Components of the Teeth - Enamel

Question 1

what does cariogenic mean

Answer 1

this is something that creates caries - “cariogenesis” is the creation of caries

Question 2

how does acid lead to the development of caries

Answer 2

it removes certain components of the tooth structure

Question 3

what is the structure of enamel essential for

Answer 3

the development of caries

Question 4

give a brief summary of the features of enamel

Answer 4

• it is the hardest tissue in the body
• resists abrasion
• brittle
• supported by dentine
• covers the crown of the tooth
• varies in thickness
• translucent
• transparency of enamel increases with mineralisation

Question 5

why is enamel the hardest tissue in the body

Answer 5

it is often exposed to traumas like biting and chewing that it needs to be resilient for

Question 6

what is attrition

Answer 6

this is the normal wear of a tooth throughout its lifetime.

Question 7

what is abrasion

Answer 7

wear over a very strong activity in which there is a more pathological wear. this includes activities like grinding of teeth, or dents in a tooth where there is constant contact and wear.

Question 8

how must teeth be restored in older invididuals

Answer 8

in such a way that looks natural, including colour and level of wear. designing to make them look like the teeth of a teenager will not look natural on them

Question 9

explain what is meant by describing enamel as brittle

Answer 9

this means it is breakable, where without any support the enamel would break apart from force

Question 10

why does the enamel not break apart from force if it so brittle

Answer 10

it is cushioned by the dentine underneath the surface. if left unsupported when doing a tooth restoration, it would certainly break apart if any force was applied to it

Question 11

what does it mean to say enamel is translucent

Answer 11

the light can pass thrugh it. the colour of tooth is actually due to the dentine underneath, rather than the actual enamel on the top surface.

Question 12

where do enamel and dentine grow from

Answer 12

the amelo dentino junction

Question 13

what are the cells that produce enamel called

Answer 13

ameloblasts

Question 14

in what structure is enamel produced in

Answer 14

rods, or otherwise known as prisms.

Question 15

what is the thickness of enamel dependent on

Answer 15

the function of the tooth

Question 16

describe the regional variations of enamel

Answer 16

the surface enamel is more mineralised and harder than deeper enamel due to long term wear
the hardness of enamel decreases from the cusp tip (posterior teeth) or incisal edge (anterior teeth) to the cervical region
these properties have both functional and clinical significance

Question 17

give a brief outline of the enamel rods

Answer 17

these are the basic units of enamel, and run from the amelo dentino junction to the surface. they contain hydroxyapatite crystallites, and their orientation of these crystallites will vary within and along the rod

Question 18

what does rod structure arise from in relation to crystallites

Answer 18

their orientation

Question 19

breakdown the different components and their composition within enamel

Answer 19

• hydroxyapatite makes up 95% of the weight of enamel, and about 90% of its volume
• water makes up 4% of weight and around 5-10% volume
• the organic matric makes up 1% of the wight and around 1-2% of the volume

Question 20

what can be found within the organic matrix of enamel

Answer 20

proteins, like amelogenins, enamelins, peptides and amino acids

Question 21

what are the different surface types found on enamel

Answer 21

smooth surface
pits and fissures

Question 22

is surface enamel always different to deeper enamel

Answer 22

no, they are exactly the same at the start point of their lifetime but over time changes as the tooth is exposed

Question 23

what does the hardness of enamel depend on

Answer 23

its mineralising and demineralising

Question 24

what defines crystallites

Answer 24

the proteins

Question 25

when is enamel formed

Answer 25

it is made before the tooth erupts in the mouth, by ameloblasts, which die once the tooth erupts.

Question 26

why does the tooth lose its ability to make enamel

Answer 26

the ameloblasts die as soon as the tooth erupts

Question 27

what is responsible for giving bone much of its hardness

Answer 27

hydroxyapatite

Question 28

which protein makes up most of the enamel proteins

Answer 28

amelogenins

Question 29

what are the three stages of amelogenesis

Answer 29

presecretory, secretory, and maturation.

