Teeth (singular
tooth) are small,
calcifiedCalcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Mineral balance:...
, whitish structures found in the
jawThe jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
s (or mouths) of many
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
s that are used to tear, scrape, and chew
foodFood is any substance, usually composed of carbohydrates, fats, proteins and water, that can be eaten or drunk by an animal, including humans, for nutrition or pleasure. Items considered food may be sourced from plants, animals or other categories such as fungus or fermented products like alcohol...
. Some animals, particularly
carnivoreA carnivore , meaning 'meat eater' , is an animal that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of vertebrate and/or invertebrate animal tissue, whether through predation or scavenging...
s, also use teeth for hunting or defense. The roots of teeth are covered by
gumThe gingiva , or gums, consists of the mucosal tissue that lies over the alveolar bone.-General description:Gingiva are part of the soft tissue lining of the mouth. They surround the teeth and provide a seal around them...
s. Teeth are not made of bone, but rather of tissues of varying density and hardness.
Teeth are among the most distinctive (and long-lasting) features of
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
species.
PaleontologistsPaleontology
[from Greek: παλαιός "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought"] is the study of prehistoric life, including organisms' evolution and interactions with each other and their environments...
use teeth to identify
fossilFossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers is known as the fossil record...
species and determine their relationships. The shape of the animal's teeth are related to its diet. For example, plant matter is hard to digest, so
herbivoreA herbivore is an animal that is adapted to eat plants and not meat.Herbivory is a form of predation in which an organism consumes principally autotrophs such as plants, algae and photosynthesizing bacteria....
s have many molars for chewing.
CarnivoreA carnivore , meaning 'meat eater' , is an animal that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of vertebrate and/or invertebrate animal tissue, whether through predation or scavenging...
s, on the other hand, need canines to kill prey and to tear meat.
Mammals are
diphyodontA Diphyodont is an animal with two successive sets of teeth, first the "deciduous" set and later the "permanent" set. Diphyodontia is characteristic of mammals. Diphyodonts contrast with Polyphyodonts, such as many fish, whose teeth are constantly replaced....
, meaning that they develop two sets of teeth. In humans, the first set (the "baby," "milk," "primary" or "
deciduousDeciduous teeth, otherwise known as milk teeth, baby teeth, temporary teeth and primary teeth, are the first set of teeth in the growth development of humans and many other mammals. They develop during the embryonic stage of development and erupt—that is, they become visible in the mouth—during...
" 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 teethNatal teeth are teeth that are present at birth.Neonatal teeth are teeth that emerge through the gingiva during the first month of life.The incidence of neonatal teeth varies considerably, between 1:700 - 1:30,000 depending on the type of study...
. Normal
tooth eruptionTooth eruption is a process in tooth development in which the teeth enter the mouth and become visible. It is currently believed that the periodontal ligaments play an important role in tooth eruption. Primary teeth erupt into the mouth from around 6 months until 2 years of age. These teeth are...
at about six months is known as
teethingTeething is the process by which an infant's teeth sequentially appear by breaking through the gums. Teething may start as early as three months or as late, in some cases, as twelve months. The typical time frame for new teeth to appear is somewhere between six and nine months. It can take up to...
and can be painful.
Some animals develop only one set of teeth (monophyodont) while others develop many sets (polyphyodont).
SharkSharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs....
s, for example, grow a new set of teeth every two weeks to replace worn teeth.
RodentRodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
incisors grow and wear away continually through gnawing, maintaining relatively constant length. Many rodents such as
voleA vole is a small rodent resembling a mouse but with a stouter body, a shorter hairy tail, a slightly rounder head, and smaller ears and eyes. There are approximately 155 species of voles. They are sometimes known as meadow mice or field mice in North America...
s (but not
miceMICE is an acronym for:*Muon Ionization Cooling Experiment*"Money, Ideology, Compromise, Ego", four factors by which spies may be recruited. See MICE .*"Meetings, Incentives, Conferencing, Exhibitions", terminology for banquets, etc., in a hotel....
) and
guinea pigThe guinea pig , also commonly called the Cavy, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, these animals are not pigs, nor do they come from Guinea...
s, as well as
rabbitRabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. There are seven different genera in the family classified as rabbits, including the European rabbit , Cottontail rabbit , and the Amami rabbit...
s, have continuously growing molars in addition to incisors.
Anatomy
The bottom teeth are used more for the grinding of food and the top front teeth are mainly used for biting.
Dental anatomy is a field of
anatomyAnatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy and plant anatomy...
dedicated to the study of tooth structures. The development, appearance, and classification of teeth fall within its field of study, though
dental occlusionOcclusion, in a dental context, means simply the contact between teeth. More technically, it is the relationship between the maxillary and mandibular teeth when they approach each other, as occurs during chewing or at rest....
, or contact among teeth, does not. Dental anatomy is also a
taxonomicalTaxonomy is the practice and science of classification. The word finds its roots in the Greek , taxis and , nomos...
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
cementoenamel junctionThe cementoenamel junction, frequently abbreviated as the CEJ, is an anatomical landmark identified on a tooth. It is the location where the enamel, which covers the crown of a tooth, and the cementum, which covers the root of a tooth, meet...
(CEJ). The majority of the crown is composed of dentin with the pulp chamber in the center. The crown is within bone before
eruptionTooth eruption is a process in tooth development in which the teeth enter the mouth and become visible. It is currently believed that the periodontal ligaments play an important role in tooth eruption. Primary teeth erupt into the mouth from around 6 months until 2 years of age. These teeth are...
. After eruption, it is almost always visible. The anatomic root is found below the cementoenamel junction and is covered with
cementumCementum is a specialized calcified substance covering the root of a tooth. Cementum is excreted by cells called cementoblasts within the root of the tooth and is thickest at the root apex. Its coloration is yellowish and it is softer than enamel and dentin due to being less mineralized.Cementum's...
. 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 rootsSupernumerary roots is a condition found in teeth there may be a larger number of roots than expected. The most common teeth affected are mandibular canines, premolars, and molars, especially third molars. Canines and most premolars, except for maxillary first premolars, usually have one root. ...
.
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 (upper)
maxillaThe maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes , the maxilla is sometimes called "upper maxilla", with the mandible being the "lower maxilla"...
and the other 10 in the (lower)
mandibleThe mandible or inferior maxillary bone forms the lower jaw and holds the lower teeth in place. It also refers to both the upper and lower sections of the beaks of birds; in this case the "lower mandible" corresponds to the mandible of humans while the "upper mandible" is functionally equivalent...
. 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 incisorThe maxillary central incisor is a human tooth in the front upper jaw, or maxilla, and is usually the most visible of all teeth in the mouth. It is located mesial to the maxillary lateral incisor. As with all incisors, their function is for shearing or cutting food during mastication . There are...
,
maxillary lateral incisorThe maxillary lateral incisor is the tooth located distally from both maxillary central incisors of the mouth and mesially from both maxillary canines. As with all incisors, their function is for shearing or cutting food during mastication, commonly known as chewing. There are no cusps on the...
,
maxillary canineThe maxillary canine is the tooth located laterally from both maxillary lateral incisors of the mouth but mesial from both maxillary first premolars...
,
maxillary first premolarThe maxillary first premolar is the tooth located laterally from both the maxillary canines of the mouth but mesial from both maxillary second premolars. The function of this premolar is similar to that of canines in regard to tearing being the principal action during mastication, commonly known...
,
maxillary second premolarThe maxillary second premolar is the tooth located laterally from both the maxillary first premolars of the mouth but mesial from both maxillary first molars. The function of this premolar is similar to that of first molars in regard to grinding being the principle action during mastication,...
,
maxillary first molarThe maxillary first molar is the tooth located laterally from both the maxillary second premolars of the mouth but mesial from both maxillary second molars. The function of this molar is similar to that of all molars in regard to grinding being the principle action during mastication, commonly...
,
maxillary second molarThe maxillary second molar is the tooth located distally from both the maxillary first molars of the mouth but mesial from both maxillary third molars. This is true only in permanent teeth. In deciduous teeth, the maxillary second molar is the last tooth in the mouth and does not have a third...
, and
maxillary third molarThe maxillary third molar is the third molar located laterally from both the maxillary second molars of the mouth with no tooth posterior to it in permanent teeth. In deciduous teeth, there is no maxillary third molar...
