Short answer: Functional appliances are orthodontic devices that use the natural forces of the jaw and surrounding muscles to support harmonious growth of the upper and lower jaws in growing children. The main types are the activator, the Frankel and the Twin Block. They can be more meaningful when used while bone growth is still ongoing. Which appliance is suitable and when to start are determined by an orthodontic examination.
In children, the growth of the jawbones is as important as the alignment of the teeth, and it may be possible to guide this growth during the growth years. Functional appliances are orthodontic devices that aim to support the upper and lower jaws in growing in harmony with each other by using the natural strength of the chewing, swallowing and jaw muscles. In this article we explain the logic of functional orthodontics, the main types of appliances, the problems they are used for and how treatment progresses.
What is a functional appliance?
A functional appliance is an intraoral device that supports jaw growth by redirecting the pressure of the jaw muscles and surrounding tissues such as the lips, cheeks and tongue, without using wires or brackets that move teeth on their own. It is usually made of acrylic and wire components, and most are removable.
While conventional braces move teeth directly, a functional appliance has an indirect effect by changing the resting position of the jaw and the bite. Positioning the lower jaw forward, restricting the growth of the upper jaw or balancing jaw width are examples of this approach. For a general overview of the appliance concept, you can read our what is an orthodontic appliance article, and you can find the full list of types on our orthodontic appliances page.
Why are functional appliances effective during the growth years?
Functional appliances can give more meaningful results when used in childhood and early adolescence, while the jawbones are still growing and tissues respond more readily to guidance. Once bone growth is complete, the skeletal effect gradually decreases and tooth movement comes to the fore.
In growing children, bone has the capacity to adapt to the forces exerted by the surrounding muscles. Even so, the extent of the effect of functional appliances on bone varies from person to person, and research shows that a significant part of the correction may come from the teeth and their supporting tissues. That is why the realistic expectation for families should not be "the jaw will change completely" but rather "intervention at the right time can make later treatment easier." The orthodontist determines when to start based on age, skeletal maturity and the child's oral development.
What types of functional appliances are there?
There are many types of functional appliances, and all aim to correct the relationship between the jaws; the differences lie in their design and how they are worn. The most commonly mentioned types are:
- Activator appliance: A removable acrylic device that holds the upper and lower teeth in a single piece; it is usually worn at night and at home and guides the lower jaw forward.
- Frankel appliance: A device with broad acrylic shields and wires that aims to remove the pressure of the cheek and lip muscles and create room for jaw growth.
- Twin Block: Consists of two separate acrylic plates for the upper and lower jaws; it can be worn throughout the day and guides the bite into a position that brings the lower jaw forward. We cover this device, which is often used for a retruded lower jaw, in a separate article.
- Bionator and similar designs: Removable devices with a slimmer design aimed at balanced function of the tongue and cheek muscles.
- Fixed functional devices: Mechanisms fixed to the teeth, used when the child's compliance cannot be relied on.
Which device is suitable is decided together with the orthodontist based on the child's age, jaw structure, dental development stage and the family's ability to keep up with follow-up.
For which problems are they used?
Functional appliances are mostly considered in cases where the lower jaw is set back or the upper jaw is too far forward, the upper front teeth protrude noticeably and growth potential remains. They can also help with some deep bites and certain jaw discrepancies.
On the other hand, they may not be enough on their own, or a different plan may be needed, in the following situations:
- When there is significant crowding or a lack of space for the teeth.
- When the upper jaw is narrow; expansion may be needed first.
- In teenagers whose growth is largely complete.
- When the child cannot wear the device consistently.
When the relationship between the upper and lower jaws is reversed, that is, when the lower jaw sits in front, a different approach is usually followed; our orthodontic face mask article covers this topic.
How long does treatment take?
The functional appliance phase lasts between six months and a year and a half in most children; a second phase may then be needed to align the teeth or for retention. This range is not a fixed duration and is determined by the orthodontist's examination.
