Might be better served by /r/AskAnthropology
Ninja edit for spelling.
fyi, you'll find a few related posts in the FAQ
This is from a health perspective (nursing student) rather than a historical perspective... It probably came about as a result of having a diet higher in carbohydrates (think, sugars: sucrose, glucose and fructose). The breakdown of sugars in the mouth produces an acid (lactic acid) which wears down the enamel and causes dental caries. Proteins, fats and fiber produce less acid in the mouth in comparison. Early humans (hunters and gatherers) would not have as many dental caries as early farming civilizations due to diets higher in proteins, fats, roots, et cetera (but then again, they also probably didn't live as long). Tooth care was an inevitable growth of human civilization.
... http://www.nlm.nih.gov/medlineplus/ency/article/001055.htm ... http://en.m.wikipedia.org/wiki/Dental_caries ... http://sciweb.hfcc.net/biology/jacobs/micro/caries/