Lecture 3: Enamel Tissue

Question 1

four mineralized tissues of the body

Answer 1

• enamel (hardest)
• dentin
• cementum
• bone

Question 2

what are the characteristics that differentiate enamel from the other 4 mineralized tissues of the body?

Answer 2

• 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

Question 3

what are the first two mineralized tissues to arise in the body?

Answer 3

dentin first and then enamel

Question 4

what hardness scale is used for enamel?

Answer 4

Mohs mineral hardness scale

1 to 10 (1=talc 2=apatite 3=diamond)

Question 5

what does enamel need to maintain its integrity?

Answer 5

a wet environment (saliva)

Question 6

enamel is subject to three deformities. what are they and which ones are normal?

Answer 6

• attrition (normal)
• abrasion (not normal)
• erosion (not normal)

Question 7

pathways in enamel for diffusion of small molecules such as water

Answer 7

microporosity

electrochemical effects on pore walls lead to carious lesions

Question 8

mineral is returned to the molecular structure of enamel BY WAY OF SALIVA

Answer 8

remineralization

when demineralization exceeds remineralization cavitation occurs

Question 9

what are the percentages of enamel?

Answer 9

96% inorganic (hydroxyapatite crystals)
1% organic (AMELOGENIN)
3% water (forms a hydration shell around the tooth)

Question 10

what are some of the age changes of enamel?

Answer 10

• wears slowly (attrition)
• darkens in color
• flouride INC at the surface
• DEC porosity
• DEC suseptibility to caries

Question 11

from most common to least common, what are the three CEJ relationships

Answer 11

• cementum overlaps enamel (most common)
• cementum meets enamel
• cementum does not meet enamel (least common)

Question 12

growth lines of enamel that look like tree rings

Answer 12

lines (strae) of Retzius

Question 13

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

Answer 13

perikymata

Question 14

structural unit of enamel that has a DENSE CORE and is formed by only ONE ameloblast. is perpendicular to the surface of the dentin

Answer 14

enamel rods

*hydroxyapetite crystals are most dense in the center of the rod and run parallel to the long axis of the rod

Question 15

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)

Answer 15

enamel sheath

Question 16

between the sheaths of enamel rods, created from TWO OR MORE ameloblasts

Answer 16

interrod substance

Question 17

extend from varying depth from the enamel surface and are clinically significant due to caries and stain substances

Answer 17

enamel lamella

Question 18

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)

Answer 18

enamel tuft

Question 19

extend from the dentin cross the DEJ into the enamel for a short distance. (contributes to spread of caries along the DEJ)

Answer 19

enamel spindle

Question 20

alternating layers of light and dark of varying width. they originate at the DEJ border and pass outward.

Answer 20

hunter-schreager bands

Question 21

what causes hunter-schreager bands?

Answer 21

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)