Dentine histology

Question 1

Where does dentin originate from?

Answer 1

Ectomesenchyme. Dentin is the mineralised tissue that forms the bulk of the tooth.

Question 2

What is dentin formed from?

Answer 2

Odontoblasts formed in the ectomesenchyme.

Question 3

What other process uses the initiation of dentin formation for it to take place?

Answer 3

Enamel formation

Question 4

Which part of the tooth is dentin covered by enamel and which part by cementum?

Answer 4

Root = cementum

Crown = enamel

Question 5

What properties distinguish dentin from enamel?

Answer 5

Dentin is sensitive

Dentin is formed throughout life, increasing in thickness at the expense of the dental pulp.

Question 6

What are the physical properties of dentin?

Answer 6

Dentin and enamel have complementary physical properties.

Fresh dentin is pale yellow in colour and contributes to the appearance of the tooth through the translucent enamel.

Dentin is harder than bone + cementum and softer than enamel.

Dentin can handle compressive forces well due to its organic matrix and tubular architecture.

Dentin is permeable, depending on the size and patency of the tubules which declines with age.

Question 7

What is the chemical composition of dentin?

Answer 7

70% inorganic, 20% organic 10% water by MASS.

50% inorganic, 30% organic and 20% water by VOLUME

Inorganic part is calcium hydroxyappatite crystals. The crystallites are calcium poor and carbonate rich in comparison to pure hydroxyappatite.

Organic matrix is composed of collagen fibrils which are located around the crystallites as well as non-collagenous proteins.

Question 8

What happens to the size of collagen fibrils in dentin when it is mineralised?

Answer 8

They became larger in diameter and are more closely packed than in predentin.

Question 9

What are the non-collagenous proteins seen in dentin?

Answer 9

Dentine phosphoproteins, proteoglycans, Gla proteins, other acid proteins and growth factors

Question 10

What are dentin phosphoproteins (PP-H)?

Answer 10

The term relates to the highly phosphorylated protein species which are important for binding calcium which is implicated in the process of mineralization

Question 11

What do proteoglycans in dentin do?

Answer 11

Their major function is their role in collagen fibril assembly and their cell mediated effects such as cell adhesion, migration, proliferation and differentiation.

Question 12

What do phospholipids do in denitn?

Answer 12

May be involved in the formation and growth of hydroxyapatite crystals

Question 13

What direction do dentinal tubules move?

Answer 13

Dentin is permeated by tubules, the dentinal tubules, that run from the pulpal surface to the enamel-dentin and cementum-dentin junctions.

The dentin tubules follow a curved sigmoid course. They also taper from 2.5 to 1 µm or less peripherally

Dentinal tubules are approximately circular in transverse section although their appearance is obviously dependent on the plane in which the tissue is sections.

Question 14

How dense are dentin tubules in different dentinal sections?

Answer 14

It ranges from 20000/mm2 in outer dentin to 50000/mm2 in inner dentin and 40000/mm2 in middle dentin

Question 15

Where do dentinal tubules branch the most?

Answer 15

The most profuse branching is in the periphery near the enamel-dentin junction

Question 16

How is predentin different to normal dentin?

Answer 16

The walls of the dentinal tubules in recently formed intertubular dentin at the pulp surface are comprised of mineralised type 1 collagen.

During maturation another type of dentin is deposited on the walls of the dentinal tubule narrowing the size of the lumen (peritubular dentin or intratubular dentin.

Question 17

How is peritubular dentin different to intertubular dentin?

Answer 17

Peritubular dentin is about 15% more mineralised than intertubular dentin.

Peritubular dentin occupies 2/3rds of the CSA of the tissue; near predentin only 3%

Question 18

What are the dentinal tubules composed of?

Answer 18

They contain the processes of the odontoblasts that are responsible for their formation.

In some parts of the tissue they also contain different nerve terminals.

It is also possible that processes from antigen presenting cells in the peripheral pulp may extend for a short distance into the tubules.

Question 19

What happens in the dentinal tubules?

Answer 19

Initially the process of odontoblasts grows into the tubule and dentin is deposited while the peripheral termination remains at the outer end of the tubule.

The process reaches a predetermined length and moves pulpally as dentin is formed leaving behind an empty tubule in which peritubular dentin forms.

Th peripheral end of the process degrades sequentially and its remains form part of the matrix for the peritubular dentin.

Question 20

What is predentin?

Answer 20

Predentin is the innermost unmineralised layer, where new dentin is being deposited throughout life.

Question 21

What is the first dentin-formed layer in the crown?

Answer 21

The mantle dentin

Question 22

What are the dentin zones in the root?

Answer 22

2 morphologically recognisable outer zones:

Hyaline layer

Granular layer (of Tomes)

Question 23

What does predentin look like in demineralised sections?

Answer 23

The innermost layer of dentin, the predentin, has a distinct pale-staining appearance.

The predentin is the initially laid down dentin matrix before its mineralisation.

Question 24

What do odontoblast processes do in predentin?

Answer 24

They secrete matrix components.

Question 25

What type of dentin forms most of the tooth? and where is it located?

Answer 25

Primary dentin which outlines the pulp chamber and is referred to as circumpulpal dentin.

The outer layer is mantle dentin and it is mineralized differently

Question 26

How does mantle dentin differ from the circumpulpal dentin?

Answer 26

It is slightly less mineralized (~5%)

Collagen fibers are largely oriented perpendicular to the enamel dentin junction.

The dentinal tubules branch profusely here

It undergoes mineralisation in the presence of matrix vesicles.