I agree that smothering isn't the right word here.  I believe that when a
toddler (or any age baby with teeth) chomps down and bites, if you pull him
in to the breast, the jaw relaxes and releases the bite.  If the baby is
pulled away he will clamp down harder to keep the nipple from getting away.
All five of mine have gone through a stage where, just as they drop off to
sleep they chomp down.  YIKES!!!  It wasn't until baby # 4 that I learned to
pull the baby in tight.  It really works.  I would NEVER use the word
smother, or even suggest that this action has anything to with interupting
the baby's ability to breath.

Nancy Sherwood  mother of 5 who sometimes wonders how many gallons of milk
I've produced in the past 18 years of non-stop breastfeeding!