<s>[INST] hi i have been feeling some strange sensation on the back of my teeth , on the front bottom ones... i looked at them and i found out some yellow n blackish stuff on them which wont go away by brushing..  it feels very strange when i touch them with my tounge and a feeling of dryness and like something sucking my teeth ... [/INST] Thanks for your query, I have gone through your query. As far as the black and yellow stuff on your teeth is concerned, I have two possibilities. It can be secondary to the stains or deposits due to poor oral hygiene. The other cause could be because of the decayed tooth. Consult an oral physician and get it ruled out. If it is because of the deposits, then get your teeth cleaned and maintain oral hygiene. If it is secondary to decay, then get the teeth restored. I hope my answer will help you, take care. </s>