TEST 3: Enamel – amelogenesis, morphology, composition and physiology

Question 1

1. At what stage of the development of the tooth germ does the histogenesis of the enamel begin?
   a. Bud stage;
   b. Cap stage;
   c. Early bell stage;
   d. Late bell stage.

Answer 1

c

Question 2

2. Which of the following statements regarding the changes in the dental papilla are correct?

a. Preameloblasts are the inner layer of the enamel organ;
b. Preameloblasts are the outer layer of the enamel organ;
c. The odobtoblasts are situated in the periphery of the dental papilla;
d. The odontoblasts are situated in the central area of the dental papilla;
e. Between the preameloblast and odontoblasts is the basal lamina.

A – a, b, c, d. B – a, c, d C – c, d, e D – a, b, e. E – a, c, e

Answer 2

E

Question 3

3. Describe the formation of the enamel-dentin junction

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Answer 3

Answer – It is building on membrana limitans. The disintegration of the basement membrane allows the preameloblasts to come into contact with the newly formed predentin. This indicates the preameloblasts to differentiate into ameloblasts. Ameloblasts begin deposition of enamel matrix. Preodontoblasts and ameloblasts deposit an organic matrix that begins to mineralize. Then the odontoblasts begin production of very thin dentine, which is sufficient to stop nutrients from the dental papilla to the preameloblasts.

Question 4

4. The origin of the dentin-enamel junction is:
   a) Ectodermal;
   b) Mesodermal;
   c) Endodermal and mesodermal; d) Ectodermal and mesodermal;

Answer 4

D

Question 5

5. Which of the following statements regarding the changes in the enamel organ are correct?
   a. Folding the outer cuboidal epithelium;
   b. Intracellular organelles of the ameloblasts are changing its positions;
   c. Ameloblasts are in their protective phase;
   d. Maturation stage begins;
   e. Formation of Tomes’ process.

A – a, b, c B – b, c, e C – c, d, e D – a, b, e E – a, b, c, e

Answer 5

D

Question 6

6. Which are the phases of the amelogenesis?
   a. ……………………………………
   b. ……………………………………
   c. ……………………………………

Answer 6

Answer –

a. Enamel matrix formation;
b. Mineralization;
c. Maturation.

Question 7

7. The life cycle of ameloblast described in as many as six phases but generally is subdivided into three main functional stages which are:
   a) Presecretory stage;
   b) Secretory stage;
   c) Maturation stage;
   d) Postmaturative stage;
   e) Transitional stage

A - a, b, c B - a, b, d C - b, c, e. D - a, b, d

Answer 7

A

Question 8

8. Which of the following six stages about the life cycle of ameloblasts are in the correct order?
   a. Morphogenic stage, Oragnizing stage, Maturative stage, Protective stage, Formative stage, Desmolytic stage;
   b. Morphogenic stage, Maturative stage, Oragnizing stage, Protective stage, Desmolytic stage, Formative stage;
   c. Morphogenic stage, Oragnizing stage, Formative stage, Maturative stage, Desmolytic stage, Protective stage;
   d. Morphogenic stage, Formative stage, Oragnizing stage, Maturative stage, Desmolytic stage, Protective stage;
   e. Morphogenic stage, Oragnizing stage, Formative stage, Maturative stage, Protective stage, Desmolytic stage.

Answer 8

E

Question 9

9. What are the phases of ameloblast’s life?
   a. ……………………………………
   b. ……………………………………
   c. ……………………………………

Answer 9

a. Presecretory stage;
b. Secretory stage;
c. Maturation stage.

Question 10

10. What happens in the presecretory stage?
    a) The cells of the inner epithelium differentiate into odontoblasts;

b) The cells of the inner epithelium differentiate into ameloblasts;
c) The superficial cells of the dental papilla differentiate into odontoblasts;
d) The superficial cells of the dental papilla differentiate into ameloblasts;
e) Odontoblasts secrete an organic matrix and they mineralize it to form the first layer of dentin;
f) Odontoblasts secrete an organic matrix and they mineralize it to form the first layer of enamel;
g) The new source for nutrients for the ameloblasts is the dental papilla;
h) The new source for nutrients for the ameloblasts is the dental follicle;

A - a, c, e, h B - b, c, e, g C - b, c, e, h
D - a, d, f, g

Answer 10

C

Question 11

11. Which of the following statements regarding the secretory stage are correct?
    a. As the ameloblast differentiates, the matrix is synthesizing within the RER, which then migrates to Golgy’s apparatus, where is condensed the packaged in membrane-bound granules;
    b. The initial layer if enamel does not contain enamel rods;
    c. The secretion of the enamel matrix becomes at two sites;
    d. The enamel is forming in the space provided by the enamel organ;
    e. Ameloblasts secrete the enamel proteins enamelin and amelogenin, which later will help of the mineralization.