. The mandibular teeth are the
mandibular central incisorThe mandibular central incisor is the tooth located on the jaw, adjacent to the midline of the face. It is mesial from both mandibular lateral incisors. As with all incisors, its function includes shearing or cutting food during mastication, commonly known as chewing. There are no cusps on the...
,
mandibular lateral incisorThe mandibular lateral incisor is the tooth located distally from both mandibular central incisors of the mouth and mesially from both mandibular canines. As with all incisors, their function is for shearing or cutting food during mastication, commonly known as chewing. There are no cusps on...
,
mandibular canineThe mandibular canine is the tooth located distally from both mandibular lateral incisors of the mouth but mesially from both mandibular first premolars...
,
mandibular first premolarThe mandibular first premolar is the tooth located laterally from both the mandibular canines of the mouth but mesial from both mandibular second premolars. The function of this premolar is similar to that of canines in regard to tearing being the principal action during mastication, commonly...
,
mandibular second premolarThe mandibular second premolar is the tooth located distally from both the mandibular first premolars of the mouth but mesial from both mandibular first molars. The function of this premolar is assist the mandibular first molar during mastication, commonly known as chewing...
,
mandibular first molarThe mandibular first molar or six-year molar is the tooth located distally from both the mandibular second premolars of the mouth but mesial from both mandibular second molars...
,
mandibular second molarThe mandibular second molar is the tooth located distally from both the mandibular first molars of the mouth but mesial from both mandibular third molars. This is true only in permanent teeth...
, and
mandibular third molarThe mandibular third molar is the third molar located distally from both the mandibular second molars of the mouth with no tooth posterior to it in permanent teeth. In deciduous teeth, there is no 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 teethHyperdontia is the condition of having supernumerary teeth, or teeth which appear in addition to the regular number of teeth.-Types:The most common supernumerary tooth is a mesiodens, which is a mal-formed, peg-like tooth that occurs between the maxillary central incisors.Fourth and fifth molars...
.
Most teeth have identifiable features that distinguish them from others. There are several different
notation systemsDentists, in writing or speech, use several different Dental notation systems for associating information to a specific tooth. The three most commons systems are the FDI World Dental Federation notation, Universal numbering system , and Palmer notation method...
to refer to a specific tooth. The three most common systems are the
FDI World Dental Federation notationFDI World Dental Federation notation is widely used by dentists internationally to associate information to a specific tooth.Developed by the FDI World Dental Federation, World Dental Federation notation is also known as ISO-3950 notation....
, the
universal numbering systemThe Universal numbering system is a dental notation system for associating information to a specific tooth, and is commonly used in the United States.The designations "left" and "right" on the chart correspond to the patient's left and right, respectively....
, and Palmer notation method. The FDI system is used worldwide, and the universal is used widely in the United States.
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
dentinDentin is a calcified tissue of the body, and along with enamel, cementum, and pulp is one of the four major components of teeth. Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp...
,
cementumCementum is a specialized calcified substance covering the root of a tooth. Cementum is excreted by cells called cementoblasts within the root of the tooth and is thickest at the root apex. Its coloration is yellowish and it is softer than enamel and dentin due to being less mineralized.Cementum's...
, and dental pulp. It is normally visible and must be supported by underlying dentin. Ninety-six percent of enamel consists of mineral, with water and organic material composing 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
cuspA cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
, up to 2.5 mm, and thinnest at its border, which is seen clinically as the
cementoenamel junctionThe cementoenamel junction, frequently abbreviated as the CEJ, is an anatomical landmark identified on a tooth. It is the location where the enamel, which covers the crown of a tooth, and the cementum, which covers the root of a tooth, meet...
(CEJ).
Enamel's primary mineral is hydroxyapatite, which is a
crystalA crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography...
line
calcium phosphateCalcium phosphate is the name given to a family of minerals containing calcium ions together with orthophosphates , metaphosphates or pyrophosphates and occasionally hydrogen or hydroxide ions.It is the principal form of calcium found in bovine milk...
. 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
boneBones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
, enamel does not contain
collagenCollagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. It is naturally found exclusively in metazoa, including sponges. In muscle tissue it serves as a major component of endomysium...
. Instead, it has two unique classes of
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s called
amelogeninAmelogenin is a protein found in developing tooth enamel, and it belongs to a family of extracellular matrix proteins. Developing enamel contains about 30% protein, and 90% of this is amelogenins...
s and
enamelinEnamelin was described in older literature as an EDTA soluble enamel protein. It turned out in recent research to be albumin derived from blood contamination....
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.
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
dentinogenesisDentinogenesis is the formation of dentin, a substance that forms the majority of teeth. Dentinogenesis is performed by odontoblasts, which are a special type of biological cells on the outside of dental pulps, and it begins at the late bell stage of a developing tooth...
. 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 tissueConnective tissue is a form of fibrous tissue.. It is one of the four types of tissue in traditional classifications ....
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.
Cementum
Cementum is a specialized bony substance covering the root of a tooth. It is approximately 45% inorganic material (mainly hydroxyapatite), 33% organic material (mainly
collagenCollagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. It is naturally found exclusively in metazoa, including sponges. In muscle tissue it serves as a major component of endomysium...
) and 22% water. Cementum is excreted by
cementoblastA cementoblast is a biological cell that forms from the follicular cells around the root of a tooth, and whose biological function is cementogenesis, which is the creation of cementum ....
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 ligamentThe periodontal ligament, commonly abbreviated as the PDL is a group of specialized connective tissue fibers that essentially attach a tooth to the alveolar bone within which it sits...
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. The more permeable form of cementum, cellular cementum, covers about ⅓ of the root apex.
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,
macrophageMacrophages are white blood cells within tissues, produced by the division of monocytes. Human macrophages are about in diameter...
s and T lymphocytes. The pulp is commonly called "the nerve" of the tooth.
Development
Tooth development is the complex process by which teeth form from
embryoAn embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
nic
cellsThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
,
growThe term cell growth is used in the contexts of cell development and cell division . When used in the context of cell division, it refers to growth of cell populations, where one cell grows and divides to produce two "daughter cells".-Cell populations:Cell populations go through a type of...
, and erupt into the
mouthThe mouth, buccal cavity, or oral cavity is the first portion of the alimentary canal that receives food and begins digestion by mechanically breaking up the solid food particles into smaller pieces and mixing them with saliva...
. Although many diverse
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
have teeth, non-human tooth development is largely the same as in humans. For
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
teeth to have a healthy oral environment,
enamelTooth enamel is the hardest and most highly mineralized substance of the body, and with dentin, cementum, and dental pulp is one of the four major tissues which make up the tooth in vertebrates. Tooth enamel is also found in the dermal denticles of sharks. It is the normally visible dental tissue...
,
dentinDentin is a calcified tissue of the body, and along with enamel, cementum, and pulp is one of the four major components of teeth. Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp...
,
cementumCementum is a specialized calcified substance covering the root of a tooth. Cementum is excreted by cells called cementoblasts within the root of the tooth and is thickest at the root apex. Its coloration is yellowish and it is softer than enamel and dentin due to being less mineralized.Cementum's...
, and the
periodontiumPeriodontium refers to the specialized tissues that both surround and support the teeth, maintaining them in the maxillary and mandibular bones. The word comes from the Greek terms peri-, meaning "around" and -odons, meaning "tooth." Literally taken, it means that which is "around the tooth"...
must all develop during appropriate stages of
fetal developmentPrenatal or antenatal development is the process in which an embryo or fetus gestates during pregnancy, from fertilization until birth. Often, the terms fetal development, foetal development, or embryology are used in a similar sense.After fertilization the embryogenesis starts...
.
Primary (baby) teethDeciduous teeth, otherwise known as milk teeth, baby teeth, temporary teeth and primary teeth, are the first set of teeth in the growth development of humans and many other mammals. They develop during the embryonic stage of development and erupt—that is, they become visible in the mouth—during...
start to form between the sixth and eighth weeks
in uteroThe uterus is a major female hormone-responsive reproductive sex organ of most mammals, including humans. It is within the uterus that the fetus develops during gestation. The term uterus is used consistently within the medical and related professions; the Germanic term, womb is more common in...
