Is this considered dental neglect?

My niece (6) lives with my brother and in October of 2009, the school has a dentist come in for children who are on medical coupons and they look at their teeth. The dentist sent home a paper saying that she needed to get some teeth fixed since she had several cavities. My brother didn't do it, and my sister also reminded him over a course of several months to get her into the dentist. I just saw her on the 15th of May 2010 and I looked at her teeth because she said that they were hurting. She said she tells her daddy that they hurt and it hurts to eat certain things. Her teeth on the bottom, not the front ones, looked like they were rotten. One was almost completely hollow and it looked maybe to the gum or nerve. I'm not a teeth specialist but I know that it didn't look right. I informed my brother that her teeth look horrible and that he needs to get her into a dentist and he COMPLETELY IGNORED ME! Is this considered dental neglect especially since he won't really let her see the rest of the family because he says he has "appointments" which I found out to be dental appointments for himself but not his daughter? I would appreciate professional opinions since we are going to try to take this to a legal standpoint and hopefully have custody of her.