Hello! I've helped test this bug with someone who had this same issue - we determined the bug to be tied to the PYXIS default replacement teeth, which have not been updated since 2017.
If you had these teeth in your game when this bug occurred, your sim (and save) is very likely corrupted. You would need to clone those sims and move them to a new save to remedy this if that is the case.
Even if you don't use PYXIS replacements, any other default replacements (perhaps barring the ones by IceCream4Breakfast as they've been updated) are subject to causing the same issues.
I do not use default replacement teeth in my game and did not run into issues at all with losing teeth after this patch.
