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Oral Histology > Enamel Tissue > Flashcards

Flashcards in Enamel Tissue Deck (52):
1

T/F - Enamel is the hardest of the 4 mineralized tissues of the body

True

2

T/F - All 4 mineralized tissues of the body are connective tissue

False - Enamel is NOT a connective tissue

3

T/F - All mineralized tissues have a partially mineralized (immature) stage, and a fully mineralized (mature) stage

False - Enamel is the only mineralized tissue that goes through an immature stage....the other 3 go from unmineralized to mineralized (never partially mineralized)

4

T/F - Enamel formation is finite

True - Ameloblasts complete its enamel formative cycle once the thickness of enamel is reached at a site

5

What is the first appearing mineralized tissue in a developing tooth? What is second?

Dentin is first
Enamel is second

6

What is lacking in enamel?

Enclosed cells (acellular)
Nerves (aneural)
Blood vessels (avascular)
Lymph vessels (alymphatic)

7

What tissue in a tooth contains enclosed cells, nerves, blood vessels, and lymph vessels?

Pulp

8

Enamel definition

A composite biological mineral with apatite crystals oriented in a complex, three-dimensional pattern

9

Hardness of enamel

5 on Moh's scale - comparable to mild steel
Can withstand both shearing and impact forces well
Brittle without dentin support

10

Enamel translucency

Hue depends on location, surface condition of enamel, attraction to stain substances, and age changes

11

What is required for enamel to maintain its integrity?

A wet environement

12

Attrition

Normal, slow wearing of tooth substances under the stress of mastication

13

Abrasion

Abnormal wearing of tooth substance from extraoral substances (toothpick)

14

Erosion

Abnormal wearing of tooth substances from acid

15

Microporosity of enamel

The pathway for diffusion of small molecules such as water
Electrochemical effects on pore walls lead to carious lesions

16

Remineralization of enamel

Mineral is returned to the molecular structure of enamel by the way of saliva
When demineralization exceeds remineralization, cavitation occurs

17

Inorganic substances of enamel

96% of enamel by weight
Hydroxyapatite crystals - principle component is calcium hydroxyapatite

18

How do enamel crystals compare to other mineralized tissues?

Enamel crystals are larger and consist of more impurities (fluoride, carbide)

19

Organic substances of enamel

1% by weight

20

What are the types of proteins unique to enamel?

Amelogenin and non-amelogenin

21

What are some non-amelogenin proteins

Enamelin
Amelin
Tuftelin

22

What is the most prominent organic substance of enamel?

Amelogenin - a seed protein for normal mineralization

23

Enamel protein arrangement

Arranged in a lace-like patern throughout the volume of enamel and clsoesly associated with the surface of the crystals

24

Enamel is the only mineralized tissue that does not contain what?

Collagen fibers

25

Water in enamel

3% of weight
Distributed throughout the volume of enamel by the way of micropores between crystals and proteins
Most of the water forms a hydration shell around the crystals

26

What is the clinical importance of water to the enamel?

-Provides a route for fluoride ions, calcum, and phosphorous ions for remineralization
-Provides distribution for whitening substances, artificial, and natural substances
-Provides distribution for acidophilic microorganisms, age changes, etc

27

Age changes to enamel

Enamel wears slowly (attrition)
Color darkens
Composition of surface changes
Fluoride increases at the surface
Porosity is reduced
Less susceptible to caries
Subject to changes due to systemic age changes

28

What are the different CEJ relationships?

Cementum overlaps enamel (most common)
Cementum meets enamel
Cementum does not meet enamel (least common)

29

What is the clinical significance of CEJ relationship?

The CEJ relationships vary around the tooth and form tooth to tooth

30

DEJ configuration at the coronal area

Scalloped to help adapt to withstand occlusal forces

31

DEJ configuration at cervical areas

Smooth - these are non-load bearing areas

32

Formation of enamel

Inner epithelial cells of enamel organ differentiate into ameloblasts (columnar epithelial cells)

33

Line of Retzius

Growth lines that go from the DEJ coronally
They end on the enamel surface as grooves/ridges called Perikymata

34

Perikymata

Numerous small transverse ridges on the exposed surfaces of enamel
Surface manifestations of lines of Retzius
Anthrpologists uses these to determine the age and origin of specimins

35

Hunter-Schrager bands

Alternating dark and light bands of varying width
Originate at the DEJ border and pass outward ending at some distance from the outer enamel surface

36

What causes Hunter-Schrager bands

Different direction of enamel rods in adjacent layers
-the change in rod direction is a functional adaptation that minimizes the risk of cleavage in the axial direction under the influence of masticatory forces

37

What is the clinical significance of Hunter-Schrager bands

Whe performin operative dentistry, need to be mindful of the direction the rods are going so we don't leave anything unsupported

38

What is the main structural unit of enamel

Enamel rods

39

Enamel rods size

Diameter = 5-6um
Length = up to 2.5mm

40

What is the structure of enamel rods

Hydroxyapatite crystals densely packed a core of the rod and run parallel to the long axis of the rod
Built of segments separated by dark lines that give it a striated apperance

41

What forms one rod?

One ameloblast

42

What causes the enamel rods to be segmented?

Rods are secreted in a rhythmic manner
-there is a rest period of an ameloblast marked by an interrod striation

43

Striations

The dark lines that segment the enamel rods

44

Enamel sheath

Outer surface of the enamel rod
Crystals are less dense than the core and run in a different direction
Here, the highest percentage of organic material is amelin

45

Interrod substance

Between the sheaths of the rods
Crystals are more dense and run at different directions than those of the sheath (still less dense than core)
Two or more ameloblasts contribute to the secretion of interrod substance

46

What are the different types of hypomineralized enamel structures?

Enamel lamella
Enamel tuft
Enamel spindle

47

Enamel lamella

Originate from the coronal surface of the enamel and extend for varying depths
Consist of longitudinally oriented defects with enamel protein or organic debris form the oral cavity

48

Enamel lamella clinical significance

Can create access of acidophilic organisms (caries) and stain substances (esthetic considerations)

49

Enamel tuft

Tufts project from the dentinoenamel junction for a short distance into the enamel and contain a greater concentraiton of enamel protein (tuftelin)

50

Enamel tuft clinical significance

Contributes to the spread of caries at the DEJ

51

Enamel spindle

Extend from the dentin, across the DEJ, into the enamel for a short distance
Dentin forms first with processes that go past the DEJ, and some of these processes get stuck between forming enamel rods

52

Enamel spindle clinical significance

Contributes to the spread of caries along the DEJ