Tooth enamel is the hardest and most highly mineralized substance of the body, and 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 pulpThe dental pulp is the part in the center of a tooth made up of living soft tissue and cells called odontoblasts.- Anatomy :Each person can have a total of up to 52 pulp organs, 32 in the permanent and 20 in the primary teeth....
is one of the four major tissues which make up the
toothTeeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to tear, scrape, and chew food. Some animals, particularly carnivores, also use teeth for hunting or defense. The roots of teeth are covered by gums...
in vertebrates. Tooth enamel is also found in the dermal denticles of
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. It is the normally visible dental tissue of a tooth 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
appearanceVariations in the physical appearance of humans, known as human looks, are believed by anthropologists to be an important factor in the development of personality and social relations, in particular, physical attractiveness. There is a relatively low sexual dimorphism between human males and...
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
hydroxylapatiteHydroxylapatite, also called hydroxyapatite, is a naturally occurring mineral form of calcium apatite with the formula Ca53, but is usually written Ca1062 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the...
, 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. Tooth enamel ranks 5 on
Mohs hardness scaleThe Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science...
and a
Young's modulusIn solid mechanics, Young's modulus is a measure of the stiffness of an isotropic elastic material. It is also known as the Young modulus, modulus of elasticity, elastic modulus or tensile modulus...
of 83 GPa. Dentin, less mineralized and less brittle, 3–4 in hardness, 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 a framework support, among other functions.
Structure
The basic unit of enamel is called an
enamel rodAn Enamel rod is the basic unit of tooth enamel. The antiquated term is enamel prism. Measuring 4 μm wide to 8 μm high, an enamel rod is a tightly packed, highly organized mass of hydroxyapatite crystals...
. Measuring 4–8 μm in diameter an enamel rod, formerly called an enamel prism, is a tightly packed mass of hydroxyapatite crystals in an organized pattern. In cross section, it is best compared to a keyhole, with the top, or head, oriented toward the crown of the tooth, and the bottom, or tail, oriented toward the root of the tooth.
The arrangement of the crystals within each enamel rod is highly complex. Both ameloblasts (the cells which initiate enamel formation) and
Tomes' processTomes' processes are a histologic landmark identified on an ameloblast, cells involved in the production of tooth enamel. During the synthesis of enamel, the ameloblast moves away from the dentin, forming a projection surrounded by the developing enamel...
es affect the crystals' pattern. Enamel crystals in the head of the enamel rod are oriented parallel to the long axis of the rod. When found in the tail of the enamel rod, the crystals' orientation diverges slightly from the long axis.
The arrangement of enamel rods is understood more clearly than their internal structure. Enamel rods are found in rows along the tooth, and within each row, the long axis of the enamel rod is generally perpendicular to the underlying dentin. In permanent teeth, the enamel rods near the cementoenamel junction (CEJ) tilt slightly toward the root of the tooth. Understanding enamel orientation is very important in restorative dentistry, because enamel unsupported by underlying dentin is prone to fracture.
The area around the enamel rod is known as
interrod enamelInterrod enamel is histologically identified on microscopic views of tooth enamel. Because interrod enamel is located around enamel rods, the areas of interrod enamel enhances the "keyhole" appearance of enamel rods by acting as its border...
. Interrod enamel has the same composition as enamel rod, however a
histologicHistology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining a thin slice of tissue under a light microscope or electron microscope...
distinction is made between the two because crystal orientation is different in each. The border where the crystals of enamel rods and crystals of interrod enamel meet is called the
rod sheathThe rod sheath is an area identified in histologic sections of a tooth. It is found where enamel rods, the functional unit of enamel, meet interrod enamel. The crystals of both types of enamel meet at sharp angles and form the appearance of a space called the rod sheath...
.
