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1
PRESENTER DR.PUNIT
(I YEAR PG)
2
CONTENTS
Introduction
Synonyms
Shape of pdl
Development
Composition
PDL as specialized connective tissue
Blood supply
Nerve supply
Function
Clinical considerations
Conclusion
References
3
INTRODUCTION
Periodontium/Attachment
apparatus/Supporting tissues of
teeth):
gingiva
attachment apparatus (alveolar bone,
periodontal ligament and cementum)
• Main function –It attaches the tooth to
the bone of jaws.
Maintains the integrity of the surface
of masticatory mucosa of the oral
cavity 4
A ligament is defined as a band of fibrous tissue binding
together skeletal elements.
The root of tooth connected to the socket in alveolar bone by
dense fibrous connective tissue which can be regarded as a
ligament.
PDL is very unique from all other ligaments in the body
connects and restricts the hard tissues-tooth cementum and
alveolar bone.
5
The periodontal ligament is a soft, fibrous specialized
connective tissue which is present in the periodontal space,
which is situated between the cementum of root of the tooth
and the bone forming the socket wall.
The periodontal ligament extends coronally up to the most
apical part of connective tissue of gingiva
6
DEFINITIONS
Periodontal ligament is composed of soft complex vascular and
highly cellular connective tissue that surrounds the tooth root and
connects to the inner wall of the alveolar bone (Mc Culloch CA,
Lekic P, Mc Kee MD Periodontol 2000 24:56,2000)
ACCORDING TO BERKOVITZ:
“it is the dense fibrous connective tissue that occupies theperiodontal ligament space between the roots of teeth andalveolus. It is derived from the dental follicle above alveolarcrest and is continuous with connective tissue of gingiva andthe apical foramen which is further continuation with dentalpulp.
7
It is a narrow and highly cellular CT that forms theinterface between alveolar bone and cementum.(Periodontol 2000,vol.3,1993)
Soft, richly vascular and cellular connective tissue whichsurrounds the roots of the teeth and joins the rootcementum with the socket wall. (Jan Lindhe 5th ed)
The periodontal ligament occupies the periodontal space,which is located between the cementum and theperiodontal surface of alveolar bone and extends coronallyto the most apical part of the lamina propria of the gingiva.(Orban’s)
8
COMPOSITION 53 – 74 % of periodontal ligament volume consists of
collagen and oxytalan fibers.
1 – 2 % consist of vascular elements.
Remainder consists of cells and neural elements.
The connective tissue of periodontal ligament
comprises collagen
Proteoglycan, glycoprotein and small amount of
glycogen.
Major component is Type – I collagen with Type III
collagen accounting for 15 – 20 % of total collagen
9
SHAPE OF PERIODONTAL LIGAMENT
HOUR GLASS SHAPE
Thinnest around the middle third of the root & widens both
apically and near the crest.
10
It is neither a typical membrane nor typical ligament .
However , because it is a complex, soft connective tissue
providing continuity between two mineralized tissue
(cementum and bone).
Width variable = average 0.15 mm– 0.38mm.
11
Age in years
Width
11-16 0.21mm
32-52 0.18mm
51-67 0.15mm
PERIODONTAL LIGAMENT DECREASES WITH AGE(TENCATE 6TH EDITION)
12
SYNONYMS OF PERIODONTAL LIGAMENT
1. Desmondont
2. Pericementum
3. Dental Periosteum
4. Alveolodental ligament
5. Periodontal membrane
(PERIO 2000 volume 3)
13
EVOLUTION Reptiles have ankylosed teeth.
During the period of transition following changestakes place :
a. Size of jaw decreased
b. Change in articulation of jaw
c. Change in size and shape of the teeth
(ORBANS TEXTBOOK 13TH EDITION)
14
DEVELOPMENT
15
DEVELOPMENT OF PERIODONTAL LIGAMENT
16
Development of periodontal ligament begins with root
formation ,prior to the tooth eruption. Continuous proliferation
of internal and external epithelium forms cervical cusp of tooth
bud. Sheath of epithelial cells grows apically in form of
HERTWIG’S ROOT SHEATH.
(Jan Lindhe 5th edition and Berkovitz 2nd edition)
17
Sheath forms a circumferential structure enclosing dental
papilla separating it from the dental follicle cells. Dental follicle
cells located between alveolar bone and epithelial root sheath
composed of two cells:
A. mesenchymal cells of dental follicle proper
B. proliferative mesenchyme
18
Mesenchymal cells of perifollicular mesenchyme bounded bydental follicle proper & developing alveolar bone is stellateshaped. Cells are widely separated & contain euchromaticnucleus, very little cytoplasm, short cisternae of roughendoplasmic reticulum, mitochondria, free ribosomes.
As the root formation continues cells in perifollicular area gaintheir polarity and cellular volume & synthetic activity increases.These cells become elongated & contain increased amount ofROUGH ENDOPLASMIC RETICULUM, mitochondria &active Golgi complex. As a result actively synthesize collagenfibrils
19
DEVELOPMENT OF PRINCIPAL FIBERS
Immediately before tooth eruption active fibroblasts adjacent to
cementum of coronal third of root aligned in oblique direction to
long axis of the tooth. Soon thereafter the First collagen fiber
bundles of ligament become discernible and these are the
precursor of alveolar crest fiber bundles.
Further apically organized fibers are not seen but examination of
root surface at higher magnification reveals fine brush like fibers
extending from cementum.
20
Similar fibers are observed on the adjacent osseous surfaces of
the developing alveolar process . Both set of fibers cemental
and alveolar continue to elongate towards each other ultimately
to meet intertwine and fuse.
By the time first occlusal contact of the tooth with its
antagonist the principal fibers around the coronal third of root
the horizontal group are almost completely developed.
21
Oblique fibers in the middle of the root still being formed as
eruption continues & definite occlusion is established there is
progressive apical migration of oblique fiber bundles. With the
formation of apical fiber group definite periodontal architecture
is established.
22
Development….
Fig 2 Fig 1 Fig 3
DEVELOPMENT OF CELLS
Prior to the root formation cells of follicle show very feworganelles. With onset of root formation organelles in cellsincrease, collagen & ground substance formation begins &fills in extracellular space.
Stem cells which give rise to cementoblasts, osteoblasts &fibroblasts in perivascular location. Osteoclasts appear atthe alveolar bone surface allowing remodeling of bone inassociation with tooth eruption.
24
PERIODONTAL LIGAMENT
HOMEOSTASIS
Studies have indicated that population of the cells of
periodontal ligament both during development and
regeneration secrete molecules that can regulate the extent
of mineralization and prevent the fusion of the tooth root
with surrounding bone (ankylosis).
Various molecules have been proposed which play a role in
maintaining an unmineralized periodontal ligament.
MSX2 prevents osteogenic differentiation of periodontal
ligament fibroblasts by repressing RUNX2(RUNT RELATED
TRANSCRIPTION FACTOR 2)also known as cbfa1(core
binding factor alpha1)
25
Balance between activities of bone sialoprotein and osteopontin
also contributes towards maintaining an unmineralized
periodontal ligament region.
MATRIX ‘GLA’ protein an inhibitor of mineralization is also
present in periodontal ligament. It plays a role preserving
periodontal ligament region.
26
RGD-CEMENTUM ATTACHMENT PROTEIN a collagen
associated protein play a role in maintaining the unmineralized
state of periodontal ligament.
TGF-BETA isoforms synthesized by periodontal ligament cells
can induce mitogenic effects and also downregulate osteoblastic
differentiation of periodontal ligament cells.
