Dentine

Question 1

dentine is not seen unless the enamel is worn away. what are the differences between dentine and enamel

Answer 1

dentine is yellow, enamel translucent
dentine = sensitive, enamel= not sensitive
dentine is formed throughout life, enamel isn’t
dentine has a collagen protein matrix, enamel does not

Question 2

what is dentine

Answer 2

a tissue made of small tubules arranged parallel within a collagen matrix

Question 3

what is the diameter of the dentine tubules

Answer 3

3 um

Question 4

what do the dentine tubules contain

Answer 4

odontoblasts- dentine forming cells

fluid

Question 5

what is the composition of dentine

Answer 5

65% inorganic HAP

35% organic and water

Question 6

how is HAP arranged in dentine

Answer 6

HAP is found on/in collagen fibrils of organic matrix

Question 7

how are the collagen fibrils arranged in dentine

Answer 7

they run in PARALLEL to the pulpal surface

Question 8

dentinal tubules run from the pulpal surface to the EDJ/CDJ. what course do they follow

Answer 8

a curved, sigmoid course = produces primary curvatures
and secondary curvatures
more branched at the EDJ, wider at the pulpal surface

Question 9

what is the difference between the primary and secondary curvatures

Answer 9

the secondary curvatures are smaller, more frequent, wave-like tubules

Question 10

what is peri-tubular dentine

Answer 10

over-time, the dentine that is deposited within the walls of the dentinal tubules= narrows lumen

Question 11

what two things are distinct about the matrix of peri-tubular

Answer 11

does not have collagen fibres- rather an unidentified protein
it is hyper-mineralised

Question 12

what are the incremental lines of dentine

Answer 12

1. Von Ebners- daily incremental line, diurnal rhythm, 4um spacing
2. Andresons line- superimposed on von ebner’s, 20um apart, more prominent, long-period lines
3. Contour lines of Owen- congruence of secondary curvatures, seen due to optical effects
4. Schreger line- congruence of primary curvatures, seen due to optical effects

Question 13

dentine may be classified by its region. what does this include

Answer 13

mantle dentine- region beneath enamel, first formed

circumpulpal dentine

primary dentine- dentine made during initial tooth development, fast forming

secondary dentine- dentine made over life, slow forming

peritubular dentine- dentine in the walls of dentinal tubules

inter-tubular dentine- dentine found in between the dentintal tubules

Question 14

what are the different types of dentine

Answer 14

sclerotic dentine
dead tract
irregular secondary dentine (reactionary/ reparative)

Question 15

how is sclerotic dentine formed

Answer 15

with matruation, the dentinal tubueles become filled with peritubular dentine
the intertubular dentine and dentinal tubules both have the same refractive index= region of translucency= sclerotic dentine

Question 16

why does sclerotic dentine form

Answer 16

normal ageing process

defensive response to stimuli (severe attrition, slow forming caries)

Question 17

why is irregular secondary dentine formed

Answer 17

when there is fast caries lesion progression, more dentine is laid down at the pulpal surface.

Question 18

secondary dentine can be divided into…

Answer 18

reactionary- dentine made by the existing odontoblasts which did recover from the insult. the dentine is ordered

reparative- dentine made by odnotoblast-like cells because odontoblasts did not recover from insult. the dentine laid down is IRregular and BONE-LIKE

Question 19

what are dead tracts

Answer 19

this defines the layer of dentinal tubules below a lesion that does not contain odontoblast processes, filled with air/debris= appear black

Question 20

what is different about the mineralisation of dentine that makes it similar to bone

Answer 20

occurs on a mineralisation front

involves calco-spherates fusing one by one with the mineralisation front

Question 21

what are calco-spherates

Answer 21

calcification spheres

Question 22

what is inter-globular dentine

Answer 22

hypo-mineralised area
caused by calco-spherates fusing with one another BEFORE fusing with the mineralisation front hence do not get mineralised properly

Question 23

which cells produce the dentine matrix

Answer 23

odontoblasts

Question 24

what is the mineralisation front

Answer 24

where the HAP is deposited.

Question 25

in which direction does the mineralisation front move across all the zones of dentine

Answer 25

mineralised dentine
un-mineralised pre-dentine 
the odontoblast layer
the cell free zone- fewer cell bodies
body of the pulp

Question 26

what is found in un-mineralised pre-dentine

Answer 26

calco-spherates
no mineral
lots of type 1 collagen fibres, and non-collagenous proteins

Question 27

describe how mineralisation occurs in dentine

Answer 27

1. odontoblasts produce dentine matrix where dentine is deposited. the front travels in this direction
2. at the pre-dentine, the calco-spherates each fuse with the front to become subsumed within the bulk of mineralised dentine