Amelogenesis

Question 1

Characteristics of amelogenesis and enamel

Answer 1

Acellular tissue. 
No collagen in matrix.
Formation involves both secretory and resorptive activates of ectoderm ally derived cells.
Enamel is 5x harder than dentin.
Enamel is the hardest tissue in the body

Question 2

Enamel rod compared to other mineralized tissues

Answer 2

the Ca++ hydroxyapatite crystals are extremely large, highly oriented, and packed into rod-like structures.

Question 3

The basic rod structure of enamel exhibits some degree of

Answer 3

flexibility

Question 4

Composition of enamel

Answer 4

1% of water.
3% organic components
96% Inorganic - Ca++ hydroxyapatite

Question 5

Tyrosine-Rich Amelogenin Protein (TRAP)

Answer 5

Amelogenin constitutes 90% of the protein in enamel.
Enamelin (5% of the protein)
Tuftelin (found in enamel tufts at DEJ)
Sheathlin

Question 6

Amelogenin exhibits thixotropic properties

Answer 6

The ability to flow under pressure (thixotropy)

Question 7

As the enamel crystal size increases

Answer 7

The amelogenin flows away from btw the crystals and back towards the ameloblasts where it degraded by proteolytic enzymes (serine proteases and enamelysin)

Question 8

Unlike other hard tissue proteins in which the organic matrix remains stable (ex: bone, cementum, dentin)

Answer 8

in the case of enamel the organic protein is labile and exhibits both quantitative and qualitative changes

Question 9

Enamelin is

Answer 9

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

Question 10

Tuftelin appears

Answer 10

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 11

Shealthlin

Answer 11

is initially found throughout the rod sheath and interrod enamel. It is preferentially located in the rod sheaths

Question 12

Reciprocal induction

Answer 12

Pre-tooth bud stage ectoderm specifies the “dental nature” of the underlying mesenchyme (neural crest cells)

Question 13

Neural crest cells

Answer 13

Ectomesenchyme then induces formation and proliferation of the dental lamina

Question 14

Dental lamina eventually separates into

Answer 14

an outer and inner dental epithelium

Question 15

Reciprocal induction

Answer 15

the inner enamel epithelium induces differentiation of odontoblasts.

Question 16

Odontoblasts secrete

Answer 16

the mantle layer of dentin

Question 17

What happens after the mantle layer of dentin is formed

Answer 17

ameloblast differentiation is initiated and amelogenesis begins shortly

Question 18

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

Answer 18

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

Question 19

What are the stages of ameloblast function

Answer 19

Morphogenic stage
Differentiation stage (increase in size)
Secretory stage (alkaline phosphatase) 
Maturation stage (ruffles border - increases surface area so it can remove excess proteins and water to harden the enamel)
Protective stage

Question 20

Enamel rods and ____ _ _____ run in different directions bc the different angles of enamel production

Answer 20

Striae of retries (incremental lines of retzius)

Question 21

Four individual ameloblasts contribute to the composition of what

Answer 21

1 enamel rod - a key hole structure

Question 22

what are the structural features of enamel

Answer 22

Striae of retzius
Perikymata
Hunter-schreger bands
Gnarled enamel
Enamel lamellae
Enamel tufts
Enamel spindle

Question 23

Striae of Retzius

Answer 23

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

Question 24

Cross striations

Answer 24

on each rod represents 24 hours of enamel matrix productions about 4mM/day

Question 25

Perikymata

Answer 25

External (surface) manifestations of the striae of retzius. Ridge like

Question 26

Hunter-schreger bands

Answer 26

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

Question 27

Gnarled Enamel

Answer 27

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

Question 28

Enamel Lamellae

Answer 28

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

Question 29

Enamel crack

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 that are rich in enameling and tuftelin

Question 31

Enamel Spindles

Answer 31

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

Question 32

Hypomineralization

Answer 32

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

Question 33

Hypoplasia

Answer 33

A type of enamel dysplasia - induced by infectious diseases of childhood (like measles, rheumatic fever, mumps, etc) which leave a defect in those parts of the teeth actively developing at the time of the infection

Question 34

Mottled

Answer 34

Enamel dysplasia: Fluorosis.
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 35

Amelogenesis Imperfecta

Answer 35

Defective enamel matrix deposition which voids the possibility of enamel mineralization. Resulting in soft enamel, didn’t mineralize good. Multiple types of it and more common types are autosomal dominant inherited.

Question 36

Enamel pearls & cervical enamel projections (CEP)

Answer 36

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

Question 37

Dens-In-Dente

Answer 37

A deep invagination of the crown or root that is lined with enamel. Prevalence rate of 0.4% to 10% of all patients. Usually the maxillary incisor

Question 38

Enamel thickness ranges from _______ over the cusps

Answer 38

2 to 2.5mm

Question 39

neonatal line represents

Answer 39

an exaggerated hypomineralized striae of Retzius that forms at birth.

Question 40

Imbrication lines of pickerill

Answer 40

Perikymata (enamel surface manifestations of the striae of retzius)

Question 41

Enamel cuticle (aka primary enamel cuticle or Nasmyths membrane)

Answer 41

comprised of the remnants of the reduced enamel epithelium

Question 42

Enamel pellicle (aka acquired pellicle or salivary pellicle)

Answer 42

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