Enamel tufts are hypomineralized ribbon-like structures that run longitudinally to the

tooth 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, tea ...

axis and extend from the dentinoenamel junction (DEJ) one fifth to a third into the enamel. They are called ''tufts'' due to their wavy look within the enamel microstructure.

Biomechanically Biomechanics is the study of the structure, function and motion of the mechanical aspects of biological systems, at any level from whole organisms to organs, cells and cell organelles, using the methods of mechanics. Biomechanics is a branch of ...

, enamel tufts are ''closed cracks'' or

defect Defect or defects may refer to: Related to failure * Angular defect, in geometry * Birth defect, an abnormal condition present at birth * Crystallographic defect, in the crystal lattice of solid materials * Latent defect, in the law of the sale o ...

s which, in their manner of propagating, act to prevent enamel

fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...

s. This aspect is being studied to see how to make more fracture-resistant materials. However, they can also form without stress during enamel development. Enamel tufts are most common in the enamel of molars of animals that crush hard food objects, such as nuts (crushed by

ape Apes (collectively Hominoidea ) are a superfamily of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and Europe in prehistory, and counting humans are found global ...

s) and shellfish (crushed by

sea otter The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern Pacific Ocean, North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of ...

s).

Microstructure

Each tuft consists of several unconnected leaves that start near the dentinoenamel junction. These defects as they pass through the

enamel rod An enamel prism, or enamel rod, is the basic unit of tooth enamel. Measuring 3-6 μm in diameter in primates, enamel prism are tightly packed hydroxyapatite crystals structures. The hydroxyapatite crystals are hexagonal in shape, providing rigidi ...

s to the surface become progressively more fragmented and fibrillar. Scanning electron micrography finds that there are two kinds: one that is continuous with the enamel-dentine membrane at the dentinoenamel junction and that is acid-resistant, and another that is made up of empty spaces between the prisms and hard walls covered with organic matter. Enamel tufts are particularly common on low-crowned, blunt-cusped molars used in crushing; these are called " bunodonts".

Development

The origin of enamel tufts is not fully understood. It appears, however, that they may arise during enamel development in areas where enamel rods are crowded at the boundaries where they are bundled together, creating periodic weakened mineral reduced planes. These weaknesses then produce transient longitudinal cracks in the transverse plane of the developing enamel. Their formation has been attributed to

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phra ...

and are considered a form of defect. However, stress upon the enamel is not needed to produce them since they occur in impacted

third molar The third molar, commonly called wisdom tooth, is the most posterior of the three molars in each quadrant of the human dentition. The age at which wisdom teeth come through ( erupt) is variable, but this generally occurs between late teens a ...

s that are not affected by biting forces.

Enamel fractures

Some sources consider tufts to be of no clinical significance. However, they have been noted to be an important potential source of enamel fractures that arise after extended use or overloading. It appears that, although enamel easily starts to form the fracture defects of enamel tufts, they then enable enamel to resist the further progress of these fractures, ultimately preventing mechanical failure. This fracture resistance is why tooth enamel is three times stronger than its constituent

hydroxyapatite Hydroxyapatite (International Mineralogical Association, IMA name: hydroxylapatite) (Hap, HAp, or HA) is a naturally occurring mineral form of calcium apatite with the Chemical formula, formula , often written to denote that the Crystal struc ...

crystallites that make up its

s. Enamel tufts do not normally lead to enamel failure, due to these defects stabilizing potential fractures. The processes involved include the creation of ''stress shielding'' by increasing the

compliance Compliance can mean: Healthcare * Compliance (medicine), a patient's (or doctor's) adherence to a recommended course of treatment * Compliance (physiology), the tendency of a hollow organ to resist recoil toward its original dimensions (this is a s ...

of enamel next to the

dentin Dentin ( ) (American English) or dentine ( or ) (British English) () is a calcified tissue (biology), tissue of the body and, along with tooth enamel, enamel, cementum, and pulp (tooth), pulp, is one of the four major components of teeth. It i ...

