Enamel Flashcards
What are some enamel characteristics?
- Hardest mineralized tissue in the body
- Nonvital (acellular, avascular & no nerve)
- Inorganic (hydroxyapatite crystals) composition is more than organic composition
- Lacks collagenous proteins
Enamel Rod
- Basic morphological/structural unit of enamel
- Enamel prisms
- “Keyhole” shape consisting of a head and a tail (classic concept)
- Crystals parallel to rod axis
- Bound by interprismatic substances
- Each rod formed in increments by 1 secretory ameloblast w/ Tomes’ process
Interrod enamel
- Bound by interprismatic substance
- Cylindrical rods embedded in interrod enamel (current concept)
- The tail of the keyhole shape
Enamel rod and Interrod enamel similarities
Both are made of enamel crystals
Enamel rod and Interrod enamel crystal orientation differences
Crystal orientation is different
Rod: crystals parallel to rod axis
Interrod: crystals at angle to rod
How many ameloblasts form 1 classical enamel rod?
Four
Enamel Rod orientation
- Extend approximately from DEJ to enamel surface.
- Perpendicular to DEJ and enamel surface, but slightly S-shaped in both horizontal and vertical planes.
What are the 5 Enamel Micro features?
- DEJ (dentino-enamel junction)
- Cross striations
- Lines (Stria) of Retzius
- Hunter-Schreger bands
- Gnarled enamel
List the DEJ features
- Scalloped junction in section.
- Convex surface faces dentin.
- Prevents shear forces from separating enamel from dentin.
- 1st formed enamel and dentin located here.
List the Cross striations features
- Daily incremental growth lines
- Run at right angle to rod axis
- Enamel layers deposited over a period of 24 hrs
- Ladder-like appearance with enamel rod
What structures form a ladder-like appearance?
Cross striations and enamel rod
List the Lines (Striae) of Retizus features
- Incremental growth lines
- Enamel layer represents 5 to 10 days
- Increased organic content & are indicative of the rhythmic variation in the calcification of the enamel matrix
- Formed during the secretory phase of amelogenesis.
- Accentuated by diseases and changes in nutrition
- neonatal line!!!
What do the retzius striae represent?
The spaces between a series of successively larger cones stacked one outside the other
What do the Lines (Striae) of Retizus appear like in a cross section? Are they parallel?
Tree rings
NOT parallel in longitudinal section
What is the neonatal line?
- Most accentuated Stria of Retzius
- Reflects physiologic changes (disturbances to amelogenesis) occurring during birth
- In all primary teeth, sometimes cusps of first permanent molars
What is the Perikymata?
- Imbrication lines.
- Horizontal shallow grooves on enamel surface.
- More prominent on facial side of newly erupted teeth.
- Usually lost through wear.
List the Hunter-Schreger Bands features
- Represent alternating groups of cross
sectioned enamel rods and longitudinally sectioned enamel rods. - Extend only ~ 2/3 distance from DEJ toward enamel surface.
- Observed only with reflected light or scanning EM.
What bands correspond to cross-sectioned enamel rods?
Dark bands
What bands represent longitudinally sectioned enamel rods?
Light bands
How do light and dark bands appear in reflected light?
Appear as an alternating light and dark bands extending from DEJ toward the enamel surface in reflected light
List the Gnarled enamel features
- Represents groups of twisted enamel rods.
- The DEJ is toward enamel surface.
- Only found at the cuspal and incisal areas.
- Increase resistance of enamel to fracture to mastication stress.
What is enamel demineralization?
- Carbonated apatites are more susceptible to demineralization compared to hydroapx and fluoroap
- Crystal ends first to dissolve, then along core.
- Dissolves from inside out.
Compare crystal ends vs. their sides
-Crystals dissolve more readily at their ends than on their sides.
- Crystals lying perpendicular to the enamel surface are more vulnerable.
Compare crystal orientation in enamel rod and interrod enamel
- Rod crystal ends are perpendicular to enamel surface
- Interrod crystal ends are not exposed
