Oral physiology (occlusion included)
Periodontal Ligament & Cementum
E-mail [email protected]
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