Striae of RetziusThe Striae of Retzius are incremental growth lines seen in enamel and are results of enamel's development. When viewed microscopically in cross-section, they appear as concentric rings. In a longitudinal section, they appear as a series of dark bands...
are stripes that appear on enamel when viewed microscopically in cross section. Formed from changes in diameter of Tomes’ processes, these stripes demonstrate the growth of enamel, similar to the annual rings on a tree. Perikymata are shallow furrows where the striae of Retzius end. Darker than the other stripes, the
neonatal lineThe neonatal line is a particular band of incremental growth lines seen in histologic sections of a deciduous tooth. It belongs to a series of a growth lines in tooth enamel known as the Striae of Retzius. The neonatal line is darker and larger than the rest of the striae of Retzius...
is a stripe that separates enamel formed before and after birth.
Gnarled enamelGnarled enamel is a description of enamel seen in histologic sections of a tooth underneath a cusp. The appearance of enamel appears different and very complex under the cusp, but this is not due to a different arrangement of dental tissues. Instead, the enamel still has the same arrangement of...
is found at the cusps of teeth. Its twisted appearance results from the orientation of enamel rods and the rows in which they lie.
Development
Enamel formation is part of the overall process of
tooth developmentTooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans...
. When the tissues of the developing tooth are seen under a microscope, different cellular aggregations can be identified, including structures known as 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...
,
dental laminaThe dental lamina is a band of epithelial tissue seen in histologic sections of a developing tooth. The dental lamina is first evidence of tooth development and begins at the sixth week in utero or three weeks after the rupture of the buccopharyngeal membrane. It is formed when cells of the oral...
, and
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...
. The generally recognized stages of tooth development are the bud stage, cap stage, bell stage, and crown, or calcification, stage. Enamel formation is first seen in the crown stage.
AmelogenesisAmelogenesis is the formation of enamel on teeth and occurs during the crown stage of tooth development after dentinogenesis, which is the formation of dentine. Since dentine must be present for enamel to be formed, this prerequisite is an example of the biologic concept, termed reciprocal...
, or enamel formation, occurs after the first establishment of dentin, via cells known as ameloblasts. Human enamel forms at a rate of around 4 μm per day, beginning at the future location of cusps, around the third or fourth month of pregnancy. As in all human processes, the creation of enamel is complex, but can generally be divided into two stages. The first stage, called the secretory stage, involves proteins and an organic matrix forming a partially mineralized enamel. The second stage, called the maturation stage, completes enamel mineralization.
In the secretory stage, ameloblasts are polarized columnar
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...
. In the rough endoplasmic reticulum of these cells, enamel proteins are released into the surrounding area and contribute to what is known as the enamel matrix, which is then partially mineralized by the enzyme
alkaline phosphataseAlkaline phosphatase is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation. As the name suggests, alkaline phosphatases are most...
. When this first layer is formed, the ameloblasts move away from the dentin, allowing for the development of Tomes’ processes at the apical pole of the cell. Enamel formation continues around the adjoining ameloblasts, resulting in a walled area, or pit, that houses a Tomes’ process, and also around the end of each Tomes’ process, resulting in a deposition of enamel matrix inside of each pit. The matrix within the pit will eventually become an enamel rod, and the walls will eventually become interrod enamel. The only distinguishing factor between the two is the orientation of the calcium phosphate crystals.
In the maturation stage, the ameloblasts transport substances used in the formation of enamel. Histologically, the most notable aspect of this phase is that these cells become striated, or have a ruffled border. These signs demonstrate that the ameloblasts have changed their function from production, as in the secretory stage, to transportation. Proteins used for the final mineralization process compose most of the transported material. The noteworthy proteins involved are
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,
ameloblastinAmeloblastin, also known as amelin, is a gene-specific protein found in tooth enamel. Although less than 5% of enamel consists of protein, ameloblastins comprise 5%-10% of all enamel protein. This protein is formed by ameloblasts during the early secertory to late maturation stages of amelogenesis...
s,
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, and
tuftelinTuftelin is an acidic phosphorylated glycoprotein found in tooth enamel. In humans, the Tuftelin protein is encoded by the TUFT1 gene.- Function :This protein is formed for a short time during amelogenesis...
s. During this process, amelogenins and ameloblastins are removed after use, leaving enamelins and tuftelin in the enamel. By the end of this stage, the enamel has completed its mineralization.
