When we talk about canines， we refer to the situation that the sharp teeth at the side of the lips grow out of the dental arch； a canine is not a special tooth， but an individual of the common teeth. Because it looks like the teeth of predators and often grows in a special position， it gets the nickname， “tigers tooth”.

It turns out that the special shape of canine is decided by human genes. Each tooth within the dentition has its own name， shape， position and function. The most frontal 4 are relatively flat and sharp， which are at the most front of the dental arch and are mainly in charge of cutting and esthetic function； the two sharp teeth at their sides have their crowns in large curves and are of thick and long roots， responsible for supporting the mouth and protecting the beauty of the entire dentition. When people are smiling， the so called “smile line” is affected by maxillary canines； and beside them there are two teeth with two dental cusps on each side， which are called bicuspid teeth， helping to preliminarily grind the food and deliver them to the molar teeth at the end of the dental arch.

（Answer： Meijuan ZHANG， dentist）

（From： Science China）

（Editor in charge： Yin WANG）