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pdl Flashcards

1
Q

what is the pdl?

A

dense fibrous connective tissue occupying the periodontal
space between root cementum and
alveolar bone of tooth socket
closest we can get to it = passing perio probe into gingival sulcus

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2
Q

average width of periodontal space

A

0.25mm

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3
Q

what is pdl continuous w

a) above the alveolar crest
b) at the apical foramen

A

a) connective tissues of the gingiva

b) the dental pulp

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4
Q

how many connective tissues does the periodontum consist of

A

4

2 calcified and 2 non-calcified

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5
Q

what are the 2
a) calcified
b) non-calcified
tissues of the periodontum

A

a) cementum on root surface
alveolar bone of the socket wall (aka lamina dura - prominent white line on radiograph or cribiform plate - as perforated w numerous channels containing blood vessels)
(appear darker pink on staining)
b) lamina propria of the gingiva
pdl
boundary between these 2 = horizontal line at level of alveolar crest
(appear lighter pink on staining)

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6
Q

composition: which connective tissue cells are found in the pdl

A

mostly fibroblasts

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7
Q

composition: what is then extracellular matrix composed of

A 
mainly fibrils of Type I collagen
glycosaminoglycans
proteoglycans
glycoproteins 
water
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8
Q

composition: what collagen-synthesising cells are in the pdl

A

cementoblasts

osteoblasts

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9
Q

composition: what other cell types are found in the pdl

A

1) resorbing cells for the surrounding hard
tissues (osteoclasts and odontoclasts)
2) defense cells (monocytes and macrophages)

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10
Q

what cells does the pdl contain unusually

A

epithelial cells in form of epithelial cell rests of Malassez

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11
Q

pdl cell types: role of fibroblasts

A 
- synthesis and
degradation of collagen
- secretion of all
components of pdl ground
substance
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12
Q

pdl cell types: role of cementoblasts and osteoblasts

A
  • formative cells
  • cover surface of cementum and alveolar bone
  • mesenchymal origin
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13
Q

pdl cell types: role of osteoclasts + odontoclasts

A
  • resorbing cells
  • on surface of bone and cementum
  • derived from monocyte/macrophage lineage from blood
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14
Q

role of stem cells and pdl cell types: precursors ie preosteoblasts
+ precementoblasts) and epithelial cells (rests of Malassez)

A
  • undifferentiated mesenchymal cells

- remnant of epithelial root sheath

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15
Q

pdl cell types: role of monocytes

A
  • defense cell
  • blood-borne
  • enter pdl from blood
    vessels
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16
Q

pdl cell types: role of macrophages

A
  • defense cell
  • derived from
    monocyte
    monocytes + macrophages = small % of cell population
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17
Q

components of the pdl extracellular matrix

A

1) collagen (crestal, horizontal, OBLIQUE, apical, interradicular)
2) ground substance (proteoglycans, glycoproteins)
3) oxytalan (pre-elastin)

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18
Q

main constituent of pdl extracellular matrix, what does the collagen form

A

type I collagen (70%)

- gathered together to form bundles termed ‘principal fibres’

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19
Q

what other collagen types are found in the pdl extracellular matrix

A
  • type 3 (20% = unusual, found throughout tissue + into periphery of sharpeys fibre attachements into the alveolar bone) = not fully understood but associated w rapid turnover in other body sites (granulation tissues, foetal connective tissues)
  • types IV, V, VI, VII, XII (trace amnts)
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20
Q

what are the 4 other fibres found in the pdl extracellular matrix

A

1) oxytalan = 3% of periodontal fibres
2) elastin = restricted to walls of blood vessels
3) elaunin = found around blood vessels, provide mechanical protection for vascular system
4) reticulin = type 3 collagen, they crosslink + form fine meshwork to aid tissue support

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21
Q

what can be found between collagen fibrils and what are its functions

A

ground substance
- water binding
- control of collagen fibrillogenesis and fibre
orientation
- binding of growth factors
(imp in regulating fibroblast activities)

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22
Q

what 4 functions does the pdl have

A

1) resists displacing forces (tooth support mechanism) + protects dental tissues from damage caused by excessive occlusal loads (esp at root apex)
2) responsible for mechanisms where tooth attains + maintains its functional position (tooth eruption, support - recovery response aft loading + maintain its attachment to socket during post-eruptive tooth movements (drift))
3) its cells form, maintain + repair alveolar bone + cementum
4) its mechanoreceptors = involved in neurological control of mastication / protective responses (ie reflex jaw opening), contribute to sensations of touch + pressure on tooth

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23
Q

what is the lamina propria of the gingiva

A

dense fibrous connective tissue w insertions into tooth and bone of the
alveolar crest

