Smile

- Closed lip smile

- a fake smile to be polite, or the person is embarrassed by their teeth (this applies to many more people than you may think)

- Whole face smile

– a genuine smile, indicating honesty and openness to communication

- Covering the mouth (or parts of the face)

–while you are talking, they could be surprised by what you said

–when they are talking, they could be lying or uncomfortable with the conversation

The fake smile

The genuine smile

Look, it is obvious that we looked more genuine with teeth. So, be yourself. 
You don't looked bad, you are just being yourself.