Dentine - Ish'aaq

Question 1

Describe the regional variation in dentinal tubules

Answer 1

• Tubules are wider at the pulpal end as there’s more peritubular dentine on the wall at the crown end so smaller lumen
• Tubules are widely seperated at coronal ends and more tightly packed near the pulp

Question 2

Give 3 chemical properties of dentine

Answer 2

• Smaller and shorter hydroxyapatite crystals than enamel but more impurities than enamel so mineral is more soluble in acid
• Crystals are arranged along and inbetween collagen fibrils with the fibrils forming a meshwork
• Dentine is a composite material, consisting of apatite crystals on an organic scaffold composed of collagen

Question 3

Give 3 physical properties of dentine

Answer 3

• Tubules are present, which are channels running from the pulp to the ADJ
• Harder than bone + cementum, softer than enamel
• Dentine is permable

Question 4

How does the pulp help limit progress of chemicals and toxins, through the dentine, towards the pulp

Answer 4

Positive pressure from the pulp

Question 5

How is peritubular dentine different to intertubular dentine

Answer 5

• Peritubular dentine lacks collagen fibre matrix and consists of small crystals in a non-fibrillar matrix

Question 6

Hows the strong bonding between acellular extrinsic cementum and dentine produced

Answer 6

• Odontoblasts mineralise the first formed dentine layer and the first few micrometres of the fibrous fringe
• Cementoblasts then secrete non-collagenous proteins which also strengthen the mineralisation

Question 7

What are dentine tubules

Answer 7

Channels where the Tommes fibre can be found

Question 8

What is intertubular dentine

Answer 8

The bulk of dentine and less mineralised than peritubular dentine

Question 9

What is peritubular dentine

Answer 9

The ring directly around dentinal tubules and is where the odontoblasts deposit dentine

Question 10

What are growth factors used for in dentine

Answer 10

Released during progress of dental caries to induce production of reparative dentine

Question 11

What are lipids used for in dentine

Answer 11

• Mineralisation as found on mineralisation front between collagen fibrils
• Forms of phospholipids and cholesterol

Question 12

What are proteoglycans important for

Answer 12

Collagen fibril assembly and cell mediated effects (cell adhesion, proliferation, differentiation)

Question 13

When does interglobular dentine form

Answer 13

• When dentine mineralisation is incomplete
• Usually found in circumpulpal dentine

Question 14

When does peritubular dentine form

Answer 14

When the Tommes fibre reaches its pre-determined length and moves towards pulp with odontoblasts

Question 15

What happens to the dentine as the caries gets past the enamel and the ADJ

Answer 15

• Carious lesion in dentine follows the path of the dentine tubules
• Tubules make the dentine more permeable than enamel + allows for acid and plaque biofilm toxins to dissolve the hydroxyapatite and move towards the pulp
• As there’s more impurities in dentine hydroxyapatite than enamel, its easier to dissolve

Question 16

What are celospherites

Answer 16

Isolated islands of mineral deposited in the circumpulpal dentine

Question 17

Whats found inside the dentinal tubules

Answer 17

• Ameloblastic processes present at the pulpal end and occupies the full width of tubules in developing dentine, but not seen in outer dentine
• APCs from pulp and afferent sensory nerve axons
• Dentinal fluid

Question 18

What is primary curvature

Answer 18

• Overall shape of the dentinal tubules
• Sinusoidal shape

Question 19

What is primary dentine (circumpulpal dentine)

Answer 19

Bulk of dentine in the root + crown which is uniform in structure except at the peripheral where interglobular dentine can be found

Question 20

Whats reactionary tertiary dentine

Answer 20

Dentine which forms in response to damage, when the damaged odontoblasts recover and continue to form dentine despite it being a little irregular with fewer tubules

Question 21

What is reparative tertiary dentine

Answer 21

A stimulus completely destroys original odontoblasts, new calcified tissue is found by newly differentiated odontoblast like cells

Question 22

What is secondary curvature in dentine

Answer 22

Smaller changes in direction of the tubules, they’re like little kinks in the tubules

Question 23

What is secondary dentine

Answer 23

Dentin formed from original odontoblasts. Once predetermined thickness of primary dentin has been reached, odontoblasts change direction and lay secondary dentine throughout life

Question 24

Whats tertiary dentine and how is it formed

Answer 24

• Tertiary dentine is all hard tissue deposited on the pulpal surface in response to an external stimulus
• Rapid progression of caries may mean sclerotic dentine can not form on outer dentine, so inserted tertiary dentine at pulpal end

Question 25

What are the 3 theories for how pain is felt in the dentine

Answer 25

- Direct stimulation on nerves theory - Odontoblasts acting as receptors theory - Hydrodynamic theory - most likely mechanism

Question 26

What's the 'odontoblasts acting as receptors theory' and what are the objections

Answer 26

- Impulse travels down the odontoblastic process and into the odontoblast body and then transferred to nerve synapses and on to the plexus of raschkow - Odontoblastic processes don't always extend to outer dentine and odontoblasts haven't been shown to have synaptic junctions

Question 27

Whats the direct stimulation on nerves theory and what are the objections

Answer 27

- Nerve extends from the plexus of raschkow right to end of dentinal tubules it can be acted on directly from external stimuli - Objections are theres no nerve axons in outer parts of dentine which is the most sensitive region

Question 28

Whats the hydrodynamic theory and what are the evidences

Answer 28

- Effective stimulus applies to dentine triggers a flow of fluid within tubules which depolarise nerve endings and depolarisation is carried to plexus of raschkow - Evidences are that tubules are narrower at outer dentine so flow of fluid would be at a faster rate, leading to greater stimulus and increased sensitivity in that region

Question 29

Whats the granular layer

Answer 29

Found at the coronal end of dentinal tubules where Tommes fibre of odontoblast folds on itself

Question 30

What is the hyaline layer of hopwell smith

Answer 30

- The most peripheral layer of dentine that forms directly under the CEJ - The final layer of dentine to mineralise

Question 31

Whats the main non-collagenous protein in dentine

Answer 31

Dentin phosphoprotein and dentine matrix protein 1 are both important in mineralisation

Question 32

Whats the role of mantle dentine and what is it

Answer 32

- Help protect cracks, which have developed in the enamel from spreading into the dentine - First formed layer of dentine and closest layer to enamel - Slightly less mineralised than circumpulpal dentine displayed branching of tubules and its fibrils are perpendicular to the ADJ

Question 33

Whats translucent dentine and how does it differ from sclerotic

Answer 33

- Translucent dentine partially allows light through as its formed as peritubular dentine colludes dentinal tubules from root apex and extends cervically and occurs due to age - Differs from sclerotic dentine due to disease and trauma, not age - Sclerotic is transparent not translucent

Question 34

Dentinal tubules follow the 's' shape path of the odontoblasts. Where can you find branching of these tubules

Answer 34

Enamel-dentino junction

Question 35

Why is acid etching difficult on dentine

Answer 35

It remains damp due to a high organic and water content