Stephan Guyenet had a series of blog posts called "Malocclusion: Disease of Civilization" on dental health. As I remember, as usual, decline in dental health was linked to moving away from traditional diets. The problem with teeth "overcrowding" was linked, basically, to not chewing enough of tough foods. People that ate plenty of tough foods as part of their diets had better developed jaws and space enough for all their teeth.
For many human movements, the relation between intensity and injury is a u-curve with high risk at extremely low intensity (atrophy) and extremely high intensity (overuse/repetitive strain), and low risk at moderate intensity.
http://wholehealthsource.blogspot.dk/search/label/dental%20h...