Enamel rod
Encyclopedia
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. In cross section, it is best compared to a keyhole with the top, or head, oriented toward the crown of the tooth and the bottom, or tail, oriented toward the root of the tooth.
Enamel rods are found in rows along the tooth. Within each row, the long axis of the enamel rod generally is perpendicular to the underlying enamel-dentine junction. In permanent teeth, the enamel rods near the cementoenamel junction
(CEJ) tilt slightly more toward the root of the tooth than would be expected. Knowing the orientation of enamel is very important in restorative dentistry because enamel unsupported by underlying dentin
is prone to fracture and usually is avoided.
The arrangement of crystals within each enamel rod is highly complex. For the most part, the enamel crystals are oriented parallel to the long axis of the rod. The further away the crystals are from the central axis, the more their own orientation diverges.
The area around the enamel rod is known as interrod enamel
. Interrod enamel has the same composition as the enamel rods. Nonetheless, a histologic distinction is made between the two because crystal orientation is different in each. The crystals lie nearly perpendicular to the enamel rod.
Direction of Enamel Rod...
Permanent tooth:- From the dentinoenamel junction apically in the cervical third of the crown.
Primary tooth:- From the dentinoenamel junction occlusally in the cervical third of the crown.
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...
. Measuring 4 μm wide to 8 μm high, an enamel rod is a tightly packed, highly organized mass of hydroxyapatite crystals. In cross section, it is best compared to a keyhole with the top, or head, oriented toward the crown of the tooth and the bottom, or tail, oriented toward the root of the tooth.
Enamel rods are found in rows along the tooth. Within each row, the long axis of the enamel rod generally is perpendicular to the underlying enamel-dentine junction. In permanent teeth, the enamel rods near the cementoenamel junction
Cementoenamel junction
The cementoenamel junction, frequently abbreviated as the CEJ, is an anatomical border identified on a tooth. It is the location where the enamel, which covers the anatomical crown of a tooth, and the cementum, which covers the anatomical root of a tooth, meet...
(CEJ) tilt slightly more toward the root of the tooth than would be expected. Knowing the orientation of enamel is very important in restorative dentistry because enamel unsupported by underlying 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...
is prone to fracture and usually is avoided.
The arrangement of crystals within each enamel rod is highly complex. For the most part, the enamel crystals are oriented parallel to the long axis of the rod. The further away the crystals are from the central axis, the more their own orientation diverges.
The area around the enamel rod is known as interrod enamel
Interrod enamel
Interrod enamel is histologically identified on microscopic views of tooth enamel. Because interrod enamel is located around enamel rods, the areas of interrod enamel enhances the "keyhole" appearance of enamel rods by acting as its border...
. Interrod enamel has the same composition as the enamel rods. Nonetheless, a histologic distinction is made between the two because crystal orientation is different in each. The crystals lie nearly perpendicular to the enamel rod.
Direction of Enamel Rod...
Permanent tooth:- From the dentinoenamel junction apically in the cervical third of the crown.
Primary tooth:- From the dentinoenamel junction occlusally in the cervical third of the crown.