Dental anatomy is a field of anatomy dedicated to the study of human tooth structures. The development and classification of teeth fall within its purview. Tooth formation begins before birth, the teeth's eventual morphology is dictated during this time. Dental anatomy is a taxonomical science: it is concerned with the naming of teeth and the structures of which they are made, this information serving a practical purpose in dental treatment. There are 20 primary teeth and 28 to 32 permanent teeth, the last four being third molars or "wisdom teeth", each of which may or may not grow in. Among primary teeth, 10 are found in the maxilla and the other 10 in the mandible. Among permanent teeth, 16 are found in the other 16 in the mandible. Most of the teeth have distinguishing features. Tooth development is the complex process by which teeth form from embryonic cells and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is the same as in humans. For human teeth to have a healthy oral environment, dentin and the periodontium must all develop during appropriate stages of fetal development.
Primary teeth start to form between the sixth and eighth weeks in utero, permanent teeth begin to form in the twentieth week in utero. If teeth do not start to develop at or near these times, they will not develop at all. A significant amount of research has focused on determining the processes that initiate tooth development, it is accepted that there is a factor within the tissues of the first branchial arch, necessary for the development of teeth. The tooth bud is an aggregation of cells that forms a tooth and is organized into three parts: the enamel organ, the dental papilla and the dental follicle; the enamel organ is composed of the outer enamel epithelium, inner enamel epithelium, stellate reticulum and stratum intermedium. These cells give rise to ameloblasts, which produce the reduced enamel epithelium; the growth of cervical loop cells into the deeper tissues forms Hertwig's Epithelial Root Sheath, which determines the root shape of the tooth. The dental papilla contains cells. Additionally, the junction between the dental papilla and inner enamel epithelium determines the crown shape of a tooth.
The dental follicle gives rise to three important entities: cementoblasts and fibroblasts. Cementoblasts form the cementum of a tooth. Osteoblasts give rise to the alveolar bone around the roots of teeth. Fibroblasts develop the periodontal ligaments which connect teeth to the alveolar bone through cementum. Tooth development is divided into the following stages: the bud stage, the cap, the bell, maturation; the staging of tooth development is an attempt to categorize changes that take place along a continuum. 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. Teeth are named by their sets and arch, class and side. Teeth can belong to one of two sets of teeth: permanent teeth. "deciduous" may be used in place of "primary", "adult" may be used for "permanent". "Succedaneous" refers to those teeth of the permanent dentition. Succedaneous would refer to these teeth as a group. Further, the name depends upon.
The term, "maxillary", is given to teeth in the upper jaw and "mandibular" to those in the lower jaw. There are four classes of teeth: incisors, canines and molars. Premolars are found only in permanent teeth. Within each class, teeth may be classified into different traits. Incisors are divided further into lateral incisors. Among premolars and molars, there are first and second premolars, first and third molars; the side of the mouth in which a tooth is found may be included in the name. For example, a specific name for a tooth may be "permanent maxillary left lateral incisor." There are several different dental notation systems for associating information to a specific tooth. The three most commons systems are the FDI World Dental Federation notation, Universal numbering system, Palmer notation method; the FDI system is used worldwide, the universal is used in the United States. Although the Palmer notation was superseded by the FDI World Dental Federation notation, it overwhelmingly continues to be the preferred method used by dental students and practitioners in the United Kingdom.
