Lectures 3 & 4 Dentine & Pulp Flashcards
1
Q
List physical characteristics of dentine
A
- translucent, yellowish
- resilient
- slightly harder than bone and softer than enamel
2
Q
Describe what’s inside the structure of dentine and dentine tubules
A
- consists of mineral - calcium hydroxyapatite - plus organic material - matrix (ground substance), collagen, & odontoblast processes. (collagen is mostly parallel to pulp surface & crystals follow the direction of collagen).
3
Q
Describe dentine tubules
A
Elongated canals within the dentine following a sigmoid course from DEJ to pulp throughout much of the dentine but are fairly straight in the incisive tips & in the root.
4
Q
What do each tubule contain?
A
A single odontoblast process, which does not quite fill the tubule diameter - still uncertain whether they extend the full length of the tubule. Also contains small amounts of collagen, glycosaminoglycans and sometimes a nerve.
5
Q
Dentine tubules are tapered (_______) & are narrower at DEJ
A
2.5 um to 1um
6
Q
Dentine and dentine tubules have numerous fine vertical branches especially in middle and outer zones (these may interconnect).
A
False, fine lateral branches
7
Q
Dentine tubules do not branch at the DEJ
A
False, they branch dichotomously (into two equal sized branches) at DEJ.
8
Q
Odontoblasts are restricted to?
A
to the outer surface of the pulp & only cytoplasmic processes (odontoblast processes) are within the dentine in dentine tubules.
9
Q
How are odontoblasts different to bone?
A
This is different to bone that has bone forming cells both on its surface & within the matrix of bone (in cavities called lacunae).
10
Q
Bone cells within the bone matrix have single processes rather than just one process, which is the case with odontoblasts.
A
False, they have multiple processes in bone.
11
Q
Dentine forms the bulk of the tooth & is composed of?
A
70% inorganic (hydroxyapatite), 20% organic material (collagen, protein, glycoprotein) & is 10% water.
12
Q
Describe odontoblasts `
A
- Dentine forming cells
- Forms a single layer lining the periphery of the pulp
- Taller in the crown than in the root
- Each has a single odontoblast process which enters an adjacent dentinal tubule.
- If damaged can be replaced with new odontoblasts
13
Q
Describe odontoblast processes
A
- Occupy dentine tubules although it is still not known whether they extend the full length of the tubule
- Relative few organelles
- An organic matrix is formed first by the odontoblasts which then mineralizes extracellularly.
- Dentine is formed throughout life provided there are viable odontoblasts present in the outer pulp. These form organic matrix so there is always unmineralized or partly mineralized predentine adjacent to the odontoblasts.
14
Q
Dentinal matrix consists of?
A
Of about 90% collagen (Type 1) & 10% ground substance. The collagen is in the form of fibrils (i.e. not organized into bundles which are called collagen fibres)
15
Q
How are dentinal matrix fibrils oriented?
A
Oriented parallel to the surface of the pulp.
16
Q
What are the two mechanisms of mineralization?
A
Matrix vesicles & collagen associated mineralization.
17
Q
What are matrix vesicles
A
- Membrane bound structures associated with extracellular mineralization in all immature mineralized tissues (except enamel).
- They bud off from the matrix forming cell (osteoblast, odontoblast, cementoblast) into the extracellular matrix.
18
Q
During bone formation, matrix vesicles are associated with what during bone formation ?
A
Endochondral & intramembranous ossification
19
Q
Matrix vesicles contain?
A
Phospholipids and enzymes which bind calcium leading to the initial formation of hyrdoxyapatite
20
Q
Matrix vesicles are only found in immature bone and they play an ongoing role in remodelling.
A
False, it’s uncertain whether either is true.
21
Q
There is an alternative mechanism of mineralization that also occurs along collagen fibres as a result of non collagen molecules associated with the fibre. Some of these have the ability to bind calcium.
A
True
22
Q
Collagen , like all other hard tissues mineralization of enamel does involve matrix vesicles or collagen.
