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Kids’ orthodontics · Habits & function
Habit & Functional Appliances for Thumb Sucking, Tongue Thrust and Mouth Breathing
Long-lasting habits such as thumb sucking, tongue thrust and mouth breathing can push teeth out of place and influence how the jaws grow. At Yonsei Baro in Seoul, orthodontist Dr. Sally Chaekyung Lee finds the cause first, then explains in English whether gentle support, a habit appliance or a functional appliance would help.
Habit appliances at a glance
| Question | At Yonsei Baro |
|---|---|
| Habits we look at | Thumb or finger sucking, tongue thrust and low tongue posture, mouth breathing |
| Possible effects | Open bite, protruding upper front teeth, narrow upper jaw, crossbite |
| First step | Find the cause; some children need an ENT or speech-therapy opinion |
| Appliances | Habit reminders, tongue guides, expanders, functional appliances, chosen per child |
| Typical ages | Usually from about 6–7, when adult front teeth come in |
| Treated by | Dr. Sally Chaekyung Lee, board-certified orthodontist, in English |
How can habits change the bite?
Teeth sit in balance between the lips and cheeks on the outside and the tongue on the inside. A thumb resting between the front teeth for hours, a tongue that pushes forward with every swallow, or a mouth that stays open to breathe can shift that balance. Over time, the result can be:
- An open bite , where the front teeth do not meet
- Upper front teeth that tip forward and lower front teeth that tip back
- A narrow upper jaw and a crossbite of the back teeth
- Lips that do not close comfortably at rest
How much a habit matters depends on how often, how long and how hard it happens, and on a child’s growth pattern. Not every habit causes a problem.
Thumb and finger sucking
Sucking is a natural comfort habit for babies and toddlers, and many children stop on their own in the preschool years. It becomes more of a concern when it continues as the adult front teeth come in, usually around age 6 to 7.
We start with encouragement rather than an appliance: praise, reminders and noticing when the habit happens, such as while watching a screen or falling asleep. If a child wants to stop but finds it hard, a small habit appliance behind the upper front teeth can act as a reminder. It is designed to help, not to punish. Our guide to thumb sucking and pacifiers has more tips for parents.
Tongue thrust and tongue posture
Some children push the tongue forward between the front teeth when they swallow or speak, or rest it low in the mouth. This can keep an open bite from closing and may contribute to a narrow upper jaw.
Depending on the child, Dr. Lee may suggest tongue exercises, a tongue guide or crib that reminds the tongue where to rest, or an expander when the upper jaw is narrow. When speech is also affected, a speech-language therapist can help alongside orthodontic care.
Mouth breathing
Children who breathe mainly through the mouth often hold the lips apart and the tongue low. Long-term mouth breathing has been linked with a narrow upper jaw, crowding and changes in how the face grows.
The cause matters most. Enlarged tonsils or adenoids, allergies or a blocked nose may need assessment by an ENT (ear, nose and throat) doctor, and Dr. Lee may suggest this before or alongside orthodontic treatment. Orthodontic options can include widening a narrow upper jaw and appliances that encourage the lips to close and the tongue to rest in the palate.
Types of habit and functional appliances
Habit reminder appliances
Fixed or removable appliances that sit behind the front teeth and make the habit harder to continue, so a child notices it and stops.
Expanders
Gently widen a narrow upper jaw while a child is growing, which can correct a crossbite and make more room for the tongue.
Functional appliances
Appliances that guide the jaws and muscles during growth, often used as part of growth guidance .
Clear aligners for children
For some children, Angel Aligner KiD or Invisalign First can address the tooth positions while habits are also being managed. Dr. Lee will explain which option fits your child’s problem.
A plan that fits your child
Habit correction goes more smoothly when the child is on board. Dr. Lee, who previously led pediatric and adolescent orthodontics at CDC Children’s Dental Clinic, explains each step to your child in simple terms and to you in English. Habit and functional appliances are one of four approaches in our children’s orthodontics program, and are often part of early treatment .
Habit appliance FAQs
At what age should thumb sucking stop?
Many children stop on their own before school age. Orthodontists become more concerned when frequent or intense sucking continues as the adult front teeth come in, usually around 6 to 7. If your child still sucks a thumb or finger at that age, a check lets Dr. Lee see whether the habit is affecting the bite and suggest gentle next steps.
Does a habit appliance hurt?
Most children need a few days to get used to a habit appliance. Speech and eating may feel different at first, and the tongue may be tender while it adjusts. It should not be painful. If something pokes or comes loose, send us a photo and we will advise you and arrange a visit if needed.
How long does a child wear a habit appliance?
It varies. Many children wear one for several months, and Dr. Lee often keeps it in place for a while after the habit stops so it does not return. You receive an estimated timeline after the examination, and progress is reviewed at each visit.
Will an open bite close once the habit stops?
In young children, a mild open bite caused by thumb sucking often improves after the habit stops, as the teeth and tongue settle. If the open bite is large, linked to tongue posture or to the way the jaws are growing, it is less likely to close by itself, and Dr. Lee will discuss treatment options.
Should my child see an ENT doctor for mouth breathing?
Often, yes. When a child breathes through the mouth because the nose or throat is blocked, for example by enlarged tonsils, adenoids or allergies, that cause needs medical assessment. Dr. Lee looks at how mouth breathing is affecting the teeth and jaws, and may suggest an ENT opinion before or alongside orthodontic treatment.
Medically reviewed by Dr. Sally Chaekyung Lee, DDS, PhD
Board-certified orthodontist (Korea Ministry of Health and Welfare) · Adjunct Professor of Orthodontics, Yonsei University · Last updated October 2026
This page is general information, not a diagnosis. Treatment results and duration vary from person to person. Orthodontic treatment can cause temporary discomfort and, in some cases, root shortening, gum recession or tooth decay if oral hygiene is poor; teeth can relapse if retainers are not worn as instructed.
Worried about a habit?
Book a check with Dr. Lee. She will look at how the habit is affecting your child’s teeth and explain the options in English. Isu Station Exit 2 · Open until 9 PM Mon & Thu · Saturdays 9 AM–2 PM.