At some point before the tooth erupts into the mouth, but after the maturation stage, the ameloblasts are broken down. Consequently, enamel, unlike many other tissues of the body, has no way to regenerate itself. After destruction of enamel from decay or injury, neither the body nor a dentist can restore the enamel tissue. Enamel can be affected further by non-pathologic processes. The discoloration of teeth over time can result from exposure to substances such as
tobaccoTobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as an organic pesticide, and in the form of nicotine tartrate it is used in some medicines. In consumption it most commonly appears in the forms of smoking, chewing, snuffing, or...
,
coffeeCoffee is a brewed beverage prepared from roasted seeds, commonly called coffee beans, of the coffee plant. They are seeds of "coffee cherries" that grow on trees in over 70 countries. It has been said that green coffee is the second most traded commodity in the world behind crude oil. Due to its...
, and
teaTea is the agricultural product of the leaves, leaf buds, and internodes of the Camellia sinensis plant, prepared and cured by various methods...
. This is partly due to material building up in the enamel, but is also an effect of the underlying dentin becoming sclerotic. As a result, tooth color gradually darkens with age. Additionally, enamel becomes less permeable to fluids, less soluble to acid, and contains less water.
Progress of enamel formation for primary teeth
| |
Amount of enamel formed at birth |
Enamel mineralization completed |
Primary
maxillary
tooth |
Central incisor |
5/6 |
1.5 months after birth |
| Lateral incisor |
2/3 |
2.5 months after birth |
| Canine |
1/3 |
9 months after birth |
| 1st molar |
Cusps united; occlusal completely calcified
and 1/2 to 3/4 crown height |
6 months after birth |
| 2nd molar |
Cusps united; occlusal incompletely calcified;
calcified tissue covers 1/5 to 1⁄4 crown height |
11 months after birth |
Primary
mandibular
tooth |
Central incisor |
3/5 |
2.5 months after birth |
| Lateral incisor |
3/5 |
3 months after birth |
| Canine |
1/3 |
9 months after birth |
| 1st molar |
Cusps united; occlusal
completely calcified |
5.5 months after birth |
| 2nd molar |
Cusps united; occlusal
incompletely calcified |
10 months after birth |
Destruction
The high mineral content of enamel, which makes this tissue the hardest in the human body, also makes it susceptible to a demineralization process which often occurs as
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...
, otherwise known as cavities. Demineralization occurs for several reasons, but the most important cause of tooth decay is the ingestion of sugars.
Tooth cavities are caused when acids dissolve tooth enamel:
-
- Ca10(PO4)6(OH)2(s) + 8H+(aq) → 10Ca2+(aq) + 6HPO42-(aq) + 2H2O(l)
Sugars from
candiesCandy, specifically sugar candy, is a confection made from a concentrated solution of sugar in water, to which flavorings and colorants are added...
,
soft drinkA soft drink is a drink that does not contain alcohol . Soft drinks are often carbonated and commonly consumed while cold. The most common soft drinks are colas, flavored water, sparkling water, iced tea, sweet tea, lemonade, squash and fruit punch....
s, and even
fruit juicesJuice is a liquid naturally contained in fruit or vegetable tissue. Juice is prepared by mechanically squeezing or macerating fresh fruits or vegetables without the application of heat or solvents. For example, orange juice is the liquid extract of the fruit of the orange tree. Juice may be...
play a significant role in tooth decay, and consequently in enamel destruction. The mouth contains a great number and variety of
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...
, and when
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...
, the most common of sugars, coats the surface of the mouth, some intraoral bacteria interact with it and form
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 decreases the pH in the mouth. Then, the hydroxylapatite crystals of enamel demineralize, allowing for greater bacterial invasion deeper into the tooth. The most important bacterium involved with tooth decay is
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:...
, but the number and type of bacteria varies with the progress of tooth destruction.
Furthermore, tooth morphology dictates that the most common site for the initiation of dental caries is in the deep grooves, pits, and fissures of enamel. This is expected because these locations are impossible to reach with a toothbrush and allow for bacteria to reside there. When demineralization of enamel occurs, a dentist can use a sharp instrument, such as a
dental explorer100px|right|thumb|A No. 23 explorer, also known as a 'sickle probe'A dental explorer is an instrument in dentistry commonly used in the dental armamentarium. A sharp point at the end of the explorer is used to enhance tactile sensation....
