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What are the 2 types of cellular classification cementum?

1. Cellular
2. Acellular


What are the 4 types of collagen classification cementum?

1. Intrinsic fibre
2. Extrinsic fibre
3. Mixed fibre
4. Afibrillar


Describe acellular cementum

Forms next to dentine
Greater proportion cervically and less apically


Describe cellular cementum

Found apically and overlying acellular cementum
Formed during functional needs
Numerous cementocytes


Describe extrinsic fibre cementum

All collagen derived from Sharpey's fibres
From PDL


Describe intrinsic fibre cementum

From cementoblasts
All intrinsic fibres running parallel to root surface
No role in tooth attachment


Describe mixed fibre cementum

Collagen fibres of organic matrix derived from both extrinsic and intrinsic fibres


Describe afibrillar cementum

No collagen fibres: thin, acellular layer
Localised regions of mineralised GS cover cervical enamel


What is the clinical implication of the thickness of cementum?

Gingival recession will expose thin cementum cervically which is easily abraded by tooth brushing, will reveal dentine which is highly sensitive


What are the 2 cells involved in cementum deposition?

1. Cementoblasts: deposit cementoid (unmineralised, pre-cementum)
2. Cementocytes: cementoblasts entombed in cementum


Describe cementoblasts

Produce cementum throughout life
Reside in the PDL space lining cementum surface
Similar to osteoblasts


Describe cementocytes

Former cementoblasts trapped within cementum matrix
Found in lacunae and have cellular processes that extend along caniculi which connect to each other


Describe the formation of cementum

Begins as Hertwig's root sheath disintegrates
Undifferentiated cells come into contact with newly formed dentine
Induces differentiation to immature cementoblasts
Cementoblasts migrate to cover root dentine, laying cementum matrix (cementoid)
Become trapped in matrix forming mature cemetocytes

Process continues throughout life allowing for continual reattachment/new attachment of PDL fibres


Describe the incremental lines of cementum

Acellular: thin and even
Cellular: thicker, irregular


Describe the 3 patterns possible at the CEJ

1. C overlaps E as E comes down
2. C and E meet and join
3. C fails to meet E: sensitivity w/ slightest root exposure


Describe the resorption of cementum

Less susceptible than bone under same pressure yet most roots still show signs of resorption

Reasons unclear

Multinucleated odontoclasts resorb cementum


What are cementicles?

Small, globular masses of cementum found on roots
Either attached to cementum surface or free in PDL
More common apically and mid. 1/3 root and bifurcation of root


What is the PDL?

Dense fibrous CT that occupies space between root, cementum and alveolar bone


Described the appearance of the PDL

Hour glass: narrowest mid root
Varies depending on functional state of tooth i.e. high occlusal force, unerupted


Describe the boundaries of the PDL

From apex to CEJ
Alveolar crest: continuous with gingivae
Apical foramen: continuous with pulp


Describe the properties of the PDL

Richly vascularised, has nerve endings
Uncalcified: is living, maintain shock absorbance
Appear as radiolucent line around root in radiography


What are the 8 functions of the PDL?

1. Attachment between tooth and alveolar bone
2. Resist, displace occlusal forces
3. Physiological mobility allows normal tooth function
4. Keeps teeth in functional position
5. Protects teeth from excessive occlusal load
6. Sensory inputs allow jaw reflex activities via mechanoreceptors
7. Neurological control of mastication
8. Cells form alveolar bone and cementum


Describe the structure of PDL

Neurovascular channels, blood and lymphatics
Cells: fibroblasts, cementoblasts/clasts, odontoblasts/clasts, undifferentiated mesenchymal cells


What are the 6 PDL fibres from most cervical to apical?

1. Transseptal
2. Alveolar crest
3. Horizontal
4. Oblique: principal
5. Apical
6. Inter-radicular


Describe the principal fibres of PDL

Embedded in cementum or in bone lining socket known as Sharpey's fibres
Attachment site smaller at cementum than alveolar bone
T1 (90%) and some T3 fibres arranged in bundles that provide elasticity to teeth


Describe the 2ndary fibres

Oxytalan, elastin
Randomly oriented between principal fibres
Can connect to bone or cementum, don't become Sharpey's fibres
Supportive role for principal fibres, blood vessels and nerve endings


What are the 5 main components of PDL GS?

1. Hyalironidate GAGs
2. Proteoglycans
3. Glycoproteins
4. Fibronectin
5. Tenascin


What are the 6 cell types in PDL?

1. Fibroblasts
2. Osteoblasts/clasts
3. Cementoblasts/clasts
4. Undifferentiated mesenchymal cells
5. Defence cells
6. Epithelial cells (Cell Rests of Malassez)


Described the innervation of the PDL

Sensory: nociception and mechanoreception
Autonomic: associated w/ periodontal blood supply
Enter PDL through root apex or from openings in alveolar wall
Myelinated at apex and unmyelinated coronally


What are the clinical implications of the PDL in terms of disease?

Gingivitis, periodontitis, periapical infection
Causes loss of PDL, deeper pocket formation
Inc. motility of tooth due to dec. tooth attachment

If remove diseased tissue or regenerate tissue allows PDL to regenerate