Enamel

Question 1

Underlying dentin support is critical for enamel functions because of what property of enamel?

Answer 1

Brittleness

Question 2

What are the 3 main components of enamel?

Answer 2

• Organic (1-2% enamel proteins, NOT collagen)
• Water (2-3%)
• Inorganic hydroxyapatite

Question 3

Enamel crystals pack closely together to form what two structures?

Answer 3

-Enamel rods and interrod enamel

Question 4

What are the three main variations of hydroxyapatite?

Answer 4

• Carbonatoapetite (more vulnerable to acid)
• Magnesium incorporated (more vulnerable to acid)
• Flourapetite (less vulnerable to acid)

Question 5

Where are carbonate and magnesium incorporated enamel more prevalent?

Answer 5

Inner enamel

Question 6

Each enamel crystal is roughly 60-70 nm wide, 25-30 nm thick, very long and what general shape?

Answer 6

Hexagonal

Question 7

In what orientation would you expect to find enamel rods in reference to the DEJ?

Answer 7

Perpendicular, or close to it, possibly curving and intertwining as they approach the surface

Question 8

The protein rich areas surrounding enamel rods are called?

Answer 8

Rod Sheath

*runs 3/4 of the way around the rod, connecting rod and interrod enamel crystals

Question 9

What are two examples of enamel rod sheath proteins?

Answer 9

1-Ameloblastins

2-Amelogenins

Question 10

Rather than the keyhole analogy, what is a more accurate way to describe the rod-interrod relationship?

Answer 10

Columns embedded in interrod enamel

Question 11

Ameloblasts contribute to what structures in the enamel?

Answer 11

An enamel rod and the surrounding interrod enamel

Question 12

As enamel matures organic component is ________ and mineralization ________

Answer 12

decreases, increases

Question 13

What are the 3 general phases of ameloblast maturation?

Answer 13

1-Pre-secretory
2-Secretory
3-Maturation (reduction of organic matrix, increase mineralization)

Question 14

The youngest ameloblasts are found where on the tooth?

Answer 14

Cervical portion

Question 15

What binds ameloblasts together to keep them moving in sync?

Answer 15

Junctional complexes (terminal bars)

Question 16

When is enamel in an amorphous state rather than in rods?

Answer 16

initial enamel (tomes process is not yet formed)
outermost enamel (tomes process have retracted)

Question 17

What are tomes processes responsible for?

Answer 17

forming the enamel rod structure

Question 18

Disruption of the proteins in the unique basal lamina at the external surface of enamel can result in what?

Answer 18

enamel Hypoplasia

Question 19

Infiltration and incorporation of calcium ions into crystals occurs during which mature ameloblast conformation?

Answer 19

Ruffled cell

*Also secretes proteolytic enzymes

Question 20

The diffusion out of protein fragments from the enamel, occurs during which mature ameloblast conformation?

Answer 20

Smooth cell

Question 21

The last secretory product of ameloblasts is called what?

Answer 21

Primary enamel cuticle

Question 22

The remains of the reduced enamel epithelium merged with oral epithelium is called what?

Answer 22

Secondary enamel cuticle

*is removed due to mechanical forces

Question 23

The inner _______ of enamel are somewhat interwoven while the outer _______ is much straighter

Answer 23

2/3, 1/3

Question 24

What are three examples of enamel deposition proteins?

Answer 24

1-Amelogenin
2-Ameloblastin
3-Enamelin

Question 25

Only expressed while enamel is being produced, which protein restricts lateral HA crystal growth and is the main protein family (80-90%) in developing enamel?

Answer 25

Amelogenin *no rods without it

Question 26

Expressed all the way through maturation, which protein adheres ameloblasts to developing enamel and make up about 10% of the organic material in enamel?

Answer 26

Ameloblastin *no enamel without it

Question 27

Only present on the leading edge of enamel deposition, which protein possibly promotes crystal elongation and is least abundant (5%)?

Answer 27

Enamelin *no enamel without it

Question 28

Found during enamel deposition, which protein is an MMP and chops up ameloblastin and enamelin, and is critical for removal of organic component of enamel?

Answer 28

Enamelysin

Question 29

Secreted during modulation events of enamel maturation, which protein degrades amelogenins?

Answer 29

Enamel matrix serine protease

Question 30

Instead of using collagen, the basal lamina on the enamel is made up of what?

Answer 30

Other proteins such as ODAM and Amelotin

Question 31

Etching tends to be more effective by dissolving how?

Answer 31

Inside out, along the core. Carbonated apatite in core are most vulnerable

Question 32

What are the 3 types of enamel etching?

Answer 32

Type I- Preferential removal of rods (most common) Type II-Interrod enamel removed Type III-Irregular and indiscriminate pattern (least common)

Question 33

What are three kinds of enamel wear?

Answer 33

1-Abrasion (ie. aggressive brushing) 2-Abfraction (notch like cervical lesion caused by cyclical loading) 3-Erosion (Break down of crystals, acid attack)

Question 34

How does enamel change with age?

Answer 34

``` 1-Color (stain, thin enamel) 2-Surface layer chemistry (fluoride) 3-Decrease water content 4-Increased brittleness 5-Decreased permeability ```

Question 35

What are the three categories of structural features of enamel?

Answer 35

1-Periodic features (Striae of Retzius, cross striations) 2-Optical features (Hunter-Schreger bands, gnarled enamel) 3-Histological features (tufts, lamellae, spindles)

Question 36

Longitudinal lines running from DEJ to enamel surface likely due to cohorts of ameloblasts activating at the same time are called what?

Answer 36

Striae of Retzius *Follow appositional growth pattern, may indicate weekly rhythm in enamel deposition

Question 37

What is an example of an accentuated striae indicative of physiological disturbance?

Answer 37

Neonatal line (birth line)

Question 38

Visible on the enamel surface, what optical feature are manifestations of Striae of Retzius?

Answer 38

Perikymata

Question 39

Running at a right angle to the rod direction, what feature is indicative of daily deposition of enamel?

Answer 39

Cross Striations *roughly 4 um/day which is how far apart these striations are

Question 40

An optical phenomenon caused by light scattering off alternating rods, appearing as alternating light/dark bands are called what?

Answer 40

Bands of Hunter-Schreger *Extend 2/3 distance from DEJ to surface. Outer 1/3 is straighter

Question 41

Mostly seen around the DEJ under cusps, what feature forms complex twisting rods?

Answer 41

Gnarled enamel

Question 42

Projecting about 1/3-1/2 into enamel, what feature contains more enamel proteins and thus are hypo calcified and look like cracks or grass?

Answer 42

Enamel tufts *Possibly due to initial crowding of ameloblasts, gives the enamel a bit of "give", helping to prevent fracture

Question 43

Appearing as cracks transversing the length of enamel, what feature is an area where enamel proteins were not completely removed?

Answer 43

Enamel Lamellae

Question 44

Resulting from odontoblastic processes that penetrate the enamel, what feature often appear at incisal and cuspal tips a very short distance into enamel?

Answer 44

Enamel Spindles *not really enamel

Question 45

What are 4 disturbances to enamel formation?

Answer 45

1-Genetic dysplasia 2-Disruptions in ameloblast function or life 3-Tetracycline (stains brown) 4-Fluoride (chalky white