, and "feel a stick" at the location of the decay. As enamel continues to become less mineralized and is unable to prevent the encroachment of bacteria, the underlying dentin becomes affected as well. When dentin, which normally supports enamel, is destroyed by a physiologic condition or by decay, enamel is unable to compensate for its brittleness and breaks away from the tooth easily.
The extent to which tooth decay is likely, known as
cariogenicityCaries is a progressive destruction of any kind of bone structure, including the skull, ribs and other bones, or the teeth. Caries can be caused by osteomyelitis, which is a bacterial disease. A disease that involves caries is mastoiditis, an inflammation of the mastoid process, in which the bone...
, depends on factors such as how long the sugar remains in the mouth. Contrary to common belief, it is not the amount of sugar ingested but the frequency of sugar ingestion that is the most important factor in the causation of tooth decay. When the pH in the mouth initially decreases from the ingestion of sugars, the enamel is demineralized and left vulnerable for about 30 minutes. Eating a greater quantity of sugar in one sitting does not increase the time of demineralization. Similarly, eating a lesser quantity of sugar in one sitting does not decrease the time of demineralization. Thus, eating a great quantity of sugar at one time in the day is less detrimental than is a very small quantity ingested in many intervals throughout the day. For example, in terms of oral health, it is better to eat a single
dessertDessert is a course that typically comes at the end of a meal, usually consisting of sweet food but sometimes of a strongly-flavored one, such as some cheeses...
at dinner time than to snack on a bag of
candyCandy, specifically sugar candy, is a confection made from a concentrated solution of sugar in water, to which flavorings and colorants are added...
throughout the day.
In addition to bacterial invasion, enamel is also susceptible to other destructive forces.
BruxismBruxism is characterized by the grinding of the teeth and is typically accompanied by the clenching of the jaw. It is an oral parafunctional activity that occurs in most humans at some time in their lives. In most people, bruxism is mild enough not to be a health problem...
, also known as clenching of or grinding on teeth, destroys enamel very quickly. The wear rate of enamel, called
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 8 micrometers a year from normal factors. A common misconception is that enamel wears away mostly from chewing, but actually teeth rarely touch during chewing. Furthermore, normal tooth contact is compensated physiologically by 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 (pdl) and the arrangement of 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....
. The truly destructive forces are the parafunctional movements, as found in bruxism, which can cause irreversible damage to the enamel.
Other nonbacterial processes of enamel destruction include
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...
(involving foreign elements, such as toothbrushes),
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...
(involving chemical processes, such as lemon juice), and possibly
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...
(involving compressive and tensile forces).
Though enamel is described as tough, it has a similar brittleness to
glassIn general Glass refers to a solid, brittle, transparent material, commonly used for windows, bottles, or eyewear. Examples of glassy materials include, but are not limited to, soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovy-glass, or aluminium oxynitride. The term glass...
making it unlike other natural crack-resistant
laminate structuresComposite materials are engineered materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure.- History :The most primitive composite materials were straw...
such as
shellAn exoskeleton is an external skeleton that supports and protects an animal's body, in contrast to the internal endoskeleton of, for example, a human. Some animals, such as the tortoise, have both an endoskeleton and an exoskeleton...
and
nacreNacre , also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer. It is very strong, resilient, and iridescent....
potentially vulnerable to
fractureA fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures, or to crystals or crystalline materials, such as gemstones or metal. Sometimes, in crystalline materials, individual crystals...
. In spite of this it can withstand the bite forces as high as 1,000 N many times a day during chewing. This resistance is due in part to the microstructure of enamel which contains processes,
enamel tuftsEnamel tufts are hypomineralized ribbon-like structures that run longitudinally to the tooth axis and extend from the dentinoenamel junction one fifth to a third into the enamel...
, that stabilize the growth of such fractures at the dentinoenamel junction. The configuration of the tooth also acts to reduce the
tensile stressesIn continuum mechanics, the concept of stress, introduced by Cauchy around 1822, is a measure of the average amount of force exerted per unit area of a surface within a deformable body on which internal forces act...
that cause fractures during biting.