, and
permanent teethPermanent teeth are the second set of teeth formed in humans. There are thirty-two permanent teeth, consisting of six maxillary and six mandibular molars, four maxillary and four mandibular premolars, two maxillary and two mandibular canines, four maxillary and four mandibular incisors.The first...
begin to form in the twentieth week in utero. 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 archIn the development of vertebrate animals, the pharyngeal arches are anlage for a multitude of structures. In humans, they develop during the fourth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx...
that is necessary for the development of teeth.
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. 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
cellsThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
that eventually forms a tooth. It is organized into three parts: the
enamel organright|250pxThe enamel organ, also known as dental organ, is a cellular aggregation seen in histologic sections of a developing tooth. It lies above a condensation of ectomesenchymal cells called the dental papilla...
, the
dental papillaThe dental papilla is a condensation of ectomesenchymal cells called odontoblasts, seen in histologic sections of a developing tooth. It lies below a cellular aggregation known as the enamel organ. The dental papilla appears after 8-10 weeks intra uteral life...
and the
dental follicleThe dental follicle is a sac containing the developing tooth and its odontogenic organ.-References:*Cate, A.R. Ten. Oral Histology: development, structure, and function. 5th ed. 1998. ISBN 0-8151-2952-1....
. The
enamel organ is composed of the
outer enamel epitheliumThe outer enamel epithelium, also known as the external enamel epithelium, is a layer of cuboidal cells located on the periphery of the enamel organ in a developing tooth. This layer is first seen during the bell stage....
,
inner enamel epitheliumThe inner enamel epithelium, also known as the internal enamel epithelium, is a layer of cells located on the rim nearest the dental papilla of the enamel organ in a developing tooth. This layer is first seen during the bell stage....
,
stellate reticulumThe stellate reticulum is a group of cells located in the center of the enamel organ of a developing tooth. These cells are star shaped and synthesize glycosaminoglycans. As glycosamingoglycans are produced, water is drawn in between the cells and stretch them apart...
and
stratum intermediumThe stratum intermedium in a developing tooth is a layer of two or three cells between the inner enamel epithelium and the newly forming cells of the stellate reticulum. It first appears during the early bell stage of tooth development, at around the 14th week of intrauterine life. The stratum...
. These cells give rise to
ameloblastAmeloblasts are cells, present only during tooth development, that deposit tooth enamel, the hard outermost layer of the tooth that forms the chewing surface....
s, which produce enamel and the
reduced enamel epitheliumThe reduced enamel epithelium, sometimes called reduced dental epithelium, overlies a developing tooth and is formed by two layers: a layer of ameloblast cells and the adjacent layer of cuboidal cells from the dental lamina. As the cells of the reduced enamel epithelium degenerate, the tooth is...
. The growth of
cervical loopThe cervical loop is the location on an enamel organ in a developing tooth where the outer enamel epithelium and the inner enamel epithelium join. The cervical loop is a histologic term indicating a specific epithelial structure at the apical side of the tooth germ, consisting of loosely aggregated...
cells into the deeper tissues forms
Hertwig's Epithelial Root SheathThe Hertwig's epithelial root sheath is a proliferation of epithelial cells located at the cervical loop of the enamel organ in a developing tooth. Hertwig's epithelial root sheath initiates the formation of dentin in the root of a tooth by causing the differentiation of odontoblasts from the...
, which determines a tooth's root shape. The
dental papilla contains cells that develop into
odontoblastAn odontoblast is a biological cell of neural crest origin that is part of the outer surface of the dental pulp, and whose biological function is dentinogenesis, which is the creation of dentin, the substance under the tooth enamel...
s, which are dentin-forming cells. Additionally, the junction between the dental papilla and inner enamel epithelium determines the crown shape of a tooth. The
dental follicle gives rise to three important entities:
cementoblastA cementoblast is a biological cell that forms from the follicular cells around the root of a tooth, and whose biological function is cementogenesis, which is the creation of cementum ....
s,
osteoblastAn osteoblast is a mononucleate cell that is responsible for bone formation. Osteoblasts produce osteoid, which is composed mainly of Type I collagen. Osteoblasts are also responsible for mineralization of the osteoid matrix...
s, and
fibroblastA fibroblast is a type of cell that synthesizes the extracellular matrix and collagen, the structural framework for animal tissues, and plays a critical role in wound healing...
s. Cementoblasts form the cementum of a tooth. Osteoblasts give rise to the
alveolar boneThe alveolar process is the thickened ridge of bone that contains the tooth sockets on bones that bear teeth. It is also referred to as the alveolar bone. In humans, the tooth-bearing bones are the maxilla and the mandible...
around the roots of teeth. Fibroblasts develop the
periodontal ligamentThe periodontal ligament, commonly abbreviated as the PDL is a group of specialized connective tissue fibers that essentially attach a tooth to the alveolar bone within which it sits...
s which connect teeth to the alveolar bone through cementum.
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. Another, known as the cushioned hammock theory, resulted from microscopic study of teeth, which was thought to show a
ligamentIn anatomy, the term ligament is used to denote three different types of structures:# Fibrous tissue that connects bones to other bones. They are sometimes called "articular ligaments", "fibrous ligaments", or "true ligaments"....
around the root. It was later discovered that the "ligament" was merely an 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.
Supporting structures
The
periodontiumPeriodontium refers to the specialized tissues that both surround and support the teeth, maintaining them in the maxillary and mandibular bones. The word comes from the Greek terms peri-, meaning "around" and -odons, meaning "tooth." Literally taken, it means that which is "around the tooth"...
is the supporting structure of a tooth, helping to attach the tooth to surrounding tissues and to allow sensations of touch and pressure. It consists of the cementum, periodontal ligaments, alveolar bone, and
gingivaThe gingiva , or gums, consists of the mucosal tissue that lies over the alveolar bone.-General description:Gingiva are part of the soft tissue lining of the mouth. They surround the teeth and provide a seal around them...
. 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
alveolusDental alveolus are sockets in the jaws in which the roots of teeth are held in the alveolar process of maxilla with the periodontal ligament. The lay term for dental alveoli is tooth sockets...
, or "socket". Lying over the bone is the
gingivaThe gingiva , or gums, consists of the mucosal tissue that lies over the alveolar bone.-General description:Gingiva are part of the soft tissue lining of the mouth. They surround the teeth and provide a seal around them...
or gum, which is readily visible in the mouth.
Periodontal ligaments
The
periodontal ligamentThe periodontal ligament, commonly abbreviated as the PDL is a group of specialized connective tissue fibers that essentially attach a tooth to the alveolar bone within which it sits...
is a specialized
connective tissueConnective tissue is a form of fibrous tissue.. It is one of the four types of tissue in traditional classifications ....
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 - 0.38 mm, but this size decreases over time. The functions of the periodontal ligaments include attachment of the tooth to the bone, support for the tooth, formation and
resorptionBone resorption is the process by which osteoclasts break down bone and release the minerals, resulting in a transfer of calcium from bone fluid to the blood....
of bone during tooth movement, sensation, and eruption. The cells of the periodontal ligaments include osteoblasts, osteoclasts, fibroblasts, macrophages, cementoblasts, and
epithelial cell rests of MalassezIn dentistry, the epithelial cell rests of Malassez or epithelial rests of Malassez are part of the periodontal ligament cells around a tooth. They are discrete clusters of residual cells from Hertwig's epithelial root sheath that didn't completely disappear...
. Consisting of mostly Type I and III
collagenCollagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. It is naturally found exclusively in metazoa, including sponges. In muscle tissue it serves as a major component of endomysium...
, 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. 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. 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. Like any other bone in the human body, alveolar bone is modified throughout life.
OsteoblastAn osteoblast is a mononucleate cell that is responsible for bone formation. Osteoblasts produce osteoid, which is composed mainly of Type I collagen. Osteoblasts are also responsible for mineralization of the osteoid matrix...
s create bone and
osteoclastAn osteoclast is a type of bone cell that removes bone tissue by removing its mineralized matrix and breaking up the organic bone . This process is known as bone resorption...
s destroy it, especially if force is placed on a tooth. As is the case when movement of teeth is attempted through orthodontics, an area of bone under
compressivePhysical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. The opposite of compression is rarefraction tension.- Explanation :...
forceIn physics, a force is any agent that causes a change in the motion of a free body, or that causes stress in a fixed body. It can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a...
from a tooth moving toward it has a high osteoclast level, resulting in
bone resorptionBone resorption is the process by which osteoclasts break down bone and release the minerals, resulting in a transfer of calcium from bone fluid to the blood....
