cementum /certified fixed orthodontic courses by Indian dental academy

CEMENTUM

INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education
www.indiandentalacademy.com


CONTENTS
• 1. Introduction.
• 2. Physical characteristics.
• 3. Chemical composition.
• 4. Cementogenesis.
• 5. Structure & Classification.
• 6. Cementodentinal Junction & Intermediate Cementum.
• 7. Cementoenamel Junction.
• 8. Function.
• 9. Hypercementosis.
• 10. Clinical Considerations.
• 11. Conclusion.


INTRODUCTION
• Definition:
• Cementum is a hard, avascular, mineralized
connective tissue covering the anatomic roots of human
teeth.
• It was first demonstrated microscopically in 1835
by two pupils of purkinje.
• It begins at the cervical portion of the tooth at the
Cementoenamel Junction and continues to the apex.
• Cementum furnishes a medium for the
attachment of collagen fibers that binds the tooth to the
surrounding structures.


PHYSICAL
CHARACTERISTICS
• Cementum is light yellow in colour & can be
distinguished from enamel by its lack of luster &
its darker hue.
• It exhibits a lighter colour than dentin & is
also softer and more permeable.
• The relative softness of cementum
makes it susceptible to abrasion when ever the
cemental surface is exposed to the oral
environment such as by gingival recession.


3. CHEMICAL COMPOSITION
• On a dry weight basis, cementum from fully formal
permanent teeth contains about 45% to 50% inorganic
substances and 50% to 55% organic material and water.
• The inorganic portion consists mainly of
calcium and phosphate in the form of hydroxyapatite.
• Cementum has the highest fluoride content
of all the mineralized tissues.
• The organic portion of cementum consists
primarily of type I collagen and protein polysaccharides
(proteoglycans).
•


• Other collagans associated with cementum include
typeIII, a less cross-linked collagen found in high
concentrations during development and during repair
and regeneration of mineralized tissues.
• Type XII collagen, a fibril-associated collagen with
interrupted triple helixes that binds to type I collagen and
also to noncollagenous proteins.
• Type XII collagen is found in high concentrations in
ligamentous tissues including the PDL, and may function
in maintaining a mature ligament that can withstand the
forces of occlusion.


Noncollagenous proteins identified in cementum also are

associated with bone and include the following:

• Alkaline phosphatase
• Bone sialoprotein
• Fibronectin
• Osteocalcin
• Osteonectin
• Osteopontin
• Proteoglycans
• Proteolipids
• Vitronectin & several growth factors.
• Bone sialoprotein and osteocalcin appear to be
specific to mineralized tissues, except for enamel.


• Two apparently unique cementum
molecules, an adhesion molecule
(cementum attachment protein) and a
growth factor (insulin – like growth factor)
have been identified, but further studies
are warranted to confirm the existence
and function of these molecules.


4. CEMENTOGENESIS
• Although cementum formation takes place along the
entire root, its initiation is limited to the advancing root
edge.
• At this site, Hertwig’s epithelial root sheath (HERS),
which derives from the coronoapical extension of the
inner and outer dental epithelium, is believed to send an
inductive message, possibly by secreting some enamel
proteins, to the facing ectomesenchymal pulp cells.
• These cells differentiate into odontoblasts and
produce a layer of predentin.


• Soon after, HERS
becomes interrupted and
ectomesenchymal cells
from the inner portion of
the dental follicle then
can come in contact with
the predentin.
• The next series of
events results in
formation of cementum
on the root surface.


CURRENT THEORIES INCLUDES
THE FOLLOWING:
• Infiltrating dental follicle cells receive a reciprocal
inductive signal from the dentin or the surrounding
HERS cells and differentiate into cementoblasts.
• HERS cells transform into cementoblasts, other reports
indicate that during tooth root maturation, cells within
the HERS undergo apoptosis, and some cells from the
fragmentad root sheath form discrete masses
surrounded by a basement membrane, known as
epithelial cell rests of Malassez, which persist in the
mature PDL.


