Enamel tufts

Enamel tufts are hypomineralized ribbon-like structures that run longitudinally to the tooth 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. Enamel tufts are hypomineralized ribbon-like structures that run longitudinally to the tooth 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, enamel tufts are ‘‘closed cracks’’ or defects which, in their manner of propagating, act to prevent enamel fractures. 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 molars of animals that crush hard food objects, such as nuts (crushed by apes) and shellfish (crushed by sea otters). Each tuft consists of several unconnected leaves that start near the dentinoenamel junction. These defects as they pass through the enamel rods 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'. 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 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. 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 rods. 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 of enamel next to the dentin. Decussation is another factor by which cracks form wavy stepwise extensions that arrest their further development. Enamel tufts also self-heal 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.