Permanent teeth
Encyclopedia
Permanent teeth are the second set of teeth
Tooth
Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...

 formed in humans. There are thirty-two permanent teeth, consisting of six maxillary
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...

 and six mandibular molars
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....

, four maxillary and four mandibular premolar
Premolar
The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...

s, two maxillary and two mandibular canine
Canine tooth
In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...

s, four maxillary and four mandibular incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...

s.

The first permanent tooth usually appears in the mouth
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....

 at around six years of age, and the mouth will then be in a transition period with both deciduous teeth
Deciduous teeth
Deciduous teeth, otherwise known as reborner teeth, baby teeth, temporary teeth and primary teeth, are the first set of teeth in the growth development of humans and many other mammals. In some Asian countries they are referred to as fall teeth as they will eventually fall out, while in almost all...

 and permanent teeth (mixed dentition) until the last deciduous tooth is lost. The first of the adult teeth to erupt are the permanent first molars that come through the gums at the back, right behind the last 'milk' molars. These first permanent molars are the most important teeth for the correct development of an adult dentition. Up to the age of thirteen years, twenty-eight of the thirty-two permanent teeth will appear.

The full permanent dentition is completed much later. The four last adult teeth, one at the back of every arch will appear between the ages of seventeen and twenty-one years. This is the reason they are named wisdom teeth.

In rare occurrences, a third set of teeth is possible. It's been reported to happen to very elderly humans and in even more rare cases of younger people who have had their permanent teeth removed.

In light of the very rare occurrence of multiple "sets" of teeth in humans, some new studies have proposed that the OSR2 gene
OSR2 (gene)
Protein odd-skipped-related 2 is a protein that in humans is encoded by the OSR2 gene. In mice, it is involved in the development of the palate and in suppressing the formation of teeth after the eruption of adult teeth.-Further reading:...

could be responsible for this.
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