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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
Q

how do fibres in the lamina propria work together with tissue fluid

A

to support free gingiva + hold attached gingiva against tooth
this region of attachment (gingiva to tooth) = ‘GINGIVAL CUFF’

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26
Q

what is part of the gingival cuff (but not the periodontium)

A

junctional epithelium = forms soft tissue attachment to tooth - gingival cuff
derived from reduced enamel epithelium of tooth germ

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27
Q

what is the junctional epithelium

A
  • specialised non-keratinised stratified squamous epithelium
  • between the lamina propria and enamel
  • unusual in having a basal lamina on both surfaces
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28
Q

how do cells attach to the basal lamina which is deposited on the enamel surface

A

via hemi-desmosomes

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29
Q

what is the basic unit of collagen in pdl and what happens to these

A 
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
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30
Q

what are classical fibrils and what larger structures are these arranged into

A
  • fibrils w characteristic banding at 64nm

- bundles (visible histologically, 1um+)

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31
Q

bundles are arranged to give what

A

overall tissue

architecture – the principle fibre bundles

32
Q

what do structural features of pdl (ie collagen fibril diameters) suggest

A

the ligament acts in

compression

33
Q

what is visible in an electron micrograph of small fibrils from pdl cut transversely

A
  • uniform diameter of 40m

- large amnt of space between fibrils occupied by ground substance

34
Q

explain the tooth support mechanism

A
  • 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
Q

what does evidence suggest is involved in tooth support

A

pdl’s collagen fibres, vasculature + ground substance

36
Q

what orientations of principle collagen fibres are seen in different regions of the pdl

A

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
Q

how do pdl fibres attach to cementum and alveolar bone

A

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
Q

where are sharpeys fibres

a) mineralised
b) unmineralised
c) abundant

A

a) in cementum
b) in ligament
c) acellular cementum

39
Q

what are sharpeys fibres formed by

A

periodontal fibroblasts

40
Q

how do sharpeys fibre insertions into alveolar bone differ from insertions into cementum

A

larger but less numerous

41
Q

how are sharpeys fibres seen in microscopy

A

horizontal lines in bone and cementum

42
Q

so what are sharpey fibres

A

ends of the pdl fibres inserted into root

cementum and alveolar bone of the tooth socket

43
Q

what % of the extracellular fibre composition do oxytalan fibres constitute and what is their function

A
  • no more than 3%

- aid fibroblast migration in the pdl

44
Q

where do oxytalan fibres run in outer part of the ligament

A

obliquely down from the cementum to terminate

in the vicinity of the periodontal capillaries

45
Q

how do oxytalan fibres run in the pdl

A
  • longitudinally oriented

- cross oblique fibre bundles perpendicularly

46
Q

what do the ultrastructural characteristics of oxytalan fibres suggest

A

theyre immature elastin fibres = ‘pre-elastin’

unlike mature elastin, theres no central amorphous core

47
Q

how does the pdl resemble immature, foetal-like connective tissues

A
  • 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
Q

what is the problem with thinking of the pdl as a

fibrous connective tissue

A
  • matrix may only occupy 50% of tissue space

- of that 50%, 60% may be ground substance (not collagen fibrils)

49
Q

why is pdl being foetal-like good clinically

A
  • 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
Q

what is the functional significance of the pdl being foetal like

A

its structural, ultrastructural + biochemical features dont depend primarily on mechanical demands
BUT high rates of turnover = greater role in determining characteristics

51
Q

what is the pdl derived from

A

dental follicle

52
Q

what is the process to make the predentine layer once the crown has fully formed

A

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
Q

explain the development of the cells of the pdl

A

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
Q

describe collagen fibre formation

A

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
Q

explain the close association between

principal fibres and fibroblasts of the pdl

A

cellular processes surround / envelop fibre bundles
processes from adjacent cells = joined by
intercellular contacts to form cellular network

56
Q

what do the organelles of fibroblasts confer

A

large amounts of rough endoplasmic reticulum so v metabolically active
suggestive of cell producing large amnts of protein for export

57
Q

how are pdl fibroblasts metabolically coordinated

A

significant no of gap junctions between

adjacent cells = help coordinate matrix turnover activities

58
Q

how is fibrillar collagen degraded by fibroblasts in the pdl, how do we know this and what does it enable?

A

‘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
Q

how is fibrillar collagen degraded in most connective tissues

A

extracellularly

- cells secrete collagenases into extracellular environment

60
Q

what is the blood supply to the periodontium

A

V RICH

derived from superior or inferior alveolar arteries

61
Q

what is the origin of most pdl capillaries what does this source of blood supply allow

A
  • 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
Q

what do capillaries and

arterioles in the pdl form

A

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
Q

as well as high capillary volume how are capillaries themselves specialised

A

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
Q

why is the fenestration of pdl capillaries significant

A

fibrous connective tissues usually have continuous

capillaries w no fenestrations

65
Q

what are volkmanns canals

A

channels through socket wall
carry blood vessels between the ligament and
intraboney blood spaces

66
Q

what are Epithelial cell rests of Malassez

A
  • 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
Q

how do cells of the junctional epithelium immediately adjacent to the tooth attach to the tooth

A
  • 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
Q

describe the junctional epithelium

A

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
Q

explain soft tissue attachment of junctional epithelium to tooth

A

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
Q

unique features of junctional epithelium

A
  • rapid rate of turnover

- permeable to GCF AND host defence cells helps defend underlying tissue against bacterial invasion

71
Q

what are the collagen fibres of the lamina propria

A

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
Q

how can we distinguish the extracellular matrix of lamina propria from connective tissue of the pdl

A

1) less ground substance
2) lesstype III collagen
3) hyaluronan-rich
4) lower turnover rate

73
Q

what different fibres can be seen in the lamina propria

A 
dentogingival 
longitudinal 
circular 
alveologingival
dentoperiosteal 
transseptal 
semicircular 
transgingival 
interdental 
vertical
74
Q

pdl functions in health

A

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
Q

presence of pdl

A 
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

IOE (22 decks)

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