Agree with scylla here. If you go out and buy dental insurance now, there is usually a waiting period before you can use it. Otherwise, the insurance would lose money because people would get insurance, get dental work and then cancel it again. If you have dental insurance through your job, the same might apply but you would have to ask.
If you have a credit card, you can use it. If you don't, you would have to ask the dentist about a payment plan. You can get a letter from your employer, called a bank letter. It will state how much money you make. You could offer to leave them a security like your passport which you will get back when you pay.
