Research Review

Conservation of Intraoral Pressure Changes During Swallowing

Personally, I’m very interested in intra-oral suction during swallowing, i.e., the negative pressure that occurs prior to the actual swallow to move the contents to the tongue.  It’s apparently quite difficult to prove, study, and measure intra-oral suction.  No doubt because it happens behind closed lips and it’s abstract. 


The terms intra-oral suction and intra-oral pressure mean two different things.  When researchers site “pressures” they mean lingual pressure, i.e., lingual contact on or against teeth, hard palate, soft palate, etc. 


I keep hoping to find definitive studies on intra-oral suction.  If you know of one, please let me know.



Main Purpose:  This study explored intra-oral pressure changes on the roof of the mouth during normal swallowing, and assessed swallowing pattern differences on different commands of saliva and water.  They also wanted to see if there was a difference in saliva swallows (higher viscosity; thicker) when compared with water swallows (lower viscosity; thinner).  (There was no significant difference.)


Overall Method:  The researchers custom-made a palatal appliance fit with miniature pressure transducers along the midline in the front, middle, and back.  The participants were eight healthy 24 to 35 year-olds with full permanent dentition (and presumed correct swallows).  Each volunteer swallowed 10 mL of water (about 2 teaspoons full, so one single-sip), three times on 5 separate days, and asked to swallow saliva on command.


Findings and Application:  There was no significant difference in pressure amplitude between swallowing saliva (spontaneous and on command) and swallowing water (on command).  Prior to the study, they thought there would be.  They concluded, “an individual’s pattern of response to a command swallow does not differ substantially from the pattern seen during a spontaneous swallow.  It suggests that we can assume that the responses we observe when an individual makes a conscious effort to swallow closely resemble the responses that occur during automatic swallowing.”

This is important info for therapy.  I like to teach single-sip drinking, then continuous drinking, then saliva swallows, in that order, over several weeks.  I can now reliably tell the client that the saliva swallow (the Bite-Squeeze-Lift part) is the same as the single-sip.  Continuous drinking is another animal, however.


In addition, each participant had a distinct pressure response pattern during each of their saliva and water swallows.  On the chart (on page 326), the pattern of tongue-palate compression is distinctly different for each person, but consistent for each swallow done by each person.

Therefore, not everyone must apply the same amount of pressure at the same time on the roof of the mouth, but everyone must compress the contents back and down from front to middle to back.


Nothing was mentioned as to how the water was transported into the mouth and then onto the tongue.  That’s an important point that I believe is frequently missed.  The tongue--a bundle of muscles--is the contents recipient and occasional food dislodger.  Intra-oral suction moves water (and saliva and food).  once the water is discreetly sucked from the glass, intra-oral suction arbitrates and transport the water back to the waiting tongue.  The tongue in coordination with the roof of the mouth, dispatches the water from front to back, and swallows it.  As this article points out, the broad view of the swallow is that the tongue swallows front-middle-back.  The specific detailed view of the swallow is that each person’s unique style of tongue-palate activity is different for each person.  In my estimation, as a therapist, my concern is the broad view.  Once my client has the general pattern down (Suction: Bite-Squeeze-Lift), they are free to personalize the pattern so it’s comfortable and serviceable for them.

by Char Boshart, M.A., CCC-SLP
Bolter C, Raniga N, Waddell JN, Kieser, J. (2012) Conservation of intraoral pressure changes during swallowing. Journal of Dental Sciences, 7, 324-329.

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