The Negative Effects of Thumb-Sucking

Most parents know that thumb-sucking can have a negative effect on the position of their child’s teeth, but most do not understand the significance of its impact on a growing face nor all of the other accompanying unfavourable sequelae.

Most parents believe that thumb-sucking will result in protrusive, splayed or “buck” upper front teeth. What they may not realize is that it can result in a serious anterior open-bite malocclusion, an increase in lower face height, a backwards rotation of the lower jaw and palatal constriction. This type of malocclusion is the most difficult for orthodontists to correct. The correction may involve a combination orthodontics and jaw surgery. In addition, open-bite type malocclusions are the least stable long-term especially if they are not addressed early enough or if treatment is delayed until later in the full permanent dentition and corrected by means of conventional orthodontics (braces alone).

When the thumb or fingers are put in the mouth enough of the time throughout the day, it prevents the natural eruption

Teeth showing the negative effects of thumb sucking.

of the upper and lower incisor teeth towards each other into a positive vertical overlap or overbite. Instead the teeth are prevented from growing together and the teeth become more and more separated into an anterior open-bite scenario. At the same time the back teeth are separated when the thumb is inserted, and this promotes over-eruption of these teeth into the space provided between them. This results in an increase in the lower vertical height of the face measured from the base of the nose to the bottom of the chin. As a consequence of this increase in lower face height, the lower jaw rotates backwards into an unfavourable retrusive position.

The sucking action causes an inward force from the cheeks on the side teeth and results in a narrowing of upper dental arch. The tongue that normally serves to maintain the width of the upper arch is positioned below the thumb when it is inserted and cannot retain the arch-form. If the upper jaw is narrowed or constricted, an arch width discrepancy develops with the lower jaw and dental crossbite relationships are generated. A crossbite is defined as an upper tooth or teeth positioned or fitting inside of a lower tooth or teeth. It is not unusual to observe multiple tooth crossbites on one or both sides of the dental arch in thumb-sucking patients.

When thumb-sucking has caused the upper and lower front teeth to be separated by a space (anterior open-bite) another habit develops, tongue thrusting. In a normal swallowing pattern, the teeth are closed together, the tongue rests gently up against the palate, lips are closed, and we swallow. In a patient with an anterior open-bite, the back teeth are closed together, the tongue is positioned or thrust forward to fill the space between the separated front teeth, lips are closed and then this individual would swallow. So, while the thumb-sucking habit may have been the initial cause of the open-bite, tongue thrusting, necessary to seal off the front of the mouth in order to swallow, maintains it even after a thumb habit is ceased.

If your child continues to suck their thumb beyond the time the permanent incisors begin their eruption (age 6-7), a visit to the orthodontist is recommended. The sooner this type of issue is addressed, the more successfully and less invasively it can be managed.

About the Author

Dr. Virginia Luks

Dr. Virginia Luks wanted to be an orthodontist like her father since she was a child. In 1997, after extensive training and accreditation, she joined her father's practice at Luks Orthodontics. She became one of the youngest orthodontists to attain Diplomate status in the American Board of Orthodontics and the first woman to be elected to Ontario's Dental Licensing Board, the Royal College of Dental Surgeons of Ontario. Dr. Luks thrives on clinical practice and creating new smiles every day. So for over twenty years, that’s what you’ll find her doing.

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