You could try dental schools in your area. The students do the work for the cost of materials, labor is free. It's good practice for them for the "real" world after school.

Also, ask your dentist about payment plans, how long they are willing to run one for you. The longer that they will run one, the cheaper the monthly bill would be.

As far as I know, there is no government funded dental assistance for adults. The private programs I know of are discount programs, you pay a monthly fee for % off medical bills.