Jaw Movement

Jeffrey Sirianni audioman at hctc.net
Fri Oct 22 11:23:00 EST 1999


Case for Discussion:

Patient is a 70+ year old male with steeply sloping HF SNHL (near normal at
500 Hz, moderate loss at 1000 Hz, severe by 2000 Hz).  He wears binaural
BTE's (two channel WRDC) successfully.  He is a fairly sharp individual and
so is his perception of sounds in his environment, and he seems to report
such observations to me.

He has experienced concha and EAC changes over the last three years which
has caused unacceptable amounts of feedback, which were not present when
initially fitted.  He also reported that when he opens his mouth, he seems
to hear better with his aids.  Opening his mouth without the aids does not
seem to create this phenomena, although with this amount of HF SNHL, I
doubt he can detect any change, if present.  Examination of the EAC shows
some movement when he opens and closes his mouth.  New earmolds were
ordered with longer canals to try to minimize EAC changes with jaw
movements and to reduce feedback.   Earmold impressions were taken while
chewing gum.

He says he still notices a change when he opens his mouth, and reports that
the high frequency response (perception of HF) improves when his mouth is
slightly open.  I really don't want to shorten these earmolds as I suspect
that feedback will come back and I can't make the canal length long again
once shortened.  I also predict that any changes in the EAC with jaw
movement will still be present with a shortened canal.

I think this is a case of explaining to the patient that by shortening the
canal length of the earmold may or may not reduce this open jaw effect, but
will definitely increase the chance of feedback, and that feedback control
is more important than the slight high frequency drop when his mouth is
closed.

I would like to hear other opinions or recommendations from the group.  Am
I missing something?

Jeff




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* Jeffrey Sirianni, M.A., CCC-A, FAAA             *
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