Tooth enamel
Overview
 
Tooth enamel, along with dentin
Dentin
Dentine 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...

, cementum
Cementum
Cementum 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. These cementoblasts develop from undifferentiated mesenchymal cells in the connective tissue of the dental...

, and dental pulp
Pulp (tooth)
The dental pulp is the part in the center of a tooth made up of living connective 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 that make up the tooth
Tooth
Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...

 in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of shark
Shark
Sharks 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....

s. It is the normally visible dental tissue of a tooth because it covers the anatomical crown and must be supported by underlying dentin. Ninety-six percent of enamel consists of mineral, with water and organic material composing the rest.
Encyclopedia
Tooth enamel, along with dentin
Dentin
Dentine 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...

, cementum
Cementum
Cementum 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. These cementoblasts develop from undifferentiated mesenchymal cells in the connective tissue of the dental...

, and dental pulp
Pulp (tooth)
The dental pulp is the part in the center of a tooth made up of living connective 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 that make up the tooth
Tooth
Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...

 in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of shark
Shark
Sharks 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....

s. It is the normally visible dental tissue of a tooth because it covers the anatomical crown and must be supported by underlying dentin. Ninety-six percent of enamel consists of mineral, with water and organic material composing the rest. In humans, enamel varies in thickness over the surface of the tooth, often thickest at the cusp
Cusp (dentistry)
A 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 with the cementum
Cementum
Cementum 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. These cementoblasts develop from undifferentiated mesenchymal cells in the connective tissue of the dental...

 at the cementoenamel junction
Cementoenamel junction
The cementoenamel junction, frequently abbreviated as the CEJ, is an anatomical border identified on a tooth. It is the location where the enamel, which covers the anatomical crown of a tooth, and the cementum, which covers the anatomical root of a tooth, meet...

 (CEJ).

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 material underneath the enamel strongly affects the appearance
Human physical appearance
Human physical appearance refers to the outward phenotype or look of human beings. There are infinite variations in human phenotypes, though society reduces the variability to distinct categories...

 of a tooth. The enamel on primary teeth has a more opaque crystalline form and thus appears whiter than on permanent teeth.

Enamel's primary mineral is hydroxylapatite
Hydroxylapatite
Hydroxylapatite, 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 hydroxyl endmember of the complex apatite group...

, which is a crystal
Crystal
A 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 known as crystallography...

line calcium phosphate
Calcium phosphate
Calcium 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 ....

. 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 scale
Mohs scale of mineral hardness
The 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 geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...

 and a Young's modulus
Young's modulus
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...

 of 83 GPa. Dentin, less mineralized and less brittle, 3–4 in hardness, compensates for enamel and is necessary as a support. On radiographs, the differences in the mineralization of different portions of the tooth and surrounding periodontium can be noted; enamel appears more radiopaque (or lighter) than either dentin and pulp since it is denser than both, both of which appear more radiolucent (or darker).

Enamel does not contain collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...

, as found in other hard tissues such as dentin and bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They 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...

, but it does contain two unique classes of protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s - amelogenin
Amelogenin
Amelogenin 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 enamelin
Enamelin
Enamelin was described in older literature as an EDTA soluble enamel protein. It accounts for the organic portion of enamel, which represents 4% of enamel's mass. 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 for minerals to form on, among other functions. Once it is mature, enamel is almost totally absent of the softer organic matter. Enamel is avascular and has no nerve supply within it and is not renewed, however, it is not a static tissue as it can undergo mineralization changes.

Structure

The basic unit of enamel is called an enamel rod
Enamel rod
An Enamel rod is the basic unit of tooth enamel. 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
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

 in diameter an enamel rod, formally 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' process
Tomes' process
Tomes' 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 enamel, 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(65 degrees) 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 enamel
Interrod enamel
Interrod 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 histologic
Histology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination 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 sheath
Rod sheath
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. As a result of this space,...

.