A – a, b, d, e B – d, c, d, e C – All of them D – a, b, d, e. E – a, b, c

Answer 11

C

Question 12

12. Describe the secretory phase of amelogenesis:
    a) Tome’s process (TP) develops at the distal end of ameloblast
    b) The secretion of enamel matrix stops
    c) One enamel rod involves 4 TPs (1 head and 3 tails)
    d) Secretions made at TP
    e) This stage ends when full thickness enamel is laid down and TP retracts and a thin layer of aprismatic enamel is laid
    f) Ameloblast shortens and the no is reduced to 50%
    g) Protein synthesising organelle are destroyed

A - a, c, d, e B - a, c, d, f C - b, e, f, g D - a, b, d, f

Answer 12

A

Question 13

13. What is typical for the maturation stage:
    a) The ameloblasts lose Tomes’ process;
    b) The ameloblasts become involved in the removal of water and inorganic material;
    c) The ameloblasts become involved in the removal of water and organic material;
    d) additional inorganic material is introducing;
    e) additional organic material is introducing;
    f) ameloblasts increase their volume and height;
    g) ameloblasts decrease their volume and height;
    h) the apical end of the ameloblast becomes ruffled along the enamel surface;

A - b, c, e, f, h B - a, c, d, g, h. C - c, d, g, h. D - a, b, d, g, h

Answer 13

B

Question 14

14. Which are the proteins of the enamel?

………………………………………………………………………………………….

Answer 14

amelogenins, ameloblastins, enamelin, tuftelin

Question 15

15. Describe the major extracellular events involved in enamel formation:
    a. ………………………………………………………………..
    b. ………………………………………………………………..
    c. ………………………………………………………………..
    d. ………………………………………………………………..
    e. ………………………………………………………………..

Answer 15

a. Delineation of space by the secretory ameloblasts and dentin-enamel junction;
b. Self-assembly of amelogenin proteins to form the supramolecular structural framework;
c. Trasportation of calcium and phosphate ions by the ameloblasts resulting in supersaturated solution;
d. Nucleation of apatite crystallites;
e. Elongated growth of the crystallites.

Question 16

16. Which of the following statements regarding the mineralization of the enamel matrix are correct?
    a. The initial deposition of mineral amounts is approximately 25% of the total enamel;
    b. 70% of enamel mineral is result if the crystal’s growth;
    c. Matrix formation and mineralization continue peripherally to the tips of the cusps, laterally on the sides of the crowns;
    d. Mineralization begins laterally to the cervix and continues to the top of the tooth;
    e. As the enamel matrix is completing and tuftelin is depositing, the matrix begins to mineralize.

A – a, b, c B – b, c, e. C – a, b. D – d, e E – b, c, d

Answer 16

A

Question 17

17. Which are the two stages of the maturation?
    a. ……………………………………..
    b. ……………………………………..

Answer 17

a. Ruffle-ended maturation stage;

b. Smooth-ended maturation stage.

Question 18

18. Which of the theories for the mineralization of the enamel does the following statement correspond for?

Amelogenins have the remarkable spontaneous self-assembly and hierarchical organization of amelogenin “ microribbons” and have ability to facilitate oriented growth of apatite crystals .

a. Booster mechanism;
b. Seeding mechanism;
c. Matrix vesicle concept; d. Nanosphere theory.

Answer 18

D

Question 19

19. Which of the following statements regarding enamel rod structures are correct?
    a. Each rod is formed by four ameloblasts;
    b. Enamel is composed of rods that extend from DEJ, to the enamel outer surface;
    c. The rods run almost perpendicular to the enamel surface at the cervical region;
    d. Near to the cusps the rods are perpendicular;
    e. The rod has a keyhole-shaped form.

