Cementum Flashcards
What is Cementum?
- Thin layer of calcified tissue covering radicular tissue
- Cervically (top of root) it’s 10-15μm in thickness
- Could exceed 600μm at root apex
- Adheres to dentine and to the periodontal ligament
- Capable of repair and regeneration
- Formed throughout life; allowing re-attachment of the periodontal ligament
- Layer of uncalcified precementum
What are the physical properties?
- Pale yellow in colour
- Dull surface
- Softer and more permeable than dentine
- Easily abraded cervically (at CEJ)
What’s the chemical composition of Cementum?
65% inorganic:
- Mainly hydroxyapatite
- Thin plate like apatite crystals
23% organic:
- Collagen type I
- Non-collagenous elements similar to bone (Sialoprotein & Osteopntin)
12% water by weight
What are the classifications of Cementum?
Presence or absence of cells:
+ Cellular cementum
+ Acellular cementum
Nature and origin of the organic matrix:
+ Extrinsic fibre cemen.
+ Intrinsic fibre cemen.
Mixed fibre cemen.
Combination of both: \+ Acellular extrinsic fibre cementum \+ Cellular intrinsic cementum \+ Mixed fibre cementum (cellular and acellular) \+ Afibrillar cementum
What’s Cellular cementum?
- Cementum containing cementocytes in lacunae within cementum matrix
What’s Acellular cementum?
- Cementum without any cells in its matrix
What’s Fibrillar cementum?
- Cementum with a matrix that contains well-defined fibrils of type I collagen
What’s Afibrillar cementum?
- Cementum that has a matrix devoid of detectable type I collagen fibrils - the matrix tends to have a fine, granular consistency
What’s Extrinsic fibre cementum?
- Cementum which contains primarily extrinsic fibres
- I.e Sharpey’s fibres that are continuous with the principle fibres of the periodontal ligament
- Since Sharpey’s fibres were originally produced by periodontal ligament fibroblasts, they are orientated perpendicularly to the cementum surface
- Play a major ole in tooth anchorage
What’s Intrinsic fibre cementum?
- Cementum which contains primarily intrinsic fibres
- Fibres produced by cementoblasts and that are orientated more or less parallel to the cementum surface
- Located primarily at sites undergoing repair, following surface resorption
- No role in tooth anchorage
Specific types of cementum: What’s Acellular, afibrillar cementum?
- Cementum is mostly composed of mineralised matrix, without detectable collagen fibrils or cementocytes
- Produced exclusively by cementoblasts
- Typically found as coronal cementum on human teeth
Specific types of cementum: What’s Acellular, extrinsic cementum?
- The cementum has a matrix with well defined, type I collagen fibrils
- Fibrils are part of the densely packed Sharpey’s fibres; that are continuous with the principle fibres of the periodontal ligament
- Due to being densely packed, the individual Sharpey’s fibres that form the bulk of the matrix may not by identifiable as individual fibres within the cementum layer
- Cementum is acellular, located in the cervical 2/3 of the root of human teeth
- Major role in tooth anchorage
Specific types of cementum: What’s Cellular, intrinsic fibre cementum?
- Contains cementocytes in a matrix composed almost exclusively of intrinsic fibre cementum
- Located almost exclusively at sites of cementum repair
- No role in tooth anchorage
- May be covered over by extrinsic or mixed fibre cementum; both of which provide new anchorage
Specific types of cementum: What’s Cellular, mixed fibre cementum?
- Found on apical 3rd of the root and in furcations
- Rate of cementum formation is more rapid compared to cervical region
- Mineralised, extrinsic collagen fibres (Sharpey’s) run a more irregular course than in acellular, extrinsic fibre cementum
- Intrinsic fibres are found interspersed among the etrinsic fibres of the cementum matrix; meaning individual Sharpey’s fibres are more readily identifiable than in extrinsic fibre cementum
- Cementoblasts are trapped in lacunae where they become cementocytes
Which variation of cementum is cellular and which is acellular?
- Primary cementum = acellular
- Secondary cementum = cellular
What’s the appearance of acellular cementum?
- Structureless
What causes the difference between cellular and acellular cementum?
- Formation rate of both tissues
What’s the orientation of the cementocytes canaliculi?
- Face the periodontal ligament - direction of nutrients
Are cementocytes active or inactive?
- No not in acellular cementum
- Low cytoplasmic/nuclear ratio
- Minute amounts of energy and protein sythesising organelles
- Deposited with an irregular rhythm resulting in INCREMENTAL LINES OF SALTER
What do the incremental lines mark?
- Differences in both mineralisation and in organic matrix composition
What are the 3 arrangements between cementum and enamel at the Cemento-Enamel Junction?
Pattern 1: cementum overlaps enamel (60%)
Pattern 2: Cementum and enamel meet at butt joint (30%)
Pattern 3: Cementum and enamel fail to meet and the dentine between them is exposed (10%)
ALL THESES PATTERNS MAY BE PRESENT IN A SINGLE TOOTH
At the Cenemto-dentinal junction; cementum acts as an intermediate layer between which 2 tissues?
Dentine and Periodontal ligament fibres
How do Periodontal ligaments attach to the cementum?
- Fibres in the Periodontal ligament run into the organic matrix of the precementum
- Mineralisation of the precementum leads to the incorporation of the fibres = SHARPEY’S FIBRES
What can cause cementum resorption and repair?
- Associated with trauma and pressure
- Via multinucleated odontoclasts
Can deficiencies in dentine be resolved by cementum?
YES
- Resorption in dentine can be filled by deposition of cementum
- A reversal line is visible; boundary where repair cementum is located against the Dentine
- Less mineralised and has smaller crystals compared to regular cementum
What are Cemenicles?
- Calcified masses within the cementum - attached or free
- Typically in the apical and middle thirds & furcation areas
