عرض مصدر Human tooth

{{For|other uses of tooth or teeth|Tooth (disambiguation)}}
{{Infobox anatomy
| Name        = Teeth
| Latin       = dentes
| GraySubject = 
| GrayPage    = 
| Image       = Human tooth diagram-en.svg
| Caption     = Diagram of a human molar showing its major constituents
| Width       = 
| Image2      = Denticao.jpg
| Caption2    = CGI posterior view of teeth taken from inside mouth
| ImageMap    = 
| MapCaption  = 
| Precursor   = 
| System      = 
| Artery      = 
| Vein        = 
| Nerve       = 
| Lymph       = 
| MeshName    = Tooth
| MeshNumber  = 
| Code        = 
| Dorlands    = eight/000109449
| DorlandsID  = Tooth
}}
The '''human teeth''' function to [[Mastication|mechanically break down]] items of [[food]] by cutting and crushing them in preparation for swallowing and digestion. Humans have four types of teeth: incisors, canines, premolars, and molars, each with a specific function. The incisors cut the food, the canines tear the food and the molars and premolars crush the food.  The roots of teeth are embedded in the [[maxilla]] (upper jaw) or the [[Human mandible|mandible]] (lower jaw) and are covered by [[gingiva|gums]]. Teeth are made of multiple tissues of varying density and hardness.

Teeth are among the most distinctive (and long-lasting) features of [[mammal]] species. Humans, like other mammals, are [[diphyodont]], meaning that they develop two sets of teeth. The first set (called the "baby", "milk", "primary", or "[[deciduous teeth|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 painful.

==Anatomy==
{{Main article|Dental anatomy}}
[[Dental anatomy]] is a field of [[anatomy]] dedicated to the study of tooth structure. The development, appearance, and classification of teeth fall within its field of study, though [[occlusion (dentistry)|dental occlusion]], or contact among teeth, does not. Dental anatomy is also a [[Taxonomy (general)|taxonomic]] 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 (tooth)|crown]] of a tooth is the area covered in enamel above the [[cementoenamel junction]] (CEJ) or "neck" of the tooth.<ref>{{cite book | last = Clemente | first = Carmine | title = Anatomy, a regional atlas of the human body | publisher = Urban & Schwarzenberg | location = Baltimore | year = 1987 | isbn = 0-8067-0323-7 }}</ref><ref name="ash6">{{harvnb|Ash|2003|page=6}}</ref> Most of the crown is composed of dentin (dentine in British English) with the pulp chamber inside.<ref name="Cate3">{{harvnb|Cate|1998|page=3}}</ref> The crown is within bone before [[tooth eruption|eruption]].<ref name="ash9">{{harvnb|Ash|2003|page=9}}</ref> After eruption, it is almost always visible. The anatomic root is found below the CEJ and is covered with [[cementum]]. As with the crown, dentin composes most of the root, which normally has a [[root canal|pulp canals]]. A tooth may have multiple roots or just one root (single-rooted teeth). Canines and most premolars, except for [[maxillary (disambiguation)|maxillary]] first premolars, usually have one root. Maxillary first premolars and [[mandible|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 (deciduous, "baby" or "milk") teeth and 32 permanent (adult) teeth. Teeth are classified as [[incisor]]s, [[Canine tooth|canines]], [[premolar]]s (also called ''bicuspids''),<ref>[http://medical-dictionary.thefreedictionary.com/Bicuspid+teeth "Bicuspid teeth"]. The Medical Dictionary. Retrieved on 2013-02-21.</ref> and [[Molar (tooth)|molars]]. Incisors are primarily used for biting pieces from foods such as raw [[carrot]]s or [[apple]]s and peeled but uncut [[banana]]s, while molars are used primarily for grinding foods after they are already in bite size pieces inside the mouth.

Most teeth have identifiable features that distinguish them from others. There are several different [[Dental notation|notation systems]] to refer to a specific tooth. The three most common systems are the [[FDI World Dental Federation notation]], the [[Universal numbering system (dental)|universal numbering system]], and [[Palmer Notation Method|Palmer notation method]]. The FDI system is used worldwide, and the universal is used widely in the United States.

===Primary teeth===
Among [[Deciduous teeth|deciduous (primary) teeth]], ten are found in the maxilla (upper jaw) and ten in the mandible (lower jaw), for a total of 20. The [[dentition|dental formula]] for primary teeth is {{DentalFormula|upper=2.1.0.2|lower=2.1.0.2}}.

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 normally later replaced with their permanent counterparts.

===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 {{DentalFormula|upper=2.1.2.3|lower=2.1.2.3}}.

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 [[Hyperdontia|supernumerary teeth (hyperdontia)]].<ref>{{Cite journal|vauthors=Kokten G, Balcioglu H, Buyukertan M |title=Supernumerary fourth and fifth molars: a report of two cases |journal=Journal of Contemporary Dental Practice |volume=4 |issue=4 |pages=67–76 |year=2003 |pmid=14625596 |url=http://www.thejcdp.com/issue016/kokten/index_nlm.htm |deadurl=yes |archiveurl=https://web.archive.org/web/20081121090806/http://www.thejcdp.com/issue016/kokten/index_nlm.htm |archivedate=November 21, 2008 }}</ref> Development of fewer than the usual number of teeth is called [[hypodontia]].

