Dentin

Question 1

what is the composition of dentin by weight ?

Answer 1

70% inorganic material
30%(20% protein 10% water) organic material

Question 2

the protein content of dentin is made up of :

Answer 2

90% collagenous protein and 10% non-collagenous protein

Question 3

what are some physical properties of dentin ?

Answer 3

-pale yellow in color
-elastic quality that provides flexibility and prevents fracture of overlying brittle enamel
-harder than bone

Question 4

what is primary dentin ?

Answer 4

tooth dentin that is formed before root formation is complete

Question 5

primary dentin which outlines the pulp chamber is known as ___

Answer 5

circumpulpal dentin

Question 6

outermost part of circumpulpal dentin is known as ___

Answer 6

mantle dentin

Question 7

what is secondary dentine ?

Answer 7

dentine secreted after root formation has ended

Question 8

what are the differences between primary and secondary dentin ?

Answer 8

secondary dentinal tubules are less regular with different orientation

-there is a line of demarcation between primary and secondary dentin that is present due to the difference in orientation

Question 9

what is tertiary dentin ?

Answer 9

reactive or reparative dentin secreted as a reaction to stimuli such as caries or attrition

• tertiary dentin is secreted only by the cells directly affected

Question 10

how thick is mantle dentine ?

Answer 10

about 20 microns thick and it is LESS mineralized

Question 11

what is the organic matrix of mantle dentin formed of ?

Answer 11

thick collagen fibrils called von korffs fibers

these fibers are different becasue they are perpendicular to the DEJ while other collagen fibers are parallel

Question 12

describe the process of dentin mineralization by globular calcification :

Answer 12

odontoblasts secrete vesicles containing minerals .they are initially small spherical areas ,which become larger and fuse with one another to form calcification front

Question 13

explain dentin mineralization by liner calcification

Answer 13

minerals are deposited on organic matrix (collagen ) parallel to DEJ

Question 14

What happens if globules fail to join together during globular calcification?

Answer 14

hypo mineralized space called inter-globular spaces form between the globules

Question 15

what happens to the organic and inorganic material when preparing a ground section?

Answer 15

organic material is burnt while the inorganic material remains

Question 16

what course of the dentinal tubule in crown of tooth is___(primary curvature)

Answer 16

S-shaped (primary curvature )

Question 17

dentine tubules have branches which allow them to communicate with eachother

Question 18

what is the secondary curvature of dentinal tubules ?

Answer 18

wavy dentinal tubules formed by slight undulations by odontoblast during deposition of dentin

Question 19

what is the difference between intra-tubular dentine and inter-tubular dentin ?

Answer 19

intra tubular dentine is the dentine that lines the dentinal tubules and it is highly mineralized (is is also known as peri-tubular dentin )

inter-tubular dentine is the dentin found between the dnetinal tubules and it is less mineralized

Question 20

what is the granular layer of tomes ?

Answer 20

granular layer found in root dentin that can be observed when ground section is examined in transmitted light zone

-dot like hypo mineralized structures found near cementum

Question 21

incremental lines of dentin that signify cyclic activity are known as:

Answer 21

incremental lines of von ebner. they appear as fine striations in dentin

-they run at a right angle to dentinal tubules and correspond to incremental lines of enamel

Question 22

where is the cell body of the odontoblast located?

Answer 22

at the pulpal surface (pre-dentin)

Question 23

what are the contour lines of owen?

Answer 23

accentuated deficiencies in mineralization , highlighter incremental lines of von ebner

Question 24

what is the neonatal line ?

Answer 24

accentuated contour line separating prenatal and postnatal dentin

Question 25

what are the different types of tertiary dentine ?

Answer 25

the type of tertiary dentin secreted is dependent on the urgency of the stimuli it is facing
-if the stimuli is not very aggressive then the odontoblasts have time to form and secrete normal dentine with tubules.

-if the stimuli is a little bit on the aggressive side then the odontoblasts do not have the luxury of secreting normal dentine and they instead secrete atubular dentine as a rapid response to aggressive stimuli

-if the stimuli is extremely aggressive then the odontoblasts dont even have time to move backwards as they secrete the dentin . which results in then being trapped in their own secretion . this results in a bone like apperance and it is called osteodentin

Question 26

what is a dead tract ?

Answer 26

a dead tract is a dentinal tubule that is empty because the odontoblastic process has either died or been retracted by the odontoblast when dentin is damaged

Question 27

how does a dead tract appear in a ground section ?

Answer 27

dark areas

Question 28

what are blind tracts ?

Answer 28

dead tracts that have been filled in completely by minerals . the dentin found in blind tracts is called sclerotic dentin

Question 29

what is the dentine that fills up blind tracts called?

Answer 29

sclerotic dentin

Question 30

what is the advantage of blind tracts ?

Answer 30

The adaptive advantage of blind tracts is the sealing off of the dentinal tubules to prevent bacteria from entering the pulp cavity.

Question 31

what is the most accepted theory for dentin sensitivity ?

Answer 31

hydrodynamic theory: fluid in the dentinal tubule which surround tome’s fiber moves as a result of stimuli —> causes pressure on nerve fiber in pulp tissue which then transmits pain –> so the dentin is sensitive but the pain is actually felt in the pulp

Question 32

intra-tubular nerves are found accompanying ____ of the odontoblastic process

Answer 32

30-70%

Question 33

intratubular nerves extend ___

Answer 33

100-150 microns (not to the DEJ which is the most sensitive area)