I'm an American, but I don't smile by showing my teeth, though I will sometimes do a closed lip smile. For me I don't think it is cultural, but rather that smiling always feels to me like baring my teeth, i.e. aggressive and threatening. I don't honestly know why I feel that way, I don't have any history or experiences that would seem to cause that, but it just feels wrong to do. I've always wondered if there are other people have the same reaction?

Note: I don't see other people's smiles as threatening, it just feels that way when I do it.