==Parts==

===Enamel===
{{Main article|Tooth enamel}}

Enamel is the hardest and most highly mineralized substance of the body. It is one of the four major tissues which make up the tooth, along with [[dentin]], [[cementum]], and [[dental pulp]].<ref>{{harvnb|Ross|2002|page=441}}</ref> 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.<ref>{{harvnb|Cate|1998|page=1}}</ref> 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 (dentistry)|cusp]], up to 2.5mm, and thinnest at its border, which is seen clinically as the CEJ.<ref name="Cate, A. R 1998 p. 219">{{harvnb|Cate|1998|page=219}}</ref> The wear rate of enamel, called attrition, is 8 micrometers a year from normal factors.{{Citation needed|date=January 2014}}

Enamel's primary mineral is [[hydroxyapatite]], which is a [[crystal]]line [[calcium phosphate]].<ref name = "biology"/> The large amount of minerals in enamel accounts not only for its strength but also for its brittleness.<ref name="Cate, A. R 1998 p. 219"/> Dentin, which is less mineralized and less brittle, compensates for enamel and is necessary as a support.<ref name="biology">Johnson, Clarke (1998). "[http://www.uic.edu/classes/orla/orla312/BHDTwo.html Biology of the Human Dentition]". uic.edu.</ref> Unlike dentin and [[bone]], 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.<ref>{{harvnb|Cate|1998|page=198}}</ref>

===Dentin===
{{Main article|Dentin}}

Dentin is the substance between enamel or cementum and the pulp chamber. It is secreted by the odontoblasts of the dental pulp.<ref name = "ross448"/> 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.<ref name = "Cate150"/> 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.<ref name="ross450">{{harvnb|Ross|2002|page=450}}</ref> The diameter of these tubules range from 2.5 μm near the pulp, to 1.2 μm in the midportion, and 900&nbsp;nm near the dentino-enamel junction.<ref name="Cate152">{{harvnb|Cate|1998|page=152}}</ref> 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===
{{Main article|Cementum}}

Cementum is a specialized bone like substance covering the root of a tooth.<ref name = "ross448"/> 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 principal 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.<ref name="Cate236">{{harvnb|Cate|1998|page=236}}</ref> The more permeable form of cementum, cellular cementum, covers about ⅓ of the root apex.<ref name="Cate241">{{harvnb|Cate|1998|page=241}}</ref>

=== Pulp ===
{{Main article|Pulp (tooth)}}
The dental pulp is the central part of the tooth filled with soft connective tissue.<ref name = "Cate150"/> This tissue contains blood vessels and nerves that enter the tooth from a hole at the apex of the root.<ref name="Ross451">{{harvnb|Ross|2002|page=451}}</ref> Along the border between the dentin and the pulp are odontoblasts, which initiate the formation of dentin.<ref name="Cate150">{{harvnb|Cate|1998|page=150}}</ref> Other cells in the pulp include fibroblasts, preodontoblasts, [[macrophage]]s and [[T cells|T lymphocytes]].<ref name="Walton11thru13">Walton, Richard E. and Mahmoud Torabinejad. ''Principles and Practice of Endodontics.'' 3rd ed. 2002. pp. 11–13. ISBN 0-7216-9160-9.</ref> The pulp is commonly called "the nerve" of the tooth.

==Development==
{{Main article|Tooth development}}

[[File:Molarsindevelopment11-24-05.jpg|thumb|Radiograph of lower right third, second, and first molars in different stages of development.]]

Tooth development is the complex process by which teeth form from [[embryo]]nic [[cell (biology)|cells]], [[cell growth|grow]], and erupt into the [[human mouth|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 [[Human mouth|oral]] environment, [[tooth enamel|enamel]], [[dentin]], [[cementum]], and the [[periodontium]] must all develop during appropriate stages of [[fetal development]]. [[Deciduous teeth|Primary teeth]] start to form between the sixth and eighth weeks [[Uterus|in utero]], and [[permanent teeth]] begin to form in the twentieth week in utero.<ref>{{harvnb|Cate|1998|page=95}}</ref> 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.<ref name = "cate81"/>

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.<ref name="cate81">{{harvnb|Cate|1998|page=81}}</ref> 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.

The [[tooth bud]] (sometimes called the tooth germ) is an aggregation of [[cell (biology)|cells]] that eventually forms a tooth. It is organized into three parts: the [[enamel organ]], the [[dental papilla]] and the [[dental follicle]].<ref name = "utmb"/> The ''enamel organ'' is composed of the [[outer enamel epithelium]], [[inner enamel epithelium]], [[stellate reticulum]] and [[stratum intermedium]].<ref name = "utmb"/> These cells give rise to [[ameloblast]]s, which produce enamel and the [[reduced enamel epithelium]]. The growth of [[cervical loop]] cells into the deeper tissues forms [[Hertwig's Epithelial Root Sheath]], which determines a tooth's root shape. The ''dental papilla'' contains cells that develop into [[odontoblast]]s, which are dentin-forming cells.<ref name="utmb">[http://web.archive.org/web/20070203050136/http://cellbio.utmb.edu/microanatomy/digestive/tooth.htm Lab Exercises: Tooth development]. University of Texas Medical Branch.</ref> Additionally, the junction between the dental papilla and inner enamel epithelium determines the crown shape of a tooth.<ref name="cate86and102">{{harvnb|Cate|1998|pages=86 and 102}}.</ref>  The ''dental follicle'' gives rise to three important entities: [[cementoblast]]s, [[osteoblast]]s, and [[fibroblast]]s. Cementoblasts form the cementum of a tooth. Osteoblasts give rise to the [[Alveolar process of maxilla|alveolar bone]] around the roots of teeth. Fibroblasts develop the [[periodontal ligament]]s which connect teeth to the alveolar bone through cementum.<ref name = "ross453">{{harvnb|Ross|2002|page=453}}</ref>

== Eruption ==
{{Main article|Tooth eruption}}

[[File:ToothLost-2917.jpg|thumb|right|Bottom teeth of a seven-year-old, showing primary teeth ''(left)'', a lost primary tooth ''(middle)'', and a permanent tooth ''(right)'']]
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. 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 (observational)|artifact]] created in the process of preparing the slide. Currently, the most widely held belief is that the periodontal ligaments provide the main impetus for the process.

