Twenty-five percent of Americans older than 60 don’t have any of their natural teeth. With dental decay, gum disease and normal wear and tear, teeth give out. Dental advances have made implants a nearly perfect option for people whocan afford them, but affording them can be a tall order. The alternative is dentures, which can wobble and pinch and cover the palate, taking much of the pleasure out of eating. What’s worse, the bone under the gum will resorb, or lose substance, without teeth embedded in it; it eventually disappears,robbing the denture of its resting place and putting greater stress on the gum.