Amelogenesis

Question 1

What are the characteristics of enamel?

Answer 1

acellular tissue
no collagen
hardest tissue in body

Question 2

Enamel is ___ times harder than dentin

Answer 2

5

Question 3

What does formation of enamel involve?

Answer 3

both secretory and resorptive activities of ectodermally derived cells

Question 4

What are the calcium hydroxyapatite crystals that are extremely large, highly oriented, and packed into rod-like structures called?

Answer 4

enamel rods

Question 5

What percent of the enamel rod is mineral?

Answer 5

96%

Question 6

What is the composition of enamel?

Answer 6

• 1% water
• 3% organic components (tyrosine-rich amelogenin protein or TRAP)
• 96% inorganic (calcium hydroxyapatite)

Question 7

What unique property does amelogenin exhibit?

Answer 7

thixotrophic properties (ability to flow under pressure)

Question 8

What happens to the amelogenin in the enamel crystals?

Answer 8

As the enamel crystal size increases, the amelogenin flows away from between the crystals and back towards the ameloblasts where it is degraded by proteolytic enzymes

Question 9

What are the characteristics of enamelin?

Answer 9

acidic
phosphorylated
glycosolated protein

Question 10

What is the largest enamel matrix protein?

Answer 10

enamelin

Question 11

What is the possible role of enamelin?

Answer 11

crystal growth and nucleation

Question 12

What is the possible role of tuftelin?

Answer 12

induction, the initiation of mineralization, and possibly functions as a junctional protein linking enamel and dentin

Question 13

Where is tuftelin restricted to?

Answer 13

DEJ in enamel tufts

Question 14

Where is sheathlin located?

Answer 14

throughout the rod and interrod enamel but it is preferentially located in the rod sheaths

Question 15

What is the process of reciprocal induction?

Answer 15

• Pre-tooth bud stage ectoderm specifies the “dental nature” of the underlying mesenchyme (neural crest cells)
• Neural crest cells (ectomesenchyme) then induces formation and proliferation of the dental lamina
• The dental lamina eventually separates into an outer and inner dental epithelium
• The inner enamel epithelium induces differentiation of odontoblasts
• Odontoblasts secrete the mantle layer of dentin
• Once the mantle layer of dentin is formed ameloblast differentiation is initiated and amelogenesis begins shortly thereafter

Question 16

The gradient of cellular differentiation, matrix secretion, and mineralizationduring tooth development is…

Answer 16

anterior to posterior (dentition) and coronal to apical (individual teeth)

Question 17

What are the stages of ameloblast function?

Answer 17

 Morphogenic Stage
 Differentiation Stage
 Secretory Stage
 Maturation Stage
 Protective Stage

Question 18

What are the striae of retzius?

Answer 18

Incremental lines produced by periodic constriction of Tomes process associated with corresponding increase in the face forming the interrod enamel

Question 19

How many individual ameloblasts contribute to the composition of one enamel rod?

Answer 19

four

Question 20

Each striae of retzius represents about _______ days of rhythmic enamel matrix apposition

Answer 20

4-8 days

Question 21

What are perikymata?

Answer 21

External (surface) manifestations of the Striae of Retzius

Question 22

What are hunter-schreger bands?

Answer 22

an optical phenomenon produced by changes in direction of the enamel rods. Seen only in ground histologic sections viewed by reflected light

Question 23

What is gnarled enamel?

Answer 23

most commonly found in cusp tips. Enamel rods appear to be twisted in a complex arrangement. Very resistant to fracture and abrasion

Question 24

What are enamel lammellae?

Answer 24

Hypomineralized areas of enamel extending from the DEJ for considerable distances into the enamel. May be involved with smooth surface caries.

Question 25

What is an enamel crack?

Answer 25

Cracks extend from the enamel surface to variable distances into the enamel. May extend into the dentin.

Question 26

What are enamel tufts?

Answer 26

Hypomineralized areas of enamel at the DEJ that are rich in enamelin and tuftelin.

Question 27

What are enamel spindles?

Answer 27

Represent extensions of odontoblastic processes and tubules across the basal lamina during initial stages of matrix formation

Question 28

What is hypomineralization of enamel primarily related to?

Answer 28

delay in the removal of amelogenin during materation

Question 29

What is hypoplasia of enamel usually induced by?

Answer 29

infectious diseases of childhood

Question 30

What causes mottled enamel?

Answer 30

diet containing high levels of fluoride

Question 31

What is amelogenesis imperfecta?

Answer 31

Defective enamel matrix deposition which, in turn, voids the possibility of enamel mineralization

Question 32

What are enamel pearls and cervical enamel projections?

Answer 32

Defects that occur during apposition and maturation stages of tooth development due to displacement of ameloblasts to root surface

Question 33

Where are enamel pearls most often?

Answer 33

maxillary molars

Question 34

Where are cervical enamel projections most often?

Answer 34

mandibular molars

Question 35

What is dens-in-dente?

Answer 35

A deep invagination of the crown or root that is lined with enamel

Question 36

What is the prevelence of dens-in-dente?

Answer 36

0.4-10% of all patients

Question 37

Where is dens-in-dente most common?

Answer 37

maxillary incisors

Question 38

Enamel thickness ranges from _____ mm over the cusps

Answer 38

2 – 2.5 mm

Question 39

The _______________ _________ represents an exaggerated hypomineralized striae of Retzius that forms at birth

Answer 39

neonatal line

Question 40

The perikymata (enamel surface manifestations of the striae of Retzius) are also known as the...

Answer 40

imbrication lines of Pickerill

Question 41

What is the enamel cuticle (nasmyth's membrane) composed of?

Answer 41

comprised of the remnants of the reduced enamel epithelium

Question 42

What is the enamel pellicle composed of?

Answer 42

comprised of glycoprotein precipitates derived from saliva and/or gingival crevicular fluids