Dentists and researchers have come up with the formula for the perfect smile, from the size and width of each tooth to the curve, colour and shape of the teeth, and the overall width of the smile.

　　牙医和研究学者已经研究出完美笑容秘诀，从每颗牙齿的大小、宽度到牙齿的曲线、颜色和形状以及张开的嘴宽度都有讲究。