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Oral Biology - Quiz 2 > Enamel I > Flashcards

Enamel I Flashcards

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1
Q

Tell me about mature enamel. 6 things

A

Acellular

Non-vital, non-vascular

ECTODERMAL origin

Hardest (most mineralized: 98%, tissue in the body)

Brittle - underlying dentin is critical for function

Can be demin/remin

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2
Q

Tell me properties of mature enamel. 5 things.

A

Translucent

Covers crown - thicker at crown, around 2.5mm, thin at cervical line

Composed of hydroxyapatite crystals

96-98% inorgo, 1% orgo, 3% water

Small, but essential protein component: organization of crystals (controls the crystals)

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3
Q

What is mature enamel composed of?

A
  • NO COLLAGEN IN THE MATRIX OF ENAMEL*
  • No collagen scaffold like every other mineralized tissue in the body

Inorgo: Hydroxyapatite

Water: 2-3%

Orgo: 1-2% distributed b/t HA (Hydroxyapatite crystals) (Immature: 30-40%)
-Major proteins: amelogenins, ameloblastins, enamlein, tuftelin, etc.

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4
Q

Closely packed enamel crystals form what?

A

Long ribbons

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5
Q

Many crystals packed together form both the ______ ______ and the _______ enamel.

A

Enamel rods

Interrod

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6
Q

What is carbonated apatite called?

A

Cabonatoapatite

  • Lots of enamel crystals are actually carbonated
  • Usually found in the depths of enamel

**More vulnerable to acid attack

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7
Q

Carbonatoapatite comes from what?

A

CO2 from the metabolism of amelogins when depositing of enamel

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8
Q

_______ and ________ incorporated more in the inner enamel, while _______ in the ______ enamel.

A

Carbonate

Magnesium

OUTER

*Outer enamel are more resilient in acid attack

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9
Q

What is interrod enamel?

A

Enamel b/t enamel rods

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10
Q

What is the shape of an enamel crystal?

A

Hexagonal, and reflective of individual HA unit cell

  • 60-70 nm wide, 65-30 nm thick
  • Very long, and may run the entire length of the enamel layer
  • *Hexagonal symmetry increases as crystals mature, but fully mature lose their shape and crowd together
  • This prevents permeability
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11
Q

What is a rod?

A

Cylindrical accumulation of enamel crystals, lined up along the long axis of the rod

Rods generally run perpendicular to the DEJ (Pulp)

THEY RUN OUTWARDS FROM THE CENTER

Curve somewhat as they progress towards surface, THEY ARE NOT COMPLETELY STRAIGHT

*These are not prisms

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12
Q

1 ameloblast = ____ rod(s).

A

1

ONLY ONE

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13
Q

The shape of the DEJ determines the shape of the what?

A

Shape of the crown

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14
Q

Histologically, in mature teeth what space is at the crown?

A

Enamel space

*The tooth is demineralized to cut sections and this creates the enamel space at the crown

**IF we get a question about a histological section of the tooth, enamel will not be there because it was demineralized in the slide production. It’s the enamel space

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15
Q

T/F - Rods overlap each other.

A

TRUE

*This maximizes strength and minimizes permeability

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16
Q

What is the rod sheath?

A

“Protein rich” area of enamel that surrounds the rods - the protein in mature enamel is found here in this sheath

Runs 3/4 the way around each rod, separating rod and interrod enamel

The gaps in the rod sheath are where enamel crystals are continuous with interrod enamel, linking the two
-the 1/4 not covered “bends out”

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17
Q

Crystal orientation is mainly parallel to the long axis of rods, except where?

A

At the gaps in the sheath area

-They bend outwards and become continuous with interrod enamel

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18
Q

What proteins are in the rod sheath?

A

Ameloblastins

Amelogenins

*Rod sheaths are much more prominent in higher mammals (not so much in rodents)

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19
Q

T/F - Interrod enamel has the same composition as rods, but simply different enamel crystal orientation.

A

TRUE

*THEY FILL IN THE GAPS B/T RODS, LIKE A KEYHOLE

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20
Q

One ameloblast makes one rod, but how does it contribute to the interrod enamel?

A

It contributes to the interrod enamel all the way around it

21
Q

Caries are thought to penetrate thru the higher protein rod sheath areas, b/t what?

A

Rod and interrod enamel

This is the most vulnerable part

22
Q

What is the signal for the synthesis of enamel proteins by the ameloblasts?

