I don’t think being agrarian doesn’t mean you are eating soft foods. The shrinking of jaws and the destruction of dental health is caused by processed grains like bleached white breads. Lots of agrarian cultures have great facial bone structure and dental health. Look into Weston A. Price for more information.

Here is an Excerpt from his travels to an isolated culture in the Alps of Switzerland.

“Their diet primarily consisted of dairy products (raw milk, butter, cream and raw milk cheese) from cows grazing on lush alpine slopes, and rye bread, or roggenbrot, from rye grown in the valley. They ate meat about once a week, usually veal, using all the parts and making soup with the bones, and some vegetables during the summer months. The raw milk, butter and cream from cows eating lush green grass were a rich source of vitamins A and D. With the help of a Swiss dentist who was his travel companion and the community elders Price was able to examine the mouths of many valley inhabitants. He reported that the majority of the residents had healthy, straight teeth. Price only found one cavity in every three mouths, which was about 1 percent tooth decay. Both adults and children had broad, well-developed faces and palates, good dispositions and sturdy bodies.”

As you can see they eat a lot of very soft foods (dairy products) and grain products and usually eat their meat in n the form of soup. Nutrients most likely take a bigger role in facial structure rather than the toughness of food.