Dentine Flashcards
1
Q
What type of material is dentine and what is it made up of?
A
It is a composite material consisting of apatite crystal on an organic scaffold predominantly composed of collagen
2
Q
What is the bulk of the teeth made up of?
A
Dentine
3
Q
Describe dentine
A
It is a bone like material which has a protein matrix
4
Q
Is the dentine usually visible?
A
No it is only visible is severe occlusal attrition has occurred causing the enamel to wear away
5
Q
What colour is dentine?
A
A yellow colour
6
Q
What happens to the pulp as you get older?
A
It shrinks with age as more dentine is laid down on its inner surface
7
Q
What is the inorganic mineral component of dentine?
A
The inorganic mineral component is in the form of hydroxyapatite crystals
8
Q
What do some hydroxyapatite crystals contain?
A
Impurities in tiny amount such as carbonate
9
Q
What is the difference between hydroxyapatite found in enamel and dentine?
A
The hydroxyapatite found in dentine is a similar shape but much smaller than those in enamel
10
Q
What are the dimensions of dentine hydroxyapatite in comparison to enamel hydroxyapatite?
A
Dentine: 35nm x 10nm
Enamel: 68nm x 28nm
11
Q
How are the hydroxyapatite crystals in dentine arranged?
A
Arranged along and between collagen fibres
12
Q
What makes up the organic dentine extracellular matrix ?
A
Collagen Proteoglycans Glycoproteins Phosphoproteins Lipids Serum derived proteins Growth factors
13
Q
What makes up 90% of the organic matrix in dentine?
A
Collagen fibrils
14
Q
What type of collagen makes up the dentine organic extracellular matrix?
A
The principle collagen fibril is type 1 collagen
Traces of type III and V are also present
15
Q
What is the difference between pre dentine collagen and mature dentine collagen?
A
Collagen fibrils in mineralised dentine are of larger diameter and are more closely packed than in pre dentine
16
Q
What is the difference between collagen in the periodontal ligament and mature dentine collagen?
A
The fibrils in dentine are not assembled into bundles as they are in the periodontal ligament
17
Q
How are the collagen fibrils arranged in dentine?
A
Most of the collagen fibrils in dentine run parallel to the Enamel dentine junction
18
Q
What makes up 8% of the organic matrix in dentine?
A
Non collagenous proteins
19
Q
Give examples of non collagenous proteins?
A
Dentine phosphoproteins,
Proteoglycans
Glycoproteins
Growth factors
20
Q
Give examples of proteoglycans found in dentine
A
Chondroitin 4-sulphate- containing proteoglycans
21
Q
Give examples of glycoproteins found in dentine
A
Osteonectin
Dentine sialoproteins
Bone sialoproteins
Osteopontin
22
Q
Give examples of phosphoproteins
A
Dentine phosphoproteins
Dentine matrix protein 1
23
Q
Give examples of growth factors
A
TGF betas
Bone morphogenic proteins (BMPS)
Insulin like growth factors (IGFs)
24
Q
Which proteins are important during mineralisation?
A
Dentine phosphophoryn and dentine matrix protein 1 (DMP-1)
25
Which proteins have an important role in collagen fibril assembly and cell-mediated effects ?
Proteoglycans
26
What are some cell mediated effects?
Cell adhesion, migration, proliferation and differentiation.
27
When are growth factors released?
They can be released during the progress of dental caries and induce the production of reactionary or reparative dentine
28
What makes up 2% of the organic content of the dentine's extracellular matrix?
Lipids
29
Where are lipids detected ?
They are detected at the mineralising front and they are thought to play a role in mineralisation
30
What forms can lipids take?
They can take the form of phospholipids and cholesterol
31
What does dentine consists of?
Consists of a large numbers of small parallel dentinal tubules in a mineralised collagen matrix
32
Inorganic hydroxyapatite crystals makes up how much of the dentine (by weight)?
65-70% inorganic hydroxyapatite crystals
33
Organic matrix makes up how much of the dentine (by weight)?
20% organic matrix
34
Water makes up how much of the dentine (by weight)?
