I also don't know about treating stomatitis, other than full extraction, but I do know they can test for it to be sure that's what it is.
I like to use flower essences when I can. I have no idea if
Immune Support from Green Hope Farms will help but stomatitis is an auto immune disease. I've had good luck with these essences from this particular company but you also have to be open to the fact that there is healing energy in flower essences. I find that, typically, flower essences work best as part of an holistic strategy which might include a few modalities.