![Molarsindevelopment11-24-05](https://upload.wikimedia.org/wikipedia/commons/1/19/Molarsindevelopment11-24-05.jpg)
Tooth development or odontogenesis is the complex process by which
teeth
A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
form from
embryonic cell
In biology, a blastomere is a type of Cell (biology), cell produced by cleavage (embryo), cell division (cleavage) of the zygote after fertilization; blastomeres are an essential part of blastula formation, and blastocyst formation in mammals.
Hum ...
s,
grow, and erupt into the
mouth. For
human teeth
The human teeth function to mechanically break down items of food by cutting and crushing them in preparation for swallowing and digesting. As such, they are considered part of the human digestive system. Humans have four types of teeth: inci ...
to have a healthy
oral
The word oral may refer to:
Relating to the mouth
* Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid
**Oral administration of medicines
** Oral examination (also known as an oral exam or or ...
environment, all parts of the tooth must develop during appropriate stages of
fetal development
Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal devel ...
.
Primary (baby) teeth start to form between the sixth and eighth week of prenatal development, and
permanent teeth
Permanent teeth or adult teeth are the second set of teeth formed in diphyodont mammals. In humans and old world simians, there are thirty-two permanent teeth, consisting of six maxillary and six mandibular molars, four maxillary and four mandibul ...
begin to form in the twentieth week.
[Ten Cate's Oral Histology, Nanci, Elsevier, 2013, pages 70-94] If teeth do not start to develop at or near these times, they will not develop at all, resulting in
hypodontia
Hypodontia is defined as the developmental absence of one or more teeth excluding the third molars. It is one of the most common dental anomalies, and can have a negative impact on function, and also appearance. It rarely occurs in primary teet ...
or
anodontia
Anodontia is a rare genetic disorder characterized by the congenital absence of all primary or permanent teeth. It is divided into two subsections, complete absence of teeth or only some absence of teeth. It is associated with the group of skin ...
.
A significant amount of research has focused on determining the processes that initiate tooth development. It is widely accepted that there is a factor within the tissues of the first
pharyngeal arch
The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arche ...
that is necessary for the development of teeth.
Overview
![Toothbud11-19-05labeled](https://upload.wikimedia.org/wikipedia/commons/a/aa/Toothbud11-19-05labeled.jpg)
The tooth germ is an aggregation of cells that eventually forms a tooth.
[University of Texas Medical Branch.] These cells are derived from the
ectoderm
The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from t ...
of the first pharyngeal arch and the
ectomesenchyme
Ectomesenchyme has properties similar to mesenchyme. The origin of the ectomesenchyme is disputed. It is either like the mesenchyme, arising from mesodermic cells, or conversely arising from neural crest cells. The neural crest is a critical group ...
of the
neural crest
Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm germ layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, per ...
.
The tooth germ is organized into three parts: the
enamel organ
The enamel organ, also known as the dental organ, is a cellular aggregation seen in a developing tooth and it lies above the dental papilla. The enamel organ which is differentiated from the primitive oral epithelium lining the stomodeum.The enam ...
, the
dental papilla
In embryology and prenatal development, 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 ...
and the
dental sac or follicle.
The ''enamel organ '' is composed of the
outer enamel epithelium
The outer enamel epithelium, also known as the external enamel epithelium, is a layer of cuboidal cells located on the periphery of the enamel organ in a developing tooth. This layer is first seen during the bell stage.
The rim of the enamel org ...
,
inner enamel epithelium
The inner enamel epithelium, also known as the internal enamel epithelium, is a layer of columnar cells located on the rim nearest the dental papilla of the enamel organ in a developing tooth. This layer is first seen during the cap stage, in wh ...
,
stellate reticulum
The stellate reticulum is a group of cells located in the center of the enamel organ of a developing tooth. These cells are star-shaped and synthesize glycosaminoglycans. As glycosaminoglycans are produced, water
Water (chemical formula ...
and
stratum intermedium
The stratum intermedium in a developing tooth is a layer of two or three cells between the inner enamel epithelium and the newly forming cells of the stellate reticulum. It first appears during the early bell stage of tooth development, at aroun ...
.
These cells give rise to
ameloblast
Ameloblasts are cells present only during tooth development that deposit tooth enamel, which is the hard outermost layer of the tooth forming the surface of the crown.
Structure
Each ameloblast is a columnar cell approximately 4 micrometers in ...
s, which produce enamel and become a part of the
reduced enamel epithelium The reduced enamel epithelium, sometimes called reduced dental epithelium, overlies a developing tooth and is formed by two layers: a layer of ameloblast cells and the adjacent layer of cuboidal cells (outer enamel epithelium) from the dental lam ...
(REE) after maturation of the enamel. The location where the outer enamel epithelium and inner enamel epithelium join is called the
cervical loop
The cervical loop is the location on an enamel organ in a developing tooth where the outer enamel epithelium and the inner enamel epithelium join. The cervical loop is a histologic term indicating a specific epithelial structure at the apical s ...
.
The growth of cervical loop cells into the deeper tissues forms
Hertwig Epithelial Root Sheath, which determines the root shape of the tooth. During tooth development there are strong similarities between
keratin
Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...
ization and
amelogenesis
Amelogenesis is the formation of enamel on teeth and begins when the crown is forming during the advanced bell stage of tooth development after dentinogenesis forms a first layer of dentin. Dentin must be present for enamel to be formed. Amelob ...
. Keratin is also present in epithelial cells of tooth germ and a thin film of keratin is present on a recently erupted tooth (
Nasmyth's membrane or enamel cuticle).
The ''dental papilla'' contains cells that develop into
odontoblast
In vertebrates, an odontoblast is a cell of neural crest origin that is part of the outer surface of the dental pulp, and whose biological function is dentinogenesis, which is the formation of dentin, the substance beneath the tooth enamel on t ...
s, which are dentin-forming cells.
Additionally, the junction between the dental papilla and inner enamel epithelium determines the crown shape of a tooth.
Mesenchymal
Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every ...
cells within the dental papilla are responsible for formation of tooth
pulp
Pulp may refer to:
* Pulp (fruit), the inner flesh of fruit
Engineering
* Dissolving pulp, highly purified cellulose used in fibre and film manufacture
* Pulp (paper), the fibrous material used to make paper
* Molded pulp, a packaging material
...
.