10% water
35
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
36
Describe the physical properties of enamel
Enamel is hard and inflexible
37
What gives dentine its compressive and flexural strength?
Its organic matrix and tubular architecture provide it with greater compressive and flexural strength than enamel
38
What makes dentine more resistant to propagation of cracks than enamel?
Its intimate association of small apatite crystal with strong protein fibres
39
How hard is dentine in comparison to enamel (in Knoop numbers)?
Dentine: 64
Enamel: 296
Enamel is harder
40
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)
41
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)
42
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)
43
Where are the dentinal tubules found?
They run from the pulpal surface to the enamel-dentine and cementum-dentine junctions
44
What are the tubules between the dentine called?
Intertubular dentine
45
What forms the walls of recently formed tubules?
Intertubular dentine
46
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.
47
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
48
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)
49
Where is the contour line of Owen usually seen?
It is evident at the junction of the primary and secondary dentine
50
What happens to the terminal part of the tubules in the roots?
They branch and then the branches loop
51
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
52
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
53
Where are dentinal tubules more spread out?
Dentinal tubules are more widely separated at their peripheries, near the EDJ,
54
Where are dentinal tubules less spread out?
Dentinal tubules are more tightly packed near the pulp
55
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
56
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
57
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
58
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
59
Where are the processes from antigen presenting cells found?
They are found in the peripheral pulp and can extend into the dentinal tubules
60
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
61
Where do the processes from antigen presenting cells reside from?
Peri-odontoblastic space, and possibly post-odontoblastic space
62
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
63
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
64
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.
65
When does dentine formation occur?
Immediately before enamel formation
66
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
67
Tubules that form an 'S' shaped pathway are called what?
Primary curvatures
68
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
69
What is a key difference between enamel and dentine formation?
Dentine formation continues after tooth eruption and throughout the life of the pulp
70
What is the mineralisation of the collagen matrix facilitated by?
Facilitated by the modification of the collagen matrix by various non collagenous proteins
71
When does mineralisation of the collagen matrix happen?
Gradually follows the secretion of the extracellular collagen matix
72
Where is the most recently formed layer of dentine found?
The most recently formed layer of
| dentine is always on the pulpal surface.
73
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.
74
Of what origin is dentine?
It is of ectomesenchymal origin
75
Where does dentine develop from?
Develops from the peripheral cells of the dental papilla of the tooth germ
76
What is the principle role of the odontoblasts process in pre dentine?
It is vital for the secretion of matrix components
77
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
78
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
79
What is collagen secreted by?
Collagen is primarily secreted by the cell body of the odontoblasts
80
What does the odontoblast process secrete?
1. Secretes the other non-collagenous proteins such that a complex of collagen and non-collagenous proteins is formed at the junction of the predentine and calcified dentine (the mineralisation front)
2. Non-collagenous protein dentine phosphoprotein is released from the odontoblast process consistent with its important role in mineralisation and allowing it to bypass some of the predentine.
81
What are odontoblasts a key component of?
Initiating and controlling mineralisation
82
What happens to the calcium transported by the odontoblasts?
Calcium transported by the odontoblasts becomes a crystalline mineral in the dentine by deposition onto a template formed by type I collagen fibrils.
83
What are dentine phosphoproteins thought to be involved in?
Dentine phosphoproteins are thought to be involved in hydroxyapatite nucleation and control of crystal growth.
84
What is the key difference between dentine mineralisation and normal bone mineralisation?
Dentine mineralises in mostly the same way as bone with mineral crystals being added along a mineralisation front.
However, unlike bone, it also mineralises by the combining of isolated
islands of mineral called calcospherites.
85
What are calcospherites?
Isolated
| islands of mineral
86
What 2 other processes have been implicated in addition to the DPP mediated nucleation on collagen fibrils in the initiation of mineralisation?
1. Very early in mantle dentine formation matrix vesicles in which mineral crystals develop may have a role in initiating mineralisation
2. Calcospherite formation and fusion may account for the irregular appearance of the mineralising front seen at some sites.
