Information AboutTooth |
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Teeth (singular, '''tooth''') are structures found in the Jaw s of many Vertebrate s that are used to tear, scrape, and chew Food . Some animals, particularly Carnivore s, also use teeth for hunting or defense. The roots of teeth are covered by Gum s. Teeth are among the most distinctive (and long-lasting) features of Mammal species. Paleontologists use teeth to identify Fossil species and determine their relationships. The shape of an animal's teeth is related to its diet. For example, plant matter is hard to digest, so Herbivore s have many molars for Chewing . Carnivore s, on the other hand, need Canines to kill and tear meat. Humans are diphyodont, meaning that they develop two sets of teeth. The first set (the "baby," "milk," "primary" or " Deciduous " set) normally starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth. Normal Tooth Eruption at about six months is known as Teething and can be quite painful for an infant. Some animals develop only one set of teeth (monophyodont) while others develop many sets (polyphyodont). Shark s, for example, grow a new set of teeth every two weeks to replace worn teeth. Rodent incisors grow and wear away continually through gnawing, maintaining relatively constant length. Some rodent species, such as the sibling vole and the guinea pig, have continuously growing molars in addition to incisors.Tummers M and Thesleff I. Root or crown: a developmental choice orchestrated by the differential regulation of the epithelial stem cell niche in the tooth of two rodent species. Development (2003). 130(6):1049-57.AM Hunt. A description of the molar teeth and investing tissues of normal guinea pigs. J Dent Res. (1959) 38(2):216-31. ANATOMY See Also: Dental anatomy Dental anatomy is a field of Anatomy dedicated to the study of tooth structures. The development, appearance, and classification of teeth fall within its purview, though Dental Occlusion , or contact among teeth, does not. Dental anatomy is also a Taxonomical science as it is concerned with the naming of teeth and their structures. This information serves a practical purpose for dentists, enabling them to easily identify teeth and structures during treatment. The anatomic crown of a tooth is the area covered in enamel above the .Ash, Major M. and Stanley J. Nelson, 2003. ''Wheeler’s Dental Anatomy, Physiology, and Occlusion.'' 8th edition. Page 9. ISBN 0-7216-9382-2. After eruption, it is almost always visible. The anatomic root is found below the cementoenamel junction and is covered with Cementum . As with the crown, dentin composes most of the root, which normally have pulp canals. A tooth may have multiple roots or just one root. Canines and most premolars, except for maxillary (upper) first premolars, usually have one root. Maxillary first premolars and mandibular molars usually have two roots. Maxillary molars usually have three roots. Additional roots are referred to as Supernumerary Roots . Humans usually have 20 primary teeth (also called deciduous, baby, or milk teeth) and 32 permanent teeth. Among primary teeth, 10 are found in the Maxilla and the other 10 in the Mandible . Teeth are classified as incisors, canines, and molars. In the primary set of teeth, there are two types of incisors, centrals and laterals, and two types of molars, first and second. All primary teeth are replaced with permanent counterparts except for molars, which are replaced by permanent premolars. Among permanent teeth, 16 are found in the maxilla with the other 16 in the mandible. The maxillary teeth are the Maxillary Central Incisor , Maxillary Lateral Incisor , Maxillary Canine , Maxillary First Premolar , Maxillary Second Premolar , Maxillary First Molar , Maxillary Second Molar , and Maxillary Third Molar . The mandibular teeth are the Mandibular Central Incisor , Mandibular Lateral Incisor , Mandibular Canine , Mandibular First Premolar , Mandibular Second Premolar , Mandibular First Molar , Mandibular Second Molar , and Mandibular Third Molar . Third molars are commonly called " Wisdom Teeth " and may never erupt into the mouth or form at all. If any additional teeth form, for example, fourth and fifth molars, which are rare, they are referred to as Supernumerary Teeth .Kokten G, Balcioglu H, Buyukertan M. Supernumerary Fourth and Fifth Molars: A Report of Two Cases. Journal of Contemporary Dental Practice, 2003 November; (4)4:067-076. Page accessed February 10, 2007. Most teeth have identifiable features that distinguish them from others. There are several different Notation Systems to refer to a specific tooth. The three most commons systems are the FDI World Dental Federation Notation , the Universal Numbering System , and Palmer Notation Method . The FDI system is used worldwide, and the universal is used widely in the United States. PARTS Enamel See Also: Tooth enamel Enamel is the hardest and most highly mineralized substance of the body and is one of the four major tissues which make up the tooth, along with of a tooth. Enamel varies in thickness over the surface of the tooth and is often thickest at the Cusp , up to 2.5 mm, and thinnest at its border, which is seen clinically as the Cementoenamel Junction (CEJ).Cate, A. R. Ten, "Oral Histology: Development, Structure, and Function", 5th ed. (Saint Louis: Mosby-Year Book, 1998), p. 219. Enamel's primary mineral is , enamel does not contain Collagen . Instead, it has two unique classes of Protein s called Amelogenin s and Enamelin s. While the role of these proteins is not fully understood, it is believed that they aid in the development of enamel by serving as framework support among other functions.Cate, A. R. Ten, "Oral Histology: Development, Structure, and Function", 5th ed. (Saint Louis: Mosby-Year Book, 1998), p. 198. Dentin See Also: Dentin Dentin is the substance between enamel or cementum and the pulp chamber. It is secreted by the odontoblasts of the dental pulp.Ross, Michael H., Gordon I. Kaye, and Wojciech Pawlina, 2003. ''Histology: a text and atlas.'' 4th edition. Page 448. ISBN 0-683-30242-6. 