Why do some people smile with their lips closed? I’m referring to people with nice teeth, who have nothing to hide.
Barbra Streisand. In the 4th row is one showing her teeth. They are normal. And if she doesn’t like her teeth, she can certainly afford to change them.
Well. maybe she wishes she had more gum, like Geena Davis.
Not sure if you even CAN buy that…
Speaking of gums, there’s Chelsea Clinton, who can barely close her mouth.
I seem to recall Barbra having said something once in an interview about an early photo session where the photographer tactlessly lectured her about faces and angles, and told her that she should always insist on being photographed from the left side, chin slightly out, head tilted, never face the camera directly, and do the Mona Lisa smile and not a toothy grin, to downplay her nose and facial asymmetry.
IIRC, she said something about how she was very insulted, but when she looked at the photographs, she had to agree with him, and has made a habit out of posing that way ever since.
because we don’t know what you’re expecting or why we should care how you think we should smile.
For me it is physically uncomfortable and feels like weird contortion to smile with my mouth open. I assume I can’t be the only person in the world like that.
Yep. Open-mouthed smiles difficult or painful for some of us, and actually ugly when we try to smile that way. I blame the way my jaw is hinged. Closed mouth smiles are not only more comfortable, they look better, too.
I have never been a toothy smiler. My natural smile is squint-eyed with my lips barely showing. kinda like a smiley face smile 
I can pose smiling close-mouthed for a picture for a while, while everyone gets ready, and still manage to look natural, but I can’t manage to do that with my teeth showing. It just has to do with face muscles becoming fatigued. There are some candid shots of me smiling open-mouthed-- or laughing-- that happen to look good, but there are also candid shots of me with one eye closed, or looking like I’m mid-sneeze.
Not to mention, I had really crooked teeth and a bad overbite before I had braces, and it took me a while to get over being shy about the way my teeth looked, even long after I got the braces off.