CEMENTOBLASTS
• Soon after Hertwig’s sheath breaks up, undifferentiated
mesenchymal cells from adjacent connective tissue
differentiate into cementoblasts.
• Cementoblasts synthesize collagen and protein
polysaccharides (proteoglycans), which make up the
organic matrix of cementum.
• Cementoblasts have numerous mitochondria, a well
formed Golgi apparatus, and large amounts of granular
endoplasmic reticulum, & these ultrastructural features
can be observed in other cells actively producing
proteins and polysaccharides.


• After some cementum matrix has been laid down, its
mineralization begins.
• The uncalcified matrix is called cementoid.
• Mineralization of cementoid is a highly ordered event
and not the random precipitation of ions into an organic
matrix.
• Under normal conditions growth of cementum is a
rhythmic process, and as a new layer of cementoid is
formed, the old one calcifies.
• The cementoid tissue is lined by cementoblasts.


• Connective tissue fibers from
the PDL pass between the
cementoblasts into the
cementum.
• These fibers are
embedded in the cementum
and serve to attach the tooth to
surrounding bone.
• These embedded
portions of collagen fibrils that
pass well into the cementum
are known as Sharpey’s fibers.


5. STRUCTURE
• With light microscope two kinds of cementum can be
differentiated:
• Acellular & Cellular.
• In Acellular cementum, some layers of cementum do not
incorporate cells, spiderlike cementocytes in their
lecumae.
• It may cover the root dentin from the CEJ to the apex but
is often missing on the apical third of the root.
• In cellular cementum, cementocytes are present in their
lacunae and they are present in the apical third of the
root.


THICKNESS OF CEMENTUM
• Cementum is thinnest at the cementoenamel
junction (20 to 50 µm) and thickest toward the
apex (150 to 200 µm).
• The cells incorporated into cellular cementum,
cementocytes, are similar to osteocytes.
• They lie in spaces designated as lacunae.
• A typical cementocyte has numerous cell
• Processes (or) canaliculi radiating from its cell
body.


• These processes may branch,
and they frequently
anastomose with those of a
neighbouring cell.
• Most of the processes are
directed toward the periodontal
surface of the cementum.
• The cytoplasm of
cementocytes in deeper layers
of cementum contains few
organelles, the endoplasmic
reticulum appears dilated, and
mitochondria are sparse.


• These characteristics indicate that cementocytes are
either degenerating (or) are marginally active cells.
• When cementum remains relatively thin, sharpey’s fibers
cross the entire thickness of the cementum.
• The attachment proper is confined to the most superficial
or recently formed layer of cementum.
• This would seem to indicate that the thickness of
cementum does not enhance functional efficiency by
increasing the strength of attachment of the individual
fibers.


CLASSIFICATION
• Cementum is classified according to three
factors:
• time of formation (primary or secondary)
• the presence (or) absence of cells within its
matrix (acellular and cellular) and
• the origin of the collagenous fibers of the matrix
(intrinsic fibers resulting from cementoblast
activity (or) extrinsic fibers resulting from the
incorporation of periodontal ligament fibers.)


Accordingly, the following types of
cementum are described:
• Accordingly, the following types of cementum
are described:
• Primary acellular intrinsic fiber cementum
• Primary acellular extrinsic fiber cementum
• Secondary cellular intrinsic fiber cementum
• Secondary cellular mixed fiber cementum
• Acellular afibrillar cementum.
• Two other types of cementum are named
depending on location and patterning, namely,
intermediate and mixed stratified cementum.


