Oral physiology (occlusion included)

Periodontal Ligament & Cementum

E-mail cweijen1@tmu.edu.tw

1. let the student to understand the base knolwedge of oral physisology.

2.The student can firsther studying the advance courses of dental science.

1.Applied Oral Physiology, 2nd ed. Christopher L.B.Lavelle Butterworths& Co.Lts, 1998

2.Physiology for dental students 1st ed. D.B.Ferguson. Butterworths & Co.Lts, 1998.

Periodontal Ligament & Cementum

Periodontium

The attachment apparatus of the tooth and consists of cementum, PDL, bone

lining the alveolus, and part of the gingiva

Periodontal Ligament The PDL is composed of a

complex vascular and highly cellular connective tissue that surrounds the tooth root and connects it to the inner wall of the alveolar bone

The average width of the PDL is about 0.2 mm, ranging from 0.15 to 0.38 mm. The width decrease with age

The thinnest portion is around the middle third of the root

Cells of the Periodontal Ligament

Connective tissue cellsEpithelial rest cells Immune system cellsCells associated with

neurovascular elementsUndifferentiated

mesenchymal cells

Connective Tissue Cells Fibroblasts

Most common cells in PDL Appear as ovoid or elongated cells

along the principal fibers Pseudopodia-like process Producing collagen which has high

turnover rate Cementoblasts

Line the ligament surface of the cementum

Most often seen in resting phase Cementum does not remodel,

cementoclasts (odontoclasts) are not normally found in the ligament

Osteoblasts Osteoclasts Odontoclasts

Epithelial rest cells The epithelial rests of

Malassez form a latticework in the PDL and appear as either isolated clusters of cells or interlacing stands

Considered remnants of Hertwigs root sheath

Contain keratinocytegrowth factors

Participate in the formation of periapicalcysts and lateral root cysts

Defense Cells

Neutrophils Lymphocyte

s Macrophage

s Mast cells Eosinophils

Undifferentiated mesenchymal cells (Progenitor cells)

Although it has been demonstrated that they are a source of new cells for the PDL, it is not known whether a single progenitor cell gives rise to daughter cells that differentiate into fibroblasts, osteoblasts, and cementoblasts, or whether there are separate progenitors for each cell line

Periodontal Fibers The most important

elements of PDL are the principal fibers, collagenous and arranged in bundles

The terminal portions of the principal fibers that are inserted into cementum and bone are termed Sharpeysfibers

Collagen

The term collagen derives from the greekwork for glue, it yields gelatin on boiling

The main constituent of skin, bone, cartilage, tendon and is also present in specialized structure such as basement membranes, vitreous, cornea, aorta and other tissue

Triple-chain helix

Collagen A protein composed of different amino acids, the

most important of which are glycine, proline, hydroxylysine and hydroxyproline

At least 19 recognized collagen species encoded by at least 25 separate genes, dispersed among 12 chromosome

The principal fibers are composed mainly of collagen type I, whereas reticular fibers are composed of collagen type III. Collagen type IV is found in the basal lamina

Collagen Biosynthesis Occurs inside the

fibroblasts to form tropocollagen molecules

Tropocollagen molecules aggregate into microfibrilthat are packed together to form fibrils

Collagen is synthesized by fibroblasts, chondroblasts, osteoblasts, odontoblasts, and other cells

Collagen Biosynthesis Intracellular steps

Transcription of individual genes

Translation Hydroxylation of prolyl &

Lysyl residues Helix formation & secretion

Extracellular steps Processing Fibril formation Cross linking & fibril

stabilization

Principal Fibers Transseptal group Alveolar crest group

Prevent the extrusion of the tooth

Horizontal group Oblique group

Bear the brunt of vertical masticatory stress & transform them into tension on the alveolar bone

Apical group Interradicular group

In the furcation area

Gingival Ligament

Dentogingival group Alveologingival group Circular group Dentoperiosteal

group Transseptal fiber

system

Oxytalan & Eluanin

Although the PDL does not contain mature elastin, two immature forms are found: oxytalanand eluanin

Oxytalan fibers run parallel to the root surface in a vertical direction and bend to attach to the cementum

Regulate vascular flow Oxytalan fibers have been shown to develop de

novo in the regenerated PDL

Other fibers

Small collagen fibers associated with the larger principal collagen finers have been described

Run in all directions Indifferent fiber plexus

Extracellular Matrix

Ground substance

Ground Substance Filling spaces between

fibers & cells Main components:

Glycosaminoglycans Hyaluronic acid proteoglycon

Glycoprotein Fibronectin Laminin

Glycolipids Calcified masses:

cementicles Calcified epi rests Calcified Sharpeys fiber Calcified, thrombosed

vessels

Physical Functions Provision of a soft tissue casing to protect the

vessels and nerves from injury by mechanical forces

Transmission of occlusal forces to the bone Attachment of the teeth to the bone Maintenance of the gingival tissues in their

proper relationship to the teeth Resistance to the impact of occlusal forces

(shock absorption)

Shock absorption

Tensional theory When a force is applied to the crown, the

principal fibers first unfold and straighten and then transmit forces to the alveolar bone, cause an elastic deformation of the bony socket.

Finally when the alveolar bone has reached its limit, the load is transmitted to the basal bone

Shock absorption Viscoelastic system theory

The displacement of the tooth is largely controlled by fluid movements, with fibers having only a second role

When forces are transmitted to the tooth, the extracellular fluid passes from the PDL into the marrow spaces of bone through foramina in the cribriform plate

After depletion of tissue fluids, the fiber bundles absorb the slack and tighten, which lead to a blood vessel stenosis. Arterial back pressure causes ballooning of the vessel and passage of the blood ultrafitrates into the tissue, thereby replenishing the tissue fluid

Transmission of Occlusal Forces to the Bone

The arrangement of the principal fibers is similar to a suspension bridge or a hammock.

