What is the medical term for when an adult still has one baby tooth without a permanent one above it?

Hypodontia: The medical term for the congenital absence of a permanent tooth with a retained baby tooth still in place is "hypodontia".

Congenitally missing: It's not uncommon for a baby tooth to be retained and not lost due to the lack of a permanent tooth being developed under the baby tooth. As long as the baby tooth is in good condition and good oral hygiene is performed, the baby tooth can be retained for many years, even into your 40's or 50's. Sometimes there may be a good reason to have it removed and an implant placed. Your dentist can advise.

Retained deciduous : When an adult tooth fails to develop and the primary tooth remains mixed in with the adult dentition, it is called a retained deciduous tooth. This is often a genetic or family trait, so advise your children. Also, these teeth will not last a lifetime, so plan at some point having it replaced with a dental implant and implant crown. Talk to your dentist about the appropriate timing.

Retained: Retained deciduous tooth. Means the primary tooth is still present.

Retained primary: teeth. Primary teeth may be retained for a variety of reasons, the most common being developmental absence of the permanent tooth. Hope it helps.

Retained primary : Retained primary tooth due to missing permanent tooth. Genetics usually are to blame when you are missing an adult tooth to replace your baby tooth. I've seen them last into people's 40s. Sometimes they need to pulled and an implant or alternative treatment is needed to maintain the space.

2 terms: Retained primary tooth means baby tooth still present long after it should have fallen out. Congenitally missing permanent tooth means it never formed. The two often are coincident. As baby tooth different size than permanent tooth would have been, consultation with an Orthodontist (Initial Examination usually free) would be wise.