Cementum Flashcards
What is cementum
Mineralised connective tissue lining the root of the tooth, helping to attach the tooth to the alveolar bone lining the tooth socket
What is the role of cementum
To maintain the integrity of the tooth and help to maintain the tooth in its functional position
How is cementum formed
Slowly but continuously, allowing for continuous reattachment of the PDL fibres
What are the similarities between cementum and the alveolar bone + dentine
- Both contain hydroxyapatite + collagen type 1
- Structure is similar to compact bone
- Both composed of cells and + mineralised extracellular matrix
What are the differences between cementum and the alveolar bone + dentine
- Cementum lacks extensive vascular, neural and cellular elements
- Cementum is less readily absorbed
- Cementum’s capacity for repair is more limited
- Cementum is slightly softer than dentine
What is cementum’s organic matrix mainly composed of
- Collagen Type I
- Collagen Type III is also found in small amounts during tissue development and repair
What are different classification systems for cementum
- Presence/absence of cells (cellular or acellular cementum)
- Origin of collagen fibres within its matrix (intrinsic, extrinsic and mixed fibre cementum)
Where is cellular and acellular cementum found
- Thin layer of acellular cementum covers most of the root surface
- Cellular cementum is found mainly in the apical third, overlying the acellular cementum
What type of cementum is known as primary cementum
Acellular cementum (formed first)
What type of cementum is known as secondary cementum
Cellular cementum (formed second)
What is the main differences between cellular cementum and acellular cementum
Cellular cementum contains cementocytes (cementoblasts), acellular cementum does not
How is the arrangement of cementocytes different to that of osteocytes in the alveolar bone
- They’re widely dispersed
- More randomly arranged
- Canaliculi are mostly orientated towards the PDL
What are intrinsic fibres
Collagen fibres found in cementum that have been produced by cementoblasts
What are extrinsic fibres
Collagen fibres inserted from the PDL principal fibres
Where is acellular extrinsic fibre cementum found?
What does acellular extrinsic fibre cementum contain?
What’s the role of acellular extrinsic fibre cementum?
(AEFC)
- Found in the cervical two-thirds of the root
- Contains bundles of Sharpey’s fibres inserted into primary cementum
- Role = Tooth attachment
Where is cellular intrinsic fibre cementum found?
What does cellular intrinsic fibre cementum contain?
Whats the role of cellular intrinsic fibre cementum?
(CIFC)
- Found in the apical third of the root + interradicular areas
- Contains only intrinsic fibres of secondary cementum
- Role = repair in root surface
Where is cellular mixed stratified cementum found?
What is cellular mixed stratified cementum?
(CMSC)
- Close to the root apex
- AEFC and CIFC are present in alternating layers
Where can cellular mixed fibre cementum be found occasionally?
Where cellular intrinsic cementum gives attachment to some intrinsic fibres arising from the PDL
Where are cementoblasts found
At the surface of the forming cementum
What are collagen fibrils that are embedded in the acellular cementum formed by
PDL fibrils
What does mineralisation of precementum incorperate
Extrinsic fibres as Sharpey’s fibres
What are sharpey’s fibres formed by
Periodontal fibroblasts
Where are Sharpey’s fibres abundant
Acellular cementum
Where are cementocytes found
Cellular cementum
When do cementocytes become relatively inactive
Once they’re embedded within the cementum matrix
Why does cementum have unevenly spaced lines
The cementum is deposited in an irregular rhythm
What are incremental lines like in acellular cementum
Close together, thin and even
What are incremental lines like in cellular cementum
Further apart, thicker and more irregular
What are the 3 different types of cemento-enamel junction (CEJ)
- Cementum overlaps the enamel
- Cementum and enamel meet as a butt joint
- Cementum and enamel fail to meet and dentine between them is exposed
What does damage or a loss of the reduced enamel epithelium enable the cells of the dental follicle to do
Enables cells of the dental follicle to come into contact with the enamel surface where they’re induced to form cementoblasts
What layer ‘anchors’ the PDL fibres to the dentine
The ‘intermediate’ layer that exists between cementum and dentine
What is the relationship between the intermediate layer and cementogenesis
The intermediate layer may have an important role as a precursor for cementogenesis - repairs damage at the root surface
What can masticatory forces cause and lead to
- Can cause microtrauma to the root surfaces
- Can lead to localised areas of resorption
What is resorption carried out by
- Multinucleated odontoclasts
- May continue into the root dentine
What may resorption deficiencies be filled by
Repair cementum
What may the reversal line be seen doing
May be seen separating the repair tissue from the normal underlying dental tissues
Why is cementum much more resistant to reabsorption than dentine
- Non-mineralised layer of precementum acting as a barrier
- Cementum’s surface is covered by a tightly packed collagen so the mineralised surface is inaccessible - Unmineralised surface layer of collagen protects against the action of odontoclasts
- Cementoblasts lining the root surface don’t move away from cementum, so do not expose the surface to resorptive cells
How does cementum change with age
- Smooth root surface becomes irregular
- Accumulative damage can occur due to cementum
- Cementum is insensitive to pain without nerves, and is readily removed by abrasion which then exposes sensitive root dentine
- Cementum loss following root exposure can’t undergo physiological repair or replacement
