Predominant type of collagen in cementum is:
a. Type I
b. Type II
c. Type III
d. Type IV
Ans a Type I (Type I is the predominant collagen type in Cementum)
Composition of cementum:
• Inorganic :45% to 50% hydroxyapatit
• Organic: 50% collagen and non-collagenous matrix protein
Type of Collagen in Cementum
Type I collagen:
• Predominant collagen of cementum
• Constitutes up to 90% of the organic components in cellular cementum
Type II collagen
• Less cross-linked collagen
• Present in higher concentrations during development and during repair and regeneration of mineralized
Type XII collagen
• Fibril-associated with interrupted triple helices that bind to type I collagen and non collagenous proteins
• Found in high concentrations in ligamentous tissues, including PDL
• Functions: Maintains a mature ligament that withstands the forces of occlusion.
Types V, VI, and XIV collagen:
Trace amounts (may be contaminants from the POL region produced by POL fibroblasts associated with the collagen fibres that are inserted into the cementum.)
Non-collagenous matrix proteins found in Cementum:
- Alkaline phosphatase
- Bone sialoprotein
- Dentin matrix protein
- Dentin sialoprotein
- Osteocalcin, osteonectin, osteopontin
- Proteoglycans, proteolipids, tenascin
- Enamel proteins
- Insulin-like growth factor
IMPORTANT POINTS ABOUT CEMENTUM
Two main types of Cementum are known: Cellular and Acellular cementum
|Acellular Cementum||Cellular Cementum|
|Covers the upper(cervical) portion of the root||Covers the lower (apical) portion of the root|
|Sharpey’s fibres mostly present||Sharpey’s fibres occupy the smallest portion|
|Slowly formed||Rapid deposition|
|Organized arrangement of collagen fibres||Irregular arrangement|
|Forms during root formation before tooth reaches occlusal plane||Forms after eruption of tooth once it reaches occlusal plane|
|Anchors the PDL fibre bundles to the tooth||Adaptive role formation is inresponse to the functional demands|
|Primary Cementum||Secondary Cementum|
Schroeder classification of Cementum is according to presence of fibres in cementum
• Mostly composed of mineralized matrix, without collagen fibrils or cementocytes.
• Produced by Cementoblasts
• Found typically as coronal cementum
Acellular, extrinsic fiber cementum
• Matrix of well-defined, type I collagen fibrils.
• Fibrils are part of densely packed Sharpey’s fibers (which are in continuation with the principal fibers of PDL
• Because of dense packing-the individual Sharpey’s fibers may no longer be identifiable as individual fibers.
• Located in the cervical 2/3rd of the root.
• Major role in tooth anchorage.
Cellular, intrinsic fiber cementum
• Has cementocytes in a matrix composed of intrinsic fiber cementum
• Located at sites of cementum repair.
• No part in tooth anchorage (When covered over by extrinsic or mixed fiber cementum may provide new anchorage
Cellular, mixed fiber cementum
- Found on the apical third of the root and in furcations
- Mineralized, extrinsi_c collagen fibers (Sharpey’s fibers) run a more irregular course
- Intrinsic fibers are found interspersed with extrinsic fibers (individual Sharpey’s fibers are readily identifiable)
- Cementoblasts are trapped in lacunae where they become cementocytes
Fibrillar cementum can further be classified by the origin of the matrix fibers :
- Extrinsic fiber cementum: Primarily has extrinsic fibers, i.e. Sharpey’s fibers that are continuous with the principal fibers of the PDL. These fibers are orientated, more or less perpendicularly, to the cementum surface and play a major role in tooth anchorage.
- Intrinsic fiber cementum: Primarily has intrinsic fibers, i.e. fibers produced by cementoblasts and that are orientated more or less parallel to the cementum surface. It is predominantly present at sites undergoing repair, following surface resorption. It plays no role in tooth anchorage.
- Mixed fiber cementum: Contains a mixture of extrinsic and intrinsic fiber cement
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