Fortunately, one of the recommended foods for messy poops/diarrhea is pumpkin - nice, soft unseasoned pumpkin. Baby food squash seems to help firm things back up too.
It makes sense to me that any change in diet is likely to upset a hedgie tummy. Sensitive little creatures they are. Check and look how the ingredients on the old and new food compare - is it the same brand, just canned? Same ingredients? Similar percentages of protein, fat, etc?
I tried a number of different things when my Satin needed softer food... putting her regular kibble in a grinder and wetting it, baby food, smaller kibble (RC Babycat), wet cat food... Perhaps some of those ideas might help??
Other than the teeth and diarrhea, how's your little one doing? What's her name? How old is she?