Tissue of the teeth. Dr Jamal Naim PhD in Orthodontics. Enamel. Amelogenesis. Enamel formation Enamel maturation Maturation means also mineralization and does not wait the complete formation of Enamel. Amelogenesis. Enamel formation: Dentino-enamel membrane:
Dr Jamal Naim
PhD in Orthodontics
Maturation means also mineralization and does not wait the complete formation of Enamel.
Maturation occurs by the growth of the primary crystals till they fuse together
COLOUR they fuse together
Yellowish white to grayish white; it depends on:
It is thick at the incisal edge and cusp tip of molars and premolars (2-2.5mm) and ends cervically as knife edge.
It is the hardest calcified tissue in human body because of its high calcification and crystal orientation.
It is greater at the outer surface and decrease at the DEJ.
It is greater at the cusp tip or incisal edge and decrease at the cervical line.
Although of its hardness, enamel is brittle especially when looses the underlying elastic healthy dentin.
Enamel acts as a semi-permeable membrane for certain ions from:
the organic substance is burnt and the inorganic substance remain
the inorganic substance is dissolved and the organic substance remain
Enamel is formed of:
Rod and interrod enamel:
The border between rod and interrod enamel is distinct because part of the ameloblast membrane is “nonsecretory,” which creates gaps in the mineralization front.
The apatite crystals are oriented parallel to the long axes of the rod in its body and deviate about 65 as they fan out into the margin and the tail.
The rod and interrod enamel differ in the orientation of their crystallites
The interrod enamel
By electron microscopy a common key-hole or paddle-shaperod is seen in cross section.
The head of the rod is toward the occlusal or incisal surface where the tail is cervically.
The enamel rod is perpendicular to the dentin surface;
In deciduous teeth ; the enamel rod is vertical at the cusp tip or incisal edge then become oblique toward the occlusal surface at the middle part and become horizontal at the cervical area (so enamel ends cervically abruptly).
In permanent teeth; the direction of the enamel rods are similar to that of the deciduous teeth at the occlusal 2/3 but at the cervical region are directed root wise (so the enamel ends cervically as a knife edge).
Course: the enamel rod starts straight at dentino-enamel junction (D.E.J.) for about 30 µ then has a wavy course till near the outer surface of enamel where it become straight once more.
Wavy course of enamel rods
Wavy course of enamel rods
At the incisal edge or cusp tip the enamel rod has a twisted course and is called gnarled enamel
Twisted course of enamel rods
Electron micrographs of the Dentino-enamel-Junction orientation.
The surface of Dentin after removing of Enamel
It is an odontoblastic process which extends in between the cells of inner dental epithelium before the formation of enamel.
hypo-calcified prisms and inter-prismatic substance
Enamel cracks post-eruptive, can reach dentine
Enamel cracks pre-eruptive,
can reach dentine
Filled with epithelial cell or connective tissue
Filled with organic contentsof saliva
It is limited to enamel
To differentiate between true lamella and crack we do careful decalcification:
the true lamella will remain where cracks will disappear.
Enamel lamella could act as caries spread way.
striae of Retzius
It is an enlarged stria of Retzius which present in all deciduous teeth and 1st permanent molar.
This line separates between enamel formed before birth and enamel formed after birth.
This line is due to the sudden change of nutrition and environment due to birth.
The quality of enamel formed before birth is better than that formed after birth, because of the more protected conditions and constant nutrition of the fetus.
Hunter - shreger bands:
It is an optical phenomenon caused by changes of rod direction (the wavy course).
They are seen clearly by longitudinal ground section viewed by reflected light at cervical 2/3.
The phenomenon appears as dark and light alternating bands, starting from the D.E.J. and ends shortly from the outer surface of enamel where the enamel rods run straight to the surface.
Hunter - shreger bands
The external manifestation of the incremental lines of Retzius represented as transverse wave like grooves on the surface of the enamel are known as perikymata.
Structure less enamel:
This layer is highly mineralized than the rest of enamel and its thickness is 30 microns.
This surface layer of enamel is aprismatic.
A fibrilar cementum:
A type of cementum formed on the cervical part of the enamel for a short distance.
It is formed due to the degeneration of the reduced dental epithelium covering the cervical area of the enamel before eruption.
A fibrilar cementum