You could be forgiven for thinking that the smile has no history; it has always been the same. However, just as different cultures in our own day have different rules about smiling, so did different societies in the past. In fact, amazing as it might seem, it was only in late eighteenth century France that western civilization discovered the art of the smile. In the 'Old Regime of Teeth' which prevailed in western Europe until then, smiling was quite literally frowned upon. Individuals were fatalistic about tooth loss, and their open mouths would often have been visually repulsive. Rules of...