Enamel rod

Enamel rod

An Enamel rod is the basic unit of tooth enamel. The antiquated term is enamel prism. 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 dentin. 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.

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  • enamel rod — n one of the elongated prismatic bodies making up the enamel of a tooth called also enamel prism …   Medical dictionary

  • enamel rod — noun : one of the elongated prismatic bodies making up the enamel of a tooth …   Useful english dictionary

  • enamel prism sheath — enamel rod sheath a sheath of organic tissue completely or partially surrounding each enamel prism. Called also prism s. and rod s …   Medical dictionary

  • Rod sheath — The rod sheath is an area identified in histologic sections of a tooth. It is found where enamel rods, the functional unit of enamel, meet interrod enamel. The crystals of both types of enamel meet at sharp angles and form the appearance of a… …   Wikipedia

  • enamel rods — the approximately parallel rods or prisms forming the enamel of teeth. They are enclosed in a sheath of organic matter (the enamel rod sheath, or prism sheath) and are embedded in the interprismatic or cement substance …   Medical dictionary

  • rod sheath — enamel prism s …   Medical dictionary

  • Rod — A type of specialized light sensitive cell (photoreceptor) in the retina of the eye that provides side vision and the ability to see objects in dim light (night vision). By contrast, the cones are the retinal photoreceptors that provide sharp… …   Medical dictionary

  • Tooth enamel — Labeled molar Latin enamelum Code TA …   Wikipedia

  • 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. The location where the… …   Wikipedia

  • Gnarled enamel — is a description of enamel seen in histologic sections of a tooth underneath a cusp. The appearance of enamel appears different and very complex under the cusp, but this is not due to a different arrangement of dental tissues. Instead, the enamel …   Wikipedia

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