A
False, it is unlike the other hard tissues mineralization.
23
Q
Where are incremental lines best seen?
A
Best seen in longitudinal ground sections
24
Q
What are the incremental lines the result of?
A
the result of rhythmic or incremental laying down of mineral over a single day or longer times
25
Describe diurnal lines
About 4 um apart, represents one days growth (not readily seen without special staining) (To get an idea of how large 4um is at the magnification you are using, compare with the dentinal tubules which are 2.5 um wide).
26
How far apart are 5 day incremental lines
20 um
27
Describe lines of owen
Long term, irregular, resulting from events causing profound disturbances in mineralization
28
What is mantle dentine?
The dentine which is formed first adjacent to the DEJ or CEJ. Slightly less mineralized than primary dentine
29
What is primary dentine?
Dentine which makes up the bulk of the tooth & forms during development of the tooth.
30
What does primary dentine consist of?
Peritubular & intertubular dentine. May be globular
31
When does globular or interglobular dentine occur?
Mineralization may start along a linear front, or may start as globules (separate blobs of mineral) in the organic matrix which generally fuse together. If complete fusion does not occur then areas of hypomineralization between the globules result, then this globular dentine occurs. Globular dentine is variable and not always present.
32
How are globular dentine recognized?
They're recognised as dark areas or in demineralised sections as paler areas within the pink dentine.
33
What is peritubular (intratubular) dentine
More highly mineralized dentine WITHIN the rim of each dentinal tubule which is a result of deposition of mineral after the tubule has formed. Can approach 1 um thick and may ultimately block at least some tubules completely.
34
Appearance of peritubular dentine?
Lighter than the surrounding dentine in ground sections (more mineral) but is not retained in demineralised sections as it is so highly mineralized that it is lost during demineralization
35
What is the granular layer of tomes?
- Feature of root dentine only
- Tiny black granules or "speckles" located just below the hyaline layer and cementodentine junction (CDJ)
- Granules are actually tiny spaces representing looped terminal portions of dentinal tubules (fill with air during grinding)
36
What is secondary dentine?
Dentine formed throughout life. Secondary dentine is laid down at a slower rate after root formation and eruption.
37
Where is secondary dentine deposited?
Deposited around the entire periphery of the pulp chamber but more in roof and floor of pulp chamber and less in the root.
38
Secondary dentine pulp size is reduced as a result of secondary dentine formation.
True
39
What happens when pulp size is reduced as a result of secondary dentine formation?
This leads to crowding and loss of some odontoblasts and thus the dentinal tubules undergo rearrangement. This can include bending at the junction of primary and secondary dentine.
40
Reduction in size of pulp chamber means?
Means a lower risk of exposing a pulp horn during dental restoration in older individuals.
41
Tertiary dentine is laid down __________________.
Laid down locally in response to noxious stimuli, e.g. caries, attrition.
42
How are tubules in tertiary dentine formed?
Formed by replacement odontoblasts do not have continuity with the tubules of the adjacent primary or secondary dentine.
43
Another name for tertiary dentine
Reparative dentine
44
Where are tertiary dentine found?
Found in the region under the noxious stimuli not all around the pulp chamber.
45
Rate of tertiary dentine deposition relates to?
Relates roughly to severity of injury.
46
Tertiary dentine may have an irregular pattern of tubules or even cellular inclusions.
True
47
The types of collagen in reparative dentine are same as primary and secondary dentine.
False, it is different.
48
odontoblasts adjacent to the noxious stimuli may die resulting in?
Loss of the odontoblast processes.
49
Subsequent grinding forces ______?
Forces air into empty tubules.
50
Dark regions of empty air filled tubules are called ________.
Dead tracts
51
When does sclerotic dentine form?
Occurs when most or all of the tubules in a region of the dentine become occluded with mineral (see peritubular dentine). May occur in reparative dentine under dead tracts, presumably as a defensive reaction.
52
Dentine is stable generally once formed
True
53
When does dentine undergo normal breakdown?
when roots of deciduous teeth are broken down prior to the shedding of the tooth.
