Knowledge of the anatomy of teeth is indispensable not only in order to understand the pathological process, but also the possible therapies.
Teeth are found in the oral cavity, and their roots are inserted in the alveolar processes of the upper and lower jaw.
The permanent dentition of an adult is composed of 32 teeth, indicated with Arabic numbers from 1 to 8.
Teeth are identified as: INCISORS, CANINE TEETH, PREMOLARS AND MOLARS.
The tooth is composed of two parts: the CROWN and the ROOT.
Two different types of dental tissues cover these two structures.
The line of junction between the crown and the root is called the CEMENTUM-ENAMEL JUNCTION (CEJ – NECK). teeth
The CROWN is the part of the tooth that emerges from the bone and it is covered by Enamel.
The ROOT is the part of the tooth that is inserted into the bone and it is coated by Cementum.
In healthy conditions of the oral cavity it is not visible.
In clinical practice, the dental arches are usually distinguished in 4 quadrants, tracing two lines: a horizontal line that divides the upper arch from the lower one, and a vertical line that passes between the 2 central incisors of the upper and lower arch.
These lines thus delimit two upper quadrants (Right and Left) and the two lower quadrants (Right and Left) and this division makes it possible to indicate the precise position of teeth. Conventional abbreviations are used to indicate each tooth and its location.
The most commonly used system to effect annotations in clinical charts and to communicate among operators, is the following: the quadrants are numbered from 1 to 4, starting form the right upper jaw and proceeding in the clockwise direction.
The number of the tooth is combined with the quadrant in which the tooth is located.
Therefore, a number composed of two figures is assigned to each tooth: the first indicates the quadrant and the second indicates the single tooth.
The DENTIN constitutes the principal part of the tooth and it is present in both the crown and the root.
The ENAMEL is the hardest of the calcified tissues and it forms a thick layer on the Dentin in the area that corresponds to the crown of the tooth.
The CEMENTUM coats the Dentin in the area that corresponds to the root of the tooth. The tooth encloses a hollow space within the Dentin called the PULP CAVITY.
This cavity has an opening at the apex of the root called the APICAL FORAMEN.
The walls of the pulp cavity are lined with ODONTOBLASTS, distributed in a single layer. They produce Dentin.
The remaining part of the pulp cavity is occupied by the dental pulp, which contains cells and numerous blood vessels and nerves that pass through the apical foramen; these are all necessary to keep the tooth alive.
DENTIN The Dentin is a calcified tissue, 72% of which is composed of inorganic salts, that are CRYSTALS OF HYDROXYAPATITE (Calcium Phosphate).
It is produced by the ODONTOBLASTS that, as already said, line the walls of the pulp cavity.
If a cross section of the Dentin is examined, the extensions of the Odontoblasts, called DENTINAL FIBERS or TOMES’ FIBERS, are visible. They extend towards the outside through many canaliculi called DENTINAL TUBULES.
The maximum production of Dentin performed by the Odontoblasts takes place during the development of the tooth; however this production never stops and continues, very slowly, even after the tooth has erupted.
The dental fibers are enveloped by nerves, therefore when the Dentin is exposed there is direct contact between the nerves and the external environment, and this causes pain.
ENAMEL 95-97% of the Enamel is composed of inorganic salts (Crystals of Hydroxyapatite). It is produced by cells called AMELOBLASTS which cease their activity when the tissue has been completely formed.
The structure of the Enamel is composed of PRISMS which extend from the external surface to the internal surface of the Enamel. An organic matrix is interposed between one prism and another (INTERPRISMATIC SUBSTANCE).
Each prism contains Crystals of Hydroxyapatite, that have a hexagonal section, and that are closely-packed and well aligned.
The Cementum-Enamel Junction at the neck of the tooth may have one of the three aspects described below:
- In 10% of the cases the Cementum and the Enamel are not in contact and a small portion of the Dentin remains exposed.
- In 30% of the cases the Cementum and the Enamel are in linear contact.
- In 60% of the cases the Cementum covers a small portion of the Enamel.