A 52-year-old arrives for a second opinion she did not ask for. Her dentist took a radiograph before fitting a planned crown, saw something unexpected around the root of a lower left premolar, and sent her on. She is faintly baffled by the whole thing: that tooth has never given her a moment of trouble in her life — nothing spontaneous, nothing at night, no twinge with hot or cold — and left to herself she would never have known anything was there.