Medicare Medically Necessary Dental Care Act of 2021 This bill allows for coverage of certain medically necessary dental services under Medicare. Specifically, the bill allows for coverage of dental services that are furnished (1) in conjunction with treatment relating to a prosthetic heart valve replacement, cancer of the head or neck, lymphoma, leukemia, or organ transplantation; and (2) within one year after the date of diagnosis or the date of the related surgical or medical treatment for the diagnosis, whichever is later.