I urge you to examine white people’s teeth as hard as you do ‘black folks.’ You will see those same imperfections, as well as others. Also, you may have only observed black people who have no interest in paying for expensive dental work and see their ‘gaps’ as signs of character (like the model Laura Hutton and Madonna do). The gold tooth thing is just a cultural thing, usually among lower-class black people. There is no explanation for it, other than they think gold teeth are cool (just like some people think pierced tongues are cool). And gold looks particularly attractive against darker skin.