Some of my older relatives have lost their teeth and started wearing dentures. I've noticed that their jaw line is weaker and it tends to press up against the front of the face. Have you noticed any other changes?
Very interesting question. I've not sculpted a toothless person before, but the main difference I'm seeing from image searches is that the lips seem to "suck backward" into the mouth cavity:
Which makes sense with no teeth for the lips to press against. Apparently DaVinci drew a fairly famous toothless man. I don't see immediate evidence that missing teeth affects the jaw line directly...I'm thinking it could be more of a general old age thing when it comes to the jaw. I could be wrong though.