4. Four tissue supporting the tooth in the
jaw
◦ Cementum
◦ Periodontal ligament
◦ Alveolar bone
◦ Gingivae
Periodontium
5. Thin layer of calcified tissue covering the
root in the human teeth
Present in the crowns of some mammals
◦ Adaptation to herbivorous diet
One of four tissues supporting the tooth
(periodontium)
The least known of
◦ Periodontium tissues
◦ All mineralized tissues
Cementum
6. 1) It covers and protects the root dentin
(covers the opening of dentinal tubules)
2) It provides attachment of the periodontal
fibers
3) It reverses tooth resorption
Role of Cementum
7. Varies in thickness
◦ Thick @ apex (50-200 µm) &
inter-radicular regions
◦ Thin cervically (10-15 µm)
Contiguous with PDL
Firmly adherent with root
dentine
Highly responsive mineralized
tissue
◦ Maintenance of root integrity
◦ Maintenance of functional position
of tooth
◦ Tooth repair & regeneration
Cementum
8. Varies in thickness: thickest in the apex and
In the inter-radicular areas of multirooted
teeth, and thinnest in the cervical area
10 to 15 m in the cervical areas to
50 to 200 m (can exceed > 600 m) apically
9. Slowly-formed throughout life
Allowing continual reattachment of PDL
fibers
Cementum can be regarded as a
mineralized component of PDL
Precementum - a thin mineralized layer
on the surface of the cellular cementum
Similar to bone, however -
◦ Avascular & not innervated
◦ Less rapidly resorbed – orthodontics
Cementum
10. Cement-
enamel
junction
Pattern I
◦ Cementum overlaps enamel for a short distance
◦ Most predominant – 60% of sections
Pattern II
◦ Enamel meet cementum at butt joint
◦ Occurs in 30% of sections
Pattern III
◦ Enamel fails to meet cementum
◦ Dentine between them is exposed
◦ 10% of sections
11. Pale yellow
Softer than dentine
Permeability
◦ Varies with age and type of cementum
◦ Decreases with age
◦ Cellular is more permeable
◦ More permeable than dentine
Readily removed by abrasion after
gingival recession
Physical properties
12. Chemical properties
Inorganic Organic Water
By weight 65% 23% 12%
By volume 45% 33% 22%
Hydroxyapatite crystals similar to those in bone
More concentration of trace elements (F) at
surface
F levels higher in acellular
Collagenous organic matrix, primarily type I
Molecules involved in PDL fiber reattachment
&/or mineralization
◦ Bone sialoprotein, osteopontin & cementum-specific
elements
13. Cellular and Acellular Cementum
Acellular cementum: covers the root
adjacent to dentin whereas cellular
cementum is found in the apical area
Cellular: apical area and overlying
acellular cementum. Also common in
interradicular areas
Cementum is more cellular as the
thickness increases in order to maintain
Viability
The thin cervical layer requires no cells
to maintain viability as the fluids bathe
its surface
A: Acellular cementum (primary cementum)
B: Cellular Cementum (secondary cementum)
14. A: Acellular cementum
B: Hyaline layer of Hopwell-Smith
C: Granular layer of Tomes
D: Root dentin
Cellular: Has cells
Acellular: No cells and has no structure
Cellular cementum usually overlies acellular cementum
15. Acellular
Cellular
Variations also noted where acellular and cellular reverse in position
and also alternate
16. CEMENTUM
Canaliculus
GT
Lacuna of cementocyte
Dentin
Acellular cementum
Cellular cementum
Hyaline layer
(of Hopewell Smith)
Granular layer of tomes
Dentin with tubules
17. Cementoblast and cementocyte
Cementocytes in lacunae and the channels that their processes extend are
called the canaliculi
Cementoid: Young matrix that becomes secondarily mineralized
Cementum is deposited in increments similar to bone and dentin
18.
19. Are acellular and cellular cementum formed from two different
sources?
One theory is that the structural differences between acellular and cellular
cementum is related to the faster rate of matrix formation for cellular
cementum. Cementoblasts gets incorporated and embedded in the tissue
as cementocytes.
