Thumb Sucking and Teeth Guide: When to Worry and How to Reduce It

Thumb sucking is a natural behavior by which babies soothe themselves, so in infancy it can mostly be watched. However, if the habit is strong and continues until permanent teeth come in, it can affect tooth alignment and jaw growth, for example by pushing the upper front teeth forward or leaving the upper and lower front teeth not touching. The KDCA (Korea Disease Control and Prevention Agency, 질병관리청) sees around 54-65 months as the time permanent teeth come in and recommends a dental checkup, so if the habit remains around then, it is good to have the dentist check the dental arch.

Published 2026-11-08 · Updated 2026-11-08 · DentalStatics editorial team

Key facts

Guidance on when permanent teeth appear	Around 54-65 months (dental checkup recommended in this period) (source: Korea Disease Control and Prevention Agency (KDCA))
Infant oral checkup	4 times between 18 and 65 months, no out-of-pocket cost (source: National Health Insurance Service (NHIS, 국민건강보험공단))
Topics at the oral checkup consultation	Oral hygiene care, eating habits, fluoride use, dental history and symptoms (source: Korea Disease Control and Prevention Agency (KDCA))
Oral habits that strain the jaw	Biting nails or lips, tongue thrusting, mouth breathing, etc. (source: Korea Disease Control and Prevention Agency (KDCA))
Insurance principle for orthodontics	Orthodontics for appearance is non-covered (except notified exceptions) (source: National Health Insurance Service (NHIS))

Why do children suck their thumbs?

Sucking is a reflex babies are born with, and it can carry over as a way to calm themselves when sleepy or anxious. So thumb sucking in infancy is not a problem in itself; it is something to watch for the strength of the habit and how long it lasts.

In many children it fades naturally as they start daycare or become interested in other play. Others keep it for a long time only in particular situations, such as when falling asleep or watching television, so noting when the child sucks makes it easier to choose how to respond.

How can thumb sucking affect the teeth?

When the thumb repeatedly pushes the upper front teeth forward and the lower front teeth inward, the upper front teeth can stick out, or a gap can form between the upper and lower front teeth even when the mouth is closed. Strong sucking can also affect the shape of the palate and how the upper and lower molars fit together.

Changes in the baby-tooth stage can partly reverse once the habit stops, but if the habit continues after permanent teeth come in, the changes can become fixed. If a habit of pushing the tongue between the front teeth or breathing through the mouth develops as well, the change in tooth alignment can be greater, so these are checked together.

When should a dentist check?

In Korea, the infant oral checkup can be taken 4 times between 18 and 65 months at no out-of-pocket cost, which makes it a good chance to ask when the habit is a worry. The checkup questionnaire asks about oral hygiene care, eating habits and dental symptoms, so mention the thumb-sucking habit there too.

When permanent teeth have begun to come in and the habit continues
When there seems to be a gap between the upper and lower front teeth even with the mouth closed
When the upper front teeth look noticeably pushed forward
When the child sucks so often that calluses or sores form on the finger
When speech sounds leaky or the tongue is seen pushing between the front teeth

How can you reduce a thumb-sucking habit?

Scolding or forcibly pulling the hand out can make the child more anxious and lead to sucking in hiding. It works better to notice and praise times when the child is not sucking, increase play that uses the hands, and create substitute behaviors, such as hugging a doll or holding a hand when falling asleep.

If the child is old enough to understand, explain in simple words why to cut back and let the child set a goal. Making successful days visible, for example by putting stickers on a calendar, helps the child stay motivated.

Record when sucking happens to find the cause (sleepy, bored, anxious)
Reduce situations that trigger the habit, such as screen time
Celebrate successful days together and do not blame failed days

When are habit-breaking appliances or orthodontics needed?

If the habit remains into the permanent-tooth stage even though the child tries to cut back, a dentist may recommend a habit-breaking appliance worn in the mouth. The appliance makes it feel less like sucking when the thumb goes in, helping to break the habit, and works better when the child agrees and understands.

If changes in front-tooth alignment or jaw growth have already occurred, an orthodontic consultation may follow after the habit stops. Orthodontics for appearance is non-covered by National Health Insurance in principle in Korea, so check the appliance and orthodontic costs item by item before starting.

Common myths and facts

Myth: Sucking a thumb always makes the teeth stick out.

The effect depends on the strength, frequency and duration of sucking. A mild habit in infancy often fades as the child grows, so it is not automatically treated as a problem.

Myth: Putting bitter medicine on the finger fixes it right away.

A bitter taste or a glove is only an aid to help the child notice the habit. If the child has no wish to cut back, the child may suck in hiding or shift to another habit.

Frequently asked questions

Which is better, a pacifier or thumb sucking?

Both can affect front-tooth alignment if used for a long time. A pacifier is easier for a caregiver to control the time of use, so set the situations for use and gradually reduce it.

My child sucks a thumb only while asleep. Is that okay?

A long-lasting habit during sleep can also put force on the teeth. Gently remove the hand after the child falls asleep, and create other calming methods before sleep, such as reading a book or holding hands.

A thumb habit opened up the front teeth. Will they return on their own?

If the habit stops in the baby-tooth stage, it can partly reverse. If a gap remains after the permanent teeth come in, have the dentist check the dental arch and jaw and watch the progress together.

Are nail biting or lip sucking similar problems?

The KDCA explains that oral habits such as biting nails or lips and tongue thrusting strain the jaw muscles and joints. While breaking thumb sucking, also watch that the child does not shift to another habit.

From what age is a habit-breaking appliance used?

It is decided by the stage of permanent tooth eruption and whether the child can understand and cooperate with the appliance, rather than by age. Even with an appliance, praise and creating substitute behaviors must go with it so that thumb sucking does not return.

References

Korean version →