Prostaglandins which are also produced by the periodontal
ligament cells can inhibit mineralized bone nodule formation and
prevent mineralization by periodontal ligament cells in vitro
27
The periodontal ligament has the capacity to adapt to functional
changes, when functional changes increase width of periodontal
ligament increases as much as by 50% and fiber bundles also
increases its thickness.
A reduction in function leads to narrowing of the ligament and
decrease in number and thickness of fiber bundles.
28
PERIODONTAL LIGAMENT:
EXTRACELLULAR
CELLULAR
29
EXTRACELLULAR STRUCTURES
Collagen Proteoglycans
Elastic Glycoproteins
RETICULAR Glycosaminoglycan's
INDIFFERENT FIBER PLEXUS
OXYTALAN
FIBERS GROUND
SUBSTANCE
30
PERIODONTAL FIBERS
Most important elements of periodontal ligament arethe principal fibers which are collagenous & arrangedin bundles & follow a wavy course when viewed inlongitudinal section.
Terminal portions of principal fibers are inserted intocementum called SHARPEY’S FIBERS. It forms acontinuous anastomosing network b/w tooth andbone.
31
Sharpey’s fibers are abundant non collagenous proteins found in
bone and cementum among these are OSTEOPONTIN AND
SIALOPROTEIN(regulators of mineralization).
Collagen is protein of different amino acids most important are
GLYCINE,
PROLINE,HYDROXYPROLINE,HYDROXYLYSINE.
32
33
1.Mesenchymal Cells & Their Derivatives
FIBROBLASTS ( major cells )
Chondrocytes
Osteoblasts
Odontoblasts
CEMENTOBLASTS
COLLAGEN
It is a protein – most abundant protein in animalkingdom.
Derived from – Greek – kolla(glue) and gene.- French – glue producing constituents.
Rigid, rod-like structure-resists stretching and fibers madeof collagen have high tensile strength.
Also participates in biologic functions-cell shape,differentiation.
It is an important constituent of PDL where mechanicalforces must be transmitted without loss
34
SEQUENCE OF EVENTS
A. Sequence of intracellular collagen biosynthesisAssembly pro-alfa chains (directed by specific mRNAs)
Proline hydroxylation
Lysine hydroxylation
Hydroxylysine glycosylation
Disulphide bond formation/incorporation of C Terminal Propeptides.Secretion
35
several enzymes are involved in the destruction of matrix
components collage breakdown is mediated primarily by
the COLLAGENASES ( Type of MMP) These are
specialized enzymes that have evolved specifically to
hydrolyze collagens ,because their triple helical collagen
structure is resistant to most common proteinases.
36
38
Fibroblasts are responsible for theproduction of the extracellular matrixcomponents.They reside in close proximity to thecollagen fibers.The nucleus appears as an elongated or disklike structure in H & E preparations. Thethin, pale staining, flattened processes thatform the bulk of the cytoplasm are usuallynot visible.
Myofibroblast is an elongate, spindle
connective tissue cell that displays typical
characteristics of the fibroblast along with
characteristics of smooth muscle cells
Sequence of extracellular collagen biosynthesis
Amino terminal extension cleavage (procollagen aminopeptidase)
Carboxyl terminal extension cleavage ( procollagen carboxypeptidase)
formation of collagen fibrils and spontaneous arrangement of fibrils
cross link formation by the action of lysyl oxidase enzyme,deamination of lysyl
residues and maturation of cross-links. Growth and reorganization of fibers.
39
CHARACTERISTIC FEATURES OF COLLAGEN1)Triple helical structure- alfa chains-left handed helices.The triple helix may be continuous/interrupted by non-collagenous segments.
2)Within triple helical domain, glycine –every 3rd
position in the amino acid sequence Gly-X-Y,where X , Y –amino acids other than glycine.(Proline)
3) Contains 2 unique amino acids- Hydroxyproline andHydroxylysine.
4)Collagen is stabilized through formation of Lysine-derivedintra- and intermolecular cross-links.
42
COLLAGEN TYPES
So far 19 types of collagen have been discovered.
Collagen classes
a. Interstitial collagens ---- Type I,II,III
b. Basement membrane type ---- Type IV,VI,VII
c. Short chain collagens ---- Type IX,X
43
Based on their ability to form fibrils, collagens are of 3 groups:
-FIBRIL-FORMING : triple helix has uninterrupted stretch of Gly-X-Y
residues. Includes types 1,2,3,5,11.
-FACIT : (Fibril Associated Collagens with Interrupted Triple helices)-collagenous domains interrupted by non-
collagenous sequences. Includes Types 9,12,14(contains GAG) and may be16
-NON-FIBRILLAR: Forms sheets/membranes enclosing tissues andorganisms.
Types 4,8,10- Network forming
Type 6-Beaded
Type 7-Anchoring fibrils
44
Collagen is responsible for maintenance of frameworkand tone of tissue biosynthesis of collagen insidefibroblasts to form procollagen molecules. It has atransverse striations with characteristic periodicity of64nm. These striations are caused by overlappingarrangement of tropocollagen molecules.
45
Collagen is gathered to form bundles approximately 5micrometers in diameter. These bundles are calledPRINCIPAL FIBERS. within each bundle subunits arepresent called COLLAGEN FIBRILS.
46
Type I, III, V, XII – Periodontal Ligament
Type VI, II – cartilage
Type IV - Basement membrane
Type VI – Ligaments, skin, bone
Type VII - Anchoring fibrils of basement
membrane
Type IX - Cartilage
Type X, XI - Cartilage, Bone
Type XIII - Epidermis Cartilage
Collagen is synthesized by fibroblasts , chondroblasts ,osteoblasts, odontoblasts and other cells.
47
Principal fibers composed of mainly TYPE I
RETICULAR FIBERS COMPOSED OF TYPE III
BASAL LAMINA COMPOSED OF TYPE IV
48
TYPES OF COLLAGEN FIBERS TYPE I – SKIN,TENDON, VASCULAR
LIGATURE,ORGANS,BONE
TYPE II – CARTILAGE
TYPE III – RETICULAR
TYPE IV – FORMS BASAL LAMINA
49
TYPE V – CELL SURFACES , HAIR AND PLACENTA
TYPE VI – SUBSTANCE FOR CELL ATTACHMENT & AS AN ANCHORING MESHWORK THAT CONNECTS COLLAGEN FIBERS , NERVES & BLOOD VESSELS TO SURROUNDING MATRIX.
50
TYPE VII – ACTS AS AN ANCHORING FIBRILS.
TYPE XII – ASSOCIATED WITH TOOTHDEVELOPMENT,ALIGNMENT, ORGANIZATION OFPERIODONTAL FIBERS.
51
NON-COLLAGENOUS PROTEINSFIBRONECTIN:-2 forms-soluble plasma form(pFN) & cross-linked fibrillar
form in most tissues (cellular/cFN) .
-Functions: -Within matrix, bridge between cells & collagen-(cell adhesion, migration)
-Has specific domains to bind to Heparin, fibrin,collagen hence role in matrix
assembly & stabilization-Reservoir for cytokines, growth factors.
-In wounds, it’s a chemotactic, helps to clear fibrinfrom inflamed sites.
52
LAMININ In embryonic tissues-the first extracellular protein detected &
in mature tissues –universally found as the major noncollagen component in basement membranes.
-Involved in cell attachment, cell proliferation and cell differentiation .
-Has domains for the attachment of cells, heparin ,elastin,
type IV collagen , nidogen,entactin and galactoside-binding lectins.
- Associated with cell rests of Malassez of PDL.
53
OSTEOCALCIN / BONE Gla ProteinOsteocalcin is a small protein –odontoblasts & osteoblasts .
-Osteocalcin is highly specific for calcified tissues.
-The post-translational vitamin K dependent carboxylation ofglutamic acid residues allows the osteocalcin molecule tobind calcium .
