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Oral Biology > PDL and Cementum > Flashcards

PDL and Cementum Flashcards

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1
Q

What are the functions of the periodontal ligament?

A

Tooth attachment, tooth support, sensory function, nutritive, shock absorber, for maintenance, repair and regeneration

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2
Q

What are the functions of the cementum?

A

Attaches the PDL fibers to the root, contributes to the repair of the root surface after damage, maintains the tooth in its functional position, and is involved in tooth repair and regeneration

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3
Q

What are the changes in cementum as we age?

A

Increase in cemental width: 5-10 times with increasing age, increase width is greater apically and lingually.

Accumulation of resorption bays results in increased surface irregularity

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4
Q

What are the changes in periodontal ligament as we age?

A

Decreased numbers of fibroblasts,

more irregular structure,

decreased organic matrix production and epithelial cell rests,

increased amounts of oxytalan (elastic fibers),

hypofunction: width of PDL decreases,

Decreased PDL cell proliferation (impairment of repair potential)

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5
Q

What is the shape of the PDL?

A

Hourglass

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6
Q

Where is the PDL narrowest?

A

At mid-root level

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7
Q

In which teeth are PDL wider?

A

Deciduous teeth and teeth under heavy occlusal loading

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8
Q

In which teeth are PDL narrower

A

Non-functional teeth or unerupted teeth

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9
Q

What is the PDL?

A

It is a soft, richly vascular and cellular connective tissue that surrounds the teeth and joins the cementum with the lamina dura (alveolar bone that surrounds the tooth)

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10
Q

What are the main functions of PDL?

A
  • Tooth attachment: attaches cementum to lamina dura
  • Tooth support: mediated by PDL principal fibres, supports tooth in the socket like a net, prevents loosening of teeth
  • Sensory function: Richly supplied with nerve endings that are receptors for pain and pressure (nociceptors)

-Shock absorber: Light forces cushioned by interstitial fluid that is forced out of blood vessels
Moderate forces absorbed by extravascular tissue fluid that is forced out of PDL space into the adjacent marrow spaces
Heavy forces absorbed by the principal fibres

-Maintenance, repair and regeneration
PDL contains undifferentiated ectomesenchymal cells that can differentiate into osteoblasts, cementoblasts and fibroblasts
Contains odontoclasts, osteoclasts and cemtoclasts for remodelling

-Nutritive: well vascularised, maintain the vitality of various cells

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11
Q

What are the 5 principal fibres?

A
  1. Alveolar crest
  2. Horizontal
  3. Oblique
  4. Apical
  5. Interradicular
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12
Q

Where are alveolar crest fibres located? In which direction?

A

Attach to cementum below CEJ. Apically and outwards from cementum to bone

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13
Q

Where are horizontal fibres located? In which direction?

A

From alveolar crest to apical fibres. Perpendicular to long axis of tooth from cementum to alveolar bone

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14
Q

Where are oblique fibres located and in which direction?

A

From cementum in oblique direction to insert into bone coronally

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15
Q

Where are apical fibres located and in which direction?

A

Radiating from cementum around apex of root to bone forming the base of the socket

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16
Q

Where are interradicular fibres located and in which direction?

A

From cementum into bone forming crest of interradicular septum

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17
Q

Which teeth are interradicular fibres not found in?

A

Single rooted teeth

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18
Q

What are oblique fibres largely responsible for?

A

Main support against masticatory forces

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19
Q

What forces do horizontal fibres resist?

A

horizontal and tipping

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20
Q

Which fibres resist both vertical and intrusive

A

alveolar crest and oblique

21
Q

What forces do apical fibres resist?

A

Vertical

22
Q

What forces do interradicular fibres?

A

Vertical and lateral

23
Q

How do PDL develop?

A

Initially only oblique fibres well developed, become more obvious as tooth erupts.
Once in occlusion cervical fibres more organised than apical portion
After some time in function, collagen fibres follow classical orientation

24
Q

What are the fibre components of PDL

A

Reticulum fibres: type 3 collagen, acts as a supporting mesh by forming lattice in the PDL

Oxytalan fibres: immature elastic fibres, attached to cementum at root, course out into PDL in various directions, rarely incorporate into alveolar bone

Principal fibres: type 1 collagen (90%), type 3, type 12-> formed by fibroblast, turnover rate higher than other connective tissue

Elastin fibres: Restricted to the walls of blood vessels

25
Q

What cells are present in the PDL?

