Tooth Microstructure Flashcards
How many deciduous teeth are there?
20
How many permanent teeth are there?
32 (Many have 28 after removal of 3rd molars)
Function of inscisors
Cut and shear food
phonetics and function
esthetics
Function of canines
Seize pierce tear and cut food
Key to occlusion (protection)
What teeth have the longest roots and the thickest enamel?
Canines
Function of premolars
Grind and tear
Fine chewing
Function of molars
crushing grinding and chewing
Two parts of the crown of a tooth
Clinical-what you can see w/ gums in place
Anatomical-where enamel ends
Characteristics of enamel
- Hard (Hardest tissue in body)
- Translucent white
- Shell structure
Characteristics of dentin
- Yellowish
- Softer
4 layers of a tooth
Enamel
Dentin
Pulp complex
Cementum
Composition of enamel
1-2% Protein
6% water
90-92% inorganic (hydroxyapitite)
How is enamel organized
- 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
How does enamel develop?
- Has epithelial origin
- Ameloblasts grow from DEJ and become extinct
Crystallites characteristics
- 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
How do rods travel from DEJ to surface
Wavy and spiraling path
Gnarled enamel at cervical and incisal/occlusal areas (harder to cleave)
Physical properties of enamel
- Hard brittle and stiff parallel to rod
- Low tensile strength perpendicular to rod direction
What are enamel fracture lines called
Craze lines if dentin below is still intact
Enamel is iso or aniso-tropic?
anisotropic. Looks different depending on perspective
Best way to prep enamel
90 degrees w/ edge of tooth so that enamel stays supported by dentin
Dentin composition
50% vol HA
25% vol collagen
25% water
Pattern of dentin
striated like enamel
Dentin development
- Mesenchymal origin
- Odontoblasts grow from DEJ and remain alive
Dentinal tubules
- more mineralized than other dentin matrix
- extend from pulp chamber to DEJ
- related to cells that line pulpal wall (odontoblast)
Why is the dentin just after the DEJ so sensitive
Dentinal tubules branch out near DEJ so its more likely to hit one
What is peritubular dentin
Dentin that lines dentinal tubules
What is intertubular dentin
Dentin between dentinal tubules
What are odontoblastic processes (Tomes Fibers)
Deep portion of dentinal tubules before odontoblasts
What is predentin
New dentin that has not mineralized yet located between odontoblasts and dentin.
Found on pulpal wall
Function of dentinal tubules
Allow fluid movement and ion transport
- remineralization
- apposition of peritubular dentin
- pain perception
Superficial vs deep dentinal tubules
Fewer and smaller tubules in superficial section
Dentin organization
Not uniformly mineralized
Peritubular dentin vs intertubular dentin
Peritubular dentin is more mineralized
Dentin structure
- Principal organic component is collagen=tough
- HA crystals w/in collagen
- Crystal smaller than enamel
Properties of dentin
- 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)
Dentin types
- 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)
How does dentin differ from enamel?
1) Less mineral content
2) Tubules run throughout so more fluid and ion transport
3) Ability to repair/regenerate
Radiograph appearance
Enamel is whiter and more radiopaque due to mineralization
What is cementum
Light yellow (slightly lighter than dentin), hard avascular structure that attaches bone to tooth
Cementum composition
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
Why does cementum have so much fluoride?
Soft and porous
Cementum development
Formed continually acellularly and cellularly from cementoblasts
Cementoblast development
from undifferentiated mesenchymal cells in connective tissue of dental follicle
Cementum organization
CDJ: cementodentinal junc
CEJ: Cementoenamel junc aka cervical line