Different rates of cementum formation also reflected in more widely
spaced incremental lines in cellular cementum
20. Presence or absence of cells
◦ Cellular cementum
◦ Acellular cementum
Nature & origin of organic matrix
◦ Extrinsic fiber cementum
◦ Intrinsic fiber cementum
◦ Mixed fiber cementum
Combinations
Classification of cementum
21. Most common pattern- adjacent to
dentine
Structureless
Afibrillar cementum
◦ Exists between
Acellular cementum
Hyaline layer (of Hopewell-Smith)
◦ Mineralized GS
◦ Covers cervical enamel
◦ Results following loss of REE
Acellular cementum
23. Most common pattern
◦ Apical area
◦ Inter-radicular areas
◦ Overlying acellular dentine
Cementocytes
◦ Inactive
◦ In lacunae – appear dark in GS
◦ Processes present in canaliculi
◦ Processes connected via gap junctions
Cellular cementum
25. Organic fibrous framework, ground
substance, crystal type, development
Lacunae
Canaliculi
Cellular component
Incremental lines (also known as “resting”
lines; they are produced by continuous but
phasic, deposition of cementum)
Cementum simulates bone
27. Cementocytes vs.
osteocytes
Cementocytes
◦ More widely dispersed
◦ Randomly arranged
◦ Canaliculi oriented towards
PDL – nutrition
Osteocytes
◦ Osteon – Haversian system
◦ Organized cells
◦ Circumferential lamellae
28. More common pattern
◦ Acellular – cervically
◦ Acellular closer to dentine
◦ Cellular – apically
◦ Cellular covers acellular
Less common patterns
◦ Alternating
◦ Acellular overlies cellular
Relationship between acellular
& cellular cementum
29. Extrinsic fiber cementum
◦ Fibers derived from inserting Sharpy’s fibers of
PDL
Intrinsic fiber cementum
◦ Run parallel to root surface at right angles to
extrinsic fibers
◦ Fibers derived from cementoblasts
Extrinsic & intrinsic fiber
cementum
30. AEFC
Over cervical half – 2/3s of the root
Bulk of cementum in premolars
First formed cementum - acellular
Thickness of 15 µm
All collagen are from Sharpy’s fibers
Though GS from cementoblasts
Fibers well-mineralized
Acellular extrinsic fiber
cementum
31. CIFC
Fibers deposited by cementoblasts
Fibers run parallel to root surface
No role of tooth attachment
In apical 1/3 & inter-radicular areas
May be
◦ Temporary – extrinsic fibers gain reattachment
◦ Permanent – without attaching fibers
Cellular intrinsic fiber cementum
32. If cementum forms slowly in CIFC
Acellular intrinsic fiber cemetum
33. Alternating AEFC with CIFC
Root apex
Furcation areas
Cellular mixed stratified
cementum
34. Collagen fibers derived from
◦ Extrinsic fibers
◦ Intrinsic fibers
Intrinsic fibers run between the extrinsic
fibers
Two types – rate of formation
◦ Acellular mixed-fiber cementum
Well mineralized fibers
◦ Cellular mixed-fiber cementum
Less well mineralized fibers
Mixed-fiber cementum
35. Irregular rhythm of deposition
Not related to activity & quiescence
Related to
◦ Difference in the degree of mineralization
◦ Composition of organic matrix
Imprecise periodicity
Acellular – closer, thinner & regular lines
Cellular - farther apart, thicker & irregular
lines
Cemental incremental lines
36. Development of Cementum
Cementum formation occurs along the
entire tooth
Hertwig’s epithelial root sheath (HERS) –
Extension of the inner and outer dental
epithelium
HERS sends inductive signal to ectomesen-
chymal pulp cells to secrete predentin by
differentiating into odontoblasts
HERS becomes interrupted
Ectomesenchymal cells from the inner portion
of the dental follicle come in with predentin by
differentiating into cementoblasts
Cementoblasts lay down cementum
37. How cementoblasts get activated to lay down
cementum is not known
3 theories:
1. Infiltrating dental follicle cells receive reciprocal signal from
the dentin or the surrounding HERS cells and differentiate
into cementoblasts
2. HERS cells directly differentiate into cementoblasts
3. What are the function of epithelial cell rests of Malassez?
38. Derive from dental follicle
Transformation of epithelial cells
Cementoblasts
39. Incremental lines
Cementum is formed rhythmically and can
be seen as being composed of layers
40. Less susceptibility to resorption than bone
Localized resorption areas occur
Could be caused by microtrauma
May continue to root dentine
By multinucleated odontoclasts
Resorption filled by mineralized tissue
(resembles cellular cementum)
Reversal line
Resorption & repair of cementum
41. Wider uncalcified zone
Less mineralized
Smaller crystals
Calcific globules are present
Differences are related to
different speed of formation
Reparative cementum vs.
