The molars or molar teeth are large, flat
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, ...
at the back of the
In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...
. They are more developed in mammals
. They are used primarily to grind food
. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone tooth", from ''mola'',
Millstones or mill stones are stones used in gristmills, for grinding wheat or other grains. They are sometimes referred to as grindstones or grinding stones.
Millstones come in pairs: a wikt:convex, convex stationary base known as the ''be ...
and ''dens'', tooth. Molars show a great deal of diversity in size and shape across mammal groups. The third molar of humans is sometimes
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
In humans, the molar teeth have either four or five cusps
. Adult humans have 12 molars, in four groups of three at the back of the mouth. The third, rearmost molar in each group is called a
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 ...
. It is the last tooth to appear, breaking through the front of the gum at about the age of 20, although this varies from individual to individual. Race can also affect the age at which this occurs, with statistical variations between groups. In some cases, it may not even erupt at all.
The human mouth contains upper (maxillary) and lower (mandibular) molars. They are: maxillary first molar
, maxillary second molar
, maxillary third molar
, mandibular first molar
, mandibular second molar
, and mandibular third molar
In mammals, the crown of the molars and premolars is folded into a wide range of complex shapes. The basic elements of the crown are the more or less conical projections called cusps and the valleys that separate them. The cusps contain both dentine and enamel, whereas minor projections on the crown, called crenulations, are the result of different enamel thickness. Cusps are occasionally joined to form ridges and expanded to form crests.
''Cingula'' is a genus of minute sea snails, marine gastropod mollusks or micromollusks in the family Rissoidae
Rissoidae is a large family of very small and minute sea snails with an operculum, marine gastropod mollusks in the superfamily ...
are often incomplete ridges that pass around the base of the crown.
Mammalian, multicusped cheek teeth
Cheek teeth or post-canines comprise the molar and premolar teeth in mammals. Cheek teeth are multicuspidate (having many folds or tubercles). Mammals have multicuspidate molars (three in placentals, four in marsupials, in each jaw quadrant) and p ... probably evolved from single-cusped teeth in synapsids, although the diversity of therapsid molar patterns and the complexity in the molars of the earliest mammals make determining how this happened impossible. According to the widely accepted "differentiation theory", additional cusps have arisen by budding or outgrowth from the crown, while the rivalling "concrescence theory" instead proposes that complex teeth evolved by the clustering of originally separate conical teeth. Therian mammals (placentals and marsupials) are generally agreed to have evolved from an ancestor with tribosphenic cheek teeth, with three main cusps arranged in a triangle.
Each major cusp on an upper molar is called a cone and is identified by a prefix dependent on its relative location on the tooth: proto-, para-, meta-, hypo-, and ento-. Suffixes are added to these names: -id is added to cusps on a lower molar (e.g., protoconid); -ule to a minor cusp (e.g., protoconulid). A shelf-like ridge on the lower part of the crown (on an upper molar) is called a cingulum
; the same feature on the lower molar a cingulid, and a minor cusp on these, for example, a cingular cuspule or conulid.
The design that is considered one of the most important characteristics of mammals is a three-cusped shape called a tribosphenic molar. This molar design has two important features: the trigonid, or shearing end, and the talonid, or crushing heel. In modern tribosphenic molars, the trigonid is towards the front of the jaw and the talonid is towards the rear.
The tribosphenic tooth is found in insectivore
s and young
The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or mono ...
es (adults have no teeth). Upper molars look like three-pointed mountain ranges; lowers look like two peaks and a third off to the side.
The tribosphenic design appears primitively in all groups of mammals. Some paleontologists believe that it developed independently in monotreme
s (or australosphenidans), rather than being inherited from an ancestor that they share with
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in ...
s and placental
s (or boreosphenidans); but this idea has critics and the debate is still going on. For example, the dentition of the
The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145& ...
monotreme '' Steropodon
'' is similar to those of '' Peramus
'' and dryolestoids
, which suggests that monotremes are related to some pre-tribosphenic therian mammals, but, on the other hand, the status of neither of these two groups is well-established.
The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
mammals, such as '' Shuotherium
'' and '' Pseudotribos
'', have "reversed tribosphenic" molars, in which the talonid is towards the front. This variant is regarded as an example of
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
From the primitive tribosphenic tooth, molars have diversified into several unique morphologies. In many groups, a fourth cusp, the hypocone
(hypoconid), subsequently evolved (see below).
Quadrate (also called quadritubercular or euthemorphic) molars have an additional fourth cusp on the lingual (tongue) side called the hypocone, located posterior to the protocone. Quadrate molars appeared early in mammal evolution and are present in many species, including hedgehog
s, and many
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter includin ...
s, including humans.
There may be a fifth cusp.
