An article at Ptak Science Books offers this thought:
"Did teeth exist in the Renaissance? Well, while breezing through a bunch of art monographs for that period, it struck me that the tooth wasn’t making its way from the artists’ palettes to the canvas. Not only that, it also occurred to me for the first time that people—in the large part—weren’t even opening their mouths..."The commentary goes on to list many famous paintings, including of course the Mona Lisa, and notes that dental hygiene was not a total mystery at that time. Perhaps people did have terrible teeth, but conversely many of the subjects of the paintings were mythical or allegorical; there's no reason Ulysses could not be portrayed with glistening teeth.
There are some additional thoughts and suggestions in the essay and its comment thread. I'm not offering an opinion - just noting the subject matter as an interesting phenomenon. The photo I've embedded is a portrait of Falstaff (1921) by Eduard von Grützner.