- The molecule undergoes a conformational shift
when associated with hydroxyapatite.
-Serum osteocalcin levels correlates with histomorphometricanalysis of new bone.
54
BONE SIALOPROTEIN (BSP II)
Major structural protein of bone matrix, expressed byfully differentiated osteoblasts.
-15% of non-collagenous proteins.
-Found in reversal lines of rapidly remodeling bone
-Expressed by cementoblasts during cementogenesis &also during early formation of dentin
55
OSTEOPONTIN
High content –serine,asparagine,glutamate.
-Found primarily in bone & several nonskeletal tissues (thecentral nervous system, kidney and placenta).
-In bone, the synthesis and release of Osteopontin by osteoblasts -endocrine (calcitriol, corticosteroids, and parathyroid hormone)and paracrine(TGF) control.
-Functions not clear-proposed that Osteopontin is involved inboth the attachment and movement of osteoblasts andosteoclasts in bone via integrin mediated cell binding.
- implicated in calcium regulation
56
HOW OSTEOPONTIN HELPS IN
MINERALIZATION??
In native bone tissue 10-30% of the tissue mass is proteinaceous and the
remaining 70-90% is comprised of calcium phosphate mineral, which is
primarily hydroxyapatite (HA).
The protein component of bone has been shown to be ∼90% collagenous,
while the remaining 10% of the protein content is believed to play a role in
bone formation, growth, repair, and cellular adhesion to the matrix.
The primary group of non-collagenous proteins found in bone are the SIBLING (small integrin-binding ligand, N-linked glycoprotein) family of proteins and they are believed to play a key role in these processes.
57
Continuation…….
The SIBLING family of proteins consists of five members: osteopontin (OPN),
matrix extracellular phosphoglycoprotein (MEPE), bone sialoprotein (BSP),
dentin matrix protein 1 (DMP1), and dentin sialophosphoprotein (DSPP).
The SIBLING proteins have a number of shared characteristics including a
collagen binding domain, a HA binding domain, and a cell binding arganine-
glycine-aspartic acid (RGD) sequence. Additionally, they are all located on the
same human chromosome (4q21)
all of the proteins are post-translationally phosphorylated and have been immunolocalized in mineralized tissues.Together, these characteristics suggest that the SIBLING family of proteins play an important role in bone development by facilitating cellular adhesion, mineral nucleation, and mineral maturation.
58
MEPE has been shown to be a potent inhibitor of mineralization both in
vitro and in vivo and therefore is not expected to play a role in the induction of
biomineralization.
DMP1 is believed to regulate the mineralization process, possibly mediating
the transformation of amorphous calcium phosphate to crystalline HA.
OPN has been shown to either inhibit or induce mineralization based on its
phosphorylation state, but most likely regulates the mineralization process in
bone.
59
SPARC / OSTEONECTIN
-SPARC: Secreted protein acidic and rich in cysteine.
-Found in greatest abundance in osseous tissue, tissuescharacterized by high turnover ,basement membranes .
-Osteonectin is expressed -chondrocytes,fibroblasts, platelets,endothelial cells, epithelial cells, Leydig cells, Sertoli cells,adrenal cortical cells and numerous neoplastic cell lines.
-Functions- mineralization of bone and cartilage-inhibiting mineralization.-modulation of cell proliferation.-anti adhesive, disrupts focal adhesion in fibroblasts.
60
TENASCIN/CYTOTACTIN
-Star shaped structure with central knot.
-Binds to fibronectin, chondrointin sulphate.
-Mediates both adhesive & repulsive interactions.
-Detected in attachment zone of periodontal ligament atinterface between mineralized & non mineralized tissues.
-Role in wound healing, tumourogenesis and cell migration.
61
NIDOGEN/ ENTACTIN
-Dumb bell shaped with 2 globular domains.
-Crucial role in basement membrane organization & stabilization.
-Interacts with both cell surface proteins & extra cellular matrix proteins.
-Binds to laminin & type 4 collagen
62
PERIODONTAL LIGAMENT FIBERS
63
ARRANGED IN 6 GROUPS TRANSSEPTAL
OBLIQUE
INTERRADICULAR
APICAL
ALVEOLAR CREST
HORIZONTAL
64
TRANSSEPTAL FIBERS:
Extend interproximally over alveolar crest and are embedded in cementum of adjacent tissue.
Reconstructed even after destruction of alveolar bone resulting from periodontal disease.
65
ALVEOLAR CREST GROUP:
Extend obliquely from cementum just beneath cementoenamel junctional epithelium to alveolar crest.
Fibers also run from cementum over the alveolar crest & to the fibrous layer of periosteum covering the alveolar bone.
66
These fibers RESIST TILTING, INTRUSIVE, EXTRUSIVE, ROTATIONAL FORCES.
It is often confused with the dentoperiosteal groups of fibers.
Any collagenous fibers located apical to the line joining the height of the each interdental bony septum termed as periodontal and those coronal to the line is gingival.
67
HORIZONTAL GROUP:
These fibers run at right angles to the long axis of the tooth from cementum to alveolar bone and parallel to the occlusal plane of the arch.
Found immediately apical to the alveolar crest group. These fibers pass from their cemental attachment directly across the periodontal ligament space to become inserted in alveolar process as sharpey’s fibers .
68
Limited to the coronal one- fourth of periodontal ligament space.
These fibers RESIST HORIZONTAL AND TIPPING FORCES.
69
OBLIQUE GROUP:
These are the most numerous and occupy nearly 2/3rd of the ligament.
Inserted into the alveolar bone at a position coronal to their attachment to cementum resulting in their oblique orientation within periodontal space. RESIST VERTICAL AND INTRUSIVE FORCES
70
APICAL GROUP :
From cementum at the root tip , fibers of the apicalbundles radiate through the periodontal space tobecome anchored into the fundus of bony socket.
RESIST FORCES OF LUXATION, PREVENT TOOTHTIPPING & PROTECT DELICATE BLOOD AND LYMPHVESSELS AND NERVES TRAVERSING PERIODONTALLIGAMENT SPACE AT ROOT APEX.NOT SEEN ININCOMPLETE FORMED ROOTS.
71
INTERRADICULAR GROUP:
Principal fibers of this group are inserted into thecementum from crest of interradicular septum inmultirooted tooth.
RESIST TOOTH TIPPING , TORQUING ANDLUXATION.
72
These fibers are lost if age related gingival recession proceeds to the extent that the furcation area is exposed. Total loss of these fibers occur in chronic inflammatory periodontal disease.
73
Some author consider GINGIVAL FIBER GROUP to be part of the principal fibers of the periodontal ligament.
The gingival fiber groups are found within the lamina propria of marginal gingiva. These gingival fibers are separate but adjacent fiber groups which support the marginal gingival tissues to maintain the relationship of the teeth.
74
SHARPEYS’ FIBERS ;
Collagen fibers are embedded into the cementum on one side of the periodontal space & into the alveolar bone on the other.
The embedded fibers are called SHARPEY’S FIBERS.
75
76
These are the most numerous but smaller at their attachment into cementum than alveolar bone. The mineralized parts of the sharpey’s fibers in alveolar bone proper appear as projecting stubs covered with mineral clusters.
The mineralization is at right angles to long axis of fibers, indicating that fibers are subjected to tensional forces.
77
Sharpey’s fibers in primary acellular cementum aremineralized fully those in cellular cementum and boneare mineralized partially at their periphery.
Few Sharpey's fibers pass uninterruptedly through thebone of alveolar process termed (TRANSALVEOLARFIBERS)to continue as principal fibers of adjacentperiodontal ligament or mingle buccally or linguallywith fibers of periosteum that cover the outer plates ofalveolar process.