TABLE SHOWING CLASSIFICATION

TYPE ORIGIN OF FIBERS LOCATION FUNCTION
ACELLULAR EXTRINSIC FROM CERVICAL ANCHORAGE
(PRIMARY) MARGIN TO APICAL
THIRD
CELLULAR INTRINSIC MIDDLE TO APICAL ADAPTATION AND
(SECONDARY) THIRD AND REPAIR
FURCATIONS
MIXED INTRINSIC AND APICAL PORTIONA ADAPTATION
(ALTERNATING EXTRINSIC ND FURCATIONS
LAYERS OF
ACELLULAR AND
CELLULAR
ACELLULAR - SPURS AND NO KNOWN
AFIBRILLAR PATCHES OVER FUNCTION
ENAMEL AND DENTIN
ALONG THE CEJ


6. CEMENTODENTINAL
JUNCTION
• The dentin surface upon which cementum is
deposited is relatively smooth in permanent
teeth.
• The cementodentinal junction in deciduous
teeth, however, is sometimes scalloped.
• The attachment of cementum to dentin either
case is quite firm although the nature of this
attachment is not fully understood.


INTERMEDIATE CEMENTUM

• Intermediate cementum (IC) is described
as a highly calcified amorphous layer
found at the cementodentinal junction in
mammalian roots.
• Intermediate cementum was first
described in 1878 by Bodecker as the
“interzonal layer” between dentin and
cementum.

• In 1920 Hopewell-Smith described a thin
homogeneous layer devoid of any identifiable
histologic elements between the granular layer
of Tomes and the internal acellular layer of
cementum.
• He speculated that this layer acted as a barrier
to the external passage of medicaments placed
in the root canal in the treatment of pulpless
teeth.


• Bencze in 1927 is credited with the first
use of the term “intermediate cementum”
(he actually called it the “intermediary
layer of cementum”) in his description of
an ill-defined area between cementum and
dentin that had microscopic characteristics
unlike either tissue.


– The cells of the root sheath have a further
function:- they are involved in the formation of
a structureless highly mineralized layer some
10 µm thick on the surface of the root dentin.
– This layer has variously been described as
dentin (the hyaline layer of Hopewell – Smith)
and as intermediate Cementum, but a study of
its development suggests that it is neither and
instead may be a form of enamel.


– As the large collagen fibers of mantle dentin form,
they are deposited slightly away from the basement
membrane supporting the root sheath , leaving a gap
filled with ground substance and a very fine fibrillar
material.
– The basement membrane supporting the root sheeth
breaks up.
– The root sheath cells develop profiles of Rough
endoplasmic reticulum and actively secrete a distinct
class of enamel proteins closely related to the
amelogenin family into this gap.


– The mineralisation of
mantle dentin does not
involve this layer, which
mineralizes both later and
separately, largely because
of its distinct matrix.
– Thus the dentin of the root
surface is covered by an
epithelial product of the
root sheath cells that is
more mineralized than
other dentin.


– It has been proposed that its function is to ‘cement’
cementum to the dentin as well as provide the initial
attachment of ligament fibrils to the tooth.
– Other functions are i) a permeability barrier between
cementum and dentin (i.e.. between the external root
surface and the inernal [pulpal] root surface), ii) a
precursor for cementogenesis in root development,
and iii) a precursor for cementogenesis in would
healing.


– In studies of ligament repair new cementum may be
deposited on denuded dentin, but in histologic section
there is always an artifactual split between the newly
deposited cementum, and the dentin, suggesting a
week union between these two tissues in the absence
of this hyaline layer.
– Because it seems to have a cementation function, is
of epithelial origin, and lies between the dentin and
primary cementum, the term ‘intermediate epithelial
cement layer’ is also proposed.


7. CEMENTOENAMEL
JUNCTION
• The relation between cementum and enamel at
the cervical region of teeth is variable.
• In approximately 30% of all teeth, cementum
meets the cervical end of enamel in a relatively
sharp line.
• In about 10% of the teeth, enamel & cementum
do not meet.
• Presumably this occurs when enamel epithelium
in the cervical portion of the root is delayed in its
separation from dentin.


• In such cases there is no cementoenamel
Junction. Instead a zone of the root is devoid of
cementum and is, for a time, covered by
reduced enamel epithelium.
• In approximately 60% of the teeth , cementum
overlaps the cervical end of enamel for a short
distance.
• This occurs when the enamel epithelium
degenerates at its cervical termination,
permitting connective tissue to come in direct
contact with the enamel surface.


