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On April 18th, I posted a question on whether the location of
canker sores varies with their causes.  Below I've tried to
summarize responses that seemed to be most helpful.

First, here is the original posting:
"I found that gluten-containing foods give me canker sores, and so I
have sworn-off every gluten I can think of.  Now I never get canker
sores on the lips and that is a huge improvement.  However, I
notice that maybe every two weeks or so I get a canker sore on the
inside of the cheeks.  I have been putting this down to something I
ate, like too much salt on popcorn, or too much chocolate.  It
occurred to me recently that maybe gluten, for people who can't
tolerate it, causes the sores to break-out on the lips while some
other agent(s) cause the sores to break-out on the cheeks.

Of course the sores on the cheeks are often precipitated by me
accidentally biting my cheek.

Perhaps the surfaces of those different sites are sensitive to
something produced by the particular agent, but not by the other
agent.

Has anyone else thought the same?"

Here are the responses.  I've put a comment after each in square
brackets [ ].

********************

"Look at toothpaste. I suffered through these for years and years
before I was diagnosed with CD. It is not uncommon to get minor
little scratches and nicks in your mouth during brushing and eating
some foods (like chips, doritos, etc.) The gluten in the toothpaste
contacts the open sore and is inflamed (or at least that's my
theory). I have problems with pastes and anything containing
baking soda. I do best with non tartar gels."

[On an Internet bulletin board devoted entirely to the subject of
canker sores, there is a hot thread on using baking soda (sodium
bicarbonate) to heal active canker sores and as a mouthwash to
prevent the formation of new canker sores.  In other words, there
are many on that board who claim that baking soda is a
cure/preventive for canker sores.  My toothpaste is Oral-B's
Zendium toothpaste, and as far as I can see from reading the very
detailed label of ingredients, there is no gluten in this toothpaste.]

  The canker sore bulletin board is at:

www.saveyoursmile.com/wwwboard/wwwboard.shmtl

********************

"As for location/cause I think it is simply a matter of where there is
an open sore. Note that since toothpaste is NOT for consumption,
ingredients are not listed so I've found it to be trial and error."

[I find that almost every toothpaste I have looked at has a detailed
list of ingredients on the package or container.  The reason I've
made such a study of toothpaste labels is that there is some
evidence that a sudsing or foaming agent common to many
toothpastes, sodium lauryl sulfate, causes canker sores.  I am
leaning more and more to agreeing that breaks in the soft tissue
and the harder tissue of the inside of the mouth often lead to
canker sores.  Why I and others get canker sores while most of
the rest of the population do not is the $64 question.  Also, the
kernel of my original question still remains:  why does going gluten-
free stop me from getting any canker sores at all on the inside of
my lips (even where I have accidentally bitten them) but not from
getting them on the insides of my cheeks?]

********************

"...what you are experiencing is an oral blood blister.  Or so says
my Dentist.  He cured my problem with cheek biting by doing a bit
of adjustment to the bite of my teeth.  (it started when I got a new
crown placed)."

[I know what an oral blood blister is, because I have gotten a few of
them, but they don't always turn into canker sores, while a cheek
bite will often become a canker sore unless I treat it immediately
with iodine or something like that.  Working to prevent biting the
cheek sounds like a good idea, but it doesn't solve the problem of
why biting my lip doesn't lead to canker sores nowadays. Of
course preventing any canker sores from breaking out would be a
wonderful step even if I don't ever find out why I've been "cured."]

********************

"...I have been rescued by my dentist from a miserably sore mouth.
My mouth is somewhat dry and inflamed (no cause known), and
during the winter months the inside of cheeks, especially on one
side became ulcerated and painful. All I could think about was how
bad my mouth felt. I was awake for hours every night and went to
work feeling like a zombie.

Finally, I realized that I must be biting my cheeks at night and I
asked my dentist for help. She ground and reshaped teeth that
seemed to be causing trouble. That alone helped, but then she
ordered a mouth guard for me to wear at night. It's just a small
plastic shield that goes over my top teeth and protects my cheeks.
Now, I have no more mouth pain, although I still have to be very
careful to take care of my mouth because of the dryness."

[The mouth guard idea sounds like a very practical approach.  The
thought of my dentist grinding on my side teeth sounds almost as
bad as having canker sores!  Just kidding.  I'll have to have my
teeth looked-at.  The Oral-B Zendium toothpaste has enzymes
added to treat dry mouth, but despite using that toothpaste, I still
get the cheek canker sores.]

********************

"...your letter makes me wonder how long  you have been avoiding
gluten.  I wonder if perhaps you haven't learned all the tricks for
avoiding the hidden glutens and are getting a little by mistake, but
perhaps not enough to bring on the sores on the lips."

[A very good point.  I've only been off gluten since January of 2000,
although as soon as I quit gluten my canker sore frequency
dropped dramatically, and on the two or so occasions I
accidentally ate some gluten-containing foods, I had some bad
sores within one or two days.  I'm trying my best to keep away
from anything with wheat, rye, barley and oats.]

********************

Several responses recommended yogurt, l-lysine, various bacterial
culture-containing intestinal health mixes and so on.  I've done all
these things in the years leading up to the discovery, thanks to this
wonderful site on celiac disease, that gluten was the cause of the
majority of my canker sores.  Nothing except going gluten-free ever
worked for me.  Now if I could just learn what it is about biting the
cheek that causes canker sores, I would be one step closer to
bliss.  Thanks to all who responded, and apologies if I did not use
your response (I certainly would be miffed if someone didn't use a
response I made!)