78
These fibers pass through the alveolar process only when process consists entirely of compact bone and contains no haversian system.
Once embedded in either the wall of alveolus or the tooth Sharpey’s fibers calcify to certain degree & are associated with abundance of non collagenous proteins namely OSTEOPONTIN AND BONE SIALOPROTEIN.
79
INTERMEDIATE PLEXUSES :
It was believed that principal fibers frequently followed a wavy course from cementum to alveolar bone and are joined in the mid region of periodontal space giving rise to a zone of distinct appearance called INTERMEDIATE PLEXUSES
80
The plexuses was considered to be an area of high metabolic activity in which splicing and unsplicing of fibers might occur. Studies have indicated that once cemental fibers meet and fuse with the bone no such plexuses remains.
81
ELASTIC FIBERS :
There are three types of elastic fibers which are histochemically and ultrastructurally different.
They are :
MATURE ELASTIC FIBERS
ELASTIN FIBERS
ELAUNIN FIBERS
OXYTALAN FIBERS
(BERKOVITZ 2ND edition)
82
MATURE ELASTIC FIBERS:
Consist of microfibrillar component surrounding an amorphous core of elastin protein. Elastin protein contains high percentage of GLYCINE,PROLINE , HYDROPHOBIC RESIDUES with LITTLE HYDROXYPROLINE & NO HYDROXYLYSINE.
83
Microfibrillar component is located around the periphery & scattered throughout the amorphous component.
These fibers are observed only in walls of different blood vessels where they constitute the elastic laminae of larger arterioles and arteries of greater caliber.
84
ELAUNIN FIBERS :
These are seen as bundles of microfibrils embedded in a relatively small amount of amorphous elastin.
These fibers found within the fibers of gingival ligament. An elastic meshwork has been described in pdl as being composed of many elastin lamellae with peripheral oxytalan fibers and elaunin fibers .
85
OXYTALAN FIBERS:
It is a type of immature elastic fibers, consist of microfibrillar component only.
It forms a three dimensional meshwork that extends from cementum to peripheral periodontal blood vessels. The meshwork is largely oriented in apico-occlusal plane & interconnected with fine lateral fibrils.
86
87
Depending on site & species oxytalan fibers measures between 0.2 -1.5 micrometer in diameter in electron microscope and occupy 3% pdl in humans.
In contrast in light microscopy they measure 0.5 – 2.5 micrometer in diameter.
These fibers are not susceptible to acid hydrolysis .
88
Orientation of oxytalan fibers is completely different when compared to the other collagen fibers.
Instead of running from bone to cementum they run in axial direction. One end being embedded in cementum or bone and other end in wall of blood vessel.
89
In the cervical region they follow the course of gingival and trans septal fibers. Within the periodontal ligament proper, these fibers are longitudinally arranged, crossing the oblique fibers perpendicularly. In the vicinity of the apex they form a complex network.
90
Function of oxytalan fibers is unknown but it has been suggested that they may a play a pivotal role in supporting the blood vessels of periodontal ligament.
They are thicker and more numerous in teeth subjected to high loads as in orthodontic tooth movement. Thus, these fibers play a role in tooth support.
91
RETICULAR FIBERS:
These are fine immature collagen fibers with argyrophilic staining properties and are related to basement membrane of blood vessels and epithelial cells which lie within the periodontal ligament. These fibers are composed of TYPE III collagen.
92
SECONDARY FIBERS:
These are located between and among the principal fibers.
These fibers are relatively non directional and randomly oriented.
Represent newly formed collagenous elements that have not yet incorporated into principal fiber bundles.
93
These fibers traverse the periodontal ligament space corono-apically and are often associated with paths of vasculature and nervous elements.
94
INDIFFERENT INTERMEDIATE PLEXUSES :
Small Collagen fibers in association with the larger principal collagen fiber
Run in all directions forming a plexus
Described by Shackleford, 1971
Once the tooth has erupted into clinical occlusion such an intermediate plexus is no longer demonstrable
Intermediate plexus has been reinterpreted by Sloan as representing merely an optical effect explained entirely by the arrangement of middle layer collagen into sheets rather than bundles.
95
Small collagen fibers associated with large principal collagen fibers have been described.
These fibers run in all directions forming a plexus called INDIFFERENT FIBER PLEXUSES.
Some studies reported this plexuses seen in ground section examined under scanning electron microscope but not under transmission electron microscope. Hence, some authors consider it to be an artifact.
96
continuation of indifferent fiber plexuses:
CELLS OF PERIODONTAL LIGAMENT The principal cells of healthy, functioning periodontal
ligament are concerned with the synthesis andresorption of alveolar bone and fibrous connective ofthe ligament and cementum . The cells of the PDLmay be divided as -
Synthetic cells
Resorptive cells
Cells rests of malassez
97
FIBROBLASTS:
The fibroblasts is the predominant cell in the pdl . Thesefibroblasts origin in part of from the ectomesenchyme ofinvesting layer of dental papilla and from the dental follicle .Pdl contains a fibroblasts cell populations with differentfunctional characteristics .
98
These fibroblasts are regularly distributed throughout theligament and are oriented with their long axis parallel tothe direction of collagen fibrils .
Fibroblasts of pdl generate an organizational pattern asthey have ability to both synthesize and shape the proteinsof the extracellular matrix in which collagen fibrils formbundles that insert into tooth and bone as SHARPEY’Sfibers .
Once embedded in the wall of alveolus or tooth ,these fibers calcify to a certain degree and are associatedwith an abundance of non collagenous proteins found inthe bone i.e. osteopontin and bone sialoprotein .
99
Difference b/w periodontal and gingival fibroblasts
Periodontal ligament fibroblasts are ectomesenchymalin origin whereas gingival fibroblasts are mesodermalin origin.
Expression of alkaline phosphatase & cyclic AMP ismore in periodontal ligament fibroblasts. Gingivalfibroblasts are less proliferative.
Periodontal ligament fibroblasts can generate force fortooth eruption as they are motile and contractile
Fibroblasts of pdl are capable of collagen degradation.
(Orban’s textbook of histology 13 th edition)
100
OSTEOCLASTS • These cells covering the periodontal surface of the alveolar
bone constitute a modified endosteum and not a periosteum .
• A cellular layer but not an fibrous layer is present on the
periodontal surface of the alveolar bone . The surface of the
bone is covered largely by osteoblasts as well as by occasional
osteoclasts .
• These are the cells lining the tooth socket and are cuboidal in
shape with a prominent round nucleus at the basal end of the
cell .
• These cells appear basophilic due to the presence of abundant
rough endoplasmic reticulum . The cells contact one another
through desmosomes and tight junctions .
101
CEMENTOBLASTS Its distribution is similar to that of osteoblasts on the
bone surface . These cells line the surface of cementum. They are cuboidal with a large vesicular nucleus ,with one ore more nucleoli and abundant cytoplasm.
All the organelles are required for protein synthesisand secretion are present . Cells actively depositingcellular cementum exhibit abundant basophiliccytoplasm and cytoplasmic processes
102
103
RESORPTIVE CELLS
OSTEOCLASTS : - These resorb bone and tend tobe large and multinucleated but can also be small andmononuclear . Multinucleated osteoclasts are formedby fusion of precursor cells similar to circulatingmonocytes.
These when viewed in light microscope are cellsoccupy bays in bone or surround end of bone spicule .
The part of plasma membrane lying adjacent to bonethat is being resorbed is raised in characteristic foldsand is termed the ruffled or striated border.
104
105
The ruffled border is separated from the rest of plasma membrane by a zone of specialized membrane that is closely applied to the bone the underlying cytoplasm of which tends to be devoid of organelles and has been called the clear zone .
