Oral Histology & Development

Enamel Characteristic


Enamel lamellae


Appearance:
It’s seen as a crack on the surface of the enamel that extends inwards

Cause:
Defects in enamel. (Contains abnormally high levels of organic material)



Enamel tufts

Appearance:
Grass like, branched, dark, short lines that extend outward from DEJ into 1/5th to 1/10th of enamel thickness

Cause:
Due to rod orientation changes as a result of the presence of a high level of protein compared to the surrounding enamel


Enamel spindles:

Appearance:  
They appear as short dark finger extensions that extend from DEJ to the enamel.

Cause:
Before the mineralisation process occur the odontoblastic processes pass across the basement membrane to the dentinoenamel junction, but some of them are trapped during enamel mineralisation resulting in the formation of enamel spindles.


Striae of Retzius

Appearance:
Longitudinal tooth section - seen as dark striations / lines running from the DEJ to enamel surface in a cuspal direction.

Cause:
These structural differences are either due to: 

    
  • Normal physiological changes of the ameloblasts 

  • As a result of functional interruption such as the neo-natal line,  

  • It relates to the incremental deposition of enamel and recruitment of newly differentiated secretory ameloblasts 

Neonatal line

Appearance:
  • Appears as a darkened line that may or may not be present
  • Represents the border line between the enamel matrix formed before and after birth

Cause:
May be formed due to a sudden change in the environment after birth which lead to metabolic disturbance of the ameloblasts


Hunter-Schreger bands

Appearance:
Appear as dark and light alternating zones that can be reversed by changing the direction of light, seen in longitudinal sections in the inner 2/3 of enamel.

Cause:
Different rod orientations of groups of rods. Many theories but non is proven for sure
.


Enamel Surface

Perikymata

Appearance:
Concentric linear grooves where striae of Retzius reach the enamel surface, they  are parallel to  the CEJ and they are separated by ridges

Cause:
  • Varying physiology of tooth crown
  • Growth and development


Aprismatic enamel

Appareance:
Smooth with round depressions of varying depths.

Cause:
The loss of Tome's process by the ameloblasts, toward the end of enamel formation.