Unlike bone however human cementum is avascular and noninnervated Cementum is thinnest at the cemento enamel junction and thickest toward the apex Like dentin cementum can form throughout the life of a tooth ID: 918461
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Slide1
Cementum
Slide2Cementum:Is a mineralized dental tissue that covering the anatomic roots of human teeth. Cementum furnishes a medium for the attachment of collagen fibers that bind the tooth to surrounding structures.
Unlike bone, however, human cementum is
avascular
and
noninnervated
.
Cementum is thinnest at the cemento- enamel junction and thickest toward the apex.
Like dentin, cementum can form throughout the life of a tooth.
Slide3PHYSICAL CHARACTERISTICS
1-The hardness of fully mineralized cementum is less than that of dentin.
2-Cementum is light yellow in color and can be distinguished from enamel by its lack of luster and its darker hue. Cementum is somewhat lighter in color than dentin.
3- Cementum has been shown to be permeable to a variety of materials.
Slide4CHEMICAL COMPOSITION
On a dry weight basis, cementum from fully formed 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
hydroxy
- apatite.
Numerous trace elements are found in cementum in varying amounts. It is of interest that 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
) .
Slide6CEMENTOGENESIS
Breaks occur in the epithelial root sheath allowing the newly formed dentin to come in direct contact with the cells of dental follicle.
Cells derived from his connective tissue are called
cementoblast
. They are responsible for the formation of cementum.
Slide7Some sheath cells migrate away from the dentin toward the dental sac, whereas others remain near the developing tooth and ultimately are incorporated into the cementum.
Sheath cells that migrate toward the dental sac become the
epithelial rests of Malassez
found in the periodontal ligament of fully developed teeth.
Slide8Slide9Cementoblasts
Cementoblasts
synthesize collagen and protein polysaccharides, which make up the organic matrix of cementum.
At the superficial surface, the collagen fibrils produced by the
cementoblast
form a fibrous fringe perpendicular to periodontal space.
Slide10Slide11Slide12Cementoid tissue
Under normal conditions ; growth of cementum is a rhythmic process, and as a new layer of
cementoid
is formed, the old one calcifies.
A thin layer of
cementoid
can usually be observed on the
cemental
surface. This
cementoid
tissue is lined by
cementoblasts
.
Connective tissue fibers from the periodontal ligament pass between the
cementoblasts
into the cementum.
Slide13Slide14These fibers are embedded in the cementum and serve to attach the tooth to surrounding bone. Their embedded portions are known as
Sharpey’s
fibers
.
Each
Sharpey’s
fiber is composed of numerous collagen fibrils that pass well into the cementum .
Cementoid
tissue is not observed in AEFC.
Slide15Slide16*
Light microscopic observations reveal two basic types of cementum, hence they are usually classified on the basis of presence of cementocytes (cellular cementum) or its absence (
acellular
cementum).
It can also be classified on the basis of the type of fibers (intrinsic/extrinsic fibers) presence or their absence (
afibrillar
cementum).
STRUCTURE
Slide17*The
acellular
extrinsic fiber cementum is regarded as primary cementum, because it forms first.
*The cellular cementum are also known as
secondary cementum,
because it forms later than primary cementum
A-acellular cementum
1-Acellular
afibrillar
cementum (AAC):
is a mineralized ground substance containing no cells and is devoid of extrinsic and intrinsic collagen fibers. This type of cementum is seen chiefly as coronal cementum
Slide202-Acellular extrinsic fiber cementum:
extends from cervical margin to apical 1/3rd. It is the only type of cementum seen in single rooted teeth. The extrinsic fibers are seen perpendicular to surface of cementum and they are known as
Sharpey’s
fibers
. When cementum remains relatively thin,
Sharpey’s
fibers cross the entire thickness of the cementum. With further apposition of cementum, a larger part of the fibers is incorporated in the cementum. The attachment proper is confined to the most superficial or recently formed layer of cementum .The main function of this type of cementum is anchorage especially in single rooted teeth.
Slide21Slide22Slide23B-Cellular cementum:
is also known as secondary cementum as this is formed later than the AEFC.
The cellular cementum found in the
apical third
is mainly of two types
—
1-
the cellular mixed fiber cementum which forms the bulk of secondary cementum and occupies the
apical and
interradicular
regions
and the
2-
CIFC:
which
is present in the
middle and apical third
. These types are mainly involved in the
adaptation and repair
of
cementum
Since the secondary cementum is formed rapidly the incremental lines are placed further apart than in AEFC.
