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Ohs > Enamel > Flashcards

Enamel Flashcards

1
Q

Ameologenins

A

Low molecular weight proteins and hydroponic (90%)

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2
Q

Nonamelgenins

A

High molecular weight proteins

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3
Q

What are the three stages amelogensis is broken down into how many stages?

A

Three stages

  • Presecretory
  • Secretory
  • Maturation
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4
Q

What are the 6 stages of amelogenesis

A

Morphogenic, organizing (differentiation) , secretory (formative), maturative, protective and desmolytic

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5
Q

What stages are in the pre - secretory stages of amelogenesis ?

A

Morphogenesis and differentiation

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6
Q

What happen in the morphogenesis stage of amelogenesis?

A

In this stage the ameloblast aren’t fully differentiated and before they are they interact with the adjacent mesenchyme cells determining the shape of the ADJ and crown.

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7
Q

How do the cell look during morphogenesis ?

A

The cells are short columnar with large oval nuclei.

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8
Q

What happens during organization (differentiation) stage

A

The cells of the inner enamel epithelium differentiate the become elongated which causes their nuclei to shift proximally towards the stratum intermedium.

The basement membrane which supports the pre ameloblast disintegrates after the deposition of dentin and during differentiation.

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9
Q

What happens after the differentiation stage and the secretory stage?

A

The formation of dentin by odontoblast.

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10
Q

What happen in the secretory stage of amelogenesis?

A
  • The cells of the ameloblast develops blunt processes which penetrate the basal lamina and protrudes into the Predentin so the basement membrane is fragmented.
  • the cell organelles of the ameloblast are increased.
  • the cells begin to release hydroxyapatite crystals which are parallel to one another and interdigitates with the crystal of dentin in this initial layer.
  • when this first increment of enamel is formed the ameloblast begin to move away from the dentin surface and as they do each cell forms a conical projection called a Tomes process.
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11
Q

aprismatic enamel

A

At the end of the secretory stage, ameloblasts lose their Tomes’ process and produce a thin layer of aprismatic enamel

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12
Q

How will the TP secrete granules ? (SS)

A

They secrete granules perpendicularly to the tp membrane.

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13
Q

What two sites are enamel secreted from ( SS)

A

Proximal site of tp which forms interrod enamel.

The distal portion of tp which fill the pits with matrix (enamel rods)

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14
Q

Difference between interrod enamel and rods.

A

The structure - there cells have different orientations

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15
Q

What happens during maturation?

A
  • The ameloblasts undergo significant reduction in the height and a decrease in its volume and organelle content.
  • Next the water and organic materials are selectively removed from the enamel while the additional inorganic material is introduced.
  • partial mineralization during matrix formation, 25-30% of the total mineralization.
  • second stage mineralization will be completed.
  • The maturation of the crystals begins at its dentinal end and progress to the outer surface.
  • Maturation occurs by the growth of the primary crystals till they fuse together
    The fibrils between the crystals will become thinner.
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16
Q

Protective

A

After complete formation and mineralization of enamel the ameloblast forms 3-4 layers of stratified epithelium that covers the enamel called reduced enamel epithelium.

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17
Q

What is the purpose of reduced enamel epithelium?

A

Protect enamel my separating it from the connective tissue until the teeth erupts.

18
Q

Desmolytic stage

A

Reduced enamel epithelium has the function of secreting desmolytic enzymes which cause degeneration of the connective tissue that separates the tooth from the oral epithelium

19
Q

What is enamel formed from ?

A

Enamel crystallite, enamel rod , enamel sheath and interrod substance.

20
Q

What are enamel crystallites ?

A

Smallest unit of enamel which are hexagonal in form.

21
Q

Size of enamel crystallites

A

40-70 nm

22
Q

What organize crystallites into rod enamel and interrod enamel?

A

The Tomes Process

23
Q

What enamel crystallites form the rod enamel and interrod enamel ?

A

Rod enamel - crystallites that elongates near the tip of the times process.

Interrod - crystallites that lengthen near intercellular junctions

24
Q

What difference between interrod and rod enamel ?

A

The orientation

25
Q

Where is head of the rod enamel located?

A

Occlusal or Incisal end

26
Q

The number of rod is equal to _______

A

To the number of ameloblast

27
Q

The number of the enamel rods varies from ____ millions in lower lateral incisor to ____ millions in the upper first permanent molar

A

5 and 12

28
Q

What is diameter of enamel rod ?

A

5 micrometers

29
Q

Direction of rod enamel in the

  1. Dentin surface
  2. Cuspal region
  3. Deciduous teeth
  4. Permanent teeth
A

Right angle to dentin surface

Vertical in cuspal area more oblique as they go cervically

Horizontal cervically

Directed more to gingival cavity

30
Q

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.

True or false

A

True

31
Q

What is the rod sheath ?

A

It is the peripheral part of the enamel that forms a complete envelope around the prism.

32
Q

Interrod substance

A

The enamel rods, which are not in direct contact with each other, are cemented together by inter-rod substance.

33
Q

Gnarled enamel

A

At the inscial or cusp tip the enamel rod has a twisted course.

34
Q

What causes gnarled enameled to be twisted ?

A

Gnarled enamel is found at the cusps of teeth . Its twisted appearance results from the orientation of enamel rods and the rows in which they lie.

35
Q

Where is rodless enamel found ?

A

At enamel surface

36
Q

Why does rodless enamel occur ?

A

Absence of tomes process on ameloblast which was responsible for development of the enamel rods.

37
Q

Describe the cells of the rodless enamel

A

Closely packed crystal that’s parallel to one another and perpendicular to the incremental lines of Retzius.

38
Q

What are the lines of Retzius?

A

This layer is more highly mineralized than the bulk of enamel beneath it.

39
Q

Function of gnarled enamel

A

Functionally, changes in rod directions between different layers may increase the strength of this enamel, making it less prone to fracture and more resistant to wear.

40
Q

What is the dentinoenamel junction?

A

The junction in which the dentin and enamel meet as in seen as scallop border with convextites of the scallops are directed towards the dentin
.

Ohs (1 decks)

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