Research on Jaw Stability

By Pam Marshalla

features01Q: In your workshop on the lisps and R, you said that we now have numbers to define jaw stability. Can you share them here?

Yes! I would love to!

As we all know, the mouth can move in a range that far exceeds that necessary for correct speech articulation, therefore it has to have mechanisms to hold its moving parts in place. This process is called oral stability. Oral stability consists of three parts: jaw stability, lip stability, and tongue stability. Your question is about jaw stability.

This is what we know about jaw stability:

  1. The jaw moves up-and-down in a range of 25 mm during mature adult speech. That’s just under one inch (.98 inch). The highest position occurs on S and the lowest on Ah. This one-inch of vertical movement can be seen with the naked eye during a speech examination.
  2. The jaw moves left-and-right in a range of 2-3mm (about one eighth inch) from midline on either side during mature adult speech. This is a range of no more than 6 mm (1/4 inch) from the far left to the far right side. This very small range of lateral movement means that the naked eye registers the jaw as functioning essentially at midline during speech.
  3. The jaw moves forward-and-back in a maximum range of about 5 mm (.19 or 1/10 inch) during mature adult speech. The lower incisors are never positioned more anterior than the upper incisors.


  • Vatikiotis-Bateson, E., & Ostry, D. J. (1995). An analysis of the dimensionality of jaw motion in speech. Journal of Phonetics, 23, p. 101-117.

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