The onset of primary tooth loss has been found to correlate strongly with somatic and psychological criteria of school readiness.<ref>Kranich, Ernst-Michael (1990) "Anthropologie", in F. Bohnsack and E-M Kranich (eds.), ''Erziehungswissenschaft und Waldorfpädagogik'', Reihe Pädagogik Beltz, Weinheim, p. 126, citing F. Ilg and L. Ames (Gesell Institute), ''School Readiness'', p. 236 ff</ref><ref>{{cite journal|quote=...the loss of the first deciduous tooth can serve as a definite indicator of a male child's readiness for reading and schoolwork|title=Second Dentition and School Readiness|journal=New York State Dental Journal |volume=43 |pages=155–8|pmid=264640|year=1977|last1=Silvestro|first1=JR|issue=3}}</ref>{{Clarify|date=January 2012}}

==Supporting structures==
[[File:Eruptingtoothwithlabels11-24-05.jpg|thumb|Histologic slide of tooth erupting into the mouth. <br />A: tooth <br />B: gingiva
<br />C: bone
<br />D: periodontal ligaments]]

The [[periodontium]] is the supporting structure of a tooth, helping to attach the tooth to surrounding tissues and to allow sensations of touch and pressure.<ref name = "ross452"/> It consists of the cementum, periodontal ligaments, [[alveolar bone]], and [[gingiva]]. Of these, cementum is the only one that is a part of a tooth. Periodontal ligaments connect the alveolar bone to the cementum. Alveolar bone surrounds the roots of teeth to provide support and creates what is commonly called an [[Dental alveolus|alveolus]], or "socket". Lying over the bone is the [[gingiva]] or gum, which is readily visible in the mouth.

===Periodontal ligaments===
The [[periodontal ligament]] is a specialized [[connective tissue]] that attaches the cementum of a tooth to the alveolar bone. This tissue covers the root of the tooth within the bone. Each ligament has a width of 0.15–0.38mm, but this size decreases over time.<ref name="Cate256">{{harvnb|Cate|1998|page=256}}</ref> The functions of the periodontal ligaments include attachment of the tooth to the bone, support for the tooth, formation and [[Bone resorption|resorption]] of bone during tooth movement, sensation, and eruption.<ref name = "ross453"/> The cells of the periodontal ligaments include osteoblasts, osteoclasts, fibroblasts, macrophages, cementoblasts, and [[epithelial cell rests of Malassez]].<ref name="Cate260">{{harvnb|Cate|1998|page=260}}</ref> Consisting of mostly Type I and III [[collagen]], the fibers are grouped in bundles and named according to their location. The groups of fibers are named alveolar crest, horizontal, oblique, periapical, and interradicular fibers.<ref>Listgarten, Max A. "[http://web.archive.org/web/20130520224440/http://www.dental.pitt.edu/informatics/periohistology/en/gu0404.htm Histology of the Periodontium: Principal fibers of the periodontal ligament]," University of Pennsylvania and Temple University. Created May 8, 1999, revised 16 January 2007.</ref> The nerve supply generally enters from the bone apical to the tooth and forms a network around the tooth toward the crest of the gingiva.<ref name="Cate270">{{harvnb|Cate|1998|page=270}}</ref> When pressure is exerted on a tooth, such as during chewing or biting, the tooth moves slightly in its socket and puts tension on the periodontal ligaments. The nerve fibers can then send the information to the central nervous system for interpretation.

===Alveolar bone===
The [[alveolar bone]] is the bone of the jaw which forms the alveolus around teeth.<ref name="Cate274">{{harvnb|Cate|1998|page=274}}</ref> Like any other bone in the human body, alveolar bone is modified throughout life. [[Osteoblast]]s create bone and [[osteoclast]]s destroy it, especially if force is placed on a tooth.<ref name="ross452">{{harvnb|Ross|2002|page=452}}</ref> As is the case when movement of teeth is attempted through orthodontics, an area of bone under [[compression (physical)|compressive]] [[force]] from a tooth moving toward it has a high osteoclast level, resulting in [[bone resorption]]. An area of bone receiving [[tension (mechanics)|tension]] from periodontal ligaments attached to a tooth moving away from it has a high number of osteoblasts, resulting in bone formation.

===Gingiva===
The [[gingiva]] ("gums") is the [[mucous membranes|mucosal]] tissue that overlays the jaws. There are three different types of epithelium associated with the gingiva: gingival, junctional, and sulcular epithelium. These three types form from a mass of epithelial cells known as the epithelial cuff between the tooth and the mouth.<ref name="Cate247and248">{{harvnb|Cate,|1998|pages=247 and 248}}</ref> The gingival epithelium is not associated directly with tooth attachment and is visible in the mouth. The junctional epithelium, composed of the [[basal lamina]] and [[hemidesmosome]]s, forms an attachment to the tooth.<ref name="ross453"/> The sulcular epithelium is [[Epidermis (skin)|nonkeratinized]] [[Squamous epithelium|stratified squamous]] tissue on the gingiva which touches but is not attached to the tooth.<ref name="Cate280">{{harvnb|Cate|1998|page=280}}</ref>

