I like "Oral cancers.....it's not just for smokers anymore"

and

" go ahead.....stick your tongue out at your dentist........make his day.........save your life!!!!!!!! "

or a variation of this idea......maybe:

" it's ok to be rude....sticking your tongue out at your dentist can save your life......"

here's one from my personal experience

"my dentist saved my life.....is your dentist screening for oral cancer?"

Sandra