Oral hygiene and fluoride
Considering the vulnerability of enamel to demineralization and the daily menace of sugar ingestion, prevention of tooth decay is the best way to maintain the health of teeth. Most countries have wide use of
toothbrushThe toothbrush is an instrument consisting of a small brush on a handle used to clean teeth through tooth brushing. Toothpaste, often containing fluoride, is commonly added to a toothbrush to aid in cleaning. Toothbrushes are offered with varying textures of bristles, and come in many different...
es, which can reduce the number of bacteria and food particles on enamel. Some isolated societies do not have access to toothbrushes, but it is common for those people to use other objects, such as sticks, to clean their teeth. In between two adjacent teeth,
flossDental floss is either a bundle of thin nylon filaments or a plastic ribbon used to remove food and dental plaque from teeth. The floss is gently inserted between the teeth and scraped along the teeth sides, especially close to the gums...
is used to wipe the enamel surfaces free of
plaqueDental plaque is biofilm that builds up on the teeth. If not removed regularly, it can lead to dental cavities or periodontal problems ....
and food particles to discourage bacterial growth. Although neither floss nor toothbrushes can penetrate the deep grooves and pits of enamel, good general oral health habits can usually prevent enough bacterial growth to keep tooth decay from starting.
These methods of
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:...
have been helped greatly by the use 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...
. Fluoride can be found in many locations naturally, such as the ocean and other water sources. Consequently, many seafood dishes contain fluoride. The recommended dosage of fluoride in
drinking waterDrinking water or potable water is water of sufficiently high quality that it can be consumed or used without risk of immediate or long term harm...
depends on air temperature; in the U.S. it ranges from from 0.7 to 1.2 mg/L (milligrams per
liter
). Fluoride catalyzes the diffusion of calcium and phosphate into the tooth surface, which in turn
remineralizesRemineralisation of teeth is a process in which minerals are returned to the molecular structure of the tooth itself. Teeth are porous allowing fluids and demineralisation beneath the surface of the tooth. When demineralised, these pores become larger...
the crystalline structures in a dental cavity. The remineralized tooth surfaces contain fluoridated hydroxyapatite and
fluorapatiteFluorapatite, often with the alternate spelling of fluoroapatite, is a mineral with the formula Ca
53F . Fluorapatite is a hard crystalline solid. Although samples can have various color , the pure mineral is colorless as expected for a material lacking transition metals...
, which resist acid attack much better than the original tooth did.
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 used to help prevent dental decay.
Many groups of people have spoken out against
fluoridated drinking waterWater 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...
. One example used by these advocates is the damage fluoride can do as
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...
. Fluorosis is a condition resulting from the overexposure to fluoride, especially between the ages of 6 months to 5 years, and appears as mottled enamel. Consequently, the teeth look unsightly and, indeed, the incidence of dental decay in those teeth is very small. However, it is important to note that most substances, even beneficial ones, are detrimental when taken in extreme doses. Where fluoride is found naturally in high concentrations, filters are often used to decrease the amount of fluoride in water. For this reason, codes have been developed by dental professionals to limit the amount of fluoride a person should take. These codes are supported by the American Dental Association and the American Academy of Pediatric Dentistry. The acute toxic dose of fluoride is ~5 mg/kg of body weight. Furthermore, whereas topical fluoride, found in toothpaste and mouthwashes, does not cause fluorosis, its effects are also less pervasive and not as long-lasting as those of systemic fluoride, such as when drinking fluorinated water. For instance, all of a tooth's enamel gains the benefits of fluoride when it is ingested systemically, through fluoridated water or salt fluoridation (a common alternative in Europe). Only some of the outer surfaces of enamel can be reached by topical fluoride. Thus, despite fluoridation's detractors, most dental health care professionals and organizations agree that the inclusion of fluoride in public water has been one of the most effective methods of decreasing the prevalence of tooth decay.