== Tooth decay ==
{{See also|Tooth pathology}}

=== Plaque ===
{{Main article|Dental plaque}}

Plaque is a [[biofilm]] consisting of large quantities of various [[bacteria]] that form on teeth.<ref>[http://web.archive.org/web/20080125151851/http://www.ada.org/public/topics/plaque.asp "Oral Health Topics: Plaque"], American Dental Association.</ref> If not removed regularly, plaque buildup can lead to [[periodontal]] problems such as [[gingivitis]]. Given time, plaque can mineralize along the gingiva, forming ''[[Calculus (dental)|tartar]]''. The [[microorganism]]s that form the biofilm are almost entirely [[bacteria]] (mainly [[streptococcus]] and [[Anaerobic organism|anaerobes]]), with the composition varying by location in the mouth.<ref>[http://www.dentistry.leeds.ac.uk/OROFACE/PAGES/micro/micro2.html Introduction to dental plaque], Leeds Dental Institute.</ref> ''[[Streptococcus mutans]]'' is the most important bacterium associated with dental caries.

Certain bacteria in the mouth live off the remains of foods, especially [[sugar]]s and starches. In the absence of [[oxygen]] they produce [[lactic acid]], which [[Solvation|dissolves]] the [[calcium]] and [[phosphorus]] in the enamel.<ref name="ross448">{{harvnb|Ross|2002|page=448}}</ref><ref>Ophardt, Charles E. "[http://web.archive.org/web/20141025132424/http://www.elmhurst.edu/~chm/vchembook/548toothdecay.html Sugar and tooth decay]", Elmhurst College.</ref> This process, known as "demineralisation", leads to tooth destruction. [[Saliva]] gradually neutralises the [[acid]]s which cause the pH of the tooth surface to rise above the critical pH. This causes '[[remineralisation]]', the return of the dissolved minerals to the enamel. If there is sufficient time between the intake of foods then the impact is limited and the teeth can repair themselves. Saliva is unable to penetrate through plaque, however, to neutralize the acid produced by the bacteria.

===Caries (cavities)===
[[File:Toothdecay.png|right|thumb|150px|Advanced tooth decay on a premolar.]]
{{Main article|Dental caries}}
Dental caries (cavities), described as "tooth decay", is an infectious disease which damages the structures of teeth.<ref name="medline">[http://www.nlm.nih.gov/medlineplus/ency/article/001055.htm Dental Cavities], ''MedlinePlus Medical Encyclopedia''.</ref> The disease can lead to [[pain]], [[tooth loss]], and infection. Dental caries has a long history, with evidence showing the disease was present in the [[Bronze Age|Bronze]], [[Iron age|Iron]], and [[Middle Ages|Middle]] ages but also prior to the [[neolithic]] period.<ref name=SeilerSpielman2013>{{cite journal| vauthors=Seiler R, Spielman AI, Zink A, Rühli F| title=Oral pathologies of the Neolithic Iceman, c.3,300 BC. | journal=Eur J Oral Sci | year= 2013 | volume= 121 | issue= 3 Pt 1 | pages= 137–41 | pmid=23659234 | doi=10.1111/eos.12037 | type= Historical Article. Research Support, Non-U.S. Gov't }}</ref> The largest increases in the prevalence of caries have been associated with diet changes.<ref name="suddickhistorical">{{Cite journal|vauthors=Suddick RP, Harris NO |title=Historical perspectives of oral biology: a series |journal=Crit. Rev. Oral Biol. Med. |volume=1 |issue=2 |pages=135–51 |year=1990 |pmid=2129621 |doi=10.1177/10454411900010020301|doi-broken-date=2016-10-19 }}</ref> Today, caries remains one of the most common diseases throughout the world. In the United States, dental caries is the most common [[chronic (medicine)|chronic]] childhood disease, being at least five times more common than [[asthma]].<ref>[http://web.archive.org/web/20101219084119/http://healthypeople.gov/Document/HTML/Volume2/21Oral.htm Healthy People: 2010]. Healthy People.gov.</ref> Countries that have experienced an overall decrease in cases of tooth decay continue to have a disparity in the distribution of the disease.<ref name="DCPP">"[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=dcp2.section.5380 Dental caries]", from the Disease Control Priorities Project.</ref> Among children in the United States and Europe, 60–80% of cases of dental caries occur in 20% of the population.<ref name="Tougersugars">{{Cite journal|vauthors=Touger-Decker R, van Loveren C |title=Sugars and dental caries |journal=Am. J. Clin. Nutr. |volume=78 |issue=4 |pages=881S–892S |year=2003|pmid=14522753 }}</ref>

Tooth decay is caused by certain types of acid-producing bacteria which cause the most damage in the presence of [[fermentation (food)|fermentable]] [[carbohydrate]]s such as [[sucrose]], [[fructose]], and [[glucose]].<ref name="Hardie1982">{{Cite journal|author=Hardie JM |title=The microbiology of dental caries |journal=Dent Update |volume=9 |issue=4 |pages=199–200, 202–4, 206–8 |year=1982|pmid=6959931}}</ref><ref name="holloway1983">{{Cite journal|author=Moore WJ |title=The role of sugar in the aetiology of dental caries. 1. Sugar and the antiquity of dental caries |journal=J Dent |volume=11 |issue=3 |pages=189–90 |year=1983|pmid=6358295 |doi= 10.1016/0300-5712(83)90182-3|last2=Moore|first2=W.J.}}</ref> The resulting acidic levels in the mouth affect teeth because a tooth's special mineral content causes it to be sensitive to low [[pH]]. Depending on the extent of tooth destruction, various treatments can be used to [[dental restoration|restore]] teeth to proper form, function, and [[aesthetics]], but there is no known method to [[regeneration (biology)|regenerate]] large amounts of tooth structure. Instead, dental health organizations advocate preventative and prophylactic measures, such as regular [[oral hygiene]] and dietary modifications, to avoid dental caries.<ref name = "adaoralhealth"/>

