An overveiw on the histology of cementum

1. Periodontium
Periodontium consists of
 Cementum
 Periodontal ligament
 Bone lining the alveolus
Together they form a joint called
Gomphosis

2. Cementum
 Hard, avascular connective tissue that
covers the roots of teeth
 Classified into
◦ Acellular cementum
◦ Cellular cementum
 Development divided into
◦ Prefunctional stage
◦ Functional stage
◦ At cervical margin it is 50µm thick,
progresses apicallly to 200µm.

4. Composition of Cementum
Similar to bone
 45-50% inorganic (hyroxyapatite)
 50% organic (Collagens & non-
collagenous proteins)

5. Organic components
 90% is type 1 collagen
 Other collagens include Type III, V, VI, XII &
XIV
 Type XII is found in ligamentous tissues and
PDL
 Non-collagenous proteins:
◦ Alkaline phosphatase
◦ Bone sialoprotein & Dentin sialoprotein
◦ Dentin matrix protein 1
◦ Fibronectin
◦ Osteocalcin, Osteonectin & Osteopontin
◦ Proteoglycans & Proteolipids
◦ Tenascin
◦ Growth factors including Insulin like growth
factor, platelet derived growth factor

6. Cementum formation
 Cementum formation initiates at the
advancing root edge
 HERS sends inductive signals to ecto-
mesenchymal pulp cells >
odontoblasts > predentin > interruption
of HERS > contact of predentin with
dental follicle > differentiate into
cementoblasts
 Another theory says HERS
differentiate into cementoblasts

8. Fate of HERS
 Some cells undergo apoptosis
 Some fragments form discrete masses
surrounded by basal lamina, these are
called Epithelial rests of Malassez
 Have a role in maintenance &
regeneration of PDL
 Some odontogenic tumours are
believed to arise from these rests
 If they remain attached to the forming
root surface, they form enamell-pearls

10. Factors regulating
cementogenesis
 Growth factors
 Adhesion molecules
 Epithelial/Enamel proteins
 Collagens
 Gla Proteins
 Transcription factors
 Signalling Molecules

11. Growth factors
 Transforming growth factor ß superfamily
◦ Promotes cell differentiation &
cementogenesis during development &
regeneration
 Platelet & Insulin derived growth factor
◦ Promote cementum formation by altering cell
cycle activities
 Fibroblast growth factor
◦ Promote formation & regeneration of PDL
tissue by inducing cell proliferation &
vasculogenesis

12. Adhesion molecules
 Bone Sialoprotein/Osteopontin
◦ Promote adhesion of cells to newly
forming root
◦ BSP promotes mineralization &
osteopontin regulates the extent of crystal
growth

13. Others
Epithelial/Enamel Proteins:
Periodontal repair & regeneration
Collagens
Type I & III have a role in development &
regeneration of PDL
Type XII maintains the PDL space
Gla Proteins (∂-carboxyglutamic acid)
Prevent ectopic calcifications & preserve
PDL width
Osteocalcin regulates crystal growth &
extent of mineralization

14. Others
Transcription factors
i. Runt-related transcription factor
2(Runx-2)
ii. Osterix
Believed to induce cementoblast
differentiation
Signaling molecules
Osteoprotegrin & RANKL are produced by
osteoblasts & PDL fibroblasts, they
mediate bone & root resorption by
osteoclasts

15. Cementum Types
 Acellular
◦ Acellular extrinsic fiber cementum
◦ Acellular afibrillar cementum
 Cellular Intrinsic Fiber Cementum

16. Acellular Extrinsic Fiber
Cementum
(Primary Cementum)
Formation:
 Principle tissue of attachment, covers
2/3rd of tissue or more
 Cementoblasts align along the newly
formed unmineralized predentin (mantle
dentin)
 These cementoblasts extend their cell
processes into this predentin & deposit
collagen fibrils within it
 Mineralization of mantle dentins starts
from inside out & spreads across the
cementum

18. Formation
 Initial layer of short fiber fringe > cells
on root surface move away to deposit
another 15-20µm of cementum
(lengthens & thickens the initial FF
plus non-collagenous proteins) > PDL
fibroblasts deposit collagen fibrils that
become stitched to the FF >
cementoblasts secrete only non-
collagenous proteins

