---snip--- Americans travel to Mexico for stomach surgery, eye exams and routine checkups. But it is the dentistas - thousands strung along the border - who are in the vanguard in attracting U.S. health consumers. Mexican dentists often charge one-fifth to one-fourth of those north of the border. Their operating costs are substantially lower, and because the Mexican legal system makes it almost impossible to sue them, they don't have to worry about high malpractice premiums.