Decussation Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. . Similarly, the anatomical term Chiasm (anatomy), chi ...

is another factor by which cracks form wavy stepwise extensions that arrest their further development. Enamel tufts also

self-heal ''Prunella'' is a genus of herbaceous plants in the family Lamiaceae, also known as self-heals, heal-all, or allheal for their use in herbal medicine. Habitat Most are native to Europe, Asia, and North Africa, but ''Prunella vulgaris'' (comm ...

through a process of being filled with protein rich fluids. Odontologically they can be filled by light-cured composite resin when applied in two applications.

Animals with enamel tufts

While a common feature of animal

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology ...

, enamel tufts are particularly found in animals that crush hard materials with their teeth such as

nuts Nut often refers to: * Nut (fruit), fruit composed of a hard shell and a seed * Nut (food), a dry and edible fruit or seed, including but not limited to true nuts * Nut (hardware), fastener used with a bolt Nut, NUT or Nuts may also refer to: A ...

and

mollusc shell The mollusc (or mollusk) shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes. Not all shelled ...

s. Tufts are found especially in the enamel of

primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

s such as

chimpanzee The chimpanzee (; ''Pan troglodytes''), also simply known as the chimp, is a species of Hominidae, great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close rel ...

orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ...

s and

gorilla Gorillas are primarily herbivorous, terrestrial great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or five su ...

s. They are also found in

bear Bears are carnivoran mammals of the family (biology), family Ursidae (). They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats ...

pig The pig (''Sus domesticus''), also called swine (: swine) or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus '' Sus''. Some authorities cons ...

peccaries Peccaries (also javelinas or skunk pigs) are pig-like ungulates of the family Tayassuidae (New World pigs). They are found throughout Central and South America, Trinidad in the Caribbean, and in the southwestern area of North America. Peccari ...

, and

Biomimicry importance

Enamel is as

brittle A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. ...

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

and yet it can constantly withstand bite forces during

chewing Chewing or mastication is the process by which food is crushed and ground by the teeth. It is the first step in the process of digestion, allowing a greater surface area for digestive enzymes to break down the foods. During the mastication proc ...

as high as 1,000 N many times a day. As such, it has been argued, that enamel tufts is an example of how nature has created a biomechanical solution to the problem of weak internal interfaces that laminate structures would otherwise have. The solutions involved (such as filling growing defects with fluids) has inspired

scientists A scientist is a person who researches to advance knowledge in an area of the natural sciences. In classical antiquity, there was no real ancient analog of a modern scientist. Instead, philosophers engaged in the philosophical study of nature ...

to make novel bioinspired (or

biomimicry Biomimetics or biomimicry is the emulation of the models, systems, and elements of nature for the purpose of solving complex human problems. The terms "biomimetics" and "biomimicry" are derived from (''bios''), life, and μίμησις ('' mīm ...

) materials.

Not to be confused with

Enamel tufts are frequently confused with enamel lamellae, which are also enamel defects, but which differ in two ways: lamella are linear, and not branched, and they exist primarily extending from the enamel surface, through the enamel and towards the dentinoenamel junction, whereas enamel tufts project in the opposite direction. Enamel tufts should also not be confused with the similar

enamel spindles Enamel spindles are "short, linear defects, found at the dentinoenamel junction (DEJ) and extend into the enamel, often being more prevalent at the cusp tips."Histology Course Notes: "Mature Enamel", New Jersey Dental School, 2003-2004, page 2. T ...

. Enamel spindles are also linear defects, similar to lamellae, but they too can be found only at the dentinoenamel junction, similar to enamel tufts. This is because they are formed by entrapment of

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 ...

processes between

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 prior to and during

amelogenesis Amelogenesis is the process of forming tooth enamel, the hard, protective outer layer of teeth. This process begins during tooth development after the initial formation of dentin ( dentinogenesis), the layer beneath the enamel. The inner enamel e ...

References

{{DEFAULTSORT:Enamel Tufts Dental enamel Fracture mechanics Acquired tooth pathology