Lecture 3: Enamel Tissue Flashcards
four mineralized tissues of the body
- enamel (hardest)
- dentin
- cementum
- bone
what are the characteristics that differentiate enamel from the other 4 mineralized tissues of the body?
- only one that is NOT connective tissue (ectodermal ameloblasts)
- only one not to have an unmineralized or prenamel stage (immature stage —-> mature stage
- formation is finite
- subject to malformations
- does NOT have enclosed cells, nerves, or blood or lymph vessels
what are the first two mineralized tissues to arise in the body?
dentin first and then enamel
what hardness scale is used for enamel?
Mohs mineral hardness scale
1 to 10 (1=talc 2=apatite 3=diamond)
what does enamel need to maintain its integrity?
a wet environment (saliva)
enamel is subject to three deformities. what are they and which ones are normal?
- attrition (normal)
- abrasion (not normal)
- erosion (not normal)
pathways in enamel for diffusion of small molecules such as water
microporosity
electrochemical effects on pore walls lead to carious lesions
mineral is returned to the molecular structure of enamel BY WAY OF SALIVA
remineralization
when demineralization exceeds remineralization cavitation occurs
what are the percentages of enamel?
96% inorganic (hydroxyapatite crystals)
1% organic (AMELOGENIN)
3% water (forms a hydration shell around the tooth)
what are some of the age changes of enamel?
- wears slowly (attrition)
- darkens in color
- flouride INC at the surface
- DEC porosity
- DEC suseptibility to caries
from most common to least common, what are the three CEJ relationships
- cementum overlaps enamel (most common)
- cementum meets enamel
- cementum does not meet enamel (least common)
growth lines of enamel that look like tree rings
lines (strae) of Retzius
numerous small transverse ridges on the surface of enamel. lines of retzius end on the enamel surface as grooves, and ridges are created between the grooves
perikymata
structural unit of enamel that has a DENSE CORE and is formed by only ONE ameloblast. is perpendicular to the surface of the dentin
enamel rods
*hydroxyapetite crystals are most dense in the center of the rod and run parallel to the long axis of the rod
outer surface of enamel rods that are LESS DENSE and have crystals that run in different directions (there is also a higher content of ORGANIC substance)
enamel sheath
between the sheaths of enamel rods, created from TWO OR MORE ameloblasts
interrod substance
extend from varying depth from the enamel surface and are clinically significant due to caries and stain substances
enamel lamella
projects from the DEJ for a short distance into enamel and contain a great concentration of enamel protein. (contributes to spread of caries at the CEJ)
enamel tuft
extend from the dentin cross the DEJ into the enamel for a short distance. (contributes to spread of caries along the DEJ)
enamel spindle
alternating layers of light and dark of varying width. they originate at the DEJ border and pass outward.
hunter-schreager bands
what causes hunter-schreager bands?
different direction of enamel rods in adjacent layers
(regarded as a functional adaptation, minimizing the risk of cleavage in the axial direction under the influence of masticatory forces)