==Tooth care==
===Oral hygiene===
[[File:Toothbrush 20050716 004.jpg|right|thumb|[[Toothbrush]]es are commonly used to help clean teeth.]]
{{Main article|Oral hygiene}}

Oral hygiene is the practice of keeping the mouth clean and is a means of preventing dental caries, [[gingivitis]], [[periodontal disease]], [[halitosis|bad breath]], and other dental disorders. It consists of both professional and personal care. Regular cleanings, usually done by dentists and dental hygienists, remove [[Calculus (dental)|tartar]] (mineralized plaque) that may develop even with careful [[tooth brushing|brushing]] and [[Dental Floss|flossing]]. Professional cleaning includes [[tooth scaling]], using various instruments or devices to loosen and remove deposits from teeth.

The purpose of cleaning teeth is to remove plaque, which consists mostly of bacteria.<ref>[http://www.dentistry.leeds.ac.uk/OROFACE/PAGES/micro/micro2.html Introduction to Dental Plaque]. Leeds Dental Institute.</ref> Healthcare professionals recommend regular brushing twice a day (in the morning and in the evening, or after meals) in order to prevent formation of plaque and tartar.<ref name="adaoralhealth">[http://web.archive.org/web/20080222223237/http://www.ada.org/public/topics/cleaning.asp Oral Health Topics: Cleaning your teeth and gums]. American Dental Association.</ref> A toothbrush is able to remove most plaque, except in areas between teeth. As a result, flossing is also considered a necessity to maintain oral hygiene. When used correctly, dental floss removes plaque from between teeth and at the [[gum line]], where [[periodontal disease]] often begins and could develop caries.

Electric toothbrushes are a popular aid to oral hygiene. A user without disabilities, with proper training in manual brushing, and with good motivation, can achieve standards of oral hygiene at least as satisfactory as the best electric brushes, but untrained users rarely achieve anything of the kind. Not all electric toothbrushes are equally effective and even a good design needs to be used properly for best effect, but: "Electric toothbrushes tend to help people who are not as good at cleaning teeth and as a result have had oral hygiene problems." <ref>[http://news.bbc.co.uk/1/hi/health/2679175.stm Thumbs down for electric toothbrush], BBC News, January 21, 2003.</ref> The most important advantage of electric toothbrushes is their ability to aid people with dexterity difficulties, such as those associated with [[rheumatoid arthritis]].

===Protective treatments===
[[Fluoride therapy]] is often recommended to protect against dental caries. [[Water fluoridation]] and [[fluoride]] supplements decrease the incidence of dental caries. Fluoride helps prevent dental decay by binding to the hydroxyapatite crystals in enamel.<ref>{{harvnb|Cate|1998|page=223}}</ref> The incorporated fluoride makes enamel more resistant to demineralization and thus more resistant to decay.<ref name = "ross453"/> Topical fluoride, such as a fluoride [[toothpaste]] or [[mouthwash]], is also recommended to protect teeth surfaces. Many dentists include application of topical fluoride solutions as part of routine cleanings.

[[Dental sealant]]s are another preventive therapy often used to provide a barrier to bacteria and decay on the surface of teeth. Sealants can last up to ten years and are primarily used on the biting surfaces of molars of children and young adults, especially those who may have difficulty brushing and flossing effectively. Sealants are applied in a dentist's office, sometimes by a dental hygienist, in an procedure similar in technique and cost to a flouride application.

==Restorations==
[[File:dent,tooth,zub.jpg|right|thumb|A restored premolar.]]
After a tooth has been damaged or destroyed, [[Dental restoration|restoration]] of the missing structure can be achieved with a variety of treatments. Restorations may be created from a variety of [[Dental restorative materials|materials]], including [[Glass ionomer cement|glass ionomer]], [[Amalgam (dentistry)|amalgam]], [[gold]], [[Dental porcelain|porcelain]], and [[Dental composite|composite]].<ref>"[http://web.archive.org/web/20090830062420/http://www.ada.org/public/topics/fillings.asp Oral Health Topics: Dental Filling Options]". ada.org.</ref> Small restorations placed inside a tooth are referred to as "intracoronal restorations". These restorations may be formed directly in the mouth or may be cast using the [[lost-wax casting|lost-wax technique]], such as for some [[inlays and onlays]]. When larger portions of a tooth are lost, an "extracoronal restoration" may be fabricated, such as an [[crown (dentistry)|artificial crown]] or a [[veneer (dentistry)|veneer]], to restore the involved tooth.