It was termed the "Zsigmondy system" after the Austrian dentist Adolf Zsigmondy who developed the idea in 1861, using a Zsigmondy cross to record quadrants of tooth positions. The Palmer notation consists of a symbol designating in which quadrant the tooth is found and a number indicating the position from the midline. Permanent teeth are numbered 1 to 8, primary teeth are indicated by a letter A to E; the universal numbering system uses a unique number for each tooth. The uppercase letters A through T are used for primary teeth and the numbers 1 - 32 are used for permanent teeth; the tooth designated "1" is the right maxillary third molar and the count continues along the upper teeth to the left side. T
A wisdom tooth or third molar 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 is variable, but occurs between late teens and early twenties. Most adults have four wisdom teeth, one in each of the four quadrants, but it is possible to have none, fewer, or more, in which case the extras are called supernumerary teeth. Wisdom teeth may get stuck against other teeth if there is not enough space for them to come through normally. While this does not cause movement of other teeth, it can cause tooth decay if the impaction makes oral hygiene difficult. Wisdom teeth which are erupted through the gum may cause inflammation and infection in the surrounding gum tissues, termed pericoronitis. Wisdom teeth are extracted when or before these problems occur; however some recommend against the prophylactic extraction of disease-free impacted wisdom teeth. Agenesis of wisdom teeth differs by population, ranging from zero in Aboriginal Tasmanians to nearly 100% in indigenous Mexicans.
The difference is related to the PAX9, MSX1 gene. There is significant variation between the reported age of eruption of wisdom teeth between different populations. For example, wisdom teeth tend to erupt earlier in black people compared to white people. Wisdom teeth are stated as erupting most between age 17 and 21. Eruption may start as early as age 13 in some groups. Sometimes they can erupt up to age 25. If they have not erupted by age 25, oral surgeons consider that the tooth will not erupt spontaneously by itself. Wisdom teeth are vestigial third molars, it is thought that the skulls of human ancestors had larger jaws with more teeth, which helped to chew foliage to compensate for a lack of ability to efficiently digest the cellulose that makes up a plant cell wall. After the advent of agriculture over 10,000 years ago, soft human diets became the norm, including carbohydrate and high energy foods; such diets result in jaws growing with less forward growth than our paleolithic ancestors and not enough room for the wisdom teeth.
Wisdom teeth have long been identified as a source of problems and continue to be the most impacted teeth in the human mouth. The oldest known impacted wisdom tooth belonged to a European woman of the Magdalenian period. A lack of room to allow the teeth to erupt results in a risk of periodontal disease and dental cavities that increases with age. Less than 2% of adults age 65 years or older maintain the teeth without cavities or periodontal disease and 13% maintain unimpacted wisdom teeth without cavities or periodontal disease. Impacted wisdom teeth are classified by the direction and depth of impaction, the amount of available space for tooth eruption and the amount soft tissue or bone that covers them; the classification structure allows clinicians to estimate the probabilities of impaction and complications associated with wisdom teeth removal. Wisdom teeth are classified by the presence of symptoms and disease. Treatment of an erupted wisdom tooth is the same as any other tooth in the mouth.
If impacted, treatment can be localized to the infected tissue overlying the impaction, extraction or coronectomy. Although formally known as third molars, the common name is wisdom teeth because they appear so late – much than the other teeth, at an age where people are "wiser" than as a child, when the other teeth erupt; the term came as a translation of the Latin dens sapientiae. Their eruption has been known to cause dental issues for millennia. Cases have been known in women upwards of eighty years old where at the close of life the wisdom-teeth have come up, causing great pain in their coming; this happens, when it does happen, in the case of people where the wisdom-teeth have not come up in early years. Nonetheless, molar impaction was rare prior to the modern era. With the Industrial Revolution, the affliction became ten times more common, owing to the new prevalence of soft and sugary foods. National Institute of Clinical Health and Excellence Guideline to Wisdom teeth removal Wisdom tooth extraction WebMD article
The cementoenamel junction abbreviated as the CEJ, is a visible anatomical border identified on a tooth. It is the location where the enamel, which covers the anatomical crown of a tooth, the cementum, which covers the anatomical root of a tooth, meet. Informally it is known as the neck of the tooth; the border created by these two dental tissues has much significance as it is the location where the gingiva attaches to a healthy tooth by fibers called the gingival fibers. Active recession of the gingiva reveals the cementoenamel junction in the mouth and is a sign of an unhealthy condition. There exists a normal variation in the relationship of the cementum and the enamel at the cementoenamel junction. In about 60–65% of teeth, the cementum overlaps the enamel at the CEJ, while in about 30% of teeth, the cementum and enamel abut each other with no overlap. In only 5–10% of teeth, there is a space between the enamel and the cementum at which the underlying dentin is exposed. Biology-Online
Anatomical terminology is a form of scientific terminology used by anatomists and health professionals such as doctors. Anatomical terminology uses many unique terms and prefixes deriving from Ancient Greek and Latin; these terms can be confusing to those unfamiliar with them, but can be more precise, reducing ambiguity and errors. Since these anatomical terms are not used in everyday conversation, their meanings are less to change, less to be misinterpreted. To illustrate how inexact day-to-day language can be: a scar "above the wrist" could be located on the forearm two or three inches away from the hand or at the base of the hand. By using precise anatomical terminology such ambiguity is eliminated. An international standard for anatomical terminology, Terminologia Anatomica has been created. Anatomical terminology has quite regular morphology, the same prefixes and suffixes are used to add meanings to different roots; the root of a term refers to an organ or tissue. For example, the Latin names of structures such as musculus biceps brachii can be split up and refer to, musculus for muscle, biceps for "two-headed", brachii as in the brachial region of the arm.
