Teeth are perhaps one of the most interesting parts of the human body. Mistakenly believed by some to be bone, teeth are actually layers of multiple tissues that vary in hardness and density. Teeth can be used for a variety of things: chewing food, ripping soft fabric, opening bottles, gripping things in your mouth, fighting, etc. And of course, smiling! Human teeth come in two sets: a baby set, and an adult set. The first set, also called “milk teeth” or “deciduous teeth,” first emerge at roughly six months of age. The process is called “teething” and typically involves the teeth breaking through the gums and can be quite painful. A child will have these teeth until the age of 6, when the first permanent teeth start to emerge. A baby tooth will loosen and start to wobble, finally falling out when the root is dead. The permanent tooth under the lost milk tooth will emerge through the hole. The process of replacing all of the baby teeth can take another few years. A full set of adult teeth counts as many as 32 teeth- 16 in the upper jaw and 16 in the bottom jaw. Humans are a specialized type called heterodonts, meaning they have teeth that are different sizes and shapes. Teeth on the right side usually match the teeth on the left side, making pairs of teeth of the same shape. The shapes of teeth mostly depend on placement in the mouth. Years of evolution have developed teeth to have different purposes. For instance, teeth in the front of the mouth have been designed to rip while teeth in the back of the mouth are used for chewing. There are four types of human teeth, each with a specific shape, size and function. Adult teeth have 8 incisors all in the front of the mouth (four on top and four on bottom). Incisors are used to cut food, and are sharp to do that most efficiently. On either side of the incisors are the canines, sometime called eyeteeth. These teeth are very pointy, and their task is to tear food, much like a dog. After the canines are bicuspids, also known as premolars, that are flat with ridges to mash and grind food. There are two pairs of bicuspids, or four of these teeth, in each jaw. After the bicuspids are molars, which is where you chew most of your food. They are like bicuspids, but larger and with more pronounced ridges to help grind food. Humans have twelve molars, unless they have their third molars, or “wisdom teeth,” removed, as is common today.