Effects of dental procedures
Dental restorations
Most
dental 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...
s involve the removal of enamel. Frequently, the purpose of removal is to gain access to the underlying decay in the dentin or inflammation in the
pulpThe dental pulp is the part in the center of a tooth made up of living soft tissue and cells called odontoblasts.- Anatomy :Each person can have a total of up to 52 pulp organs, 32 in the permanent and 20 in the primary teeth....
. This is typically the case in
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...
restorations and
endodontic treatmentA root canal is the space within the root of a tooth. It is part of a naturally occurring space within a tooth that consists of the pulp chamber , the main canal, and more intricate anatomical branches that may connect the root canals to each other or to the surface of the root.The smaller branches...
.
Nonetheless, enamel can sometimes be removed before there is any decay present. The most popular example is the
dental sealantDental sealants are a dental treatment consisting of applying a plastic material to one or more teeth, for the intended purpose of preventing dental caries or other forms of tooth decay.-Development:...
. The process of placing dental sealants in the past involved removing enamel in the deep fissures and grooves of a tooth and replacing it with a restorative material. Presently, it is more common to only remove decayed enamel if present. In spite of this, there are still cases where deep fissures and grooves in enamel are removed in order to prevent decay, and a sealant may or may not be placed depending on the situation. Sealants are unique in that they are preventative restorations for protection from future decay and have shown to reduce the risk of decay by 55% over 7 years.
Aesthetics is another reason for the removal of enamel. Removing enamel is necessary when placing
crownsA 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...
and
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...
s to enhance the appearance of teeth. In both of these instances, it is important to keep in mind the orientation of enamel rods because it is possible to leave enamel unsupported by underlying dentin, leaving that portion of the prepared teeth more vulnerable to fracture.
Acid-etching techniques
Invented in 1955, acid-etching employs dental etchants and is used frequently when bonding dental restoration to teeth. This is important for long-term use of some materials, such as
compositesDental 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...
and
sealantsDental sealants are a dental treatment consisting of applying a plastic material to one or more teeth, for the intended purpose of preventing dental caries or other forms of tooth decay.-Development:...
. By dissolving minerals in enamel, etchants remove the outer 10 micrometers on the enamel surface and make a porous layer 5–50 micrometers deep. This roughens the enamel microscopically and results in a greater surface area on which to bond.
The effects of acid-etching on enamel can vary. Important variables are the amount of time the etchant is applied, the type of etchant used, and the current condition of the enamel.
There are three types of patterns formed by acid-etching. Type 1 is a pattern where predominantly the enamel rods are dissolved; type 2 is a pattern where predominantly the area around the enamel rods are dissolved; and type 3 is a pattern where there is no evidence left of any enamel rods. Besides concluding that type 1 is the most favorable pattern and type 3 the least, the explanation for these different patterns is not known for certain but is most commonly attributed to different crystal orientation in the enamel.
Tooth whitening
Tooth whitening or
tooth bleachingDental bleaching, also known as tooth whitening, is a common procedure in general dentistry but most especially in the field of cosmetic dentistry. A child's deciduous teeth are generally whiter than the adult teeth that follow. As a person ages the adult teeth often become darker due to changes in...
procedures attempt to lighten a tooth's color in either of two ways: by chemical or mechanical action.
Working chemically, a bleaching agent is used to carry out an oxidation reaction in the enamel and dentin. The agents most commonly used to intrinsically change the color of teeth are
hydrogen peroxideHydrogen peroxide is a very pale blue liquid, slightly more viscous than water, that appears colorless in dilute solution. It is a weak acid, has strong oxidizing properties, and is a powerful bleaching agent. It is used as a disinfectant, antiseptic, oxidizer, and in rocketry as a propellant...
and
carbamide peroxideCarbamide peroxide, also called urea peroxide, urea hydrogen peroxide, and percarbamide, is an oxidising agent, an adduct of hydrogen peroxide and urea. The molecular formula is CH
6N
2O
3, or CH
4N
2O.H
2O
2...
. A tooth whitening product with an overall low pH can put enamel at risk for decay or destruction by demineralization. Consequently, care should be taken and risk evaluated when choosing a product which is very acidic.
Tooth whiteners in toothpastes work through a mechanical action. They have mild abrasives which aid in the removal of stains on enamel. Although this can be an effective method, it does not alter the intrinsic color of teeth.
