Lack of free healthcare and heavier consumption of sugar (portions of sugar in Europe are regulated). Europeans tend to eat healthier due to tradition and governments promoting more healthy ways of life.
That would explain the overall better health of Europeans. Amount of people doesn't matter, it is just the way things are handled to make people live better. The amount of hours at work, being treated like crap and fired easily, bad healthcare and education system (until university), and the things I have already mentionned above.
Not exactly a good combo to create healthy people, that includes teeth.