enamel tissue

Question 1

from what germ layer is enamel derived?

Answer 1

ectoderm…formed by ameloblasts (which come from the inner epithelial layer of enamel organ)

Question 2

what 2 stages is enamel in

Answer 2

1. immature 2. mature….never in an unmineralized form

Question 3

when does the ameloblast complete its enamel formative cycle

Answer 3

once the thickness of enamel is reached at a particular site

Question 4

does enamel appear before or after dentin

Answer 4

after

Question 5

enamel does not have

Answer 5

b.v, cells, nerves, lymphatic vessels (acellular, avascular, aneural, alymphatic)

Question 6

microporosity defined

Answer 6

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

Question 7

remineralization

Answer 7

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

Question 8

chemical components of enamel

Answer 8

1. inorganic substance (96%) 2. organic substance (1%) 3. water (3%)

Question 9

inorganic substance is made of

Answer 9

calcium hydroxyapetite crystals…these crystals are larger and have more impurities (than other mineralized tissues)

Question 10

organic substance is made of

Answer 10

proteins. amelogenin is the main protein, but other non-amelogenin proteins exist. NO COLLAGEN.

Question 11

what is a hydration shell

Answer 11

water forms a hydration shell around each crystal. this water distribution is the route of fluoride, calcium, and phosphorous ions for remineralization (also whitening substances, and acidophilic microorganisms)

Question 12

how does enamel change with age

Answer 12

wears slowly, darkens in color, composition of surface changes, fluoride increases at surface, reduced porosity, reduced susceptibility to caries

Question 13

DEJ configuration at the coronal area

Answer 13

wavy/scalloped to adapt to occlusal forces

Question 14

DEJ configuration at the cervical area

Answer 14

smooth at non-loading bearing areas

Question 15

what is the most common CEJ configuration

Answer 15

cementum overlapping enamel…but this relationship varies around a tooth and from tooth to tooth

Question 16

what are lines of retzius

Answer 16

growth lines of enamel

Question 17

what are perikymata

Answer 17

transverse ridges on the exposed surface of enamel. created by lines of retzius

Question 18

what are the structural components of enamel

Answer 18

1. enamel rods
2. enamel sheath
3. interrod substance

Question 19

what is an enamel rod composed of

Answer 19

several million crystallites are packed in each rod. crystals are most dense in the center/core of the rod. the crystals run parallel to the long axis of the rod. each rod is formed by one ameloblast

Question 20

what is the enamel sheath composed of

Answer 20

outer surface of the rod. crystals are less dense than the rod. crystals run in different directions. there is a higher % of organic substance here (highest % of amelin…protein)

Question 21

what is interrod substance composed of

Answer 21

b/w the sheaths of the rods. crystals are more dense than sheath. crystals run at different directions than sheath crystals. 2 or more ameloblasts secrete the interrod substance.

Question 22

dark lines that separated segments of enamel rods

Answer 22

interrod striations. the rod is segmented because it’s secreted in a rhythmic manner (the rest period of a ameloblast is marked by an interrod striation)

Question 23

3 types of hypomineralized enamel structures

Answer 23

1. enamel lamella
2. enamel tuft
3. enamel spindle

Question 24

enamel lamella

Answer 24

extend for varying depths from the surface of enamel. consist of longitudinally oriented defects filled with enamel protein or organic debris

Question 25

what is the clinical significance of enamel lamella

Answer 25

access by acidophilic microorganisms (caries) and stain substance (esthetics)

Question 26

enamel tuft

Answer 26

tufts project from DEJ into the enamel and contain greater concentration of enamel protein than the rest of enamel (tuftelin)

Question 27

clinical significance of enamel tuft

Answer 27

contributes to the spread of caries at the DEJ

Question 28

enamel spindle

Answer 28

extend from the dentin cross the DEJ into the enamel

Question 29

clinical significance of enamel spindle

Answer 29

contributes to spread of caries along the DEJ

Question 30

formation of enamel spindles

Answer 30

cell processes of odontoblasts extend b/w ameloblasts and when enamel formation begins the processes become embedded within the newly secreted enamel

Question 31

hunter schreager bands

Answer 31

alternating dark and light bands or varying width. originate at the DEJ border and pass outward ending at some distance from the outer enamel surface. they are caused by the different direction of enamel rods in adjacent layers. (this is a functional adaptation to minimize the risk of cleavage in the axial direction during masticatory functions)

Question 32

where dues differentiation of the inner epithelial cells and the peripheral cells of the dental papilla begin

Answer 32

in the coronal most sit of the future DEJ

Question 33

what is the name for ectopic enamel formation

Answer 33

enamel pearls

Question 34

tetracycline stain is caused by

Answer 34

antibiotics

Question 35

mulberry molars are caused by

Answer 35

congenital syphilis