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24
Q

where do fibres in the lamina propria run

A

run in numerous directional groups both around and

between adjacent teeth in the arch

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25
how do fibres in the lamina propria work together with tissue fluid
to support free gingiva + hold attached gingiva against tooth this region of attachment (gingiva to tooth) = 'GINGIVAL CUFF'
26
what is part of the gingival cuff (but not the periodontium)
junctional epithelium = forms soft tissue attachment to tooth - gingival cuff derived from reduced enamel epithelium of tooth germ
27
what is the junctional epithelium
- specialised non-keratinised stratified squamous epithelium - between the lamina propria and enamel - unusual in having a basal lamina on both surfaces
28
how do cells attach to the basal lamina which is deposited on the enamel surface
via hemi-desmosomes
29
what is the basic unit of collagen in pdl and what happens to these
``` triple helical tropocollagen molecule 1) secreted outside the cell 2) cleaved + spontaneously aggregated in staggered fashion 3) first as a five membered micro-fibrils 4) then into classical fibrils ```
30
what are classical fibrils and what larger structures are these arranged into
- fibrils w characteristic banding at 64nm | - bundles (visible histologically, 1um+)
31
bundles are arranged to give what
overall tissue | architecture – the principle fibre bundles
32
what do structural features of pdl (ie collagen fibril diameters) suggest
the ligament acts in | compression
33
what is visible in an electron micrograph of small fibrils from pdl cut transversely
- uniform diameter of 40m | - large amnt of space between fibrils occupied by ground substance
34
explain the tooth support mechanism
- biphasic, ‘visco-elastic’, response to axial loading demonstrated by pdl - some load applied to tooth is dissipated through the oblique fibre system - BUT pdl resists intrusive loads primarily by compression + fluid flow
35
what does evidence suggest is involved in tooth support
pdl's collagen fibres, vasculature + ground substance
36
what orientations of principle collagen fibres are seen in different regions of the pdl
1) dentoalveolar crest fibres 2) horizontal fibres 3) oblique fibres 4) apical fibres (at bottom of root) 5) interradicular fibres (between the roots of a tooth)
37
how do pdl fibres attach to cementum and alveolar bone
1) unmineralised fibres of pdl run into organic matrix of precementum (secreted by cementoblast) 2) causes mineralisation of precementum 3) mineralisation incorporates the extrinsic fibres as Sharpey fibres (their orientation differs from fibres produced by cementoblasts) BUT PDL ALSO forms sharpeys fibres in the alveolar bone
38
where are sharpeys fibres a) mineralised b) unmineralised c) abundant
a) in cementum b) in ligament c) acellular cementum
39
what are sharpeys fibres formed by
periodontal fibroblasts
40
how do sharpeys fibre insertions into alveolar bone differ from insertions into cementum
larger but less numerous
41
how are sharpeys fibres seen in microscopy
horizontal lines in bone and cementum
42
so what are sharpey fibres
ends of the pdl fibres inserted into root | cementum and alveolar bone of the tooth socket
43
what % of the extracellular fibre composition do oxytalan fibres constitute and what is their function
- no more than 3% | - aid fibroblast migration in the pdl
44
where do oxytalan fibres run in outer part of the ligament
obliquely down from the cementum to terminate | in the vicinity of the periodontal capillaries
45
how do oxytalan fibres run in the pdl
- longitudinally oriented | - cross oblique fibre bundles perpendicularly
46
what do the ultrastructural characteristics of oxytalan fibres suggest
theyre immature elastin fibres = 'pre-elastin' | unlike mature elastin, theres no central amorphous core
47
how does the pdl resemble immature, foetal-like connective tissues
- high rate of turnover of extracellular matrix (unlike other adult connective tissues) - high proportion of type III collagen - high cellularity - presence of oxytalan fibres
48
what is the problem with thinking of the pdl as a | fibrous connective tissue
- matrix may only occupy 50% of tissue space | - of that 50%, 60% may be ground substance (not collagen fibrils)
49
why is pdl being foetal-like good clinically
- potential source of ‘embryonic’ stem cells - aid our understanding of inflammatory perio disease (understanding of repair/perio reattachment may benefit from appreciation of mode of repair of foetal wounds)
50
what is the functional significance of the pdl being foetal like
its structural, ultrastructural + biochemical features dont depend primarily on mechanical demands BUT high rates of turnover = greater role in determining characteristics
51
what is the pdl derived from
dental follicle
52
what is the process to make the predentine layer once the crown has fully formed
1) IEE + EEE proliferate down as double-layered sheet of flattened epithelial cells (epithelial root sheath of Hertwig) that outlines shape of root 2) sheath induces peripheral cells of dental papilla to differentiate into odontoblasts + begin producing predentine 3) sheath in contact w initial predentine layer for short time before continuity of its cells is lost
53
explain the development of the cells of the pdl
1) adjacent cells of dental follicle come lie close to surface of newly formed unmineralised dentine 2) before root formation = cells of dental follicle have characteristics of undifferentiated mesenchymal cells 3) onset of root formation = they show inc in cytoplasmic organelles (esp those associated w protein synthesis + secretion) 4) they differentiate into cementoblasts, fibroblasts + osteoblasts of pdl (connective tissue-forming cells) 5) cells of inner layer of dental follicle differentiate into cementoblasts (form initial layer of cells on surface of root dentine)
