As the distance between rich and poor grows in the United States, few consequences are so overlooked as the humiliating divide in dental care. High-end cosmetic dentistry is soaring, and better-off Americans spend well over $1 billion each year just to make their teeth a few shades whiter. Millions of others rely on charity clinics and hospital emergency rooms to treat painful and neglected teeth. Unable to afford expensive root canals and crowns, many simply have them pulled. Nearly 1 in 5 Americans older than 65 do not have a single real tooth left.