There's a big difference in being a temporary guardian and a court appointed guardian. I'll give some details of some of the aid she already has, and the one piece of aid that I got for her. None of this is related to dentistry aside from a quick horror story, but maybe you'll find some inspiration or get some ideas.
The only state aid that I've used has been the Pennsylvania OVR (Office of Vocational Rehabilitation). The kid was in special ed, and I could get the OVR office involved. She had to see a state psychologist, and I was allowed to sign off on that. She was deemed to be eligible for aid from the OVR office.
The state, through OVR, is paying for driving lessons from a driving school. They're helping just a tiny bit with upcoming college costs, and assigned her an adviser to help keep her on track (she's turning 18 next month and will attend community college this August). And, they'll help her find and maintain employment. She has other benefits, as well, like free mental health counseling if she wants or needs it, and I even think they'll help with housing in some capacity. I mean - the state is willing to invest, because it's better to pay a few grand now and have a person with taxable income, rather than someone reliant on state aid. They really wanted to help.
Community college is essentially free. Because I was not a court appointed guardian, my income has no bearing on her FAFSA loans and grants. Her parents have only disability and welfare with no other income! That's something to look into!
Sadly, I have nothing to do with her medical coverage. She uses medicaid (or medicare - I forget which is which), due her parents income status. Because I'm only a temporary guardian, my income has no bearing on that. But, because I am a guardian, I can sign off on any medical procedures she might need while her folks are away!
She doesn't have dental coverage. My kid also has an older sister. That girl is now 25, but she ran off at 18 and had a baby with some 40 year-old abusive dude. She's missing her two front teeth! All her teeth are just black with rot and the two front ones apparently just snapped in half sometime last year. My kid has bad teeth, too and I don't quite know what to do. But, she's turning 18 soon, so I figure I should just wait for that to happen. I just stay on top of her brushing and mouth-washing like a hawk, because she's like a 5 year-old when it comes to dental hygiene.
The only hindrance I have encountered has been welfare payments and food stamps. During the winter, when I took full custody of the kid, her parents were supposed to notify the state so her benefits would stop. Then they'd notify the state when the kid returned to their custody to restart the welfare and food stamps. During the first year, the parents tried to trick the state so they could could keep her benefits, but since I was involved with the school some red flags came up and the department of fraud paid everyone a visit. I was in no trouble at all. I did nothing wrong and was trying to help the kid. I just had to write a letter stating the kid was in my care from X-Y dates, and her folks had their benefits cut back to make up what they essentially defrauded the state.