19. AEFC
 Cells remain on the surface therefore
called acellular cementum
 Light microscope shows two sets of
striations
◦ Incremental deposition running parallel to
root surface
◦ Inserted PDL collagen fiber bundles as short
striations perpendicular to root surface
 No cementoid is present
 Innermost layer is less mineralized &
outer layer shows alternative bands of
more & less mineralization

21. Cellular Intrinsic Fiber
Cementum
(Secondary root is formed, a rapidly
 After half the cementum)
forming less mineralized variety of
cementum is laid called CIFC
 Fount in the apical third
 Confined to the apical & inter-radicular
regions of the tooth (usually absent in
incisors & canines)
 Because of rapid cementum deposition,
an un-mineralized layer of cementum is
present called cementoid & cells become
entrapped in the extra-cellular matrix to
form cementocytes

22. Cementocytes
 Similar to osteocytes
as they reside in
lacunae but their
processes within the
canaliculi do not
form syncytium to
the root surface
 Nourishment occurs
by diffusion so the
cementocytes in
deeper layers may
not be vital

23. CIFC
 After a rapid initial haphazard deposition,
it slows down & becomes more
directional
 In this phase cells do not become
entrapped so may lead to acellular
cementum
 Collagen laid by cementocytes is parallel
to the root surface
 After the PDL fibers are incorporated into
the cementum, they become partially
mineralized > Cellular mixed fiber

25. How to differentiate from
AEFC
 On light microscope
◦ Cementocytes within lacunae
◦ Laminated structure
◦ Cementoid on its surface

28. Cementocytes

29. How to differentiate EF & IF
 Intrinsic fibers are fine, paralled to root
surface & uniformly mineralized
 Extrinsic fibers are larger, haphazard,
mineralized variably & run
perpendicular to the root surface

30. Acellular Afibrillar Cementum
 Lacks collagen
 No cementocytes
 No role in tooth attachment
 Appears uniform under light
microscope
 Deposited over dentin & enamel near
CEJ

31. Cemento-enamel junction
 Three types of
joints are seen
◦ Cementum overlaps
enamel (majority)
◦ Butt joint
◦ Gap between
cementum & enamel
leaving the dentin
exposed

33. Alveolar Process
 Bone of the jaws containing sockets
for the teeth
 Consists of
◦ Cortical plates (buccal & lingual)
◦ Spongiosa
◦ Alveolar bone (lining the socket)
 Cortical plate & alveolar bone meet at
alveolar crest which is 1.5-2mm below
CEJ

34. Alveolar bone
 Inner & outer components
 Contains many foramina b/c of which
is also called cribriform plate.
 Because of increased radio-opacity
also called lamina dura
 Inner alveolar bone incorporates PDL
bundle fibers, therefore, also called
bundle bone
 Bundle bone may be apposed on a
lamellar bone or not

36. Cortical plates
 Surface layer of lamellar bone with
haversian systems
 Central part of spongy bone
 Cortical plates are thinner in maxilla,
thickest on buccal aspect of mandibular
molars
 Spongy bone has yellow marrow rich in
adipose cells, rarely has hematopoietic
marrow
 Trabecular bone is absent in anterior
teeth where cortical & alveolar bones
fuse

38. Cementum
Canaliculus
GT
Lacuna of cementocyte
Dentin
Acellular cementum
Cellular cementum
Hyaline layer
(of Hopewell Smith)
Granular layer of tomes
Dentin with tubules

39. Aging
Smooth surface becomes
irregular due to
calcification of ligament
fiber bundles where they
are attached to cementum
Continues deposition of
cementum occurs with
age in the apical area.
[Good: maintains tooth
length; bad:
obstructs the foramen
3. Resorption of root dentin
occurs with aging which is
covered by cemental
repair

40. Cemental repair
 Protective function of
cementoblasts after
resorption of root dentin or
cementum
 Resorption of dentin and
cementum due to trauma
(traumatic occlusion, tooth
movement, hypereruption)
 Loss of cementum
accompanied by loss of
attachment
 Following reparative
cementum deposition
attachment is restored

41. Clinical Correlation
Cellular cementum is similar to bone but has no nerves.
Therefore it is non-sensitive to pain. Scaling produces
no pain, but if cementum is removed, dentin is exposed
causes sensitivity
Cementum is resistant to resorption especially in younger
Patients. Thus, orthodontic tooth movement causes alveolar
one resorption and not tooth root loss

42. The End