The area of bone that is sealed off by virtue of active pumping of protons by the osteoclast into this environment .
106
FIBROBLASTS: - These cells show rapid degradation of collagen by fibroblast phagocytosis and is the basis for fast turnover in periodontal ligament . Collagen degradation was an extracellular event involving the activity of the enzyme collagenase .
Intracellular collagen profiles are organelles present . These are associated with the degradation of collagen that has been ingested from extracellular environment . Some studies suggested that collagen degradation is intracellular .
The extracellular elements in degradation of collagenase involve Collagenase which cleaves the triple helical portion of molecules within the fibrils .
107
INTRACELLULAR DEGRADATION - Fibroblasts arecapable of phagocytosing collagen fibrils from extracellularenvironment and degrading them inside phagolysomalbodies . Collagenase is not involved in the intracellularphase of degradation of collagen fibrils .
CEMENTOCLASTS: - These resemble osteoclasts andsometimes found in normally functioning periodontalligament . Cementum is not remodeled in the fashion ofalveolar bone and periodontal ligament . Its origin isunknown bit it is conceivable that they arise in the samemanner as osteoclasts .
108
PROGENITOR CELLS : - All connective tissues includingperiodontal ligament contain progenitors for synthetic cells thathave the capacity to undergo mitotic division .
If they were not present there would be no cells available to replacedifferentiated cells lying at the end of their life span or as a result oftrauma.
These cell populations within the ligament appear to be in highestconcentrations in locations adjacent to blood vessel and exhibitsome of the classical cytological features .
109
Epithelial rests of malassez
The ligament contains epithelial cells that are found closeto the cementum . At the time of cementum formation thecontinuous layer of epithelium that covers the surface ofnewly formed dentin breaks into lacelike stands . Theepithelial rests persist as a network stands islands ortubelike structures near and parallel to the surface of theroot .
Their function is not clear but they could be involved inperiodontal repair and generation .
These cells rests can be distinguished from fibroblasts inpdl by the close packing of their cuboidal cells and theirnucleus stains more deeply . They are more numerous inolder individuals and more numerous in children . Thesecells may proliferate to form cysts and tumors. These cellsmay undergo calcification to become CEMENTICLES.
110
111
DEFENCE CELLS
MAST CELLS – These are relatively small round or oval cell having a diameter of about 12 to 15 um . Mast cells are often associated with blood vessels . These cells are characterized by numerous cytoplasmic granules which frequently obscure the small , round nucleus .
112
Mast cells histamine plays a role in the inflammatoryreaction and have been shown to de granulate in response toantigen – antibody reaction on their surface .
The release of histamine into the extracellular environmentcauses proliferation of endothelial cells and mesenchymalcells .
113
MACROPHAGES- These are found in the ligament and are predominantly located adjacent to blood vessels . The wandering type are derived from blood monocytes has a characteristic ultrastructure that permits it to be readily distinguished from fibroblasts .
114
EOSINOPHILLS – These are seen in the periodontal ligament . They posses granules that consist of one or more crystalloid structures . These are capable of phagocytosis
115
GROUND SUBSTANCE Ground substance composed of glycoproteins and
proteoglycans . Ground substance has been estimated to contain 70 % water and is thought to have a significant effect on the tooth ‘s ability to withstand stress loads .
Ground substance is a gel like matrix in which are embedded the cellular components such as collagen . Berkovitz et al estimated that ground substance accounted for 65 % of the volume in the pdl
116
All anabolites reaching the cells from the microcirculation in the ligament and all catabolites passing in the opposite direction must pass through the ground substance . Its integrity is essential if the cells of ligament are to function properly
117
The ground substance consists of mainly ofhyaluronate , glycosaminoglycans , proteoglycans andglycoproteins . All components are presumed to besecreted by fibroblasts .
Proteoglycans are compounds containing anionicpolysaccharides covalently attached to a protein .
Glycosaminoglycans are linear polymers ofdisaccharide repeat sequence which contains ahexosamine,,heparin sulfate and hexuronic acid .
118
Substrate adhesion molecules such as tenascin ,osteonectin , laminin , undulin , and fibronectin have beenidentified in pdl .
INTERSTITIAL TISSUE
Some of blood vessels , lymphatics , and nerves of the pdlare surrounded by loose connective tissue and can be readilyrecognized in light microscope .
119
STRUCTURES PRESENT IN CONNECTIVE TISSUE
The following discrete structures are present in connective tissue of pdl
Blood vessels
Lymphatics
Nerves
Cementicles
120
The blood supply to the periodontal ligament are derived from three sources:
-Branches from apical vesselssupplying the dental pulp.
-Branches from intra-alveolar vessel, runs horizontally through nutrient canals.
-Branches from gingival vessels, enter the PDL from the coronal direction.
BLOOD SUPPLY OF PERIODONTAL LIGAMENT
121
-Vessels form basket-like network.
-Runs parallel to long axis of tooth between the principle fibres.
-Main supply: SUPERIOR & INFERIOR ALVEOLAR artery- intraostealcourse – gives alveolar branches ascending within the bone.
-Branches then run horizontally, penetrating alveolar bone and then PDL. Hence called PERFORATING ARTERIES.
-Maximum in mandible & maximum in posterior teeth.
-Single rooted teeth-more in the gingival third followed by apical third.( Significant in wound healing).
122
The interradicular arteries branch into vessels of lesser caliber to emerge from the cribiform plate as perforating arteries and supply the pdl along most of the coronoapicalextent including the bifurcation and trifurcation arteries .
The interdental artery also exit the bone to supply the middle three fifth of the pdl though most of the interdental arteries emerge from the crest of the alveolar process and supply the coronal aspect of pdl .
The pdl has some specialized features in the vasculature namely the presence of large number of fenestrations in the capillaries and a cervical plexus of capillary loops .
123
124
Alignment of alpha chains by formation of disulphide bonds at C-terminal ends
Formation of collagen alpha chains
Hydroxylysine residues are glycosylated by addition of galactosein the presence of galactosyltransferase
Hydroxylation of proline and lysine residues by vitamin C-dependent enzyme prolylhydroxylase and lysylhydroxylase
Translocated into lumen of RER for post-translational modifications
Initial polypeptides formed (one and a half times longer than final collagen molecule as they have N- and C- terminal extensions)
m-RNA directs specific amino acids into polypeptide chains on ribosomes associated with RER
VENOUS DRAINAGE- The venous channels accompanying their arterial counterparts . The channels are larger in diameter with mean average of 28 um . These channels receive blood from the capillary network and also specialized shunts called glomera in the pdl . These shunts provides an arteriovenous anastomosis .
125
126
LYMPHATIC DRAINAGE - A network of lymphatic vessels following the path of the blood vessels , provides the lymph drainage of the pdl . The flow is from the ligament toward and into the adjacent alveolar bone .
It may course apically through the substance of pdl to arise and pass through the fundus of the socket or may through the cribiform plate . They finally enter into larger channels after pursuing intraosseous path .
The flow is via the alveolar lymph channels which are joined by the dental and interrradicular lymph channels
127
NERVES – The pdl has functionally two types of nerve fibers sensory and autonomic . The sensory fibers are associated with nociception and of mechanoception , with touch , pressure , pain and proprioceptive sensations . The autonomic fibers are associated with pdl vessels .
All pdl innervations are mediated by the dental branches of alveolar nerves which enter through apical perforation of the tooth socket and perforating branches of interalveolar nerves traversing the bone .
128
INNERVATION OF LIGAMENT
According to Tencate:
There are 3 patterns of nerve innervation
i)general anatomic configuration
ii)regional variation in termination of neural elements
iii)types of neural terminations.
