The Normal Periodontium PDL

7/28/2019 The Normal Periodontium PDL

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The Normal PeriodontiumIIThe Periodontal Ligaments

Periodontology 1

DENT 371

Dr. Hisham Al-Shorman, PhD


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The periodontium

Gingiva

Periodontal ligaments

Cementum

Alveolar bone


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Physically small,functionally important

Subjected to

continuous mechanical

loading

High turnover rate

Periodont

al

Ligament

The Periodontal Ligament


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Composed of:

Fibers

Cells

ECM

Nerves

blood & lymphaticvessels

The Periodontal Ligament


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Fibers

Most important are the

principal fibers Other fibres are

immature elastic fibres:

Oxytalan Eluanin

Indifferent fiber plexus


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Principal fibres Type I and III collagen :

fibrils form fibers

In type I collagen: fibers

are arranged in bundles

Follow a wavy course

Terminal portionsinserted into cementum

and bone: Sharpeys

fibres


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Fibers

Mechanical strength of PDL is derived from

the molecular structure of type I collagen

AND its arrangementinto fibers

Tensile strength > steel

Unique in that they connect 2 mineralized

tissues

Resemble a stretched fishing net


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Groups of fibres

Transseptal group

Connect adjacent teeth

Alveolar crest group

Resist extrusion, lateral

movements

Horizontal group

Resist lateral movements

Oblique group

Receive the bulk of vertical

forces


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Apical group

Resist intrusion &

extrusion

Inter-radicular group

Furcation areas of multi-

rooted teeth

Groups of fibres


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The PDL is derived from ectomesenchymal cells of

the dental follicle

Sharpeys fibres start to form before cementum and

alveolar bone are mineralised

Fibroblasts produce tropocollagen molecules,

which aggregate into microfibrils, that are packed

together to form fibrils. Fibrils aggregate together

to form fibres, and fibres aggregate to form

bundles. Collagen fibrils are cross-striated

Formation of Principal Fibres


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Collagen Fiber Bundles


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Sharpeys fibers

At insertion, PDL fibers are fully or

partially mineralized

High levels of non-collagenous proteins,

such as osteopontin


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Cells

C.T cells:

Fibroblasts, Osteoblasts, Cementoblasts

Osteoclasts, odonoclasts

Defence cells:

macrophages, mast cells, eosinophils

Sensory cells

Epithelial rests of Malassez:

remnants of HERS

Undifferentiated Cells


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The Fibroblast

The most common cell in

PDL

Formation & remodeling ofPDL fibers

Highly dynamic cell

Their long axis is orientedparallel to direction of

collagen fibers

Signals are partly

mediated by forces


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Epithelial Rests of Malassez


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Ground Substance

60% of PDL by volume

Water (70%)

Glycoproteins: fibronectin, laminin

Glycosaminogycans: hyalurnic acid,

proteoglycans

May contain cementicles


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Functions of PDL

Supportive functionattaches the tooth to

the bony socket and suspends the tooth so

it does not grind on the bone duringchewing

Sensory functiontransmits tactile

pressure and pain sensationsNutritive functionhas blood vessels that

provide nutrients to the cementum and the

bone


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Functions of PDL

Formative functioncontains

cementoblasts that produce the cementum

throughout the life of the tooth

Resorptive functioncontains osteoclasts

that can resorb the bone and the cementum


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Periodontal Ligament Space

Variable in width, (average 0.2 mm)

Reduced in:

Unerupted & non-functional teeth

With age

In permanent teeth

Increased with:

Heavy occlusal stress


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Thank you

The Normal Periodontium PDL

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