In many mammals, additional smaller cusps called conules appear between the larger cusps. They are named after their locations, e.g. a paraconule is located between a paracone and a metacone, a hypoconulid is located between a hypoconid and an entoconid.
In bunodont molars, the cusps are low and rounded hills rather than sharp peaks. They are most common among omnivores such as pigs, bears, and humans.
Bunodont molars are effective crushing devices and often basically quadrate in shape.
dentition is characterized by high-crowned teeth and enamel that extends far past the gum line, which provides extra material for wear and tear.
Some examples of animals with hypsodont dentition are
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...
and horses, all animals that feed on gritty, fibrous material. Hypsodont molars can continue to grow throughout life, for example in some species of Arvicolinae
Hypsodont molars lack both a crown and a neck. The occlusal surface is rough and mostly flat, adapted for crushing and grinding plant material. The body is covered with cementum both above and below the
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.
The gums are part of the soft tissue l ...
l line, below which is a layer of enamel covering the entire length of the body. The cementum and the enamel invaginate
into the thick layer of dentin.
The opposite condition to hypsodont is called brachydont or brachyodont (from ''brachys'' 'short'). It is a type of dentition characterized by low-crowned teeth. Human teeth are brachydont.
A brachydont tooth has a crown above the gingival line and a neck just below it, and at least one root. A cap of enamel covers the crown and extends down to the neck. Cementum is only found below the gingival line. The occlusal surfaces tend to be pointed, well-suited for holding prey and tearing and shredding.
Zalambdodont molars have three cusps, one larger on the lingual side and two smaller on the labial side, joined by two crests that form a V- or λ
-shape. The larger inner cusp might be homologous
with the paracone in a tribosphenic molar, but can also be fused with the metacone. The protocone is typically missing. The two smaller labial cusps are located on an expanded shelf called the stylar shelf. Zalambdodont molars are found in, for example, golden mole
s and solenodon
Like zalambdodont molars, dilambdodont molars have a distinct ectoloph, but are shaped like two
Lambda (}, ''lám(b)da'') is the 11th letter of the Greek alphabet, representing the voiced alveolar lateral approximant . In the system of Greek numerals, lambda has a value of 30. Lambda is derived from the Phoenician Lamed . Lambda gave ri ...
s or a W. On the lingual side, at the bottom of the W, are the metacone and paracone, and the stylar shelf is on the labial side. A protocone is present lingual to the ectoloph. Dilambdodont molars are present in
Shrews (family Soricidae) are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to differ ...
s, and some insectivorous bat
Lophodont teeth are easily identified by the differentiating patterns of ridges or lophs of enamel interconnecting the cusps on the crowns. Present in most herbivores, these patterns of lophs can be a simple, ring-like edge, as in
mole rats Mole-rat or mole rat can refer to several groups of burrowing Old World rodents:
* Bathyergidae, a family of about 20 hystricognath species in six genera from Africa also called blesmols.
*''Heterocephalus glaber'', the naked mole-rat.
* Spalacida ...
, or a complex arrangement of series of ridges and cross-ridges, as those in
Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla (, ), are animals—ungulates—who have reduced the weight-bearing toes to three (rhinoceroses and tapirs, with tapirs still using four toes on the front legs) o ...
, such as
Equidae (sometimes known as the horse family) is the taxonomic family of horses and related animals, including the extant horses, asses, and zebras, and many other species known only from fossils. All extant species are in the genus '' Equus' ...
Lophodont molars have hard and elongated enamel ridges called lophs oriented either along or perpendicular to the dental row. Lophodont molars are common in herbivores that grind their food thoroughly. Examples include
Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a pig, with a short, prehensile nose trunk. Tapirs inhabit jungle and forest regions of South and Central America, with one species inh ...
s, and many rodents.
When two lophs form transverse, often ring-shaped, ridges on a tooth, the arrangement is called bilophodont. This pattern is common in primates, but can also be found in
The lagomorphs are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (hares and rabbits) and the Ochotonidae (pikas). The name of the order is derived from the Ancient Greek ''lagos'' (λαγ� ...
(hares, rabbits, and pikas) and some rodents.
Extreme forms of lophodonty in
Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantida ...
s and some rodents (such as '' Otomys
'') is known as loxodonty.
The African elephant
belongs to a genus called ''Loxodonta'' because of this feature.
molars (so-named after moon goddess Selene
), the major cusp is elongated into crescent-shaped ridge. Examples include most even-toed ungulates, such as cattle and
Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the re ...
Many carnivorous mammals have enlarged and blade-like teeth especially adapted for slicing and chopping called carnassial
s. A general term for such blade-like teeth is secodont or plagiaulacoid.
* Dental formula
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, ...
Overview of molar morphology and terminology
Types of teeth