That's not physically possible In specific, while you can be born without a working mouth, without a tongue/jaw/whatever it usually causes other birth defects and you definitely wouldn't look like that. So I call bull on your inability to research something you want to give an OC

Also, an OC is MUCH MUCH more than their physical appearance. Are you really going to point that out as the very first thing and not like... His PERSONALITY? Oh wait, it's one of your ocs, he probably doesn't have one.

It's not about realism, it's about making a good character. Which you don't know how to do. try springhole.net there are a lot of good character creation resources there, including the Mary Sue litmus test

That doesn't actually say anything about his character though. I have a character who looks shy around new peple, but is in reality an opinionated person who makes a lot of dirty jokes and really loves cuddling. You'd never get that from a drawing of him when you first meet him! Another of my characters looks cold and apathetic on the surface but she is intensely loyal and hiding a minor depressive episode whenever she gets especially cold. WHO WOULD HAVE KNOWN FROM HER DEMEANOR? If your character is just "he's shy, but that's about it and there isn't subtext" you have failed as a character creator.

Sorry I get really passionate about characters and I hate it when people are dismissive of their characters as if they don't really matter that much to be developed or they're "just OCs" give them some thought, some life!!