A – All of them B – a, b, c, d. C – b, c, d
D – a, b, c, e E – c, d, e

Answer 19

D

Question 20

20. How many ameloblasts does it take to make a complete rod and sheath?

a) It takes two amelolasts;
b) It takes three ameloblasts; c) It takes four ameloblasts;
d) It takes five ameloblasts

Answer 20

C

Question 21

21. How many ameloblasts does it take to make the head and the tail? a) One for the head and three for the tail;

b) Two for the head and two for the tail;
c) Three for the head and one for the tail;
d) Two for the head and three for the tail;

Answer 21

A

Question 22

22. Complete the sentence

The areas between adjacent prisms are called …………………………….

Answer 22

interprismatic

Question 23

23. Which of the following statement regarding the Striae of Retzius is correct?
    a. They are optical phenomen;
    b. They are a weekly rhythm in enamel production resulting in a structural alteration of the rod;
    c. They are made of crystals, but arranged at a different angle from those in the prism;
    d. This is the border between the enamel and dentin;
    e. They are defect in the innermost layer of the enamel.

Answer 23

B

Question 24

24. What are the striae of Retzius?
    a) An accentuated incremental line that occurs at the time of birth due to stress of birth;
    b) Indicate a daily variation in the secretory activity of the ameloblasts;
    c) They are a weekly rhythm in enamel production resukting in structural alteration of the rod;
    d) An optical phenomen produced by changes in direction between adjacent groups of rods;
    e) A defect in the innermost layer of the enamel;

Answer 24

C

Question 25

25. What are the bands of Hunter and Schreger?
    a) An accentuated incremental line that occurs at the time of birth due to stress of birth;
    b) Indicate a daily variation in the secretory activity of the ameloblasts;
    c) They are a weekly rhythm in enamel production resulting in structural alteration of the rod;
    d) An optical phenomen produced by changes in direction between adjacent groups of rods;
    e) A defect in the innermost layer of the enamel;

Answer 25

D

Question 26

26. What are the enamel tufts?
    a) An accentuated incremental line that occurs at the time of birth due to stress of birth;
    b) Indicate a daily variation in the secretory activity of the ameloblasts;
    c) They are a weekly rhythm in enamel production resukting in structural alteration of the rod;
    d) An optical phenomen produced by changes in direction between adjacent groups of rods;
    e) A defect in the innermost layer of the enamel;

Answer 26

E

Question 27

27. Describe the Enamel Tufts

…………………………………………………………………………………………

Answer 27

They are defect in the innermost layer of the enamel. They extend at right angles to the enamel-dentin border and are slightly mineralized. They are many residues of enamel protein, mainly enamelin.

Question 28

28. Describe the Enamel spindles

…………………………………………………………………………………………

Answer 28

Enamel spindles represent the terminal end of the odontoblasts process. They extend from the DEJ and point to the surface of the enamel

Question 29

29. Write the chemical composition of enamel

…………………………………………………………………………………………

Answer 29

The mineral composition is from xydroxyapatite, fluorapatite, carbonateapatite. In the intercrystalline spaces, they are amorphous calcium carbonate, manganese, zinc, copper, magnesium, aluminum,

Question 30

30. Which is a larger crystal, fluorapatite or hydroxyapatite

Answer 30

Fluorapatite

Question 31

31. The major extracellular events involved in enamel formation are:
    a) delineation of space by the secretory ameloblasts and the dentino-enamel junction;
    b) self-assembly of amelogenin proteins to form the supramolecular structural framework;
    c) transportation of calcium and phosphate ions by the ameloblasts resulting in a supersaturated solution;
    d) elongated growth of the crystallites;

A - a, d. B - a, b, c, d C - c, d D - b, c, d

Answer 31

B

Question 32

32. Write the stages of ionic exchange in the enamel
    a. …………………………………………….
    b. …………………………………………….
    c. …………………………………………….
    d. …………………………………………….

Answer 32

a. The first stage of the ionic exchange is reversible – the ions diffuse into the superficial hydration layer;
b. The second stage is easily reversible – the ions enter into the subsurface layer of absorbed ions neutralize their charges;
c. The third stage is difficult to reverse – the ions are included in the surface of the crystal;
d. The fourth stage is irreversible – the ions replace defects inside of the crystal lattice.

Question 33

33. True or false?

Primary mineralization: deposited enamel matrix, needle shaped crystals appear after deposition of thickness, 50 nm of matrix initially thin widespread dispersed, rapidly increase in size and become hexagonal.

Answer 33

TRUE

Question 34

34. True or false?

Secondary mineralization: occurs the dental-enamel junction, rapid process, cannot be easily distinguish from initial phase, enamel is transformed from soft material into hard substance, large quantities inorganic material deposited in matrix.

Answer 34

IDK