That’s so incredibly rude. It may be obvious to anyone talking to you that have dentures, it may not. What’s not debatable is that you don’t say that to someone.

OP mentioned they were on a phone call together.

Your coworker was unquestionably rude to mention that your speech sounded like you were wearing a retainer.

That being said, according to you, your speech has been affected by your dentures. If you really don’t want people to know about your dentures, you need to practice, practice, practice, until you can figure out how to compensate for your new mouth shape and make it an automatic, ingrained, part of your speech. I had a mouthpiece in college for TMJ that dramatically altered the shape of my upper palate, so I can sympathize with the difficulty and frustration, but know that you can overcome your articulation issues.

I would say "what exactly is your point?"

"That's rude"

Say this, OP. Look them straight in the eye and say it clearly and calmly. Wait while maintaining eye contact until they look away and mumble something.

Because:
A, it's the truth
B, this person needs to be put in their place otherwise they will continue being rude.

Do not disclose confidential information.

Invisalign causes a lisp too, so you could claim that if you wanted. But you don’t owe them an explanation.

When someone is this rude, I’ll say, “What on earth would make you ask that?” And then stare them down.

Are you uncomfortable about your lisp? Are you embarrassed that you have one or that she said something?

Frankly they were probably complaining about your audio device (or they thought they were). Do you have a crappy headset or use speakerphone? Some people are sensitive to that and may say insensitive things-- "you sound like you're calling from the toilet" or "you sound like you have a cat sitting on your face" because they they think it's equipment and not personal.

That is so rude, omg.

Just own up to having a speech impediment. "I know I have a lisp - can we get back to the report now? On row 16 ..."

Wow that is so rude. I would tell them you wear a dental prosthetic device (you don’t owe them specifics) and that it can affect your speech.

I would get HR involved.

I'd tell them about the dentures, but yeah, that's pretty rude of them.

Wow, your co-worker is rude.

Was on a call with a coworker who suddenly said ‘it sounds like you’re wearing a retainer’. I have partial dentures and don’t really want anyone to know, but it’s obviously similar to retainers as I wear a full palatal plastic plate and a lower plate so speech is lispy. I just laughed it off without commenting but they said it again on the next call too. Should I tell them about my dentures to avoid further comments or just try and ignore it?