Introduction to Human Dentition
From an anatomical perspective, humans have two sets of teeth and hence, are classified as diphyodonts. The very first set of teeth are called primary teeth or milk teeth. It usually erupts when children reach around 6 months of age.
And by the time infants grow to 2 years or older, they will usually have 20 primary teeth, with 10 on each jaw. The first permanent teeth start replacing the primary teeth at the age of 6. The teeth structure also changes, with 16 found in the mandible and the other 16 in the maxilla. Hence, adult humans have a total of 32 teeth. Moreover, male and female teeth showcase minor differences.
Usually, teeth and jaws in males tend to be larger than their female counterparts. Other differences between the sexes also include varying proportions of dental tissues – with females having proportionately more enamel while males have proportionately more dentine.
Parts of a Tooth
A human tooth consists of the following parts:
- Dental Pulp
Enamel is the white, outer part of the teeth. It is also the hardest part of the teeth. It is composed primarily of calcium phosphate and is supported by the underlying dentin. The normal colour of enamel is usually white, but can vary – from light yellow to grayish white. The enamel is thickest at the cusp and thinnest at the edge.
The layer that lies under the enamel is called dentin. Anatomically, this material has a yellow hue and is porous. It is primarily composed of inorganic materials. However, since it is softer than enamel, dentin tends to decay much quicker. It can also lead to severe cavities if dental problems are left untreated.
The cementum “cements” the roots of the teeth to the gums and jawbone. It consists of inorganic materials, collagen and other organic materials. This material is created by special cells called cementoblasts which are found in the tooth’s roots. Moreover, it is softer than enamel and even dentin.
This is the central part of the tooth and it contains blood vessels and nerves. The dental pulp also contains other specialised cells such as odontoblasts, pre-odontoblasts, fibroblasts and macrophages.
Types of Teeth
As stated above, adult humans have a total of 32 teeth, and are classified into 5 types:
- Wisdom teeth
Adult humans have a total of 8 incisors, with four on the upper jaw and four on the lower jaw. They are the middle most teeth and are suitable for cutting and shearing.
Humans have 4 canines, with two at each corner of each jaw. They are perfectly adapted to gripping and slicing food.
There are a total of 8 molars, with 4 at the rear of each jaw. They are best suited for grinding food.
Premolars are the teeth that are present between the molars and canines. They share features of both types of teeth.
The last set of teeth to erupt are the wisdom teeth. These are often called the third molars and are usually removed to prevent displacement of existing teeth.
Interestingly, babies can also be born with one or more visible teeth. Such teeth are called natal teeth or neonatal teeth. However, the incidence of neonatal teeth varies according to medical reports – which can be as high as 1:700 or as rare as 1:30,000 births. These neonatal teeth are usually associated with certain syndromes such as Pierre Robin Syndrome or Hallermann-Streiff Syndrome.
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