Lecture 9 Flashcards by George Magnus

What is the anatomical crown?

The part of the tooth that is covered by enamel

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What is the clinical crown?

Part of the tooth exposed above the gingiva

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What is the hardest part of the body? Second hardest?

Enamel. Dentin

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About what percentage of enamel is composed of minerals? Percentage of dentin? Percentage of cementum?

Enamel is about 96% mineral.
Dentin about 70% mineral.
Cementum is about 45-60% miineral

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What is the hardness of enamel similar to?

Mild steel

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Is enamel malleable?

No it is not malleable, it is brittle

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Why does dentin influence the color of enamel?

Because enamel is translucent and the underlying dentin tends to be yellow

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What mineral is enamel mostly made of?

An apatite of calcium phosphate

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What other minerals may be incorporated into enamel during its formation?

Strontium, magnesium, lead and fluoride

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How can water and dissolved ions still be absorbed into mature enamel?

The slightly porous enamel, due to its crystalline organization, allows some water absorption

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What are apatites?

Various chemical forms of calcium phosphate and other elements

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Of the three common apatites in enamel, which is most common?

Hydroxyapatite

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What concentration of chronic fluoride ingestion may cause flurosis? What is the recommended concentration of fluoride in drinking water?

5 ppm.

.7 to 1.2 ppm

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What are enamel rods?

Hydroxyapatite crystals of enamel are organized into long, thin rods, sometimes called prisms.

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How long can enamel rods be?

As long as the entire thickness of the enamel layer

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What are enamel rods surrounded by?

By interlocking additional hydroxyapatite crystals

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What are the three typical patterns of acid-etched enamel?

Rod preferentially eroded
Interrod preferentially eroded
Indiscriminate erosion

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What type of force does the irregular shape of the DEJ help to resist?

Shearing force

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What are enamel lamellae?

Linear defects that can span the full thickness of enamel

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What are enamel lamellae filled with?

Organic material from trapped pieces of the enamel organ or CT surrounding the developing tooth

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What are enamel tufts?

Higher concentration of enamel protein that projects a short distance from the DEJ into the enamel

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What are enamel spindles?

Left over pieces of odontoblasts that extend into the ameloblast epithelium and become trapped there as enamel begins to form

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Is dentin a living tissue?

Yes

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What do the odontoblasts remain attached to throughout the life of the tooth?

DEJ

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In which direction do odontoblasts grow from the DEJ?

To the pulp chamber

Why does the size of the pulp chamber and root canal become smaller with age?

Dentin continues to grow into the pulp

What are odontoblasts nourished by?

Blood vessels in the pulp

The odontoblasts processes extend to the DEJ via what structure?

Dentinal tubule

About how many tubules are there per square mm of dentin?

59,000-76,000

What is the name of newly deposited dentin?

Predentin

What kind of dentin makes up most of the tooth?

Primary dentin

What is secondary dentin?

Dentin that develops after root formation is complete. Proceeds slowly and reduces the size of the pulp cavity

What is mantle dentin?

Dentin that forms under the enamel of the crown

What is tertiary dentin?

Dentin that is produced locally in response to caries, attrition and dental restoration

What are the two subclasses of tertiary dentin?

Reactionary dentin and Reparative dentin

How is reactionary dentin formed? Reparative dentin?

It is deposited by existing odontoblasts. | Reparative dentin is deposited by newly differentiated odontoblasts

T/F The boundaries of dentinal tubules are established by a meshwork of collagen fibrils

True

What are the three possible mechanisms of dentin sensitivity?

1. Dentin is directly innervated 2. Odontoblasts act as receptors 3. Fluid movement through tubules stimulates receptors in pulp

Which of the three dentin sensitivity theories is the best supported hypothesis?

The Fluid Movement Through Dentinal Tubules theory

Does cementum have blood supply?

No, it is avascular

Cementum is similar to what connective tissue?

Bone

What are cells that produce cementum called?

Cementoblasts

What do cementoblasts look like?

Fibroblasts

What are mature cementoblasts called? What do the look like?

Cementocytes. Look like osteocytes.

What are the four categories into which cementum is classified?

Acellular Cellular Mixed - alternating layers of acellular and cellular Acellular Afibrillar

Which cementum type is also called the primary? Which one is also called secondary?

Acellular is also primary | Cellular is also Secondary

What is the origin of fibers of acellular cementum? What is its location on a tooth?

Extrinsic fiber origin. | Cervical margin to 2/3 down towards the apex

What is the function of acellular cementum?

Anchorage to PDL

What is the origin of fibers of cellular cementum? What is its location on a tooth?

Intrinsic fiber origin | Located in the periapical and interradicular (furcations) regions

What is the function of cellular cementum?

Adaptation to tooth wear and movement and repair

What is the granular layer of Tomes?

Thought to be a mix of collagen and non-collagenous matrix proteins at the dentin-cementum interface

Which teeth often only have the acellular cementum?

Incisors and canines

Why is Acellular Extrinsic Fiber Cementum (AEFC) called "acellular"?

Because the cementoblasts remain on the surface of the the cementum proximal to the PDL

Why is AEFC called "extrinsic"?

Because the cementoblasts secrete primarily noncollagenous matrix proteins that mix with the collagen fibers produced by fibroblasts of the PDL

What is one noncollagenous protein produces by AEFC?

Osteoponin

What is the mineralization of cementum regulated by?

Regulated by noncollagenous matrix proteins such as osteoponin

Cellular Intrinsic Fiber Cementum (CIFC) is produced by what kind of cementoblasts?

By cementoblasts that produce collagen fibrils into newly produced and unmineralized dentin of tooth roots

At what point in the formation of the tooth root does CIFC form?

After at least half of the root is formed

Which cementum type is produced during wound healing and regeneration of tissues?

CIFC

What is the layer of unmineralized matrix on the surface of the CIFC called?

Cementoid

What happens to the cementoid as it matures?

It becomes mineralized with calcium and entraps cementoblasts that also mature into cementocytes

These entrapped "intrinsic" cementocytes have reduced ______ function

secretory

What do the intrinsic cementocytes grow towards the vascular PDL?

Thin processes

Where is the cementum relative to the enamel in the majority of the cementoenamel junctions?

In 60% of the cases cementum overlaps the enamel

If the enamel does not overlap the enamel at the cementoenamel junction then how else does it lie relative to the enamel?

In 30% of the cases the cementum merely abuts with the superior enamel. In 10% of the cases insufficient cementum actually does not join with the enamel and leaves root dentin exposed

What are the two principal cells in the pulp of a tooth What other cells may be found in the pulp?

Odontoblasts and fibroblasts. | Other cells include undifferentiated (stem cells) ectomesenchymal cells, macrophages, and leukocytes

In the pulp, where are the odontoblasts localized?

Next to the dentin

What are the four zones of the pulp?

1. Odontoblastic zone 2. Cell-free zone 3. Cell-rich zone 4. Pulp core Mnemonic: Old Celery Creates Pus

What is the odontoblastic zone composed of?

The cell bodies of odontoblasts

Where does the cell-free zone lie in the pulp?

It lies between the odontoblast bodies and a relatively dense region of fibroblasts

What is the cell-free zone composed of?

Loosely arranged CT fibers and ECM

What does the cell-rich zone consist of?

Fibroblasts, leukocytes, and stem cells

The pulp core itself consists of what?

Blood vessels and nerves

What are the blood vessels and nerves of the pulp core suspended in?

A gelatinous CT matrix