Striae of Retzius
Striae of Retzius
The striae of Retzius are incremental growth lines or bands seen in tooth enamel and are the result of disrupted enamel development.-Appearance:...

 are incremental lines that appear brown in a stained section of mature enamel. These lines are composed of bands or cross striations on the enamel rods that, when combined in longitudinal sections, seem to traverse the enamel rods. Formed from changes in diameter of Tomes’ processes, these incremental lines demonstrate the growth of enamel, similar to the annual rings on a tree on transverse sections of enamel. The exact mechanism that produces these lines is still being debated. Some researchers hypothesize that the lines are a result of the diurnal, or 24 hour, metabolic rhythm of the ameloblasts producing the enamel matrix, which consists of an active secretory work period followed by an inactive rest period during tooth development. Thus, each band on the enamel rod demonstrates the work/rest pattern of the ameloblasts that generally occurs over a span of a week. Perikymata which are associated with the Striae are shallow grooves noted clinically on the nonmasticatory surfaces of some teeth in the oral cavity. Perikymata are usually lost through tooth wear, except on the protected cervical regions of some teeth, especially the permanent maxillary central incisors, canines, and first premolars, and may be confused as dental calculus. Darker than the other incremental lines, the neonatal line
Neonatal line
The 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 incremental line that separates enamel formed before and after birth. The neonatal line marks the stress or trauma experienced by the ameloblasts during birth, again illustrating the sensitivity of the ameloblasts as they form enamel matrix. As one would expect, the neonatal line is found in all primary teeth and in the larger cusps of the permanent first molars. They contain irregular structures of enamel prisms with disordered crystal arrangements basically formed by the abrupt bending of the prisms towards the root; usually, the prisms gradually bent back again to regain their previous orientation.

Gnarled enamel
Gnarled enamel
Gnarled 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.

Enamel is covered by various structures in relation to the development of tooth:
Nasmyth's membrane
James Nasmyth
James Hall Nasmyth was a Scottish engineer and inventor famous for his development of the steam hammer. He was the co-founder of Nasmyth, Gaskell and Company manufacturers of machine tools...

 or enamel cuticle, structure of embryological origin is composed of keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...

 which gives rise to the enamel organ
Enamel organ
The 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...

.
Acquired pellicle, structure acquired after tooth eruption is composed of food debris, calculus, dental plaque (organic film).

Development

Enamel formation is part of the overall process of tooth development
Tooth development
Tooth 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 organ
Enamel organ
The 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 lamina
Dental lamina
The 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 papilla
Dental papilla
The 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.

Amelogenesis
Amelogenesis
Amelogenesis is the formation of enamel on teeth and occurs during the crown stage of tooth development after dentinogenesis, which is the formation of dentine. Although dentine must be present for enamel to be formed, it is also true that ameloblasts must be present in order for dentinogenesis to...

, 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 cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, 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 phosphatase
Alkaline phosphatase
Alkaline 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...

. 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 amelogenin
Amelogenin
Amelogenin 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, ameloblastin
Ameloblastin
Ameloblastin, 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 secretory to late maturation stages of amelogenesis...

s, enamelin
Enamelin
Enamelin was described in older literature as an EDTA soluble enamel protein. It accounts for the organic portion of enamel, which represents 4% of enamel's mass. It turned out in recent research to be albumin derived from blood contamination....

s, and tuftelin
Tuftelin
Tuftelin 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 tobacco
Tobacco
Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...

, coffee
Coffee
Coffee is a brewed beverage with a dark,init brooo acidic flavor prepared from the roasted seeds of the coffee plant, colloquially called coffee beans. The beans are found in coffee cherries, which grow on trees cultivated in over 70 countries, primarily in equatorial Latin America, Southeast Asia,...

, and tea
Tea
Tea is an aromatic beverage prepared by adding cured leaves of the Camellia sinensis plant to hot water. The term also refers to the plant itself. After water, tea is the most widely consumed beverage in the world...

. The staining occurs in the interprismatic region internally on the enamel, which causes the tooth to appear darker or more yellow overall. In a perfect state, enamel is colorless, but it does reflect underlying tooth structure with its stains since light reflection properties of the tooth are low.

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 caries
Dental caries
Dental caries, also known as tooth decay or a cavity, is an irreversible infection usually bacterial in origin that causes demineralization of the hard tissues and destruction of the organic matter of the tooth, usually by production of acid by hydrolysis of the food debris accumulated on the...

, 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 candies
Candy
Candy, specifically sugar candy, is a confection made from a concentrated solution of sugar in water, to which flavorings and colorants are added...

, soft drink
Soft drink
A soft drink is a non-alcoholic beverage that typically contains water , a sweetener, and a flavoring agent...

s, and even fruit juices
Juice
Juice is the liquid that is naturally contained in fruit or vegetable tissue.Juice is prepared by mechanically squeezing or macerating fruit or vegetable flesh without the application of heat or solvents. For example, orange juice is the liquid extract of the fruit of the orange tree...

 play a significant role in tooth decay, and consequently in enamel destruction. The mouth contains a great number and variety of bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

, and when sucrose
Sucrose
Sucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...