87
What is the difference between Peritubular and interlobular dentine ?
Peritubular dentine lacks a collagenous fibrous matrix
| Peritubular dentine is also about 5-12% more mineralised than intertubular dentine
88
What is Peritubular dentine made up of?
It consists of small crystals in an amorphous (non fibrillar) matrix consisting of glycoproteins, proteoglycans, lipids, osteonectin, osteocalcin
and bone sialoprotein
89
What is the main mineral component os peritubular dentine?
The mineral component of peritubular
dentine is mainly carbonated apatite but its
crystalline form is distinct from that of
intertubular dentine
90
Where is peritubular dentine found?
Mainly found in un-erupted teeth
| Predominantly distributed in apical dentine
91
What type of tissue is petirubular dentine: a response change tissue or an age change tissue?
An age change tissue
92
When are peritubular dentine formed?
Peritubular dentine is formed at
about the same time as
intertubular dentine
93
Describe some things that have happened once primary dentine formation is complete
All peripheral tubules have a lining of peritubular dentine that
extends from the enamel–dentine junction to within 50–100 μm of the predentine.
94
How much of the outer dentine does the peritubular dentine occupy?
In outer
dentine, peritubular dentine occupies two-thirds
of the cross-sectional area of the tissue
near to
the predentine it occupies only approximately 3%
95
Why and how does translucent dentine arise?
With physiological ageing (Especially in the tooth dentine) the dentinal tubules become completely occluded with peritubular dentine formation
The contents of the tubule acquire the same refractive index as the intertubular dentine
96
What happens to the amount of translucent dentine as you get older?
The amount of ttranslucent dentine increases linearly with age and is not affected by function or external irritation
97
If the contents of the tubule acquire the same refractive index as the intertubular dentine what will happen if the dentine is put into water
As water has a similar refractive index to dentine regions blocked by peritubular dentine will appear translucent (‘translucent dentine’), while regions with patent tubules will fill with water and appear opaque
98
As you get older what happens tot he dentine tubules?
Dentine tubules become infilled at the root apex adjacent to the cementum and extend cervically and towards the root canal with age.
99
What part of dentistry can translucent dentistry be helpful in and how?
Useful in forensic dentistry to determine the age of teeth.
100
What other dentine type has similar features o translucent dentine?
Scierotic dentine
101
What are 2 examples of responsive tissue found in dentine?
Scierotic dentine
| Dead tracts
102
What causes the formation of sclerotic dentine?
The filling of dentinal tubules due to an external stimuli such as under slowly advancing caries or beneath areas of severe attrition
103
What is a similarity between both sclerotic and translucent dentine?
Both appear transparent
104
What mineral are thought to make up sclerotic dentine?
The mineral is crystalline and possibly an apatite, although plate-like crystals of octocalcium phosphate have also been reported.
105
What are dead tracts in dentine?
If the primary odontoblasts are killed by an eternal stimulus, or they retract before particular dentine occludes the tubules then empty tubules will be left and these empty tubules are described as dead tracts
Dead tracts can be sealed at their pulpal end by tertiary dentine
106
Why are dead tracts called dead tracts?
Because under the microscope, transmitted light will be totally internally reflected and empty tubules will appear as dark 'dead tracts'.
107
Why is the pulp important to the dentine
It maintains the dentine structure
Takes part in the innervation of the tooth
Provides a defensive mechanism which is activated in response to caries, tooth wear and trauma via formation of tertiary dentine
108
Describe the pulp and its where its main blood vessels enter from
It is a richly vascularised and innervated tissue with the main arterioles, venules and nerves entering via the apical foramen and occupying the central core of the pulp
109
What is the major cell type that occupies pulpal tissue
Bulk of pulpal tissue is occupied by loose connective tissue, the major cell type being the fibroblasts
110
What is the plexus of small nerves beneath the cell rich zone called?
The Raschkow's plexus
111
What exits the Raschkows plexus?
Small, unmyleinated nerves exit this plexus and travel up to and terminate around the odontoblasts
112
What are the 4 main lines in the dentine
1. Von Ebner lines
2. Adresen lines
3. Contour lines of Owen
4. Schreger lines
113
How do incremental lines arise?
