The second, permanent set of 28 teeth appears (erupts) between the ages of six and 12 years in the human dentition. The old set is pushed out of the jaw as the new set erupts. The third molars (the wisdom teeth) are the final teeth to erupt, usually around age 20. However, it is common for the wisdom teeth not to erupt at all; this is often the case in small jaws without room to support the extra teeth. It is possible, though rare, for a person to have fourth molars, and there have been instances where fifth molars have been present in the dentition. Human molar permanent teeth are evenly distributed across the mouth's quadrants.

Teeth are attached to the underlying bone of the jaw via the periodontal ligament, though the teeth themselves are not made of bone. The white part of the tooth, which can be seen in the mouth, is the enamel. Immediately one to three mm below the enamel is a slightly softer, yellow tissue called dentin. Dentin is supported by the pulp (commonly called 'the nerve', although it contains many other structures which are not nerves), which lies in the center of the tooth. The teeth's composition is specialized to resist the harsh environment of the oral cavity and withstand the large forces imposed upon them by mastication, or chewing.