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Knowing you need a lot of dental work, it might be a good idea to pursue better dental insurance. Sometimes plans are offered with “high” options that have greater allowances. On the other front, can you discuss your insurance and payment problems openly with the dentist? Perhaps you and s/he can come up with a treatment plan that prioritizes the most critical treatments and waits on less urgent issues? Also, the dentist may offer a payment plan so you can spread the cost out over multiple months.
My advice – don’t wait on any dental issues that are causing pain, or fillings that have fallen out. I put those issues off due to dental phobia and ended up with days of excruciating pain, an extraction and a root canal in a period of less than 2 weeks.