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IOE Dentistry - Dental Anatomy > Dental Enamel > Flashcards

Dental Enamel Flashcards

1
Q

In healthy gums which part of the tooth is visible

A

Only the enamel of the tooth crown

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2
Q

Describe enamel

A

The white, hard outer covering of the tooth

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3
Q

What is the anatomical crown

A

The part of the tooth covered in enamel

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4
Q

What is the part of the tooth covered in enamel called

A

The anatomical crown

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5
Q

Why do teeth appear yellower as you age

A

As the enamel wears away with age giving teeth a yellower appearance as more dentin is visible

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6
Q

What is the main disease that affects enamel

A

Dental caries

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7
Q

Does enamel have a cell population

A

No

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8
Q

What is the name of the group of non syndromic genetic defects that can affect enamel

A

Amelogenesis imperfecta

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9
Q

What percentage (by weight) of enamel is mineral?

A

95%

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10
Q

What is the name of the main mineral that makes up enamel

A

Inorganic hydroxyapatite crystals

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11
Q

What else makes up enamel apart from minerals? And state the percentage (by weight) of these other components in enamel

A

The other 5% is made up of unique enamel proteins, water and lipid material
In mature enamel 1-3% by weight is organic matrix (ie proteins but NOT collagen)
2% is water

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12
Q

How thick are hydroxyapatite crystallises in enamel?

A

25-30nm thick

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13
Q

How wide are hydroxyapatite crystallises in enamel?

A

60-90nm in width

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14
Q

What is the nature of the origin of enamel?

A

Enamel has ectodermal origin. It develops from the internal enamel epithelium of the tooth germ

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15
Q

Name the 4 proteins in enamel

A

Amelogenin
Ameloblastin
Enamelin
Tuftelin

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16
Q

State the possible functions of amelogenin

A

It may stabilise the amphorous Ca-P phase
May control crystal morphology and organisation
May control enamel thickness

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17
Q

State the possible functions of ameloblastin

A

May be a cell adhesion protein
May control cell differentiation
May maintain the integrity of the enamel rods/prisms

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18
Q

State the possible functions of enamelin

A

May control mineral nucleation and elongates growth (possibly with the help of amelogenin)

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19
Q

State the possible functions of tuftelin

A

May be involved in cell signalling

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20
Q

Why can enamel withstand both shearing and impact force?

A

As it is highly mineralised

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21
Q

As enamel is highly mineralised it can….

A

Withstand shearing and large impact force

It is the hardest biological tissue

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22
Q

List the physical properties of enamel

A 
Has a high abrasion resistance 
Is brittle 
Has a low tensile strength 
Has a high modulus of elasticity 
Enamel can not undergo repair or replacement
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23
Q

What is the benefit of enamel having a high abrasion resistance

A

It wears down slowly

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24
Q

What is the benefit of enamel having a high modulus of elasticity

A

It minimises the chances of fractures

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25
Q

From which process does all secretion and modification of the matrix undergo

A

Tomes process

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26
Q

What appearance do mineralised surfaces of enamel have

A

Pit like appearance

The pits are surrounded by inter rod (inter prismatic) enamel

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27
Q

Which region between two processes secretes first:

The proximate region or the distal region

A

The proximal region between two processes always secrets ahead if the distal region
This forms a wall that represents the periphery of the prism and inter prismatic regions

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28
Q

What gives enamel its prismatic structure

A

The infilling of the pits as AMELOBLASTS retreat to form the main core (head) of the enamel prism

29
Q

What is a prism?

A

The basic unit of enamel

30
Q

Why are prism boundaries visible

A

Due to the sudden changes in crystallite orientation between the prism cores (heads) and inter prismatic enamel (tail) of adjacent prism

31
Q

By how many degrees do prisms at the boundary deviate from the core

A

60°

32
Q

How many ameloblasts make up each prism

A

One

33
Q

How many ameloblasts make up the inter prismatic enamel

A

Four

34
Q

Enamel prisms run from the ________ to the _________

What is the diameter and length of these prisms

A

Enamel dentine junction (EDJ)
Surface
Diameter: 5-6 micrometers
Length: 2-5 micrometers

35
Q

Give the definition of diazones

A

Within longitudinal sections, areas where the prisms are sectioned transversely are termed diazones

36
Q

Give the definition of parazones

A

Within longitudinal sections, areas where the prisms are sectioned longitudinally are termed parazones

37
Q

What is gnarled enamel?

A

Area under the cusps of teeth where prisms appear to be disordered

38
Q

Name the 4 lines visible in enamel

A

Hunter Schreger Lines
Striae of Ritzius
Incremental lines: cross striations and enamel striae

39
Q

What are cross striations?

