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DEN1DSB > WEEK 6 - ENAMEL > Flashcards

WEEK 6 - ENAMEL Flashcards

1
Q

what makes enamel a unique tissue?

A

it lacks cells within or on its surface

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2
Q

Enamel is the most ________________ tissue

A

highly mineralized

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3
Q

how many pounds per square inch can enamel withstand?

A

100,000

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4
Q

What does the colour of enamel determine?

A

the degree of calcification

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5
Q

Is yellow or grey enamel stronger?

A

yellow

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6
Q

Where is enamel the thickest?

A

incisal/occlusal surface

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7
Q

How thick can enamel be?

A

0-2.6 mm

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8
Q

What makes enamel so hard?

A

high mineral content and complex crystal orientation

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9
Q

Hardness and density of enamel decreases from where to where?

A

the surface towards interior, and incisal tip to cervical margin

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10
Q

What makes enamel brittle?

A

Large amounts of minerals

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11
Q

Why is dentine so important?

A

it is less mineralized therefore it compensates for enamels brittleness. It supports enamel

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12
Q

Is enamel permeable?

A

it is a semi permeable membrane for fluoride ions and saliva

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13
Q

what is the chemical composition of enamel?

A

96% inorganic, 1% organic and 3% water

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14
Q

What is the functional unit of enamel?

A

rods

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15
Q

how many enamel rods are on permanent lower incisors?

A

5 million

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16
Q

how many enamel rods are on permanent upper first molars?

A

12 million

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17
Q

What is the direction of enamel rods?

A

wavy

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18
Q

What are gnarled enamel?

A

complex course of enamel rods at the incisal edge to withstand chewing

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19
Q

What are the 6 stages of ameloblast formation?

A

differentiating, secretory, transitional, maturative, protective, desmolytic

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20
Q

What happens in the differentiation stage?

A

the inner enamel epithelium differentiates into preameloblasts and the outer cells of the dental papilla are induced to differentiate into odontoblasts.

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21
Q

What is Induction?

A

preamoblasts inducing the formation of odontoblasts

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22
Q

Secretory Stage: What is reciprocal induction?

A

preameloblasts changing into ameloblasts by signals from odontoblasts

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23
Q

What happens during the secretory stage after reciprocal induction?

A

the ameloblasts begin amelogenesis, the oppositional growth of enamel matrix by laying it down on their side of the disentegrating basement membrane

24
Q

What is secreted from Tomes process during the secretory stage?

A

enamel matrix

25
Q

What is tomes process?

A

a conical process responsible for the different orientation of crystals in the enamel rod

26
Q

What is the transitional stage?

A

ameloblasts change from a secretory to a maturation form

27
Q

What stops during the transitional stage?

A

enamel secretion

28
Q

what signals the transitional stage?

A

a reduction in the height of the ameloblasts and there is a withdrawal of tomes’ process.

29
Q

what happens to the ameloblasts that remain at the end of the transitional stage?

A

they are reduced or killed by autophagocytois

30
Q

What are the two types of ameloblasts in the maturative stage?

A

ruffled ended - 80% and smooth ended (20%)

31
Q

What happens during the protective stage?

A

the layers of the enamel organ become reduced forming the REE (reduced enamel endothelium)

32
Q

What happens during the desmolytic stage?

A

reduced enamel epithelium secretes desmolytic enzymes for the elimination of the dental sac and allowing fusion between REE and oral epithelium

33
Q

What does the desmolytic stage allow?

A

tooth eruption without bleeding

34
Q

what are the two types of histological preparation for the examination of hard tissues?

A

decalcified and ground section

35
Q

What type of histological preparation is best for enamel? Why?

A

ground section because the crystals dissolve during decalcification

36
Q

Which type of histological preparation is best for dentine and pulp?

A

ground section

37
Q

What are the incremental lines of enamel?

A

cross striations, incremental lines of Retzius and neonatal line

38
Q

What are incremental lines of enamel?

A

short period (cross striations) and long period (straie of retzius)

39
Q

what forms cross striations?

A

daily rest of ameloblasts.

40
Q

what is the distance between cross striations?

A

4 microns

41
Q

what forms the striae of retzius?

A

the weekly rests of ameloblasts

42
Q

what is the distance between the striae of retzius?

A

16 microns

43
Q

what is the neonatal line?

A

a pronounced line formed at birth

44
Q

what does the neonatal line represent?

A

a few days after birth

45
Q

What are enamel tufts?

A

small, dark brushes with their bases near the DEJ

46
Q

how far into the enamel do enamel tufts reach?

A

1/3

47
Q

What is unique to the enamel tufts in comparison to the rest of the enamel?

A

hypomineralised and contain the highest protein content

48
Q

What is the dentino enamel junction?

A

hypocalcified scalloped junction that prevents shearing of the enamel

49
Q

What is enamel lamellae?

A

cracks from the enamel surface to the dentin

50
Q

what is the uncalcified structure of enamel?

A

enamel spindles

51
Q

what are enamel spindles?

A

ends of odontoblastic processes which cross the DEJ

52
Q

What is attrition?

A

the wearing of the incisal or occlusal surfaces

53
Q

What is abrasion due to?

A

mechanical forces

54
Q

what is erosion due to?

A

chemical agents or acids

55
Q

what happens if a fluoride ion is incorporated into hydroxyapatite crystal?

A

the crystal becomes more resistant to acid dissolution

56
Q

what does acid etching do?

A

removes enamel rods

DEN1DSB (10 decks)

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