What is a retruded lower jaw?
With a retruded lower jaw (mandibular retrognathia), the lower jaw sits further back than the upper jaw. In orthodontics this is usually called a “Class II” bite. In profile the chin may look set back, the upper front teeth may sit well in front of the lower teeth and closing the lips may be difficult. For more information, see the retruded lower jaw and advancement page.
How does mandibular advancement with clear aligners work?
In this method, small projections called “precision wings” are added to the side sections of the clear aligners. When the mouth closes, these wings rest against each other and hold the lower jaw in a more forward position. The aim is to help the lower jaw adapt to this position during growth. The same aligners can continue aligning the teeth while the advancement is under way.
This approach is based on a principle similar to that of conventional functional appliances; the difference is that it is built into the clear aligners rather than being a separate appliance.
Who may it suit?
- Children and teenagers who still have growth potential (usually during the growth spurt)
- A Class II bite with the lower jaw set back
- Cooperative patients who can wear the aligners consistently
In adults who have finished growing, it is not possible to guide the growth of the lower jaw. In these cases dental corrections (camouflage) or, in advanced cases, orthognathic surgery are considered.
Why does timing matter?
The period when the lower jaw grows fastest is called the growth spurt, and it usually starts earlier in girls than in boys. To identify this period, age, rate of height gain, dental development and, if needed, the appearance of the hand-wrist or neck vertebrae on X-ray can be taken into account. Timing treatment to coincide with this period increases the chance of making use of growth.
The treatment process
- Examination, cephalometric (lateral skull) X-ray and intraoral 3D scan
- Preparatory alignment of the teeth before advancement, if needed
- The advancement phase with winged aligners and regular check-ups
- Detailed alignment of the teeth after advancement
- Retention phase
Comparison with a functional appliance
| Feature | Advancement with clear aligners | Conventional functional appliance |
|---|---|---|
| Appearance | Less noticeable | More noticeable |
| Tooth alignment | Can be done at the same time | Usually done in a separate phase |
| Speaking and eating | Taken out for meals; getting used to speaking is quick | Varies with the type of appliance |
| Dependence on wear | High | High with removable appliances, low with fixed ones |
The choice of method depends on the severity of the problem, the stage of growth and the patient's cooperation.