You both buy the type of toothpaste that you like (I don't want anybody using my toothpaste, even if I'm married to them).
I can't fathom someone buying a type of toothpaste that smells/tastes so bad their partner wouldn't want to kiss them. It's toothpaste, they're all pretty much the same.
If it is actually a problem get them to swish some water around in their mouth and that will get rid of a lot of the problem or have them use some mouthwash you both don't mind the smell/taste of.
Or just talk to them and ask if they'll switch, it shouldn't be a big deal. If it is, why did you marry them?