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
