Enamel Tissue

Question 1

what is the hardest one of the 4 mineralized tissues of the body?

Answer 1

enamel

Question 2

True or false: enamel is only one that is not a connective tissue.

Answer 2

true

its an ectodermal derived tissue (formed by a specialized epithelial cell- ameloblast)

Question 3

true or false: enamel is not the only one that does not have an unmineralized or preenamel formation stage

Answer 3

false

most of enamel has an immature stage (partially mineralized) and a mature stage (fully mineralized)

Question 4

is enamel formation finite?

Answer 4

yes
ameloblast completes its enamel formative cycle once the thickness of enamel is reached at a site (most advanced coronally)

Question 5

is enamel the first mineralized tissue to appear in a developing tooth?

Answer 5

no

dentin is the first to appear, enamel second

Question 6

what does enamel subject to?

Answer 6

malformations (genetic and external factors), age changes, self-induced habits

Question 7

does enamel have enclosed cells, nerves, or lymph vessels?

Answer 7

no

Question 8

what is enamel tissue?

Answer 8

composite biological mineral with apatite crystals oriented in a complex 3d pattern

Question 9

physical properties of enamel

Answer 9

most clinically significant tissue of tooth, esp at surface, pits, grooves, ridges, caps, cracks
hardest and most highly mineralized bioloogical tissue.
5 on mineral hardness scale. 1-talc, 10 diamond
withstands both shearing and impact forces well
brittle without dentin support
translucent
needs wet environment to maintain integrity***
subject to attrition, abrasion, erosion

Question 10

what is attrition?

Answer 10

normal slow wearing away of tooth substance under the stress of mastication

Question 11

what is microporosity?

Answer 11

pathways for diffusion of small molecules such as water, electrochemical effects on pore walls lead to carious lesions

Question 12

what is remineralization?

Answer 12

mineral is returned to the molecular structure of enamel by way of the saliva. when demineralization exceeds remineralization, cavitation occurs

Question 13

inorganic substance within enamel

Answer 13

96% by weight
hydroxyapatite crystals.
enamel crystals are larger and consist of more impurities than other 3 types

Question 14

organic substance within enamel

Answer 14

1% by weight. enamel is the only one of the 4 mineralized tissue that does not contain collagen fiber - can dissolve in weak acid

Question 15

water within enamel

Answer 15

3% by weight
distributed throughout the volume of enamel by ways of micropores between crystals and proteins.
most of water forms a hydration shell around each crystal.
its distribution is clinically important bc its the route of fluoride ions, calcium and phosphorous ions for remineralization and whitening substances artificial and natural substances, acidophilic microorganisms, age changes

Question 16

what are the age changes of enamel?

Answer 16

wears slowly- attrition- darkens in color, composition of surface changes, fluoride increased at surface- reduced porocity- reduced susceptiility to caries.

Question 17

what are the 3 CEJ relationships?

Answer 17

most common: cementum overlaps enamel
next common: cementum meets enamel
least common: cemetum does not meet enamel

Question 18

DEJ configuration around tooth

Answer 18

scalloped at coronal areas: adaptation to occlusal forces

smooth at cervical areas: non- load bearing areas

Question 19

what are ameloblast?

Answer 19

columnar epithelial cells

Question 20

what are lines of retzius?

Answer 20

growth lines

Question 21

what is perikymata?

Answer 21

numerous small transverse ridges on the exposed surfaces of enamel
lines of retzius end on enamel surfaces as grooves. perikymata (ridges) are created between the grooves

Question 22

how are the structural components of enamel formed?

Answer 22

due to the direction and density of the apatite crystals in each site

Question 23

what are the three structural components of enamel?

Answer 23

enamel rods
enamel sheath
interrod substance

Question 24

enamel rods

Answer 24

structural unit of enamel
hydroxyapatite crystals are most dense in the center or core of the rod and run parallel to the long axis of the rod
each rod is formed by one ameloblast***

Question 25

enamel sheath

Answer 25

outer surface of the rod crystals are less dense than those of core and run in different directions, higher % of organic substance formed by one ameloblast along with the rod

Question 26

interrod substance

Answer 26

between he sheaths of rods crystals ar more dense and run at different directions than those of the sheath two or more amelobalst secrete the interrod substance

Question 27

what is the direction of rods?

Answer 27

right angles to dentin surface

Question 28

what are interrod striations?

Answer 28

each enamel rod is built up of segments separated by dark lines that give it a striated appearance. segmented bc its secreted in a rhythmic manner- rest period of ameloblast marked by interrod striation

Question 29

what are the 3 hypomineralized enamel structures

Answer 29

enamel lamella enamel tuft enamel spindle

Question 30

enamel lamella

Answer 30

extend for varying depths from the surface of enamel and consist of longitudinally oriented defects filled with enamel protein or organic debris from the oral cavity originates at enamel surface and passes toward dentin clinical significance: due to their access by acidophilic microorganisms and to stain substances

Question 31

enamel tuft

Answer 31

tufts project from the DEJ for a short distance into enamel and contain greater concentration of enamel protein clinical signicance: contributes to the spread of caries at the DEJ

Question 32

enamel spindle

Answer 32

spindles extend from the dentin across the DEJ into the enamel for a short distance formed when before secretion of dentin and enamel begins, some cell processes of odontoblast extend between ameloblast and when enamel formation begins, the processes become embedded within the newly secreted enamel. clinical signicance: contributes to spread of caries along the DEJ

Question 33

hunter schreager band

Answer 33

alternating dark and light bands of varying width- originate at the DEJ border and pass outward ending at some distance from the outer enamel surface: caused by the different direction of enamel rods in adjacent layers change in rod direction is regarded as a functional adaptation, minimizing the risk of cleavage in the axial direction under the influence of masticatory forces

Question 34

where does differentiation first occur?

Answer 34

differentiation of inner epeithelial cells of the enamel organ into ameloblasts and of the peripheral cells of the dental papillar into odontoblasts begins in the coronalmost side of future dej

Question 35

how does enamel and dentin first form?

Answer 35

ameloblast form partially mineralized or immature enamel moving outward odontoblast forming predentin: moving inward toward center of pulp