When an axial force is applied to a tooth, a tendency toward displacement of the root into the alveolar occurs

The oblique fibers alter their wavy, untensed pattern; assume their full length; and sustain the major part of the axial force

The apical portion of the root moves in a direction opposite to the coronal portion

In areas of tension, the principal fiber bundles are taut rather than wavy. In areas of pressure, the fibers are compressed

Formative & Remodeling Function

Cells of the PDL participate in the formation and resorption of cementum and bone, which occur in physiologic tooth movement; in the accommodation of the periodontium to occlusal forces; and in the repair of injuries

The PDL is constantly undergoing remodeling. Fibroblasts form the collagen fibers, and the residual mesenchymal cells develop into osteoblasts, cememtoblasts, and fibroblasts affect the rate of formation of collagen, cementum and bone

The rate of collagen synthesis is twice as fast as that in the gingiva and four times as fast as that in the skin

Nutritional & Sensory Function

The PDL supplies nutrients to the cementum, bone, and gingiva by way of the blood vessels and also provides lymphatic drainage

In relation to other ligaments and tendons, PDL is highly vascularized

This high blood vessel content may provide hydrodynamic damping to applied forces, as well as high perfusion rates to the PDL

Nutritional & Sensory Function The PDL is abundantly supplied with sensory

nerve fibers capable of transmitting tactile, pressure, and pain sensations by the trigeminal pathways

The bundles divide into single myelinated fibers, which ultimately lose their myelin sheaths and end in one of four types of neural termination: Free ending Ruffini-like mechanoreceptors, primarily in the

apical area Coiled meissners corpuscles, mainly in the midroot

region Spindlelike pressure and vibration endings, mainly

in the apex

Nerve terminals in a human

Free ending

Ruffini-like mechanoreceptors

Coiled meissnerscorpuscles

Spindlelike endings

Functions of PDL

PhysicalFormative

RemodelingNutritionalsensory

Cementum

The calcified, avascularmesenchymal tissue that forms

the outer covering of the anatomic root

Cementum

Acellular (primary) cementum

Cellular (secondary) cementum

Both consist of a calcified interfibrillarmatrix and collagen fibrils

Cementum

The two main sources of collagen fibers in cementum are Sharpeys fiber (extrinsic): embedded portion of the

principal fibers of the PDL and formed by fibroblasts Fibers that belong to the cementum matrix (intrinsic)

and are produced by the cememtoblasts Cementoblasts also form the noncollagenous

components of the interfibrillar ground substance, such as proteoglycans, glycoproteins, and phosphoproteins

Cementum

The major proportion of the organic matrix of a cementum is composed of type I (90%) and type III (about 5%) collagens.

Sharpeys fibers are composed of mainly type I collagen where the type III collagen appears to coat the type I collagen of Sharpeys fibers

Acellular Cementum Acellular cememtum is the first cementum formed,

covers approximately the cervical third or half of the root

Formed before the tooth reaches the occlusal plane. Its thickness ranges from 30 to 230 m

Sharpeys fibers make up most of the structure of acellular cementum. Most fibers are inserted at approximately right angle into the root surface. Their size, number and distribution increase with function

Acellular Cementum

Sharpeys fibers are completely calcified, with the mineral crystals oriented parallel to the fibrils

Acellular cementumalso contains calcified intrinsic collagen fibrils

Cellular Cementum

Formed after the tooth reaches the occlusalplane

Cellular cementum is less calcified than the acellular type

Cellular Cementum More irregular and

contains cells (cementocytes) in individual spaces (lacunae) that communicate with each other through a system of anastomosingcanaliculi

Cementum Both acellular cementum and cellular cementum are

arranged in lamellae separated by incremental lines parallel to the long axis of the root

These lines represent rest periods in cementumformation and are more mineralized than the adjacent cementum

The inorganic content of cementum (hydroxyapatite) is 45% to 50%, which is less than that of bone (65%), enamel (97%), or dentin (70%)

Acellular cementum and cellular cementum are very permeable. The permeability of cementum diminishes with age

Schroeders Classification Acellular afibrillar cementum (AAC)

Contains neither cells nor extrinsic or intrinsic collagen fibers, except for mineralized ground substance. Coronal cementum. (1-15 m)

Acellular extrinsic fiber cementum (AEFC) Composed almost entirely of densely packed bundles of

Sharpeys fibers. Cervical third of roots. (30-230 m) Cellular mixed stratified cementum (CMSC)

Composed of extrinsic & intrinsic fibers and may contain cells. Co-product of fibroblasts and cementoblasts. Apical third of the roots, apices and furcation areas. (100-1000 m)

Schroeders Classification

Cellular intrinsic fiber cementum (CIFC) Contains cells but no extrinsic collagen fibers.

Formed by cementoblasts. It fills resorptionlacunae

Intermediate cementum Poorly defined zone near the cementodentinal

junction of certain teeth Contain cellular remnants of Hertwigs sheath

embeded in calcified ground substance

Cementoenamel Junction Three types of

relationships: In about 60-65%,

cementum overlaps the enamel

In about 30%, edge-to-edge butt joint exists

In 5-10%, the cementum and enamel fail to meet

Cementoenamel Junction

Studies with the SEM indicate that the cementoenameljunction exhibits all of the above forms and shows considerable variation when trace circumferentially

Cementoenamel Junction Summary