Enamel Rods Structure in Teeth

Enamel Rods

• Enamel rods have a keyhole shape in transverse section.
• Each rod has a head formed by the rod, commonly directed towards the incisal or occlusal aspect, and a tail formed by interrod, directed towards the cervical region of the teeth.
• Each rod is formed by four ameloblasts, contributing to four different rods.

Structure of Enamel Rods

• Enamel is built from closely packed and long ribbon-like crystals, specifically apatite crystals.
• The length of these crystals ranges from 0.05 to 1 micrometer, with an average thickness of 30 nanometers and a width of 90 micrometer.

Course of Enamel Rods

• Enamel rods run a tortuous course from the dentino-enamel junction (DEJ) to the enamel surface.
• The rods have an oblique direction and wavy course, with their length greater than the thickness of the enamel.
• Rods in the cusp region are longer than those in the cervical region.

Striations

• Each enamel rod is built of segments separated by dark lines, giving it a striated appearance.
• The segments are approximately 4 micrometer in length.

Direction of Rods

• Enamel rods are oriented at right angles to the dentin surface.
• In deciduous teeth, the rods are approximately horizontal in the central part, and increasingly oblique in the cusp and incisal regions.
• In permanent teeth, the rods are similar in the occlusal third, and deviate from horizontal in an apical direction in the cervical region.

Gnarled Enamel

• Gnarled enamel appears when the disks are cut in an oblique plane, especially near the dentin, leading to an optical appearance of enamel rods intertwining irregularly.

Clinical Significance

• The irregular twist and intertwining of enamel rods may be associated with increased strength of enamel, enabling it to withstand strong masticatory forces.

Hunter Schreger Bands

• Hunter Schreger bands originate at the DE border and pass outward, ending at some distance from the outer enamel surface.
• These bands consist of alternate zones of slightly different permeability and organic material content.

Incremental Lines / Striae of Retzius

• These are incremental growth lines in enamel, representing the rhythmic deposition of enamel.
• In longitudinal sections of the tooth, they appear as a series of dark lines extending from the dentinoenamel junction toward the tooth surface.

Surface Structures

• Enamel cracks
• Enamel lamellae
• Neonatal lines
• Enamel spindles
• Gnarled enamel
• Enamel tufts
• Dentinoenamel junction
• Odontoblastic processes