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micro > Enamel > Flashcards

Enamel Flashcards

1
Q

What is Enamel made of

A

Organic Matrix 4%
water
proteins: amelogenins & enamelins

Inorganic matrix 96%
hydroxyapatite: calcium phosphate

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2
Q

How is Enamel made? (Amelogensis)

A

3 phases: Presecretory –> Secretory –> Mineralization

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3
Q

What is the presecretory phase

A

Making an Ameloblast:
cytodifferentiation during tooth
development.

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4
Q

What is the secretory phase

A

Production of organic matrix:
amelogenin and enamelin

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5
Q

What is the mineralization phase

A
  1. Calcification/Mineralization
  2. Inorganic matrix: Hydroxyapatite
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6
Q

What happens during the early bell stage

A

Inner Enamel
Epithelial cells
differentiate into
pre-ameloblasts

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7
Q

What happens during the bell stage

A

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

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8
Q

What happens during the Crown stage

A

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

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9
Q

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

A

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

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10
Q

What happens after the dentin- enamel junction is formed

A

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

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11
Q

What is the mineralization phase

A

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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12
Q

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

A

Helps withstand enamel erosion

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13
Q

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

A

True

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14
Q

What is Tome’s process

A

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

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15
Q

What does Tome’s process secrete

A

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

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16
Q

What is the initial mineralization stage

A

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

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17
Q

what is the maturation mineralization stage

A

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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18
Q

What is an enamel prism

A

structural unit of enamel
secreted by
ameloblast

basic unit of enamel

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19
Q

How is the enamel oriented

A

Oriented perpendicular
to the dentinal surface

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20
Q

What dictates the shape of the enamel prism

A

The shape of the Tome’s process

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21
Q

What does the keyhole shape of the enamel prism consist of

A

Body
Interrod Substance
Rod sheaths

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22
Q

How is the keyhole shape made

A

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

23
Q

What gives rise to the interrod substance

A

first ameloblasts secrete from the sides of Tome’s Process

65-degree angle from tip of Tomes process

24
Q

Tomes process

A
  1. Ameloblasts
    secrete from the
    sides of Tome’s
    Process
  2. 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

25
Q

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

A

True

26
Q

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.

A

true

27
Q

What is the rod sheaths of the enamel prism

A

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

28
Q

What is the body of enamel prisms

A

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

29
Q

What is the interrod substance:

A

Apatite crystals are oriented about 65o to
those in rod

30
Q

What is key to the organization of the enamel

A

Tomes’ process is the secretory tip of ameloblast

31
Q

Where can prism-less enamel be found

A

At the DEJ and the surface of the enamel

32
Q

What are prism-less enamel

A

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

33
Q

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

A

more highly calcified (hypercalcified)

harder

less porous than the prismatic enamel

34
Q

true/false: the enamel has pores

A

true

35
Q

What are pores

A

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

36
Q

What can pores do

A

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

37
Q

With age, what happens to the pores?

A

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

38
Q

How are enamel prisms oriented

A

perpendicular to the dentinal surface

wavy course from the DEJ to surface

39
Q

What are hunter shrager bands

A

Run in parallel to the
Enamel Prisms

  • Demarcate the different
    orientations of adjacent
    groups of enamel prisms
  • Provides maximum
    stability, reducing
    chance of fracture
40
Q

Gnarled enamel

A

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

41
Q

What are striations

A

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

42
Q

What is stria of retzius

A

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

43
Q

What is stria of retzius made up of

A

made up of aligned
dark bands of
adjacent prisms

44
Q

What is the orientation of Retzius

A

Run perpendicular to the
course of enamel rods/prisms

45
Q

What is the perikymata

A

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.

46
Q

What is hypocalcification enamel tufts

A

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

47
Q

What happens when the tooth erupts

A

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

48
Q

What causes overcrowding of ameloblasts

A

The areas between the cusps on molars and premolars are concave

49
Q

What is the result of overcrowding of ameloblast

A

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

50
Q

What happens to the enamel when an enamel fissure occurs

A

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

51
Q

What does the DEj provide

A

Provides strong bond between layers of the enamel and dentin

52
Q

What is the morphology of the DEJ

A

pitted and scalloped

53
Q

What happens to the terminal ends of the odontoblast processes

A

trapped in enamel during tooth development

micro (3 decks)

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