Dentine Structure

Question 1

Dentine:

Dentine:
Forms the —- of the tooth
Gives the yellow colour to the tooth
—- and so supports the hard but brittle enamel to prevent fracture during —-, dentine has some elasticity and ‘give’
Functionally, should not be considered in isolation but as a dentine-pulpal complex - it is a vital tissue
Perforated by —- from the pulp to the EDJ and carrying fluid from the pulp (dentinal fluid). Tubular structure in dentine, path odontoblasts take as they —- from the enamel-dentine junction where the odontoblast process extends into. That is the path the odontoblast take to the living position.

Answer 1

bulk

Resilient

chewing

tubules

retract

Question 2

Give the composition of the enamel:

Answer 2

Inorganic: 70% weight / 50% volume
- Calcium hydroxyapatite
- Hexagonal prisms
- Found on and between collagen fibrils (where crystals are laid down)
Organic: 20% weight, 30% volume
- 90% collagen type I (trace of collagen 3 and 5)
- 8% non-collagenous proteins
- 2% lipids
Water: 10% weight, 20% volume

Question 3

What are the main parts of the organic matrix?

Answer 3

Collagen type 1
Phosphoproteins
Glycoproteins 
Proteoglycans 
Growth factors
Metalloproteinases
Serum-derived proteins

Question 4

What are problems for bonding composites to teeth?

Answer 4

• Composite fillings are hydrophobic. Fluid flow outwards due to plural pressure towards EDJ limits the bonding of these agents (dentine has a water content).
• Dentine has both mineral and organic elements so a bond has to be made with both of these
• Slightly flexible so the bond has to resist movement

Question 5

Give the names of the dentine types in order

Answer 5

Crown:
Mantle dentine
Circumpulpal dentine

Radicular:
Hyaline layer
Granular layer
Circumpulpal

Question 6

What does primary and secondary dentine consist of?

Answer 6

Primary = mantle and circumpulpal
- laid down as tooth develops and erupts until root apex closes
Secondary = circumpulpal
- firms after apex closure

Question 7

Give details on primary and secondary curvature

Answer 7

Primary: curved, sigmoid course from enamel-dentine junction towards the pulp

Secondary: change in direction every few um, form contour line of Owen when these coincide in adjacent tubules. Goes through quiescent and active periods which changes direction and diameter of the tubule

Question 8

Give 4 bullet points on dentine tubules

Answer 8

• Marked branching can be seen just below EDJ
• Less obvious below this layer
• Also visible in unmineralised predentine
• Branching (and loops) responsible for granular layer of Tomes in root dentine

Question 9

What is the contents of dentine tubules?

Answer 9

• Odontoblast process (microtubules and intermediate filaments run longitudinally, do not contain many organelles in mineralised tissue)
• Some peritubular space (but not at predentine or innermost mineralised dentine, space is filled with dentinal fluid which has a positive outwards pressure)
• Possibly smaller odontoblast processes
• Commonly beneath cusps (possibly process of antigen presenting cells, sensory terminal fibres have been identified but no obvious synapse demonstrated)

Question 10

What causes sensitivity in teeth?

Answer 10

Hydraulic action (movement of fluid in tubule causing a change in pressure which triggers pain fibres within the pulp).

Question 11

What is intratubular dentine?
- what is it formed of?
- what happens with age?
- compare to intertubualar dentine
ect

Answer 11

Reduces diameter of dentine tubules.

Increased with age and eventually occluded tubules.
(in root gives rise to translucent dentine).

Hypercalcified compared to intertubular dentine (15% more mineralised).

Non-collagenous matrix

• glycoproteins
• proteoglycans
• lipids
• osteonectin
• osteocalcin
• bone sialoprotein

Form almost at the same time as intertubular dentine

Question 12

Is intertubular or intratubular dentine more calcified?

Answer 12

Intra tubular

Question 13

Where does filling material penetrate into to help lock it in place?

Answer 13

Tubular space

Question 14

What happens to the tubules next to the pulp?

Answer 14

Size and density of tubules increase

Question 15

Explain how etching works on dentine

Answer 15

Strong acid, but not as strong as needed on enamel this is more mineralised.
Want to remove this mineral in dentine to expose the collagen.
Filling material can penetrate tubule but also the collagen fibrils. The fibrils are at a nanometer level and tubules at micron level. These different levels help lock and seal the material restoration onto the tooth.

