Is tea tree oil safe?

I just bought some tea tree oil for oral hygiene -- I want to add a couple drops to water for a mouthwash or add it to my toothpaste. i read on the bottle that it's not safe to ingest -- but several website say it's okay to use as long as you don't swallow it. I'm still concerned about the toxicity issue -- has anyone used a few drops of it and had any issues??