. An area of bone receiving
tensionIn physics, tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. It is the opposite of compression. As tension is the magnitude of a force, it is measured in newtons and is always measured parallel to the string on which it applies...
from periodontal ligaments attached to a tooth moving away from it has a high number of osteoblasts, resulting in bone formation.
Gingiva
The
gingivaThe gingiva , or gums, consists of the mucosal tissue that lies over the alveolar bone.-General description:Gingiva are part of the soft tissue lining of the mouth. They surround the teeth and provide a seal around them...
("gums") is the 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. The gingival epithelium is not associated directly with tooth attachment and is visible in the mouth. The junctional epithelium, composed of the
basal laminaThe basal lamina is a layer of extracellular matrix on which epithelium sits and which is secreted by the epithelial cells. It is often confused with the basement membrane, and sometimes used inconsistently in the literature, see below....
and
hemidesmosomeHemidesmosomes are very small stud- or rivet-like structures on the inner basal surface of keratinocytes in the epidermis of skin. They are similar in form to desmosomes when visualized by electron microscopy. While desmosomes link two cells together, hemidesmosomes attach one cell to the...
s, forms an attachment to the tooth. The sulcular epithelium is
nonkeratinizedThe epidermis is the outer layer of the skin, composed of terminally differentiated stratified squamous epithelium, acting as the body's major barrier against an inhospitable environment...
stratified squamousIn anatomy, squamous epithelium is an epithelium characterised by its most superficial layer consisting of flat, scale-like cells called squamous cell...
tissue on the gingiva which touches but is not attached to the tooth. This leaves a small potential space between the gingiva and tooth which can collect bacteria, plaque, and calculus.
Plaque
Plaque is a
biofilmA biofilm is an aggregate of microorganisms in which cells are stuck to each other and/or to a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance . Biofilm EPS, which is also referred to as "slime," is a polymeric jumble of...
consisting of large quantities of various bacteria that form on teeth. If not removed regularly, plaque buildup can lead to dental cavities (caries) or periodontal problems such as
gingivitisGingivitis around the teeth is a general term for gingival diseases affecting the gingiva . As generally used, the term gingivitis refers to gingival inflammation induced by bacterial biofilms adherent to tooth surfaces.- Causes :Gingivitis can be defined as inflammation of the gingival tissue...
. Given time, plaque can mineralize along the gingiva, forming
tartarIn dentistry, calculus is a form of hardened Dental plaque and is synonymous with tartar. It is caused by the continual accumulation of minerals from saliva on plaque on the teeth...
. The
microorganismA microorganism or microbe is an organism that is microscopic...
s that form the biofilm are almost entirely
bacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
(mainly
streptococcusStreptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...
and
anaerobeAn anaerobic organism or anaerobe is any organism that does not require oxygen for growth and may even die in its presence. There are three types: obligate anaerobes, which cannot use oxygen for growth and are even harmed by it; aerotolerant organisms, which cannot use oxygen for growth, but...
s), with the composition varying by location in the mouth.
Streptococcus mutansStreptococcus mutans is a Gram-positive, facultatively anaerobic bacterium commonly found in the human oral cavity and is a significant contributor to tooth decay.The microbe was first described by Clarke in 1924.-Role in tooth decay:...
is the most important bacteria associated with dental caries.
Certain bacteria in the mouth live off the remains of foods, especially
sugarSugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many...
s and starches. In the absence of
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
they produce
lactic acidLactic acid , also known as milk acid, is a chemical compound that plays a role in several biochemical processes. It was first isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele, and is a carboxylic acid with a chemical formula of C
3H
6O
3...
, which
dissolvesSolvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute...
the
calciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust...
and
phosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks. Elemental phosphorus exists in two major forms - white phosphorus and red phosphorus...
in the enamel. This process, known as "demineralisation", leads to tooth destruction.
SalivaSaliva is the watery and usually frothy substance produced in the mouths of humans and most other animals. Saliva is produced in and secreted from the salivary glands...
gradually neutralises the
acidAn acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0...
s which cause the pH of the tooth surface to rise above the critical pH. This causes '
remineralisationIn biogeochemistry, remineralisation refers to the transformation of organic molecules to inorganic forms, typically mediated by biological activity....
', 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)
Dental caries, also described as "tooth decay" or "dental cavities", is an infectious disease which damages the structures of teeth. The disease can lead to
painPhysical Pain is the unpleasant feeling common to a headache and a stubbed toe. It typically consists of negative affect and aversion, and has location, duration, intensity and a distinctive quality...
,
tooth lossTooth loss is when one or more teeth come loose and fall out. Tooth loss is normal for deciduous teeth , when they are replaced by a person's adult teeth. Otherwise, losing teeth is undesirable and is the result of injury or disease, such as mouth trauma, tooth injury, tooth decay, and gum disease...
, infection, and, in severe cases, death. Dental caries has a long history, with evidence showing the disease was present in the
BronzeThe Bronze Age of a culture is the period when the most advanced metalworking in that culture utilised bronze. This could either have been based on the local smelting of copper and tin from ores, or trading for bronze from production areas elsewhere...
,
IronIn archaeology, the Iron Age is the prehistoric period in any area during which cutting tools and weapons were mainly made of iron or steel. The adoption of this material coincided with other changes in society, including differing agricultural practices, religious beliefs and artistic styles.The...
, and
MiddleThe Middle Ages of European history is a period of European history covering roughly a millennium in the 5th century through 16th centuries. More specific starting and ending points are sometimes adopted by scholars to suit their respective specializations or current focus...
ages but also prior to the
neolithicThe Neolithic Age, Era, or Period, or New Stone Age, was a period in the development of human technology, beginning about 9500 BCE in the Middle East that is traditionally considered the last part of the Stone Age...
period. The largest increases in the prevalence of caries have been associated with diet changes. Today, caries remains one of the most common diseases throughout the world. In the United States, dental caries is the most common
chronicIn medicine, a chronic disease is a disease that is long-lasting or recurrent. The term chronic describes the course of the disease, or its rate of onset and development. A chronic course is distinguished from a recurrent course; recurrent diseases relapse repeatedly, with periods of remission in...
childhood disease, being at least five times more common than
asthmaAsthma is a predisposition to chronic inflammation of the lungs in which the airways are reversibly narrowed. Asthma affects 7% of the population of the United States, and 300 million worldwide...
. Countries that have experienced an overall decrease in cases of tooth decay continue to have a disparity in the distribution of the disease. Among children in the United States and Europe, 60-80% of cases of dental caries occur in 20% of the population.
Tooth decay is caused by certain types of acid-producing bacteria which cause the most damage in the presence of
fermentableFermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. A more restricted definition of fermentation is the chemical conversion of sugars into ethanol...
carbohydrateCarbohydrates
[Means "hydrates of carbon"] or saccharides
[The word comes from the Greek σάκχαρον, sákcharon, meaning "sugar").] are the most abundant of the four major classes of biomolecules...
s such as
sucroseSucrose, commonly called table sugar, is a moosaccharide of glucose and fructose with the molecular formula C12H22O11. This white, odorless, crystalline powder has a pleasing, sweet taste. It is best known for its role in human nutrition...
,
fructoseFructose is a simple monosaccharide found in many foods. It is a white solid that dissolves readily in water. Honey, tree fruits, berries, melons, and some root vegetables, contain significant amounts of the fructose derivative sucrose...
, and
glucoseGlucose , a monosaccharide also known as - grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate...
. The resulting acidic levels in the mouth affect teeth because a tooth's special mineral content causes it to be sensitive to low
pHpH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations...
. Depending on the extent of tooth destruction, various treatments can be used to
restoreA dental restoration or dental filling is a dental restorative material used to restore the function, integrity and morphology of missing tooth structure. The structural loss typically results from caries or external trauma. It is also lost intentionally during tooth preparation to improve the...
teeth to proper form, function, and
aestheticsAesthetics is commonly known as the study of sensory or sensori-emotional values, sometimes called judgments of sentiment and taste...
, but there is no known method to
regenerateIn biology, an organism is said to regenerate a lost or damaged part if the part regrows so that the original function is restored.Regenerative capacity is inversely related to complexity: in general, the more complex an animal is the less regeneration it is capable of. Whereas newts, for example,...
large amounts of tooth structure. Instead, dental health organizations advocate preventative and prophylactic measures, such as regular
oral hygieneTeeth cleaning is the removal of dental plaque from teeth, to prevent cavities , gingivitis, and periodontitis. It is part of a complete program of oral hygiene.-Brushing:...
and dietary modifications, to avoid dental caries.
