• THE PERIDONTIUM IS
DEFINED AS THOSE
TISSUES SUPPORTING AND
INVESTING THE TOOTH
THAT CONSISTS OF
2. PERIODONTAL LIGAMENT
3. BONE LINING THE
4. PART OF THE GINGIVA
FACING THE TOOTH
• THE PDL IS THAT SOFT SPECIALIZED
CONNECTIVE TISSUE SITUATED
BETWEEN THE CEMENTUM
COVERING THE ROOT OF THE
TOOTH AND THE BONE FORMING
THE SOCKET WALL
FUNCTIONS OF PDL.
• SUPPORT: PDL supports teeth in their socket.
It prevents loosening of teeth.
• MASTICATORY LOAD: PDL permits teeth to
withstand the considerable forces of
• SENSORY: PDL is supplied by abundant
receptors and nerves that sense the
movement when teeth are in function. Helps
in the proper positioning of the jaws during
• NUTRITIVE: Blood vessels of ligament provide
essential nutrients for the ligament’s vitality
and hard tissue of cementum and alveolar
• Fibroblasts, osteoblasts, cementoblasts, and
even resorptive osteoclasts and macrophages
• CLINICAL CORRELATION: Bone, PDL, and the
cementum together form a functional unit of
special importance when the orthodontic tooth
movement is undertaken. Orthodontic forces
causes compression and constriction of blood
vessels, soft tissue changes occur.
• Hence loss of alveolar bone occurs, now blood
flow occurs in the spaces. And the mesenchymal
cells of PDL repair the tissues.
• MAINTAINENCE: Tissues are maintained
under the influence of heavy masticatory
• ADAPTIVE ROLE
• SHOCK ABSORBER : It absorbs the shock of
PDL is formed within the
developing dental follicle.
Ligament space consists of
tissue with short fiber
bundles extending into it
from bone and cemental
cells begin to secrete
collagen (mainly collagen
The developing periodontal ligament
fiber bundles extend into the
unorganized ligament space from both
the cementum surface and the surface of
the alveolar bone.
• The predominant collagens of PDL are types I,
III and XII.
• They are arranged in distinct and definite fiber
• They are able to adapt to the continual
stresses placed on them.
PRINCIPAL FIBER BUNDLES OF PDL
1. THE ALVEOLAR CREST
These are attached to
the cementum just
and running downward
and outward to insert
into the rim of the
2.THE HORIZONTAL GROUP2.THE HORIZONTAL GROUP
• These are just apical toThese are just apical to
the alveolar crest fibersthe alveolar crest fibers
and running at rightand running at right
angles to the long axis ofangles to the long axis of
the tooth from thethe tooth from the
cementum to the bonecementum to the bone
below the alveolar crest.below the alveolar crest.
3. THE OBLIQUE GROUP3. THE OBLIQUE GROUP
• They are the most
numerous in the PDL
and running from the
cementum in an oblique
direction to insert into
the bone coronally
4.THE APICAL GROUP:
• These are radiating from
the cementum around
the apex of the root to
the bone forming the
base of the socket.
5.THE INTERADICULAR GROUP
• Found only in the multi-
rooted teeth and
running from the
cementum into the bone
forming the crest of the
• At each end all the
principal fibers of the
PDL are embedded in
the cementum or the
bone and this
embedded portion is
referred to as the
• CEMENTUM IS A HARD,
THAT COVERS THE
ROOTS OF THE TEETH.
• CEMENTUM is excreted by
the root of the tooth.
• CEMENTOBLASTS are the
formative cells of
• It is thickest at the root
DEVELOPMENT OF CEMENTUM
• The development of cementum has been
• PREFUNCTIONAL STAGE, which occurs
through out root formation.
• FUNCTIONAL STAGE, which starts when the
tooth is in occlusion and continues through
TYPES OF CEMENTUM
• CEMENTUM is classified
according to the presence or
absence of cells within its
• CELLULAR CEMENTUM, which
has an adaptive role in response
to tooth wear and movement
and is associated with repair of
• ACELLULAR CEMENTUM, which
provides attachment for the
A- CELLULAR CEMENTUM
PHYSICAL CHARACTERSTICS AND
• COLOR: YELLOW.