Slide24Slide25Slide26Slide271-Cellular intrinsic fiber cementum (CIFC):
This cementum contains cells but has no extrinsic fibers. The fibers present are intrinsic fibers which are secreted by the
cementoblasts
. It is formed on the root surface and in
cases of repair
.
Slide28Slide292-Cellular mixed fiber cementum (CMFC):
The cellular mixed fiber cementum is a variant formed at a faster rate with less mineralized fibers. The collagen fibers of CMFC are derived from the periodontal ligament fibroblasts and the
cementoblasts
. These intrinsic and extrinsic fibers form an intricate pattern running between each other at almost right angles and different orientations, though the number of intrinsic fibers is comparatively less than the extrinsic fibers. The fiber bundles originating from the fibroblast are ovoid or round and the fibers originating from the
cementoblasts
are much more delicate and smaller measuring
Slide30Slide313-Cellular mixed stratified cementum (CMSC):
In this type of cementum the cellular intrinsic fiber cementum alternates with
acellular
extrinsic fiber cementum. It is formed by
cementoblasts
and fibroblasts. It appears primarily on
apical third of the root and
furcation
areas
Slide32Slide33Cementocytes :The cells incorporated into cellular cementum, 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 neigh- boring cell.
Slide34Most of the processes are directed toward the periodontal surface of the cementum. They are best viewed in mineralized ground sections.
These characteristics indicate that cementocytes are either degenerating or are marginally active cells and lacunae in the deeper layers of cementum appear to be empty, suggesting complete degeneration of cementocytes located in these areas.
Slide35Slide36Slide37Differences between cementocytes and osteocytes
Though the cementocytes resemble the
osteocytes
, there are a few important differences. The lacunae of cementocytes varies from being ovoid or tubular, but the
osteocytic
lacunae is invariably oval.
The canaliculi are less complicated and sparse, with the majority of them facing the periodontal ligament when compared to
osteocytes
, whose canaliculi are radiating, more dense and arranged in a complex network. However in both, the
cytoplasmic
processes are connected with the cells lining the surface
Slide38CEMENTODENTINAL JUNCTION(CDJ):
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 in either case is quite firm. increased water content which contributes to the stiffness.
This reduction in its mechanical property, helps it to redistribute occlusal loads to the alveolar bone.
Sometimes dentin is separated from cementum by a zone known as the intermediate cementum layer
, which does not exhibit characteristic features of either dentin or cementum .As it appears hyaline (
structureless
), it is also known as Hyaline layer.
Slide41This layer is predominately seen in the apical two thirds
of roots of molars and premolars and is only rarely observed in incisors or deciduous teeth.
It is believed that this layer represents areas where cells of
Hertwig’s
epithelial sheath become trapped in a rapidly deposited dentin or cementum matrix.
The intermediate cementum layer is considered to be of dentinal origin.
Slide42It contains no tubules but wide spaces which are thought to be enlarged terminals of dentinal tubules. It appears very similar to
aprismatic
enamel, as it is an amorphous layer of
noncollagenous
material devoid of odontoblasts and
cementoblasts
.
it is ether a continuous layer or in isolated areas. The probable function might be to seal the sensitive root dentin.
Slide43CEMENTOENAMEL JUNCTION
1-In about 10% of the teeth, enamel and cementum do not meet. this occurs when enamel epithelium in the cervical portion of the root is delayed in its separation from dentin. Instead, a zone of the root is devoid of cementum and is, for a time, covered by reduced enamel epithelium
Slide44Slide452- 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.
Slide463-In approximately 30% of all teeth enamel and cementum meeting edge to edge. CEJ may exhibit all of these patterns in teeth of an individual.
Slide47FUNCTIONS:
1-Anchorage
The primary function of cementum is to furnish a medium for the attachment of collagen fibers that bind the tooth to alveolar bone. Since collagen fibers of the periodontal ligament cannot be incorporated into dentin, a connective tissue attachment to the tooth is impossible without cementum. This is dramatically demonstrated in some cases of
hypophosphatasia
, a rare hereditary disease in which loosening and premature loss of anterior deciduous teeth occurs. The exfoliated teeth are characterized by an almost total absence of cementum.