Tooth care
Oral hygiene is the practice of keeping the mouth clean and is a means of preventing dental caries,
gingivitisGingivitis around the teeth is a general term for gingival diseases affecting the gingiva . As generally used, the term gingivitis refers to gingival inflammation induced by bacterial biofilms adherent to tooth surfaces.- Causes :Gingivitis can be defined as inflammation of the gingival tissue...
,
periodontal diseasePeriodontitis refers to a number of inflammatory diseases affecting the periodontium — that is, the tissues that surround and support the teeth. Periodontitis involves progressive loss of the alveolar bone around the teeth, and if left untreated, can lead to the loosening and subsequent loss of...
,
bad breathHalitosis, or most commonly bad breath are terms used to describe noticeably unpleasant odors exhaled in breathing – whether the smell is from an oral source due to bacteria....
, and other dental disorders. It consists of both professional and personal care. Regular cleanings, usually done by dentists and dental hygienists, remove
tartarIn dentistry, calculus is a form of hardened Dental plaque and is synonymous with tartar. It is caused by the continual accumulation of minerals from saliva on plaque on the teeth...
(mineralized plaque) that may develop even with careful brushing and 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. 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. A toothbrush is able to remove most plaque, excepting 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 diseasePeriodontitis refers to a number of inflammatory diseases affecting the periodontium — that is, the tissues that surround and support the teeth. Periodontitis involves progressive loss of the alveolar bone around the teeth, and if left untreated, can lead to the loosening and subsequent loss of...
often begins and could develop caries.
Electric toothbrushAn electric toothbrush is a toothbrush that uses electric power to move the brush head, normally in an oscillating pattern, though electric toothbrushes are sometimes called 'rotary' toothbrushes.- History :...
es are not considered more effective than manual brushes for most people. The most important advantage of electric toothbrushes is their ability to aid people with dexterity difficulties, such as those associated with
rheumatoid arthritisRheumatoid arthritis is a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks the joints producing an inflammatory synovitis that often progresses to destruction of the articular cartilage and ankylosis of the joints...
.
In addition,
fluoride therapyFluoride therapy is the delivery of fluoride to the teeth topically or systemically in order to prevent tooth decay which results in cavities. Most commonly, fluoride is applied topically to the teeth using gels, varnishes, toothpaste/dentifrices or mouth rinse. Systemic delivery involves...
is often recommended to protect against dental caries,
water fluoridationWater fluoridation is the controlled addition of fluoride to a public water supply to reduce tooth decay. Fluoridated water has fluoride at a level that is effective for preventing cavities; this can occur naturally or by adding fluoride...
and
fluorideFluoride is the anion F
−, the reduced form of fluorine. Both organic and inorganic compounds containing the element fluorine are sometimes called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are distinct relative to other...
supplements decrease the incidence of dental caries. Fluoride helps prevent dental decay by binding to the hydroxyapatite crystals in enamel. The incorporated fluoride makes enamel more resistant to demineralization and thus more resistant to decay. Topical fluoride, such as a fluoride
toothpasteToothpaste is a paste or gel dentifrice used with a toothbrush to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it can aid in the removal of dental plaque and food from the teeth, aid in the elimination and/or masking of halitosis and deliver...
or
mouthwashMouthwash or mouth rinse is a product used to enhance oral hygiene. Antiseptic and anti-plaque mouth rinse claim to kill the bacterial plaque causing caries, gingivitis, and bad breath. Anti-cavity mouth rinse uses fluoride to protect against tooth decay. But, it is generally agreed that the use...
, is also recommended to protect teeth surfaces. Many dentists include application of topical fluoride solutions as part of routine cleanings.
Restorations
After a tooth has been damaged or destroyed,
restorationA dental restoration or dental filling is a dental restorative material used to restore the function, integrity and morphology of missing tooth structure. The structural loss typically results from caries or external trauma. It is also lost intentionally during tooth preparation to improve the...
of the missing structure can be achieved with a variety of treatments. Restorations may be created from a variety of materials, including glass ionomer,
amalgamDental Amalgam is the most commonly used dental restorative material used for dental fillings. First introduced in France in the early 1800s, it contains a mixture of mercury with at least one other metal. Amalgam has been the restorative method of choice for many years due to its low cost, ease of...
,
goldGold is a chemical element with the symbol Au and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold is...
,
porcelainDental porcelain is a porcelain used by a dental technician to create biocompatible lifelike crowns, bridges, and veneers for the patient...
, and
compositeDental composite resins are types of synthetic resins which are used in dentistry as restorative material or adhesives. Synthetic resins evolved as restorative materials since they were insoluble, aesthetic, and insensitive to dehydration and were inexpensive. It is easy to manipulate them as well...
. 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 technique, such as for some inlays and onlays. When larger portions of a tooth are lost, an "extracoronal restoration" may be fabricated, such as a
crownA Crown is a type of dental restoration which completely caps or encircles a tooth or dental implant and is typically bonded to the tooth using a dental cement. Crowns can be made from many materials, which are usually fabricated using indirect methods...
or a
veneerIn dentistry, a veneer is a thin layer of restorative material placed over a tooth surface, either to improve the aesthetics of a tooth, or to protect a damaged tooth surface. There are two main types of material used to fabricate a veneer, composite and porcelain...
, to restore the involved tooth.
When a tooth is lost,
denturesDentures are prosthetic devices constructed to replace missing teeth, and which are supported by surrounding soft and hard tissues of the oral cavity. Conventional dentures are removable, however there are many different denture designs, some which rely on bonding or clasping onto teeth or dental...
,
bridgesA bridge, also known as a fixed partial denture, is a dental restoration used to replace a missing tooth by joining permanently to adjacent teeth or dental implants....
, or
implantA dental implant is an artificial tooth root replacement and is used in prosthetic dentistry to support restorations that resemble a tooth or group of teeth. There are several types of dental implants. The major classifications are divided into osseointegrated implant and the fibrointegrated implant...
s may be used as replacements. Dentures are usually the least costly whereas implants are usually the most expensive. Dentures may replace complete arches of the mouth or only a 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.
Abnormalities
Tooth abnormalities may be categorized according to whether they have environmental or developmental causes. 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.
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 hypoplasiaEnamel hypoplasia is the defect of the teeth in which the tooth enamel is hard but thin and deficient in amount. This is caused by defective enamel matrix formation with a deficiency in the cementing substance....
is a condition in which the amount of enamel formed is inadequate. 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 a systemic event, such as an
exanthemAn exanthem is a widespread rash usually occurring in children. Exanthems can be caused by toxins or drugs, microorganisms, or can result from autoimmune disease.It can be contrasted with an enanthem.-Types:...
atous
feverFever is a frequent medical sign that describes an increase in internal body temperature to levels above normal...
.
Turner's hypoplasiaTurner's hypoplasia is an abnormality found in teeth. Its appearance is variable, though usually is manifested as a portion of missing or diminished enamel on permanent teeth...
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
antineoplasticAntineoplastics are drugs that inhibit and combat the development of neoplasms.In the Anatomical Therapeutic Chemical Classification System, they are classified under L01D.- Health effects/occupational exposure :...
therapy.
Dental fluorosisDental fluorosis is a health condition caused by a child receiving too much fluoride during tooth development. The critical period of exposure is between 1 and 4 years old; children over age 8 are not at risk. In its mild form, which is the most common, fluorosis appears as tiny white streaks or...
is condition which results from ingesting excessive amounts of
fluorideFluoride is the anion F
−, the reduced form of fluorine. Both organic and inorganic compounds containing the element fluorine are sometimes called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are distinct relative to other...
and leads to teeth which are spotted, yellow, brown, black or sometimes pitted. Enamel hypoplasia resulting from
syphilisSyphilis is a sexually transmitted disease caused by the spirochetal bacterium Treponema pallidum subspecies pallidum. The route of transmission of syphilis is almost always through sexual contact, although there are examples of congenital syphilis via transmission from mother to child in utero.The...
is frequently referred to as
Hutchinson's teethHutchinson's teeth are a sign of congenital syphilis. Babies with this have teeth that are smaller and more widely spaced than normal and which have notches on their biting surfaces...
