I am sure if you are 27 and out on a first date, with a FULL set of dentures, it isn't the first thing that is going to come up on your long list of "why you should ask me out again." That being said, if you are married to the person for over 3 years and your partner STILL does not know that you wear dentures, I would say that is a bit misleading.
That is exactly what my mother-in-law overheard while she was in recovery from an apendectomy. She saw a girl in her later 20s furvishly trying to convince the doctor to let her put her dentures back in before her husband could see her... because he didn't know she had fake teeth! SURPRISE!
Sure, I don't share all of my womanly secrets with my husband either, and I guess I just don't have anything that embarassing to share, but I can tell you that if I found something of that magnitude out ("Dude, where are your teeth?") about my husband I would be rather put out.