Incremental lines arise from the incremental deposition of dentine matrix and its subsequent mineralisation
114
What are the 2 types of incremental lines dentine has?
Dentine has regular. incremental:
| Short period or long period marking
115
What are the long period incremental lines called?
Adresen lines
116
How do Adresen lines form?
Long period lines are associated with changes in collagen fibrils orientation about every week
20 micrometres apart
117
What are found between each long period line?
6-10 pairs of short period lines giving this 6-10 day periodicity similar to the long- period striae of Retzius in enamel
118
What are short period incremental lines called?
Von Ebner lines
119
What do von ebner lines appear as?
Alternating dark and light bands
| Each pair reflects the diurnal rhythm of dentine formation
120
How far apart adjacent dark bands of von ebner in the cusp dentine?
In cuspal dentine deposition is most rapid
| The distance between adjacent dark bands is approximately 4 μm
121
How far apart adjacent dark bands of von ebner in the root dentine?
In the root dentine deposition is slower and the distance is 2 μm.
122
Where do the Contour lines of Owen and Schreger lines originate from?
These lines originate from coincidence of curvatures in the dentinal tubules (optical effects)
123
Which lines are associated with the primary curvatures of the dentinal tubules?
The Schreger lines
124
Where are schreger bands broader?
Where the peaks of the sigmoid primary curvatures coincide they form broad bands
125
Which lines are associated with the secondary curvatures of the dentinal tubules?
The contour lines of Owen
126
What happens when the secondary curvatures coincide?
They give rise to an optical effect, resulting in the appearance of contour lines of Owen
127
What is the neonatal line?
A line seen between dentine formed before and dentine formed after birth
128
What are the 8 regional variations in dentine
```
Mantle dentine
Interglobular dentine
Granular layer in dentine
Hyaline layer in dentine
Circumpulpal dentine
Predentine
Secondary dentine
Tertiary dentine
```
129
Where is the mantle dentine found?
Periphery of dentine in the crown
130
Where is the interglobular dentine found?
Typically outer part of crown
131
Where is the granular layer in dentine found?
In the outer part of root dentine beneath hyaline layer
132
Where is the hyaline layer in dental found?
Outermost part of the root dentine
133
Where is the circumpulpal dentine found?
Bulk of dentine in crown and root dentine
134
Where is the predentine found?
Unmineralised innermost dentine in crown and root
135
Where is the secondary dentine found?
Innermost layer of dentine between circumpulpal dentine and predentine
136
Where is the tertiary dentine found?
Inner layer of dentine formed mainly in crown response to serious insult
137
What are the 9 regions of varying dentine structure?
```
Enamel
Mantle dentine
Circumpulpal dentine
Hyaline layer
Granular layer
Cementum
Predentine
Secondary dentine
Tertiary dentine
```
138
Describe the mantle dentine
It is in the crown this first formed and most peripheral layer beneath the enamel
139
How do the mantle dentine and the circumpulpal dentine differ?
The special properties of mantle dentine help prevent small cracks developing in the enamel near the EDJ from spreading into the dentine
Mantle dentine is slightly less mineralised (approx 5%)
Mantle dentine displays branching of dentinal tubules
Mantle dentine has fibrils orientated perpendicular to the EDJ.
140
What does circumpulpal dentine form?
Forms the bulk of the dentine between the mantle layer and the zone of mineralisation
It is uniform in structure except at its edges where peripherally, interglobular dentine marks incomplete initial mineralisation and, centrally, the mineralising front represents ongoing mineralisation
141
Describe the interglobular dentine
It is the outer part of the circumpulpal dentine beneath the mantle layer
It is often incompletely mineralised and has a characteristic appearance when seen in ground sections
142
What is interglobular dentine
If a significant number of calcospherites do not fuse completely with the advancing mineralisation front then an area of interglobular dentine results
143
Where is pre dentine formed?