, the most common of sugars, coats the surface of the mouth, some intraoral bacteria interact with it and form lactic acid
Lactic acid
Lactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...

, 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 mutans
Streptococcus mutans
Streptococcus mutans is a facultatively aerobic, Gram-positive coccus-shaped bacterium commonly found in the human oral cavity and is a significant contributor to tooth decay.The microbe was first described by J Kilian Clarke in 1924.-Introduction:...

, 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 explorer
Explorer (dental)
100px|right|thumb|A No. 23 explorer, also known as a 'sickle probe'A dental explorer or sickle probe 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 cariogenicity
Caries
Caries 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 microorganism disease. A disease that involves caries is mastoiditis, an inflammation of the mastoid process, in which the...

, 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 dessert
Dessert
In cultures around the world, dessert is a course that typically comes at the end of a meal, usually consisting of sweet food. The word comes from the French language as dessert and this from Old French desservir, "to clear the table" and "to serve." Common Western desserts include cakes, biscuits,...

 at dinner time than to snack on a bag of candy
Candy
Candy, 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. Bruxism
Bruxism
Bruxism is characterized by the grinding of the teeth and typically includes 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 attrition
Attrition (dental)
Attrition 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. Erosion is a very important contributing factor to...

, 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 ligament
Periodontal ligament
The periodontal fiber or 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 occlusion
Occlusion (dentistry)
Occlusion, 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 abrasion
Abrasion (dental)
Abrasion 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), erosion
Erosion (dental)
Acid 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 abfraction
Abfraction
Abfraction is the loss of tooth structure from flexural forces. It is hypothesized that enamel, especially at the cementoenamel junction , undergo this pattern of destruction by separating the enamel rods....

 (involving compressive and tensile forces).

Though enamel is described as tough, it has a similar brittleness to glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

  making it, unlike other natural crack-resistant laminate structures
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...

 such as shell
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...

 and nacre
Nacre
Nacre , also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer; it is also what makes up pearls. It is very strong, resilient, and iridescent....

, potentially vulnerable to fracture
Fracture
A 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...

. 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 tufts
Enamel tufts
Enamel 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 stresses
Stress (physics)
In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...

 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 toothbrush
Toothbrush
The toothbrush is an oral hygiene instrument used to clean the teeth and gums that consists of a head of tightly clustered bristles mounted on a handle, which facilitates the cleansing of hard-to-reach areas of the mouth. Toothpaste, which often contains fluoride, is commonly used in conjunction...

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, floss
Dental floss
Dental floss is made of 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. Dental floss may be flavored or unflavored, and...

 is used to wipe the enamel surfaces free of plaque
Dental plaque
Dental plaque is a biofilm, usually a pale yellow, that develops naturally on the teeth. Like any biofilm, dental plaque is formed by colonizing bacteria trying to attach themselves to a smooth surface...

 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 hygiene
Oral hygiene
Teeth cleaning is part of oral hygiene and involves the removal of dental plaque from teeth with the intention of preventing cavities , gingivitis, and periodontal disease. People routinely clean their own teeth by brushing and interdental cleaning, and dental hygienists can remove hardened...

 have been helped greatly by the use of fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...

. Fluoride can be found in many locations naturally, such as the ocean and other water sources. Naturally occurring calcium fluoride is not the same as sodium fluoride, a byproduct of the fertilizer industry and the fluoride that is added to drinking water. The recommended dosage of fluoride in drinking water
Drinking water
Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...

 depends on air temperature; in the U.S. it ranges from 0.7 to 1.2 mg/L
Litér
- External links :*...

. Fluoride catalyzes the diffusion of calcium and phosphate into the tooth surface, which in turn remineralizes
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...

 the crystalline structures in a dental cavity. The remineralized tooth surfaces contain fluoridated hydroxyapatite and fluorapatite
Fluorapatite
Fluorapatite, often with the alternate spelling of fluoroapatite, is a mineral with the formula Ca53F . 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 therapy
Fluoride therapy
Fluoride 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 water
Water fluoridation
Water 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 fluorosis
Dental fluorosis
Dental fluorosis is a developmental disturbance of dental enamel caused by excessive exposure to high concentrations of fluoride during tooth development. The risk of fluoride overexposure occurs between the ages of 3 months and 8 years. In its mild forms , fluorosis often appears as unnoticeable,...

