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Craniofacial and Tooth Biology > 22. Periodontal Ligament > Flashcards

22. Periodontal Ligament Flashcards

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1
Q

Tooth root formation is coordinated with development of …
Why?

A
  • periodontium
  • PDL attaches tooth to alveolar bone
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2
Q

3 differentiations of dental follicle cells

A
  • cementoblasts for cementum
  • fibroblasts for periodontal ligament
  • osteoblasts for alveolar bone
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3
Q

Which genetic factors regulate differential formation of periodontal tissues?

A
  • insufficiently investigated
  • FGFs (cell proliferation, migration) and BMPs (cell differentiation, bone formation)
  • use of growth factors e.g FGF2, BMP2, 7
  • stem cells in PDL as source for regenerative therapies in periodontal disease
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4
Q

List functions of periodontal ligament

A
  • tooth attachment
  • withstand forces of mastication
  • sensory receptor
  • remodelling
  • nutritive
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5
Q

How is the periodontal ligament for tooth attachment?

A
  • PDL fibres insert into cementum and alveolar bone
  • forms fibrous joint with very little/no movement (gomphosis/synarthrosis)
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6
Q

How is the periodontal ligament for withstanding force of mastication?

A

shock absorber

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7
Q

How is the periodontal ligament for sensory reception?

A
  • sensations of pain and tension/compression
  • repositioning of teeth to achieve occlusion
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8
Q

How is the periodontal ligament for remodelling function?

A
  • high turnover of extracellular matrix and collagen fibres
  • source of progenitor/stem cells
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9
Q

How is the periodontal ligament for nutrition?

A
  • highly vascularised tissue
  • connected to dental arteries, bone marrow and gingiva
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10
Q

Timing of PDL development and differentiation varies …

A
  • among species
  • between tooth types
  • between primary and permanent teeth
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11
Q

What is the first stage of PDL development?

A
  • initiation
  • ligament space between cementum and bone consists of unorganised connective tissue (mainly fibroblasts and ECM)
  • short fibre bundles are formed near the cementum and bone surface and extend only a short distance into ligament space
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12
Q

What happens in PDL formation after initiation stage?

A
  • fine brush-like fibres emerge from cementum and only a few fibres project from alveolar bone into ligament space
  • fibroblasts produce more collagen fibrils that assemble as fibre bundles and gradually extend from bone to cementum to establish a continuous attachment
  • bone side is thick fibre bundles, cementum side is thin fibre bundles, fine intermediate meshwork
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13
Q

There are … and … PDL fibres at alveolar bone side whereas they’re … and … at cementum side

A
  • thick and widely spaced
  • thin and closely spaced
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14
Q

Once fibres have formed between cementum and bone in PDL development, what happens?

A
  • alveolar crest fibres are formed first at cemento-enamel junction
  • as root forms, fibre formation then proceeds apically
  • orientation is initially oblique, then horizontal, then oblique again
  • PDL is continuously modified by eruptive tooth movements and occlusal forces
  • thick fibre bundles only form when teeth occlude and begin to function
  • role of PDL in tooth eruption likely but still controversial
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15
Q

5 principle fibre groups of PDL

A
  • alveolar crest group
  • horizontal group
  • oblique group
  • apical group
  • interradicular group
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16
Q

Explain alveolar crest group

A
  • below CEJ - rim of alveolus
  • resist extrusive forces
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17
Q

Explain horizontal PDL fibre group

A
  • below alveolar crest group
  • at right angle to tooth axis
  • resist horizontal forces/’tipping’
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18
Q

Explain oblique PDL fibre group

A
  • most abundant
  • resist intrusive compressive forces in mastication
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19
Q

Explain apical PDL fibre group

A
  • radiates around tooth apex
  • forms base of socket
  • resist extrusive forces
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20
Q

Explain interradicular PDL fibre group

A
  • only multi-rooted teeth
  • connects to crest of interradicular septum
  • resist extrusive forces
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21
Q

Each collagen fibre bundle resembles …
What happens with individual fibrils? Overall fibre?

