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Flashcards in Cementum and PDL Deck (41)
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What is the cementum

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


Where is the cementum thicker

Thinner cervically
Thicker apically


What is the function of the cementum

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


What minerals and organic material make up the cementum matrix

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


How does cementum's properties differ from that of bone

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


Describe the permeability of cementum

- More permeable than dentine
- Permeability increased in cellular type
- Permeability decreases with age (similar to other dental tissues)


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

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


What is the difference between primary and secondary cementum

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


Where do cementoblasts reside

in the periodontal ligament space lining the cementum surface


What is the first thing cementoblasts lay down

pre-cementum (unmineralised)


Where are cementocytes found

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


Where is the collagen in the extrinsic fibre cementum derived from

Sharpey's fibres from the PDL


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

Parallel to the root surface
This cementum plays no role in tooth attachment


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

Perpendicular to the root surface


Where are the fibres from intrinsic fibre cementum made



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

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


What is fibrillar cementum

- Type of cementum with no collagen fibres
- Localized regions of mineralized ground substance covering cervical enamel


Describe cementum formation

• 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)


Describe how cementum formation continues throughout life

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


Describe how the incremental lines of cementum are formed

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


What are cementicles

• 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


What can result in cementicles

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


What are the more common areas for cementicles to be found

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


What are the orthodontic implications of cementum being resistant to resorption

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


What is the periodontal ligament

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


What is the role of the PDLd

• 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)


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

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


What are the different structure of the PDL

- 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


Name as many of the different PDL fibres as you can

Gonna have to look up what the differences are

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


Describe the oblique (principal) fibres of the PDL

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