Question 30

what is dental papilla

Answer 30

a condensation of odontoblasts

Question 31

what happens to the translucency of teeth as people age

Answer 31

increases

Question 32

what colour is young enamel

Answer 32

white

Question 33

what composition of enamel is hydroxyapatite crystals

Answer 33

95%

Question 34

describe the structure of the hydroxyapatite crystals in enamel

Answer 34

long flat ribbons that are rhomboidal in cross section analysis. some of them can be distorted by crowding during development.

Question 35

are the hydroxyapatite crystals wtihin enamel larger or smaller than in dentine

Answer 35

larger

Question 36

why are there incremental lines on enamel

Answer 36

due to the phasic way that enamel develops

Question 37

what makes up enamel

Answer 37

the enamel rods/prisms. these are a basic structural unit of enamel and are keyhole shaped, and are formed by the hydroxyapatite crystals.

Question 38

how can enamel be described in relation to its composition of cells

Answer 38

it lacks cells and is a calfified tissue

Question 39

where is enamel thickest on the tooth

Answer 39

the cusp and incisal edge

Question 40

where is enamel thinnest on the tooth

Answer 40

the cervical margin

Question 41

why does the thickness of enamel vary depending on the location on the tooth

Answer 41

the areas that suffer more attrition has more enamel and will have a reduced risk of fracture

Question 42

how does the hardness and density of enamel change through its depth

Answer 42

these features decrease as you go from the surface enamel to the interior, subsurface layer

Question 43

how are incremental lines removed from enamel

Answer 43

attrition and abrasion

Question 44

what are the different types of incremental lines

Answer 44

straie of retzius and cross striations

Question 45

describe the straie of retzius

Answer 45

these are a type of incremental line found on the surface of enamel. they run obliquely along the enamel prisms to the surface, and when they reach the surface they form perikymata

Question 46

describe cross striations

Answer 46

these are short period incremental lines on the enamel that are formed parallel to the secretory face of ameloblasts. they cross enamel prisms at right angles

Question 47

what causes the small pits on perikymata

Answer 47

the impressions of the ends of ameloblasts

Question 48

how many days does it take for enamel to reach its full thickness

Answer 48

625

Question 49

how many crystallites are found within each enamel prism

Answer 49

several million

Question 50

how many different patterns of enamel prisms are there

Answer 50

three

Question 51

what is type 1 of enamel prisms

Answer 51

these form complete prism boundaries

Question 52

what is type 2 and 3 of enamel prisms

Answer 52

the prism boundaries are incomplete, and have a keyhole pattern. the tail points cervically

Question 53

give a description of surface enamel

Answer 53

this is the most clinically relevent form of enamel as it is susceptible to caries, erosion etc. it is harder, less porous and less soluble than subsurface enamel.

Question 54

when does enamel restrict fracture the most effectively

Answer 54

in regions where prisms make an acute angle with the surface

Question 55

give a description of the pores found within enamel

Answer 55

the pores are waterfilled spaces that are found between the crystallites.

Question 56

where are the enamel pores that are accessible for larger molecules located

Answer 56

prism boundaries

Question 57

what are some features that extend from the dentine into the enamel at the amelodentine junction

Answer 57

enamel spindles, tufts and lamellae

Question 58

what are enamel lamellae

Answer 58

features that are hypomineralised and extend from the junction to the surface of the enamel.

Question 59

what are enamel spindles

Answer 59

narrow tubules

Question 60

what are enamel tufts

Answer 60

these are features that resemble tufts of grass, and they contain tuftelin

Question 61

which area of enamel is more soluble

Answer 61

the core is more soluble than the periphery of enamel

Question 62

what determines the strength and resistance to fracture of enamel

Answer 62

arrangement of crystallites and prisms

Question 63

when is the effect of fluoride on enamel strength and remineralisation most effective

Answer 63

when it has replaced 50% of the hydroxyl groups

Question 64

are there prisms on the narrow surface zone of enamel

Answer 64

no

Question 65

presecretory stage of amelogenesis

Answer 65

- inner enamel epithelial cells differentiate to form ameloblasts by stretching and becoming tall columnar cells

Question 66

secretory stage of amelogenesis

Answer 66

ameloblasts secrete organic matrix to form the full enamel thickness

Question 67

maturation stage of amelogenesis

Answer 67

ameloblasts carry out activities that help with degradation of enamel matrix and replacement by minerals or inorganic material