If you are getting SSI, I'm pretty sure that makes you automatically eligible for Medicaid. If your dad can no longer provide you with coverage through his job, you should be eligible for Medicaid. Him not talking to you is a problem. Is your dad your legal guardian?

If, at age 27, you are your own guardian, then you need to go to your Income Support Office and apply for Medicaid. Once you get it, you will be covered for everything, including dental.

I don't know much about how you might get benefits based on your father's history. I'm sorry about the loss of your mother. It sounds like you need a source of moral support outside of your home. If your dad is claiming a tax deduction based on helping support you as a dependent, then he has an obligation to cooperate with you and help you get what benefits you are eligible for.