54
describe collagen fibre formation
1) once cementogenesis begins, cells of remaining dental follicle become obliquely oriented along root surface + show incd content of intracellular organelles becoming FIBROBLASTS of the pdl 2) fibroblasts secrete collagen of pdl into extracellular compartment 3) becomes embedded as sharpeys fibres into developing acellular cementum at tooth surface + developing bone at alveolar surface
55
explain the close association between | principal fibres and fibroblasts of the pdl
cellular processes surround / envelop fibre bundles processes from adjacent cells = joined by intercellular contacts to form cellular network
56
what do the organelles of fibroblasts confer
large amounts of rough endoplasmic reticulum so v metabolically active suggestive of cell producing large amnts of protein for export
57
how are pdl fibroblasts metabolically coordinated
significant no of gap junctions between | adjacent cells = help coordinate matrix turnover activities
58
how is fibrillar collagen degraded by fibroblasts in the pdl, how do we know this and what does it enable?
‘phagocytic’ process 1) lysosomes fuse w the ‘phogosome’ containing collagen fibril 2) form ‘phago-lysosome’ where fibril is degraded know bc fibroblasts contain intracellular vacuoles containing fragments of fibrillar collagen enables cells to control degradative process more precisely
59
how is fibrillar collagen degraded in most connective tissues
extracellularly | - cells secrete collagenases into extracellular environment
60
what is the blood supply to the periodontium
V RICH | derived from superior or inferior alveolar arteries
61
what is the origin of most pdl capillaries what does this source of blood supply allow
- intra-bony spaces in the alveolus, arterioles in gingivae may also be involved - allows pdl to function following severing of blood vessels at root apex during endodontic treatment
62
what do capillaries and | arterioles in the pdl form
plexus around tooth (primarily situated towards socket wall, between principal fibre bundles, may occupy <50% of periodontal space = high compared to other adult connective tissues)
63
as well as high capillary volume how are capillaries themselves specialised
FENESTRATIONS - in certain regions their endothelial lining becomes thin - fenestration occluded by single membrane perforate the wall - their presence = due to high metabolic rate of the tissue (matrix turnover) or a requirement for fluid movement between compartments
64
why is the fenestration of pdl capillaries significant
fibrous connective tissues usually have continuous | capillaries w no fenestrations
65
what are volkmanns canals
channels through socket wall carry blood vessels between the ligament and intraboney blood spaces
66
what are Epithelial cell rests of Malassez
- islands of epithelial cells close to cementum - remnants of epithelial root sheath (of Hertwig) which disintegrates following root development - normal feature of pdl - inactive hence 'rests' - may be triggered to proliferate and form peri-apical cysts
67
how do cells of the junctional epithelium immediately adjacent to the tooth attach to the tooth
- hemidesmosomes - basal lamina (in contact w tooth = internal basal lamina) other surface of junctional epithelium in contact w lamina propria = normal / external basal lamina
68
describe the junctional epithelium
forms an epithelial collar that surrounds the cervical part of the crown + extends from the base of the gingival crevice to the cementum-enamel junction (CEJ) ‘upper’ surface forms ‘adhesive’ bond between gingiva and enamel (not enough to oppose masticatory forces which push the gingiva away from tooth surface) so added force of the fibres + tissue turgor in gingival cuff beneath junctional epithelium = 1) maintains integrity of junction between tooth and gingiva 2) seals underlying connective tissue of periodontium from oral environment
69
explain soft tissue attachment of junctional epithelium to tooth
forms this as attaches to enamel constituting the epithelial attachment attachment provided by the lamina propria to the tooth = connective tissue attachment both these attachments = ‘biologic width’
70
unique features of junctional epithelium
- rapid rate of turnover | - permeable to GCF AND host defence cells helps defend underlying tissue against bacterial invasion
71
what are the collagen fibres of the lamina propria
1) mostly type I collagen 2) dense principal fibre bundles whos functions inc… support of free gingiva binding of attached gingiva to alveolar bone and tooth = resisting masticatory loads linkage of teeth principal fibre groups given names based on their orientation + attachments
72
how can we distinguish the extracellular matrix of lamina propria from connective tissue of the pdl
1) less ground substance 2) lesstype III collagen 3) hyaluronan-rich 4) lower turnover rate
73
what different fibres can be seen in the lamina propria
``` dentogingival longitudinal circular alveologingival dentoperiosteal transseptal semicircular transgingival interdental vertical ```
74
pdl functions in health
tissues within this space do not mineralise =SO ligament can support tooth in its socket allowing a small amount of movement helping protect tooth against forces of mastication
75
presence of pdl
``` permits forces (from mastication + other tooth contacts) to be transmitted to the alveolar process via bone lining the socket wall acts as protective scaffold for cells, vessels, and nerves ```

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