A

Fibroblasts: principal cells of PDL, simultaneous synthesis and degradation of collagen, PDL remodelling

Cementoblasts

Defence cells: monocytes-> macrophages, 4% of PDL cells, located near nerves and blood vessels

26
Q

What other non-collagenous ECM components are present in PDL?

A

GAGs and proteoglycans

27
Q

What are the roles of ECM?

A

Cell growth, differentiation and gene expression

Organises cells into tissues

Production and reservoir of growth factors, hormones and proteases

Regulate cell attachment, migration and shape

Regulate intercellular communication and signaling through cellular adhesion molecules

Support and provide anchorage for cells

Transport nutrients and waste products

28
Q

What is the blood supply of the PDL?

A

Superior and inferior alveolar arteries
Lingual and palatine arteries from the gingiva

vessels lie between principal fibre bundle and close to the wall of the alveolar bone

Vessel branch and anastamose to form a capillary plexus around the root of teeth

29
Q

What does hypofunction and excessive occlusal loading do to PDL width?

A

Decrease and increase respectively

30
Q

What happens during the aging of PDL

A

Decreased number of fibroblasts

More irregular structure

Decreased organic matrix production and epithelial cell rests (rests of Malassez, remnants of HERS)

Increased amounts of oxytalan

Decreased PDL cell proliferation (impairement of repair potential)

Increased number of elastic fibers

31
Q

Where is the cementum the thickest and thinnest?

A

thickest apically, or interradicularly for multirooted teth

Thinnest cervically

32
Q

Does cementum have any blood vessels?

A

No it is avascular, no blood, nerves, lymph vessels

33
Q

How is cementum deposited?

A

Continuous deposition through life, no remodelling or resorption

34
Q

Which is more permeable- cementum or dentine?

A

cementum

35
Q

What forms cellular cementum and acellular cementum?

A

Cementoblasts form cellular,

fibroblasts form acellular

36
Q

Is first formed cementum cellular or acellular?

A

acellular

37
Q

What is the difference between cellular and acellular cementum?

A

Cellular dentine forms quickly, acellular slowly

Acellular mainly incorporates extrinsic fibres (Sharpey’s) perpendicular, cellular contains cementocytes and intrinsic fibres parallel to the root

Acellular located mainly over cervical half of root, cellular at apical area and furcations

Cellular dentine has precementum layer

Acellular more calcified

38
Q

What are the other types of cementum?

A

Mixed fibre cementum

Afibrillar cementum: no function in tooth attachment

39
Q

What are the functions of acellular cementum?

A

Attaches to the PDL fibers to the root

40
Q

What are the functions of cellular cementum?

A

Maintains the tooth at its functional position: attrition of teeth will cause cementum to be deposited at the apex of the root to keep the height of the root as similar as possible, HYPERCEMENTOSIS

Tooth repair and regeneration

Contributes to repair of root surface after damage

41
Q

What is the function of cementoblasts?

A

Forms the cementum and remodels PDL (allows for continual reattachment of PDL)

42
Q

Where can cementoblasts be found?

A

Line the root surface and inteposed between bundles of Sharpey’s fibers

43
Q

What are cementocytes?

A

Trapped cementoblasts in lacunae of cementum

44
Q

What’s the difference between bone and cementum?

A

Avascularity of cementum, as cementum layer gets thicker, cementocytes unable to receive nutrients and will be degenerated, leaving lacunae empty

45
Q

What are the clinical implications of cementum?

A

Cementicles

Hypercementosis

Ankylosis

46
Q

What are cementicles?

A

Small globular masses of cementum found in 35% of human roots, may be free floating in PDL, result in microtrauma

47
Q

What is hypercementosis?

A

Prominent thickening of cementum

May be significantly formed at the root apex as a result of inflammation or disease, or compensatury tooth eruption in response to attrition

Harder to extract

48
Q

What is ankylosis

A

Fusion of cementum with alveolar bone, obliteration of PDL

Due to chronic inflammation, tooth replantation and occlusal trauma

Root resorption and replacement by bone tissue

Requires surgical extraction

49
Q

What happens during aging of cementum?

A

Increase in cemental width, 5-10X with increasing age

Increase width is greater apically and lingually

Accumulation of resorption bays results in increased surface irregularity

Thicker cementum at areas with more tensional force

Thicker cementum at root surface concavities and furcations

Reduced activity and cell number of cementocytes, more empty lacunae

Oral Biology (4 decks)

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