Teeth. Artwork of an open mouth showing an entire set of healthy permanent teeth. Humans have 20 primary teeth that erupt in infancy and early childhood but these are replaced by the 32 permanent teeth. The same symmetrical arrangement of teeth is found on the lower and upper jaw. From the back of the mouth there are the third, second, and first molars used for grinding food. The third molar or wisdom tooth is the last to erupt and in some people never appears. Next are the two premolars (bicuspids). The sharp canine used for tearing is next. Four biting incisors lie along the front of the jaw.