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.Cate, A.R. Ten. ''Oral Histology: development, structure, and function.'' 5th ed. 1998. Page 150. ISBN 0-8151-2952-1. 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.Ross, Michael H., Gordon I. Kaye, and Wojciech Pawlina, 2003. ''Histology: a text and atlas.'' 4th edition. Page 450. ISBN 0-683-30242-6. 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.Cate, A.R. Ten. ''Oral Histology: development, structure, and function.'' 5th ed. 1998. Page 152. ISBN 0-8151-2952-1. 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. Cementum See Also: Cementum Cementum is a specialized bony substance covering the root of a tooth.Ross, Michael H., Gordon I. Kaye, and Wojciech Pawlina, 2003. ''Histology: a text and atlas.'' 4th edition. Page 448. ISBN 0-683-30242-6. It is approximately 45% inorganic material (mainly Hydroxyapatite ), 33% organic material (mainly Collagen ) and 22% water. Cementum is excreted by Cementoblast s within the root of the tooth and is thickest at the root apex. Its coloration is yellowish and it is softer than either dentin or enamel. The principle role of cementum is to serve as a medium by which the Periodontal Ligament s can attach to the tooth for stability. At the cementoenamel junction, the cementum is acellular due to its lack of cellular components, and this acellular type covers at least ⅔ of the root.Cate, A.R. Ten. ''Oral Histology: development, structure, and function.'' 5th ed. 1998. Page 236. ISBN 0-8151-2952-1. The more permeable form of cementum, cellular cementum, covers about ⅓ of the root apex.Cate, A.R. Ten. ''Oral Histology: development, structure, and function.'' 5th ed. 1998. Page 241. ISBN 0-8151-2952-1. Pulp See Also: Pulp (tooth) The dental pulp is the central part of the tooth filled with soft connective tissue.Cate, A.R. Ten. ''Oral Histology: development, structure, and function.'' 5th ed. 1998. Page 150. ISBN 0-8151-2952-1. This tissue contains blood vessels and nerves that enter the tooth from a hole at the apex of the root.Ross, Michael H., Gordon I. Kaye, and Wojciech Pawlina, 2003. ''Histology: a text and atlas.'' 4th edition. Page 451. ISBN 0-683-30242-6. Along the border between the dentin and the pulp are odontoblasts, which initiate the formation of dentin.Cate, A.R. Ten. ''Oral Histology: development, structure, and function.'' 5th ed. 1998. Page 150. ISBN 0-8151-2952-1. Other cells in the pulp include fibroblasts, preodontoblasts, Macrophage s and T Lymphocyte s.Walton, Richard E. and Mahmoud Torabinejad. ''Principles and Practice of Endodontics.'' 3rd ed. 2002. Pages 11-13. ISBN 0-7216-9160-9. The pulp is commonly called "the nerve" of the tooth. DEVELOPMENT See Also: Tooth development Tooth development is the complex process by which teeth form from Embryo nic Cells , Grow , and erupt into the Mouth . Although many diverse Species have teeth, non-human tooth development is largely the same as in humans. For Human teeth to have a healthy Oral environment, Enamel , Dentin , Cementum , and the Periodontium must all develop during appropriate stages of Fetal Development . Primary (baby) Teeth start to form between the sixth and eighth weeks In Utero , and Permanent Teeth begin to form in the twentieth week in utero.A. R. Ten Cate, ''Oral Histology: Development, Structure, and Function'', 5th ed. (Saint Louis: Mosby-Year Book, 1998), p. 95. ISBN 0-8151-2952-1. If teeth do not start to develop at or near these times, they will not develop at all. A significant amount of research has focused on determining the processes that initiate tooth development. It is widely accepted that there is a factor within the tissues of the first Branchial Arch that is necessary for the development of teeth.A. R. Ten Cate, ''Oral Histology: Development, Structure, and Function'', 5th ed. (Saint Louis: Mosby-Year Book, 1998), p. 81. ISBN 0-8151-2952-1. Tooth development is commonly divided into the following stages: the bud stage, the cap, the bell, and finally maturation. The staging of tooth development is an attempt to categorize changes that take place along a continuum; frequently it is difficult to decide what stage should be assigned to a particular developing tooth.A. R. Ten Cate, ''Oral Histology: Development, Structure, and Function'', 5th ed. (Saint Louis: Mosby-Year Book, 1998), p. 81. ISBN 0-8151-2952-1. This determination is further complicated by the varying appearance of different histologic sections of the same developing tooth, which can appear to be different stages.
ERUPTION See Also: Tooth eruption Tooth eruption in humans is a process in tooth development in which the teeth enter the mouth and become visible. Current research indicates that the periodontal ligaments play an important role in tooth eruption. Primary teeth erupt into the mouth from around six months until two years of age. These teeth are the only ones in the mouth until a person is about six years old. At that time, the first permanent tooth erupts. This stage, during which a person has a combination of primary and permanent teeth, is known as the mixed stage. The mixed stage lasts until the last primary tooth is lost and the remaining permanent teeth erupt into the mouth. There have been many theories about the cause of tooth eruption. One theory proposes that the developing root of a tooth pushes it into the mouth.Harris, Edward F. ''Craniofacial Growth and Development.'' In the section entitled "Tooth Eruption." 2002. pp. 1-3. Another, known as the cushioned hammock theory, resulted from microscopic study of teeth, which was thought to show a Ligament around the root. It was later discovered that the "ligament" was merely an Artifact created in the process of preparing the slide.Harris, Edward F. ''Craniofacial Growth and Development.'' In the section entitled "Tooth Eruption." 2002. p. 3. Currently, the most widely held belief is that the periodontal ligaments provide the main impetus for the process.Harris, Edward F. ''Craniofacial Growth and Development.'' In the section entitled "Tooth Eruption." 2002. p. 5. SUPPORTING STRUCTURES |
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