The Structure Of Enamel

The Structure Of Enamel

Describe the structure of enamel (or) Describe the histology of enamel.
Answer:

Structure of enamel:

• Enamel mainly consists of

1. Enamel rods or prisms.
2. Interprismatic cementing substance
3. Rod sheath.

1. Enamel rods or prims:

• They are long, slender cylindrical structures.

Enamel Number:

• It varies.
  • 5 million – in lower lateral incisors
  • 12 million – in upper first molars.

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Course:

• It has a wavy course.
• It extends from the dentin enamel junction to the surface of the tooth.

Enamel Size:

• The length is greater than the thickness of the enamel.
• Size is 5 pm in breadth, 9 pm in length, and diameter averages 4 pm
• However, the diameter increases from the dentin enamel junction towards the enamel surface at a ratio of about 1:2.

Enamel Outlines:

• Arcade outlines are seen near DEJ.
• Keyhole-shaped outlines are seen at the enamel surface.

Direction:

• Perpendicular to the surface of the dentin.
• Vertical – near the cusp tip.
• Horizontal – at cervical in primary teeth.
• Apically oriented – at the cervical area in permanent teeth.

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2. Interprismatic region:

• It surrounds each rod
• Its crystals are oriented in a direction different from those making up the rod.
• It is usually less titan 1 micron in width.

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3. Rod sheath:

• The boundary between rod and interrod enamel is delimited by a narrow space containing organic material known as rod sheath.
• The rod sheath occurs because of the greater space that exists between the ends of the crystals of the interrod region as these crystals meet at sharp angles.

Several other structures are present:

1. Incremental lines of retail:

• They are a series of dark lines extending from the dentin enamel junction toward the tooth surface.
• They reflect incremented growth of the enamel.
• In the cervical parts, they run obliquely while from the DEJ to the surface they deviate occlusal.

2. Neonatal line:

• It is an enlarged stria of Retzius that apparently reflects the great physiologic changes occurring at birth.

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3. Dentino enamel junction:

• It is the junction between two hard tissues enamel and dentin.
• It is a scalloped line.
• The convexities of the scallops are directed towards the dentin.

4. Enamel lamellae:

• They consist of linear, longitudinally oriented defects filled with organic material.

5. Enamel tufts:

• They project from the DEJ for a short distance into the enamel.
• They appear to be branched and contain a greater concentration of enamel proteins.

6. Enamel spindles:

• They seem to originate from the odontoblastic process.

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7. Suiface structures:

Perikymata:

• They are transverse, wave-like grooves.
• They are continuous around a tooth and usually lie parallel to each other and to the CEJ.

Rod ends:

• They are concave and vary in depth and shape.
• They are shallowest in the cervical area and deepest near incisal and occlusal edges.

Crocks:

1. They are narrow, fissure-like structures that are seen on almost all surfaces.
2. They are the outer edges of lamellae.