cementum
42. Cemental callus
◦ Root fracture
◦ No remodeling to original dimensions of the
root
Cementicles
◦ Free or attached pieces in PDL
◦ Microtrauma
◦ Apical & middle 1/3s of root
◦ Root furcation
Clinical considerations
43. Clinical considerations
Supra-eruption of teeth
Tooth wear
Local hypercementosis
◦ Reaction to PA inflammation
◦ Difficulty in extraction
◦ Paget’s disease – multiple teeth
with hypercementosis
Cementum narrowing root
canal and shifting the
junction between dental pulp
& PDL cervically
◦ Pulp removal in RCT up to that
point
44.
45. Dense fibrous connective tissue
Occupies the area between the root of the
tooth and the walls of the alveolar socket
Derived from the dental follicle
Continuous with
◦ the connective tissue of the gingiva above the
alveolar crest
◦ The dental pulp at the apical foramen
Periodontal ligament PDL
46. Variable in width,
average 0.2 mm
looks hourglass in shape
Reduced in unerupted &
non-functional teeth
Increased in teeth
subjected to heavy
occlusal stress
Narrows slightly with
Periodontal ligament
age
space
Narrower in permanent
teeth
47. Attachment
Has a role in tooth eruption
and support
Its cells repair the alveolar
bone & cementum
Neurological control of
mastication through its
Functions of PDL
mechanoreceptors
49. Collagen
◦ Type I (70% of fibers)
◦ Type III (20% of fibers)
Found in the periphery of Sharpy’s fibers attachment into
alveolar bone
◦ Small amounts of type V, VI as well as basement
membrane collagen IV & VII associated with the epithelial
rests
◦ Highest turnover of collagen is in PDL
Higher near apex
Even across the width of PDL
Rate could be related to the amount of occlusal stress
Oxytalan (in humans) or elastin
Fibers of PDL
◦ Attached into cementum
◦ May have a role in tooth support
50. Fibers exist as bundles
(principal fibers) running in
different orientations in
different regions
◦ Dentoalveolar crest fibers
◦ Horizontal fibers
◦ Oblique fibers
◦ Apical fibers
Principal fibers of PDL
◦ Interradicular fibers
From crest of interradicular septum
to furcation
52. Principal fibers
embedded into
cementum and
bone
More numerous
but smaller at
cemental end
Mineralized and
Sharpy’s fibers
unmineralized
parts
53. 60% of PDL by volume
Main components
◦ Hyaluronate GAGs
◦ Proteoglycans
◦ Glycoproteins
Functions of GS
◦ Ion and water binding & exchange
◦ Control of collagen fibrillogenesis & fiber
Ground substance of
orientation
◦ Tooth support & eruption - high tissue fluid
PDL pressure
54. Fibroblasts
◦ Fusiform cells with
many processes Cells of PDL
◦ Functions – secretion
and turnover of fibers
Regeneration of tooth
support apparatus
Adaptive responses to
mechanical loading
Cementoblasts
◦ Cement-forming cells
lining cemental surface
◦ Cuboidal cells
Osteoblasts
◦ Bone-forming cells
lining tooth socket
◦ Resemble
cementoblasts
55. Cementoclasts & osteoclasts
◦ Resorbing cells
◦ Howship’s lacunae
Epithelial rests cells
◦ Cuboidal cells that stain deeply
◦ Close to cemental surface
Defence cells
◦ Macrophages
◦ Mast cells
Cells of PDL
◦ Eosinophils
56. Separate from those entering pulp
Some from alveolar bone through foramina
Some from pulp through accessory canals
Major vessels lie between principal fiber
bundle close to alveolar bone
Capillary plexus around the tooth
Crevicular plexus of capillary loops
Veins do not follow arteries but drain into
intraalveolar venous networks
Blood vessels of PDL
57. Sensory
◦ Nociception
◦ Mechanoreception
Sensitivity to occlusal loads
Guidance to intercuspation
Autonomic
◦ Associated with blood vessels
Innervation of PDL
58. The alveolar process develops during the
eruption of teeth
Grows at a rapid rate at the free border
Proliferates at the alveolar crest
No distinct boundary exists between the
body of the maxilla or mandible and the
alveolar process
If teeth are lost the alveolar bone
disappears
Alveolar process
59. Development of bony crypt
Deciduous tooth &
permanent
successor initially
share crypt
Bone subsequently
forms to encase
permanent tooth
