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Oral Biology (Oral Cavity) > Cementum and PDL > Flashcards

Cementum and PDL Flashcards

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1
Q

What is the cementum

A

A thin layer of calcified tissue covering the dentine of the root

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2
Q

Where is the cementum thicker

A

Thinner cervically

Thicker apically

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3
Q

What is the function of the cementum

A

To cover the dentine and provide attachment of the tooth to the periodontal ligament

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4
Q

What minerals and organic material make up the cementum matrix

A

Minerals - mainly calcium and phosphate in the form of hydroxyapatite crystals
Organic - mainly collagen but also various glycoproteins and proteoglycans

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5
Q

How does cementum’s properties differ from that of bone

A
  • Avascular, lack of blood vessels
  • No innervation
  • Less readily resorbed - important in orthodontic tooth movement
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6
Q

Describe the permeability of cementum

A
  • More permeable than dentine
  • Permeability increased in cellular type
  • Permeability decreases with age (similar to other dental tissues)
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7
Q

What are the clinical implications of the softness and thinness of cementum

A
  • Readily removed by abrasion with the presence of gingival recession
  • Dentine sensitivity.
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8
Q

What is the difference between primary and secondary cementum

A

primary - acellular, forms next to dentin, greater proportion cervically; less apically
secondary - cellular, formed during functional needs

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9
Q

Where do cementoblasts reside

A

in the periodontal ligament space lining the cementum surface

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10
Q

What is the first thing cementoblasts lay down

A

pre-cementum (unmineralised)

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11
Q

Where are cementocytes found

A

Former cementoblasts within lacunae and cellular processes extending along the canaliculi are connected to each other

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12
Q

Where is the collagen in the extrinsic fibre cementum derived from

A

Sharpey’s fibres from the PDL

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13
Q

How do the intrinsic fibre cementum fibres run relative to the root surface

A

Parallel to the root surface

This cementum plays no role in tooth attachment

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14
Q

How do the extrinsic fibre cementum fibres run relative to the root surface

A

Perpendicular to the root surface

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15
Q

Where are the fibres from intrinsic fibre cementum made

A

cementoblasts

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16
Q

Where is most of the extrinsic and intrinsic fibre cementum found on the root

A 
Extrinsic = cervical 2/3rds of root
Intrinsic = apical 1/3rd of root
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17
Q

What is fibrillar cementum

A
  • Type of cementum with no collagen fibres

- Localized regions of mineralized ground substance covering cervical enamel

18
Q

Describe cementum formation

A
  • Begins as Hertwig’s root sheath disintegrates.
  • Undifferentiated cells come into contact with the newly formed surface of root dentine.
  • Contact induces the cells to become immature cementoblasts.
  • Cementoblasts migrate to cover the root dentine laying down cementum matrix, or cementoid.
  • Cementoblasts become entrapped and become mature cementocytes (unlike ameloblasts and odontoblasts)
19
Q

Describe how cementum formation continues throughout life

A
  • Slowly, the surface gets covered by a layer of uncalcified matrix or precementum
  • Allows for the continual reattachment/new attachment the PDL fibres
20
Q

Describe how the incremental lines of cementum are formed

A
  • Cementum layer deposition rate irregular compared to dentine and enamel
  • Acellular cementum: thin and even incremental lines
  • Cellular cementum: thicker and more irregular
21
Q

What are cementicles

A
  • Small globular masses of cementum found on 35% of human roots
  • Not always attached to the cemental surface
  • May be located free in the PDL
22
Q

What can result in cementicles

A

Micro trauma that causes stress on the sharpers fibres causing a tear in the cementum

23
Q

What are the more common areas for cementicles to be found

A

• More common in apical and middle 1/3 of the root and root furcation areas

24
Q

What are the orthodontic implications of cementum being resistant to resorption

A

allows for orthodontic tooth movement without destroying the root – only the surrounding alveolar bone is remodelled

25
Q

What is the periodontal ligament

A

• The dense fibrous connective tissue that occupies the space between the cementum and of the root and the alveolar bone

26
Q

What is the role of the PDLd

A

• Connects the tooth root to the surrounding alveolar bone, yet it does not become calcified
• Resists, displaces occlusal forces
• Protects dental tissues from damage caused by excessive occlusal load (especially at the apex)
- Responsible for mechanisms to maintain the functional position of a tooth
- Provides sensory input for reflex jaw activities via mechanoreceptors
- Neurological control of mastication (by mechano-receptors)

27
Q

What does the PDL width depends on, and what teeth is it wider in

A

Age and functionality - wider in teeth with heavy loading and narrower in un-errupted teeth, or lacking opposing teeth

28
Q

What are the different structure of the PDL

A
  • Fibres
  • Neurovascular channels (sensory fibres for pain, pressure, proprioception), blood vessels and lymphatics
  • Cellular elements (fibroblasts, cementoblasts/clasts, osteoblasts/clasts, undifferentiated mesenchymal cells)
  • Ground substance
29
Q

Name as many of the different PDL fibres as you can

Gonna have to look up what the differences are

A 
A. Transseptal (Gingival) 
B. Alveolar crest
C. Horizontal
D. Oblique (principal)
E. Apical
F. Inter-radicular
30
Q

Describe the oblique (principal) fibres of the PDL

A

more numerous than sharpey’s but smaller at their attachments to cementum than alveolar bone

31
Q

Describe the Sharpey’s fibres of the PDL

A

Insertions of principal fibres into cementum and bone at each end are

32
Q

What fibres are found in the PDL

A
  • Collagen - mainly type 1 or 3
  • Oxytalan fibres (small amounts)
  • Elastin fibres
33
Q

What is the function of oxytalan and elastin fibres

A

• Supportive role for the principle fibres, blood vessels and nerve endings

34
Q

Name some cells found in the PDL

A
  • Fibroblasts
  • Osteoblasts (on alveolar bone)
  • Osteoclasts
  • Cementoblasts (on cementum!)
  • Cementoclasts
  • Undifferentiated mesenchymal cells
  • Defence cells
  • Epithelial cells (Cell Rests of Malassez)
35
Q

What does the autonomic nervous system innervate in the PDL

A

Periodontal blood vessels

36
Q

Where do the autonomic nerves enter the PDL from

A

The root apex or from openings in the alveolar wall

37
Q

Are neurones myelinated or not in the PDL

A

Myelinated at apex and Non myelinated coronally

38
Q

How does inflammation affect the PDL

A
  • Inflammation causes loss of PDL and deeper pocket formation;
  • Increasing tooth mobility loss of tooth attachment in severe disease
39
Q

How does Orthodontic loading affect the PDL

A

• Tension - increased PDL space with increased connective tissue
(cells and fibres) and osteoid deposition
• Pressure – reduces PDL; increases resorption

40
Q

What treatment can allow the PDL to regrow

A

Guided tissue regeneration – allows PDL to regrow and prevents gingival connective tissue from growing down

41
Q

How does guided tissue regeneration work

A
  • After cleaning, a special membrane is inserted between the gum and bone
  • The membrane blocks unwanted tissue, allowing ligament fibres and bone to grow.
  • Once strong ligament fibres attach root to bone the membrane dissolves or is removed

Oral Biology (Oral Cavity) (15 decks)

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