I don't know of any physiological reason for it. I think that you have mentioned that your voice pitch gets higher when you are nervous. Does going without dentures make you nervous? I thought that you were used to being toothless.
@OlgaAlexeenko Have you tried putting your dentures in and recording your speech, and then saying the same words without your dentures and comparing the two recordings? You can do this in private, without anyone to see or hear you.
