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Teeth

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The teeth are anatomical structures that can be found in the oral cavity in both the upper and lower jaws. They are seated via a joint categorized as gomphosis within the alveolar processes of the maxilla and the mandible. This article will discuss the borders of the teeth, the macroanatomy of the teeth in general, the deciduous teeth and the permanent teeth. Finally a brief overview of some pathological disorders will be mentioned.

Mandible
Recommended video: Mandible
Bony structures of the mandible.

Borders

This can vary depending upon which dental arch the teeth sit in, so firstly a general overview will be concluded and then specific bits of extra information will be added for various teeth. Superiorly in the case of the mandibular teeth and inferiorly in the case of the maxillary teeth, are the articulatory surfaces of the opposing teeth. The same applies vice versa in the case of the root of the tooth, which is seated in the alveolar bone of either the maxilla or the mandible respectively and is held their via the fibers of the periodontal ligament. Medially and laterally the adjacent teeth and gingival papillae surround each tooth. Anteriorly, the oral vestibule and the inner mucosal surface of the lip or the bucca cover the teeth. Posteriorly the tongue and oral cavity proper limit the teeth. At the apex of each tooth in the alveolar bone there is a plexus of nerve fibers, vessels and lymphatics that run around the dental arch supplying the teeth. In the maxilla from the second premolar to the third molar superiorly there sits the maxillary sinus and often the roots of the maxillary molars will protrude into the sinus which causes complications when they are decayed or being extracted. Between the mandibular first and second premolar roots there lies the mental foramen which carries the mental nerve and must be anesthetized when either of those teeth are extracted.

Anatomy

Firstly, before discussing the layers and parts of the teeth in general, the surfaces of the teeth will be mentioned. The labial surface of a tooth is that which is closest to the lip and the buccal surface is its equivalent for the posterior teeth that have a surface which is closest to the bucca or the cheek. The facial surface is simply a synonym for either labial or buccal. The lingual surface is that which faces the tongue on the lower jaw and its equivalent for the maxillary teeth is the palatal surface. The mesial and distal surfaces of the tooth are either nearer or further away from the midline respectively. The occlusal surfaces are used for chewing and articulation in the posterior teeth, while the equivalent in the anterior teeth is known as the incisal edge. The crown of the tooth is categorized as either the anatomical crown or the clinical crown. The anatomical crown is the area of the tooth that is covered by enamel and the clinical crown is that which is exposed to the oral cavity. The same subcategorization occurs for the root of the tooth with regards to the cementum. The apex of the root contains a small aperture which allows the nerves and vessels to enter into the pulp cavity. The cervical line is the anatomical demarcation of the margin between the crown and the root and is known as the cementoenamel junction (CEJ).

The enamel is the hard exterior surface of the tooth that is comprised of hexagonal rods called enamel prisms that lie parallel to one another. The cementum is a thin layer that covers the anatomical surface of the root. It has a similar chemical composition to bone and thickens with age. The dentin is the hard tissue that lies under the enamel and surrounds the pulp cavity. It makes up the largest portion of the tooth structure and is a modified version of osseous tissue. It is organized into a matrix of dental tubules. A cusp is an occlusal elevation found of the articulating surface of premolars and molars. The equivalent of a cusp on the anterior teeth is the incisal edge. The pulp cavity contains the dental pulp which is a soft connective tissue web with houses the nerves and vessels which supply the tooth. It is separated into the pulp chamber in the crown of the tooth and the pulp canal which is in the root of the tooth. The cingulum is a convex elevation on the lingual surface of the clinical crown just above the cementoenamel junction.

Deciduous Teeth

The deciduous or primary teeth are the first set of baby teeth that emerge from the dental arch around the age of six months and start to fall out around the age of six years. They are used for speech and eating while the permanent tooth buds mature in the alveolar bone. As the milk teeth fall out a space is created for the permanent teeth to erupt into and remain there for the rest of a humans natural life. These teeth are small and fewer in number. There are only five milk teeth in each quadrant, therefore ten in each dental arch and there are no premolars and only two molars.

Permanent Teeth

The permanent tooth buds exist at the time of birth but take time to mature before they erupt into the oral cavity. The permanent teeth are much larger, with thicker enamel and dentin, smaller pulp chambers, more roots that are longer and bigger cusps. They start erupting around age seven as the primary teeth start to fall out and once they are fully erupted they need approximately six months to mature. This maturation process allows the enamel to harden and become resilient to acidic foods and bacteria.

Pathology

Fluorosis is a common disorder that occurs in young children. It causes staining on the teeth that can be mild to severe depending on the excess of fluoride the child ingests. White spots on the lower part of the crown close to the incisal edge of the anterior teeth are a telltale sign. Fluoride is essential for the maturation of young teeth and the prevention of tooth decay, however too much of it can cause the enamel structure to become weakened and permanently discoloured.

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Show references

References:

  • Oral Care. WebMD, LLC. 2013.
  • Neil S. Norton, Ph.D. and Frank H. Netter, MD, Netter’s Head and Neck Anatomy for Dentistry, 2nd Edition, Elsevier Saunders, Chapter 13 Oral Cavity, Boundaries of the Oral Cavity, Page 332 to 341 to 351.

Author:

  • Dr. Alexandra Sieroslawska

Illustrators:         

  • Maxillary teeth - inferior view - Yousun Koh 
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