Histology- Dentine and Pulp

Question 1

What is composition of dentine?

Answer 1

65% mineral + 25% organic matter & water.

Made from a type 1 collagen protein matrix.

Question 2

What are the properties of dentine?

Answer 2

Yellow in colour

Harder than bone but more elastic

Question 3

Describe the basic structure of dentine

Answer 3

Primary curvature ‘S shaped’ of tubules
Secondary curvature superimposed on the primary curvature (wave like projections)
The dentinal tubules are filled with fluid + odontoblast process (extensions from odontoblast cells)
Branching of dentinal tubules occurs at the ADJ

Question 4

Describe dentinal tubules.

Answer 4

Tubules are wider at pulpal end & thinner at ADJ. They get thinner as they run through pulp due to odontoblast process laying down peritubular dentine.
Tubules are more closely packed at pulpal end
Primary curvature:
Upper tip- displaced coronally (towards crown)
Lower tip displaced (toward root)

Question 5

What are the different types of lines in dentine?

Answer 5

Incremental lines
-Von Ebner lines(4um spacing as produced by odontoblast)
-Anderson Lines(20um superimposed on daily incremental lines)
Optical line
-Hunter Schreger bands (congruence of secondary structure)
-Contour lines of Owen (congruence of primary structure)

Question 6

What are the types of dentine?

Answer 6

Mantle dentine
Circumpulpal dentine:
- Primary (formed first )
- Regular secondary dentine (forms over period of tooth growth)

Question 7

Whats the difference between peritubular & intertubular dentine?

Answer 7

Peritubular dentine is laid down by odontoblast process. Intertubular dentine is found between the dentinal tubules

Question 8

What is sclerotic dentine?

Answer 8

Translucent dentine (sclerotic dentine) arises due to intertubular dentine being laid down in large amounts within dentinal tubule. 
The dentinal tubule + intertubular dentine have same refractive index so area is shown as translucent.

Question 9

Why does sclerotic dentine arise?

Answer 9

Defensive response by odontoblasts (when caries is progressing slowly)
Laid down as tooth ages (indication of age of tooth)

Question 10

What is irregular secondary dentine? (tertiary dentine)

Answer 10

When caries is progressing too fast irregular secondary dentine is produced.
Subdivided into 2 types:
- Reactionary dentine – Produced by surviving odontoblasts (usually produce secondary dentine this now produce reactionary dentine.
- Reparative dentine odontoblasts die (due to caries progressing rapidly) and pulpal cells differentiate into cells that produce reparative dentine, odontoblast processes die and form dead tracts as the dentinal tubules that were empty fill with debris

Question 11

Describe the mineralisation of dentine?

Answer 11

Minerals are added to mineralisation front + minerals are added by fusion of calcospherites
When calcospherites don’t fuse properly interglobular dentine (known as granular layer of tomes’ in the root)

Question 12

Describe odontoblasts

Answer 12

Long cells with a basal nucleus that contains odontoblast process that inserts into predentine.

Question 13

What are calcospherites?

Answer 13

Calcospherites can become larger and denser with age, they fuse with mineralisation front
When calcospherites don’t fuse properly interglobular dentine forms (poorly mineralised) they are formed when calcospherites fuse before the mineralisation front reached it.

Question 14

Describe the structure of the pulp

Answer 14

Nerves arteries + venules enter through the apex of the root via the apical foramen nerves form a plexus beneath the odontoblasts the nerves can travel into dentinal tubules (up to a third of the way into dentine)

Question 15

Describe the mechanisms of dentine sensitivity

Answer 15

Direct innervation
- Nerves in tubules provide direct stimulation Odontoblast processes
- these act as receptors (synapsing occurs)
Hydrodynamics
- fluid flow occurs within the tubules (caused by stimuli)

Question 16

Whats the most likely mechaism?

Answer 16

Fluid flow/hydrodynamics is the most accepted theory narrower tubules at enamel surface
- Most sensitive part of dentine is outer part
- No evidence for synapsing at odontoblasts
- Sensitivity is reduced by occluding tubules
Anti sensitivity toothpaste works by occluding the tubules and reducing fluid flow

Question 17

Whats the difference between true and false denticles?

Answer 17

True denticle – formed like odontoblast cells + have tubules

False denticles – don’t have tubules