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microanatomy > enamel > Flashcards

enamel Flashcards

1
Q

bud stage

A

Dental lamina ectoderm grow into neural crest/ ectomesenchyme.

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2
Q

bell stage

A

Cytodifferentiation, Morphodifferentiation,Successional lamina formation, Disintegration of the Dental lamina

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3
Q

cap stage

A

Histodifferentiation.

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4
Q

crown stage

A

When hard tissue is laid down: Dentin and then Enamel.

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4
Q

What percentage of enamel is made up of organic matrix?

A

4%

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5
Q

What are the components of the organic matrix in enamel?

A

Water

Proteins: Amelogenins(90%) and Enamelins(10%)

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6
Q

What percentage of enamel is made up of inorganic matrix?

A

96%

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7
Q

What is the primary inorganic component of enamel?

A

Hydroxyapatite (calcium phosphate)

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8
Q

What are the 3 phases of enamel formation (amelogenesis)?

A

Presecretory

Secretory

Calcification/Mineralization

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9
Q

What happens during the Presecretory phase of enamel formation?

A

During the presecretory phase, ameloblasts are formed through cytodifferentiation during tooth development.

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10
Q

What happens during the Secretory phase of enamel formation?

A

During the secretory phase, the organic matrix (amelogenins and enamelins) is produced.

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11
Q

What happens during the Calcification/Mineralization phase of enamel formation?

A

In this phase, the inorganic matrix, primarily hydroxyapatite (calcium phosphate), is deposited, mineralizing the enamel.

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12
Q

What happens when maturation begins at the future cusp of the tooth?

A

Ectomesenchymal cells of the dental papilla line up to face the inner enamel epithelium (IEE) and become pre-odontoblasts, which then stimulate the IEE cells to form pre-ameloblasts.

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13
Q

How do pre-ameloblasts contribute to tooth development?

A

Pre-ameloblasts stimulate the maturation of odontoblasts, which begin secreting dentin. The production of dentin then stimulates the maturation of ameloblasts, which secrete enamel.

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14
Q

How does the dental papilla contribute to tooth development during maturation?

A

The dental papilla elongates, providing nutrition to the ectomesenchymal cells and IEE.

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14
Q

Early Bell stage

A

Inner Enamel Epithelial cells differentiate into pre-ameloblasts

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15
Q

Bell stage

A

Pre-ameloblasts: nuclei are located close to the basement membrane

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16
Q

Crown stage

A

Ameloblasts: nuclei migrate away from the basement membrane to opposite end of the cell as it prepares to secrete enamel.

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16
Q

What happens to the basement membrane during the secretory phase of enamel formation?

A

The basement membrane is replaced by calcified tissue, becoming the Dentin-Enamel Junction (DEJ).

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17
Q

What happens to ameloblasts and odontoblasts during enamel and dentin formation?

A

Ameloblasts and odontoblasts move away from the Dentin-Enamel Junction (DEJ) in opposite directions.

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18
Q

Why is enamel unique in terms of mineralization and demineralization?

A

Enamel is so well mineralized (or calcified) that it can be completely lost upon demineralization, which doesn’t happen to any other tissue.

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19
Q

Why is enamel susceptible to damage?

A

Enamel has a high degree of calcification, which makes it very susceptible to damage by acids secreted by bacteria.

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20
Q

How does fluoride help protect enamel?

A

Incorporating fluoride into the hydroxyapatite crystals of enamel helps it withstand erosion caused by acids.

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21
Q

What is Tomes’ process, and why is it important?

A

Tomes’ process is the secretory tip of the ameloblast and is key to the organization of enamel.

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22
Q

How do inner enamel epithelium cells change during differentiation?

A

Inner enamel epithelium cells start as columnar in shape and elongate slightly as they become pre-ameloblasts.

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23
Q

What happens when inner enamel epithelium cells fully differentiate into ameloblasts?

