L7

Question 1

Enamel is a unique tissue due to its

Answer 1

high mineral content.

Question 2

Proteins are necessary for enamel formation but are not part of the

Answer 2

final product.

Question 3

The enamel structural proteins are cleaved by a

Answer 3

proteinase soon after their secretion into the matrix.

Question 4

Enamel Formation Starts at the

Answer 4

Cusp Tip and Proceeds Cervically

Question 5

Enamel starts as a

Answer 5

soft protein-rich tissue and matures into a virtually protein-free hard tissue.

Question 6

MMP-20 cleaves

Answer 6

enamel matrix proteins during early enamel development.

Question 7

Hydroxyapatite crystallites first grow in

Answer 7

length and later grow in width and thickness.

Question 8

KLK4 cleaves enamel matrix proteins during

Answer 8

late enamel development so that the proteins can be removed from the matrix

Question 9

The Maturation Stage

Answer 9

Enamel Proteinase

Kallikrein-4

Question 10

The Secretory Stage

Answer 10

Structural Enamel Proteins
Amelogenin, Ameloblastin, Enamelin
Enamel Proteinase
Matrix Metalloproteinase-20

Question 11

Spans Secretory and Maturation Stages

Answer 11

Intracellular Protein

Family with sequence similarity 83 member H

Question 12

Syndromic Enamel Malformation

Answer 12

Secreted Protein

Family with sequence similarity 20 member A

Question 13

Amelogenesis imperfecta (AI):

Answer 13

Hypoplastic: thin
(Secretory stage defects)

Hypomaturation: soft
(Maturation stage defects)

Hypocalcified: soft & thin

Question 14

Maturation stage

Answer 14

acid formation occurs, rough ended. Smooth end is when acid is dispelled.

Question 15

Amelogenin (AMELX: 85-90%): 18-25 kDa.

Answer 15

May regulate crystallite spacing, Mutations cause AI. On X chromosome.

Question 16

Ameloblastin (AMBN:5-10%): 65-70 kDa glycosylated,

Answer 16

Accumulates in the sheath space. Human gene is on chromosome 4.

Question 17

Enamelin (ENAM: 3-5%): 180-190 kDa,

Answer 17

highly glycosylated, intact enamelin is restricted to the mineralization front, Human gene is on chromosome 4.

Question 18

Matrix Metalloproteinase (MMP20)

Answer 18

Enamelysin
Secretory stage
Processes enamel proteins

Question 19

Kallikrein-4 (KLK4)

Answer 19

Serine Proteinase
Transition/Maturation Stages
Degrades enamel matrix

Question 20

Enamel formation

Answer 20

different cohorts of cells occupy differnent locations in the cell.

Question 21

Human AmelogeninGenes are on the

Answer 21

X and Y Chromosomes

Question 22

AMELX Mutation (p.P52R) Causing

Answer 22

X-Linked AI

Question 23

In general, AMELX mutations are associated with a

Answer 23

In general, AMELX mutations are associated with a smooth hypoplastic phenotype, but can also be associated with a hypomineralization/hypomaturation AI phenotype with discolored enamel.

Potentially more diagnostic than the pattern of inheritance (which may not be obvious in small families with few affected members) is the distinctive vertical banding pattern on the enamel of affected heterozygous females. The vertical bands are deposited because alternating bands of ameloblasts secrete normal or defective amelogenin after randomly inactivating either the defective or normal X-chromosome.

Question 24

AMBN Exon 6 Deletion Causes

Answer 24

AI

Question 25

The Ambn Phenotype

Answer 25

Autosomal Recessive Hypoplastic AI | Poorly Formed Rods (prisms)

Question 26

Y chromosome amelogenin is

Answer 26

nonfunctional

Question 27

The enamelin mutations result in enamel that is

Answer 27

hypoplastic. However, those heterozygous for the p.422fsX488 mutation have a mild phenotype consisting of localized pitting defects and those with the p.N197fsX227 mutation have a moderate phenotype consisting of grooves or shallow pits formed in parallel horizontal lines. When both alleles are defective, there is virtually no enamel layer.

