2. ■ Definition:
Periodontium is the attachment system of the tooth to the jaw.
■ Members:
Two Hard Tissues: Cementum and Alveolar Bone.
Two soft Tissues: Gingiva.and Periodontal ligament.
Periodontium
3. Definition:
■ Cementum is a hard calcified tissue covering the anatomical Root.
■ Cementum begin from Cemento-enamel junction ( cervical line ) to the
root apex.
■ Cementum forming an attachment media for periodontal ligament fibers
binding the tooth to the surrounding alveolar bone.
■ Cementum is a member of the periodontium.
4. • Colour:
Cementum is a light yellowish in color.
• Hardness:
Cementum is less harder than both enamel & dentin.
• Permeability:
Cementum is permeable from both:
1- Dentin side.
2- Periodontal ligament side.
Cellular cementum is more permeable than acellular cementum.
• Vascularity:
Cementum is an avascular tissue ( not contain blood vessels)
and so, not perform remodeling.
• Thickness:
1.Near cervical line 20 – 50 µm.
2.Near root apex 150 – 200 µm.
Physical Properties of Cementum
6. Chemical Composition of cementum
1- Inorganic materials (45-50 % ):
• Calcium and phosphorous in the form of Hydroxy-apatite crystals.
• The unit formula of the crystal is ]3Ca3(PO4)2.Ca(OH)2[
• Cementum Contain a Higher Level Of Fluoride Than Any Hard Tissue
Allover The Body.
2- Organic materials and water (50-55 %):
A.Collagen Fibers: Type I and small amount of type III.
B.Ground Substance: glycogen, protein, lipid, phospho-protein.
7. Classification of cementum
I- Based on cell presentation inside cementum:
1. Cellular cementum: Cementum containing cell (Cementocyte) within it.
2. Acellular cementum: no cells found within it.
II- Based on fibers presentation inside cementum:
1. Intrinsic fibers cementum: containing fibers formed from cementoblast
cells.
2. Extrinsic fibers cementum: containing fibers formed from fibroblast cells.
3. mixed fibers cementum.
4. Afibrillar cementum.
9. Acellular Cementum
✴ Definition: It is a type of cementum not
contain cells within it.
✴ Thickness: 20-50 µm.
✴ Site: Covers the coronal half of the root.
✴ Lining: Acellular cementum is Covered
from outside by a layer of cementoid
tissue lined by cementoblast cells.
✴ Attachment to PDL: Sharpey’s fibers
space can be seen in it .
✴ Alternating layers of acellular and cellular DentinCementum
10. Cellular Cementum
✴ Definition: It is a type of cementum
that contain cells within it.
✴ Thickness: 150-200 µm.
✴ Site: Covers the apical half of the root.
✴ Lining: Cellular cementum is Covered
from outside by a layer of cementoid
tissue lined by cementoblast cells.
✴ Attachment to PDL: Sharpey’s fibers
space can be seen in it.
DentinCementum
11. Afibrillar cementum
Definition Of Afibrillar Cementum:
It is a part of cementum found on the enamel at cemento-enamel junction of
overlaps type that constitute 60%.
Site: Cervical line.
How to occur?
• The crown is covered by reduced enamel epithelium that protect it until eruption
of the tooth.
• Any part of enamel become exposed to connective tissue, it may be resorbed or
become covered by cementum.
• Shrinking or injury of reduced enamel epithelium at cervical line leads to
exposure of enamel at that area and formation of cementum on the enamel.
• This type of cementum not contain fibers and termed afibrillar cementum.
12. INCREMENTAL LINES OF SALTER
✴ Definition:
It is a rythmic deposition of cementum
into layers.
✴ Structure:
Incremental line of salters are a hyper-
mineralized area within cementum.
13. 30% cementum meets
the enamel in a sharp
line.
10% cementum and
enamel doesn’t meet
(area of dentin not
covered by cementum).
60% cementum
overlaps Enamel
(afibrillar cementum)
Cemento-Enamel Junction
16. Cementoid layer
Definition:
it is the last formed layer of cementum facing toward PDL.
Site:
Facing the periodontal ligament and covering the cementum.
Structure:
1. Organic matrix without calcification.
When cementoid layer become calcified another cementoid layer will be formed.
LM.:
Cementoid layer is covered at PDL by cementoblast cells.
17. Cementoblast cells
Definition:
Cementoblasts are connective tissue cells responsible for formation of cementum
originated from dental follicle.
Site:
Cementoblasts are found within the periodontal ligament covering the cementoid
layer.
Functions:
1. Formation and secretion of collagen fibers of cementum.
2. Calcification of cementum.
LM.:
Shape: Branched oval cells.
Nucleus: Nucleus is rounded and centrally located.
Cytoplasm: Basophilic cytoplasm.
EM.:
✦ RER., Mitochondria, GC, secretory vesicles.
✦ Open faced nucleus.
✦ Active cells more seen in younger tissue.
18. Cementocyte cells
Definition, Site, and origin:
Cementocytes are connective tissue cells found within the cementum originated as
cementoblast enters within cementum matrix during cementogenesis.
Function:
1. Maintenance of cementum Calcification.
LM.:
Shape: Large Branched cells with long cytoplasmic processes.
Nucleus: Nucleus is rounded and centrally located.
Cytoplasm: Not active cells.
Branches: Most of cytoplasmic branches of osteocytes are directed toward PDL (
for nutrition).
Lacuna: Osteocytes are found within cementum within lacuna and their branches
found within canaliculi.
20. Age changes of cementum
1) Decrease permeability.
2) Hypercementosis: It is an abnormal thickening of cementum:
• May be diffuse or circumscribed.
• May affect all teeth or a single tooth, or even affect only Parts
of one tooth.
A. If the overgrowth occurs in functional teeth and improves
the functional qualities of the cementum, it is termed
cementum hypertrophy.
B. If the overgrowth occurs in nonfunctional teeth, it is termed
cementum hyperplasia.