Predentine is the innermost un-mineralised layer, where new dentine is being deposited throughout life
144
What does predentine represent
Represents the initially laid down dentine matrix before its mineralisation
145
What colour does pre dentine have when stained with haematoxylin and eosin?
It has a distinct pale staining appearance due to a difference in the composition of its matrix from that of the matrix of the mineralised circumpulpal dentine
146
What outline might the mineralising front have?
May show a globular or linear outline reflecting the mineralisation process
147
Where is secondary dentine seen?
In older teeth at the inner, pulpal part of the circumpulpal dentine
148
Describe what happens to the odontoblast in the secondary dentine as you age
Increased crowding of odontoblasts as secondary dentine formation continues throughout life and the slower rate of deposition makes the tubular pattern of a little less regular than that of primary dentine.
149
Dentine is laid down as an ________- related change
Age related change
150
What rate is the secondary dentine laid down at?
Secondary dentine is laid down as an age-related change in the rate of dentine formation once a genetically predetermined thickness of primary circumpulpal dentine has been deposited and root development is complete
151
What does tertiary dentine describe?
It is a term used for all hard tissues deposited on the pulpal surface in response to an external stimuli
152
What are examples of some external stimuli that can lead to the deposition of hard tissue on the pulpal surface (tertiary dentine)
```
Caries
Attrition
Cavity preparation
Microleakage at restoration margins
Trauma
```
153
Where is tertiary dentine found?
It is found pulpal to the circumpulpal dentine (and in older teeth the secondary dentine)
It is restricted to the region beneath the irritation
154
What does the deposition of tertiary dentine provide?
The deposition of tertiary dentine provides a barrier to the progress of caries and toxins
155
What can stimuli of different types and severity being applied to teeth at different stages of development or ageing lead to?
Can result in a response tissue that may vary considerably in appearance and composition:
It may resemble secondary dentine in having a regular tubular structure
It may have few irregularly arranged tubules OR be atubular and resemble
bone.
156
Give examples of some signalling molecules
TGF beta
| Bone morphogenic proteins (BMPs)
157
What does the term reactionary dentine refer to?
Refers to the dentine forming in response to an insult in which the existing odontoblasts (some may have died or been damaged) recover and continue to form dentine
But the dentine may ave an irregular appearance with fewer tubules
158
What are signalling molecules release by and why?
May be released by acids produced during progress of dental caries
159
What do signalling molecules in dentine do?
They are produced by acids in dental caries and can diffuse through the dentine to stimulate activity in the original odontoblasts
Or they can induce the differentiation of new odontoblasts from stem cells
160
What does the term reparative dentine refer to?
Relates to the dentine forming after a stimulus in which the original odontoblasts in the associated region have been destroyed and new calcified tissue has been formed by newly differentiated ‘odontoblast-like’ cells
161
Compare reparative dentine and circumpulpal dentine
Reparative dentine is much more irregular than circumpulpal dentine
162
Where do the odontoblast like cells differentiate from in reparative dentine?
differentiate from a stem cell population in the absence of any epithelial contribution
163
Where are the appropriate bioactive molecules necessary for differentiation of odontoblast like cells found?
They may be locally synthesised and released during the inflammatory process accompanying the stimulus
164
What are the 2 theories explaining why there is a granular layer at the peripheral region in root dentine
1. The currently accepted view is that the dentinal tubules in this area branch more profusely and loop back on themselves creating air spaces in ground sections that result in internal reflection of transmitted light
2. An alternative explanation for the granular appearance is that it is due to the incomplete fusion of calcospherites (much smaller than those found in the crown)
165
What is the granular later at the peripheral region in root dentine called?
The granular layer of Tomes
166
What is reparative dentine produced by?
The dentin is produced by differentiation of sub-odontoblastic stem cells that replace the primary odontoblasts killed from the effects of caries. The tubules are less regular and not continuous with those of the overlying dentine.
167
What is the EDJ?
The enamel dentine junction
| It is the three-dimensional scalloped architecture, particularly evident beneath cusps and incisal edges
168
What is the role of the enamel dentine junction?§
It is crucial to limiting propagation of cracks through the tooth and providing resistance to shearing forces
169
What are the 5 types of dentine?