54
Dentine in permanent teeth may undergo resorption as a result of?
Pulp inflammation
55
Dentine breakdown in permanent teeth and deciduous teeth are mediated by?
Multinucleate cells called odontoclasts.
56
Odontoclasts are derived from?
Blood monocytes as are other phagocytic cells.
57
In case of hard tissues, odontoclasts usually fuse to form?
Multinucleate structure prior to function.
58
The term odontoclast is usually used for?
For all cells capable of resorbing dental tissues under any circumstances - including the phagocytic cells involved in break down of roots of deciduous teeth (and also some of the enamel as well).
59
Cementoclasts are used for?
this term used for monocyte derived phagocytic cells which are occasionally seen resorbing areas of cementum.
60
odontoclasts/cementoclasts are similar to cells in bone remodelling - osteoclasts - with certain unique functional and regulatory aspects.
True
61
List three theories of dentine sensitivity
- Intratubular nerves
- Fluid movement in the tubules stimulating nerves in outer pulp
- Odontoblast processes are pain receptors
62
Denticles (pulp stones) are?
These are focal areas of dentine found in pulp of some teeth of some individuals.
63
Denticles may have?
Dentine tubules (true denticles) and sometimes surrounding odontoblasts or may just be masses of calcified tissue (false denticles).
64
Where are denticles located?
May be within the pulp (free denticles), attached to the inner surface of the dentine (attached denticles) or actually embedded within it (embedded denticles).
65
Dentine is laid down throughout life so this gradual deposition can result in a free denticle becoming first attached then embedded.
True
66
Describe intratubular nerves
- are present but there is no evidence that they are in the outer, most sensitive dentine
- a plexus of Raschkow & intratubular nerves arising from this plexus are not established in newly erupted teeth yet these are sensitive.
67
What is the plexus of Raschkow?
Consists of sensory nerve plexus in periphery of pulp.
68
Describe fluid movement in dentine
- There is fluid leakage from dentine tubules during cavity preparation. This means fluid flow and concurrent pressure change.
- Pressure is sensed by plexus of Raschkow endings as pain.
69
Embryological origin of odontoblast processes?
Peripheral nerves (neural crest)
70
Odontoblast processes are pain receptors
True
71
Describe odontoblast processes
- Relies on at least some odontoblast processes extending the thickness of the dentine (controversial)
- Poor evidence of connections between odontoblasts and nerves, e.g. synapses, gap junctions
- Local anaesthetic applied to dentine does not eliminate pain.
72
Describe age changes relating to dentine
- Decreased size of pulp chamber resulting from ongoing deposition of dentine.
- Narrowing of root canal with possible decrease in vascular supply
- Decrease in diameter of dentinal tubules as a result of ongoing deposition of peritubular dentine. Ultimately, this can result in occlusion of tubules with loss of odontoblast process and increased brittleness of dentine.
- Increased incidence of dead tracts.
73
Define 'pulp'
Pulp is connective tissue within pulp chamber whose primary function is to support dentine.
74
Pulp communicates with the apical periodontal ligament and surrounding tissues via its narrow apical extension, the ________.
Root canal & apical foramina.
75
________ vary in size, shape, location depending on the individual tooth. They may be single or sometimes bifurcated or multiple.
Apical foramina
76
Apical foramina may also move due to remodelling resulting from pressures, either occlusal or orthodontic
True
77
the apex can deviate to the side opposite tooth movement.
True
78
_________ (lateral canals) are fairly common (found in about 33% of teeth, though numbers vary with individual teeth).
Accessory apical foramina
79
Accessory apical foramina contain?
Small blood vessels and sometimes nerves and may be single or branched.
80
Pulp is large at the time of tooth eruption but decreases with size with age especially occlusaocervically (ie. becomes shorter vertically)
True
81
List the 4 distinct zones of pulp
1. odontoblast layer
2 cell free zone/cell free zone of weil
3. cell rich zone
4. pulp core
82
Describe the cell free zone/cell free zone of weil
Zone deficient in cell nuclei, this is most obvious in the coronal part of fully formed pulp.
