Cementum Flashcards
(25 cards)
Cementum development has been
subdivided into
:
•Pre-functional stage: •Functional stage
Why there is a tight integration of cementum and dentin
These newly formed cementoblasts extend numerous tiny cytoplasmic processes into the loosely arranged not mineralized dentinal matrix. So, the initially secreted collagen fibrils of cementum matrix is positioned among those of the dentinal matrix, leading to an intimate integration of the two different fibril populations forming the dentino-cemental junction.
So dentin don’t start mineralisation until its completely covered by collagen of cementum matrix
Cementocytes extend tiny processess into dentin matrix
And interdigitation between fibers occur
Hyaline layer of hopewell Smith role
considered as an inductive influence for beginning of cementum formation.
The role of this layer is to seals off the dentinal tubules before the Hertwig’s epithelial root sheath disintegrates.
Hyaline layer of hopewell Smith other name
Intermediate cementum
Classification of cementum acc to development
Primary cementum:
it is that part of cementum that formed during the root formation and before completion. Secondary cementum:
It is that part of cementum that formed after completion of the root.
Acellular cementum
: ( A ) It is clear and structureless, covering the granular layer of Tome’s in the cervical two thirds of the root.
When cementum is thin, Sharpey’s fibers cross the entire thickness of the cementum,
with increased deposition of the cementum a larger part of the fibers is incorporated into the cementum. It is formed of the calcified ground substance plus the embedded portion of Sharpey’s fibers.
Sharpey’s fibers of P.L inserted into this type of cementum for the attachment of the root to the surrounding structure. In ground section , sharpey’s fibers appear dark due to its degeneration.
Cementocytes description
- pale nucleus
- granular cytoplasm
- processes anastomose with neighbouring cell processes
When degeneration happens in deeper cells
Few mitochondria Dilated golgi Vesicles Clumbing of cytoplasm Few organelles
Site of intermediate cementum
This layer does not resemble either dentin nor cementum. Present in the
apical two thirds of the roots of molars and premolars, rarely seen in incisors or deciduous teeth.
Additional info About intermediate cementum
It is believed that this layer represent areas where epith root sheath of Hertwig’s become entrapped in a rapidly deposited dentin or cementum matrix.
found as a continous layer or isolated areas. Hyaline and formed of a collection of protein entrapped by cellular or acellular cementum . it is considered a weak point in cementum.
- Afibrillar cementum
: Laminated electron dense reticular structure arise due to differentiation of cells from the dental sac which come in contact with enamel near the cervical line due to premature separation of the REE . These cells differentiate into cementoblast like cells to give this structure. It is free from collagen fibers
Thickness of cementum
: the thickness of cementum at the cervical area is about 20-50 µ and gradually increases in thickness till it reaches its maximum about 150-200 µ at the apex and at the bifurcation of the root.
Permeability of cementum
: it is permeable from both the dentin and the periodontal ligament side.
With age
The permeability of cementum decreases gradually. The permeability from the periodontal side is lost except in the most recent formed layer of cementum, while permeability from dentin side remains only in the apical region.
Chemical properties of cementum
: Inorganic substances (45-50%): Consist mainly of calcium phosphate in the form of hydroxy apatite crystals.
Organic matrix (55-50%): Consist primarily of collagens as, 90% type I, 5% type III and 5% type VII, V & XIV. Amino acids analysis obtained from cementum indicate close similarities to collagen of bone and dentin.
Collagen in incremental lines of salter
Less collagen and more ground substance than neighbouring cementum
Percentage of cej relations
10
30
60
Does 2ry cementum continues deposition throughout life and why
it maintain this attachment apparatus by continuous cementum deposition on the most superficial layers
Age changes of cementum
- rough due to …
- dep of cem at apex leading to..
- dentin resorption and repair by cem
- cem resorption and deposition with reversallines
-permeability - cementicles
-hyper cementosis
8- gingival recession
9- abrasion of cementum by tooth brush
10- increase hardness due to withdrawal of organic component and water and deposition of inorganic at the surface.
7-Cementicles
: calcified ovoid or rounded nodule found in the periodontal ligament, single or multiple near the cemental surface.
It could be free, attached or embedded in cementum. It appears by aging or at site of trauma.
Mechanism of formation: It is a nidus of epithelial cell that are composed of calcium phosphate and collagen with the same amount in cementum (45% to 50% inorganic and 50% to 55% organic).
Hypercementosis
:
It is an abnormal thickening of cementum.
It may affect one tooth or may be generalized in all teeth.
- It is either limited to a small area of the root or through the whole root length.
- It has two types: 1-Cementum hyperplasia:
It is overgrowth of the cementum in a nonfunctioning or embedded tooth. It is characterized by the absence of Sharpey’s fibers.2-Cementum hypertrophy
It is physiologic thickening of the cementum found in the good functioning teeth as a response to increase the function of the tooth to improve the functional quality through increase the root surface area and thus permitting more periodontal fibers to be attached to the
Difference between light and heavy ortho forces
*Cementum is more resistant to osteoclastic resorption than is bone. Because of this difference, dentists are able to move teeth through bone by exerting light pressure on teeth. Excessive pressure on the PDL leads to cellular damage and a resulting inflammatory response and root resorption. Cementoclasts (essentially osteoclasts that resorb cementum) have the same morphology as osteoclasts
What makes cementum more resistant to resorption than bone
The properties of cementum that give it greater resistance to resorption probably do not reside in its matrix (which is essentially similar to bone). The greater resistance may be due to the inaccessibility of the mineralized cementum surface, which is covered by tightly packed, non-mineralized collagen fibrils .
Plus more fluoride conc.
How to stain resting and reversal lines of cementum
Resting lines stains with Hx & Eosin while reversal lines detected immunohistochemically to detect osteopontin.
Change in reversal lines with age and their importance
Study of reversal lines provide clues to the site of repair, resorption, cessation and activation of cellular and acellular cementum. In general reversal lines increase in number with age reflecting growth and resorption history of the tooth.
Anatomical and functional repairs of cementum
Anatomical repair. The surface of the cementum has been previously resorbed by osteoclasts but has now been replaced by new cementum to the original surface of the root. B, Functional repair. The cementum has been resorbed by previous osteoclastic activity. The cementum has not filled in this defect, but the periodontal ligament fibers have reattached to the newly formed cementum surface and are now functional.