The ''dental sac or follicle'' gives rise to three important entities:
cementoblast
A cementoblast is a biological cell that forms from the follicular cells around the root of a tooth, and whose biological function is cementogenesis, which is the formation of cementum (hard tissue that covers the tooth root). The mechanism of di ...
s,
osteoblasts, and
fibroblasts. Cementoblasts form the
cementum
Cementum is a specialized calcified substance covering the root of a tooth. The cementum is the part of the periodontium that attaches the teeth to the alveolar bone by anchoring the periodontal ligament.Illustrated Dental Embryology, Histology, a ...
of a tooth. Osteoblasts give rise to the
alveolar bone
The alveolar process () or alveolar bone is the thickened ridge of bone that contains the tooth sockets on the jaw bones (in humans, the maxilla and the mandible). The structures are covered by gums as part of the oral cavity.
The synonymous t ...
around the roots of teeth. Fibroblasts are involved developing the
periodontal ligament
The 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. It inserts into root cementum one side and onto alveolar b ...
which connect teeth to the alveolar bone through cementum.
NGF-R is present in the condensing ectomesenchymal cells of the dental papilla in the early cap stage tooth germ and plays multiple roles during morphogenetic and cytodifferentiation events in the tooth. There is a relationship between
tooth agenesis and absence of the peripheral
trigeminal nerve
In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chew ...
(see
Hypodontia
Hypodontia is defined as the developmental absence of one or more teeth excluding the third molars. It is one of the most common dental anomalies, and can have a negative impact on function, and also appearance. It rarely occurs in primary teet ...
).
All stages (bud, cap, bell, crown), growth and morphogenesis of the teeth are regulated by a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
called
sonic hedgehog.
Various
phenotypic
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
inputs modulate the size of the teeth.
Parathyroid hormone
Parathyroid hormone (PTH), also called parathormone or parathyrin, is a peptide hormone secreted by the parathyroid glands that regulates the serum calcium concentration through its effects on bone, kidney, and intestine.
PTH influences bone ...
is required for
tooth eruption
Tooth eruption is a process in tooth development in which the teeth enter the mouth and become visible. It is currently believed that the periodontal ligament plays an important role in tooth eruption. The first human teeth to appear, the decidu ...
.
Human tooth development timeline
The following tables present the development timeline of human teeth. Times for the initial calcification of primary teeth are for weeks ''in utero''. Abbreviations: wk = weeks; mo = months; yr = years.
Stages
![Toothbud annot](https://upload.wikimedia.org/wikipedia/commons/c/cd/Toothbud_annot.gif)
Tooth development is commonly divided into the following stages: the initiation stage, the bud stage, the cap stage, the bell stage, and finally maturation. The staging of tooth development is an attempt to categorize changes that take place along a continuum; frequently it is difficult to decide what stage should be assigned to a particular developing tooth. This determination is further complicated by the varying appearance of different histologic sections of the same developing tooth, which can appear to be different stages.
Initiation Stage
One of the earliest signs in the formation of a tooth that can be seen microscopically is the distinction between the
vestibular lamina and the
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 (in humans) at the sixth week in utero or three weeks after the rupture of th ...
. It occurs in the sixth to seventh week of the embryonic life. The dental lamina connects the developing tooth bud to the
epithelial
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercell ...
layer of the mouth for a significant time. This is regarded as the initiation stage.
Bud stage
The bud stage is characterized by the appearance of a tooth bud without a clear arrangement of cells. The stage technically begins once epithelial cells proliferate into the
ectomesenchyme
Ectomesenchyme has properties similar to mesenchyme. The origin of the ectomesenchyme is disputed. It is either like the mesenchyme, arising from mesodermic cells, or conversely arising from neural crest cells. The neural crest is a critical group ...
of the jaw.
Typically, this occurs when the fetus is around 8 weeks old.
The tooth bud itself is the group of cells at the periphery of the dental lamina.
Along with the formation of the dental lamina, 10 round epithelial structures, each referred to as a bud, develop at the distal aspect of the dental lamina of each arch. These correspond to the 10 primary teeth of each dental arch, and they signify the bud stage of tooth development. Each bud is separated from the ectomesenchyme by a basement membrane. Ectomesenchymal cells congregate deep to the bud, forming a cluster of cells, which is the initiation of the condensation of the ectomesenchyme. The remaining ectomesenchymal cells are arranged in a more or less haphazardly uniform fashion.
Cap stage
![capstage11-23-05](https://upload.wikimedia.org/wikipedia/commons/5/50/Capstage11-23-05.jpg)
The first signs of an arrangement of cells in the tooth bud occur in the cap stage. A small group of ectomesenchymal cells stops producing
extracellular
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
substances, which results in an aggregation of these cells called the dental papilla. At this point, the tooth bud grows around the ectomesenchymal aggregation, taking on the appearance of a cap, and becomes the enamel (or dental) organ covering the dental papilla. A condensation of ectomesenchymal cells called the dental sac or follicle surrounds the enamel organ and limits the dental papilla. Eventually, the enamel organ will produce enamel, the dental papilla will produce dentin and pulp, and the dental sac will produce all the supporting structures of a tooth, the periodontium.
Bell stage
The bell stage is known for the histodifferentiation and morphodifferentiation that takes place. The dental organ is bell-shaped during this stage, and the majority of its cells are called stellate reticulum because of their star-shaped appearance. The bell stage is divided into the ''early bell stage'' and the ''late bell stage''.
Cells on the periphery of the enamel organ separate into four important layers. Cuboidal cells on the periphery of the dental organ are known as outer enamel epithelium (OEE).
The columnar cells of the enamel organ adjacent to the enamel papilla are known as inner enamel epithelium (IEE). The cells between the IEE and the stellate reticulum form a layer known as the stratum intermedium. The rim of the enamel organ where the outer and inner enamel epithelium join is called the ''cervical loop''.
In summary, the layers in order of innermost to outermost consist of dentin, enamel (formed by IEE, or 'ameloblasts', as they move outwards/upwards), inner enamel epithelium and stratum intermedium (stratified cells that support the synthetic activity of the inner enamel epithelium) What follows is part of the initial 'enamel organ', the center of which is made up of stellate reticulum cells that serve to protect the enamel organ. This is all encased by the OEE layer.
Other events occur during the bell stage. The dental lamina disintegrates, leaving the developing teeth completely separated from the
epithelium
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
of the oral cavity; the two will not join again until the final eruption of the tooth into the mouth.
