If you have never had a crown installed on a tooth, here’s the way it works. Your dentist, hopefully a trained professional, drills your tooth down to a nub and then fits a metal and porcelain piece, shaped and dyed to look like your former tooth, over your nub and cements it in place. If I’m not mistaken, cement is the substance they use for roads and basements. Tough stuff. But every once in a while, as happens with roads and basements, the cement dries or loosens, and disarray ensues. There’s your crown, lying on the back of your tongue. The rest of the day, you are physically and philosophically unable to stop yourself from probing the immense gaping space where your crown once was.