A
  • a spliced rope
  • continuously remodelled
  • maintains core architecture and function (possible for it to adapt to varying mechanical/masticatory forces)
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22
Q

Types of PDL fibres

A
  • collagen
  • elastic
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23
Q

Explain elastic fibres in PDL fibres

A
  • oxytalan fibres contain fibrillin but no elastin
  • run perpendicular to collagen fibres in cervical region, associated with neurovascular bundles
  • form 3D meshwork surrounding root
  • possible role of regulating vascular flow
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24
Q

Sharpey’s fibres are … PDL fibres in … and …

A
  • mineralised
  • alveolar bone and cementum
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25
Q

Main function and types of fibroblasts in PDL

A
  • produce collagen fibrils to form fibre bundles and ground substance in ECM
  • have perivascular and endosteal ones - source of progenitor cells to maintain PDL
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26
Q

Jobs of fibroblasts in PDL

A
  • secrete ground substance, collagen fibrils and growth factors/cytokines
  • rich in organelles (ER, golgi) for protein production and secretion
  • high levels of collagen produced (8x skin, 2x gingiva)
  • form cell-cell contacts with adherens and gap junctions
  • well developed cytoskeleton (actin network) - shape change and migration
  • align along direction of fibre bundles
  • contractile (mediated by integrins that bind to ECM) - mechano-transduction
  • function tooth movements like mesial/vertical tooth drift
  • remodelling (synthesis and degradtion of ECM and collagen)
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27
Q

PDL fibroblasts appear morphologically similar but …

A
  • heterogenous cell population
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28
Q

What is PDL collagen half life?

A

3-23 days (variable - highest turnover at tooth apex)
- leads to scurvy

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29
Q

What kind of cell-cell junctions are in fibroblasts in PDL?

A
  • adherens
  • gap
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30
Q

How are fibroblasts in PDL contractile?

A
  • mediated by integrins that bind to ECM
  • mechano-transduction
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31
Q

Activity of fibroblasts in PDL is induced by what?

A

mecahnical or masticatory forces

32
Q

How do fibroblasts in PDL have a role in remodelling?

A
  • synthesis and degradation of ECM and collagen
  • matrix metalloproteases (MMPs)
  • a therapeutic target in periodontal disease
33
Q

Composition of the PDL

A
  • 60% ground substance
  • rest is mainly collagen fibres, blood vessels and nerves
  • fibres - 90% collagen, 10% oxytalan (elastic)
  • collagens (type 1 - 80%, type 3 - 15%, type 4,5,6,7,12)
34
Q

Type 3 collagen in PDL is what?

A
  • in reticular fibres
  • in meshwork
35
Q

Type 12 collagen is what in PDL?

A
  • fibril associated
  • links other collagens
  • only present after eruption
  • expressed on pressure side following mechanical loading
36
Q

Does collagen composition of PDL change with age?

A

no

37
Q

Composition of ground substance

A
  • complex
  • of glycosaminoglycans (hyaluronic acid, dermatan sulfate, chondroitin and heaprin sulfate)
  • proteoglycans
  • and glycoproteins
38
Q

Function of ground substance

A
  • ion and water binding
  • 70% water so acts as a shock absorber
  • orientation of collagen fibres
39
Q

How does ECM support ground substance?

A
  • ground substance orientates collagen fibres
  • ECM controls hydration of tissue and increases strength of collagen fibres
40
Q

How does composition of ground substance vary?

A
  • to developmental state
  • hyaluronic acid conc decreases in development of PDL from dental follicle
  • proteoglycan conc increases during tooth eruption
41
Q

Role of fibronectin in ground substance

A
  • mediates attachment of cells to collagen fibrils
  • influences cell migration and differentiation
  • clinically used to promote wound healing
42
Q

ECM binds what 2 things?

A
  • growth factors
  • cytokines
43
Q

List cell types in the PDL

A
  • fibroblasts
  • osteoblasts/clasts
  • cementoblasts/clasts
  • Rests of Malassez
  • mesenchymal stem cells
  • immune cells
  • blood vessels
  • nerve fibres
44
Q

Osteoblasts and clasts are associated with … in PDL and are for …

A
  • alveolar bone
  • bone remodelling
45
Q

Cementoblasts and clasts are associated with … in PDL and are for …

A
  • cementum
  • cementum remodelling
46
Q

What are the Rests of Malassez?

A
  • remnants of HERS
  • possible source of epithelial stem cells
47
Q

Role of mesenchymal stem cells in PDL

A
  • source of all mesenchymal cell types
  • e.g fibroblasts, osteoblasts, cementoblasts
48
Q

What types of immune cells are in PDL?

A
  • macrophages
  • mast cells
  • eosinophils
49
Q

What blood vessels are present in PDL?

A
  • endothelium
50
Q

What nerve fibres are present in PDL?

A

axons of neurons

51
Q

PDL is highly/poorly vascularised
Explain

A
  • highly
  • 10-30%
  • differs between species, tooth types, PDL site, erupting teeth
  • high turnover rate of PDL components needs constant nutrient supply
52
Q

What is the vascular supply of PDL?