The main factors affecting the duration are the child's growth rate, how many hours a day the device is worn, the severity of the problem and attendance at regular check-up appointments. If the device is removable, sticking to the wear time directly affects how treatment progresses. In the first weeks of treatment, slight changes in speech and chewing, tooth sensitivity and increased saliva may occur; these symptoms usually ease quickly. After the first phase during the growth years, a second phase of treatment may be planned once all the permanent teeth have come in; this two-phase approach is common in orthodontics.
How are functional appliances used in daily life?
Removable functional appliances work when worn consistently for the time set by the orthodontist; for most children, this covers certain daytime hours and the night. The device feels like a foreign object in the first days, so gradually increasing the wear time makes it easier to get used to.
- The device should be cleaned every day with water and a soft brush and should not be exposed to hot or boiling water.
- When removed, it should always be kept in its case; devices wrapped in a napkin often end up in the trash.
- Brushing the teeth is the most important step before putting the device in; otherwise bacteria build up between plaque and the acrylic.
- If the device breaks, cracks or starts to feel tight, do not try to fix it yourself; call the clinic.
- Encouraging the child with small goals and tracking charts, rather than punishment, improves compliance.
Follow-up appointments are usually every four to six weeks. At these visits the orthodontist checks the fit of the device, the position of the jaw and the eruption of the teeth, and adjusts the device if necessary.
What are the limits of functional appliances?
Functional appliances do not solve every jaw problem; their real strength lies in being used for the right child at the right time. If the teeth themselves are crowded, the jawbones are markedly mismatched or growth is already complete, they may not be enough on their own. In that case the orthodontist discusses options such as fixed braces, elastics, mini-screws or, for very advanced skeletal differences, jaw surgery.
In addition, when the device is removable, success depends largely on the child's compliance. That is why, before starting treatment, orthodontists also discuss whether the child and family will be able to use the device consistently. If necessary, methods that require less compliance are chosen. For more limited goals, such as holding space after a baby tooth is lost, you can see our space maintainer article.
Functional appliances vs. Invisalign First
A functional appliance aims to guide the position and growth of the jaws relative to each other; Invisalign First is a clear aligner system that supports tooth alignment and dental arch expansion in children in the mixed dentition stage. The two do not serve the same purpose, so one is not considered a direct alternative to the other.
If a child's main problem is only tooth alignment and lack of space, a clear aligner approach may be discussed; if there is a significant jaw discrepancy, a functional appliance or fixed device may be more suitable. In some children, the two methods are planned together in stages. For details, you can visit our Invisalign First for children page; you can find out when orthodontic treatment with Invisalign becomes an option at older ages on our what age for clear aligners page.
When should you take your child to an orthodontist?
Orthodontists recommend that children have their first orthodontic evaluation at around age seven; this examination does not mean starting treatment, it is simply for monitoring development. It becomes even more important when the lower jaw looks set back, the upper teeth protrude, tooth eruption is delayed or habits such as thumb sucking or mouth breathing continue. At our clinic in Park Oran, Çankaya, your child's growth is assessed during an examination by an orthodontist; if needed, follow-up is recommended or the treatment plan and cost information are shared in writing. You can use our contact page to book an appointment.
Frequently asked questions
At what age is a functional appliance fitted?
It is usually used in childhood and early adolescence, while growth is ongoing and the mixed dentition is present. The exact timing is determined by the orthodontist based on age, skeletal maturity and the type of problem.
Are functional appliances removable?
The activator, Frankel and Twin Block are removable types. Fixed functional devices, on the other hand, are bonded to the teeth and removed by the orthodontist. Which one is chosen is planned according to the child's compliance.
Does a functional appliance replace braces?
Usually not. A functional appliance targets the relationship between the jaws; for full alignment of the teeth, most children need a later phase with braces or clear aligners.
What happens if the device is not worn consistently?
Inconsistent wear reduces the guiding effect and can prolong treatment. If the child is having difficulty wearing the device, the family should talk to the orthodontist; a different device may be considered if necessary.
Does a functional appliance have the same purpose as Invisalign First?
No. A functional appliance targets the relationship between the jaws, while Invisalign First is mostly aimed at supporting tooth alignment and arch expansion. Which one is suitable is decided after an examination.