![Latebellstage11-18-05](https://upload.wikimedia.org/wikipedia/commons/c/cb/Latebellstage11-18-05.jpg)
The crown of the tooth, which is influenced by the shape of the inner enamel epithelium, also takes shape during this stage. Throughout the mouth, all teeth undergo this same process; it is still uncertain why teeth form various crown shapes—for instance, incisors versus canines. There are two dominant
hypotheses. The "field model" proposes there are components for each type of tooth shape found in the ectomesenchyme during tooth development. The components for particular types of teeth, such as incisors, are localized in one area and dissipate rapidly in different parts of the mouth. Thus, for example, the "incisor field" has factors that develop teeth into incisor shape, and this field is concentrated in the central incisor area, but decreases rapidly in the canine area.
The other dominant hypothesis, the "clone model", proposes that the epithelium programs a group of ectomesenchymal cells to generate teeth of particular shapes. This group of cells, called a clone, coaxes the dental lamina into tooth development, causing a tooth bud to form. Growth of the dental lamina continues in an area called the "progress zone". Once the progress zone travels a certain distance from the first tooth bud, a second tooth bud will start to develop. These two models are not necessarily mutually exclusive, nor does widely accepted dental science consider them to be so: it is postulated that both models influence tooth development at different times.
Other structures that may appear in a developing tooth in this stage are
enamel knot In tooth development, the enamel knot is a localization of cells on an enamel organ that appear thickened in the center of the inner enamel epithelium. The enamel knot is frequently associated with an enamel cord. It is formed in the cap stage and u ...
s,
enamel cord The enamel cord, also called enamel septum, is a localization of cells on an enamel organ that appear from the outer enamel epithelium to an enamel knot. The function of the enamel cord and the enamel knot is not known, but they are believed to p ...
s, and
enamel niche.
Advanced bell stage
Hard tissues, including enamel and dentin, develop during the next stage of tooth development. This stage is called the crown, or maturation stage, by some researchers. Important cellular changes occur at this time. In prior stages, all of the IEE cells were dividing to increase the overall size of the tooth bud, but rapid dividing, called
mitosis
In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...
, stops during the crown stage at the location where the
cusps of the teeth form. The first mineralized hard tissues form at this location. At the same time, the IEE cells change in shape from cuboidal to columnar and become preameloblasts. The
nuclei of these cells move closer to the stratum intermedium and away from the dental papilla as they become polarized.
![Crosssectiontooth11-24-05](https://upload.wikimedia.org/wikipedia/commons/c/c5/Crosssectiontooth11-24-05.jpg)
The adjacent layer of cells in the dental papilla suddenly increases in size and
differentiates into odontoblasts, which are the cells that form dentin. Researchers believe that the odontoblasts would not form if it were not for the changes occurring in the IEE. As the changes to the IEE and the formation of odontoblasts continue from the tips of the cusps, the odontoblasts secrete a substance, an
organic matrix
Organic may refer to:
* Organic, of or relating to an organism, a living entity
* Organic, of or relating to an anatomical organ (anatomy), organ
Chemistry
* Organic matter, matter that has come from a once-living organism, is capable of decay or ...
, into their immediate surrounding. The organic matrix contains the material needed for dentin formation. As odontoblasts deposit organic matrix termed predentin, they migrate toward the center of the dental papilla. Thus, unlike enamel, dentin starts forming in the surface closest to the outside of the tooth and proceeds inward. Cytoplasmic extensions are left behind as the odontoblasts move inward. The unique, tubular microscopic appearance of dentin is a result of the formation of dentin around these extensions.
After dentin formation begins, the cells of the IEE secrete an organic matrix against the dentin. This matrix immediately mineralizes and becomes the initial layer of the tooth's enamel. Outside the dentin are the newly formed ameloblasts in response to the formation of dentin, which are cells that continue the process of enamel formation; therefore, enamel formation moves outwards, adding new material to the outer surface of the developing tooth.
Hard tissue formation
Enamel
Enamel formation is called amelogenesis and occurs in the crown stage (advanced bell stage) of tooth development. "Reciprocal induction" governs the relationship between the formation of dentin and enamel; dentin formation must always occur before enamel formation. Generally, enamel formation occurs in two stages: the secretory and maturation stages. Proteins and an organic matrix form a partially mineralized enamel in the secretory stage; the maturation stage completes enamel mineralization.
In the secretory stage, ameloblasts release enamel proteins that contribute to the enamel matrix, which is then partially mineralized by the enzyme
alkaline phosphatase. This mineralized phase occurs very early around the 3rd or 4th month of pregnancy. This marks the first appearance of enamel in the body. Ameloblasts make enamel at the location of where the cusps of the teeth are located. Enamel grows outwards, away from the center of the tooth.
In the maturation stage, the ameloblasts transport some of the substances used in enamel formation out of the enamel. Thus, the function of ameloblasts changes from enamel production, as occurs in the secretory stage, to transportation of substances. Most of the materials transported by ameloblasts in this stage are proteins used to complete mineralization. The important proteins involved are
amelogenin
Amelogenins are a group of protein isoforms produced by alternative splicing or proteolysis from the ''AMELX'' gene, on the X chromosome, and also the ''AMELY'' gene in males, on the Y chromosome. They are involved in amelogenesis, the developme ...
s,
ameloblastin
Ameloblastin (abbreviated AMBN and also known as Sheathlin or Amelin) is an enamel matrix protein that in humans is encoded by the AMBN gene.
Function
Ameloblastin is a specific protein found in tooth enamel. Although less than 5% of enamel con ...
s,
enamelin
Enamelin is an enamel matrix protein (EMPs), that in humans is encoded by the ''ENAM'' gene. It is part of the non- amelogenins, which comprise 10% of the total enamel matrix proteins. It is one of the key proteins thought to be involved in ame ...
s, and
tuftelin Tuftelin is an acidic phosphorylated glycoprotein found in tooth enamel. In humans, the Tuftelin protein is encoded by the ''TUFT1'' gene. It is an acidic protein that is thought to play a role in dental enamel mineralization and is implicated in ...
s. By the end of this stage, the enamel has completed its mineralization.
A residue may form on newly erupted teeth of both dentitions that may leave the teeth extrinsically stained. This green-gray residue, Nasmyth membrane, consists of the fused tissue of the reduced enamel epithelium and oral epithelium, as well as the dental cuticle placed by the ameloblasts on the newly formed outer enamel surface. Nasmyth membrane then easily picks up stain from food debris and is hard to remove except by selective polishing. The child's supervising adults may need reassurance that it is only an extrinsic stain on a child's newly erupted teeth.