When a tooth is lost, [[dentures]], [[Bridge (dentistry)|bridges]], or [[dental implant|implants]] may be used as replacements.<ref name="acp">"[http://web.archive.org/web/20120615170730/http://www.prosthodontics.org/patients/procedures.asp Prosthodontic Procedures]", The American College of Prosthodontists.</ref> Dentures are usually the least costly whereas implants are usually the most expensive. Dentures may replace complete arches of the mouth or only a [[removable partial denture|partial]] number of teeth. Bridges replace smaller spaces of missing teeth and use adjacent teeth to support the restoration. Dental implants may be used to replace a single tooth or a series of teeth. Though implants are the most expensive treatment option, they are often the most desirable restoration because of their aesthetics and function. To improve the function of dentures, implants may be used as support.<ref name="aaomsimplants">"[http://web.archive.org/web/20131803035800/http://www.aaoms.org/dental_implants.php Dental Implants]", American Association of Oral and Maxillofacial Surgeons.</ref>

==Abnormalities==
[[File:Fracturedtooth.jpg|thumb|A broken upper front tooth showing the pink of the pulp.]]
Tooth abnormalities may be categorized according to whether they have environmental or developmental causes.<ref name="neville50">{{harvnb|Neville|2002|page=50.}}</ref> While environmental abnormalities may appear to have an obvious cause, there may not appear to be any known cause for some developmental abnormalities. Environmental forces may affect teeth during development, destroy tooth structure after development, discolor teeth at any stage of development, or alter the course of tooth eruption. Developmental abnormalities most commonly affect the number, size, shape, and structure of teeth.

===Environmental===

==== Alteration during tooth development ====
Tooth abnormalities caused by environmental factors during tooth development have long-lasting effects. Enamel and dentin do not regenerate after they mineralize initially. [[Enamel hypoplasia]] is a condition in which the amount of enamel formed is inadequate.<ref>{{harvnb|Ash|2003|page=31}}</ref> This results either in pits and grooves in areas of the tooth or in widespread absence of enamel. Diffuse opacities of enamel does not affect the amount of enamel but changes its appearance. Affected enamel has a different translucency than the rest of the tooth. Demarcated opacities of enamel have sharp boundaries where the translucency decreases and manifest a white, cream, yellow, or brown color. All these may be caused by nutritional factors,<ref name=KanchanMachado2015>{{cite journal|vauthors= Kanchan T, Machado M, Rao A, Krishan K, Garg AK|title=Enamel hypoplasia and its role in identification of individuals: A review of literature|date=Apr 2015|journal=Indian J Dent|volume=6|issue=2|pages=99–102|doi=10.4103/0975-962X.155887|pmid=26097340|pmc=4455163|type=Revisión}}</ref> an [[exanthem]]atous disease ([[chicken pox]], [[congenital syphilis]]),<ref name=KanchanMachado2015 /><ref name="neville51">{{harvnb|Neville|2002|page= 51}}</ref> undiagnosed and untreated [[coeliac disease|celiac disease]],<ref name=NIH>[http://celiac.nih.gov/PDF/Dental_Enamel_Defects_508.pdf Dental Enamel Defects and Celiac Disease] National Institute of Health (NIH)</ref><ref name=FerrazCampos2012>{{cite journal|vauthors=Ferraz EG, Campos Ede J, Sarmento VA, Silva LR|title=The oral manifestations of celiac disease: information for the pediatric dentist|date=2012|journal=Pediatr Dent|volume=34|issue=7|pages=485–8|pmid=23265166|type=Review}}</ref><ref name=GiucaCei2010>{{cite journal|vauthors=Giuca MR, Cei G, Gigli F, Gandini P|title=Oral signs in the diagnosis of celiac disease: review of the literature|date=2010|journal=Minerva Stomatol|volume=59|issue=1–2|pages=33–43|pmid=20212408|type=Review}}</ref> [[hypocalcaemia|hypocalcemia]], [[dental fluorosis]], [[birth injury]], [[preterm birth]], [[infection]] or trauma from a [[deciduous teeth|deciduous tooth]].<ref name=KanchanMachado2015 />  Dental fluorosis is a condition which results from ingesting excessive amounts of [[fluoride]] and leads to teeth which are spotted, yellow, brown, black or sometimes pitted. In most cases, the enamel defects caused by celiac disease, which may be the only manifestation of this disease in the absence of any other symptoms or signs, are not recognized and mistakenly attributed to other causes, such as fluorosis.<ref name=NIH /> Enamel hypoplasia resulting from [[syphilis]] is frequently referred to as [[Hutchinson's teeth]], which is considered one part of [[Hutchinson's triad]].<ref>[http://www.mayoclinic.com/health/syphilis/DS00374/DSECTION=6 Syphilis: Complications], Mayo Clinic.</ref> [[Turner's hypoplasia]] is a portion of missing or diminished enamel on a permanent tooth usually from a prior infection of a nearby primary tooth. Hypoplasia may also result from [[antineoplastic]] therapy.

====Destruction after development====
Tooth destruction from processes other than [[dental caries]] is considered a normal physiologic process but may become severe enough to become a pathologic condition. [[Attrition (dental)|Attrition]] is the loss of tooth structure by mechanical forces from opposing teeth.<ref>"[http://www.adha.org/CE_courses/course9/loss_of_structure.htm Loss of Tooth Structure]", American Dental Hygiene Association.</ref> Attrition initially affects the enamel and, if unchecked, may proceed to the underlying dentin. [[Abrasion (dental)|Abrasion]] is the loss of tooth structure by mechanical forces from a foreign element.<ref>"[http://web.archive.org/web/20100801114913/http://dentistry.umkc.edu/practition/assets/AbnormalitiesofTeeth.pdf Abnormalities of Teeth]", University of Missouri-Kansas City School of Dentistry.</ref> If this force begins at the cementoenamel junction, then progression of tooth loss can be rapid since enamel is very thin in this region of the tooth. A common source of this type of tooth wear is excessive force when using a toothbrush. [[Erosion (dental)|Erosion]] is the loss of tooth structure due to chemical dissolution by acids not of bacterial origin.<ref>{{cite journal|url=http://www.agd.org/library/2003/aug/200308_yip.pdf |pmid=15055615 |year=2003 |last1=Yip |first1=KH |last2=Smales |first2=RJ |last3=Kaidonis |first3=JA |title=The diagnosis and control of extrinsic acid erosion of tooth substance |volume=51 |issue=4 |pages=350–3; quiz 354 |journal=General dentistry |deadurl=yes |archiveurl=https://web.archive.org/web/20060907094153/http://www.agd.org/library/2003/aug/200308_yip.pdf |archivedate=September 7, 2006 }}</ref><ref>{{cite journal|author1=Gandara B.K. |author2=Truelove E.L. |url=http://www.jaypeejournals.com/eJournals/ShowText.aspx?ID=1427&Type=PAID&TYP=TOP&IN=~/eJournals/images/JPLOGO.gif&IID=121&isPDF=NO|pmid=12167897|year=1999|title=Diagnosis and management of dental erosion|volume=1|issue=1|pages=16–23|journal=The journal of contemporary dental practice}}</ref> Signs of tooth destruction from erosion is a common characteristic in the mouths of people with [[bulimia]] since [[vomiting]] results in exposure of the teeth to gastric acids. Another important source of erosive acids are from frequent sucking of [[lemon juice]]. [[Abfraction]] is the loss of tooth structure from flexural forces. As teeth flex under [[pressure]], the arrangement of teeth touching each other, known as [[occlusion (dentistry)|occlusion]], causes [[Tension (mechanics)|tension]] on one side of the tooth and [[compression (physical)|compression]] on the other side of the tooth. This is believed to cause V-shaped depressions on the side under tension and C-shaped depressions on the side under compression. When tooth destruction occurs at the roots of teeth, the process is referred to as [[internal resorption]], when caused by cells within the pulp, or [[external resorption]], when caused by cells in the periodontal ligament.

====Discoloration====
{{Main article|Tooth discoloration}}
Discoloration of teeth may result from bacteria stains, tobacco, tea, coffee, foods with an abundance of [[chlorophyll]], restorative materials, and medications.<ref name="neville63">{{harvnb|Neville|2002|page= 63}}</ref> Stains from bacteria may cause colors varying from green to black to orange. Green stains also result from foods with chlorophyll or excessive exposure to copper or nickel. Amalgam, a common dental restorative material, may turn adjacent areas of teeth black or gray. Long term use of [[chlorhexidine]], a mouthwash, may encourage extrinsic stain formation near the gingiva on teeth. This is usually easy for a hygienist to remove. Systemic disorders also can cause tooth discoloration. [[Congenital erythropoietic porphyria]] causes [[porphyrin]]s to be deposited in teeth, causing a red-brown coloration. Blue discoloration may occur with [[alkaptonuria]] and rarely with [[Parkinson's disease]]. [[Erythroblastosis fetalis]] and [[biliary atresia]] are diseases which may cause teeth to appear green from the deposition of [[biliverdin]]. Also, trauma may change a tooth to a pink, yellow, or dark gray color. Pink and red discolorations are also associated in patients with [[leprosy|lepromatous leprosy]]. Some medications, such as [[tetracycline]] antibiotics, may become incorporated into the structure of a tooth, causing intrinsic staining of the teeth.

====Alteration of eruption====
Tooth eruption may be altered by some environmental factors. When eruption is prematurely stopped, the tooth is said to be [[Wisdom teeth#Impaction|impacted]]. The most common cause of tooth impaction is lack of space in the mouth for the tooth.<ref name="neville66">{{harvnb|Neville,|2002|page=66}}</ref> Other causes may be [[tumor]]s, [[cyst]]s, trauma, and thickened bone or soft tissue. [[Tooth ankylosis]] occurs when the tooth has already erupted into the mouth but the cementum or dentin has fused with the alveolar bone. This may cause a person to retain their primary tooth instead of having it replaced by a permanent one.

A technique for altering the natural progression of eruption is employed by [[orthodontist]]s who wish to delay or speed up the eruption of certain teeth for reasons of space maintenance or otherwise preventing crowding and/or spacing. If a primary tooth is extracted before its succeeding permanent tooth's root reaches ⅓ of its total growth, the eruption of the permanent tooth will be delayed. Conversely, if the roots of the permanent tooth are more than ⅔ complete, the eruption of the permanent tooth will be accelerated. Between ⅓ and ⅔, it is unknown exactly what will occur to the speed of eruption.

===Developmental===

==== Abnormality in number ====
* [[Anodontia]] is the total lack of tooth development.
* [[Hyperdontia]] is the presence of a higher-than-normal number of teeth.
* [[Hypodontia]] is the lack of some teeth. Usually:
** Hypodontia refers to the lack of development of one or more teeth
** Oligodontia may be used to describe the absence of 6 or more teeth.
Some systemic disorders which may result in hyperdontia include [[Apert syndrome]], [[Cleidocranial dysostosis]], [[Crouzon syndrome]], [[Ehlers–Danlos syndrome]], [[Gardner syndrome]], and [[Sturge–Weber syndrome]].<ref name="neville70">{{harvnb|Neville|2002|page=70}}</ref>  Some systemic disorders which may result in hypodontia include Crouzon syndrome, [[Ectodermal dysplasia]], Ehlers–Danlos syndrome, and [[Gorlin syndrome]].<ref name="neville69">{{harvnb|Neville|2002|page=69}}</ref>

====Abnormality in size====
* [[Microdontia]] is a condition where teeth are smaller than the usual size.
* [[Macrodontia (tooth)|Macrodontia]] is where teeth are larger than the usual size.

