Tooth Microstructure

Question 1

How many deciduous teeth are there?

Answer 1

20

Question 2

How many permanent teeth are there?

Answer 2

32 (Many have 28 after removal of 3rd molars)

Question 3

Function of inscisors

Answer 3

Cut and shear food
phonetics and function
esthetics

Question 4

Function of canines

Answer 4

Seize pierce tear and cut food

Key to occlusion (protection)

Question 5

What teeth have the longest roots and the thickest enamel?

Answer 5

Canines

Question 6

Function of premolars

Answer 6

Grind and tear

Fine chewing

Question 7

Function of molars

Answer 7

crushing grinding and chewing

Question 8

Two parts of the crown of a tooth

Answer 8

Clinical-what you can see w/ gums in place

Anatomical-where enamel ends

Question 9

Characteristics of enamel

Answer 9

• Hard (Hardest tissue in body)
• Translucent white
• Shell structure

Question 10

Characteristics of dentin

Answer 10

• Yellowish

- Softer

Question 11

4 layers of a tooth

Answer 11

Enamel
Dentin
Pulp complex
Cementum

Question 12

Composition of enamel

Answer 12

1-2% Protein
6% water
90-92% inorganic (hydroxyapitite)

Question 13

How is enamel organized

Answer 13

• Rods or prisms run from DEJ to surface
• Rods about 4-8 micrometers
• Interlocking prisms made of head and tail region
• Rods surrounded by organic sheath
• Rods made of crystallites, surrounded by organic matrix

Question 14

How does enamel develop?

Answer 14

• Has epithelial origin

- Ameloblasts grow from DEJ and become extinct

Question 15

Crystallites characteristics

Answer 15

• composed of calcium phosphate (Hydroxyapitite)
• Irregular and needle like in shape
• 20nm by 160nm
• surrounded by organic matrix
• arrange in regular pattern within rod
  
  • long axis of body parallel to rod direc.
  • and tail angles up 65 degrees

Question 16

How do rods travel from DEJ to surface

Answer 16

Wavy and spiraling path

Gnarled enamel at cervical and incisal/occlusal areas (harder to cleave)

Question 17

Physical properties of enamel

Answer 17

• Hard brittle and stiff parallel to rod

- Low tensile strength perpendicular to rod direction

Question 18

What are enamel fracture lines called

Answer 18

Craze lines if dentin below is still intact

Question 19

Enamel is iso or aniso-tropic?

Answer 19

anisotropic. Looks different depending on perspective

Question 20

Best way to prep enamel

Answer 20

90 degrees w/ edge of tooth so that enamel stays supported by dentin

Question 21

Dentin composition

Answer 21

50% vol HA
25% vol collagen
25% water

Question 22

Pattern of dentin

Answer 22

striated like enamel

Question 23

Dentin development

Answer 23

• Mesenchymal origin

- Odontoblasts grow from DEJ and remain alive

Question 24

Dentinal tubules

Answer 24

• more mineralized than other dentin matrix
• extend from pulp chamber to DEJ
• related to cells that line pulpal wall (odontoblast)

Question 25

Why is the dentin just after the DEJ so sensitive

Answer 25

Dentinal tubules branch out near DEJ so its more likely to hit one

Question 26

What is peritubular dentin

Answer 26

Dentin that lines dentinal tubules

Question 27

What is intertubular dentin

Answer 27

Dentin between dentinal tubules

Question 28

What are odontoblastic processes (Tomes Fibers)

Answer 28

Deep portion of dentinal tubules before odontoblasts

Question 29

What is predentin

Answer 29

New dentin that has not mineralized yet located between odontoblasts and dentin. Found on pulpal wall

Question 30

Function of dentinal tubules

Answer 30

Allow fluid movement and ion transport - remineralization - apposition of peritubular dentin - pain perception

Question 31

Superficial vs deep dentinal tubules

Answer 31

Fewer and smaller tubules in superficial section

Question 32

Dentin organization

Answer 32

Not uniformly mineralized

Question 33

Peritubular dentin vs intertubular dentin

Answer 33

Peritubular dentin is more mineralized

Question 34

Dentin structure

Answer 34

- Principal organic component is collagen=tough - HA crystals w/in collagen * Crystal smaller than enamel

Question 35

Properties of dentin

Answer 35

- 20% as tough as enamel - Higher tensile strength but lower stiffness - isotropic (same from all views) - Dentin stops propagation of cracks in enamel (holds it together)

Question 36

Dentin types

Answer 36

- Primary dentin- forms up to 3 yrs after tooth eruption - Secondary-w/o obvious stimulus dentin direction changes and deposition slows - Reparative (tertiary) - Sclerotic (defense)

Question 37

How does dentin differ from enamel?

Answer 37

1) Less mineral content 2) Tubules run throughout so more fluid and ion transport 3) Ability to repair/regenerate

Question 38

Radiograph appearance

Answer 38

Enamel is whiter and more radiopaque due to mineralization

Question 39

What is cementum

Answer 39

Light yellow (slightly lighter than dentin), hard avascular structure that attaches bone to tooth

Question 40

Cementum composition

Answer 40

Similar to dentin but 5-10% less mineral content - 45-50% HA by weight - 50-55% organic matter (collagen protein polysacc and water) - Highest fluoride content

Question 41

Why does cementum have so much fluoride?

Answer 41

Soft and porous

Question 42

Cementum development

Answer 42

Formed continually acellularly and cellularly from cementoblasts

Question 43

Cementoblast development

Answer 43

from undifferentiated mesenchymal cells in connective tissue of dental follicle

Question 44

Cementum organization

Answer 44

CDJ: cementodentinal junc CEJ: Cementoenamel junc aka cervical line