States are required to provide dental benefits to children on Medicaid and CHIP. They choose whether to provide dental care to adults on Medicaid. Re adults, https://www.medicaid.gov/medicaid/benefits/dental/index.html says: "States have flexibility to determine what dental benefits are provided to adult Medicaid enrollees. While most states provide at least emergency dental services for adults, less than half of the states currently provide comprehensive dental care. There are no minimum requirements for adult dental coverage."

Sad to say, that's better than I had assumed (which was basically that no one except kids got dental coverage on Medicaid).