The most famous smile in history belongs to Leonardo da Vinci's famous painting, the Mona Lisa. Generations of art analysts have speculated over its meaning. Seductive? Bashful? Secretly knowing? Or could it be, given her upturned—but firmly closed lips, that she was ashamed of showing her teeth? Could they have been chipped, stained, crooked or gapped? These days there’s no need to hide your smile because your teeth aren't perfect. Modern cosmetic [...]