I decided to do some smiling tests, and it seems that I have to forth my mouth open to show my teeth during a smile. Otherwise my smile only consists of widened lips. And mustache. :O
I was wondering because I always see these people smiling on TV, that just look so fake to me, and I figured that it probably took effort to make such toothy smiles. It does for me, anyway; I look so fake when I do it.