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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
From which process does all secretion and modification of the matrix undergo
Tomes process
26
What appearance do mineralised surfaces of enamel have
Pit like appearance | The pits are surrounded by inter rod (inter prismatic) enamel
27
Which region between two processes secretes first: | The proximate region or the distal region
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
28
What gives enamel its prismatic structure
The infilling of the pits as AMELOBLASTS retreat to form the main core (head) of the enamel prism
29
What is a prism?
The basic unit of enamel
30
Why are prism boundaries visible
Due to the sudden changes in crystallite orientation between the prism cores (heads) and inter prismatic enamel (tail) of adjacent prism
31
By how many degrees do prisms at the boundary deviate from the core
60°
32
How many ameloblasts make up each prism
One
33
How many ameloblasts make up the inter prismatic enamel
Four
34
Enamel prisms run from the ________ to the _________ | What is the diameter and length of these prisms
Enamel dentine junction (EDJ) Surface Diameter: 5-6 micrometers Length: 2-5 micrometers
35
Give the definition of diazones
Within longitudinal sections, areas where the prisms are sectioned transversely are termed diazones
36
Give the definition of parazones
Within longitudinal sections, areas where the prisms are sectioned longitudinally are termed parazones
37
What is gnarled enamel?
Area under the cusps of teeth where prisms appear to be disordered
38
Name the 4 lines visible in enamel
Hunter Schreger Lines Striae of Ritzius Incremental lines: cross striations and enamel striae
39
What are cross striations?
Lines that cross enamel prisms at right angles to their long axis
40
What is the reason for incremental lines forming
As there is a circadian rhythm in enamel production which produces regular crossed striations called incremental lines
41
How many types of incremental lines are there and what are they called?
2 types: Cross striations Enamel striae
42
Cross striations are described as ________ period incremental lines
Short
43
Give 5 features of cross striations
``` They are transverse to prisms Appear throughout the enamel Are 4 micrometers apart Represents DAILY increments Prisms vary in width ```
44
Enamel striae are describes as _______ period incremental lines
Long
45
Give 5 features of enamel striae
``` Are oblique to prisms Found throughout the enamel Are 25-40 micrometers apart Represent WEEKLY increments Reach the surface at the perikymate ```
46
What are the striae of Retzius
Prominent brown lines that run obliquely across the enamel surface to the surface
47
What are perikymate grooves?
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
What are perikymate grooves separated by?
Perikymate ridges
49
What are the Hunter Schreger lines?
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
In what area of the enamel are no Hunter Schreger bands visible and why?
In the outer 1/4 of enamel all prisms run in the same direction so no bands are visible
51
How are Hunter Schreger bands an adaptation to enamel
They are an adaptation to try and break up lines of sheer within enamel to minimise chances of a fracture
52
Where are enamel trufts and lamellae seen?
In touch ground sections of enamel
53
What are tufts
They are structures radiating from the amino dentine junction for about 2/3 the thickness of enamel
54
Where do lamellae run in enamel
Lamellae run through the full thickness of enamel
55
What does scalloping aid
Scalloping aids the retention of the enamel on the dentine surface and helps resist shearing
56
What are enamel spindles
They are dark cigar shaped structures found in the cusps of teeth. They penetrate up to 50 micrometers of the enamel
57
What is the purpose of the Tomes process?
To secrete enamel
58
Where do rods extend from in the tooth?
The dentine to the outer surface of enamel
59
Where are the 2 rodless areas in the tooth?
Outermost 30-50 micrometres of enamel | Area immediately adjacent to dentine
60
What are enamel lamellae and why are they bad?
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
How and why are enamel tufts formed?
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
What do enamel spindles represent?
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
What does the neonatal line in enamel represent?
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
What happens to the enamel as you age and why
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
What percentage of immature developing enamel is made up of amelogenin?
90%
66
What percentage of immature developing enamel is made up of ameolblastin?
5%
67
What percentage of immature developing enamel is made up of enamelin?
5%
68
Which proteins and in what percentages make up the developing enamel?
Amelogenin 90% Ameolblastin 5% Enamelin 5%
69
What is 1% of the mature enamel composed of and why?
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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