Patients with
osteopetrosis
Osteopetrosis, literally "stone bone", also known as marble bone disease or Albers-Schönberg disease, is an extremely rare inherited disorder whereby the bones harden, becoming denser, in contrast to more prevalent conditions like osteoporosis ...
display enamel abnormalities, suggesting that the a3 gene mutation found in V-ATPases also plays a role in the development of hypomineralized and hypoplastic enamel.
Dentin
Dentin formation, known as dentinogenesis, is the first identifiable feature in the crown stage of tooth development. The formation of dentin must always occur before the formation of enamel. The different stages of dentin formation result in different types of dentin: mantle dentin, primary dentin, secondary dentin, and
tertiary dentin Tertiary dentin (including reparative dentin or sclerotic dentin) forms as a reaction to stimulation, including caries, wear and fractures. Tertiary dentin is therefore a mechanism for a tooth to ‘heal’, with new material formation protecting th ...
.
Odontoblasts, the dentin-forming cells, differentiate from cells of the dental papilla. They begin secreting an organic matrix around the area directly adjacent to the inner enamel epithelium, closest to the area of the future cusp of a tooth. The organic matrix contains collagen fibers with large diameters (0.1–0.2 μm in diameter).
[Cate, ''Oral Histology'', p. 128-139.] The odontoblasts begin to move toward the center of the tooth, forming an extension called the
odontoblast process
An odontoblast process (also called Tomes's fibers or Tomes fibers, or by a dated term Tomes's fibrils) is an extension of a cell called an odontoblast, which forms dentin in a tooth. The odontoblast process is located in dentinal tubules. It forms ...
.
Thus, dentin formation proceeds toward the inside of the tooth. The odontoblast process causes the secretion of hydroxyapatite crystals and mineralization of the matrix. This area of mineralization is known as mantle dentin and is a layer usually about 150 μm thick.
Whereas mantle dentin forms from the preexisting ground substance of the dental papilla, primary dentin forms through a different process. Odontoblasts increase in size, eliminating the availability of any extracellular resources to contribute to an organic matrix for mineralization. Additionally, the larger odontoblasts cause
collagen to be secreted in smaller amounts, which results in more tightly arranged, heterogeneous nucleation that is used for mineralization. Other materials (such as
lipid
Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...
s,
phosphoprotein
A phosphoprotein is a protein that is posttranslationally modified by the attachment of either a single phosphate group, or a complex molecule such as 5'-phospho-DNA, through a phosphate group. The target amino acid is most often serine, threonin ...
s, and
phospholipids) are also secreted.
Secondary dentin is formed after root formation is finished and occurs at a much slower rate. It is not formed at a uniform rate along the tooth, but instead forms faster along sections closer to the crown of a tooth. This development continues throughout life and accounts for the smaller areas of pulp found in older individuals.
Tertiary dentin, also known as reparative dentin, forms in reaction to stimuli, such as
attrition
Attrition may refer to
*Attrition warfare, the military strategy of wearing down the enemy by continual losses in personnel and material
**War of Attrition, fought between Egypt and Israel from 1968 to 1970
**War of attrition (game), a model of agg ...
or
dental caries
Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicatio ...
.
Cementum
Cementum
Cementum is a specialized calcified substance covering the root of a tooth. The cementum is the part of the periodontium that attaches the teeth to the alveolar bone by anchoring the periodontal ligament.Illustrated Dental Embryology, Histology, a ...
formation is called
cementogenesis Cementogenesis is the formation of cementum, one of the three mineralized substances of a tooth. Cementum covers the roots of teeth and serves to anchor gingival and periodontal fibers of the periodontal ligament by the fibers to the alveolar bone ( ...
and occurs late in the development of teeth.
Cementoblasts
A cementoblast is a biological cell that forms from the follicular cells around the root of a tooth, and whose biological function is cementogenesis, which is the formation of cementum (hard tissue that covers the tooth root). The mechanism of di ...
are the cells responsible for cementogenesis. Two types of cementum form: cellular and acellular.
Acellular cementum forms first. The cementoblasts differentiate from follicular cells, which can only reach the surface of the tooth's root once
Hertwig's Epithelial Root Sheath
The Hertwig epithelial root sheath (HERS) or epithelial root sheath is a proliferation of epithelial cells located at the cervical loop of the enamel organ in a developing tooth. Hertwig epithelial root sheath initiates the formation of dentin ...
(HERS) has begun to deteriorate. The cementoblasts secrete fine collagen fibrils along the root surface at right angles before migrating away from the tooth. As the cementoblasts move, more collagen is deposited to lengthen and thicken the bundles of fibers. Noncollagenous proteins, such as
bone sialoprotein
Bone sialoprotein (BSP) is a component of mineralized tissues such as bone, dentin, cementum and calcified cartilage. BSP is a significant component of the bone extracellular matrix and has been suggested to constitute approximately 8% of all ...
and
osteocalcin
Osteocalcin, also known as bone gamma-carboxyglutamic acid-containing protein (BGLAP), is a small (49-amino-acid) noncollagenous protein hormone found in bone and dentin, first identified as a calcium-binding protein.
Because osteocalcin has g ...
, are also secreted.
[Cate, ''Oral Histology'', p. 236-248.] Acellular cementum contains a secreted matrix of proteins and fibers. As mineralization takes place, the cementoblasts move away from the cementum, and the fibers left along the surface eventually join the forming periodontal ligaments.
Cellular cementum develops after most of the tooth formation is complete and after the tooth occludes (in contact) with a tooth in the opposite arch.
This type of cementum forms around the fiber bundles of the periodontal ligaments. The cementoblasts forming cellular cementum become trapped in the cementum they produce.
The origin of the formative cementoblasts is believed to be different for cellular cementum and acellular cementum. One of the major current hypotheses is that cells producing cellular cementum migrate from the adjacent area of bone, while cells producing acellular cementum arise from the dental follicle.
Nonetheless, it is known that cellular cementum is usually not found in teeth with one root.
In
premolar
The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...
s and
molars, cellular cementum is found only in the part of the root closest to the apex and in interradicular areas between multiple roots.
Formation of the periodontium
The periodontium, which is the supporting structure of a tooth, consists of the cementum, periodontal ligaments,
gingiva
The gums or gingiva (plural: ''gingivae'') consist of the mucosal tissue that lies over the mandible and maxilla inside the mouth. Gum health and disease can have an effect on general health.
Structure
The gums are part of the soft tissue lin ...
