Enamel Flashcards by Ky Nguyen

What is Enamel made of

Organic Matrix 4%
water
proteins: amelogenins & enamelins

Inorganic matrix 96%
hydroxyapatite: calcium phosphate

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How is Enamel made? (Amelogensis)

3 phases: Presecretory –> Secretory –> Mineralization

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What is the presecretory phase

Making an Ameloblast:
cytodifferentiation during tooth
development.

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What is the secretory phase

Production of organic matrix:
amelogenin and enamelin

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What is the mineralization phase

Calcification/Mineralization
Inorganic matrix: Hydroxyapatite

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What happens during the early bell stage

Inner Enamel
Epithelial cells
differentiate into
pre-ameloblasts

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What happens during the bell stage

Pre-ameloblasts:
nuclei are located
close to the
basement membrane

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What happens during the Crown stage

Ameloblasts: nuclei
migrate away from the
basement membrane to
opposite end of the cell
as it prepares to secrete
enamel.

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What phase is the dentin-enamel junction formed and how is it formed

Secretory phase: The basement
membrane is replaced
by calcified tissue and
becomes the Dentin-
Enamel Junction.

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What happens after the dentin- enamel junction is formed

The ameloblasts and
odontoblasts move away
from the DEJ in opposite
directions

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What is the mineralization phase

Ground section
Mineralized tissue is intact
Soft connective tissues are lost

Demineralized sections
Soft connective tissue and organic matrices remain.
Mineralized tissue is lost

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The incorporation of fluoride into the hydroxyapatite crystals of enamel helps with what?

Helps withstand enamel erosion

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True/False: The high degree of enamel
calcification means that it
is very susceptible to
damage by acids secreted
by bacteria.

True

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What is Tome’s process

Is the secretory tip of ameloblast: key to organization of enamel

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What does Tome’s process secrete

It secretes organic matrix:
Gel-like; glycoproteins:
amelogenins
enamelins

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What is the initial mineralization stage

Initial (25-30% mineralized).
* Inorganic matrix (apatite crystals) is rapidly
deposited on the organic matrix

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what is the maturation mineralization stage

First, ameloblasts resorb some organic matrix
(amelogenins and water)
* Finally, hydroxyapatite crystals increase in size and
hardness.
* Organic matrix (enamelins) coat
crystals and are highly bound to
these crystals. (96% mineralized)

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What is an enamel prism

structural unit of enamel
secreted by
ameloblast

basic unit of enamel

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How is the enamel oriented

Oriented perpendicular
to the dentinal surface

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What dictates the shape of the enamel prism

The shape of the Tome’s process

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What does the keyhole shape of the enamel prism consist of

Body
Interrod Substance
Rod sheaths

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How is the keyhole shape made

Is the result of the sequence of secretion from the Tome’s process

What gives rise to the interrod substance

first ameloblasts secrete from the sides of Tome’s Process

65-degree angle from tip of Tomes process

Tomes process

Ameloblasts
secrete from the
sides of Tome’s
Process
the Tomes’ processes
retreats, leaving an empty
space behind, surrounded by
interrod substance

3.The empty space is
then filled with
enamel matrix by
the tip of
retreating Tome’s
process and forms
the rod body.
Parallel to Tomes
process

True/False: Each enamel prism is made up of 4 different ameloblasts

True

True/false: Orientation of hydroxyapatite crystals is different in the two components of the enamel Prism (1-Body [“rod’] and 2- Interrod) due to shape of Tome’s process.

true

What is the rod sheaths of the enamel prism

Apatite crystals are - loosely packed at a different angle than those in rod/body - less calcification - mainly matrix

What is the body of enamel prisms

Apatite crystals are - closely packed - parallel to long axis of rod Average width is 4-6um

What is the interrod substance:

Apatite crystals are oriented about 65o to those in rod

What is key to the organization of the enamel

Tomes' process is the secretory tip of ameloblast

Where can prism-less enamel be found

At the DEJ and the surface of the enamel

What are prism-less enamel

Does not have prism because the ameloblasts don't have a Tomes process yet

What are the characteristics of a prism-less enamel at the surface of the tooth

more highly calcified (hypercalcified) harder less porous than the prismatic enamel

true/false: the enamel has pores

true

What are pores

small spaces that exist where crystals don't form between rods

What can pores do

allow fluid, ions (like fluoride), and small molecules can diffuse into enamel

With age, what happens to the pores?

With age, pores diminish in size as hydroxyapatite crystals acquire more ions and increase in size, replacing the water and organic matrix that normally occupy the pores

How are enamel prisms oriented

perpendicular to the dentinal surface wavy course from the DEJ to surface

What are hunter shrager bands

Run in parallel to the Enamel Prisms * Demarcate the different orientations of adjacent groups of enamel prisms * Provides maximum stability, reducing chance of fracture

Gnarled enamel

At the cusp of the tooth the quasi-linear arrangement of the enamel rods gets more tangly. This makes the enamel super tough here and could cause a dentist to need to change their drill bit while filling a cavity in an area with Gnarled enamel

What are striations

Transverse thin dark bands across enamel rods * Demarcate daily growth patterns of rod * Daily growth rate is approx. 4 um segments

What is stria of retzius

Transverse thin dark bands across enamel rods * Demarcate daily growth patterns of rod * Daily growth rate is approx. 4 um segments

What is stria of retzius made up of

made up of aligned dark bands of adjacent prisms

What is the orientation of Retzius

Run perpendicular to the course of enamel rods/prisms

What is the perikymata

Shallow grooves and ridges on tooth surface * Formed where the Stria of Retzius reach the tooth surface. * Become abraded with mastication so they are typical absent in teeth of adults.

What is hypocalcification enamel tufts

Resemble small, twisted brushes or wavy trees Extend from Dentin-Enamel Junction <1/2 of the way through enamel Hypomineralized areas (organic matrix not resorbed) of enamel rods

What happens when the tooth erupts

the attachment epithelium, and thus all support for the ameloblasts, is lost. With no way to get nutrients, the ameloblasts die

What causes overcrowding of ameloblasts

The areas between the cusps on molars and premolars are concave

What is the result of overcrowding of ameloblast

may result in cell death and incomplete maturation of matrix produced by these cells

What happens to the enamel when an enamel fissure occurs

Enamel around the deep end of the fissure is incompletely calcified --> The empty groove will fill with organic debris and bacteria

What does the DEj provide

Provides strong bond between layers of the enamel and dentin

What is the morphology of the DEJ

pitted and scalloped

What happens to the terminal ends of the odontoblast processes

trapped in enamel during tooth development