Enamel I+II

Question 1

enamel is derived from :

Answer 1

ectoderm

Question 2

collagen content of enamel :

Answer 2

0%

Question 3

what structural feature sets enamel apart from other collagen based mineralized tissue ?

Answer 3

the fact that it has no collagen and has extremely long enamel crystals

Question 4

why is it not possible to replace enamel biologically once the tooth erupts ?

Answer 4

because all the ameoloblasts (enamel secreting cells ) are dead by then

Question 5

what is the natural color of enamel ?

Answer 5

bluish white tint . yellow at cervical rim

Question 6

describe the thickness of enamel :

Answer 6

varies from 2.5mm over functional edge to feather edge at cervical line

Question 7

enamel is relatively impermeable

Question 8

what is the composition of enamel by weight ? (end of post secratory maturation phase)

Answer 8

96% inorganic hydroxyapatite crystals

1% organic protein

3% water

Question 9

the enamel matrix is 1% Organic protein . what is that 1% composed of

Answer 9

90%amelogenins–> regulate growth in thickness and width of crystals

and 10% amelogenins –> (ameloblastin and enamelin)–> promote and guide the formation of the enamel crystals

Question 10

the 10% non amelogenin composition of the organic matrix of enamel is composed of :

Answer 10

ameloblastin
enamelin

Question 11

what is the composition of the inorganic matrix of enamel ?

Answer 11

-calcium phosphate (hydroxyapatite) crystals

-various ions like magnesium , potassium , sodium , and fluoride(if present during enamel formation they may be incorporated into the crystal structure )

Question 12

studying enamel histologically requires the use of a ____ section

Answer 12

ground section

Question 13

describe the structure of enamel crystals :

Answer 13

they are extremely long and hexagonal shaped they are also carbonated

they also measure 60-70 nm in width and 25-30nm in thickness

Question 14

describe the structure and orientation of enamel rod

Answer 14

cylindrical shaped structure made up of crystals oriented in the same direction as the rod .

Question 15

what is the inter-rod?

Answer 15

region surrounding rod to form key hole appearance. this region contain enamel crystals which are oriented in a different direction than those making up the rod

Question 16

the basic structure of enamel consists of ___

Answer 16

rod (head)
inter rod (tail)

Question 17

during the secretory phase , enamel is made up of ___

Answer 17

30% mineral
65% protein
5% water

Question 18

in which stage does enamel have no rods

Answer 18

secretory stage

Question 19

describe what happens in the secretory stage :

Answer 19

after deposition of mantel dentine , inner enamel epithelium differentiates into ameloblasts ( develops tomes process–> saw toothed appearance which allows secretion of enamel ) . ameloblasts then move backwards , secreting the initial enamel layer which is not fully mineralized

Question 20

what happens during the post secretory transitional stage of amelogenesis ?

Answer 20

-25% of ameloblasts die
-tomes process disappears
-change of ameloblast morphology

Question 21

what happens during the maturation stage of amelogenesis ?

Answer 21

-before tooth erupts enamel hardens by action of smooth ended(removal of polypeptide fragments and water) and ruffle ended ameloblasts (allow calcium ions to enter )

-ameloblasts assume a shorter cuboidal shape

-reduced enamel epithelium forms (stratum intermedium , stellate reticulum ,outer enamel epithelium )

Question 22

what happens to the reduced enamel epithelium as the tooth passes through the oral epithelium ?

Answer 22

the part located incisally is destroyed while the part found more cervically interacts with the oral epithelium to form junctional epithelium .

Question 23

what happens to the reduced enamel epithelium located more cervically ?

Answer 23

interacts with oral epithelium —> forming junctional epithelium

Question 24

what are the 2 general families of proteinases involved in extracellular processing and degradation of enamel proteins ?

Answer 24

KLK4
MMP20

they cut amelogenin into small pieces to preform different functions in enamel formation

Question 25

Enamel has no equivelent of predentin , no matrix vesicles

Question 26

what is enamels relationshiop to matrix vesicles?

Answer 26

no matrix vesicles

Question 27

origin of periodontal ligament , cementum , and alveolar bone :

Answer 27

dental sac (ectomesenchym)

Question 28

how does enamel fair against compressive and tensile strength?

Answer 28

enamel is brittle meaning it is resistant to compressive strength but it is weak under tensile strength

Question 29

the surface of enamel is relatively impermeable but it is permeable to ___

Answer 29

fluoride or magnesium

Question 30

what structural shape achieves the maximum strength of enamel?

Answer 30

keyhole appearance of enamel rod/ inter rod

Question 31

the primary enamel cuticle is also known as ___

Answer 31

nasminths membrane