Cementum and PDL Flashcards
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
cementoblasts
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
Describe the Sharpey’s fibres of the PDL
Insertions of principal fibres into cementum and bone at each end are
What fibres are found in the PDL
- Collagen - mainly type 1 or 3
- Oxytalan fibres (small amounts)
- Elastin fibres
What is the function of oxytalan and elastin fibres
• Supportive role for the principle fibres, blood vessels and nerve endings
Name some cells found in the PDL
- Fibroblasts
- Osteoblasts (on alveolar bone)
- Osteoclasts
- Cementoblasts (on cementum!)
- Cementoclasts
- Undifferentiated mesenchymal cells
- Defence cells
- Epithelial cells (Cell Rests of Malassez)
What does the autonomic nervous system innervate in the PDL
Periodontal blood vessels
Where do the autonomic nerves enter the PDL from
The root apex or from openings in the alveolar wall
Are neurones myelinated or not in the PDL
Myelinated at apex and Non myelinated coronally
How does inflammation affect the PDL
- Inflammation causes loss of PDL and deeper pocket formation;
- Increasing tooth mobility loss of tooth attachment in severe disease
How does Orthodontic loading affect the PDL
• Tension - increased PDL space with increased connective tissue
(cells and fibres) and osteoid deposition
• Pressure – reduces PDL; increases resorption
What treatment can allow the PDL to regrow
Guided tissue regeneration – allows PDL to regrow and prevents gingival connective tissue from growing down
How does guided tissue regeneration work
- 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
