Types of Lisps - An Explanation

A person who struggles to produce a crisp /s/ and /z/ sound are often categorized as having a lisp. Many children struggle with the /s/ sound in their early sound development; however, most acquire the sound by 4 years of age. Demonstrating a lisp when producing the /s/ and /z/ sound is a common speech sound disorder, but did you know that there are four different types of lisps? The four types include: interdental, lateral, dentalized, and palatal.

The /s/ Sound

Lisps are the result of incorrect placement of the tongue in the moth and airflow.

To produce the /s/ in a clear, crisp manner, the tip of the tongue should be just behind the alveolar ridge (i.e., the bumpy part of the palate that is right behind the front teeth). The tongue should be close to the roof of the mouth but not obstructing the airflow from passing over the tongue through the front of the mouth. There should be some space down the middle of the tongue for the air to move through. The sides of the tongue should be braced on the roof of the mouth. The teeth should be together and the lips should be slightly parted with the corners slightly upturned.

Any variation to the above description on the /s/ sound will lead to a distortion of speech that is commonly referred to as a lisp. Understanding the most common types of lips will help you to understand what causes your child's speech sound disorder so you can better know how it will be treated.

What Causes Lisps?

Some lisps may be the cause of a tongue tie (i.e., ankyloglossia), which is a condition in which the blade or body of the tongue is restricted to the floor of the mouth. There are different levels of restriction which can impact the tongue's range of motion.

Some lisps can be attributed to genetics. The development of a person's jaw, teeth, and tongue can impact a person's speech quality. Abnormalities of these structures can make it difficult to speak clearly.

Some lisps can be attributed to hearing loss. Children with mild hearing loss may hear sounds at different frequencies, which can effect their ability to hear and repeat a sound correctly. A child with a history of frequent ear infections, cerumen (e.g., earwax) build up, and/or PE tubes may demonstrate sound distortions due to their acquired, temporary hearing loss.

However, most lisps are the result of a phonetic disorder. A person acquires a maladaptive motor pattern of the tongue, lips, and jaw when producing the /s/ and /z/. If this pattern continues for a persistent duration, the pattern of production becomes solidified and a lisp is born.

Sometimes a lisp can be due to a combination of the above mentioned causes.

The Four Types of Lisps

Interdental Lisp

An interdental lisp, also called a frontal lisp, is the most common type of lisp. This lisp is caused by the tongue pushing forward between the teeth, which creates a "th" sound instead of a /s/.

This type of lisp is sometimes due to a tongue thrust, a symptom of an orofacial myofunctional disorder (OMD). Prolonged thumb sucking, pacifier use, allergies, and mouth breathing can cause an OMD. These habits and conditions promote a low forward resting tongue as well as a horizontal movement pattern of the tongue, which will press the tongue between the teeth causing an interdental lisp.

Dentalized Lisp

A dentalized lisp is another common type of lisp and is similar to an interdental lisp. In this case, a child pushes their tongue against the front teeth when making the /s/ or /z/ sound but does not push through the front teeth. The sound of a dentalized lisp is of a muffled /s/. Many children have dentalized lisps when they are young; however, if a child is still lisping by 4 years of age or you feel the sound is problematic, it is important to have a speech-language pathologist assess and treat the articulation disorder.

Lateral Lisp

A lateral lisp occurs when the sides of the tongue are not high enough to anchor to the palate of the mouth. Air escapes through the sides of the mouth instead of flowing down the middle which creates slushy, wet /s/ and /z/ sounds.

This type of lisp is often caused by incorrect tongue placement. Misalignment of teeth and jaws (e.g., malocclusions) and weak muscles may also cause a lateralized lisp. Sometimes a combination of these issues is the cause.

Palatal Lisp

A palatal lisp is the lest common type of lisp. It is caused by the body of the tongue being raised too high making contact with the palate. The tongue blocks the air flow causing a slushy, similar to a lateral lisp, and muffled /s/ and /z/ sound.

Treatment for Lisps

The treatment for lisps depends on the cause of the lisp. A speech evaluation is needed to determine the type of lisp and to create a treatment plan for the individual.

Most lisps are treated with an SLP over a few months to a few years. The older the child is once therapy begins, the longer the treatment typically takes. If your child's lisp is the result of a tongue/dental/orofacial myofunctional issue, they may also need to see a dentist, orthodontist, or otolaryngologist (ear, nose, and throat doctor) to help reduce any obstruction as well as participate in orofacial myofunctional therapy.