A

When fully differentiated, the cells develop Tomes’ process, the secretory tip, and the nucleus moves away from the basement membrane.

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24
Q

When does the development of Tomes’ process occur in ameloblasts?

A

happens at the same time the ameloblast nucleus moves away from the basement membrane, as the ameloblasts become fully differentiated.

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25
Q

How does the maturation phase of enamel mineralization occur?

A

During maturation, ameloblasts resorb some of the organic matrix (amelogenins and water), and hydroxyapatite crystals increase in size and hardness.

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25
Q

What does Tome’s process secrete during enamel formation?

A

secretes the organic matrix, which includes glycoproteins(gel-like)

  • amelogenins and enamelins.
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26
Q

What is the initial stage of enamel mineralization?

A

In the initial stage, enamel is 25-30% mineralized, with inorganic matrix (apatite crystals) rapidly deposited on the organic matrix.

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27
Q

How does the maturation phase of enamel mineralization occur?

A

During maturation, ameloblasts resorb some of the organic matrix (amelogenins and water), and hydroxyapatite crystals increase in size and hardness.

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27
Q

How mineralized is enamel at the end of the maturation phase?

A

Enamel is 96% mineralized by the end of the maturation phase.

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28
Q

How is the organic matrix involved in enamel formation?

A

The organic matrix is secreted first, but it is rapidly mineralized and becomes less identifiable as a definitive layer.

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29
Q

What happens to the organic material as enamel ages?

A

As the inorganic crystals increase, the organic material diminishes over time.

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29
Q

Where is the organic matrix secreted from during enamel formation?

A

The organic matrix is secreted from both the sides and the tip of Tome’s process. This causes a change in the direction of the matrix, forming prismatic rods or prisms.

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30
Q

What is the organic substance made of?

A

The organic substance consists of high molecular weight glycoproteins, called enamelins, which are proteins with attached polysaccharide chains.

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31
Q

What is the main mineral in enamel?

A

The calcified portion of enamel is made up of tightly packed large crystals of calcium hydroxyapatite.

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32
Q

What is the enamel composition during initial formation?

A

Initially, enamel contains a relatively large amount of matrix and a small amount of mineral.

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33
Q

How does maturation affect enamel mineralization?

A

During maturation, some components (like amelogenins) are removed, allowing hydroxyapatite crystals to increase in size, further hardening the enamel.

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34
Q

What is the Enamel Prism/Rod ?

A

structural unit of enamel secreted by ameloblast

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35
Q

What is an enamel rod (prism)?

A

The basic unit of enamel, also called an enamel prism or rod, is the fundamental structure that makes up enamel.

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36
Q

How are enamel rods oriented?

A

Enamel rods are oriented perpendicular to the dentinal surface.

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37
Q

How do the enamel rods course from the DEJ to the surface?

A

The enamel rods have a wavy course as they move from the Dentin-Enamel Junction (DEJ) to the enamel surface.

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38
Q

What is the average width of an enamel rod?

A

The average width of an enamel rod is approximately 4 micrometers (µm), and it is narrower at the DEJ.

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39
Q

The shape of Tome’s process dictates what?

A

The shape of the Enamel Prism.

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40
Q

What is the shape of enamel prisms?

A

Enamel prisms have a keyhole shape.

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41
Q

What are the components of an enamel prism?

A

Body (Rod)

Interrod substance

Rod sheaths

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42
Q

Body (Rod):

A

The main part of the prism.

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43
Q

Interrod Substance:

A

The material surrounding each rod that connects them.

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44
Q

Rod Sheaths:

A

The boundary surrounding the enamel rod that helps to define the prism structure.

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45
Q

Why do enamel prisms have a keyhole shape?

A

The keyhole shape results from the sequence of secretion from Tome’s process.

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46
Q

How is the interrod substance formed?

A

Ameloblasts secrete the interrod substance from the sides of Tome’s process at a 65-degree angle from the tip.