8. FUNCTIONS

• The primary function of cementum is to furnish
a medium for the attachment of collagen fibers
that bind the tooth to alveolar bone.
• This is demonstrated in some cases of
hypophosphatasia, a rare heredity disease in
which loosening and premature loss of anterior
deciduous teeth occurs.
• The exfoliated teeth are characterized by an
almost total absence of cemetum.


• Cementum serves as the major reparative tissue
for root surfaces.
• Damage to roots such as fractures and
resorptions can be repaired by the deposition of
new cementum.
• Cementum can also be viewed as the tissue that
makes functional adaptation of teeth possible.
• For example, deposition of cementum in an
apical area can compensate for loss of tooth
substance from occlusal wear.


9. HYPERCEMENTOSIS

• Hypercementosis is an abnormal
thickening of cemetum.
• It may be diffuse or circumscribed.
• Etiology:
• accelerated elongation of a tooth
• inflammation about a tooth
• tooth repair and
• osteitis deformans (or) paget’s disease of bone.


• If the overgrowth
improves the functional
qualities of the
cementum, it is termed
Cementum hypertrophy
• If the overgrowth occurs
in non-functional teeth
(or) if it is not correlated
with increased function, it
is termed hyperplasia.


• Localized
hypercementosis may
sometimes be observed
in areas in which enamel
drops have developed on
the dentin.
• The hyperplastic
cementum covering the
enamel drops
occasionally is irregular
and sometimes contains
round bodies that may be
calcified epithelial rests.


• The same type of embedded
calcified round bodies frequently are
found in localized areas of
hyperplastic cementum & are
designated as excementoses.
• A thickening of cementum is often
observed on teeth that are not in
function.
• Hyperplasia of cementum in non
functioning teeth is characterized by
a reduction in the number of
Sharphey’s fibers embedded in the
root.


10. CLINICAL CONSIDERATIONS

• Cementum is avascular and is more
resistant to resorption than is bone, and it
is for this reason that orthodontic tooth
movement is made possible.
• When a tooth is moved by means of an
orthodontic appliance, bone is resorted on
the side of the pressure, and new bone is
formed on the side of tension.

• The difference in the resistance of bone and
cementum to pressure may be the fact that bone
is richly vascularized, whereas cementum is
avascular.
• Thus degenerative processes are much more
easily effected by interference with circulation in
bone, whereas cementum with its slow
metabolism is not damaged by a pressure equal
to that exerted on bone.


REPAIR OF THE CEMENTUM
• Anatomic Repair:
• In this type of repair the former
outline of the root is
restablished by cemental
deposition.
• Functional Repair:
• In some teeth the resorbed
area is covered only by a thin
layer of cementum. The
depression that exists is filled
by the growth of adjacent
alveolar bone. This kind of
repair is called functional
repair.


• In periodontal pockets, plaque and its by-
products can cause numerous alterations in the
physical, chemical and structural characteristics
of cementum.
• Endotoxin originating from plaque can be
recovered from exposed cementum & it is
believed that they may interfere with healing
during periodontal therapy.
• Consequently in periodontal theropy, various
procedures (mechanical and chemical) have
been proposed that are intended to remove this
altered www.indiandentalacademy.com
cemental surface.

CARIES OF CEMENTUM
• Caries of cementum also
called as Senile Carious
lesions (or) root surface caries
are those associated with the
aging process.
• They are located almost
exclusively on the root
surfaces of the teeth, but
sometimes they are associated
with partial denture clasps due
to advanced gingival
recession.


• Teeth with Hypercementosis (or) with extensive
excementoses, are of practical significance
because the extraction of such teeth may
necessitate the removal of bone.
• These can anchor the tooth so tightly to the
socket that the Jaw (or) parts of it may be
fractured in an attempt to extract the tooth.
• This possibility indicates the necessity for taking
x-rays before any extraction.


