I don’t know if this is the case with you but if you have naturally wide eyes (say, anxiety for example) then a full tooth smile is creepy looking. Relaxed eyes on the other hand (think pictures of happily stoned people) are fine showing full mouth IMO.

Although some people “grit” or “bare(/bear?)” their teeth in an attempt to fake a natural laughter smile and… no. The muscles around the mouth should be relaxed not tense. There’s no substitute for a candid laughter smile. But not many people can fake the crows feet in the eyes of a real smile, so if someone is more comfortable smiling with no teeth showing, that’s more than fine.

I’ve done a bit of photography in my day.