Question 16

What do you need to do to collagen to help composite fit better?

Answer 16

Collagen fibrils act as a scaffold for mineral crystals e,g, hydorxapatite. If you want the filling material to be able to get in the collagen and lock, you have to remove the mineral crystals to create the nano spaces to allow the resin to penetrate.

Question 17

How far apart for von Ebner’s lines and what are they due to?

Answer 17

Between 2-4um and due to circadian variation in acid-base balance

Question 18

Why does a neonatal line form?

Answer 18

when a child is born as the physiological disruption has affect on cellular development

Question 19

How does initial matrix deposition become mantle dentine?

Answer 19

Composition is different from the rest of the dentine matrix (has contributions from dental pulp cells beneath developing odontoblasts).

Collagen fibres at right angles to internal enamel epithelium.

Numerous processes lead to branching dentine tubules in this area.

20 to 150um thick

Different mineralisation process - matrix vesicles compared to nucleation on collagen fibres

Question 20

Give some details on circumpulpal dentine

Answer 20

Collagen type 1 fibres laid down parallel to dentine-pulpal border
Slight changes in orientation every 6-10 days of approx 20nm
Coincident changes - possible cause of long-period lines (Andresen lines)
Rate of deposition = rate of mineralisation
Unmineralised dentine is called predentine

Question 21

Give details on predentine

Answer 21

Initial matrix prior to mineralisation
Pale staining appearance in demineralised section (H&E stain)
Mineralising front either globular or linear
Undergoes considerable modification towards mineralisation front
10 – 40 μm thick (thicker with faster deposition
Collagen fibrils thicken through predentine:
 Proximal 20 nm
 Central 40 nm
 Distal 70 – 80 nm
 NB 80 – 100 nm in dentine

Question 22

What are circular area of mineralisation called and where are they visualised?

Answer 22

Circular areas of mineralisation are called CALCOSPHERITES

Can be visualised in ground section under polarised light

Question 23

How do areas of uncalcified dentine form?

Where are they present?

Answer 23

Formed by failure of calcospherites to fuse.

Located beneath mantle dentine and granular layer in root.

Peritubular dentine also absent in these areas.

Question 24

Tubular structure of secondary dentine?

Rate of formation?

When does formation start?

Answer 24

Tubular pattern are a little less regular as

• odontoblasts become more crowded
• slower rate of deposition

Rate can be increased by denervation and altering blood flow to tooth.

Pulp chamber size decreased and this makes endodontics are difficult.

Formation starts at completion of root formation.
This dentine can only be laid down within the tubule or within the pulp as the root apex has closed. Tubules and pulp therefore get smaller with age (harder to find pulp chamber with age for root canal treatment).

Question 25

What are the two types of tertiary dentine?

Give some details

Answer 25

Reactionary and reparative

varied appearance, may have few or no tubules, cells can get trapped inside

Question 26

What can looking at the pulp chamber help?

Answer 26

Can watch how pulp forms change shape as tertiary dentine is laid down.
This helps us look for example at how a carious lesion is developing.
More tertiary dentine laid down - means stimulus is still active as there is an active process still occurring (pulp chamber has a different appearance).

Question 27

What is translucent dentine?

Answer 27

Dentine tubules filled in as a response to an external stimuli such as attrition.
Mineral differs from that of peritubular dentine.
May be salivary components and may be precipitated mineral from carious process.

Question 28

How does reactionary and reparative dentine work?

Answer 28

reactionary = odontoblasts survive by up-regulation leads to tertiary dentine

reparative = odontoblasts die, progenitor cell recruitment, induction of odontoblast differentiation, odontoblast up-regulation causing tertiary dentine formation

Question 29

What are dead tracts?

Answer 29

Empty tubules that are sealed at their pulpal end by tertiary dentine.
Tubules can be left empty by death of odontoblasts or withdrawal of odontoblasts process.
In ground section, air will not enter the sealed tubules so they appear dark.

Question 30

Give some root dentine details

Answer 30

Hyaline layer
	 Relatively structureless – no tubules
	 Non-collagenous fine, fibrillar matrix
	 Proteins are enamel-like
	 10 μm thick
	 Obscure origin
	 May serve to bond cementum to dentine

Granular layer of Tomes (at periphery of root, present in ground section, less mineralised compared to circumpulpal, due to branching and interglobular dentine, collagen fibres run parallel to root surface)