PERIODONTIUM
Cementum
Pulp cavity
Enamel
Dentin
Gingiva
PDL
Alveolar bone
Cementum
Sharpey's fibers
Attachment
organ
Periodontal
ligament
Root canal
Alveolar bone
Apical foramen
Alveolar vessels
& nerves
TEETH IN-SITU
Periodontium (forms a
specialized fibrous joint called
Gomphosis)
•
•
•
•
Cementum
Periodontal Ligament
Alveolar bone
Gingiva facing the tooth
Cementum
The other bone
It is a hard avascular connective
tissue that covers the roots of
teeth
Role of Cementum
1) It covers and protects the root dentin
(covers the opening of dentinal tubules)
2) It provides attachment to the
periodontal fibers
3) It compensates for tooth resorption
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
Cementum simulates bone
• 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)
Differences between cementum
and bone
• Not vascularized – a reason for it being resistant
to resorption
• Minor ability to remodel
• More resistant to resorption compared to bone
• Lacks neural component – so no pain
• 70% of bone is made by inorganic salts
(cementum only 45-50%)
• 2 unique cementum molecules: Cementum
attachment protein (CAP) and IGF
Clinical Correlation
Cementum is more resistant to resorption: Important in permitting
orthodontic tooth movement
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 ectomesenchymal 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
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?
Cementoblasts
• Derive from dental follicle
• Transformation of epithelial cells
Proteins associated with
Cementogenesis
• Growth factors
– TGF
– PDGF
– FGF
• Adhesion molecules
– Bone sialoprotein
– Osteopontin
Proteins associated with
Cementogenesis
• Epithelial/enamel-like factors
• Collagens
• Gla proteins
– Matrix
– Bone
• Collagens
• Transcription factors
– Cbfa 1 and osterix
• Other
– Alkaline phosphatase
Hyaline layer of Hopewell-Smith (Intermediate Cementum)
First layer of cementum is actually
formed by the inner cells of the HERS
and is deposited on the root’s surface
is called intermediate cementum or
Hyaline layer of Hopewell-Smith
Deposition occurs before the HERS
disintegrates. Seals of the dentinal
tubules
Intermediate cementum is situated
between the granular dentin layer of
Tomes and the secondary cementum
that is formed by the cementoblasts
(which arise from the dental follicle)
Approximately 10 m thick and
mineralizes greater than the adjacent
dentin or the secondary cementum
Properties of Cementum
Physical: Cementum is pale yellow with a dull surface
Cementum is more permeable than other dental tissues
Relative softness and the thinness at the cervical portion means
that cementum is readily removed by the abrasion when gingival
recession exposes the root surface to the oral environment
Chemical Composition of Cementum
Similar to bone
45% to 50% hydroxyapatite (inorganic)
50% to 55% collagenous and noncollagenous matrix proteins
(organic)
Collagenous component
•TYPE I
• TYPE III
• TYPE XII
• TYPE V
• TYPE XIV
Classification of Cementum
• Presence or absence of cells
• Origin of collagenous fibers of the
matrix
• Prefunctional and functional
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)
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
Acellular
Cellular
Variations also noted where acellular and cellular reverse in position
and also alternate
CEMENTUM
Canaliculus
GT
Lacuna of cementocyte
Dentin
Acellular cementum
Cellular cementum
Hyaline layer
(of Hopewell Smith)
Granular layer of tomes
Dentin with tubules
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
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
Classification Based on the Nature and Origin of Collagen Fibers
Organic matrix derived form 2 sources:
1. Periodontal ligament (Sharpey’s fibers)
2. Cementoblasts
Extrinsic fibers if derived from PDL. These are in the same
direction of the PDL principal fibers i.e. perpendicular or
oblique to the root surface
Intrinsic fibers if derived from cementoblasts. Run parallel to
the root surface and at right angles to the extrinsic fibers
The area where both extrinsic and intrinsic fibers is called
mixed fiber cementum
Combined classification (see Table 9-2)
Acellular Extrinsic Fiber Cementum (AEFC-Primary Cementum)
• Located in cervical half of the root and constitutes the bulk of cementum
• The collagen fibers derived from Sharpey’s fibers and ground substance
from cementoblasts