A

Formation of first pre-dentin BY ODONTOBLASTS - preameloblasts instruct the odontoblasts to differentiate - preodontoblasts take over and secrete predentin

*Breakdown of bsmt membrane b/t the ameloblasts and odontoblasts and ameloblasts start to synthesize enamel proteins

23
Q

As enamel matures, ______ component reduced, _______ increased.

A

Organic

Mineralization

24
Q

What are the 3 phases of ameloblast maturation?

A

1 - Pre-secretory - Mature from pre-ameloblast s to ameloblasts

2 - Secretory - Deposition of enamel

3 - Maturation - Reduction of orgo matrix, increase mineralization via ion transport

25
Q

How is enamel deposited?

A

Ameloblasts deposit orgo matrix via secretory vesicles, which exit the cell apically

26
Q

Initially, the basal lamina separating the predentin and ameloblasts is penetrated by _______ __________ and are broken down.

A

Cell projections

*Crystals form on the basis of organic matrix

27
Q

What is Tome’s process?

A

In the enamel

Projects into the developing enamel and is the site of much secretory activity

Shape of Tome’s process makes the shape of the enamel rods

28
Q

Enamel is laid down directly in apposition to what?

A

Pre-dentin/mantle/first dentin

29
Q

Ameloblasts are bound together by what?

A

Junctional complexes - terminal bars

Keeps things together and keeps the mineral layer separate from the other stuff

30
Q

T/F - Initial enamel in apposition to dentin does NOT have a rod arrangement, it is UNIFORM.

A

TRUE

31
Q

________ _______ effectively forms the enamel rod structure.

A

TOMES’ process

32
Q

Ridges give what? In general

A

More surface area

33
Q

Distal Tomes’ process?

A

Towards forming enamel

34
Q

Proximal Tomes’ process?

A

Towards the DEJ (Stratum intermedium)

35
Q

Tomes’ process does what?

A

Rods, interrod enamel

36
Q

Eventually, what happens to Tomes’ process?

A

It retracts, outer rods are straighter and the final (outermost) enamel is formed without rods.

*Stuff coming out the sides of the process = interrod enamel

37
Q

What are ruffled cells?

A

Infiltrate and incorporate Ca ions into crystals, lowered pH favors mineralization and secretion of proteolytic enzymes (To remove the protein and move in ions)

38
Q

What are smooth cells?

A

Allow diffusion out of protein fragments out of enamel, which leak in between cells and laterally defuse thru cell layer

39
Q

What is the fate of the enamel organ?

A

It fuses to form reduced enamel epithelium

40
Q

Once enamel has been laid down, the ameloblasts return to what?

A

A squat cell, like a pre-ameloblast

41
Q

The loss of the stellate reticulum and fusion of the OEE and IEE result in a single layer of what?

A

REE - Reduced enamel epi

42
Q

Prior to eruption, what happens to enamel?

A

Hardens and become highly mineralized thru removal of water, orgo material, and increased HA crystal diameter

43
Q

Roughly 2/3 of amelogenesis is what?

A

MATURATION

44
Q

What does the basal lamina due at external enamel surface?

A

Helps regulate movement of fluid/material.

45
Q

What is modulation?

A

Process by which water and proteins are removed.

*Fluctuations in the distal membrane of ameloblast layers: ruffling and smoothing

46
Q

Once enamel matures, the enamel organ is ________ to the tooth until eruption.

A

Attached

  • These remnants fuse w/ oral epithelium, forming a covering over the tooth
  • Canal forms in this covering thru which the tooth erupts and the epithelial layer goes on to form dentogingival junction
47
Q

What two things make up Nasmyth’s membrane?

A

(Cells/basal lamina/debris/whatever-remaining-on-the-crown initially after eruption)

Primary enamel cuticle - Mineralized coating, last secretory product of the ameloblasts (probably the basal lamina)

Secondary enamel cuticle/Dental cuticle - Formed from what remains of the reduced enamel epi merged with oral epithelium and is removed due to mechanical forces.

48
Q

What happens to the stellate reticulum and OEE and IEE?

A

Stellate reticulum goes away and OEE and IEE fuse together

49
Q

Tell me what happens when the predentin is detected.

A

Ameloblasts break down basal lamina and begin to deposit enamel protein at that spot.

Initial deposition of enamel is amorphous, not arranged in rods and/or interrod enamel.

Tome’s process then begins to pattern enamel shape.

Oral Biology - Quiz 2 (3 decks)

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