A

Lines that cross enamel prisms at right angles to their long axis

40
Q

What is the reason for incremental lines forming

A

As there is a circadian rhythm in enamel production which produces regular crossed striations called incremental lines

41
Q

How many types of incremental lines are there and what are they called?

A

2 types:
Cross striations
Enamel striae

42
Q

Cross striations are described as ________ period incremental lines

A

Short

43
Q

Give 5 features of cross striations

A 
They are transverse to prisms 
Appear throughout the enamel 
Are 4 micrometers apart 
Represents DAILY increments 
Prisms vary in width
44
Q

Enamel striae are describes as _______ period incremental lines

A

Long

45
Q

Give 5 features of enamel striae

A 
Are oblique to prisms 
Found throughout the enamel 
Are 25-40 micrometers apart 
Represent WEEKLY increments 
Reach the surface at the perikymate
46
Q

What are the striae of Retzius

A

Prominent brown lines that run obliquely across the enamel surface to the surface

47
Q

What are perikymate grooves?

A

Over the lateral surfaces of the crown enamel striae reach the surface in a series of grooves running circumferentially to the crown known as perikymate grooves

48
Q

What are perikymate grooves separated by?

A

Perikymate ridges

49
Q

What are the Hunter Schreger lines?

A

Prisms appear to travel in layers in a sinusoidal direction from the EDJ to the surface. These periodic changes in prism direction in alternating sheets results in alternating reflecting bands on the cut surface called the Hunter Schreger bands
(Ie prisms are arranged in alternating directions from layer to layer)

50
Q

In what area of the enamel are no Hunter Schreger bands visible and why?

A

In the outer 1/4 of enamel all prisms run in the same direction so no bands are visible

51
Q

How are Hunter Schreger bands an adaptation to enamel

A

They are an adaptation to try and break up lines of sheer within enamel to minimise chances of a fracture

52
Q

Where are enamel trufts and lamellae seen?

A

In touch ground sections of enamel

53
Q

What are tufts

A

They are structures radiating from the amino dentine junction for about 2/3 the thickness of enamel

54
Q

Where do lamellae run in enamel

A

Lamellae run through the full thickness of enamel

55
Q

What does scalloping aid

A

Scalloping aids the retention of the enamel on the dentine surface and helps resist shearing

56
Q

What are enamel spindles

A

They are dark cigar shaped structures found in the cusps of teeth. They penetrate up to 50 micrometers of the enamel

57
Q

What is the purpose of the Tomes process?

A

To secrete enamel

58
Q

Where do rods extend from in the tooth?

A

The dentine to the outer surface of enamel

59
Q

Where are the 2 rodless areas in the tooth?

A

Outermost 30-50 micrometres of enamel

Area immediately adjacent to dentine

60
Q

What are enamel lamellae and why are they bad?

A

Enamel lamellae is a crack extending towards the enamel dentine junction
It contains abnormally high levels of organic material
This defect provides a pathway of entry for bacterial that may initiate caries

61
Q

How and why are enamel tufts formed?

A

Formed due to a change in the orientation of the rods
They appear as branched dark short lines
They exhibit a high level of protein
These tufts extend from the enamel dentine junction into about 1/10 of the enamel thickness

62
Q

What do enamel spindles represent?

A

Trapped odontoblast processes that failed to withdraw during enamel mineralisation
They appear as short dark finger like extensions from the enamel dentine junction into the enamel

63
Q

What does the neonatal line in enamel represent?

A

It represents the border between the enamel formed before and after birth
It can also be formed due to a sudden change in in the environment after birth which causes a metabolic disturbance in the ameloblasts

64
Q

What happens to the enamel as you age and why

A
  1. The enamel becomes less permeable due to a reduction in the spaces the crystals
  2. Teeth can become more sensitive due to attrition and wear
  3. Enamel becomes harder with age as the hydroxyapatite crystals become more mineralsied
  4. Teeth get yellower as enamel wears and dentine is visible
  5. Risk of caries decreases with age due to certain ion exchanges between the tooth and the oral environment
65
Q

What percentage of immature developing enamel is made up of amelogenin?

A

90%

66
Q

What percentage of immature developing enamel is made up of ameolblastin?

A

5%

67
Q

What percentage of immature developing enamel is made up of enamelin?

A

5%

68
Q

Which proteins and in what percentages make up the developing enamel?

A

Amelogenin 90%
Ameolblastin 5%
Enamelin 5%

69
Q

What is 1% of the mature enamel composed of and why?

A

In mature enamel, the remaining 1% by weight of protein is comprised mainly of the nonamelogenin proteins This is because the amelogenins are selectively reabsorbed during enamel maturation.

IOE Dentistry - Dental Anatomy (6 decks)

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