• Covers 2/3rds of root corresponding with the distribution of primary
acellular cementum
• Principal tissue of attachment
• Function in anchoring of tooth
• Fibers are well mineralized
Primary acellular intrinsic fiber
•
•
•
•
•
•
First cementum
Primary cementum
Acellular
Before PDL forms
Cementoblasts
15-20μm
Cellular intrinsic fiber cementum (CIFCSecondary Cementum )
• Starts forming after the tooth is in occlusion
• Incorporated cells with majority of fibers organized
parallel to the root surface
• Cells have phenotype of bone forming cells
• Very minor role in attachment (virtually absent in
incisors and canine teeth)
• Corresponds to cellular cementum and is seen in
middle to apical third and intrerradicular
• Adaptation
• Repair
Secondary cellular mixed fiber cementum
• Both intrinsic and extrinsic fibers
[Extrinsic (5 – 7 m) and Intrinsic (1 – 2 m)]
• Bulk of secondary cementum
• Cementocytes
• Laminated structure
• Cementoid on the surface
• Apical portion and intrerradicular
• Adaptation
Intrinsic fibers are uniformly mineralized but the extrinsic fibers are
variably mineralized with some central unmineralized cores
Zone of Transition
Acellular afibrillar cementum
•
•
•
•
Limited to enamel surface
Close to the CE junction
Lacks collagen so plays no role in attachment
Developmental anomaly vs. true product of epithelial
cells
Distribution of Cementum on the Root
• Acellular afibrillar: cervical enamel
• Acellular extrinsic: Cervix to practically the whole root
(incisors, canines) increasing in thickness towards the
apical portion 50200μm
• Cellular: Apical third, furcations
CE junction
The “OMG” rule
Cementum overlaps enamel
60%
Cementum just meets enamel
30%
Small gap between cementum and enamel
10%
Aging of Cementum
1.
2.
3.
4.
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]
Cementum resorption. Active for a period
of time and then stops for cementum
deposition creating reversal lines
Resorption of root dentin occurs with aging
which is covered by cemental repair
Cementicles
• Calcified ovoid or round nodule found
in the PDL
• Single or multiple near the cemental surface
• Free in ligament; attached or embedded
in cementum
• Aging and at sites of trauma
Origin: Nidus of epithelial cell that are
composed of calcium phosphate and
collagen to the same amount as
cementum (45% to 50% inorganic
and 50% to 55% organic)
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
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
Alveolar Process
Gingiva
Near the end of the 2nd
month of fetal life, mandible
and maxilla form a groove
that is opened toward the
surface of the oral cavity
As tooth germs start to
develop, bony septa form
gradually. The alveolar
process starts developing
strictly during tooth eruption.
a) outer cortical plates
b) a central spongiosa
c) bone lining the alveolus (bundle
bone)
Alveolar bone proper: The compact or dense bone that lines the tooth.
Contains either perforating fibers from periodontal ligament (Sharpey’s
fibers) or just compact bone
Sharpey’s fibers embedded into the alveolar bone proper
Present at right angles or oblique to the surface of alveolar bone and
along the root surface
Because alveolar process is regularly penetrated by collagen fiber bundles,
it is also called bundle bone. It appears more radiodense than surrounding
supporting bone in X-rays called lamina dura
Bundle Bone
It is perforated by many foramina that transmit nerves and vessels
(cribriform plate).
Radiographically, the bundle bone is the lamina dura. The lining of the
alveolus is fairly smooth in the young but rougher in the adults.
Radiodense because increased mineral content around fiber bundles
Lamina Dura
Supporting Compact Bone
Similar to compact bone anywhere else (Haversian bone)
Extends both on the lingual (palatal) and buccal side
Contains haversian and Volkman’s canals (they both form a continuous
channel of nutrient canals)
Bundle bone and Trabecular bone
Arrows: Sharpey’s fiber
The alveolar crest is found 1.5-2.0 mm below the
level of the CEJ.
If you draw a line connecting the CE junctions of
adjacent teeth, this line should be parallel to the
alveolar crest. If the line is not parallel, then there is
high probability of periodontal disease.
Clinical considerations
Resorption and regeneration of alveolar bone
This process can occur during orthodontic
movement of teeth. Bone is resorbed on the side of
pressure and opposed on the site of tension.
