Amelogenesis and Enamel

Question 1

characteristics of amelogenesis and enamel (5)

Answer 1

 Acellular tissue
 No collagen in matrix
 Formation involves both secretory and resorptive activities of ectodermally derived cells
 Enamel is 5x harder than dentin
Enamel is the hardest tissue in the body

Question 2

Compared to other mineralized tissues, the
Ca hydroxyapatite crystals are extremely
—, highly oriented, and packed into
rod-like structures, i.e., the —

Answer 2

large

“enamel rod”

Question 3

Although 96% mineral, the basic rod structure of enamel exhibits some degree of

Answer 3

flexibility

Question 4

Composition of Enamel (3)

Answer 4

1% Water
3% Organic Components
96% Inorganic

Question 5

organic components include

Answer 5

• Tyrosine-Rich Amelogenin Protein (TRAP)
 Amelogenin constitutes 90% of the protein in enamel
 Enamelin (5% of the protein)
 Tuftelin (found in enamel tufts at DEJ)
 Sheathlin

Question 6

inorganic component include

Answer 6

Ca hydroxyapatite

Question 7

Amelogenin exhibits — properties

Answer 7

thixotropic

i.e., the ability to flow under pressure (thixotropy)

Question 8

As the enamel crystal size increases, the amelogenin flows

Answer 8

away from between the crystals and back towards the

ameloblasts where it is degraded by proteolytic enzymes

Question 9

Unlike other hard tissue proteins in which the organic matrix 
remains stable (e.g., bone, cementum, dentin), in the case of 
enamel the organic protein is --- and exhibits both (2) changes

Answer 9

labile

quantitative and qualitative

Question 10

Enamelin is an (3) protein

Answer 10

acidic, phosphorylated, and glycosolated

Question 11

The largest of the enamel matrix proteins

Answer 11

enamelin

Question 12

enamelin is preferentially restricted to the

Answer 12

enamel rod area

Question 13

enamelin’s phosphorylated nature and initial accumulation

near the growing ends of crystals suggest that enamelin plays a role in (2)

Answer 13

crystal growth and nucleation

Question 14

Tuftelin

Answer 14

appears restricted to the DEJ in enamel
tufts. It is thought to play a role in induction,
the initiation of mineralization, and possibly
functions as a junctional protein linking enamel
and dentin.

Question 15

Sheathlin

Answer 15

is initially found throughout the rod and
and interrod enamel. However, it is preferentially
located in the rod sheaths.

Question 16

Reciprocal Induction (6)

Answer 16

 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 17

The gradient of cellular
differentiation, matrix
secretion, and mineralization
during tooth development is (2)

Answer 17

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

Question 18

Stages of Ameloblast Function (5)

Answer 18

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

Question 19

— individual ameloblasts contribute to the composition of one enamel rod

Answer 19

Four

Question 20

Structural Features of Enamel (7)

Answer 20

 Striae of Retzius
 Perikymata
 Hunter-Schreger Bands
 Gnarled Enamel
 Enamel Lamellae
 Enamel Tufts
 Enamel Spindle

Question 21

Striae of Retzius

Answer 21

Incremental lines produced by 
periodic constriction of Tomes 
process associated with 
corresponding increase in the 
face forming the interrod enamel. 
Represents about 4-8 days of 
rhythmic enamel matrix 
apposition.

Question 22

Cross striations

Answer 22

on each rod
represent 24 hours of enamel
matrix production, about
4 m/day.

Question 23

Perikymata:

Answer 23

External (surface) manifestations of

the Striae of Retzius.

Question 24

Hunter-Schreger Bands:

Answer 24

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

Question 25

Gnarled Enamel –

Answer 25

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

Question 26

Enamel Lamellae:

Answer 26

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

Question 27

Enamel Crack:

Answer 27

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

Question 28

Enamel Tufts:

Answer 28

Hypomineralized areas of enamel at

the DEJ that are rich in enamelin and tuftelin.

Question 29

Enamel Spindles:

Answer 29

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

Question 30

Hypomineralization

Answer 30

of enamel is primarily related to a delay
in the removal of amelogenin during maturation. Birthing
difficulties and nutritional deficiencies also commonly disturb
development.

Question 31

Hypoplasia of enamel is generally induced by

Answer 31

infectious diseases
of childhood, e.g., measles, rheumatic fever, mumps, etc., which
leave a defect in those parts of the teeth actively developing at
the time of the infection.

Question 32

Mottled enamel

Answer 32

occurs as a result of a diet containing
relatively high levels of fluoride. Severe enamel fluorosis
may manifest as opaque areas, light-brown mottling, and
surface pitting.

Question 33

Amelogenesis Imperfecta:

Answer 33

Defective enamel matrix
deposition which, in turn, voids the possibility of
enamel mineralization. Although there are multiple
types of amelogenesis imperfecta, the more common
types are autosomal dominant inherited.

Question 34

Enamel Pearls & Cervical Enamel Projections (CEP):

Answer 34

Defects
that occur during apposition and maturation stages of tooth
development due to displacement of ameloblasts to root surface.
Enamel pearls most often involve maxillary molars and CEPs
most often involve the mandibular molars.

Question 35

Dens-In-Dente

Answer 35

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

Question 36

Dens-In-Dente prevalence rate

Answer 36

0.4-10% of all patients

Question 37

Dens-In-Dente most commonly involves the

Answer 37

maxillary incisor

Question 38

Enamel thickness ranges from – mm over the cusps

Answer 38

2 – 2.5

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

— is comprised of the remnants of the reduced enamel epithelium.

Answer 41

Enamel cuticle (a.k.a. primary enamel cuticle or Nasmyth’s 
membrane)

Question 42

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

Answer 42

Enamel pellicle (a.k.a. acquired pellicle or salivary pellicle)