TOOTH RESORPTION -
DEFINITION
• According to the Glossary
– Contemporary
Terminology for
Endodontics (1998),
“Resorption is defined as
a condition associated
with either a physiologic
or a pathologic process
resulting in the loss of
dentine, cementum
and/or bone”.


RESORPTION
CLASSIFICATION
• 1. INTERNAL RESORPTION

• ROOT CANAL INTERNAL INFLAMMATORY
REPLACEMENT RESORPTION
RESORPTION
(Metaplastic
resorption) Transient Progressive


2. EXTERNAL RESORPTION

EXTERNAL EXTERNAL REPLACEMENT ANKYLOSIS
SURFACE INFLAMMATORY RESORPTION
RESORPTION RESORPTION

EXTERNAL RESORPTION (Based on location)
1. CERVICAL
2. BODY
3. APICAL


3. COMBINED INTERNAL AND EXTERNAL
RESORPTION
4. TRANSIENT APICAL BREAKDOWN

• Aetiology for External Resorption:
• 1, Replantation of tooth
• 2. Orthodontic forces
• 3. Eruption of neighbouring teeth
• 4. Root fracture
• 5. Trauma
• 6. Necrotic pulp
• 7. Root Planing
• 8. Pathology like cysts, Ameloblastoma, Giant cell
tumour, Fibrous osseous lesions
• 9. Hereditary


AETIOLOGY FOR CERVICAL
EXTERNAL RESORPTION
• Bleaching
• Trauma
• Root planning
• Hereditary
• Orthognathic surgery


EXTERNAL SURFACE
RESORPTION
• It is a transient phenomenon in which the
tooth undergoes spontaneous destruction
and repair.
• It is found in all the teeth and considered
to be a normal physiological response.
• It is a self-limiting process and does not
require any treatment.


• External inflammatory root resorption:- It
is described as a bowl shaped defect
which penetrates the dentine
• This occurs following irritation or injury of
the periodontium due to trauma,
periodontal infection or orthodontic
treatment


External Replacement Resorption:
The primary cause is due to laxative injury.
This is continuous process by which the
teeth is gradually resorbed and replaced
by bone.
It differs from Ankylosis because of the
presence of intervening inflamed
connective tissue.


ANKYLOSIS
– This is primarily associated with luxation injury
like Avulsion.
– Ankylosis is an union of tooth and bone with
no intervening connective tissue following
external resorption.


TREATMENT
– The treatment of external resorption varies
with the etiologic factor.
– If the external resorption is caused by the
extension of pulpal disease into the
supporting tissues, root canal therapy will
usually stop the resorptive process.


– External resorption produced by excessive
forces from orthodontic applicances can be
stopped by reducing these forces.
– In patients with external resorption due to
replantation of teeth, preparation of the root
canal and obturation with calcium hydroxide
paste may stop the resorptive process.


11. CONCLUSION
• -Cementum is best considered in functional terms as
two tissues, with one providing attachment and the other
adaptation to tooth wear and movement.
• -Cementum is thinnest at the cementoenamel
junction and the relative softness of the cementum
makes it susceptible to abrasion thereby exposing the
underlying sensitive dentin.
• -Therefore whenever the cemental surface is
exposed to the oral environment such as by gingival
recession, proper treatment procedures has to be
followed to prevent the increased sensitivity experienced
by the patient.


BIBLIOGRAPHY
• 1. Oral Histology – Ten Cates, 5th and 6th edition
• 2. Orban’s Oral Histology and Embryology –
S.N. Bhaskar, Eleventh Edition.
• 3. Pathways of the Pulp – 8th Edition – Stephen
Cohen, Richard C. Burns.
• 4. Textbook of Oral Pathology – William G.
Shafer.
• 5. Endodontic Practice – Louis I. Grossman,
Eleventh Edition.
• 6. OOO Journal, 1995; 79; 624-33.


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