Microabrasion techniques employ both methods. An acid is used first to weaken the outer 22–27 micrometers of enamel in order to weaken it enough for the subsequent abrasive force. This allows for removal of superficial stains in the enamel. If the discoloration is deeper or in the dentin, this method of tooth whitening will not be successful.
Systemic conditions affecting enamel
There are many different types of
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...
. The hypocalcification type, which is the most common, is an autosomal dominant condition that results in enamel that is not completely mineralized. Consequently, enamel easily flakes off the teeth, which appear yellow because of the revealed dentin. The hypoplastic type is X-linked and results in normal enamel that appears in too little quantity, having the same effect as the most common type.
Chronic bilirubin
encephalopathyEncephalopathy /ɛnˌsɛfəˈlɒpəθi/ literally means disorder or disease of the brain. In modern usage, encephalopathy does not refer to a single disease, but rather to a syndrome of global brain dysfunction; this syndrome can be caused by many different illnesses.-Terminology:In some contexts it...
, which can result from erythroblastosis fetalis, is a disease which has numerous effects on an
infantAn infant or baby is the term used to refer to the very young offspring of humans and other primates.-Infant:The term infant derives from the Latin word infans, meaning "unable to speak."...
, but it can also cause enamel hypoplasia and green staining of enamel.
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 broadly defined to encompass all deviations from normal enamel in its various degrees of absence. The missing enamel could be localized, forming a small pit, or it could be completely absent.
Erythropoietic
porphyriaPorphyrias are a group of inherited or acquired disorders of certain enzymes in the heme biosynthetic pathway . They are broadly classified as acute porphyrias and cutaneous porphyrias, based on the site of the overproduction and accumulation of the porphyrins...
is a genetic disease resulting in the deposition of
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 throughout the body. These deposits also occur in enamel and leave an appearance described as red in color and fluorescent.
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...
leads to mottled enamel and occurs from overexposure to fluoride.
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...
staining leads to brown bands on the areas of developing enamel. Children up to age 8 can develop mottled enamel from taking tetracycline. As a result, tetracycline is contraindicated in
pregnantPregnancy is the carrying of one or more offspring, known as a fetus or embryo, inside the uterus of a female. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets. Human pregnancy is the most studied of all mammalian pregnancies. Obstetrics is the surgical field...
women.
Celiac disease, a disorder characterized by an auto-immune response to gluten, also commonly results in demineralization of the enamel.
In other mammals
For the most part, research has shown that formation in animals is almost identical to formation in humans. The enamel organ, including the dental papilla, and ameloblasts function similarly. The variations of enamel that are present are infrequent but sometimes important. Differences exist, certainly, in the morphology, number, and types of teeth among animals.
Dogs are less likely than humans to have tooth decay due to the high pH of dog saliva, which prevents an acidic environment from forming and the subsequent demineralization of enamel which would occur. In the event that tooth decay does occur (usually from trauma), dogs can receive dental fillings just as humans do. Similar to human teeth, the enamel of dogs is vulnerable to
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...
staining. Consequently, this risk must be accounted for when tetracycline antibiotic therapy is administered to young dogs. Enamel hypoplasia may also occur in dogs.
The mineral distribution in
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....
enamel is different from that of monkeys, dogs, pigs, and humans. In
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...
, the enamel and dentin layers are intertwined with each other, which increases the strength and decreases the wear rate of those teeth.
See also
- 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...
- Amorphous calcium and phosphate
Amorphous calcium phosphate is a substance used as a dental treatment. Calcium and phosphate are natural building blocks of teeth, and when present in insufficient amounts, there can be sensitivity after procedures such as dental bleaching or professional dental cleaning...
- Perikymata
- Ivory
Ivory is formed from dentine and constitutes the bulk of the teeth and tusks of animals such as the elephant, hippopotamus, walrus, mammoth and narwhal....
- Remineralisation of teeth
Remineralisation of teeth is a process in which minerals are returned to the molecular structure of the tooth itself. Teeth are porous allowing fluids and demineralisation beneath the surface of the tooth. When demineralised, these pores become larger...
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