This also contains cell processes and nerve fibres and nerve endings from the plexus of Raschow.
83
Describe the cell rich zone
A cell rich zone of Hohl with numerous nuclei packed more closely than in the pulp core.
Contains undifferentiated cells and fibroblasts.
84
What does pulp core consist of?
Major nerves and vessels, fibroblasts, and other connective tissue cells, collagen and reticular fibres.
85
List the cells of the pulp
- odontoblasts
- undifferentiated cells
- fibroblasts
- macrophages
- odontoclasts
86
Odontoblasts do not divide
True
87
Describe undifferentiated cells in the pulp
When there is injury, new odontoblast-like cells develop from a reserve population or precursor cells, which are the undifferentiated cells in the pulp
88
Describe fibroblasts in pulp
They are the main cell type of pulp. They form, maintain and breakdown of all types of collagen.
89
Describe macrophages in pulp
A phagocytic cell different to odontoclasts but which are mononuclear. SPARSE except in inflammation.
90
Describe odontoclasts in pulp
- Dentine resorbing cells (similar to osteoclasts - bone resorbing cells)
- large & multinucleate, may be seen in an indentation (HOWSHIP's LACUNA) if actively eroding dentine
- most commonly seen in the resorbing dentine in roots of deciduous teeth prior to shedding.
- Also in chronic inflammation in permanent teeth
91
Describe composition of pulp fibres
- About 60% Type 1 collagen & 40% Type 3.
92
type 3 collagen fibres are sometimes called?
Reticular fibres
93
Reticular fibres have an affinity for?
Silver stains,
94
Describe the arteries in the pulp
- 1-2 arterioles enter through apical and accessory foramina - there is a sympathetic NERVe plexus on walls of pulp vessels down to at least arteriole size
95
Capillaries may extend between odontoblasts to the level of the predentine.
True
96
Where do arteries run in the pulp?
- run in central region of pulp and give off lateral branches which terminate as capilalries in the subodontoblastic zone (of Weil) in PULP.
97
Pulp has arteriovenous anastomoses to regulate blood flow according to metabolic needs.
True
98
Innervation to blood vessels in pulp?
Sympathetic only from the nerve plexus on vessel walls.
99
Veins supply to pulp?
venules (the smallest veins) coalesce to form 1-2 small veins which leave via the apical and accessory foramina.
100
Where do lymph vessels arise?
In coronal pulp
101
Describe lymph vessels in pulp
- Form 1-2 larger vessels which leave via the apical foramen
| - Thin walled, difficult to distinguish from venules
102
Describe innervation of pulp and dentine
- sensory and autonomic - mostly if not exclusively sympathetic (vasoconstrictor).
- parasympathetic innervation of pulp (vasodilator) is controversial,
- Nerves enter pulp in close association with blood vessels and generally follow the course of arterioles so that their position may be deduced although they are not seen in the light microscope unless special staining is carried out (silver staining).
- each fibre terminates in about 8 branches which form a plexus called the Plexus of Raschow or subodontoblastic plexus (or parietal plexus) in the cell free zone.
- pain is the predominant sensation but there is evidence that pulp nerves can distinguish mechanical, thermal and tactile stimulation as well.
103
Where do nerve fibres of pulp terminate?
- some fibres terminate in the Plexus of Raschow
- Others enter some of the dentinal tubules (more commonly in coronal dentine) to form intratubular nerve fibres
- Some pass into the predentine and terminate - predentine fibres
- Others loop into the predentine and return to the plexus of Raschow to terminate - recurrent fibres
104
Describe age changes to pulp
- related to lifelong deposition of dentine
- Decreased size of pulp chamber resulting from ongoing deposition of dentine
- Decrease in nerves and a concurrent decrease in sensitivity
- Narrowing of root canal with possible decrease in vascular supply
- Diffuse calcifications
