Enamel tufts
Encyclopedia
Tooth
Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...
axis and extend from the dentinoenamel junction (DEJ) one fifth to a third into the enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
. They are called ‘‘tufts’’ due to their wavy look within the enamel microstructure.
Biomechanically
Biomechanics
Biomechanics is the application of mechanical principles to biological systems, such as humans, animals, plants, organs, and cells. Perhaps one of the best definitions was provided by Herbert Hatze in 1974: "Biomechanics is the study of the structure and function of biological systems by means of...
, enamel tufts are ‘‘closed cracks’’ or defect
Crystallographic defect
Crystalline solids exhibit a periodic crystal structure. The positions of atoms or molecules occur on repeating fixed distances, determined by the unit cell parameters. However, the arrangement of atom or molecules in most crystalline materials is not perfect...
s which, in their manner of propagating, act to prevent enamel fracture
Fracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
s. This aspect of them 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 molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
s of animals that crush hard food objects, such as nuts (crushed by ape
Ape
Apes are Old World anthropoid mammals, more specifically a clade of tailless catarrhine primates, belonging to the biological superfamily Hominoidea. The apes are native to Africa and South-east Asia, although in relatively recent times humans have spread all over the world...
s) and shellfish (crushed by sea otter
Sea Otter
The sea otter is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg , making them the heaviest members of the weasel family, but among the smallest marine mammals...
s).
Microstructure
Each tuft consists of several unconnected leaves that start near the dentinoenamel junction. These defects as they pass through the enamel rodEnamel rod
An Enamel rod is the basic unit of tooth enamel. Measuring 4 μm wide to 8 μm high, an enamel rod is a tightly packed, highly organized mass of hydroxyapatite crystals...
s to the surface become progressively more fragmented and fibrillar. Scanning electron micrography
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...
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 (physics)
In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...
and are considered a form of defect. However, stress upon the enamel is not needed to produce them since they occur in impacted third molars that are not affected by biting forces.
Enamel fractures
Some sources consider them 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 crystallites that make up its enamel rodEnamel rod
An Enamel rod is the basic unit of tooth enamel. Measuring 4 μm wide to 8 μm high, an enamel rod is a tightly packed, highly organized mass of hydroxyapatite crystals...
s.
Enamel tufts do not normally lead to enamel failure, due to these defects stabilizing potential fractures. The processes involved include them creating ‘‘stress shielding’’ by increasing the compliance
Stiffness
Stiffness is the resistance of an elastic body to deformation by an applied force along a given degree of freedom when a set of loading points and boundary conditions are prescribed on the elastic body.-Calculations:...
of enamel next to the dentin
Dentin
Dentine is a calcified tissue of the body, and along with enamel, cementum, and pulp is one of the four major components of teeth. Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp...
. Decussation
Decussation
Decussation is used in biological contexts to describe a crossing.Examples include:* In the brain, where nerve fibers obliquely cross from one lateral part to the other, that is to say they cross at a level other than their origin...
is another factor by which cracks form wavy stepwise extensions that arrest their further development. Enamel tufts also self-heal
Self-healing material
Self-healing materials are a class of smart materials that have the structurally incorporated ability to repair damage caused by mechanical usage over time. The inspiration comes from biological systems, which have the ability to heal after being wounded...
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 dentitionDentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...
, enamel tufts are particularly found in animals that crush hard materials with their teeth such as nuts
Nut (fruit)
A nut is a hard-shelled fruit of some plants having an indehiscent seed. While a wide variety of dried seeds and fruits are called nuts in English, only a certain number of them are considered by biologists to be true nuts...
and mollusc shell
Mollusc shell
The mollusc 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...
s. Tufts are found especially in the enamel of primates such as chimpanzees, orangutans, and gorillas. They are also found in bears, pigs
PIGS
PIGS is a four letter acronym that can stand for:* PIGS , Phosphatidylinositol glycan anchor biosynthesis, class S, a human gene* PIGS , the economies of Portugal, Italy , Greece and Spain...
, peccaries, and sea otters.
Biomimicry importance
Enamel is as brittleBrittle
A material is brittle if, when subjected to stress, it breaks without significant deformation . Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses ...
as glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
yet can constantly withstand many times a day bite forces during chewing as high as 1,000 N. As such, it has been argued they are an example of how nature has created a biomechanical solution to the problem of laminate structures
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
that would otherwise have weak internal interfaces. The solutions involved (such as filling growing defects with fluids) have been suggested to provide ideas that might be copied technologically by scientists seeking to make novel bioinspired (or biomimicry
Biomimicry
Biomimicry or biomimetics is the examination of nature, its models, systems, processes, and elements to emulate or take inspiration from in order to solve human problems. The term biomimicry and biomimetics come from the Greek words bios, meaning life, and mimesis, meaning to imitate...
) materials.
Not to be confused with
Enamel tufts are frequently confused with enamel lamellaeEnamel lamellae
Enamel lamellae are a type of hypomineralized structure in teeth that extend either from the dentinoenamel junction to the surface of the enamel, or vice versa. In essence, they are prominent linear enamel defects, but are of no clinical consequence...
, 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
Enamel spindles are "short, linear defects, found at the dentinoenamel junction and extend into the enamel, often being more prevalent at the cusp tips." The DEJ is the interface of the enamel and the underlying dentin...
. 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
Odontoblast
In vertebrates, an odontoblast is a biological 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 creation of dentin, the substance under the tooth enamel....
processes between ameloblast
Ameloblast
Ameloblasts are cells, present only during tooth development, that deposit tooth enamel, the hard outermost layer of the tooth that forms the chewing surface....
s prior to and during amelogenesis
Amelogenesis
Amelogenesis is the formation of enamel on teeth and occurs during the crown stage of tooth development after dentinogenesis, which is the formation of dentine. Although dentine must be present for enamel to be formed, it is also true that ameloblasts must be present in order for dentinogenesis to...
.