The first word describes what is being spoken about, the second describes it, the third points to location. When describing the position of anatomical structures, structures may be described according to the anatomical landmark they are near; these landmarks may include structures, such as the umbilicus or sternum, or anatomical lines, such as the midclavicular line from the centre of the clavicle. The cephalon or cephalic region refers to the head; this area is further differentiated into the cranium, frons, auris, nasus and mentum. The neck area is called cervical region. Examples of structures named according to this include the frontalis muscle, submental lymph nodes, buccal membrane and orbicularis oculi muscle. Sometimes, unique terminology is used to reduce confusion in different parts of the body. For example, different terms are used when it comes to the skull in compliance with its embryonic origin and its tilted position compared to in other animals. Here, Rostral refers to proximity to the front of the nose, is used when describing the skull.
Different terminology is used in the arms, in part to reduce ambiguity as to what the "front", "back", "inner" and "outer" surfaces are. For this reason, the terms below are used: Radial referring to the radius bone, seen laterally in the standard anatomical position. Ulnar referring to the ulna bone, medially positioned when in the standard anatomical position. Other terms are used to describe the movement and actions of the hands and feet, other structures such as the eye. International morphological terminology is used by the colleges of medicine and dentistry and other areas of the health sciences, it facilitates communication and exchanges between scientists from different countries of the world and it is used daily in the fields of research and medical care. The international morphological terminology refers to morphological sciences as a biological sciences' branch. In this field, the form and structure are examined as well as the changes or developments in the organism, it is functional.
It covers the gross anatomy and the microscopic of living beings. It involves the anatomy of the adult, it includes comparative anatomy between different species. The vocabulary is extensive and complex, requires a systematic presentation. Within the international field, a group of experts reviews and discusses the morphological terms of the structures of the human body, forming today's Terminology Committee from the International Federation of Associations of Anatomists, it deals with the anatomical and embryologic terminology. In the Latin American field, there are meetings called Iberian Latin American Symposium Terminology, where a group of experts of the Pan American Association of Anatomy that speak Spanish and Portuguese and studies the international morphological terminology; the current international standard for human anatomical terminology is based on the Terminologia Anatomica. It was developed by the Federative Committee on Anatomical Terminology and the International Federation of Associations of Anatomists and was released in 1998.
It supersedes Nomina Anatomica. Terminologia Anatomica contains terminology for about 7500 human gross anatomical structures. For microanatomy, known as histology, a similar standard exists in Terminologia Histologica, for embryology, the study of development, a standard exists in Terminologia Embryologica; these standards specify accepted names that can be used to refer to histological and embryological structures in journal articles and other areas. As of September 2016, two sections of the Terminologia Anatomica, including central nervous system and peripheral nervous system, were merged to form the Terminologia Neuroanatomica; the Terminologia Anatomica has been perceived with a considerable criticism regarding its content including coverage and spelling mistakes and errors. Anatomical terminology is chosen to highlight the relative location of body structures. For instance, an anatomist might describe one band of tissue as "inferior to" another or a physician might describe a tumor as "superficial to" a deeper body structure.
Anatomical terms used to describe location
Maxillary first premolar
The maxillary first premolar is one of two teeth located in the upper jaw, laterally from both the maxillary canines of the mouth but mesial from both maxillary second premolars. The function of this premolar is similar to that of canines in regard to tearing being the principal action during mastication known as chewing. There are two cusps on maxillary first premolars, the buccal cusp is sharp enough to resemble the prehensile teeth found in carnivorous animals. There are no deciduous maxillary premolars. Around 10-11 years of age, the primary molars are shed and the permanent premolars erupt in their place, it takes about 3 years for the adult premolar and its root to calcify. In the universal system of notation, the permanent maxillary premolars are designated by a number; the right permanent maxillary first premolar is known as "5", the left one is known as "12". In the Palmer notation, a number is used in conjunction with a symbol designating in which quadrant the tooth is found. For this tooth, the left and right first premolars would have the same number, "4", but the right one would have the symbol, "┘", underneath it, while the left one would have, "└".
The international notation has a different numbering system than the previous two, the right permanent maxillary first premolar is known as "14", the left one is known as "24". Ash, Major M. and Stanley J. Nelson, 2003. Wheeler’s Dental Anatomy and Occlusion. 8th edition
A tooth is a hard, calcified structure found in the jaws of many vertebrates and used to break down food. Some animals carnivores use teeth for hunting or for defensive purposes; the roots of teeth are covered by gums. Teeth hardness; the cellular tissues that become teeth originate from the embryonic germ layer, the ectoderm. The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position; the teeth of mammals have deep roots, this pattern is found in some fish, in crocodilians. In most teleost fish, the teeth are attached to the outer surface of the bone, while in lizards they are attached to the inner surface of the jaw by one side. In cartilaginous fish, such as sharks, the teeth are attached by tough ligaments to the hoops of cartilage that form the jaw; some animals develop only one set of teeth. Sharks, for example, grow a new set of teeth. Rodent incisors grow and wear away continually through gnawing, which helps maintain constant length.
The industry of the beaver is due in part to this qualification. Many rodents such as voles and guinea pigs, but not mice, as well as leporidae like rabbits, have continuously growing molars in addition to incisors. Teeth are not always attached to the jaw. In many reptiles and fish, teeth are attached to the palate or to the floor of the mouth, forming additional rows inside those on the jaws proper; some teleosts have teeth in the pharynx. While not true teeth in the usual sense, the dermal denticles of sharks are identical in structure and are to have the same evolutionary origin. Indeed, teeth appear to have first evolved in sharks, are not found in the more primitive jawless fish – while lampreys do have tooth-like structures on the tongue, these are in fact, composed of keratin, not of dentine or enamel, bear no relationship to true teeth. Though "modern" teeth-like structures with dentine and enamel have been found in late conodonts, they are now supposed to have evolved independently of vertebrates' teeth.
Living amphibians have small teeth, or none at all, since they feed only on soft foods. In reptiles, teeth are simple and conical in shape, although there is some variation between species, most notably the venom-injecting fangs of snakes; the pattern of incisors, canines and molars is found only in mammals, to varying extents, in their evolutionary ancestors. The numbers of these types of teeth vary between species; the genes governing tooth development in mammals are homologous to those involved in the development of fish scales. Study of a tooth plate of a fossil of the extinct fish Romundina stellina showed that the teeth and scales were made of the same tissues found in mammal teeth, lending support to the theory that teeth evolved as a modification of scales. Teeth are among the most distinctive features of mammal species. Paleontologists use teeth to determine their relationships; the shape of the animal's teeth are related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing and grinding.
Carnivores, on the other hand, have canine teeth to tear meat. Mammals, in general, are diphyodont. In humans, the first set starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth. Normal tooth eruption at about six months can be painful. Kangaroos and manatees are unusual among mammals because they are polyphyodonts. In Aardvarks, teeth lack enamel and have many pulp tubules, hence the name of the order Tubulidentata. In dogs, the teeth are less than humans to form dental cavities because of the high pH of dog saliva, which prevents enamel from demineralizing. Sometimes called cuspids, these teeth are shaped like points and are used for tearing and grasping food Like human teeth, whale teeth have polyp-like protrusions located on the root surface of the tooth; these polyps are made of cementum in both species, but in human teeth, the protrusions are located on the outside of the root, while in whales the nodule is located on the inside of the pulp chamber.
While the roots of human teeth are made of cementum on the outer surface, whales have cementum on the entire surface of the tooth with a small layer of enamel at the tip. This small enamel layer is only seen in older whales where the cementum has been worn away to show the underlying enamel; the toothed whale is a suborder of the cetaceans characterized by having teeth. The teeth differ among the species, they may be numerous, with some dolphins bearing over 100 teeth in their jaws. On the other hand, the narwhals have a giant unicorn-like tusk, a tooth containing millions of sensory pathways and used for sensing during feeding and mating, it is the most neurologically complex tooth known. Beaked whales are toothless, with only bizarre teeth found in males; these teeth may be used for feeding but for demonstrating aggression and showmanship. In humans there are 20 primary teeth, 28 to 32 of what's known as permanent teeth, in addition to other four being third molars or wisdom teeth, each of which may or may not g
Tooth enamel is one of the four major tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the visible part of the tooth, covering the crown; the other major tissues are dentin and dental pulp. It is a hard, white to off-white mineralised substance that acts as a barrier to protect the tooth but can become susceptible to degradation by acids from food and drink. In rare circumstances enamel fails leaving the underlying dentine exposed on the surface. Enamel is the hardest substance in the human body and contains the highest percentage of minerals, 96%, with water and organic material composing the rest; the primary mineral is hydroxyapatite, a crystalline calcium phosphate. Enamel is formed on the tooth while the tooth develops within the gum before it erupts into the mouth. Once formed, enamel does not contain blood vessels or nerves. Remineralisation of teeth can repair damage to the tooth to a certain degree but damage beyond that cannot be repaired by the body.
The maintenance and repair of human tooth enamel is one of the primary concerns of dentistry. In humans, enamel varies in thickness over the surface of the tooth thickest at the cusp, up to 2.5 mm, thinnest at its border with the cementum at the cementoenamel junction. 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 blue or translucent off-white tone observable on the upper incisors. Since enamel is semitranslucent, the color of dentin and any material underneath the enamel affects the appearance of a tooth; the enamel on primary teeth has a more opaque crystalline form and thus appears whiter than on permanent teeth. The large amount of mineral in enamel accounts not only for its strength but for its brittleness. Tooth enamel has a Young's modulus 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 does not contain collagen, as found in other hard tissues such as dentin and bone, but it does contain two unique classes of proteins: amelogenins and enamelins. While the role of these proteins is not 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 totally without 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; the basic unit of enamel is called an enamel rod. Measuring 4–8 μm in diameter, an enamel rod, formally called an enamel prism, is a 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, the bottom, or tail, oriented toward the root of the tooth; the arrangement of the crystals within each enamel rod is complex.
Both ameloblasts and Tomes' processes 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 from the long axis. The arrangement of enamel rods is understood more than their internal structure. Enamel rods are found in rows along the tooth, within each row, the long axis of the enamel rod is perpendicular to the underlying dentin. In permanent teeth, the enamel rods near the cementoenamel junction tilt toward the root of the tooth. Understanding enamel orientation is 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 has the same composition as enamel rod, however a histologic 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.
Striae of Retzius are incremental lines. 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 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 lost through tooth wear, except on the protected cervical regions of some teeth the permanent maxillary central incisors and first premolars, may be confused as dental calculus.
Darker than the other incremental lines, the neonatal line is an incremental