Are pre-existing dental conditions covered?

Most pre-existing conditions are usually covered. The exceptions would be for congenital conditions and cosmetic treatment. Often, missing teeth are excluded as well. Coverage is generally provided on a no-loss/no-gain basis; however, any expenses for treatment started before an enrollee’s eligibility are the responsibility of the previous carrier. Since each contract can vary, it's best to verify coverage through your contract.

Is treatment-in-progress covered?

We will cover claims for procedures started and completed after the enrollee’s coverage effective date. However, we do not cover procedures started prior to the effective date of your plan’s coverage. See the Orth

I got this information from my insurance company's website (united healthcare)