Do Parents Have A Responsibilty To Get Orthodontics For Their Kids If They Need It?

im a young adult who needs $12,000 in dental work and jaw realignment because i didnt get orthodontics as a child when the dentist said i needed them.
my parents are seperated : my father refused to pay for anything when i was a child (hes quite wealthy) and my mother and her partner chose to be hippies living off welfare (so they had no money for it)
is it wrong of me to now ask them for the $4,000 the dentist quoted for my teeth as a child?
considering all the pain and suffering, and the fact that all these problems are a direct result of a serverly bad bite, should i be upset with them and ask for the whole amount i have to pay now?
i have a very small income and no dental insurance