Dentine - Ish'aaq Flashcards
Describe the regional variation in dentinal tubules
- 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
Give 3 chemical properties of dentine
- 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
Give 3 physical properties of dentine
- Tubules are present, which are channels running from the pulp to the ADJ
- Harder than bone + cementum, softer than enamel
- Dentine is permable
How does the pulp help limit progress of chemicals and toxins, through the dentine, towards the pulp
Positive pressure from the pulp
How is peritubular dentine different to intertubular dentine
- Peritubular dentine lacks collagen fibre matrix and consists of small crystals in a non-fibrillar matrix
Hows the strong bonding between acellular extrinsic cementum and dentine produced
- 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
What are dentine tubules
Channels where the Tommes fibre can be found
What is intertubular dentine
The bulk of dentine and less mineralised than peritubular dentine
What is peritubular dentine
The ring directly around dentinal tubules and is where the odontoblasts deposit dentine
What are growth factors used for in dentine
Released during progress of dental caries to induce production of reparative dentine
What are lipids used for in dentine
- Mineralisation as found on mineralisation front between collagen fibrils
- Forms of phospholipids and cholesterol
What are proteoglycans important for
Collagen fibril assembly and cell mediated effects (cell adhesion, proliferation, differentiation)
When does interglobular dentine form
- When dentine mineralisation is incomplete
- Usually found in circumpulpal dentine
When does peritubular dentine form
When the Tommes fibre reaches its pre-determined length and moves towards pulp with odontoblasts
What happens to the dentine as the caries gets past the enamel and the ADJ
- 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
What are celospherites
Isolated islands of mineral deposited in the circumpulpal dentine
Whats found inside the dentinal tubules
- 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
What is primary curvature
- Overall shape of the dentinal tubules
- Sinusoidal shape
What is primary dentine (circumpulpal dentine)
Bulk of dentine in the root + crown which is uniform in structure except at the peripheral where interglobular dentine can be found
Whats reactionary tertiary dentine
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
What is reparative tertiary dentine
A stimulus completely destroys original odontoblasts, new calcified tissue is found by newly differentiated odontoblast like cells
What is secondary curvature in dentine
Smaller changes in direction of the tubules, they’re like little kinks in the tubules
What is secondary dentine
Dentin formed from original odontoblasts. Once predetermined thickness of primary dentin has been reached, odontoblasts change direction and lay secondary dentine throughout life
Whats tertiary dentine and how is it formed
- 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
What are the 3 theories for how pain is felt in the dentine
- Direct stimulation on nerves theory
- Odontoblasts acting as receptors theory
- Hydrodynamic theory - most likely mechanism
What’s the ‘odontoblasts acting as receptors theory’ and what are the objections
- 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
Whats the direct stimulation on nerves theory and what are the objections
- 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
Whats the hydrodynamic theory and what are the evidences
- 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
Whats the granular layer
Found at the coronal end of dentinal tubules where Tommes fibre of odontoblast folds on itself
What is the hyaline layer of hopwell smith
- The most peripheral layer of dentine that forms directly under the CEJ
- The final layer of dentine to mineralise
Whats the main non-collagenous protein in dentine
Dentin phosphoprotein and dentine matrix protein 1 are both important in mineralisation
Whats the role of mantle dentine and what is it
- 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
Whats translucent dentine and how does it differ from sclerotic
- 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
Dentinal tubules follow the ‘s’ shape path of the odontoblasts. Where can you find branching of these tubules
Enamel-dentino junction
Why is acid etching difficult on dentine
It remains damp due to a high organic and water content