129
ANATOMIC CONFIGURATION
-Nerve fibres run from apical region towards gingival margin.
-They are joined by fibers entering laterally through the foramina of the socket wall.
-They divide into branches -one extending apically -the other gingivally .
130
-Nerve bundles divide into single myelinated fibers-then lose their myelin sheaths and end in one of the
4 neural terminations:
Free endings-tree like configuration: pain sensation Ruffini-like mechanoreceptors: primarily in apical area coiled Meissner’s corpuscles: mechanoreceptors
found in mid-root region
Spindle-like pressure and vibration endings: surrounded by fibrous capsule, located
mainly in apex.
131
132
REGIONAL VARIATION
Apical region –more nerve endings.
-Maxillary incisors-more innervated than molars.
-Dense distribution also seen in coronal half of labial PDL and also apically
133
TYPES OF NEURAL TRANSMISSION
4 types- BYERS,1985
a)Tree –like pattern:
-most frequent type
-along root length
-free nerve endings in tree like pattern.
-originate mostly from unmyelinated nerve fibres
- they carry Schwann cell envelope & processes projecting into surrounding CT.
- Endings carry-mechanoreceptors & noci receptors
134
RUFFINI CORPUSCLES Found at the root apex.
-Appears dendritic .
-Ends in terminal expansions among fiber bundles.
-Electron microscopic study -i) simple receptors – single neurite
ii) compound receptors- several terminations.
-Both have ensheathing schwann cells that are especially close to collagen fiber bundles
-Mechanoreceptors.
135
COILED MEISSENER’S CORPUSCLES
• -Nerve terminal in coiled form
• -Found in the mid region of the PDL.
• -Function and the ultra structure- not yet determined.
136
SPINDLE LIKE ENDINGS
Lowest frequency.
-Found associated with the root apex
-Consists of the spindle like endings surrounded by fibrous capsule.
-Said to sense pressure & vibration.
137
Nerves which usually are associated with blood vessels pass
through foramina in the alveolar bone including the apical
foramen to enter the pdl . In the region of apex apex they run
toward the cervix whereas along the length of root they branch
and run both coronally and apically .
Nerve fibers are either of large diameter and myelinated or
small diameter in which case they may or not be myelinated .
138
The pdl is abundantly supplied with sensory nerve fibers capable of transmitting tactile pressure and pain sensations by the trigeminal pathways . Nerve bundles pass into pdl from the periapical area and through channels from the alveolar bone that follow the course of the blood vessels .
The bundles divide into single myelinated fibers which ultimately loose their myelin sheath and end in one of four types of neural termination
139
CEMENTICLES - Calcified bodies called cementicles , sometimes found in the pdl . These bodies are seen in older individuals and they may remain free in the connective tissue and may fuse into large calcified masses or they may be joined with the cementum . As the cementum thickens with advancing age it may envelop these bodies . When they are adherent to the cementum they form excementoses. The origin of these calcified bodies is not established . It is possible that degenerated epithelial cells form the nidus for their calcification .
140
MECHANISM OF SHOCK ABSORPTION
TENSIONAL THEORY
Principal fibers of the PDL are the major factor in supporting the
tooth and transmitting forces to the bone.
When forces are applied to tooth, principal fibers unfold and
straighten and then transmit the forces to alveolar bone, causing
elastic deformation of socket.
141
Force applied to crown
Principles fibres first unfold and straighten
Transmit forces to alveolar bone(causing elastic deformation of the bony socket)
Once alveolar bone reaches its limit , load is transmitted to basal bone
142
A. Tooth in a resting state
B. The periodontal ligament fibers are
compressed in areas of pressure and
stretched in area of tension.
143
VISCOELASTIC THEORY
• According to it, the fluid movement largely controls the
displacement of the tooth, with fibers playing a secondary role.
• When forces are transmitted to the tooth, the extracellular fluid
is pushed from periodontal ligament into marrow spaces
through the cribriform plate.
• After depletion of tissue fluids, the bundle fibers absorb the
shock and tighten.
• This leads to blood vessel stenosis arterial lack pressure
ballooning of vessels tissue replenishes with fluids.
144
THIXOTROPIC GEL THEORY
PDL fluid acts as a gel.
-When pdl fibers are disturbed the gel which is present between pdl fibers becomes fluid
-Forces on tooth gel to fluid.
-Removal of forces fluid to gel.
-Helps in shock absorption.
(perio 2000 volume 13,1997)
145
TRANSMISSION OF OCCLUSAL FORCES TO BONE
Arrangement of principle fibres is similar to a suspension bridge/hammock
Axial force when applied
Root displaces into the alveolus
Oblique fibres alter their wavy course, assume full length and sustain major part of the axial force.
146
When horizontal forces are applied- 2 phases of movements occur.
i)within confines of ligament.
ii)displacement of facial & lingual bony plates.
-Force - tension & pressure areas.
-Tension side - fibres taut.
- Pressure side - fibres are compressed, tooth displaced, distortion of bone in direction of root movement.
147
AXIS OF ROTATION
Single rooted teeth: Between the apical and middle third
-In multirooted teeth: Bone between roots
-Compression resorbs
-Tension deposition
148
FUNCTIONS OF PERIODONTAL LIGAMENT
Periodontal ligament has following functions:
1.Supportive
2.Sensory
3.Nutritive
4.Homeostatic
5.Eruptive
6.Physical
149
SUPPORTIVE
When a force is applied on tooth either by mastication or orthodontic tooth
movement there is compression of pdl and other areas widening of pdl.
The compressed pdl fibers will act as support for the loaded tooth, water
molecules and other molecules bound to collagen act as cushion for
displaced tooth. The pressure of blood vessels also provides a hydraulic
cushion for the support of the teeth.
Load is dissipated to alveolar bone through oblique fibers of pdl when
placed in tension and on release elastic recoil of tissue enables the tooth in
original position.
150
SENSORY
Nerve supply of pdl provides most efficient proprioceptive mechanism and
allows to detect the application of the most delicate forces of teeth.
Mechanoprotection protects both supporting structures of the tooth and the
substances of the crown from excessive masticatory forces.
Cortin actin assembly regulates the activity of stretch activated calcium
permeable channels since forces desensitizes channels to force applications.
151
continuation
ACTIN BINDING PROTEIN – 280 plays a pivotal role in
mechanoreception by :
a. Reinforcing the membrane cortex and preventing force induced membrane
disruption.
b. Increasing the strength of cytoskeletal links to extracellular matrix
c. Desensitizing stretch activated ion channel activity
152
NUTRITIVE:
Ligament contains blood vessels provide anabolites required by the cells of
pdl.
Any extirpation of ligament results in necrosis of underlying cells.
Occlusion of blood vessels leads to necrosis of cells in affected parts of
ligament- when too heavy forces is applied to teeth in orthodontic therapy.
153
HOMEOSTATIC:
The cells of pdl have the ability to resorb and synthesize the extracellular
substance of the connective tissue of the ligament , alveolar bone and
cementum .
Alveolar bone appears to be resorbed and replaced at a rate higher than
other tissue in jaws . Furthermore the collagen of pdl is turned over at a
rate that may be the fastest of all connective tissues in the body and the cells
in the bone half of ligament may be more active than those on the
cementum side
154
ERUPTIVE
The cells of vascular elements and extracellular matrix proteins
of pdl function collectively enable the teeth to limited eruption
and adjust the position while remaining fibers attach the teeth
firmly to the alveolar bone.
It provides a space and acts as a medium for cellular
remodeling and hence continued eruption and approximal shift
occurs.