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47
Q

What happens when Tomes’ processes retreat in the formation of enamel prisms?

A

The retreating Tomes’ processes leave an empty space behind, surrounded by interrod substance.

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48
Q

How is the empty space formed by Tomes’ processes filled in enamel?

A

The empty space is filled with enamel matrix by the tip of the retreating Tomes’ process, forming the rod body.

49
Q

How do the enamel prisms align in relation to Tomes’ processes?

A

The enamel prisms are parallel to Tomes’ processes.

50
Q

Why does enamel resemble a honeycomb structure?

A

because the retreating Tomes’ processes create spaces, which are later filled by enamel matrix, forming a rod-like structure.

51
Q

During enamel deposition what is the proper sequence of events.

A

1) organic matrix secreted from the sides of Tome’s process

2) Tome’s process retreats

3) organic matrix is secreted from the tip of Tome’s process.

52
Q

How are enamel rods arranged in relation to each other?

A

Enamel rods are arranged like fish scales, with each rod body surrounded by the interrod substance of adjacent enamel rods.

53
Q

What forms the rod sheaths in enamel?

A

The rod sheaths are formed by different patterns of hydroxyapatite crystals along the juxtaposition of the rod bodies and the interrod substance.

54
Q

What is the relationship between enamel rods and interrod substance?

A

Each enamel rod body is surrounded by the interrod substance of adjacent enamel rods, with the sheaths formed by hydroxyapatite crystal patterns.

54
Q

How does the orientation of hydroxyapatite crystals differ in enamel prisms?

A

The orientation of hydroxyapatite crystals differs between the two components of the enamel prism: the body (rod) and the interrod, due to the shape of Tomes’ process.

55
Q

How do enamel crystallites form and what causes the variation in crystal orientation within a rod prism?

A

Enamel crystallites form at right angles to the face of the cell, causing two variations in crystal orientation.

56
Q

What is the orientation of crystals in the interrod substance?

A

In the interrod substance (tail), the long axis of the hydroxyapatite crystals is about 65 degrees from the long axis of the enamel rods.

56
Q

How are the hydroxyapatite crystals arranged in the body (rod) of the enamel prism?

A

In the body (rod), the hydroxyapatite crystals are parallel to the long axis of the enamel rod, except at the edges where they are less tightly packed.

57
Q

What causes the rod sheath in enamel prisms?

A

The rod sheath results from the difference in crystal angles between the rod body and the interrod substance.

58
Q

Why are rod sheaths visible in enamel prisms?

A

Rod sheaths are visible due to the extra space created by the sharp angles where rod and interrod crystals meet.

59
Q

How are apatite crystals arranged in the body of the enamel prism?

A

Crystals are closely packed, parallel to the long axis of the rod, except at the edges where they are less tightly packed and not parallel.

60
Q

What is the average width of the body (rod) of an enamel prism?

A

The average width is 4-6 micrometers.

61
Q

How are apatite crystals arranged in the rod sheaths?

A

Crystals are loosely packed, at a different angle than those in the rod, with less calcification and mainly matrix.

62
Q

What makes the rod sheath more resistant to weak acid treatment?

A

The rod sheath is more resistant because of its higher organic content and lower calcification.

63
Q

How are apatite crystals oriented in the interrod substance?

A

Crystals in the interrod substance are oriented about 65 degrees to those in the rod.

64
Q

What happens to ameloblasts during the early and late stages of enamel formation?

A

Ameloblasts do not have Tomes’ processes and secrete prism-less enamel.

65
Q

Where is the prism-less enamel located in the early and late stages of enamel formation?

A

Prism-less enamel remains at the DEJ (oldest enamel) and the outer enamel surface (youngest enamel).

66
Q

How does prism-less enamel at the surface of the tooth compare to prism enamel?

A

Prism-less enamel is more highly calcified, harder, and less porous than prism enamel.

67
Q

What are the characteristics of prism-less enamel in terms of its organic matrix and crystals?

