Functional appliances

The idea

Where a child's lower jaw sits well behind the upper one, aligning the teeth alone produces straight teeth in a poor skeletal relationship. A functional appliance holds the lower jaw in a forward posture so that growth expresses itself in a more favourable position, alongside dental changes that come with it. The aim is to set a better foundation while the foundation is still being built.

We use these appliances because getting the jaw relationship right early reduces the likelihood of two outcomes families would rather avoid later: removing permanent teeth to camouflage a discrepancy, and jaw surgery in adulthood. That is not a guarantee in any individual case, and it is not an argument for treating every seven-year-old — many children are better served by monitoring until the right moment. But where the discrepancy is genuine and growth is available, waiting has a cost.

The common types

• Herbst. Fixed, with a telescopic arm on each side connecting upper and lower. Nothing to remember, which is its great advantage. Speech and eating adapt within a week or two.
• Twin block. Removable, in two parts with interlocking bite blocks that posture the jaw forward. Comfortable and effective, and entirely dependent on wear.
• Headgear. Used less than it once was, but still appropriate in specific cases where upper jaw growth needs restraining. Night wear only in most prescriptions.

Where expansion fits

Many children who need a functional appliance also need the upper arch widened. That can be done as a separate expansion phase beforehand, or the expansion can be built into the functional appliance so a single appliance handles both the width and the jaw relationship. Both are legitimate, and the choice is made per case rather than by protocol — it depends on how much expansion is needed, how it interacts with the jaw correction, and what the child will tolerate.

Timing and sequence

Functional appliance work is usually a first phase, most often between about ten and fourteen, timed against skeletal maturity rather than birthday. A second phase of braces follows once the permanent teeth are in, to align and finish. Families sometimes read this as treatment twice; it is more accurately one treatment plan with the skeletal work done when it is possible and the dental work done when the teeth are there.