155
PHYSICAL :
1. Provision of a soft tissue “casing” to protect the vessels &nerves from injury by mechanical forces.
2. Transmission of occlusal forces to the bone.
3. Attachment of the teeth to the bone.
4. Maintenance of the gingival tissues in their properrelationship to the teeth.
5. Resistance to the impact of occlusal forces (shockabsorption
156
HOMEOSTATIC MECHANISM
• The resorption and synthesis are controlled procedures.
• If there is a long term damage of periodontal ligament, which is
not repaired, the bone is deposited in the periodontal space.
• This results in obliteration of space and ankylosis between
bone and the tooth.
• The quality of tissue changes if balance between synthesis and
resorption is disturbed.
157
• If there is deprivation of Vit. C which are essential for
collagen synthesis, resorption of collagen will continue.
• So there is progressive destruction and loss of extra
cellular substance of ligament.
• This occurs more on bone side of ligament.
• Hence, loss of attachment between bone and tooth and at
last, loss of tooth.
158
NORMAL CELL BIOLOGY
The production and destruction of tissue matix ( turnover ) in a
healthy state , involves interaction among a myriad of effector
molecules that are synthesized and secreted by resident cell of
periodontal ligament .
Cytokines are a series of multifunctional polypeptides and
glycoproteins that are secreted by one or several cell types and act
locally or systemically . These includes Interleukins , cytotoxic
factors , interferons , growth factors , colony stimulating factors.
Growth factors have been defined as substances capable of re –
initiating proliferation of cells that are in a quiescent state .
159
In vivo cytokines play an important role in numerous biological events , including development , homeostasis , regeneration , repair , inflammation and neoplasia
160
1 . Fibroblast growth factors (FGF) - Two of seven isoforms of
fibroblast growth factors have been described in particular one is
acidic and other basic .
Acidic fibroblast growth factors has effects on endothelial cell
replication and neovascularisation . It stimulates dna synthesis
and cell replication , in bone tissue cultures which results in
increased protein synthesis especially type 1 collagen .
161
Basic fibroblast growth factors has angiogenicproperties has highly chemotactic and mitogenicfor a variety of cell types . It stimulates bone cellreplication and increases the number of cells ofosteoblastic lineage .
162
2 . Platelet derived growth factor ( PGDF ) This factor ispotent growth factor for various connective tissuecells and is released from the a – granules in plateletsin conjunction with blood coagulation .
PGDF is a promoter of cell migration and a potentmitogen for cells bearing PGDF receptors . It actssynergistically with other growth factors as acompetence factor .
PGDF stimulated type v collagen formation and adrop in type III production in gingival fibroblasts .
163
Transforming Growth factor ( TGF ) : - Thesefactors are polypeptides from normal andneoplastic tissues which are known to cause achange in normal cell growth . TGF is of 2 types αand b according to relationship to EGF .
TGF – α similar isolated biological effects actingthrough EGF receptor .
TGF – β was originally purified from humanplacenta , platelets and bovine kidney . Itstimulates the synthesis of connective tissue matrixcomponents such as collagen , fibronectinproteoglycan and glycosaminoglycans .
164
. Interleukin- 1 ( IL – 1 ) : - Interleukin – 1 is apolypeptide with a great number of roles inimmunity , inflammation , tissue breakdown andtissue homeostasis . It is synthesized by various celltypes including macrophages , monocytes ,lymphocytes vascular cells brain cells skin cells andfibroblasts following cellular activation . 2 types ofIL are known interleukin – 1 α and 1β .
165
Interferon – ɤ : - It posses importantimmunomodulatory effect and thus is alymphokine as much as an interferon . Itsproduction is modulated by other cytokines suchas interleukin – 1 . Many biological activities havebeen ascribed to interferon like action on B and Tlymphocytes , antibody production , natural killercells , macrophages and tumour cells .
166
Matrix metalloproteinases and theirtissue inhibitors : - Connective tissue cellsparticipate in both the formation and breakdown ofconnective tissue matrix . Such cells are found tosynthesize and secrete a family of enzymes knownas MMP’s .
MMP gene family encodes a total 24homologous proteinases classified into collagenases, gelatinases , stromeolysins , membrane type MMPdepending on their susbstrate specificity andmolecular structures .
167
COLLAGEN TURN OVER RATE
Sodek ,1977 found collagen synthesis in PDL of adult rat to be
- two fold greater than that of gingiva,
- four fold greater than that of skin, &
- six fold greater than that of bone.
Almost all the newly synthesized collagen in the ligament was converted to
mature cross linked collagen, whereas much less was converted in the
gingiva & skin.
168
Continuation…. Half-life for collagen turnover: in ligament – 1 day,
in bone – 6 days
in gingiva - 5 days,
in skin - 15 days
According to Rippin: half life
in the apical areas 2.45 days,
in the crestal areas 6.42days,
fibers in mid-root region 5.7 days,
transseptal fibers 8.4 days
for dentogingival fibers 25 days.
169
EXTERNAL FORCES & PDL
Within physiologic limits, the pdl can accommodate increased function with
an increase in width,
a thickening of its fiber bundles, and
an increase in diameter & number of
Sharpey’s fibers.
Forces that exceed the adaptive capacity of the periodontium produce injury called trauma from occlusion.
Slight excessive pressure: resorption of bone, widening of PDL space
Slight excessive tension: elongation of PDL fibers & apposition of bone
170
Replantation & transplantation
To have any chance of success , it is essential to maintain the
viability of PDL .
Avoid dehydration of PDL.
Avoid loss of viability of its cell rests.
Transplantation
Best results when unerupted tooth with partially formed roots
as there is less damage to PDL.
171
AGE CHANGES IN PERIODONTAL LIGAMENT -Rate of collagen synthesis decreases.
-Rate of maturation of the synthesized collagen changes.
-Decrease in the number of fibers.
-Collagen fibril diameter – decreases by 50%
-Degenerative vascular changes seen.
-Sharpey's fiber insertion – the alveolar bone surface jagged and uneven with irregular fiber insertions
172
CLINICAL CONSIDERATIONS
• The primary role of periodontal ligament is to support the toothin the bony socket.
• The width of periodontal ligament varies from 0.15 to0.38mm. The average width is:
- 0.21mm at 11 to 16 years of age.- 0.18mm at 32 to 50 years of age.- 0.15mm at 51 to 67 years of age.
• So, the width of periodontal ligament decreases as age advances.
173
WIDTH OF PERIODONTAL LIGAMENT
Conflicting results have been obtained
Klein & Tozat concluded – width increases with age
Tonna et al (1972) – width decreases with age
Why the width of periodontal ligament in hour glass shape??
Root convexity
Acts as fulcrum
Width of cementum is more at center
174
With age
Less teeth present
Forces acting on remaining teeth increases
INCREASE WIDTH OF PDL SPACE WITH AGE
175
Masticatory forces decreases with age
DECREASE WIDTH OF PDL SPACE WITH AGE
Tonna et al (1972)
Klein & Tozat
• In the periodontal ligament, aging results in more number ofelastic fibers and decrease in vascularity, mitotic activity, fibroplasiaand in the number of collagen fibers and mucopolysaccharides.
• If gingivitis is not cured and supporting structure become involved,the disease is termed as periodontitis.
• There are few coccal cells and more motile rods and spirochetes inthe diseased site than in the healthy site. The bacteria consists ofgram-positive facultative rods and cocci in healthy site while indiseased site, gram-negative rods and anaerobes are more innumber.
176
• Resorption and formation of both bone and periodontal
ligament play an important role in orthodontic tooth
movement. If tooth movement takes place, the compression of
PDL is compensated by bone resorption whereas on tension
side, apposition takes place.
• Periapical area of the tooth is the main pathologic site.
Inflammation of the pulp reached to the apical periodontal
ligament and replaces its fiber bundles with granulation tissue
called as granuloma, which then progresses into apical cyst.
