Enamel I: structure and development

Question 1

Properties of Mature Enamel

Answer 1

• Acellular, non-vital,non-vascular
• ectodermal origin
• hardest (most mineralized) tissue in the body
• brittle
• somewhat dynamc tissue: de/re mineralized

Question 2

more Properties of Mature Enamel

Answer 2

• translucent, range of colors
• covers crown of tooth
• thicker at crown, around 2.5mm, relatively thin at cervical line
• composed primarily of hydroxyapatite crystals
• small but essential protein component: organization of crystals

Question 3

enamel composition

Answer 3

• organic: 1-2%distributed between HA crystals
• no collagen
• water 2-3%
• inorganic component: HA

Question 4

Major enamel proteins:

Answer 4

amelogenins
ameloblastins
enamelin
tuftelin
etc

Question 5

organization of enamel

Answer 5

enamel crystals

• closely packed, long, ribbon like
• many crystals packed together form both enamel rods and interrod enamel

Question 6

enamel crystals mineral componet

Answer 6

HA, carbonatoapatite

Question 7

carbon and magnesium incorporated more in the ____enamel, fluoride in the ____

Answer 7

inner, outer enamel

Question 8

the outer enamel could be said to be more___ in the face of an acid attack

Answer 8

resilent

Question 9

enamel crystals shape

Answer 9

hexagonal , 60-70 nm wide, 25-30 nm thick

Question 10

enamel crystals length

Answer 10

long, may run entire length of enamel, in the mm range

Question 11

Enamel Rods are

Answer 11

cylindrical accumulation of enamel crystals, line up along the long axis of the rod

Question 12

Enamel Rods runs

Answer 12

perpendicular to the DEJ

Question 13

Enamel Rods are organized

Answer 13

in rows which run in alternating directions. 1 ameloblast=1 rod

Question 14

rod sheath is a

Answer 14

relatively protein rich area of enamelthat surrounds the rods

Question 15

rod sheath runs

Answer 15

about 3/4 of the way around each rod, for the most part separating rod and interrod enamel

Question 16

in the gaps of the rod sheath, enamel crystals are

Answer 16

continouos with the interrod enamel, linkin the two together

Question 17

while crystal orientation is mainly parallel to the long axis of rods, except at the

Answer 17

gaps in the sheath area they bend outwards and become continuous with the interrod enamel

Question 18

rod sheath proteins

Answer 18

ameloblasts and amelogenins

Question 19

interrod enamel are the same basic composition as rods, simply different

Answer 19

enamel crystal orientation

Question 20

interrod enamel fills gaps between

Answer 20

rods

Question 21

formation of enamel-first

Answer 21

pre-dentin by odontoblast

Question 22

ameloblast activation and deposition of enamel: initial depostion only around

Answer 22

30% mineralized, much larger organic component

Question 23

as enamel matures, organic component

Answer 23

reduced, mineralization increases

Question 24

ameloblasts maturation three general phases:

Answer 24

1. pre secretory:mature from pre-ameloblasts to ameloblasts
2. secretory:deposition of enamel
3. maturation: reduction of organic matrix, increase mineralization via ion transport

Question 25

ameloblast deposit organic matrix via

Answer 25

secretory vesicles, which exit the cell apically

Question 26

depostition of enamel initially, the basal lamina

Answer 26

separating the pre dentin and ameloblast is penetrated by cell projections and broken down

Question 27

enamel is laid down directly in

Answer 27

apposition to predentin/mantle (first) dentin

Question 28

deposion of enamel big thing

Answer 28

tomes process

Question 29

ruffled cells

Answer 29

infiltration and incorporation of calcium ions into crystals occurs during "rufflung", lowered pH perhaps favors materialization. Secreation of proteolytic enzymes

Question 30

smooth cells

Answer 30

allow diffusion out of protein fragments out of enamel which leak in between cells and laterally defuse though cell layer