WEEK 6 - ENAMEL

Question 1

what makes enamel a unique tissue?

Answer 1

it lacks cells within or on its surface

Question 2

Enamel is the most ________________ tissue

Answer 2

highly mineralized

Question 3

how many pounds per square inch can enamel withstand?

Answer 3

100,000

Question 4

What does the colour of enamel determine?

Answer 4

the degree of calcification

Question 5

Is yellow or grey enamel stronger?

Answer 5

yellow

Question 6

Where is enamel the thickest?

Answer 6

incisal/occlusal surface

Question 7

How thick can enamel be?

Answer 7

0-2.6 mm

Question 8

What makes enamel so hard?

Answer 8

high mineral content and complex crystal orientation

Question 9

Hardness and density of enamel decreases from where to where?

Answer 9

the surface towards interior, and incisal tip to cervical margin

Question 10

What makes enamel brittle?

Answer 10

Large amounts of minerals

Question 11

Why is dentine so important?

Answer 11

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

Question 12

Is enamel permeable?

Answer 12

it is a semi permeable membrane for fluoride ions and saliva

Question 13

what is the chemical composition of enamel?

Answer 13

96% inorganic, 1% organic and 3% water

Question 14

What is the functional unit of enamel?

Answer 14

rods

Question 15

how many enamel rods are on permanent lower incisors?

Answer 15

5 million

Question 16

how many enamel rods are on permanent upper first molars?

Answer 16

12 million

Question 17

What is the direction of enamel rods?

Answer 17

wavy

Question 18

What are gnarled enamel?

Answer 18

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

Question 19

What are the 6 stages of ameloblast formation?

Answer 19

differentiating, secretory, transitional, maturative, protective, desmolytic

Question 20

What happens in the differentiation stage?

Answer 20

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

Question 21

What is Induction?

Answer 21

preamoblasts inducing the formation of odontoblasts

Question 22

Secretory Stage: What is reciprocal induction?

Answer 22

preameloblasts changing into ameloblasts by signals from odontoblasts

Question 23

What happens during the secretory stage after reciprocal induction?

Answer 23

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

Question 24

What is secreted from Tomes process during the secretory stage?

Answer 24

enamel matrix

Question 25

What is tomes process?

Answer 25

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

Question 26

What is the transitional stage?

Answer 26

ameloblasts change from a secretory to a maturation form

Question 27

What stops during the transitional stage?

Answer 27

enamel secretion

Question 28

what signals the transitional stage?

Answer 28

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

Question 29

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

Answer 29

they are reduced or killed by autophagocytois

Question 30

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

Answer 30

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

Question 31

What happens during the protective stage?

Answer 31

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

Question 32

What happens during the desmolytic stage?

Answer 32

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

Question 33

What does the desmolytic stage allow?

Answer 33

tooth eruption without bleeding

Question 34

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

Answer 34

decalcified and ground section

Question 35

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

Answer 35

ground section because the crystals dissolve during decalcification

Question 36

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

Answer 36

ground section

Question 37

What are the incremental lines of enamel?

Answer 37

cross striations, incremental lines of Retzius and neonatal line

Question 38

What are incremental lines of enamel?

Answer 38

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

Question 39

what forms cross striations?

Answer 39

daily rest of ameloblasts.

Question 40

what is the distance between cross striations?

Answer 40

4 microns

Question 41

what forms the striae of retzius?

Answer 41

the weekly rests of ameloblasts

Question 42

what is the distance between the striae of retzius?

Answer 42

16 microns

Question 43

what is the neonatal line?

Answer 43

a pronounced line formed at birth

Question 44

what does the neonatal line represent?

Answer 44

a few days after birth

Question 45

What are enamel tufts?

Answer 45

small, dark brushes with their bases near the DEJ

Question 46

how far into the enamel do enamel tufts reach?

Answer 46

1/3

Question 47

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

Answer 47

hypomineralised and contain the highest protein content

Question 48

What is the dentino enamel junction?

Answer 48

hypocalcified scalloped junction that prevents shearing of the enamel

Question 49

What is enamel lamellae?

Answer 49

cracks from the enamel surface to the dentin

Question 50

what is the uncalcified structure of enamel?

Answer 50

enamel spindles

Question 51

what are enamel spindles?

Answer 51

ends of odontoblastic processes which cross the DEJ

Question 52

What is attrition?

Answer 52

the wearing of the incisal or occlusal surfaces

Question 53

What is abrasion due to?

Answer 53

mechanical forces

Question 54

what is erosion due to?

Answer 54

chemical agents or acids

Question 55

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

Answer 55

the crystal becomes more resistant to acid dissolution

Question 56

what does acid etching do?

Answer 56

removes enamel rods