Dentine Flashcards
What type of material is dentine and what is it made up of?
It is a composite material consisting of apatite crystal on an organic scaffold predominantly composed of collagen
What is the bulk of the teeth made up of?
Dentine
Describe dentine
It is a bone like material which has a protein matrix
Is the dentine usually visible?
No it is only visible is severe occlusal attrition has occurred causing the enamel to wear away
What colour is dentine?
A yellow colour
What happens to the pulp as you get older?
It shrinks with age as more dentine is laid down on its inner surface
What is the inorganic mineral component of dentine?
The inorganic mineral component is in the form of hydroxyapatite crystals
What do some hydroxyapatite crystals contain?
Impurities in tiny amount such as carbonate
What is the difference between hydroxyapatite found in enamel and dentine?
The hydroxyapatite found in dentine is a similar shape but much smaller than those in enamel
What are the dimensions of dentine hydroxyapatite in comparison to enamel hydroxyapatite?
Dentine: 35nm x 10nm
Enamel: 68nm x 28nm
How are the hydroxyapatite crystals in dentine arranged?
Arranged along and between collagen fibres
What makes up the organic dentine extracellular matrix ?
Collagen Proteoglycans Glycoproteins Phosphoproteins Lipids Serum derived proteins Growth factors
What makes up 90% of the organic matrix in dentine?
Collagen fibrils
What type of collagen makes up the dentine organic extracellular matrix?
The principle collagen fibril is type 1 collagen
Traces of type III and V are also present
What is the difference between pre dentine collagen and mature dentine collagen?
Collagen fibrils in mineralised dentine are of larger diameter and are more closely packed than in pre dentine
What is the difference between collagen in the periodontal ligament and mature dentine collagen?
The fibrils in dentine are not assembled into bundles as they are in the periodontal ligament
How are the collagen fibrils arranged in dentine?
Most of the collagen fibrils in dentine run parallel to the Enamel dentine junction
What makes up 8% of the organic matrix in dentine?
Non collagenous proteins
Give examples of non collagenous proteins?
Dentine phosphoproteins,
Proteoglycans
Glycoproteins
Growth factors
Give examples of proteoglycans found in dentine
Chondroitin 4-sulphate- containing proteoglycans
Give examples of glycoproteins found in dentine
Osteonectin
Dentine sialoproteins
Bone sialoproteins
Osteopontin
Give examples of phosphoproteins
Dentine phosphoproteins
Dentine matrix protein 1
Give examples of growth factors
TGF betas
Bone morphogenic proteins (BMPS)
Insulin like growth factors (IGFs)
Which proteins are important during mineralisation?
Dentine phosphophoryn and dentine matrix protein 1 (DMP-1)
Which proteins have an important role in collagen fibril assembly and cell-mediated effects ?
Proteoglycans
What are some cell mediated effects?
Cell adhesion, migration, proliferation and differentiation.
When are growth factors released?
They can be released during the progress of dental caries and induce the production of reactionary or reparative dentine
What makes up 2% of the organic content of the dentine’s extracellular matrix?
Lipids
Where are lipids detected ?
They are detected at the mineralising front and they are thought to play a role in mineralisation
What forms can lipids take?
They can take the form of phospholipids and cholesterol
What does dentine consists of?
Consists of a large numbers of small parallel dentinal tubules in a mineralised collagen matrix
Inorganic hydroxyapatite crystals makes up how much of the dentine (by weight)?
65-70% inorganic hydroxyapatite crystals
Organic matrix makes up how much of the dentine (by weight)?
20% organic matrix
Water makes up how much of the dentine (by weight)?
10% water
Describe the physical properties of dentine
Dentine is rigid but elastic tissue
Dentine is elastic, not brittle
Dentine has a higher fracture toughness in comparison to enamel
Describe the physical properties of enamel
Enamel is hard and inflexible
What gives dentine its compressive and flexural strength?
Its organic matrix and tubular architecture provide it with greater compressive and flexural strength than enamel
What makes dentine more resistant to propagation of cracks than enamel?
Its intimate association of small apatite crystal with strong protein fibres
How hard is dentine in comparison to enamel (in Knoop numbers)?
Dentine: 64
Enamel: 296
Enamel is harder
How stiff is dentine in comparison to enamel (in Young’s modules)?
Dentine: 12 GN/m^2
Enamel: 131 GN/m^2
Enamel is more stiff
(GN/m^2 = giganewtons (N x10^9)
How does the compressive strength of dentine compare to enamel?
Dentine: 262 MN/m^2
Enamel: 76 MN/m^2
Dentine has a higher compressive strength
(MN/m^2 = meganewtons N x10^6)
How does the tensile strength of dentine compare to enamel?
