Amelogenesis/enamel

Question 1

enamel characteristics
cells
collagen
unique formation

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

enamel comapred to other minerlized tissues

Answer 2

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

Question 3

enamel rod flexible?

Answer 3

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

Question 4

enamel rod structure basics

acid preferenitally attacks?

Answer 4

core w crystals perpendicular to the long axis of the tooth
made of hydroxyapatite crystals
acid typically attacks the core

Question 5

enamel composition

Answer 5

1% Water
3% Organic Components
• 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
96% Inorganic
• Calcium hydroxyapatite

Question 6

amelogenin properties

dif between enamel organic matrix and other mineralized tissue organic matrix

Answer 6

 Amelogenin exhibits thixotropic properties, i.e., the ability to
flow under pressure (thixotropy).
 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
(serine proteases and enamelysin, a.k.a., MMP-20).
 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 labile and exhibits both
quantitative and qualitative changes.

Question 7

enamelin properties

Answer 7

 Enamelin is an acidic, phosphorylated, and
glycosolated protein.
 The largest of the enamel matrix proteins.
 Preferentially restricted to the enamel rod area.
 Its phosphorylated nature and initial accumulation
near the growing ends of crystals suggest that
enamelin plays a role in crystal growth and
nucleation.

Question 8

tuftelin

Answer 8

 Tuftelin 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 9

sheathlin

Answer 9

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

Question 10

reciporacal induction of amelogenesis

Answer 10

 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 11

label the following

Answer 11

Question 12

gradients of cellular dif, matrix secretion and mineralization

Answer 12

moves anterior to posterior and occlusal to apical

Question 13

stages of ameloblast function

Answer 13

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

Question 14

morhpogenic stage

Answer 14

cuboidal, inactive

Question 15

differentiation stage

Answer 15

cell increases size to columnar/tall, prolonged nuclei, increase in organelles, junctional complexes form between cells, induction of odontoblasts occurs

Question 16

secretory phase

Answer 16

tomes processes form the enamel rods

secretory granules help to mineralize the enamel matrix via alkaline phosphotase from the strantum intermedium

Question 17

maturation phase

Answer 17

decrease in cell height
ruffled border at the bottom to up SA for water and pro removal and replacement with hydroxyapatite to harden the enamel

Question 18

protective phase

Answer 18

reduced ameloblasts form the primary cuticle to protect enamel

Question 19

label the following

Answer 19

Question 20

Tome’s processes, angulation

Answer 20

forming face of enamel rods
angle of the process will determine the angle of the enamel rod
every 4-8 days will constrict and change the angle of the rod=forms striae of retzius

Question 21

1 enamel rod develops from?

Answer 21

3-5 ameloblasts

Question 22

keyhole structure of enamel rod

Answer 22

head and tail protions= looks like keyhole
head=enamel rod
tail=interrod substance

Question 23

structural features of enamel

Answer 23

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

Question 24

striae of retzius, cross striations of each rod represent?

Answer 24

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

Question 25

perikymata

Answer 25

External (surface) manifestations of
the Striae of Retzius
look like small ridges

Question 26

hunter schreger bands

Answer 26

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

Question 27

gnarled enamel

Answer 27

most commonly found in cusp tips
rods perpendicular to the DEJ/BM
portions where it isn’t perpendicular the rods will twist and link for fracture resistance
Enamel rods appear to be twisted in a complex arrangement.
Very resistant to fracture and abrasion.

Question 28

enamel lamellae, similar look to? can be involved with?

Answer 28

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

Question 29

enamel cracks

Answer 29

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

Question 30

enamel tufts

Answer 30

Hypomineralized areas of enamel at the DEJ
rich in enamelin and tuftelin.
the protiens will act as links to keep enamel attatched to underlying dentin
usually only extend the inner third of enamel matrix

Question 31

enamel spindles

Answer 31

Represent extensions of
odontoblastic processes and tubules across the basal
lamina (BM/DEJ) during initial stages of matrix formation.
processes now trapped in enamel

Question 32

enamel dysplasia types

Answer 32

hypoplasia, hypomineralized, mottled

Question 33

Enamel Dysplasia: Hypomineralization

common causes

Answer 33

related to a delay in the removal of amelogenin during maturation leads to more pro than mineralized content

Birthing difficulties and nutritional deficiencies also commonly disturbdevelopment.

Question 34

Enamel Dysplasia: Hypoplasia
induced by?
result?

Answer 34

Hypoplasia of enamel is generally induced by infectious diseases
of childhood, e.g., measles, rheumatic fever, mumps, etc., which
leave a defect of cells in those parts of the teeth actively developing at
the time of the infection.

Question 35

congenital syphallus effect on developing teeth

Answer 35

hutchinsons teeth or notch incisors

morph of teeth altered

Question 36

Enamel Dysplasia: Fluorosis

Answer 36

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.
affects the hydroxyapatite core of the enamel rods

Question 37

amelogenesis imperfecta

Answer 37

genetic disorder
Defective enamel matrix deposition
will voids the possibility of enamel mineralization
soft enamel-chips off and exposes the dentin, teeth must be crowned
multiple types of amelogenesis imperfecta: the more common
types are autosomal dominant inherited.

Question 38

Enamel Pearls & Cervical Enamel Projections (CEP), stage they occur in? PDL? most common teeth affected?

Answer 38

Defects that occur during apposition and maturation stages of tooth development
displacement of ameloblasts to root surface.
Enamel pearls most often involve maxillary molars and CEPs
most often involve the mandibular molars.
pearls can lead to perio defects: enamel too slick for the PDL to adhere

Question 39

dens in dente
most common tooth
prevalence
result?

Answer 39

A deep invagination of the crown or root that is lined with enamel.
most common at max CI
hard to clean and maintain so usually extracted
Prevalence rate of 0.4% to 10% of all patients.

Question 40

thickness enamel over cusps

Answer 40

2 – 2.5 mm over the cusps.

Question 41

neonatal line

Answer 41

represents an exaggerated hypomineralized

striae of Retzius that forms at birth.

Question 42

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

Answer 42

imbrication lines of

Pickerill.

Question 43

enamel cuticle made of?

Answer 43

remnants of the reduced

enamel epithelium.

Question 44

Enamel pellicle (a.k.a. acquired pellicle or salivary pellicle) 
is comprised of?

Answer 44

glycoprotein precipitates derived from saliva

and/or gingival crevicular fluids.