Amelogenesis and Enamel

Question 1

physical characteristics of enamel

Answer 1

1) hardest substance in body
2) composition
- 96% mineral (calcium hydroxyapatite)
- 1% organic and 3% water

Question 2

Dentin composition

Answer 2

1) 70% mineral
2) 20% organic and 10% water

Question 3

enamel crystal formation

Answer 3

1) calcium hydroxyapatite
- calcium ions, phosphate groups, hydroxyl groups
2) changes can happen in the structure of the apatite crystal
- Ca2+ for other mono and divalent cations
- PO43- for CO32-
- OH- for F-, Cl-, or CO32-

Question 4

substitution of OH- for F-

Answer 4

increases acid resistance

Question 5

OH- for CO32-

Answer 5

increases acid solubility

Question 6

dental fluorosis

Answer 6

1) taking too much fluoride when the teeth are developing under the gingiva
- children 8 or younger are at risk

Question 7

enamel matrix structure

Answer 7

1) specialized proteins
2) amelogenins 90%
- hydrophobic and regulate crystal growth and location
3) non amelogenins (10%)
- function in nucleation of enamel crystals and crystal growth
—
only about 30% hydroxyapatite right now

Question 8

non amelogenins proteins

Answer 8

1) ameloblastins. enamelings, tuftlin, serum proteins, serine and metalloproteinases

Question 9

amelogenesis imperfecta

Answer 9

1) if defects in GENES for enamelin, amelogenin, and proteases
2) enamel will not develop properly, will not assemble
3) affect 1-14000 people in US

Question 10

organization of enamel crystals

Answer 10

1) long mineral crystals
2) calcium hydroxyapatite
3) organized in rod and interrod enamel
4) enamel rod sheath
- contains organic materials (white lines)

Question 11

rodless enamel

Answer 11

1) no rod or interrod enamel is seen at the beginning of enamel secretion and at the end

Question 12

acid etch

Answer 12

1) affects the direction of the rods and interrods
2) effective way to bond the sealants, restorative materials, and brackets
- micromechanical interlock

Question 13

amelogenesis

Answer 13

1) process of enamel formation
2) ameloblasts secrete matrix proteins
- create and maintain and extracellular environment for mineral deposition

Question 14

stages of amelogenesis

Answer 14

1) pre-secretory
2) secretory
3) maturation
—
all this occurs during the bell stage of odontogenesis

Question 15

pre-secretory stage

Answer 15

1) morphogenic phase (shape)
- IEE cells elongate (tall columnar)
- stimulate dental papilla cells to become odontoblasts
- make dentin, which triggers the differentiation phase below
2) differentiation phase
- IEE cells become ameloblasts

Question 16

layers of tip of enamel organ (bell stage)

Answer 16

1) stellate reticulum
2) stratum intermedium
3) ameloblast
- migrate towards the crown
4) dentin
5) odontoblasts
- migrate towards pulp
6) dental papilla

Question 17

secretory stage

Answer 17

1) enamel matrix secretion
- 30% mineralized
2) matrix composition
- amelogenin (90%) and non-amelogenins proteins (10%)
3) tome’s process formation
- responsible for rods and interrod formation
- apical specialization

Question 18

tomes process

Answer 18

1) distal portion
- rods
2) proximal portion
- interrod

Question 19

maturation stage

Answer 19

1) after the full thickness of immature enamel has formed
2) transitional phase
- ameloblast reduce in height and volume (no tome’s process)
3) 25-50% of the cells undergo apoptosis

Question 20

maturation proper

Answer 20

1) principal activity of ameloblasts is the bulk removal of water and organic material, and introduced more inorganic ions
2) release of proteinases (MMP-20 and KLK-4)

Question 21

smooth ended ameloblast

Answer 21

1) resorption of water and degraded matrix proteins
2) triggered by low pH

Question 22

ruffle ended ameloblasts

Answer 22

1) release MMP20 and KLK4
2) transport calcium and phosphate into maturing enamel

Question 23

reduced enamel epithelium

Answer 23

1) when enamel maturation is complete, the ameloblast layer and the adjacent layers (stratum intermedium, stellate reticulum, and other enamel epithelium will fuse to form the reduced enamel epithelium

Question 24

life cycle of ameloblasts in a human tooth

Answer 24

1) morphogenetic stage
2) histodifferentiation stage
3) initial secretory stage
- no Tome’s process
4) secretory stage
- Tome’s process
5) ruffle ended
6) smooth ended ameloblast
7) protective stage

Question 25

enamel hypoplasia

Answer 25

1) underdevelopment of the ameloblasts 2) environmental factors - deficiency of vitamin A, C, D - febrile diseases (measles and scarlet fever) - hypocalcemia - local infection or trauma and drugs

Question 26

lines of retzius and perikymata

Answer 26

1) due to repetitive change (every 7-9 days) in the formation of rod vs interrod substance - due to changes in the shape of tome's process 2) serious of dark lines extending from the DEJ toward tooth surface - the tiny groove on the surface is the perikymata

Question 27

cross striations

Answer 27

1) thought to represent the daily rhythm of enamel formation and mineralization 2) regular intervals of 4 microns 3) different direction than retzius - sort of perpendicular

Question 28

hunter Schreger banding

Answer 28

1) optical phenomenon 2) when light goes through dry section of tooth 3) differences in orientation of groups of enamel rod

Question 29

gnarled enamel

Answer 29

1) variability in the direction of individual enamel rods at the cusp tips and incisal edges

Question 30

enamel spindles

Answer 30

1) trapped odontoblasts in the enamel layer 2) migrated towards enamel accidentally

Question 31

enamel tufts

Answer 31

1) projects from DEJ outward 2) appear branched and contain greater concentrations of enamel proteins

Question 32

enamel lamellae

Answer 32

1) extend from the surface inward 2) filled with organic material