, and
alveolar bone
The alveolar process () or alveolar bone is the thickened ridge of bone that contains the tooth sockets on the jaw bones (in humans, the maxilla and the mandible). The structures are covered by gums as part of the oral cavity.
The synonymous t ...
. Cementum is the only one of these that is a part of a tooth. Alveolar bone surrounds the roots of teeth to provide support and creates what is commonly called a "
socket
Socket may refer to:
Mechanics
* Socket wrench, a type of wrench that uses separate, removable sockets to fit different sizes of nuts and bolts
* Socket head screw, a screw (or bolt) with a cylindrical head containing a socket into which the hexag ...
". Periodontal ligaments connect the alveolar bone to the cementum, and the gingiva is the surrounding tissue visible in the mouth.
Periodontal ligament
Cells from the dental follicle give rise to the
periodontal ligament
The 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. It inserts into root cementum one side and onto alveolar b ...
(PDL). Specific events leading to the formation of the periodontal ligament vary between deciduous (baby) and permanent teeth and among various
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of animals.
Nonetheless, formation of the periodontal ligament begins with ligament fibroblasts from the dental follicle. These fibroblasts secrete collagen, which interacts with fibers on the surfaces of adjacent bone and cementum.
This interaction leads to an attachment that develops as the tooth erupts into the mouth. The
occlusion
Occlusion may refer to:
Health and fitness
* Occlusion (dentistry), the manner in which the upper and lower teeth come together when the mouth is closed
* Occlusion miliaria, a skin condition
* Occlusive dressing, an air- and water-tight trauma ...
, which is the arrangement of teeth and how teeth in opposite arches come in contact with one another, continually affects the formation of periodontal ligament. This perpetual creation of periodontal ligament leads to the formation of groups of fibers in different orientations, such as horizontal and oblique fibers.
Alveolar bone
As root and cementum formation begin, bone is created in the adjacent area. Throughout the body, cells that form bone are called
osteoblasts. In the case of alveolar bone, these osteoblast cells form from the dental follicle.
Similar to the formation of primary cementum, collagen fibers are created on the surface nearest the tooth, and they remain there until attaching to periodontal ligaments.
Like any other bone in the human body, alveolar bone is modified throughout life. Osteoblasts create bone and
osteoclast
An osteoclast () is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodeling of bones of the vertebral skeleton. The osteoclast disassembles and digests the composite of hydrated pro ...
s destroy it, especially if force is placed on a tooth.
[Ross, Kaye, and Pawlina, ''Histology: Text and Atlas'', p. 452.] As is the case when movement of teeth is attempted through orthodontics using bands, wires, or appliances, an area of bone under
compressive
In continuum mechanics, stress is a physical quantity. It is a quantity that describes the magnitude of forces that cause deformation. Stress is defined as ''force per unit area''. When an object is pulled apart by a force it will cause elon ...
force
In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...
from a tooth moving toward it has a high osteoclast level, resulting in
bone resorption
Bone resorption is resorption of bone tissue, that is, the process by which osteoclasts break down the tissue in bones and release the minerals, resulting in a transfer of calcium from bone tissue to the blood.
The osteoclasts are multi-nuclea ...
. An area of bone receiving
tension
Tension may refer to:
Science
* Psychological stress
* Tension (physics), a force related to the stretching of an object (the opposite of compression)
* Tension (geology), a stress which stretches rocks in two opposite directions
* Voltage or el ...
from periodontal ligaments attached to a tooth moving away from it has a high number of osteoblasts, resulting in bone formation. Thus, the tooth or teeth are slowly moved along the jaw so as to achieve a dentition that works in harmony. In this way, the width of the space between the alveoli and the root is kept about the same.
[Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 75]
Gingiva
The connection between the gingiva and the tooth is called the dentogingival junction. This junction has three epithelial types: gingival, sulcular, and junctional epithelium. These three types form from a mass of epithelial cells known as the epithelial cuff between the tooth and the mouth.
Much about gingival formation is not fully understood, but it is known that
hemidesmosomes
Hemidesmosomes are very small stud-like structures found in keratinocytes of the epidermis of skin that attach to the extracellular matrix. They are similar in form to desmosomes when visualized by electron microscopy, however, desmosomes attach t ...
form between the gingival epithelium and the tooth and are responsible for the ''primary epithelial attachment''.
Hemidesmosomes provide anchorage between cells through small filament-like structures provided by the remnants of ameloblasts. Once this occurs, junctional epithelium forms from reduced enamel epithelium, one of the products of the enamel organ, and divides rapidly. This results in the perpetually increasing size of the junctional epithelial layer and the isolation of the remnants of ameloblasts from any source of nutrition. As the ameloblasts degenerate, a
gingival sulcus
The gingival sulcus is an area of potential space between a tooth and the surrounding gingival tissue and is lined by sulcular epithelium. The depth of the sulcus (Latin for ''groove'') is bounded by two entities: apically by the gingival fi ...
is created.
Nerve and vascular formation
Frequently, nerves and blood vessels run parallel to each other in the body, and the formation of both usually takes place simultaneously and in a similar fashion. However, this is not the case for nerves and blood vessels around the tooth, because of different rates of development.
Nerve formation
Nerve fibers start to near the tooth during the cap stage of tooth development and grow toward the dental follicle. Once there, the nerves develop around the tooth bud and enter the dental papilla when dentin formation has begun. Nerves never proliferate into the enamel organ.
Vascular formation
Blood vessel
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
s grow in the dental follicle and enter the
dental papilla
In embryology and prenatal development, 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 ...
in the cap stage.
Groups of blood vessels form at the entrance of the dental papilla. The number of blood vessels reaches a maximum at the beginning of the crown stage, and the dental papilla eventually forms in the pulp of a tooth. Throughout life, the amount of pulpal tissue in a tooth decreases, which means that the blood supply to the tooth decreases with age.
The enamel organ is devoid of blood vessels because of its epithelial origin, and the
mineralized tissues
Mineralized tissues are biological tissues that incorporate minerals into soft matrices. Typically these tissues form a protective shield or structural support. Bone, mollusc shells, deep sea sponge ''Euplectella'' species, radiolarians, diato ...
of enamel and dentin do not need nutrients from the blood.