, which is considered one part of
Hutchinson's triadHutchinson's triad is named after Sir Jonathan Hutchinson . It is a common pattern of presentation for congenital syphilis, and consists of three phenomena: interstitial keratitis, Hutchinson incisors, and eighth nerve deafness....
.
Destruction after development
Tooth destruction from processes other than
dental cariesDental caries, also known as tooth decay or cavity, is a disease wherein bacterial processes damage hard tooth structure . These tissues progressively break down, producing dental cavities . Two groups of bacteria are responsible for initiating caries: Streptococcus mutans and Lactobacilli...
is considered a normal physiologic process but may become severe enough to become a pathologic condition.
AttritionAttrition is the loss of teeth structure by mechanical forces from opposing teeth. Attrition initially affects the enamel and, if unchecked, may proceed to the underlying dentin. Once past the enamel, attrition quickly destroys the softer dentin....
is the loss of tooth structure by mechanical forces from opposing teeth. Attrition initially affects the enamel and, if unchecked, may proceed to the underlying dentin.
AbrasionAbrasion is the loss of tooth structure by mechanical forces from a foreign element. 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...
is the loss of tooth structure by mechanical forces from a foreign element. 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.
ErosionAcid erosion, also known as dental erosion, is the irreversible loss of tooth structure due to chemical dissolution by acids not of bacterial origin. Dental erosion is the most common chronic disease of children ages 5–17, although it is only relatively recently that it has been recognised...
is the loss of tooth structure due to chemical dissolution by acids not of bacterial origin. 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 juiceLemon juice, a fruit juice, is the juice of lemons . Fresh lemon juice is obtained by squeezing lemons. Lemon juice, either in natural strength or concentrated, is sold as a bottled product most of the time, usually with the addition of ascorbic acid and a preservative such as E223...
.
AbfractionAbfraction is the loss of tooth structure from flexural forces. This has not been supported yet by dental research but it is hypothesized that enamel, especially at the cementoenamel junction , undergo this pattern of destruction by separating the enamel rods.As teeth flex under pressure, the...
is the loss of tooth structure from flexural forces. As teeth flex under
pressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
, the arrangement of teeth touching each other, known as
occlusionOcclusion, in a dental context, means simply the contact between teeth. More technically, it is the relationship between the maxillary and mandibular teeth when they approach each other, as occurs during chewing or at rest....
, causes
tensionIn physics, tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. It is the opposite of compression. As tension is the magnitude of a force, it is measured in newtons and is always measured parallel to the string on which it applies...
on one side of the tooth and
compressionPhysical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. The opposite of compression is rarefraction tension.- Explanation :...
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 resorptionInternal resorption is an unusual condition of a tooth when the dentin and pulpal walls begin to resorb centrally within the root canal. The first evidence of the lesion may be the appearance of a pink-hued area on the crown of the tooth; this condition is referred to pink tooth of Mummery, after...
, when caused by cells within the pulp, or
external resorptionExternal resorption is a condition of a tooth where the root surface is lost. This can be caused by chronic inflammation, cysts, tumors, trauma, reimplantation of a tooth, or sometimes the cause is unknown.-References:...
, when caused by cells in the periodontal ligament.
Discoloration
Discoloration of teeth may result from bacteria stains, tobacco, tea, coffee, foods with an abundance of
chlorophyllChlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from the Greek χλωρός and φύλλον...
, restorative materials, and medications. 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. Chlorhexidine, a mouthwash, is associated with causing yellow-brown stains near the gingiva on teeth. Systemic disorders also can cause tooth discoloration. Congenital erythropoietic porphyria causes
porphyrinPorphyrins are a group of organic compounds of which many occur in nature, most well-known as the pigment in red blood cells. They are heterocyclic macrocycles characterised by the presence of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges...
s to be deposited in teeth, causing a red-brown coloration. Blue discoloration may occur with
alkaptonuriaAlkaptonuria is a rare inherited genetic disorder of phenylalanine and tyrosine metabolism. This is an autosomal recessive condition that is due to a defect in the enzyme homogentisate 1,2-dioxygenase , which participates in the degradation of tyrosine...
and rarely with
Parkinson's diseaseParkinson's disease is a degenerative disorder of the central nervous system that often impairs the sufferer's motor skills, speech, and other functions....
. Erythroblastosis fetalis and
biliary atresiaBiliary atresia is a rare condition in newborn infants in which the common bile duct between the liver and the small intestine is blocked or absent. If unrecognised, the condition leads to liver failure but not to kernicterus. This is because the liver is still able to conjugate bilirubin, and...
are diseases which may cause teeth to appear green from the deposition of
biliverdinBiliverdin is a green tetrapyrrolic bile pigment, and is a product of heme catabolism . It is the pigment responsible for the yellowish color in bruises .- Metabolism :Biliverdin results from the breakdown of the heme moiety of hemoglobin in erythrocytes...
. Also, trauma may change a tooth to a pink, yellow, or dark gray color. Pink and red discolorations are also associated in patients with
lepromatous leprosyLeprosy , or Hansen's disease , is a chronic disease caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis. Leprosy is primarily a granulomatous disease of the peripheral nerves and mucosa of the upper respiratory tract; skin lesions are the primary external symptom...
. Some medications, such as
tetracyclineTetracycline is a broad-spectrum polyketide antibiotic produced by the Streptomyces genus of Actinobacteria, indicated for use against many bacterial infections. It is a protein synthesis inhibitor. It is commonly used to treat acne today, and more recently, rosacea, and played a historical role...
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 impacted. The most common cause of tooth impaction is lack of space in the mouth for the tooth. Other causes may be
tumorA tumor or tumour is the name for a swelling or lesion formed by an abnormal growth of cells . Tumor is not synonymous with cancer. A tumor can be benign, pre-malignant or malignant, whereas cancer is by definition malignant....
s,
cystA cyst is a closed sac having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :*Acne...
s, trauma, and thickened bone or soft tissue.
AnkylosisAnkylosis, or Anchylosis is a stiffness of a joint, the result of injury or disease. The rigidity may be complete or partial and may be due to inflammation of the tendinous or muscular structures outside the joint or of the tissues of the joint itself...
of a tooth 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 orthodontists 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 prior to the root of its succeeding permanent tooth reaching 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.
Abnormality in number
AnodontiaIn dentistry, anodontia, also called anodontia vera, is a rare genetic disorder characterized by the congenital absence of all primary or permanent teeth. It is associated with the group of skin and nerve syndromes called the ectodermal dysplasias...
is the total lack of tooth development.
HyperdontiaHyperdontia is the condition of having supernumerary teeth, or teeth which appear in addition to the regular number of teeth.-Types:The most common supernumerary tooth is a mesiodens, which is a mal-formed, peg-like tooth that occurs between the maxillary central incisors.Fourth and fifth molars...
is the presence of a higher-than-normal number of teeth, whereas
HypodontiaIn dentistry, hypodontia is the condition of naturally having fewer than the regular number of teeth. Hypodontia describes a situation when there is a missing number of 6 teeth or fewer excluding 3rd molars or wisdom teeth. The condition of missing over 6 teeth is called oligodontia excluding 3rd...
is the lack of some teeth. Usually, hypodontia refers to the lack of development of one or more teeth, and oligodontia may be used to describe the absence of 6 or more teeth. Some systemic disorders which may result in hyperdontia include
Apert syndromeApert syndrome is a form of acrocephalosyndactyly, a congenital disorder characterized by malformations of the skull, face, hands and feet. It is classified as a branchial arch syndrome, affecting the first branchial arch, the precursor of the maxilla and mandible...
,
Cleidocranial dysostosisCleidocranial dysostosis, also called Cleidocranial dysplasia, is a hereditary congenital disorder due to haploinsufficiency caused by mutations in the CBFA1 gene, located on the short arm of chromosome 6....
,
Crouzon syndromeCrouzon syndrome is a genetic disorder known as a branchial arch syndrome. Specifically, this syndrome affects the first branchial arch, which is the precursor of the maxillaand mandible...
,
Ehlers-Danlos syndromeEhlers-Danlos Syndrome is a group of inherited connective tissue disorders, caused by a defect in the synthesis of collagen . The collagen in connective tissue helps tissues to resist deformation...
, Gardner syndrome, and
Sturge-Weber syndromeSturge-Weber syndrome, sometimes referred to as encephalotrigeminal angiomatosis, is a rare congenital neurological and skin disorder. It is one of the phakomatoses and is often associated with port-wine stains of the face, glaucoma, seizures, mental retardation, and ipsilateral leptomeningeal...
