Lecture 9 Flashcards
What is the anatomical crown?
The part of the tooth that is covered by enamel
What is the clinical crown?
Part of the tooth exposed above the gingiva
What is the hardest part of the body? Second hardest?
Enamel. Dentin
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
What is the hardness of enamel similar to?
Mild steel
Is enamel malleable?
No it is not malleable, it is brittle
Why does dentin influence the color of enamel?
Because enamel is translucent and the underlying dentin tends to be yellow
What mineral is enamel mostly made of?
An apatite of calcium phosphate
What other minerals may be incorporated into enamel during its formation?
Strontium, magnesium, lead and fluoride
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
What are apatites?
Various chemical forms of calcium phosphate and other elements
Of the three common apatites in enamel, which is most common?
Hydroxyapatite
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
What are enamel rods?
Hydroxyapatite crystals of enamel are organized into long, thin rods, sometimes called prisms.
How long can enamel rods be?
As long as the entire thickness of the enamel layer
What are enamel rods surrounded by?
By interlocking additional hydroxyapatite crystals
What are the three typical patterns of acid-etched enamel?
Rod preferentially eroded
Interrod preferentially eroded
Indiscriminate erosion
What type of force does the irregular shape of the DEJ help to resist?
Shearing force
What are enamel lamellae?
Linear defects that can span the full thickness of enamel
What are enamel lamellae filled with?
Organic material from trapped pieces of the enamel organ or CT surrounding the developing tooth
What are enamel tufts?
Higher concentration of enamel protein that projects a short distance from the DEJ into the enamel
What are enamel spindles?
Left over pieces of odontoblasts that extend into the ameloblast epithelium and become trapped there as enamel begins to form
Is dentin a living tissue?
Yes
What do the odontoblasts remain attached to throughout the life of the tooth?
DEJ
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?
- Dentin is directly innervated
- Odontoblasts act as receptors
- 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?
- Odontoblastic zone
- Cell-free zone
- Cell-rich zone
- 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