A

Prism-less enamel has less organic matrix, more crystals, and the apatite crystals are parallel to one another.

68
Q

What are pores in enamel?

A

Pores are small spaces that exist where crystals don’t form between enamel rods.

69
Q

What can diffuse into enamel through the pores?

A

Fluids, ions (like fluoride), and small molecules can diffuse into enamel through the pores.

70
Q

What happens to the size of enamel pores as a person ages?

A

Pores shrink as hydroxyapatite crystals grow and replace water and organic matrix.

70
Q

What is the role of pores in enamel?

A

Pores contribute to enamel’s permeability, allowing fluid movement and diffusion.

71
Q

How do pores affect enamel’s density and hardness?

A

Pores cause variations in density and hardness, making spots more prone to demineralization.

72
Q

What happens to enamel during demineralization?

A

The crystalline structure shrinks, and pores enlarge when oral pH drops below 5.5.

73
Q

How are enamel prisms/rods oriented in relation to the dentinal surface?

A

Enamel prisms/rods are oriented perpendicular to the dentinal surface.

74
Q

What is the course of enamel prisms/rods from the DEJ to the surface?

A

Enamel prisms/rods follow a wavy course from the DEJ to the surface.

74
Q

What is the average width of enamel prisms/rods, and how does it change at the DEJ?

A

The average width is 4 micrometers, narrower at the DEJ.

75
Q

How are enamel rods arranged to reduce fracture points?

A

Enamel rods are grouped together, with adjacent rows bending in opposite directions, like packaged Roman noodles.

75
Q

Why aren’t enamel prisms arranged in a straight linear fashion?

A

A straight arrangement would make enamel too brittle and susceptible to damage.

76
Q

What is the result of the unique arrangement of enamel rods?

A

The arrangement creates a strong, stabilized substance, discouraging fractures.

77
Q

What bands are associated with the bending arrangement of enamel rods?

A

Hunter-Shrager bands.

78
Q

What are Hunter-Shrager bands in enamel?

A

bundles of rods that undulate in 3 dimensions, especially at the DEJ, showing the course of rods through enamel.

78
Q

How do Hunter-Shrager bands contribute to enamel’s strength?

A

provide maximum stability and reduce the chance of fracture by preventing straight linear arrangements.

79
Q

How do Hunter-Shrager bands appear under reflected light?

A

They appear as alternating dark and light bands due to the change in direction of adjacent enamel rods.

80
Q

What causes the dark and light bands in Hunter-Shrager bands?

A

Dark bands are caused by rods cut transversely, and light bands are from rods cut longitudinally or obliquely.

81
Q

Where do Hunter-Shrager bands originate and how do they run?

A

They originate at the DEJ and run outward toward the outer enamel surface, reflecting alternating directions of enamel rods.

82
Q

How do Hunter-Shrager bands run in relation to enamel prisms?

A

Hunter-Shrager bands run parallel to the enamel prisms.

83
Q

What do Hunter-Shrager bands demarcate?

A

They demarcate the different orientations of adjacent groups of enamel prisms.

84
Q

How do Hunter-Shrager bands contribute to enamel’s strength?

A

They provide maximum stability, reducing the chance of fracture.

85
Q

What happens to enamel rods at the cusp of the tooth?

A

The enamel rods become more tangly, creating gnarled enamel.

86
Q

How does gnarled enamel affect the strength of enamel at the cusp?

A

Gnarled enamel makes the enamel tougher at the cusp.

87
Q

What are striations in enamel?

A

Striations are transverse thin dark bands across enamel rods.

88
Q

Why might a dentist need to change their drill bit in areas with gnarled enamel?

A

The increased toughness of gnarled enamel may require a different drill bit when filling a cavity.

89
Q

What do striations demarcate?

A

Striations demarcate daily growth patterns of enamel rods.

90
Q

What is the daily growth rate of enamel rods?

