What dark brown liquid do dentists use while drilling n filling cavities? It was in a dropper like lil bottle. He used it on my wisdom tooth. Tasted bad.

Hard to be sure. It could have been any of several possibilities. If a filling was placed it could have been a desensitizer prior to the restorative material or it could have been a type of adhesive. It may have been chlorhexidine gluconate if there was a gum issue, as well. Best bet is to call and ask..