Question 28

Matrix Metalloproteinase-20 (MMP20) is expressed during

Answer 28

early enamel development and cleaves the secreted structural enamel matrix proteins including amelogenin, enamelin, and ameloblastin. Relative to the matrix proteins, MMP20 is present in trace amounts within the developing enamel matrix.

Question 29

Ameloblastin has a

Answer 29

honeycomb pattern. If you stain for C-terminal part of protein, you see that it is on top. MMP20 cleaves these proteins to perform different functions in enamel.

Question 30

Mmp20 Null Mouse Enamel has a

Answer 30

Weak Dentin-Enamel Junction

Question 31

The MMP20 Phenotype

Answer 31

Five mutations caused pigmented hypomaturation AI and AI. In all five cases, the teeth were approximately normal in size, but the enamel layer did not contrast well with dentin on radiographs and the enamel tended to chip away from the underlying dentin.   Two mutations resulted in hypoplastic-hypomaturation AI

Question 32

ameloblastin more important for

Answer 32

crystallite nucleation and growth, not just for ameloblasts.

Question 33

The genes encoding amelogenin, ameloblastin, enamelin, & Mmp20 degenerate in mammals that have lost the ability to

Answer 33

make teeth during evolution (baleen whales). There is no selective pressure to maintain these genes except in making dental enamel.

Question 34

Maturation Stage Enamel Proteins | that when Mutated can

Answer 34

Cause AI

Question 35

Kallikrein 4 (KLK4)

Answer 35

Serine protease | Mutations cause autosomal-recessive AI

Question 36

WD repeat protein 72 (WDR72)

Answer 36

Intracellular protein | Mutations caused autosomal-recessive AI

Question 37

Chromosome 4 open reading frame 26 (C4orf26)

Answer 37

Secreted, somehow helps enamel to mature

Question 38

Solute Carrier Family 24, Member 4 (SLC24A4)

Answer 38

Proton pump that may rid enamel of protons

Question 39

Kallikrein-4 (KLK4) is expressed during

Answer 39

mid-late stage enamel development when the enamel has reached its full thickness and when proteins are actively removed from the hardening matrix. KLK4 degrades proteins to facilitate their removal from the enamel matrix.

Question 40

Hunter-Schreger bands are the result of a

Answer 40

sectioning phenomenon through two enamel rod directions The rod locates laterally and occlusally from its point of origin. The purpose of the tortuous path of enamel rods is to dissipate the tremendous forces of mastication thus reducing the incidence of enamel fractures.

Question 41

Hunter-Schreger bands are the result of a

Answer 41

sectioning phenomenon through two enamel rod directions The rod locates laterally and occlusally from its point of origin. The purpose of the tortuous path of enamel rods is to dissipate the tremendous forces of mastication thus reducing the incidence of enamel fractures.

Question 42

Perikymata or Imbrication Lines

Answer 42

May be formed as crown becomes bigger and new cohorts of cells are added cervically to compensate for the increase in size.

Question 43

Family with Sequence Similarity 83 member H (FAM83H) appears to be

Answer 43

ubiquitously expressed. Interestingly, FAM83H mutations only affect dental enamel. Mutations cause autosomal dominant hypocalcified amelogenesis imperfecta (ADHCAI).

Question 44

Fam83H mutations cause

Answer 44

autosomal-dominant hypocalcified AI (ADHCAI) which is the most common form of AI in the United States. Individuals with FAM83H mutations may have enamel that is cheesy soft in consistency, light yellow in shade and nearly normal thickness. However, the abraded teeth lose contour and often become tapered toward the incisal edge or occlusal surface. The abraded surfaces are rough in texture, take up stain rapidly, and are sensitive to thermal changes.

Question 45

Family with sequence similarity 20, member A (FAM20A) is a

Answer 45

secreted glycoprotein.

Question 46

Enamel Renal Syndrome

Answer 46

Delayed eruption | Pulp calcifications

Question 47

FAM20A (17q24.2) Mutation

Answer 47

Enamel hypoplasia Gingival hypertrophy Kidney calicifications

Question 48

The FAM20A mutation causes

Answer 48

hypoplastic amelogenesis imperfecta with associated gingival hyperplasia and kidney calcifications. Also present are intrapupal calcifications, delayed tooth eruption, and a failure of tooth development.