177
• Chronic periodontal disease can lead to infusion of
microorganisms into the blood stream.
• The pressure receptors in ligament have a protective
role. Apical blood vessels are protected from excessive
compression by sensory apparatus of the teeth.
• The rate of mesial drift of tooth is related to health,
dietary factor and age. It varies from 0.05 to 0.7mm per
year.
178
Effect of hyper & hypo glycaemia on PDL
Nishimura et al, 1998 - PDL cells - susceptible to hyper & hypoglycemia & effects - mediated via the integrin system.
Hyperglycemia – increased expression of fibronectin receptor → results in reduced cellular adhesion & motility → probable tissue impairment.
Hypoglycemia – decreased expression of fibronectin receptor → lowers the viability & ultimately results in cell death & hence tissue impairment
179
PDL space Radiographic appearance
Thin radiolucent line interposed between the root & lamina dura.
Occlusal Trauma → widened PDL space or funneling of coronal aspect of PDL space.
It can also widened in case of vertical fractures & progressive systemic sclerosis (Scleroderma).
180
EMD & PDL Gestrelium et al, 1997 studied effects of EMD on periodontal ligament cell
migration, attachment, proliferation, biosynthetic activity mineral noduleformation & ability to absorb a large range of polypeptide growth factors &cytokine.
In culture, EMD formed protein aggregates which appeared to provide idealconditions for cell-matrix interactions.
Under these conditions EMD enhanced the proliferation of PDL cells,increased protein & collagen production of PDL cells & promoted mineralnodule formation by these cells.
However, no effect on migration, attachment & spreading of these cells nordid they absorb any of the growth factor or cytokine that were tested.
181
NEOPLASTIC INVOLVEMENT OF PDL
Mostly reactive rather than neoplastic.
Oxytalan fibers are found in peripheral odontogenicfibromas & Adenomatoid odontogenic tumors
Epithelial rests of malassez --- neoplastic change
Infiltration of PDL by 1º or 2° malignant tumors --- widening of PDL space--- mobility –malignant loosening of teeth.
182
BLOOD & LYMPHO RETICULAR DISORDERS
Changes due to reduced host response to plaque.
Destruction of PDL follows neutrophil defeciencies or functional defects such as defeciency of leucocyte adhesion receptors
183
PERIODONTAL CYSTS
Inflammatory ---- Radicular cyst
Developmental ---- Lateral periodontal cyst
184
SOFT C.T.DISORDERS & PDL
a. PROGRESSIVE SYSTEMIC SCLEROSIS
Radiographically ---- PDL widening upto 3mm
thickening
Collagen ---- dense, mature & more hyalinised than
normal
Oxytalan fibers increased.
185
. LATHYRISM
Condition caused by drugs that inhibit cross linking in collagen
& elastin (cystamine)
Fragile collagen fibers
Retard eruption
c. DISUSE ATROPHY
Narrowing of PDL & reduction in no. of principal fibers.
Fibers oriented parallel to the long. Axis of root & PDL shows
reduced rate of collagen turn over.
186
NUTRITION & PDL
a. FOOD TEXTURE
Little correlation between the advent of soft, fiber deficient
diet & dental health.
Significant factor in chronic inflammatory periodontal
disease is loss of natural masticatory function, leading to
accumulation of dental plaque.
Influences pattern of mastication & hence the mode of
support offered by the PDL.
187
CARBOHYDRATES
Refined carbohydrates in the diet influence the severity of PDL
disease in humans (Holloway et. Al 1963)
No direct evidence showing the direct effect of carbohydrates
per se on PDL , though in some circumstances there could be
an influence as a result of modifying the diet consistency.
188
PROTEINS
Deficiency of protein might be expected to produce changes
within it.
Reduction in PDL transseptal fibers ( Stien & Ziskin 1949; Ten
Cate et..al.1976)
Reduction in cementoblasts, fibroblasts
Occlusal trauma exacerbates these effects (Chawla & Glickman
1951)
Healing is delayed in rats fed on protein deficient diet.
189
PERIODONTITIS
CHRONIC PERIODONTITIS
AGGRESSIVE PERIODONTITIS
PERIODONTITIS AS A MANIFESTATIONS OF SYSTEMIC DISEASES
190
CHRONIC PERIODONTITIS
The most prevalent form in adults
Amount of destruction consistentwith local factors
Associated with a variable microbial pattern
Subgingival calculus frequently found
Slow to moderate rate of progression
Possibly modified by or associatedwith the following:
- Systemic diseases- Local factors predisposing
factors- Environmental factors
191
CLASSIFICATION OF CHRONIC
PERIODONTITIS
I. Localized form: <30% of sites
involved
Generalized form: >30% of sites
involved
II. Slight: 1-2 mm of clinical
attachment loss
Moderate: 3-4 mm of clinical
attachment loss
Severe: ≥5 mm of clinical
attachment loss
192
AGGRESSIVE PERIODONTITIS
Primary Features1. Except for the presence of periodontitis, patients are
otherwise clinically healthy
2. Rapid attachment loss and bone destruction
3. Familial aggregation
193
Secondary Features
1. Amounts of microbial deposits are inconsistent with the severity of periodontal tissue destruction
2. Elevated proportions of Aggregatebacter actinomycetemcomitans and, in some populations, Porphyromonas gingivalis may be elevated
3. Phagocyte abnormalities
4. Hyper-responsive macrophage phenotype, including elevated levels of PGE2 and IL-1β
5. Progression of attachment loss and bone loss may be self-arresting
194
HEALING AFTER PERIODONTAL THERAPY
REGENERATION is the reproduction or reconstitution of a lost or injured part.
REPAIR is the healing of a wound by tissue that does not fully restore the architecture or the function of the part.
PERIODONTAL REGENERATION is defined histologically as regeneration of the tooth’s supporting tissues, including alveolar bone, periodontal ligament, and cementum over a previously diseased root surface.
195
NEW ATTACHMENT is defined as the union of connective
tissue or epithelium with a root surface that has been deprived
of its original attachment apparatus. This new attachment may
be epithelial adhesion and/or connective tissue adaptation or
attachment and may include new cementum.
196
TO SUMMARIZE:PERIODONTAL LIGAMENT
The PDL is the means of attaching the tooth to the bone for mastication. As a labile connective tissue, it:
Adapts to varying load
senses loads for proprioceptive feedback controlling muscle actions
helps to move the teeth for better occlusion
supplies & nourishes cementum & alveolar bone
defends against microbes
prevents damage to cementum
197
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Carranza’s Clinical Periodontology, 10th Edition
Clinical Periodontology and Implantology by Jan Lindhe, 5th edition
Oral Histology and Embryology by Orban, 13th edition
Tencate oral histology, 5th edition
Textbook of biochemistry – HARPER’S 2nd edition
Xiong J, Gronthos S, Bartold PM. Role of the epithelial cell rests of
Malassez in the development, maintenance and regeneration of periodontal
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Bosshardt DD, Selvig KA.Dental cementum: the dynamic tissue covering of
the root. Periodontol 2000 1997;13:41-75
198
Fundamentals of Periodontics, 2nd Edition, by Thomas G. Wilson, Kennath
S. Kornman
Textbook of oral pathology by Shafer, 5th edition.
The periodontal ligament in health and disease: 2nd edition, Barry K B
Berkovitz
Bartold PM, Walsh LJ, Sampath Narayan A. Molecular and cell biology of
gingiva. Periodontol 2000, Vol. 24, 2000, 28–55
Ertsenc W, Mcculloc HG , Sodek HJ. The periodontal ligament: a unique,
multifunctional connective tissue. Periodontol 2000. Vol. 13, 1997, 20-40.
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