Tooth eruption
Tooth eruption occurs when the teeth enter the mouth and become visible. Although researchers agree that tooth eruption is a complex process, there is little agreement on the identity of the mechanism that controls eruption. Some commonly held theories that have been disproven over time include: (1) the tooth is pushed upward into the mouth by the growth of the tooth's root, (2) the tooth is pushed upward by the growth of the bone around the tooth, (3) the tooth is pushed upward by vascular pressure, and (4) the tooth is pushed upward by the cushioned hammock. The cushioned hammock theory, first proposed by Harry Sicher, was taught widely from the 1930s to the 1950s. This theory postulated that a
ligament
A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the:
* Peritoneal li ...
below a tooth, which Sicher observed under a microscope on a histologic slide, was responsible for eruption. Later, the "ligament" Sicher observed was determined to be merely an
artifact created in the process of preparing the slide.
The most widely held current theory is that while several forces might be involved in eruption, the periodontal ligaments provide the main impetus for the process. Theorists hypothesize that the periodontal ligaments promote eruption through the shrinking and cross-linking of their collagen fibers and the contraction of their fibroblasts.
Although tooth eruption occurs at different times for different people, a general eruption timeline exists. Typically, humans have 20
primary (baby) teeth and 32
permanent teeth
Permanent teeth or adult teeth are the second set of teeth formed in diphyodont mammals. In humans and old world simians, there are thirty-two permanent teeth, consisting of six maxillary and six mandibular molars, four maxillary and four mandibul ...
. Tooth eruption has three stages. The first, known as deciduous
dentition stage, occurs when only primary teeth are visible. Once the first permanent tooth erupts into the mouth, the teeth are in the mixed (or transitional) dentition. After the last primary tooth falls out of the mouth—a process known as exfoliation—the teeth are in the permanent dentition.
Primary dentition starts on the arrival of the
mandibular central incisor
The mandibular central incisor is the tooth located on the jaw, adjacent to the midline of the face. It is mesial (toward the midline of the face) from both mandibular lateral incisors. As with all incisors, its function includes shearing or cut ...
s, usually at eight months, and lasts until the first permanent molars appear in the mouth, usually at six years. The primary teeth typically erupt in the following order: (1) central
incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
, (2) lateral incisor, (3) first
molar, (4)
canine, and (5) second molar. As a general rule, four teeth erupt for every six months of life, mandibular teeth erupt before maxillary teeth, and teeth erupt sooner in females than males. During primary dentition, the tooth buds of permanent teeth develop below the primary teeth, close to the palate or tongue.
Mixed dentition starts when the first permanent molar appears in the mouth, usually at six years, and lasts until the last primary tooth is lost, usually at eleven or twelve years. Permanent teeth in the maxilla erupt in a different order from permanent teeth on the mandible. Maxillary teeth erupt in the following order: (1)
first molar
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
(2)
central incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wh ...
, (3)
lateral incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wh ...
, (4)
first premolar, (5)
second premolar, (6)
canine, (7)
second molar, and (8)
third molar
A third molar, commonly called wisdom tooth, is one of the three molars per quadrant of the human dentition. It is the most posterior of the three. The age at which wisdom teeth come through ( erupt) is variable, but this generally occurs betw ...
. Mandibular teeth erupt in the following order: (1)
first molar
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
(2)
central incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wh ...
, (3)
lateral incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wh ...
, (4)
canine, (5)
first premolar, (6)
second premolar, (7)
second molar, and (8)
third molar
A third molar, commonly called wisdom tooth, is one of the three molars per quadrant of the human dentition. It is the most posterior of the three. The age at which wisdom teeth come through ( erupt) is variable, but this generally occurs betw ...
. Since there are no premolars in the primary dentition, the primary molars are replaced by permanent premolars. If any primary teeth are lost before permanent teeth are ready to replace them, some posterior teeth may drift forward and cause space to be lost in the mouth. This may cause crowding and/or misplacement once the permanent teeth erupt, which is usually referred to as
malocclusion
In orthodontics, a malocclusion is a misalignment or incorrect relation between the teeth of the upper and lower dental arches when they approach each other as the jaws close. The English-language term dates from 1864; Edward Angle (1855-1930), ...
.
Orthodontics
Orthodontics is a dentistry specialty that addresses the diagnosis, prevention, management, and correction of mal-positioned teeth and jaws, and misaligned bite patterns. It may also address the modification of facial growth, known as dentofacial ...
may be required in such circumstances for an individual to achieve a straight set of teeth.
The permanent dentition begins when the last primary tooth is lost, usually at 11 to 12 years, and lasts for the rest of a person's life or until all of the teeth are lost (
edentulism
Toothlessness, or edentulism, is the condition of having no teeth. In organisms that naturally have teeth, it is the result of tooth loss.
Organisms that never possessed teeth can also be described as edentulous. Examples are the members of th ...
). During this stage, third molars (also called "
wisdom teeth
A third molar, commonly called wisdom tooth, is one of the three molars per quadrant of the human dentition. It is the most posterior of the three. The age at which wisdom teeth come through ( erupt) is variable, but this generally occurs betw ...
") are frequently
extracted because of decay, pain or impactions. The main reasons for
tooth loss Tooth loss is a process in which one or more teeth come loose and fall out. Tooth loss is normal for deciduous teeth (baby teeth), when they are replaced by a person's adult teeth. Otherwise, losing teeth is undesirable and is the result of inju ...
are
decay
Decay may refer to:
Science and technology
* Bit decay, in computing
* Software decay, in computing
* Distance decay, in geography
* Decay time (fall time), in electronics
Biology
* Decomposition of organic matter
* Tooth decay (dental caries ...
and
periodontal disease
Periodontal disease, also known as gum disease, is a set of inflammatory conditions affecting the tissues surrounding the teeth. In its early stage, called gingivitis, the gums become swollen and red and may bleed. It is considered the main caus ...
.
Immediately after the eruption enamel is covered by a specific film:
Nasmyth's membrane or 'enamel cuticle', structure of embryological origin is composed of
keratin
Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...
which gives rise to the
enamel organ
The enamel organ, also known as the dental organ, is a cellular aggregation seen in a developing tooth and it lies above the dental papilla. The enamel organ which is differentiated from the primitive oral epithelium lining the stomodeum.The enam ...
.
Nutrition and tooth development
As in other aspects of human growth and development, nutrition has an effect on the developing tooth. Essential nutrients for a healthy tooth include
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
,
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
, and
vitamin
A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an essential micronutrient that an organism needs in small quantities for the proper functioning of its metabolism. Essential nutrie ...
s
A,
C, and
D. Calcium and phosphorus are needed to properly form the hydroxyapatite crystals, and their levels in the blood are maintained by Vitamin D. Vitamin A is necessary for the formation of
keratin
Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...
