The Impact of Thumb or Finger Sucking

Thumb or finger sucking is considered an oral habit, which if engaged in frequently or for an extended duration, has impacts. There are many good reasons why an individual should eliminate a thumb sucking habit, including:

Overall Health

Our hands are dirty! And when an individual regularly sucks on their thumb, or other digit, they are taking in the grime. Keeping the thumb out of the mouth helps to keep germs, bacteria, staff, parasites, etc out of their digestive system.

Swallowing Development

Thumb sucking can impede a child's development in mastering a mature swallow. Swallowing is the process of moving food from the mouth to the stomach. In the mouth, food is crushed, mixed with saliva, and formed into a mass (i.e., bolus). The bolus is then pushed from the mouth into the throat by the tongue. The throat muscles move the bolus down, toward the stomach.

Swallowing develops in two stages. The first stage is known as infantile swallowing and the second is mature swallowing. The infantile swallow is characterized by a suckle-swallow pattern in which the tongue sticks out to pull in food in a back-and-forth pumping motion. By preschool, most children have a fairly mature swallow pattern. Thumb sucking can prolong the infantile swallow, which is also known as the reverse swallow or tongue thrusting.

A prolonged tongue thrust swallow can impede a child's ability to chew and swallow a variety of food/textures, lead to messy eating and open mouth chewing, and impact dental alignment (e.g., open bite).

Oral Rest Posture

Oral rest posture refers to the position the mouth assumes when not eating or speaking. When in oral rest, the mouth is quiet and the lips are closed, the tip of the tongue is elevated to "the spot" (i.e., incisive papilla behind the front teeth), and the root of the tongue is slightly suctioned to the palate.

Excessive thumb sucking may affect how an individual holds their mouth at rest, which also affects overall facial tone and appearance. The jaw may rest open, the lower lip may sag, and the tongue may lay low or even be protruding. A chronically lowered jaw can alter the way a child's face grows, resulting in a longer, thinner face. Such an individual may breathe through the mouth instead of their nose.

Speech Development

Chronic thumb sucking, as well as other oral habits, can interfere with a child's speech development in two ways. First, it can delay early speech in young children because a thumb in the mouth usually keeps a child quiet. Secondly, thumb sucking can interfere with a child's ability to learn later-developing speech sounds that require refined tongue movements.

Speech emerges in a fairly predictable way. The first sounds to emerge are typically those that are easy to produce (e.g., /m, b, w, d, n/). Early developing sounds do not require refined oral movements. However, later-developing sounds (e.g., /s, z, "sh," "ch," l, "r") require more refined oral motor movements such as:

Tongue tip elevation
lateral tongue elevation
Midline tongue depression
Lateral back tongue elevation

When thumb sucking is present and/or a child presents with a tongue thrust, an individual's ability to move the tongue in such refined ways may be impacted. The success in traditional speech sound therapy may be limited if the speech problem is the result of an oral habit. Therefore, eliminating thumb sucking may be the first step in solving erroneous speech sounds.

Dental Development

Thumb sucking can interfere with the position and alignment of an individual's teeth. This is because a slight amount of pressure applied to the teeth over a period of time causes the teeth to move and the bones around them to reshape. This same principle is found in nature - consider how flowing water (a consistent pressure on earth) changes the landscape over time. With thumb sucking, the changes that occur depend on three primary factors:

Frequency - the number of times per day that an individual sucks their thumb.
Duration - the length of time the child sucks during each occurrence.
Intensity - the effort involved in sucking.

These three factors - frequency, duration, and intensity - help determine if a child's thumb sucking will impact an individual's development and alignment of teeth and bone structure. If a child only sucks their thumb for a few minutes before falling asleep, the oral habit will mostly not have a dental impact. However, if an individual engages in thumb sucking throughout the day for extended periods and with effort, there is a greater chance their oral habit will have negative effects on their teeth and bone structure.

Summary

The impacts of thumb sucking may present differently for each child due to the three primary factors (i.e., frequency, duration, and intensity), and each individual will have their own motivations for eliminating their thumb sucking habit. A trained speech-language pathologist or orofacial myofuctional therapist will be able to evaluate an individual to determine the cause (or the why) of this habit, and to help develop a plan to eliminate thumb sucking and help them move forward in their orofacial and speech development.

Reference:

Marshalla, Pam. How to Stop Thumbsucking and Other Oral Habits. White City, Marshalla Speech & Language, 2018.