. Some systemic disorders which may result in hypodontia include Crouzon syndrome,
Ectodermal dysplasiaEctodermal dysplasia is not a single disorder, but a group of syndromes all deriving from abnormalities of the ectodermal structures. More than 150 different syndromes have been identified. Despite some of the syndromes having different genetic causes the symptoms are sometimes very similar...
, Ehlers-Danlos syndrome, and
Gorlin syndromeGorlin syndrome can refer to:* Nevoid basal cell carcinoma syndrome* Focal dermal hypoplasia...
.
Abnormality in size
MicrodontiaMicrodontia is a condition in which teeth appear smaller than normal. In the generalized form, all teeth are involved. In the localized form, only a few teeth are involved. The most common teeth affected are the upper lateral incisors and third molars....
is a condition where teeth are smaller than the usual size, and
macrodontiaMacrodontia is a condition in which the teeth appear larger than normal. It is commonly associated with gigantism....
is where teeth are larger than the usual size. Microdontia of a single tooth is more likely to occur in a
maxillary lateral incisorThe maxillary lateral incisor is the tooth located distally from both maxillary central incisors of the mouth and mesially from both maxillary canines. As with all incisors, their function is for shearing or cutting food during mastication, commonly known as chewing. There are no cusps on the...
. The second most likely tooth to have microdontia are third molars. Macrodontia of all the teeth is known to occur in
pituitary gigantismGigantism, also known as gigantism, is a condition characterized by excessive growth and height significantly above average.-Types:As a medical term, gigantism can refer to:...
and
pinealThe pineal gland is a small endocrine gland in the vertebrate brain. It produces melatonin, a hormone that affects the modulation of wake/sleep patterns and photoperiodic functions...
hyperplasiaHyperplasia is a general term referring to the proliferation of cells within an organ or tissue beyond that which is ordinarily seen . Hyperplasia may result in the gross enlargement of an organ, the formation of a benign tumor, or may be visible only upon histological analysis with a microscope...
. It may also occur on one side of the face in cases of hemifacial hyperplasia.
Abnormality in shape
GeminationThe phenomenon of gemination arises when two teeth develop from one tooth bud and, as a result, the patient has a larger tooth but a normal number of teeth overall, in contrast to fusion, where the patient would appear to be missing one tooth....
occurs when a developing tooth incompletely splits into the formation of two teeth.
FusionThe phenomenon of tooth fusion arises through union of two normally separated tooth germs, and depending upon the stage of development of the teeth at the time of union, it may be either complete or incomplete. On some occasions, two independent pulp chambers and root canals can be seen. However,...
is the union of two adjacent teeth during development.
ConcrescenceConcrescence is a condition of teeth where the cementum overlying the roots of at least two teeth join together. The cause can sometimes be attributed to trauma or crowding of teeth. Surgical separation of the teeth may be necessary if one is to be extracted....
is the fusion of two separate teeth only in their cementum. Accessory
cuspA cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
s are additional cusps on a tooth and may manifest as a
Talon cuspA talon cusp, also known as an "eagle's talon", is an extra cusp on an anterior tooth. The term refers to the same condition as dens evaginatus, but the talon cusp is the manifestation of dens evaginatus on anterior teeth. The incidence has been found to range from less than 1% to 6% of the...
,
Cusp of CarabelliThe cusp of Carabelli, or Carabelli's tubercle, or tuberculus anomalus of Georg Carabelli is a small additional cusp at the mesiopalatal line angle of maxillary first molars. This extra cusp is usually found on the first molar, and becomes progressively less likely in the second, third molars...
, or
Dens evaginatusDens envaginatus is a condition found in teeth where the outer surface appears to form an extra bump or cusp. Premolars are more likely to be affected than any other tooth. This may be seen more frequently in Asians. The pulp of the tooth may extend into the dens evaginatus. There is a risk of...
.
Dens invaginatusDens invaginatus, also known as dens in dente, is a condition found in teeth where the outer surface folds inward. There are coronal and radicular forms, with the coronal form being more common....
, 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.
TaurodontismTaurodontism is a condition found in teeth where the body of the tooth and pulp chamber is enlarged. As a result, the floor of the pulp and the furcation of the tooth is moved apically down the root....
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 syndromeTriple X syndrome is a form of chromosomal variation characterized by the presence of an extra X chromosome in each cell of a human female. The condition is also known as triplo-X, trisomy X, XXX syndrome, and 47,XXX aneuploidy. Triple X results during division of a parent's reproductive cells and...
, and
XYY syndromeXYY syndrome is an aneuploidy of the sex chromosomes in which a human male receives an extra Y chromosome, giving a total of 47 chromosomes instead of the more usual 46...
.
HypercementosisHypercementosis is an idiopathic, nonneoplastic condition characterized by the excessive buildup of normal cementum on the roots of one or more teeth. A thick layer of cementum can give the tooth a fat appearance. It is experienced as an uncomfortable sensation in the tooth, followed by an...
is excessive formation of cementum, which may result from trauma, inflammation,
acromegalyAcromegaly is a syndrome that results when the pituitary gland produces excess growth hormone after epiphyseal plate closure at puberty...
,
rheumatic feverRheumatic fever is an inflammatory disease that may develop two to three weeks after a Group A streptococcal infection . It is believed to be caused by antibody cross-reactivity and can involve the heart, joints, skin, and brain...
, and
Paget's disease of bonePaget's disease of the bone or osteitis deformans, is the most common Paget's disease. It is a chronic disorder that typically results in enlarged and deformed bones. The disease is named after Sir James Paget, the British surgeon who first described it in 1877...
. A
dilacerationDilaceration is a developmental disturbance in shape of teeth. It refers to an angulation, or a sharp bend or curve, in the root or crown of a formed tooth.-Description:The condition is thought to be due to trauma during the period in which tooth is forming...
is a bend in the root which may have been caused by trauma to the tooth during formation.
Supernumerary rootsSupernumerary roots is a condition found in teeth there may be a larger number of roots than expected. The most common teeth affected are mandibular canines, premolars, and molars, especially third molars. Canines and most premolars, except for maxillary first premolars, usually have one root. ...
is the presence of a greater number of roots on a tooth than expected.
Abnormality in structure
Amelogenesis imperfectaAmelogenesis imperfecta presents with abnormal formation of the enamel or external layer of teeth. Enamel is composed mostly of mineral, that is formed and regulated by the proteins in it...
is a condition in which enamel does not form properly or at all.
Dentinogenesis imperfectaDentinogenesis imperfecta is a genetic disorder of tooth development. This condition causes teeth to be discolored and translucent. Teeth are also weaker than normal, making them prone to rapid wear, breakage, and loss. These problems can affect both primary teeth and permanent teeth...
is a condition in which dentin does not form properly and is sometimes associated with
osteogenesis imperfectaOsteogenesis imperfecta is a genetic bone disorder. People with OI are born with defective connective tissue, or without the ability to make it, usually because of a deficiency of Type-I collagen...
.
Dentin dysplasiaDentin dysplasia is a genetic disorder of teeth, commonly exhibiting an autosomal dominant inheritance. It is characterized by presence of normal enamel but atypical dentin with abnormal pulpal morphology. There are two types. Type I is the radicular type, and type II is the coronal type...
is a disorder in which the roots and pulp of teeth may be affected.
Regional odontodysplasiaRegional odontodysplasia is an uncommon developmental abnormality of teeth, usually localized to a certain area and nonhereditary. No predilection for race, but females are more likely to get regional odontodysplasia. The enamel, dentin, and pulp of teeth are affected, and on radiographs the teeth...
is a disorder affecting enamel, dentin, and pulp and causes the teeth to appear "ghostly" on radiographs.
Non-human animals
Teeth vary greatly among animals. Some animals, such as
turtleTurtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s and
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s, are toothless. Others, such as
sharkSharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs....
s, may go through many
teethShark teeth are relics of shark evolution and biology, and as they are often the only part of the shark to survive fossilisation, represent much of the Selachimorpha fossil record, extending back hundreds of millions of years. The most ancient types of sharks date back to 450 million years ago...
in their lifetime.