A
  • branches of superior and inferior alveolar arteries
  • branches of lingual and palatine arteries
53
Q

Explain how superior and inferior alveolar arteries vascularise the PDL

A
  • branches enter at pulp apex
  • interalveolar vessels pass through alveolar process (‘perforating arteries’) - more abundant in posterior and mandibular teeth
  • form ‘interstitial areas’ within PDL
  • enables PDL function after endodontic treatment
  • tooth extractions - formation of blood clot and invasion of cells involved in wound healing
54
Q

Where do branches of lingual and palatine arteries enter oral cavity?

A

through gingiva

55
Q

Where are neurovascular bundles in PDL?

A
  • pass through perforations in alveolar bone
  • form interstitial areas in PDL
56
Q

What are the interstitial areas in PDL?

A
  • located close to alveolar bone
  • contain neurovascular bundles (with nerves and blood vessels)
  • blood vessels form capillary plexus near root surface and postcapillary plexus from which venules pass into alveolar bone
57
Q

In PDL, blood vessels in … direction and form …
Venous drainage occurs at the … and … follow the venules

A
  • apical-occlusal
  • arterio-venous anastomoses
  • root apex
  • lymphatic vessels
58
Q

Circular plexus in PDL is … and crevicular is …

A
  • surrounding the root surface
  • surrounds the tooth in region beneatjh gingival crevice
59
Q

Explain fenestrated capillaries in PDL

A
  • large numbers of pores in endothelial cells
  • special feature of PDL vasculature not seen usually in other connective tissue
  • generates increased diffusion capacity e.g for larger molecules
  • consistent with high metabolic rate of PDL especially during tooth eruption
60
Q

Innervation of PDL

A
  • well innervated and pattern of nerve fibres follows that of vasculature
  • from apex to gingival margin and through lateral perforations of alveolar bone
  • perforating nerve fibres divide into apical and gingival branch
61
Q

How does PDL innervation show regional variation?

A
  • more nerve endings in tooth apex
  • upper incisors have denser innervation than molars
  • can be related to masticatory response - initial contact with food could specify level of force required to process food
62
Q

Types of nerve fibres in PDL

A
  • myelinated fibres - sensory
  • myelinated and unmyelinated fibres for sensory and autonomic
63
Q

Roles of sensory nerve fibres

A
  • nociception
  • proprioreception - pressure
  • food sensing, position of tongue and neck muscles, salivary reflexes
64
Q

Role of autonomic fibres

A
  • regulation of blood flow (constriction and dilation of blood vessels)
65
Q

4 types of nerve endings

A
  • free ending, treelike type
  • Ruffini’s corpuscles
  • coiled type
  • encapsulated spindle type
66
Q

Explain free ending treelike type

A
  • evenly distributed across PDL
  • unmyelinated fibres (enveloped by one Schwann cell/inset)
  • extend up to cementoblast layer to sense pain and pressure
67
Q

Explain Ruffini’s corpuscle

A
  • found in PDL at root apex
  • myelinated fibres with dendritic endings
  • associate with collagen fibres - inset
  • sense pressure
68
Q

Where are coiled type nerve endings found?

A
  • found in middle region of PDL
  • unknown function
69
Q

Where are encapsulated spindle type nerve endings found?

A
  • found in PDL at root apex - infrequent
  • surrounded by fibrous capsule
70
Q

What is the general PDL thickness? Where is it thinnest?

A

0.15-0.38 mm
middle third of the root

71
Q

PDL thickness at
- 11-16 years
- 32-52 years
- 53-67 years

A
  • 0.21mm
  • 0.18mm
  • 0.15mm
72
Q

PDL thickness decreases with …

A

increasing age

73
Q

How does mastication link to PDL thickness?

A
  • mastication induces periodontal remodelling
  • results in increased PDL width by around 50% inc. thicker fibre bundles and increased alveolar bone size
  • PDL thicker in areas of tension compared to areas of compression
  • decreased function results in reduction/loss of periodontal tissues
74
Q

Capacity of PDL remodelling forms basis for …

A

orthodontic treatment
- excessive force can cause localised necrosis of PDL by cutting off the blood supply
- inhibition of orthodontic tooth movement

75
Q

Damaged PDL can be repaired. What if this goes wrong?

A
  • incorrect repair causes localised resorption and tooth ankylosis
  • fusion of tooth to bone - diagnosed using X-ray or percussion test - tapping of tooth
76
Q

Accidentally lost teeth can be replanted. But if portions of ligament are permanently damaged, …

A

external root resorption and tooth ankylosis could occur

77
Q

PDL is the target of therapies of periodontal disease. How so?

A
  • prevention of undisirable wound healing
  • growth factors, cytokines, stem cells to stimulate PDL regeneration

Craniofacial and Tooth Biology (25 decks)

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