A

The daily growth rate is approximately 4 micrometers per segment.

91
Q

What are Striae of Retzius in enamel?

A

Striae of Retzius are thicker dark bands across enamel rods.

92
Q

What do Striae of Retzius indicate?

A

They show changes in mineralization.

93
Q

What causes the formation of Striae of Retzius?

A

They are produced by systemic disturbances in enamel growth, such as birth (Neonatal Line) and fever.

94
Q

What are Striae of Retzius made up of?

A

They are made up of aligned dark bands of adjacent prisms.

95
Q

How do Striae of Retzius run in relation to enamel rods/prisms?

A

perpendicular to the course of enamel rods/prisms.

96
Q

What are Perikymata?

A

Perikymata are shallow grooves and ridges on the tooth surface.

97
Q

How are Perikymata formed?

A

formed where the Striae of Retzius reach the tooth surface.

98
Q

Why are Perikymata typically absent in adult teeth?

A

They become abraded with mastication

99
Q

What are Perikymata grossly?

A

Perikymata are incremental growth lines that appear as a series of grooves on the surface of enamel.

100
Q

How long does it take for each Perikymata to form?

A

Each Perikymata is thought to take approximately 8–10 days to form.

101
Q

How can the count of Perikymata be useful?

A

The count of Perikymata may be used to assess how long a tooth crown took to form.

102
Q

Where are Perikymata easiest to notice?

A

canines

103
Q

What do Enamel Tufts resemble?

A

Enamel Tufts resemble small, twisted brushes or wavy trees.

104
Q

How far do Enamel Tufts extend through the enamel?

A

extend from the Dentin-Enamel Junction to less than halfway through the enamel.

105
Q

What are Enamel Tufts made of?

A

hypomineralized areas where the organic matrix of enamel rods has not been resorbed.

106
Q

What are Enamel Lamellae?

A

Enamel Lamellae are hypomineralized areas where the organic matrix has not been resorbed.

107
Q

How do Enamel Lamellae appear?

A

Enamel Lamellae resemble narrow lines or needles.

108
Q

How far do Enamel Lamellae extend?

A

They may develop in planes of tension within the enamel.

109
Q

What role can Enamel Lamellae play in tooth health?

A

Enamel Lamellae may be sites of entry for bacteria.

110
Q

What causes the formation of enamel fissures on molars and premolars?

A

overcrowding of ameloblasts, which may lead to cell death and incomplete matrix maturation.

111
Q

How is enamel around the deep end of a fissure affected?

A

Enamel around the deep end of the fissure is incompletely calcified (hypomineralized).

112
Q

What fills the empty groove of an enamel fissure?

A

The empty groove fills with organic debris and bacteria, which is narrower than a dental probe.

113
Q

How does the Dentin-Enamel Junction (DEJ) appear?

A

The DEJ is pitted and scalloped.

114
Q

What is the role of the Dentin-Enamel Junction (DEJ)?

A

The DEJ provides a strong bond between the layers of enamel and dentin.

115
Q

What are Enamel Spindles?

A

terminal ends of odontoblast processes trapped in enamel during tooth development.

116
Q

Where are Enamel Spindles more common?

A

cuspal areas of the tooth.

117
Q

How do Enamel Spindles extend through the enamel?

A

extend perpendicular to the dentin, but only a short way through the enamel.

118
Q

What are Enamel Spindles remnants of?

A

remnants of dentinal tubules, continuing into the enamel.

119
Q

What happens when the Reduced Enamel Epithelium (REE) merges with the overlying oral epithelium?

A

The support for ameloblasts goes away, leading to the loss of ameloblasts.

120
Q

What happens to ameloblasts during tooth eruption?

A

Ameloblasts are lost as the REE merges with the overlying oral epithelium and loses its support.

121
Q

What happens as the tooth erupts?

A

The attachment epithelium is lost, and with it, all support for the ameloblasts.

microanatomy (9 decks)

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