The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position. The teeth of mammals have deep roots, and this pattern is also found in some fish, and in crocodilians. In most teleost fish, however, the teeth are attached to the outer surface of the bone, while in
lizardLizards are a very large and widespread group of squamate reptiles, with nearly 5,000 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s they are attached to the inner surface of the jaw by one side. In cartilaginous fish, such as sharks, the teeth are attached by tough
ligamentIn anatomy, the term ligament is used to denote three different types of structures:# Fibrous tissue that connects bones to other bones. They are sometimes called "articular ligaments", "fibrous ligaments", or "true ligaments"....
s to the hoops of
cartilageCartilage is a stiff yet flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
that form the jaw.
Neither are teeth always attached to the jaw, as they are in mammals. In many
reptileReptiles, or members of the class Reptilia, are air-breathing, generally "cold-blooded" amniotes that generally have skin covered in scales or scutes. They are tetrapods and lay amniote eggs, whose embryos are surrounded by the amnion membrane...
s and fish, teeth are attached to the
palateThe palate is the roof of the mouth in humans and vertebrate animals. It separates the oral cavity from the nasal cavity. The palate is divided into two parts, the anterior bony hard palate, and the posterior fleshy soft palate or velum...
or to the floor of the mouth, forming additional rows inside those on the jaws proper. Some teleosts even have teeth in the
pharynxThe pharynx is the part of the neck and throat situated immediately posterior to the mouth and nasal cavity, and cranial, or superior, to the esophagus, larynx, and trachea.-Functions:...
. While not true teeth in the usual sense, the denticles of sharks are almost identical in structure, and are likely to have the same evolutionary origin. Indeed, teeth appear to have first evolved in sharks, and are not found in the more primitive jawless fish - while
lampreyA lamprey is a parasitic marine animal with a toothed, funnel-like sucking mouth. Translated directly, their name means stone lickers . While lampreys are well known for those species which bore into the flesh of other fish to suck their blood, these species make up the minority...
s do have tooth-like structures on the tongue, these are in fact, composed of
keratinKeratins are a family of fibrous structural proteins; tough and insoluble, they form the hard but un-mineralized structures found in reptiles, birds, amphibians, and mammals...
, not of dentine or enamel, and bear no relationship to true teeth.
Living
amphibianAmphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic animals that metamorphose from a juvenile water-breathing form, to an adult air-breathing form. Though amphibians typically have four limbs, the Caecilians are notable for being limbless. Unlike other land...
s typically have small teeth, or none at all, since they commonly feed only on soft foods. In reptiles, teeth are generally simple and conical in shape, although there is some variation between species, most notably the venom-injecting
fangFang is a mammal's canine tooth.Fang may also refer to:* A snake's poison-injecting tooth: see snake venom* The Fang people of Central Africa* The Fang language spoken by these people...
s of
snakeSnakes are elongate legless carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic amniote vertebrates covered in overlapping scales...
s. The pattern of incisors, canines, premolars and molars is found only in mammals, and to varying extents, in their evolutionary ancestors. The numbers of these types of teeth varies greatly between species;
zoologistsZoology, also spelled zoölogy, is the branch of biology that focuses on the structure, function, behavior, and evolution of animals. The zoologist's pronunciation of "zoology" is , though a common spelling pronunciation is .-Systems of classification:...
use a standardised dental formula to describe the precise pattern in any given group.
Specific examples
WalrusThe walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...
tusks are canine teeth that grow continuously throughout life.
DogThe dog is a domesticated form of the Gray Wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history...
teeth are less likely than human teeth to form dental caries because of the very high pH of dog saliva, which prevents enamel from demineralizing.
Unlike humans whose ameloblasts die after tooth development,
rodentRodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s continually produce enamel and must wear down their teeth by gnawing on various materials.
Horse teethHorses' teeth are often used to estimate the animal's age, hence the sayings "long in the tooth", "straight from the horse's mouth" and "Don't look a gift horse in the mouth".- Types of teeth :At five years of age a horse has between 36 and 44 teeth...
include twelve premolars, twelve molars, and twelve incisors. The structure of horse teeth is different from human teeth as the enamel and dentin layers are intertwined.
Like human teeth,
whaleWhale is the common name for marine mammals of the order Cetacea. The term whale is sometimes used to refer to all cetaceans, but in more common English usage it generally excludes the members of the Delphinoidea superfamily, such as dolphins and porpoises...
teeth have polyp-like protrusions located on the root surface of the tooth. These polyps are made of cementum in both species, but in human teeth the protrusions are located on the outside of the root, while in whales the nodule is located on the inside of the pulp chamber. While the roots of human teeth are made of cementum on the outer surface, whales have cementum on the entire surface of the tooth with a very small layer of enamel at the tip. This small enamel layer is only seen in older whales where the cementum has been worn away to show the underlying enamel.
Fossil record
Because teeth are very resistant - often preserved when bones are not - and reflect the diet of the host organism, they are very valuable to archaeologists and palaeontologists. Early fish such as the thelodonts had teeth for scales, suggesting that the origin of teeth was scales which were retained in the mouth. Fish as early as the late
CambrianThe Cambrian is the first geological period of the Paleozoic era, lasting from ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux...
had dentine in their exoskeleton, which may have functioned in defense or for sensing their environment. Dentine can be as hard as the rest of teeth, and is composed of collagen fibres, reinforced with hydroxyapatite.
Decalcification removes the enamel from teeth and leaves only the organic interior intact, which comprises dentine and cementine. Enamel is quickly decalcified in acids, perhaps by dissolution by plant acids or via diagenetic solutions, or even the stomach of vertebrate predators. Enamel can also be lost by abrasion or spalling, and is lost before dentine or bone are destroyed by the fossilisation process. In such a case, the 'skeleton' of the teeth would consist of the dentine, with a hollow pulp cavity.
Dentine, conversely, is destroyed by alkalis.
See also
- Barodontalgia
Barodontalgia, commonly known as tooth squeeze and previously known as aerodontalgia, is a pain in tooth caused by a change in atmospheric pressure...
- Braces
- Dental auxiliary
- Dental assistant
Dental assistants help the dental operator provide more efficient dental treatment, by preparing the patient with a bib or goggles, washing and sterilizing instruments, passing instruments during the procedure, holding a suction device, and other non-specialized tasks...
- Dental hygienist
thumb|right|200px|A dental hygienist at workA dental hygienist is a licensed dental professional who specializes in preventive medical care, typically focusing on techniques in oral hygiene. Local dental regulations determine the scope of practice of dental hygienists. In most jurisdictions,...
- Dental technician
A dental technician is a member of the dental team who, with a written work order, produces dental appliances such as a removable prothesis, including dentures and orthodontic appliances, and adjunctive services such as denture repairs, and fixed prostheses, such as crowns and bridges.Dental...
- Dental notation
Dentists, in writing or speech, use several different Dental notation systems for associating information to a specific tooth. The three most commons systems are the FDI World Dental Federation notation, Universal numbering system , and Palmer notation method...
- Dental tourism
Dental tourism is a subset of the sector known as medical tourism. It involves individuals seeking dental care outside of their local healthcare systems.- Reasons for travel :...
- Dentistry
Dentistry is the known evaluation, diagnosis, prevention, and treatment of diseases, disorders and conditions of the soft and hard tissues of the jaw , the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is a part of stomatology...
- Dragon's teeth (mythology)
In Greek myth, dragon's teeth feature prominently in the legends of the Phoenician prince Cadmus and Jason's quest for the Golden Fleece. In each case, the dragon's teeth, once planted, would grow into fully armed warriors....
- Head and neck anatomy
Head and neck anatomy focuses on the structures of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat...
- Language
A language is a system for encoding and decoding information. In its most common use, the term refers to so-called "natural languages" — the forms of communication considered peculiar to humankind. In linguistics the term is extended to refer to the human cognitive facility of creating and using...
- Tooth Fairy
For other uses, see Tooth Fairy .The Tooth Fairy is a mythical character depicted as a fairy that gives a child money or gifts in exchange for a baby tooth that has fallen out. Children typically place the tooth under their pillow at night...
- Tooth painting
Tooth painting is a custom practiced by the Si La ethnic group. The Si La men paint their teeth red and the women paint theirs black. This practice has slowly declined with each new generation....
- Vocal tract
The vocal tract is the cavity in animals where sound that is produced at the sound source is filtered. In birds it consists of the trachea, the syrinx, the oral cavity, the upper part of the esophagus, and the beak...
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