Dentine: 33 MN/m^2
Enamel: 46 MN/m^2
(MN/m^2 = meganewtons N x10^6)
Where are the dentinal tubules found?
They run from the pulpal surface to the enamel-dentine and cementum-dentine junctions
What are the tubules between the dentine called?
Intertubular dentine
What forms the walls of recently formed tubules?
Intertubular dentine
Where and when are peritubular dentine deposited?
As the dentine matures, peritubular dentine is
deposited on the walls of the dentinal tubules narrowing their lumens.
What are primary curvatures?
They are tubules that follow a curves, sigmoid course
The convexity of these curvatures nearest the pulp is towards the root
What are secondary curvatures?
Smaller changes in direction of the tubules
Where curvatures that are adjacent to each other coincide (Contour line of Owen may be seen)
Where is the contour line of Owen usually seen?
It is evident at the junction of the primary and secondary dentine
What happens to the terminal part of the tubules in the roots?
They branch and then the branches loop
What arises due to the looping of branches in the thermal part of the root?
This looping may be responsible for the appearance of the granular layer of Tomes
What is the range of the diameter to the dentinal tubules?
1 micrometer or less at the EDJ to 2.5 micrometres at the pulp
Where are dentinal tubules more spread out?
Dentinal tubules are more widely separated at their peripheries, near the EDJ,
Where are dentinal tubules less spread out?
Dentinal tubules are more tightly packed near the pulp
Why are dentinal tubules more spread out at the peripheries?
Because the odontoblasts migrate inwards and occupy a smaller surface as dentinogenesis progresses away from the EDJ
How many dentinal tubules are there in the outer and inner dentine?
20,000/mm2 in the outer dentine
50,000mm/2 in the inner dentine
What can happen if the dentine surface is exposed by caries, tooth surface loss, trauma, cavity preparation etc
The potential for bacteria of dental caries and the toxins they produce to pass through tubules to the pulp increases
Which processes do dentinal tubules contain?
They contain the process of the odontoblasts that are responsible for their formation
In some parts of the tissue they also contain afferent nerve terminals
Where are the processes from antigen presenting cells found?
They are found in the peripheral pulp and can extend into the dentinal tubules
What are the perio-odontoblastic space and post-odontoblastic space thought to be filled with?
They are thought to be filled with extracellular dentinal fluid
Where do the processes from antigen presenting cells reside from?
Peri-odontoblastic space, and possibly post-odontoblastic space
In the early stages what does the odontoblast process occupy?
Occupies the full width of the dentinal tubule in the predestine and innermost mineralised circumpulpal dentine
What happen to the number of odontoblast processes as we move to the outer dentine?
The number of tubules seen to be occupied by odontoblasts processes decreases
When do odontoblast processes occupy the full width of the dentinal tubules?
n the predentine and innermost mineralised circumpulpal dentine, when dentine is in the early stages of development.
When does dentine formation occur?
Immediately before enamel formation
What do the odontoblasts do during dentine formation?
Odontoblasts lay down extracellular collagen matrix as they begin to move away from the future enamel dentine junction
Tubules that form an ‘S’ shaped pathway are called what?
Primary curvatures
Where does dentine formation begin?
Dentine formation begins at areas adjacent to the cusp tip or incisal edge and gradually progresses to the apex of the root
What is a key difference between enamel and dentine formation?
Dentine formation continues after tooth eruption and throughout the life of the pulp
What is the mineralisation of the collagen matrix facilitated by?
Facilitated by the modification of the collagen matrix by various non collagenous proteins
When does mineralisation of the collagen matrix happen?
Gradually follows the secretion of the extracellular collagen matix
Where is the most recently formed layer of dentine found?
The most recently formed layer of
dentine is always on the pulpal surface.
What is the pre dentine?
The organic fibrillar matrix of the dentin before its calcification.
It is the dentin matrix produced by the odontoblasts that makes up the inner layer of the dentin and when matured becomes dentin.
Of what origin is dentine?
It is of ectomesenchymal origin
Where does dentine develop from?
Develops from the peripheral cells of the dental papilla of the tooth germ
What is the principle role of the odontoblasts process in pre dentine?
It is vital for the secretion of matrix components
What is the principle role of the odontoblasts process in mineralising dentine?
Its roes into participate in the modification of the matrix and its mineralisation
At what pace is the new organic material deposited?
The deposition of new organic matrix proceeds at a pace similar to that of mineralisation, such that there is always a layer of un-mineralised matrix (the predentine) on the plural surface of the tissue