I did this with DC#1 until I changed my toothpaste to Tom's. Probably any natural toothpaste will do- it was the disgusting artificial garbage in the mainstream toothpastes that my body was objecting to. Also, keep in mind that you do not need toothpaste- you can just brush with your plain brush. Or you can try baking soda if you want something, but that might be a strong taste to handle.
Funny thing is, now, even between pregnancies, I prefer the natural pastes. The others just taste so fake to me.