Frontal Lisp and Underbite

By Pam Marshalla

Q: I have a third-grader who has a frontal lisp on /s/ and /z/. He has an underbite and produces these sounds with his tongue contacting the inside of his upper teeth. Should I discontinue therapy until he is seen by an orthodontist or is there something I should be doing in the meantime to help him compensate for his jaw and tongue positioning? I am really not sure if he’s capable of a more retracted tongue position or if this is the best he can do given his current structures.

First we need to know what he can do with his jaw. Can he pull the jaw back in to a correct position? If he can, this may be a functional underbite, not a structural one.


You can figure this out simply by asking him to pull his jaw back to bite down with the molars on a probe. If he has a true orthodontic problem, he will not be able to bite correctly. The orthodontist will be the one to assess this formally, of course, but your preliminary screening test will give you an idea of where you are going with him.

With Braces

If it is a true orthodontic problem, and he is going to get braces, then I would wait till after the braces have made some changes. Monitor his speech once a month or so. His speech may or may not change as the teeth move. Once the front teeth are aligned better (and sometimes that happens almost immediately) then start to work on his tongue position in speech.

Without Braces

If he is not going to get braces, you are going to teach him to compensate for his structural problem. This means to work together with him (and maybe his parents too) to figure out what looks and sounds the best.


Most therapists tell me that the best /s/ that they can get from a child with an untreated underbite is to produce it with the tongue-tip hiding up behind the upper central incisors. It sounds like he is almost there already! So without braces, this is exactly what I would do starting now.

3 thoughts on “Frontal Lisp and Underbite”

  1. I have a 7 year old with an underbite and difficulty with the /s/. I have focused on training tongue tip elevation without dissociated jaw movement for the /t/, /d/, /n/, and /l/ sounds in co-articulation of simple repetive stories. As he began to adequately used his tongue tip to the alveolar ridge, he independent of treatment produced a more correct /s/ sound. He has a structural, not a functional underbite.

  2. I have a 7 yr old client with generalized hypotonicity. He presented with a severe phonological disorder. Now, we are seeing the imprecise consonant production and slushy sounding speech. He presents with a functional underbite, not a structural one. Any additional ideas to add to Phyllis’???? Oral motor exercises wear him out significantly!!! He is now stimulable for correct production of all phonemes in words.

  3. I have a 10 year old client who has what appears to be a structural underbite and /l/ and /r/ look physically painful for him to say correctly. Does anyone have experience with a student having surgery for this or is it just an orthodontic issue?

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