A.A.
When my daighter's teeth came in one of her top front teeth was gray and then it broke off. The dentist said there was nothing to do unless it became absessed (it eventually did). We took her to the pediatric dentist (a wonderful guy!) and they pulled her tooth while she was under general ansthesia. She is only 4 and has a toothless grin, but all is well.
Just keep an eye on it. The good thing about teeth is that they can fix almost anything now. Good luck!