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Oral histology > Enamel > Flashcards

Enamel Flashcards

1
Q

What are some enamel characteristics?

A
  • Hardest mineralized tissue in the body
  • Nonvital (acellular, avascular & no nerve)
  • Inorganic (hydroxyapatite crystals) composition is more than organic composition
  • Lacks collagenous proteins
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2
Q

Enamel Rod

A
  • Basic morphological/structural unit of enamel
  • Enamel prisms
  • “Keyhole” shape consisting of a head and a tail (classic concept)
  • Crystals parallel to rod axis
  • Bound by interprismatic substances
  • Each rod formed in increments by 1 secretory ameloblast w/ Tomes’ process
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3
Q

Interrod enamel

A
  • Bound by interprismatic substance
  • Cylindrical rods embedded in interrod enamel (current concept)
  • The tail of the keyhole shape
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4
Q

Enamel rod and Interrod enamel similarities

A

Both are made of enamel crystals

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5
Q

Enamel rod and Interrod enamel crystal orientation differences

A

Crystal orientation is different
Rod: crystals parallel to rod axis
Interrod: crystals at angle to rod

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6
Q

How many ameloblasts form 1 classical enamel rod?

A

Four

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7
Q

Enamel Rod orientation

A
  • Extend approximately from DEJ to enamel surface.
  • Perpendicular to DEJ and enamel surface, but slightly S-shaped in both horizontal and vertical planes.
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8
Q

What are the 5 Enamel Micro features?

A
  1. DEJ (dentino-enamel junction)
  2. Cross striations
  3. Lines (Stria) of Retzius
  4. Hunter-Schreger bands
  5. Gnarled enamel
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9
Q

List the DEJ features

A
  • Scalloped junction in section.
  • Convex surface faces dentin.
  • Prevents shear forces from separating enamel from dentin.
  • 1st formed enamel and dentin located here.
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10
Q

List the Cross striations features

A
  • Daily incremental growth lines
  • Run at right angle to rod axis
  • Enamel layers deposited over a period of 24 hrs
  • Ladder-like appearance with enamel rod
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11
Q

What structures form a ladder-like appearance?

A

Cross striations and enamel rod

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12
Q

List the Lines (Striae) of Retizus features

A
  • Incremental growth lines
  • Enamel layer represents 5 to 10 days
  • Increased organic content & are indicative of the rhythmic variation in the calcification of the enamel matrix
  • Formed during the secretory phase of amelogenesis.
  • Accentuated by diseases and changes in nutrition
    - neonatal line!!!
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13
Q

What do the retzius striae represent?

A

The spaces between a series of successively larger cones stacked one outside the other

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14
Q

What do the Lines (Striae) of Retizus appear like in a cross section? Are they parallel?

A

Tree rings
NOT parallel in longitudinal section

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15
Q

What is the neonatal line?

A
  • Most accentuated Stria of Retzius
  • Reflects physiologic changes (disturbances to amelogenesis) occurring during birth
  • In all primary teeth, sometimes cusps of first permanent molars
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16
Q

What is the Perikymata?

A
  • Imbrication lines.
  • Horizontal shallow grooves on enamel surface.
  • More prominent on facial side of newly erupted teeth.
  • Usually lost through wear.
17
Q

List the Hunter-Schreger Bands features

A
  • Represent alternating groups of cross
    sectioned enamel rods and longitudinally sectioned enamel rods.
  • Extend only ~ 2/3 distance from DEJ toward enamel surface.
  • Observed only with reflected light or scanning EM.
18
Q

What bands correspond to cross-sectioned enamel rods?

A

Dark bands

19
Q

What bands represent longitudinally sectioned enamel rods?

A

Light bands

20
Q

How do light and dark bands appear in reflected light?

A

Appear as an alternating light and dark bands extending from DEJ toward the enamel surface in reflected light

21
Q

List the Gnarled enamel features

A
  • Represents groups of twisted enamel rods.
  • The DEJ is toward enamel surface.
  • Only found at the cuspal and incisal areas.
  • Increase resistance of enamel to fracture to mastication stress.
22
Q

What is enamel demineralization?

A
  • Carbonated apatites are more susceptible to demineralization compared to hydroapx and fluoroap
  • Crystal ends first to dissolve, then along core.
  • Dissolves from inside out.
23
Q

Compare crystal ends vs. their sides

A

-Crystals dissolve more readily at their ends than on their sides.
- Crystals lying perpendicular to the enamel surface are more vulnerable.

24
Q

Compare crystal orientation in enamel rod and interrod enamel

A
  • Rod crystal ends are perpendicular to enamel surface
  • Interrod crystal ends are not exposed
25
Q

What is acid etching?

A
  • Technique to remove surface minerals of enamel with dental etchants (chemicals)
  • Result in the differential etching of rod & interrod enamel.
  • Better bonding surface due to increased porosity of enamel surface.
26
Q

What is important clinically, with regards to enamel demineralization?

A
  • Fissure sealants
  • Bonding restorative materials to enamel
27
Q

What are the 3 enamel demineralization acid etching patterns?

A

Type1 (most common)
- preferential removal of rods

Type2
- reverse of Type 1, interrod enamel removed

Type3 (least frequent)
- irregular and indiscriminate pattern

28
Q

Age Changes in Enamel
What is attrition?

A
  • Enamel is non-vital.
  • Attrition (progressive breakdown) of enamel may expose dentin.
  • Pits and fissures may be eliminated.
29
Q

Age Changes in Enamel
How does color change?

A
  • Darkness ↑ w/age
  • Thinning of enamel (due to daily mastification & underlying dentin becomes thicker as time goes on)
  • Extrinsic staining
30
Q

Age Changes in Enamel
How does permeability change?

A

↓ with age.
↓ pore size between crystals; crystals ↑ in size

31
Q

Age Changes in Enamel
How does water content change?

A

↓ with age
↓ pore size forces water out

32
Q

Age Changes in Enamel
How does the nature of the surface layer change?

A
  • Changes due to ionic exchange with oral environment.
  • Fluoride ion most prevalent
    - Topical application
33
Q

Age Changes in Enamel
How does brittleness change?

A

↑ with age

34
Q

Age Changes in Enamel
How does incidence of caries change?

A

Decreased incidence of caries.
- ↑ Fluoride ion content (anticariogenic agent)
- Loss of surface areas susceptible to caries
- Change in diet (less refined carbs consumed by adults)

Oral histology (4 decks)

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