We all know someone who has a lisp, right?

There are actually four different types of lisps (see below), but the most common is an interdental lisp, when the tongue pushes through the front teeth and the /s/ sound is pronounced like a /th/. “See” sounds like “thee,” “bus” sounds like “buth...” you get the idea.

The research of what falls under “normal” development for sound acquisition varies across different researchers.

Caroline Bowen PhD, a well-known speech-language pathologist with a doctorate in clinical linguistics, believes that having a lisp is a normal developmental phase of speech/sound acquisition, until about 4 and a half years old. Others believe that its not something to address until after age 6.

Missing Teeth and that Lisp!

The /s/ sound is a sibilant, which means its a “hissing” sort of sound. It is produced when the airstream hits the back of the teeth or dental wall, and rebounds around until the air exits the mouth, creating a strident or friction sound.

When the front teeth are missing, especially when so many are missing, the airstream broadens. The air usually will come out wherever the teeth are missing. This gives it a slushy and imprecise sound. However, in the instance of only 1 or 2 teeth missing, it is still possible to produce an accurate /s/ sound.

A lisp is something that can be corrected in speech therapy. And as always, early intervention is the best intervention. If your child has a lisp, and is around 4 years old, then you may want to consult with your pediatrician and see if speech therapy is indicated.

There are four main types of lisps:

• Interdental lisp—occurs when the tongue protrudes between the front teeth and the /s/ or /z/ is pronounced like /th/.
• Dentalized lisp—occurs when the tongue pushes against the front teeth.
• Lateral lisp—sounds wet or “slushy” because the air flows around the tongue.
• Palatal lisp—the middle of the tongue touches the soft palate, or roof of the mouth, when trying to produce the /s/ sound.

For more information on speech development, check out our quick guide to sound acquisition or this articulation development chart.