My 18 months old pup has one fang tooth that is turning brown from the tip up?

She eats high dollar dog food from the feed store, she does drool more than her sibling and her mother. Just noticed this today. She does not have any plaque build up as she is given dog treats and knuckle bones to munch on. My only concern is she will eat anything she thinks is food, like my abalone shells, blankets, carpets, etc. Could this mean she has something going wrong inside?