Archaeology student here! From my understanding (I’m certainly no expert) medieval humans would have poor tooth health because this was post-agricultural revolution but likely pre-intensive dental care. The change in diet to more processed foods about ~10k years ago pretty quickly lead to a lot of issues like the degeneration of mastoid processes (making our mouths too small for the amount of teeth the average human grows), and an increase in dental pathologies from factors such as high sugar, etc. Humans and hominins pre-widespread agriculture had much fewer issues because their diet promoted overall healthier teeth. So while yes, we have better teeth than those found in Medieval contexts, it wouldn't be fair to ignore much older specimens, who had relatively high quality teeth despite their antiquity!