1. Mantle and circumpulpal
2. Primary, secondary and regular dentine
3. Peritubular and intertubular dentine
4. Irregular secondary dentine (tertiary or reparative)
5. Dead tracts
170
Describe what mantle and circumpulpal dentine looks like and where it is found
It is found directly beneath the enamel
| It looks different to dentine
171
When is primary dentine formed?
Dentine formed during tooth development
| It is the most rapidly formed dentine
172
When are secondary and regular dentine formed?
Formed more slowly over the life of the tooth and gradually fills the pulp
173
What is 'true' denticles'?
Dentine formed by odontoblast like cells and that have tubules
174
What is 'false' denticles?
Dentine formed by odontoblast like cells BUT DO NOT have tubules
175
What can the presence of denticles do?
May complicate endodontic procedures
176
What are the 6 layers of the dentine pulp interface?
1. Mineralised dentine
2. Pre-dentine
3. Odontoblasts
4. Cell free zone
5. Cell rich zone
6. Body of the pulp
177
What is interglobular dentine?
When 2 calcopherites are close enough to each other they can fuse together
This results in an area of trapped air that os cut off from its mineral supple so it doesn't mineralise at all
This area is described as being hypomineralised and becomes fossils with the mineralised dentine producing interglobular dentine
178
What are the 3 proposed mechanisms of dentine sensitivity?
1. Direct innervation
2. Odontoblasts act as a sensory ending
3. Hydrodynamics (fluid flow)
179
What is usually the response to any stimulus on dentine and why?
Pain as dentine is very sensitive
180
What is the hydrodynamic theory of dentine sensitivity?
An effective stimulus triggers a flow of fluid within the tubules
This movement is sufficient to depolarise nerve endings either within the inner parts of tubules or between odontoblasts at the pulp–predentine junction and from there to the subodontoblastic neural plexus.
The induced response is the same whether the flow is in or out.
181
What does the direct innervation theory of dentine sensitivity say?
That the pain in the dentine is due to pain 'receptors' being directly linked to nerves in the tubules
182
What does the odontoblasts acting as sensory endings theory of dentine sensitivity say?
That the odontoblasts act as a receptor of pain and that these are the target for the stimulus
But theres is no evidence for synapses between odontoblasts and adjacent nerve fibres
183
What is the most sensitive part of the dentine?
The outermost part underneath the enamel or cementum
184
How can sensitivity be reduced?
By occluding the tubules
185
Which of the 3 Proposed mechanisms of dentine sensitivity seems to be the most likely and why?
The hydrodynamic theory seems most likely as it is irrespective go the precise position or number of nerve endings
186
What are the weaknesses of the dontoblasts acting as sensory endings theory of dentine sensitivity ?
Theres is no evidence for synapses between odontoblasts and adjacent nerve fibres
187
What are the weaknesses of the innervation theory of dentine sensitivity?
Deciduous teeth are just as sensitive as adult teeth even though deciduous teeth possess much fewer intratubular axons
188
What can increase the potential of bacteria from dental caries and the toxins they produce passing through tubules to the pulp?
```
if the the dentine surface is exposed by:
Caries
Tooth surface loss
Trauma
Cavity preparation
Microleakage at restoration margins.
```
189
Where is extracellular dentinal fluid found?
In the peri-odontoblastic space, and possibly post-odontoblastic space
190
What is always found on the pulpal surface?
The most recently formed layer of dentine
191
What is the dentin matrix produced by the odontoblasts that makes up the inner layer of the dentin called?
Predentine which later matures to give dentine
192
What is the raschkow’s plexus?
It is the plexus of small nerves beneath the cell rich zone
193
Which 2 lines form as due to coincidence of curvatures in the dentinal tubules (optical effects).
Contour lines of owen and Schreger lines
194
The Schreger lines are associated with what?
The primary curvatures of the dentinal tubules
195
What happens when the primary curvatures coincide?
Where the peaks of the sigmoid primary curvatures coincide they form broad bands