Microdontia of a single tooth is more likely to occur in a [[maxillary lateral incisor]]. The second most likely tooth to have microdontia are [[wisdom teeth|third molars]]. Macrodontia of all the teeth is known to occur in [[Gigantism|pituitary gigantism]] and [[Pineal gland|pineal]] [[hyperplasia]]. It may also occur on one side of the face in cases of [[hemifacial hyperplasia]].

====Abnormality in shape====
[[File:Milk.teeth.fusion.jpg|thumb|The fusion of two deciduous teeth.]]
* [[Tooth Gemination|Gemination]] occurs when a developing tooth incompletely splits into the formation of two teeth.
* [[Tooth fusion|Fusion]] is the union of two adjacent teeth during development.
* [[Concrescence]] is the fusion of two separate teeth only in their cementum.
* Accessory [[Cusp (dentistry)|cusps]] are additional cusps on a tooth and may manifest as a [[Talon cusp]], [[Cusp of Carabelli]], or [[Dens evaginatus]].
* [[Dens invaginatus]], also called Dens in dente, is a deep invagination in a tooth causing the appearance of a tooth within a tooth.
* [[Ectopic enamel]] is enamel found in an unusual location, such as the root of a tooth.
* [[Taurodontism]] is a condition where the body of the tooth and pulp chamber is enlarged, and is associated with [[Klinefelter syndrome]], [[Tricho-dento-osseous syndrome]], [[Triple X syndrome]], and [[XYY syndrome]].<ref name = "neville85"/>
* [[Hypercementosis]] is excessive formation of cementum, which may result from trauma, inflammation, [[acromegaly]], [[rheumatic fever]], and [[Paget's disease of bone]].<ref name="neville85">{{harvnb|Neville|2002|page=85}}</ref>
* A [[dilaceration]] is a bend in the root which may have been caused by trauma to the tooth during formation.
* [[Supernumerary roots]] is the presence of a greater number of roots on a tooth than expected.

====Abnormality in structure====
* [[Amelogenesis imperfecta]] is a condition in which enamel does not form properly or at all.<ref>[http://ghr.nlm.nih.gov/condition=amelogenesisimperfecta Amelogenesis imperfecta], Genetics Home Reference, a service of the U.S. National Library of Medicine.</ref>
* [[Dentinogenesis imperfecta]] is a condition in which dentin does not form properly and is sometimes associated with [[osteogenesis imperfecta]].<ref>[http://ghr.nlm.nih.gov/condition=dentinogenesisimperfecta Dentinogenesis imperfecta], Genetics Home Reference, a service of the U.S. National Library of Medicine.</ref>
* [[Dentin dysplasia]] is a disorder in which the roots and pulp of teeth may be affected.
* [[Regional odontodysplasia]] is a disorder affecting enamel, dentin, and pulp and causes the teeth to appear "ghostly" on radiographs.<ref>{{cite journal|author=Cho, Shiu-yin|url=http://www.cda-adc.ca/jcda/vol-72/issue-8/vol72_issue8.pdf |title=Conservative Management of Regional Odontodysplasia: Case Report|volume=72|issue =8|pages=735–8|pmid=17049109|year=2006|journal=J Can Dent Assoc.}}</ref>

==See also==
{{Portal|Dentistry}}
{{Multicol}}
* [[Barodontalgia]]
* [[Dentistry]]
* [[Dental auxiliary]]
** [[Dental assistant]]
** [[Dental hygienist]]
** [[Dental technician]]
* [[Dental braces]]
{{Multicol-break}}
* [[Dental notation]]
* [[Dental tourism]]
* [[Dragon's teeth (mythology)]]
* [[Head and neck anatomy]]
* [[Regenerative endodontics]]
* [[Socket preservation]]
* [[Tooth fairy]]
* [[Tooth painting]]
* [[Tooth regeneration]]
* [[Tongue]]
{{Multicol-end}}
{{Clear}}

===Lists===
* [[List of basic dentistry topics]]
* [[List of oral health and dental topics]]

==References==

=== Notes===
{{Reflist|30em}}

===Sources===
{{Refbegin}}
* {{cite book|ref=harv|authors= Ash, Major M.; Nelson, Stanley J. |year= 2003|title=Wheeler’s Dental Anatomy, Physiology, and Occlusion|edition=8th|isbn=0-7216-9382-2}}
* {{cite book|ref=harv|last=Cate|first= A.R. Ten. |year=1998|title=Oral Histology: development, structure, and function|edition=5th|publisher= Mosby|isbn=0815129521}}
* {{cite book|ref=harv|authors= Neville, B.W.; Damm, D.; Allen, C.; Bouquot, J. |year= 2002|title=Oral & Maxillofacial Pathology|edition= 2nd|publisher=W.B. Saunders|isbn=0-7216-9003-3}}
*{{cite book|ref=harv|authors= Ross, Michael H.; Kaye, Gordon I. and Pawlina, Wojciech |year= 2002|title=Histology: a Text and Atlas|edition=4th|place= Baltimore|publisher= Lippincott Williams & Wilkins|isbn=0683302426}}
{{Refend}}

==External links==
{{Wiktionary|tooth}}
{{Commons category|Human tooth}}
* [http://traumwerk.stanford.edu/archaeolog/2006/10/the_most_personal_personal_orn.html An article on the use of human tooth used as a neolithic pendant]
* [http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/pregastric/dentalanat.html An overview of dental anatomy]
* [http://www.mchoralhealth.org/OpenWide/images/tooth_eruption_cht.htm Tooth eruption chart]

{{Tooth anatomy}}

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[[Category:Teeth|Human]]
[[Category:Human anatomy]]

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