Slide48Slide492-Adaptation
Cementum may has functional adaptation of teeth possible. For example, deposition of cementum in an apical area can compensate for loss of tooth substance from occlusal wear. The continuous deposition of cementum is of considerable functional importance. In contrast to the alternating resorption and new formation of bone, cementum is not resorbed under normal conditions. As the most superficial layer of cementum ages, a new layer of cementum must be deposited to keep the attachment apparatus intact.
3-Repair:
Cementum serves as the major reparative tissue for root surfaces. Damage to roots such as fractures and resorption can be repaired by the deposition of new cementum. Cementum formed during repair resembles cellular cementum because it forms faster but it has a wider
cementoid
zone and the apatite crystals are smaller. If the repair takes place slowly, it cannot be differentiated from primary cementum.
Slide52Slide53HYPERCEMENTOSIS
Hypercementosis is an abnormal thickening of cementum
.
This condition frequently is found in teeth that are exposed to great stress.
It may be diffuse or circumscribed
.
It may affect all teeth of the dentition
, or
be confined to a single tooth, or even affect only parts of one tooth
.
In localized hypertrophy a spur or prong like extension of cementum may be
formed which
provide a larger surface area for the attaching fibers; thus a firmer anchorage of the tooth to the surrounding alveolar bone is assured.
Slide54Slide55Excementoses:
knob like projections or 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. They too develop around degenerated epithelial rests.
Extensive
deposition of cementum is occasionally associated with
chronic periapical inflammation
. The excessive deposition is circumscribed and surrounds the root like a cuff.
A thickening of cementum is often observed on teeth that are not in function. It may extend around the entire root of the nonfunctioning teeth or may be localized in small areas teeth is characterized by a reduction in the number of
Sharpey’s
fibers embedded in the root
.
The cementum is thicker around the apex of all teeth and in the
furcation
of
multirooted
teeth than on other areas of the root.
Slide57This thickening is found in embedded and in newly erupted teeth. Hyper-
cementosis
is associated with a large number of
neoplastic
and non
neoplastic
diseases. Generalized thickening is seen in Paget’s disease.
Slide58Localized
forms can be seen in benign
cementoblastoma
, florid cemento-osseous dysplasia,
acromegaly
,
calcinosis
and some forms of arthritis Hypoplasia or
aplasia
of cementum is of rare occurrence. It is associated with
hypophosphatasia
.
Slide59The extraction of such teeth may necessitate the removal of bone. They 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 radiographs before any extraction. Small fragments of roots left in the jaw after
extraction
of teeth may be surrounded by cementum and remain in the jaw without causing any disturbance.
Slide60CLINICAL CONSIDERATIONS
Cementum is more resistant to resorption than bone, and it is for this reason that orthodontic tooth movement is possible. When a tooth is moved by means of an orthodontic appliance, bone is resorbed on the side of the pressure, and new bone is formed on the side of tension.
On
the side toward which the tooth is moved, pressure is equal on the surfaces of bone and cementum.
Slide61Resorption of bone as well as of cementum may be anticipated. so careful orthodontic treatment, cementum resorption is minimal or absent, but bone resorption leads to tooth migration. The difference in the resistance of bone and cementum to pressure may be caused by the fact that bone is richly
vascularized
,
Slide62Cementum resorption can occur after trauma or excessive occlusal forces.
In
severe cases cementum resorption may continue into the dentin
.
After resorption has ceased, the damage usually is repaired, either by formation of
acellular
or cellular cementum or by alternate formation of both
.
In
most cases of repair there is a tendency to reestablish the former outline of the root surface. This is called
anatomic repair.
However, if only a thin layer of cementum is deposited on the surface of a deep resorption, the root outline is not reconstructed, and a bay like recess remains.
In
such areas sometimes the periodontal space is restored to its normal width by formation of a bony projection so that a proper functional relationship will result.
The
outline of the alveolar bone in these cases follows that of the root surface. In contrast to anatomic repair, this change is called
functional repair.
If
teeth are subjected to a severe blow, fragments of cementum may be severed from the dentin. The tear occurs frequently at the
cementodentinal
junction, but it may also be in the cementum or dentin.
Transverse fractures of the root may occur after trauma, and these may heal by formation of new cementum. This also applies to extensive
excementosis
, as
.
In periodontal pockets, plaque and its by-products can cause numerous alterations in the physical, chemical, and structural characteristics of cementum. The surface of
pathologically
exposed cementum becomes
hypermineralized
because of the incorporation of calcium, phosphorus, and fluoride from the oral environment.