Decreased bone (osteopenia) of alveolar process
is noted when there is inactivity of tooth that does
not have an antagonist
Lack of antagonists
Periodontal Ligament
PDL is the soft specialized connective tissue situated between
cementum and alveolar bone proper
Ranges in thickness between 0.15 and 0.38 mm and is
thinnest in the middle portion of the root
The width decreases with age
Tissue with high turnover rate
Contains fibers, cells and intercellular substance
Embryogenesis
The PDL forms from the dental follicle shortly after root
development begins
FUNCTIONS OF PERIODONTIUM
Tooth support
Shock absorber: Withstanding the forces of mastication
Sensory receptor necessary for proper positioning of the
jaw
Nutritive: blood vessels provide the essential nutrients to
the vitality of the PDL
Cells
a) Osteoblasts
b) Osteoclasts (critical for periodontal disease and tooth
movement)
c) Fibroblasts (Most abundant)
d) Epithelial cells (remnants of Hertwig’s epithelial root sheathepithelial cell rests of Malassez)
e) Macrophages (important defense cells)
f) Undifferentiated cells (perivascular location)
h) Cementoblasts
i) Cementoclasts (only in pathologic conditions)
Epithelial Cell Rests of Malassez
PDL fibers
- Collagen fibers: I, III and XII. Groups of fibers that are
continually remodeled. (Principal fiber bundles of the PDL).
The average diameter of individual fibers are smaller than
other areas of the body, due to the shorter half-life of PDL
fibers (so they have less time for fibrillar assembly)
- Oxytalan fibers: variant of elastic fibers, perpendicular to
teeth, adjacent to capillaries
- Eluanin: variant of elastic fibers
Principal Fibers
Run between tooth and bone. Can be classified as dentoalveolar
and gingival group
Dentoalveolar group
a. Alveolar crest group (ACG): below CE junction, downward, outward
b. Horizontal group: apical to ACG, right angle to the root surface
c. Oblique group: most numerous, oblique direction and attaches
coronally to bone
d. Apical group: around the apex, base
of socket
e. Interradicular group: multirooted teeth
Runs from cementum and bone , forming
the crest of the interradicular septum
At each end, fibers embedded in bone
and cementum: Sharpey’s fiber
Gingival ligament fibers: the principal fibers in the gingival
area are referred to as gingival fibers. Not strictly related to
periodontium. Present in the lamina propria of the gingiva.
a. Dentogingival: most numerous; cervical cementum to f/a gingiva
b. Alveologingival: bone of the alveolar crest to f/a gingiva
c. Circular: around neck of teeth, free gingiva
d. Dentoperiosteal: runs apically from the cementum over the outer cortical
plate to alv. process or vestibule (muscle) or floor of mouth
e. Transseptal: cementum between adjacent teeth, over the alveolar crest
Transeptal
Alveolar crest
Horizontal
Oblique
Oxytalan Fibers
Type of elastic fibers present as bundes of microfibrils that run oblique
from the cementum surface to the blood vessels. Associated with neural
elements. Most numerous in the cervical area.
Function: Regulate vascular flow in relation to tooth function
The PDL gets its blood supply from perforating
arteries (from the cribriform plate of the bundle
bone).
The small capillaries derive from the superior &
inferior alveolar arteries.
The blood supply is rich because the PDL has a
very high turnover as a tissue.
The posterior supply is more prominent than the
anterior. The mandibular is more prominent than
the maxillary.
Nerve supply
The nerve supply originates from the inferior
or the superior alveolar nerves.
The fibers enter from the apical region and
lateral socket walls.
The apical region contains more nerve
endings (except Upper Incisors)
Interstitial Space
Present between each bundle of ligament fibers
Contains blood vessels and nerves
Designed to withstand the impact of masticatory forces
Ground Substance
Amorphous background material that binds tissues and fluids
A major constituent of the PDL
Similar to most connective tissue ground substance
Dermatan sulfate is the major glycosaminoglycan
70% water; critical for withstanding forces
When function is increased PDL is increased in size and fiber thickens
Bone trabeculae also increase in number and thicker
However, in reduction of function, PDL narrows and fiber bundles
decreases in number and thickness (this reduction in PDL is primarily due
to increased cementum deposition)