• HARDNESS: LESS THAN DENTIN.
• COMPOSITION: ORGANIC MATRIX (50%) AND
INORGANIC ELEMENT (45-50%)
• ORGANIC MATRIX: COLLAGENOUS AND NON-
TYPES OF COLLAGEN:
• Type I Collagen is predominant in cementum,
constitutes 90% of organic component of
• Type III, Type XII, are also present.
• Type XII is found in high concentration in PDL.
• Traces of Type V, VI and XIV are also found in
NON-COLLAGENOUS PROTEINS IN
• These proteins are also associated with bone:
• ALKALINE PHOSPHATASE.
• BONE SIALOPROTEIN.
• DENTIN SIALOPROTEIN.
• DENTIN MATRIX PROTEIN.
• PROTEOGLYCANS. ETC.
• If some HERS cells
remain attached to
forming root surface
they can produce focal
deposits of enamel like
• I have presented till here and
skipped the rest
ORIGIN OF PDL CELLS AND
DIFFERENTIATION OF CEMENTOBLASTS.
• PRECURSOR CELLS FOR CEMENTOBLASTS AND PDL:
• REGENERATION OF PDL TISSUE: STEM CELLS & LOCAL
• CEMENTOBLASTS FORMATION: EPITHELIAL CELLS
FROM HERS MAY UNDERGO EPITHELIAL-
MESENCHYMAL TRANSFORMATION INTO
MOLECULAR FACTORS REGULATING
• These molecules and factors:
• CONTROL DEVELOPMENT.
• MAINTAIN PDL.
• REGENERATE PDL.
• BONE SIALOPROTEIN & OSTEOPONTIN.
• REPAIR & REGENERATION OF PDL.
• OSTEOPONTIN: Regulate Mineral Growth.
• BONE SIALOPROTEIN: Promotes mineral
formation on root surface.
• TYPE I COLLAGEN: Abundant in cementum as
well as in PDL.
• TYPE III: Abundant during early stages of
Cementogenesis. And during development and
• TYPE XII: Abundant in PDL and lower levels in
• Relation of Cementum to Enamel
at the Cementoenamel Junction
• "OMG rule"
• In 60% of the teeth cementum
• In 30% of the teeth cementum just
forming a butt joint.
• In 10% of the teeth there is a small
GAP between cementum and
• Alveolar process is that bone
of jaws containing the sockets
(alveoli) for the teeth.
• The alveolar process consists
of OUTER (BUCCAL &
LINGUAL) CORTICAL PLATE.
• Central bone is SPONGIOSA.
• Bone lining the alveolus is
called ALVEOLAR BONE.
• Cortical plates and alveolar
bone meets at the alveolar
crest (1.5 -2m.m.) below the
level of CEJ.
• Alveolar bone is perforated
by foramina because it is
• Nerves and vessels pass
• Sometimes referred to as
• Alveolar bone is referred
as LAMINA DURA,
of its increased
• The bone directly lining
the socket i.e. the inner
aspect of alveolar bone is
known as BUNDLE BONE.
Other groups of collagen
fibers found in the
lamina propria of the
gingiva collectively form
the gingival ligament.
1. CIRCULAR GROUP:
• These fibers form a band
around the neck of the
tooth and help to bind
the free gingiva to the
2. DENTOGINGIVAL GROUP:
• These are the most
extending from the
cervical cementum to
the lamina propria of
the free and attached
• Running apically from
the cementum over
the periosteum of the
alveolar bone , these
fibers insert into the
alveolar process or
the vestibular muscle
and floor of the
4. ALVEOLOGINGIVAL GROUP
• These fibers radiate
from the bone of the
alveolar crest and
insert into the free
and attached gingiva.
5.TRANSEPTAL FIBER SYSTEM
• These fibers run interdentally from the
cementum just apical to the base of the
junctional epithelium of one tooth over the
alveolar crest and insert into the cementum of
the adjacent tooth.
• Thus they form a interdental ligament
connecting all the teeth in the arch.