We can take a lesson from nature. Which is more beautiful to you, a healthy plant or an unhealthy plant? What about in animals? Which is more beautiful, a healthy animal or a sickly animal? In virtually all cases that which is healthy is more beautiful to us than that which is in an unhealthy state. But what is it that makes a certain appearance more beautiful to us than another appearance? Well it could be that when our prehistoric ancestors set about choosing a mate, those who were attracted to healthy potential partners were more likely to reproduce and rear offspring who survived to adulthood themselves.
These offspring who inherited their parents’ appearance and good health did better at passing on their genes than those who were perhaps not as healthy. In doing this they were genetically programming our species to be attracted to a certain "look", the healthy "look". We are genetically programmed to find health much more attractive than that which is in an unhealthy state. A multibillion dollar a year industry of health and fitness and beauty is founded on this principle.
When our teeth, lips and gums are in a stable and harmonious state of health we naturally find it to be beautiful and generally find it more attractive. This is why we say that a healthy smile is a beautiful smile.
