An adult human mouth normally has 32 permanent teeth. The full set contains eight incisors, four canines, eight premolars, and twelve molars, including four third molars commonly called wisdom teeth.
The teeth are divided evenly between the upper and lower jaws: 16 in the maxilla and 16 in the mandible. Incisors cut food, canines help tear it, premolars crush it, and molars perform much of the grinding. This division of labor reflects the broad human omnivorous diet.
The number 32 describes a complete permanent dentition, not the number every adult currently has visible in the mouth. Wisdom teeth may fail to develop, remain trapped beneath the gums, or be removed because of crowding, infection, or impaction. In those cases, an adult may have 28 teeth while still being within common experience.
Children normally have 20 primary, or baby, teeth. Permanent teeth begin appearing around age six, and the third molars usually emerge in the late teens or early twenties. The first permanent molars erupt behind the baby molars, which is why they are sometimes mistakenly thought to replace them.