, as Vitamin C is for collagen. Fluoride, although not a nutrient, is incorporated into the hydroxyapatite crystal of a developing tooth and bones. The dental theory is the low levels of fluoride incorporation and very mild fluorosis makes the tooth more resistant to demineralization and subsequent decay.
Deficiencies of nutrients can have a wide range of effects on tooth development. In situations where calcium, phosphorus, and vitamin D are deficient, the hard structures of a tooth may be less mineralized. A lack of vitamin A can cause a reduction in the amount of enamel formation.
Fluoride ingestion has been noted to delay eruption of teeth for as much as a year or more from the accepted eruption dates since the initial 1940s fluoridation trials. Researchers theorize that the delay is a manifestation of fluoride's depressing impact on thyroid hormones. The delay in eruption has been suggested as the reason for the apparent difference in decay among the youngest children. Fluoride ingestion during tooth development can lead to a permanent condition known as
fluorosis with varying levels of severity, the result of fluoride's interference with the normal osteoblast development.
Undiagnosed and untreated
celiac disease
Coeliac disease (British English) or celiac disease (American English) is a long-term autoimmune disorder, primarily affecting the small intestine, where individuals develop intolerance to gluten, present in foods such as wheat, rye and barle ...
often causes dental enamel defects and can be the only manifestation of the disease, in absence of gastrointestinal symptoms or malabsorption signs.
[Dental Enamel Defects and Celiac Disease]
National Institute of Health (NIH)
Bisphenol A (BPA) is a hormone-disrupting chemical that has been implicated in having negative effects on human health, including, but not limited to, fetal development. As shown in animal studies which mimic human enamel, the mother's consumption of products with BPA during pregnancy can lead to the child's tooth development being obstructed. Those children are shown to be prone to incisor and first molar hypomineralization, a weakened state of the enamel. Additionally, it is most important for mother's to avoid BPA during pregnancy, but also avoid BPA-use in the child's products up to five months of age.
Developmental disturbances
The absence of
third molar
A third molar, commonly called wisdom tooth, is one of the three molars per quadrant of the human dentition. It is the most posterior of the three. The age at which wisdom teeth come through ( erupt) is variable, but this generally occurs betw ...
s is very common, occurring in 20–23% of the population, followed in prevalence by the
second premolar and
lateral incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wh ...
.
Anodontia
Anodontia is a rare genetic disorder characterized by the congenital absence of all primary or permanent teeth. It is divided into two subsections, complete absence of teeth or only some absence of teeth. It is associated with the group of skin ...
is a complete lack of tooth development. It is rare, most often occurring in a condition called
hypohidrotic ectodermal dysplasia
Hypohidrotic ectodermal dysplasia is one of about 150 types of ectodermal dysplasia in humans. Before birth, these disorders result in the abnormal development of structures including the skin, hair, nails, teeth, and sweat glands.Freedberg, et ...
.
Hypodontia
Hypodontia is defined as the developmental absence of one or more teeth excluding the third molars. It is one of the most common dental anomalies, and can have a negative impact on function, and also appearance. It rarely occurs in primary teet ...
is a lack of some tooth development (not including third molars). It is one of the most common developmental abnormalities, affecting 3.5–8.0% of the population. Hypodontia is often associated with the absence of a
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 (in humans) at the sixth week in utero or three weeks after the rupture of th ...
, which is vulnerable to environmental forces like infection and
chemotherapy
Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemotherap ...
medications. It is also associated with many syndromes, such as
Down syndrome
Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...
and
Crouzon syndrome
Crouzon syndrome is an autosomal dominant genetic disorder known as a branchial arch syndrome. Specifically, this syndrome affects the first branchial (or pharyngeal) arch, which is the precursor of the maxilla and mandible. Since the branchial ...
.
Hyperdontia
Hyperdontia is the condition of having supernumerary teeth, or teeth that appear in addition to the regular number of teeth (32 in the average adult). They can appear in any area of the dental arch and can affect any dental organ. The opposite ...
is the development of extraneous teeth. It occurs in 1–3% of
Caucasians and is more frequent in
Asian
Asian may refer to:
* Items from or related to the continent of Asia:
** Asian people, people in or descending from Asia
** Asian culture, the culture of the people from Asia
** Asian cuisine, food based on the style of food of the people from Asi ...
s. About 86% of these cases involve a single extra tooth in the mouth, most commonly found in the maxilla, where the
incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
s are located. Hyperdontia is believed to be associated with an excess of dental lamina.
Dilaceration is an abnormal bend found on a tooth, and is nearly always associated with trauma that moves the developing tooth bud. As a tooth is forming, a force can move the tooth from its original position, leaving the rest of the tooth to form at an abnormal angle.
Cyst
A cyst is a closed sac, having a distinct envelope and cell division, division compared with the nearby Biological tissue, tissue. Hence, it is a cluster of Cell (biology), cells that have grouped together to form a sac (like the manner in which ...
s or
tumor
A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
s adjacent to a tooth bud are forces known to cause dilaceration, as are primary (baby) teeth pushed upward by trauma into the gingiva where it moves the tooth bud of the permanent tooth.
Enamel hypoplasia
Enamel hypoplasia is a defect of the teeth in which the enamel is deficient in quantity, caused by defective enamel matrix formation during enamel development, as a result of inherited and acquired systemic condition(s). It can be identified as m ...
or hypomineralization is a defect of the teeth caused by a disturbance in the formation of the organic enamel matrix, clinically visible as enamel defects.
It may be caused by nutritional factors,
some diseases (such as undiagnosed and untreated
celiac disease
Coeliac disease (British English) or celiac disease (American English) is a long-term autoimmune disorder, primarily affecting the small intestine, where individuals develop intolerance to gluten, present in foods such as wheat, rye and barle ...
,
chicken pox
Chickenpox, also known as varicella, is a highly contagious disease caused by the initial infection with varicella zoster virus (VZV). The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab ...
,
congenital syphilis
Congenital syphilis is syphilis present ''in utero'' and at birth, and occurs when a child is born to a mother with syphilis. Untreated early syphilis infections results in a high risk of poor pregnancy outcomes, including saddle nose, lower ext ...
),
hypocalcemia
Hypocalcemia is a medical condition characterized by low calcium levels in the blood serum. The normal range of blood calcium is typically between 2.1–2.6 mmol/L (8.8–10.7 mg/dL, 4.3–5.2 mEq/L) while levels less than 2.1 mm ...
,
fluoride ingestion,
birth injury
Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the f ...
