Human teeth: Permanent teeth and their parts of Enamel and Dentin and Cementum and Dental pulp

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Permanent teeth :

Among permanent teeth, 16 are found in the maxilla and 16 in the mandible, for a total of 32. The dental formula is Permanent human teeth are numbered in a boustrophedonic sequence.

The maxillary teeth are the maxillary central incisors (teeth 8 and 9 in the diagram), maxillary lateral incisors (7 and 10), maxillary canines (6 and 11), maxillary first premolars (5 and 12), maxillary second premolars (4 and 13), maxillary first molars (3 and 14), maxillary second molars (2 and 15), and maxillary third molars (1 and 16). The mandibular teeth are the mandibular central incisors (24 and 25), mandibular lateral incisors (23 and 26), mandibular canines (22 and 27), mandibular first premolars (21 and 28), mandibular second premolars (20 and 29), mandibular first molars (19 and 30), mandibular second molars (18 and 31), and mandibular third molars (17 and 32).

 Third molars are commonly called "wisdom teeth" and usually emerge at ages 17 to 25. These molars may never erupt into the mouth or form at all. When they do form, they often must be removed. If any additional teeth form—for example, fourth and fifth molars, which are rare—they are referred to as supernumerary teeth (hyperdontia). Development of fewer than the usual number of teeth is called hypodontia.

There are small differences between the teeth of males and females, with male teeth along with the male jaw tending to be larger on average than female teeth and jaw. There are also differences in the internal dental tissue proportions, with male teeth consisting of proportionately more dentine
while female teeth have proportionately more enamel.

Parts :

Enamel :

Enamel is the hardest and most highly mineralized substance of the body. It has its origin from oral ectoderm. It is one of the four major tissues which make up the tooth, along with dentin, cementum, and dental pulp.It is normally visible and must be supported by underlying dentin. 96% of enamel consists of mineral, with water and organic material comprising the rest.

 The normal color of enamel varies from light yellow to grayish white. At the edges of teeth where there is no dentin underlying the enamel, the color sometimes has a slightly blue tone. Since enamel is
semitranslucent, the color of dentin and any restorative dental material underneath the enamel strongly affects the appearance of a tooth. Enamel varies in thickness over the surface of the tooth and is often thickest at the cusp, up to 2.5mm, and thinnest at its border, which is seen clinically as the CEJ.[10] The wear rate of enamel, called attrition, is 8 micrometers a year from normal factors.

Enamel's primary mineral is hydroxyapatite, which is a crystalline calcium phosphate. The large amount of minerals in enamel accounts not only for its strength but also for its brittleness.
Dentin, which is less mineralized and less brittle, compensates for enamel and is necessary as a
support.  Unlike dentin and bone, enamel does not contain collagen. Proteins of note in the development of enamel are ameloblastins, amelogenins, enamelins and tuftelins. It is believed that they aid in the development of enamel by serving as framework support, among other functions. In rare circumstances enamel can fail to form, leaving the underlying dentine exposed on the surface.

Dentin :

Dentin is the substance between enamel or cementum and the pulp chamber. It is secreted by the odontoblasts of the dental pulp. 

The formation of dentin is known as dentinogenesis. The porous, yellow-hued material is made up of 70% inorganic materials, 20% organic materials, and 10% water by weight.  

Because it is softer than enamel, it decays more rapidly and is subject to severe cavities if not properly treated, but dentin still acts as a protective layer and supports the crown of the tooth.

Dentin is a mineralized connective tissue with an organic matrix of collagenous proteins. Dentin has microscopic channels, called dentinal tubules, which radiate outward through the dentin from the pulp cavity to the exterior cementum or enamel border.  

The diameter of these tubules range from 2.5 μm near the pulp, to 1.2 μm in the midportion, and 900 nm near the dentino-enamel junction.

Although they may have tiny side-branches, the tubules do not intersect with each other. Their length is dictated by the radius of the tooth. The three dimensional configuration of the dentinal tubules is genetically determined.

There are three types of dentin, primary, secondary and tertiary. Secondary dentin is a layer of dentin produced after root formation and continues to form with age. Tertiary dentin is created in response to stimulus, such as cavities and tooth wear.

Cementum :

Cementum is a specialized bone like substance covering the root of a tooth. It is approximately 45% inorganic material (mainly hydroxyapatite), 33% organic material (mainly collagen) and 22% water. Cementum is excreted by cementoblasts within the root of the tooth and is thickest at the root apex. Its coloration is yellowish and it is softer than dentin and enamel. 

The principal role of cementum is to serve as a medium by which the periodontal ligaments can attach to the tooth for stability. At the cement to enamel junction, the cementum is acellular due to its lack of cellular components, and this acellular type covers at least 2⁄3 of the root.

 The more permeable form of cementum, cellular cementum, covers about 1⁄3 of the root apex.

Dental pulp :

The dental pulp is the central part of the tooth filled with soft connective tissue. This tissue contains blood vessels and nerves that enter the tooth from a hole at the apex of the root. Along the border between the dentin and the pulp are odontoblasts, which initiate the formation of dentin. Other cells in the pulp include fibroblasts, preodontoblasts, macrophages and Tlymphocytes. The pulp is commonly called "the nerve" of the tooth.