. 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, although the incidence of dental decay in those teeth is very small. It is important, however, to note that all 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. It is also claimed, 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) and that only some of the outer surfaces of enamel can be reached by topical fluoride. However, since there is no connection between the bloodstream and the enamel, ingested (systemic) fluoride works topical as well: With raised fluoride blood levels, fluoride levels in saliva increase also. Here fluoride mediates the remineralization with fluorapatite. The cavity-prevention mechanism of systemic fluoride is the same as that of fluoride from tooth paste, albeit the former usually results in prolonged fluoride presence in saliva which in turn may result in a deeper fluorapatite remineralisation. 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 restoration
Dental restoration
A 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 pulp
Pulp (tooth)
The dental pulp is the part in the center of a tooth made up of living connective 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 amalgam
Amalgam (dentistry)
Amalgam is an alloy containing mercury. The term is commonly used for the amalgam employed as material for dental fillings, which consists of mercury , silver , tin , copper , and other trace metals...

 restorations and endodontic treatment
Endodontic therapy
Endodontic therapy is a sequence of treatment for the pulp of a tooth which results in the elimination of infection and protection of the decontaminated tooth from future microbial invasion...

.

Nonetheless, enamel can sometimes be removed before there is any decay present. The most popular example is the dental sealant
Dental sealant
Dental 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 crowns
Crown (dentistry)
A crown is a type of dental restoration which completely caps or encircles a tooth or dental implant. Crowns are often needed when a large cavity threatens the ongoing health of a tooth. They are typically bonded to the tooth using a dental cement. Crowns can be made from many materials, which...

 and veneer
Veneer (dentistry)
In 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 dental 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 composites
Dental composite
Dental 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, insensitive to dehydration, easy to manipulate and reasonably inexpensive...

 and sealants
Dental sealant
Dental 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 bleaching
Tooth bleaching
Dental 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 peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...

 and carbamide peroxide
Carbamide peroxide
Carbamide peroxide, also called urea peroxide, urea hydrogen peroxide , and percarbamide, an adduct of hydrogen peroxide and urea. Like hydrogen peroxide, it is an oxidizer. This compound is a white crystalline solid which dissolves in water to give free hydrogen peroxide; the solubility of...

. Oxygen radicals from the peroxide in the whitening agents contact the stains in the interprismatic spaces within the enamel layer. When this occurs, stains will be bleached and the teeth now appear lighter in color. Teeth not only appear whiter but also reflect light in increased amounts, which makes the teeth appear brighter as well. Studies show that whitening does not produce any ultrastructural or microhardness changes in the dental tissues. Studies show that patients who have whitened their teeth take better care of them. However, 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 imperfecta
Amelogenesis imperfecta
Amelogenesis 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.

Gastroesophageal reflux disease
Gastroesophageal reflux disease
Gastroesophageal reflux disease , gastro-oesophageal reflux disease , gastric reflux disease, or acid reflux disease is chronic symptoms or mucosal damage caused by stomach acid coming up from the stomach into the esophagus...

 can also lead to enamel loss, as acid refluxes up the esophagus and into the mouth, occurring most during overnight sleep.

Chronic bilirubin encephalopathy
Encephalopathy
Encephalopathy 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:...

, which can result from erythroblastosis fetalis, is a disease which has numerous effects on an infant
Infant
A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...

, but it can also cause enamel hypoplasia and green staining of enamel.

Enamel hypoplasia
Enamel hypoplasia
Enamel 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 porphyria
Porphyria
Porphyrias are a group of inherited or acquired disorders of certain enzymes in the heme bio-synthetic 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 porphyrin
Porphyrin
Porphyrins are a group of organic compounds, many naturally occurring. One of the best-known porphyrins is heme, the pigment in red blood cells; heme is a cofactor of the protein hemoglobin. Porphyrins are heterocyclic macrocycles composed of four modified pyrrole subunits interconnected at...

s throughout the body. These deposits also occur in enamel and leave an appearance described as red in color and fluorescent.

Fluorosis
Dental fluorosis
Dental fluorosis is a developmental disturbance of dental enamel caused by excessive exposure to high concentrations of fluoride during tooth development. The risk of fluoride overexposure occurs between the ages of 3 months and 8 years. In its mild forms , fluorosis often appears as unnoticeable,...

 leads to mottled enamel and occurs from overexposure to fluoride.

Tetracycline 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 pregnant
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

 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 tetracycline 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 rodent
Rodent
Rodentia 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 teeth
Horse teeth
Horses' 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.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK