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, whereas armadillos have none.[1]

Incisor
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Permanent teeth of right half of lower dental arch, seen from above.
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The permanent teeth, viewed from the right.
Details
Identifiers
Latindens incisivus
MeSHD007180
TAA05.1.03.004
FMA12823
Anatomical terminology

Structure

Adult humans normally have eight incisors, two of each type. The types of incisor are:

Children with a full set of deciduous teeth (primary teeth) also have eight incisors, named the same way as in permanent teeth. Young children may have from zero to eight incisors depending on the stage of their tooth eruption and tooth development. Typically, the mandibular central incisors erupt first, followed by the maxillary central incisors, the mandibular lateral incisors and finally the maxillary laterals. The rest of the primary dentition erupts after the incisors.[2]

Apart from the first molars, the incisors are also the first permanent teeth to erupt, following the same order as the primary teeth, among themselves.

Other animals

Among other animals, the number varies from species to species. Opossums have 18, whereas armadillos have none. Cats, dogs, foxes, pigs, and horses have twelve. Rodents have four. Rabbits and hares (lagomorphs) were once considered rodents, but are distinguished by having six—one small pair, called "peg teeth", is located directly behind the most anterior pair. Incisors are used to bite off tough foods, such as red meat.

Cattle (cows, bulls, etc.) have none on top but a total of six on the bottom.

Function

In cats, the incisors are small; biting off meat is done with the canines and the carnassials. In elephants, the upper incisors are modified into curved tusks (unlike with Narwhals, where it is a canine that develops into a straight and twisted tusk).[3] The incisors of rodents grow throughout life and are worn by gnawing. In humans, the incisors serve to cut off pieces of food, as well as in the grip of other food items.

Additional images

3D Medical Animation Still Showing Types of Teeth

Medical animation showing Incisor teeth and its arrangement in the mouth of an adult human being.

Illu mouth

Mouth (oral cavity)

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Left maxilla. Outer surface.

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Base of skull. Inferior surface.

See also

References

  1. ^ "Archives". dentalcare.com. Archived from the original on 29 April 2018. Retrieved 29 April 2018.
  2. ^ Scheid, RC. (2012). Woelfel's dental anatomy (8 ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.
  3. ^ Nweeia, Martin; Eichmiller, Frederick C.; Hauschka, Peter V.; Tyler, Ethan; Mead, James G.; Potter, Charles W.; Angnatsiak, David P.; Richard, Pierre R.; et al. (30 March 2012). "Vestigial Tooth Anatomy and Tusk Nomenclature for Monodon Monoceros". The Anatomical Record. 295 (6): 1006–1016. doi:10.1002/ar.22449. PMID 22467529.

External links

  • Media related to Incisors at Wikimedia Commons
Bharattherium

Bharattherium is a mammal that lived in India during the Maastrichtian (latest Cretaceous) and possibly the Paleocene. The genus has a single species, Bharattherium bonapartei. It is part of the gondwanathere family Sudamericidae, which is also found in Madagascar and South America during the latest Cretaceous. The first fossil of Bharattherium was discovered in 1989 and published in 1997, but the animal was not named until 2007, when two teams independently named the animal Bharattherium bonapartei and Dakshina jederi. The latter name is now a synonym. Bharattherium is known from a total of eight isolated fossil teeth, including one incisor and seven molariforms (molar-like teeth, either premolars or true molars).

Bharattherium molariforms are high, curved teeth, with a height of 6 to 8.5 millimetres (0.24 to 0.33 in). In a number of teeth tentatively identified as fourth lower molariforms (mf4), there is a large furrow on one side and a deep cavity (infundibulum) in the middle of the tooth. Another tooth, perhaps a third lower molariform, has two furrows on one side and three infundibula on the other. The tooth enamel has traits that have been interpreted as protecting against cracks in the teeth. The hypsodont (high-crowned) teeth of sudamericids like Bharattherium are reminiscent of later grazing mammals, and the discovery of grass in Indian fossil sites contemporaneous with those yielding Bharattherium suggest that sudamericids were indeed grazers.

Dental anatomy

Dental anatomy is a field of anatomy dedicated to the study of human tooth structures. The development, appearance, and classification of teeth fall within its purview. (The function of teeth as they contact one another falls elsewhere, under dental occlusion.) Tooth formation begins before birth, and the teeth's eventual morphology is dictated during this time. Dental anatomy is also 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.

Usually, there are 20 primary ("baby") 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 usually are found in the maxilla (upper jaw) and the other 10 in the mandible (lower jaw). Among permanent teeth, 16 are found in the maxilla and the other 16 in the mandible. Most of the teeth have distinguishing features.

FDI World Dental Federation notation

FDI World Dental Federation notation is a dental notation widely used by dentists internationally to associate information to a specific tooth.Developed by the FDI World Dental Federation, World Dental Federation notation is also known as ISO 3950 notation.

Orientation of the chart is traditionally "dentist's view", i.e. patient's right corresponds to notation chart left. The designations "left" and "right" on the chart below correspond to the patient's left and right.

Globulomaxillary cyst

The globulomaxillary cyst is a cyst that appears between a maxillary lateral incisor and the adjacent canine. It exhibits as an "inverted pear-shaped radiolucency" on radiographs, or X-ray films.

The globulomaxillary cyst often causes the roots of adjacent teeth to diverge.

This cyst should not be confused with a nasopalatine cyst.

The developmental origin has been disputed. Today, most literature agree based on overwhelming evidence that the cyst is predominantly of tooth origin (odontogenic), demonstrating findings consistent with periapical cysts, odontogenic keratocysts or lateral periodontal cysts.

Human tooth development

Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. For human teeth to have a healthy oral environment, all parts of the tooth must develop during appropriate stages of fetal development. Primary (baby) teeth start to form between the sixth and eighth week of prenatal development, and permanent teeth begin to form in the twentieth week. If teeth do not start to develop at or near these times, they will not develop at all, resulting in hypodontia or anodontia.

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 that is necessary for the development of teeth.

Hutchinson's teeth

Hutchinson's teeth (also known as Hutchinson's incisor, Hutchinson's sign or Hutchinson-Boeck teeth) is a sign of congenital syphilis. Babies who are having these kind of teeth are smaller and more widely spaced than normal and which have notches on their biting surfaces. It named after Sir Jonathan Hutchinson, an English surgeon and pathologist, who first described it.

Hutchinson's teeth form part of Hutchinson's triad.

Incisive foramen

In the human mouth, the incisive foramen, also called anterior palatine foramen, or nasopalatine foramen is a funnel-shaped opening in the bone of the oral hard palate immediately behind the incisor teeth where blood vessels and nerves pass. The incisive foramen is continuous with the incisive canal, this foramen or group of foramina is located behind the central incisor teeth in the incisive fossa of the maxilla.

The incisive foramen receives the nasopalatine nerves from the floor of the nasal cavity along with the sphenopalatine artery supplying the mucous membrane covering the hard palate of the mouth.

In many other species, the incisive foramina allow for passage of ducts to the vomeronasal organ.

Incisor procumbency

In rodents, incisor procumbency refers to the orientation of the upper incisor, defined by the position of the cutting edge of the incisor relative to the vertical plane of the incisors. Proodont incisors have the cutting edge in front of the vertical plane, orthodont teeth have it perpendicular to the plane, opisthodont incisors have it behind the plane, and hyper-opisthodont teeth have the cutting edge even behind the back of the alveolus of the incisor.Phyllotini are mostly opisthodont, but Auliscomys and Galenomys are orthodont and have sometimes even been described as proodont, and Eligmodontia, Loxodontomys, and some species of Calomys are hyper-opisthodont. Irenomys, Reithrodon, and Neotomys, formerly classified as phyllotines, are also hyper-opisthodont. Oryzomyini are also mostly opisthodont, but Amphinectomys savamis, Handleyomys fuscatus, Melanomys caliginosus, Mindomys hammondi, Scolomys melanops, and Sigmodontomys aphrastus are orthodont.

Inferior alveolar artery

The inferior alveolar artery (inferior dental artery) is an artery of the face. It is a branch of the first portion of the maxillary artery.

Mandibular canal

In human anatomy, the mandibular canal is a canal within the mandible that contains the inferior alveolar nerve, inferior alveolar artery, and inferior alveolar vein. It runs obliquely downward and forward in the ramus, and then horizontally forward in the body, where it is placed under the alveoli and communicates with them by small openings.

On arriving at the incisor teeth, it turns back to communicate with the mental foramen, giving off a small canal known as the mandibular incisive canal, which run to the cavities containing the incisor teeth.It carries branches of the inferior alveolar nerve and artery.

It is continuous with the mental foramen (which opens onto front of mandible) and mandibular foramen (on medial aspect of ramus).

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 cutting food during mastication, commonly known as chewing. There are no cusps on the tooth. Instead, the surface area of the tooth used in eating is called an incisal ridge or incisal edge. Though the two are similar, there are some minor differences between the deciduous (baby) mandibular central incisor and that of the permanent mandibular central incisor. The mandibular central incisors are usually the first teeth to appear in the mouth, typically around the age of 6-8 months.

Mandibular lateral incisor

The mandibular lateral incisor is the tooth located distally (away from the midline of the face) from both mandibular central incisors of the mouth and mesially (toward the midline of the face) from both mandibular canines. As with all incisors, their function is for shearing or cutting food during mastication, commonly known as chewing. There are no cusps on the teeth. Instead, the surface area of the tooth used in eating is called an incisal ridge or incisal edge. Though relatively the same, there are some minor differences between the deciduous (baby) mandibular lateral incisor and that of the permanent mandibular lateral incisor.

In the universal system of notation, the deciduous mandibular lateral incisors are designated by a letter written in uppercase. The right deciduous mandibular lateral incisor is known as "Q", and the left one is known as "N". The international notation has a different system of notation. Thus, the right deciduous mandibular lateral incisor known as "82", and the left one is known as "72".

In the universal system of notation, the permanent mandibular lateral incisors are designated by a number. The right permanent mandibular lateral incisor is known as "26", and the left one is known as "23". 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 lateral incisors would have the same number, "2", but the right one would have the symbol, "┐", over it, while the left one would have, "┌". The international notation has a different numbering system than the previous two, and the right permanent mandibular lateral incisor is known as "42", and the left one is known as "32".

Maxillary central incisor

The maxillary central incisor is a human tooth in the front upper jaw, or maxilla, and is usually the most visible of all teeth in the mouth. It is located mesial (closer to the midline of the face) to the maxillary lateral incisor. As with all incisors, their function is for shearing or cutting food during mastication (chewing). There is typically a single cusp on each tooth, called an incisal ridge or incisal edge. Formation of these teeth begins at 14 weeks in utero for the deciduous (baby) set and 3–4 months of age for the permanent set.There are some minor differences between the deciduous maxillary central incisor and that of the permanent maxillary central incisor. The deciduous tooth appears in the mouth at 8–12 months of age and shed at 6-7 years, and is replaced by the permanent tooth around 7–8 years of age. The permanent tooth is larger and is longer than it is wide. The maxillary central incisors contact each other at the midline of the face. The mandibular central incisors are the only other type of teeth to do so. The position of these teeth may determine the existence of an open bite or diastema. As with all teeth, variations of size, shape, and color exist among people. Systemic disease, such as syphilis, may affect the appearance of teeth.

Maxillary lateral incisor

The maxillary lateral incisors are a pair of upper (maxillary) teeth that are located laterally (away from the midline of the face) from both maxillary central incisors of the mouth and medially (toward the midline of the face) from both maxillary canines. As with all incisors, their function is for shearing or cutting food during mastication, commonly known as chewing. There are generally no cusps on the teeth, but the rare condition known as talon cusps are most prevalent on the maxillary lateral incisors. The surface area of the tooth used in eating is called an incisal ridge or incisal edge. Though relatively the same, there are some minor differences between the deciduous (baby) maxillary lateral incisor and that of the permanent maxillary lateral incisor. The maxillary lateral incisors occlude in opposition to the mandibular lateral incisors.

Maxillary lateral incisor agenesis

Maxillary lateral incisor agenesis (MLIA) is lack of development (agenesis) of one or both of the maxillary lateral incisor teeth. In normal human dentition, this would be the second tooth on either side from the center of the top row of teeth. The condition is bilateral if the incisor is absent on both sides or unilateral if only one is smissing. It appears to have a genetic component.

Megalomys audreyae

Megalomys audreyae, known as the Barbudan (?) muskrat or the Barbuda giant rice-rat, is an extinct oryzomyine rodent from Barbuda in the Lesser Antilles. Described on the basis of a single mandible (lower jaw) with the first molar missing and an isolated upper incisor, both of uncertain but Quaternary age, it is one of the smaller members of the genus Megalomys. Little is known about the animal, and its provenance and distinction from "Ekbletomys hypenemus", an even larger extinct oryzomyine that also occurred on Barbuda, have been called into question. The toothrow in the lower jaw has a length of 8.7 mm at the alveoli. The third molar is relatively narrow and both the second and third molars have a wide valley between their outer cusps.

Sciurognathi

Sciurognathi is a suborder of rodents that includes squirrels, chipmunks, beavers, and many types of mice. The group is characterized by a specific shape to the lower jaw. In sciurognaths, the angular process of the jaw is in the same plane as the root of the incisors. This is in contrast to the suborder Hystricognathi where the angular process is outside the plane formed at the root of the incisor due to the presence of a shelf for muscle attachment.

The sciurognathous condition is considered to be the primitive condition in rodents, and is therefore not a good character for cladistic analysis. Although hystricognaths are almost universally accepted as representing a real evolutionary grouping, most researchers do not consider Sciurognathi as an equally valid group. In particular, gundis are thought to be more closely related to the hystricognathous rodents than to other sciurognaths. In spite of this, most texts continue to use these two suborders due primarily to a lack of a viable alternative.

Alternatively, some texts group rodents into three suborders on the basis of the shape of the infraorbital canal. According to this taxonomy the rodents are divided into the suborders Sciuromorpha, Hystricomorpha, and Myomorpha.

Tooth

A tooth (plural 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, also use teeth for hunting or for defensive purposes. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness. The cellular tissues that ultimately 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, and this pattern is also found in some fish, and in crocodilians. In most teleost fish, however, the teeth are attached to the outer surface of the bone, while in 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 (monophyodont) while others develop many sets (polyphyodont). Sharks, for example, grow a new set of teeth every two weeks to replace worn teeth. Rodent incisors grow and wear away continually through gnawing, which helps maintain relatively 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, as they are in mammals. 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 even have teeth in the pharynx. While not true teeth in the usual sense, the dermal denticles of sharks are almost identical in structure and are likely to have the same evolutionary origin. Indeed, teeth appear to have first evolved in sharks, and are not found in the more primitive jawless fish – while lampreys do have tooth-like structures on the tongue, these are in fact, composed of keratin, not of dentine or enamel, and 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 later vertebrates' teeth.Living amphibians typically have small teeth, or none at all, since they commonly feed only on soft foods. In reptiles, teeth are generally simple and conical in shape, although there is some variation between species, most notably the venom-injecting fangs of snakes. The pattern of incisors, canines, premolars and molars is found only in mammals, and to varying extents, in their evolutionary ancestors. The numbers of these types of teeth vary greatly between species; zoologists use a standardised dental formula to describe the precise pattern in any given group.

Universal Numbering System

The Universal Numbering System also called the "American System", is a dental notation system for associating information to a specific tooth used in the United States.

See video for details

https://www.youtube.com/watch?v=i5Ihx2aV7VA&t=51s

In the rest of the world, a different International Standard (DIN EN) ISO 3950:2016 is used.

Nomenclature
Teeth
Maxillary teeth
Mandibular teeth
Parts

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