The permanent dentition is made up of 32 teeth, 16 in the upper jaw and 16 in the mandible. It consists of four incisors, two canines (or cusps), four premolars (or bicuspids), four molars and two wisdom teeth (also called third molars) in each mandible. The first and second permanent central incisors, the lateral incisors, the canines and the first and second premolars replace the primary dentition. The primary molars are replaced by the permanent premolars, and the permanent molars come out after those molars.
In each arch there are two central incisors, two lateral incisors, two canines, four premolars and six molars. Larger than incisors and canines, but smaller than molars, bicuspids have a flatter upper surface with several crests that are used to grind food into smaller pieces. Bicuspids don't erupt in humans until age 10, which means that there is only one set of bicuspids that are permanent teeth. Third molars are more commonly known as wisdom teeth.
Unfortunately, these teeth generally have to be extracted because they don't fit properly in the mouth. The wisdom teeth are a functionless organ left over from our evolutionary past. Thousands of years ago, humans had larger skulls and tougher diets that required additional chewing power. Nowadays, eating has become easier and our skulls have become smaller than those of our ancestors.
This means that the third molars have trouble coming out completely and can cause problems such as pain, swelling, and infection. Finally, the 20 primary teeth are replaced by 32 permanent teeth. The primary molars are replaced by permanent premolars (also called bicuspids) and the permanent molars are placed behind the primary teeth. In most cases, the first teeth to come out are the two lower front teeth (incisors) and the first upper and lower molars, the molars closest to the front of the mouth. They are followed by the two upper front teeth.
The order in which the teeth come out may vary. Adolescents and adults have all four types of teeth in their permanent dentition and eventually develop 8 incisors, 4 canines, 8 premolars and 12 molars. Because there are more permanent teeth than there are primary teeth, the permanent premolars are located behind the primary molars. In addition, some people may have more than 32 teeth in their permanent dentition, and those extra teeth are called supernumerary teeth. It takes about six years for children, between the ages of six and 12, to lose their primary (deciduous) teeth and regain their permanent teeth. Because deciduous molars are replaced by permanent premolars, paleontologists sometimes refer to these teeth as deciduous premolars.
Finally, other methods of estimating dental age are considered, such as tooth length, tooth development tables, and dental microstructure. To sum up, humans have 20 primary teeth and 32 secondary (permanent) teeth during their lifetime. However, only three types of teeth appear in baby teeth (first dentition) because the premolars do not develop with the first dentition. The incisors are the first baby teeth to come out and fall out, as well as the first permanent teeth to come out.