012). It is more common in Chinese and Malaysian populations (Hardy et al. 2012).
- A mild dental Class III buccal segment is not an indication to treat the malocclusion by itself.
- Treatment decisions should hence be based on the other treatment indications.
The morbidities and compromises of different treatment options
- The number of treatments and the duration of treatment can cause significant burden to the patient and parents. Patient burnout needs to be considered particularly if shorter and more effective treatment options are available instead.
- Orthodontic camouflage to correct a Class III malocclusion often means a compromise on excessive proclination of upper incisors (which can be unaesthetic with a flat smile arc) and/or excessive retraction of lower incisors. The limitations of camouflage, besides the aesthetic considerations, are often the alveolar dimensions and soft tissue envelope.