,
preterm birth
Preterm birth, also known as premature birth, is the Childbirth, birth of a baby at fewer than 37 weeks Gestational age (obstetrics), gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 we ...
,
infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
or trauma from a
deciduous tooth
Deciduous teeth or primary teeth, also informally known as baby teeth, milk teeth, or temporary teeth,Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 255 are the first set of teeth in the ...
.
In some circumstances
enamel hypoplasia
Enamel hypoplasia is a defect of the teeth in which the enamel is deficient in quantity, caused by defective enamel matrix formation during enamel development, as a result of inherited and acquired systemic condition(s). It can be identified as m ...
can be so severe that last sections of enamel is missing, exposing the underlying dentin.
Some systemic conditions may cause delayed tooth development, such as nutritional factors, endocrine disorders (
hypothyroidism,
hypopituitarism
Hypopituitarism is the decreased (''hypo'') secretion of one or more of the eight hormones normally produced by the pituitary gland at the base of the brain. If there is decreased secretion of one specific pituitary hormone, the condition is know ...
,
hypoparathyroidism
Hypoparathyroidism is decreased function of the parathyroid glands with underproduction of parathyroid hormone (PTH). This can lead to low levels of calcium in the blood, often causing cramping and twitching of muscles or tetany (involuntary m ...
,
pseudohypoparathyroidism
Pseudohypoparathyroidism is a condition associated primarily with resistance to the parathyroid hormone. Those with the condition have a low serum calcium and high phosphate, but the parathyroid hormone level (PTH) is appropriately high (due to th ...
),
undiagnosed and untreated celiac disease,
anemia
Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, th ...
,
prematurity,
low birth weight
Low birth weight (LBW) is defined by the World Health Organization as a birth weight of an
infant of or less, regardless of gestational age. Infants born with LBW have added health risks which require close management, often in a neonatal inten ...
,
renal failure
Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...
,
heavy metal intoxication or tobacco smoke, among others.
Regional odontodysplasia
Regional odontodysplasia is an uncommon developmental abnormality of teeth, usually localized to a certain area of the mouth. The condition is nonhereditary. There is no predilection for race, but females are more likely to get regional odontody ...
is rare, but is most likely to occur in the maxilla and anterior teeth. The cause is unknown; a number of causes have been postulated, including a disturbance in the neural crest cells, infection, radiation therapy, and a decrease in vascular supply (the most widely held hypothesis).
[Neville, Damm, Allen, and Bouquot, ''Oral & Maxillofacial Pathology'', p. 99.] Teeth affected by regional odontodysplasia nevAmelogenesis imperfecta is an autosomal dominant disease characterized by a defect in dental enamel formation. Teeth are often free of enamel, small, misshapen, and tinted brown. The cause of these deformities is due to a mutation in enamel in expression. Dental patients with this disease should be especially cautious and visit their dentist frequently.
Natal and neonatal teeth are an anomaly that involves teeth erupting in a newborn infant's mouth earlier than usual. The incidence ranges from 1:2,000 to 1:3,500 births. Natal teeth are more frequent, approximately three times more common than neonatal teeth. Some authors reported a higher prevalence in females than males. The most common location is the mandibular region of the central incisors.
Natal teeth and neonatal teeth are associated with genetics, developmental abnormalities and certain recognized syndromes. Additional names for this condition include precocious dentition, baby teeth, and milk teeth.
See also
*
Polyphyodont
A polyphyodont is any animal whose teeth are continually replaced. In contrast, diphyodonts are characterized by having only two successive sets of teeth.
Polyphyodonts include most toothed fishes, many reptiles such as crocodiles and geckos, ...
*
Tooth regeneration Tooth regeneration is a stem cell based regenerative medicine procedure in the field of tissue engineering and stem cell biology to replace damaged or lost teeth by regrowing them from autologous stem cells.
As a source of the new bioengineered tee ...
*
Animal tooth development
Tooth development or odontogenesis is the process in which teeth develop and grow into the mouth. Tooth development varies among species.
Tooth development in vertebrates
Fish
In fish, Hox gene expression regulates mechanisms for tooth initiati ...
References
Additional references
The American Academy of Periodontology"Oral Health Information for the Public" Retrieved April 10, 2014.
The American Dental Association"Tooth Eruption Charts" Retrieved April 10, 2014.
The American Dental Hygiene Association Retrieved December 10, 2005.
The American Dental Hygiene Association Retrieved December 10, 2005.
*Ash, Major M. and Stanley J. Nelson. ''Wheeler’s Dental Anatomy, Physiology, and Occlusion.'' 8th edition. 2003. .
*Buchheim, Jason
Page accessed January 7, 2006.
*Cate, A.R. Ten. Oral Histology: development, structure, and function. 5th ed. 1998. .
*Caceci, Thomas. ''Veterinary Histology'' with subtitl
Retrieved December 15, 2005.
*Frandson, R.D. & T.L. Spurgeon, 1992. ''Anatomy and Physiology of Farm Animals.'' 5th edition. Philadelphia, Lea & Febiger. .
*Harris, Edward F. ''Craniofacial Growth and Development.'' In the section entitled "Tooth Eruption." 2002.
Health Hawaii Retrieved December 12, 2005.
*Johnson, Clarke.
. 1998.
*Kahn, Michael A. Basic Oral and Maxillofacial Pathology. Volume 1. 2001.
*''Monthly Microscopy Explorations'' "Exploration of the Month: January 1998".
*Neville, B.W., Douglas Damm, Carl Allen, Jerry Bouquot. Oral & Maxillofacial Pathology. 2nd edition. 2002. .
*Riolo, Michael L. and James K. Avery. ''Essentials for Orthodontic Practice''. 1st edition. 2003. .
*Ross, Michael H., Gordon I. Kaye, and Wojciech Pawlina. Histology: a text and atlas. 4th edition. 2003. .
*Summitt, James B., J. William Robbins, and Richard S. Schwartz. ''Fundamentals of Operative Dentistry: A Contemporary Approach.'' 2nd edition. Carol Stream, Illinois, Quintessence Publishing Co, Inc. 2001. .
University of Southern California School of Dentistry Retrieved December 11, 2005.
University of Southern California School of Dentistry Retrieved December 11, 2005.
*University of Texas Medical Branch.
*Williams, Michael E
1992. Page accessed January 7, 2006.
WebMd Retrieved December 12, 2005.
*
External links
Database on the expression of different genes in the developing tooth.
{{Tooth development
Pediatrics