Periodonttal Ligament-p.g. Seminar

Good Morning….

…the periodontal ligament

Contents.

-introduction

-cells.

-fibers.

-ground substance.

-response of periodontal ligament to external forces.

-role in eruption and tooth support.

periodontal ligament:

fibrous stroma embedded in a gel of ground substance.

fibrous stroma:

collagen

oxytalan

ground substance:

cells

blood vessels

nerves

cells…cells… ( 50% by volume)

- fibroblasts.

-defence cells macrophages, eosinophils, mast cells. -undifferentiated mesenchymal cells, epithelial cells.(rests of

malassez) -osteoblasts. -cementoblasts. -osteoclasts and odontoclasts.

the periodontal ligament: “soft connective tissue that lies between the root and bone..” fibrous stroma embedded in a gel of ground substance …. as much cellular as it is fibrous… Collagen in periodontal ligament.

arranged in the form of principal fibers,( intermediate plexus ? ). elastin (oxytalan fibers, elaunin) sharpey’s fibers.the principal fibers. bundles. wavy in nature. divided into 6 “well defined” groups. mainly constituting the collagen genre . 1)transeptal group

-extend interproximally over alveolar bone -embed themselves in the cementum of adjacent bone -remarkably constant finding. -reconstructed even after destruction.

alveolar crest group.

-extend obliquely from cementum beneath junctional epithelium to alveolar crest.

- from cementum over alveolar crest and embed in the periosteum covering the alveolar bone.

- prevent extrusion of the tooth..(carranza et al 1956)

- resist lateral tooth movements .

horizontal fibers.

- extend from cementum to alveolar bone at right angles to long axis of the tooth.

oblique fibers.

largest group.

cementum to bone in an oblique direction.

vertical masticatory forces.

apical group.

-radiate from the cementum to bone in the apical region.

interradicular group

fan out from cementum to bone in furcation areas.

Apical fibers Interradicular fibers

Tooth bud is formed in a crypt of bone.

The collagen fibers produced by the fibroblasts in the loose connective tissue around the tooth bud are embedded into the newly formed cementum immediately apical to the CEJn.

The true PDL fibres (Principal fibers) develop in conjunction with tooth eruption.

Later, more apically positioned bundles of oriented collagen fibres are seen.

The orientation of the collagen fiber bundles gets altered continously during tooth eruption and stabilises once the tooth reaches in occlusion.

First, small, fine, brush-like fibrils are detected arising from the root cementum and projecting into the PDL space. The surface of the bone is covered by osteoblasts.

Later the number and thickness of fibers entering the bone increase. The fibers originating from the cementum are still short while those entering the bone gradually become longer.

The fibers originating from the cementum subsequently increase in length and thickness and fuse in the periodontal ligament space with the fibers originating from the alveolar bone.

Orientation of the fibers as the tooth erupts.

intermediate plexus.

fibers of the middle zone spliced together to form the intermediate plexus.

facilitates remodelling during eruption.

(sicher 1923,42)

…. histological artefact

caused by transverse

sectioning.( ciancio et al, 1967)

….optical effect (sloan et al)

owing to arrangement

in sheets.

other “less” well defined fiber groups… elastin fibers… oxytalan. elaunin. collagen types in the periodontal ligament.collagen types in the periodontal ligament.

18 species recognised/isolated from xtracellular connective tissue. fibrillar collagens. ( with triple helices)

fibril associated collagens. (Interupted triple helices)

mmajor type: coll type 1 (> 70%)

others: type 3 ( upto 20% ) (associated with foetal/granulation tissue)

type 4, 5, 6,12.

fibril diameters. 3-10 micrometer (cementum associated bundles) 10-20 micrometer ( bone associated bundles) 1-4 micrometer (the rest of the periodontal ligament) Merriliees and Flint ( 1980) tension : 30 nm – 150 nm compression : 30 nm. complex 3 dimensional arrangement , constant intersplicing in the adjacent layers. state of tension elastic fibers. oxytalan, elastin and elaunin. oxytalan: lie parallel to the root surface. (apico-occlusal direction 3 dimensional meshwork. from cement to blood vessels. closely associated with blood vessels. distinguished from collagen : parellel assemblage and no cross banding.

functions.

1) increase rigidity of the periodontal ligament (tooth support)

??? - …. Closely associated with collagen fibers.

- …. Increased oxytalan cited in areas of increased tension.

(Jonas and Reide 1980)

orthodontic loading : fibroplasia.

fiber lengthening.

narrowed out oxytalan diameters.

2) as guides to cellular migration? (fibroblasts) (beertsen et al

1974)

3) in close association with blood vessels….

mechanoreceptive system….? (sims 1977)

relapse after orthodontic treatment…

oxytalan…?

frequently encountered relapse situations:

-rotations.

-opening up of tooth contacts following extractions.

- edwards et

al 1968

collagen turnover. continuous and rapid.

one of the most rapid in the body.

J.W. Rippin 1976

½ life -2.45 days in the apical areas.

-6.42 days in the crestal areas.

- uniform all along the width of the ligament.

intermediate plexus or the “zone of shear”

objective for high rates of turnover ….

need for movement (eruption)

and rapid adaptation .. ( orthodontic loads )

turnover rates may increase in hypofunctional ligaments as well..

collagen fibers and functional adaptation.collagen fibers and functional adaptation.

“tooth support is not the domain of a single entity”

internal orientation of collagen fibers influences

Mechanical properties of the connective tissue

Collagen fibers best adapt themselves to axially directed forces horizontal and oblique placement.

Minns et al 1973

periodontal ligament not a flat plane but a complex 3 dimensional structure

bundle overlap

resistence to rotational forces

Overlap of collagen bundles

Rotational and intrusive forces

always in tension

In summation: - oblique qnd horizontal fibers resist axial forces. - overlap resist rotational and intrusive forces.

….the collagen “crimp”

SEM of the crimp.

periodicity of structure of variable scale.microscopic (not very obvious ) anatomic (quite apparent ) the waveform that describes this periodicity is called the crimp…

… due to

- well defined zigzag arrangement of collagen fiber bundles.

-micro anatomical arrangement of fibers into sheets and bundles.

functions: unfold and absorb

-absorb tensile loads without extending the

fibers

-no heat generation in the process.

- role in tooth support…?

sharpey’s fibers.

-the terminal ends of principal fibers embedding themselves into the bone.

sharpey’s fibers

-concentrated in the .crestal portion.-pass right through alveolar crest

transalveolar fibers…?

-embedded in Collagen type 3.- poorly mineralised core.

elasticity properties.

coarse unmineralised fibers characteristic of intramembranous bone.

-Generaly associated with foetal connective tissue-could be playing a role in skeletal integrity.-periphery mineralised local mechanical advantage against axial forces…?

biochemistry of the fibers.

Triple helix. -basic structure made up of 3 polypeptide chains (‘alpha’ chains) (trimeric) ramachandran 1967 -each polypeptide contains 1056 amino acids. -each chain in the form of repeating tri-residue motif (gly-x-y) glycine x -proline y –hydroxyproline.

the individual alpha chains. with the gly-x-y repeats.

Relationship of alpha chains in cross section Interchain hydrogen bondsProline and hydroxyproline make the pyrollidine rings

H bond

Pyrodine rings

Superhelix

basic structural unit : tropocollagen the ordered arrangement of millions of such units

Cross banded collagen fibrils

….the quarter stagger parallel array.

collagen synthesis and assembly.

divided into 3 phases:

-procollagen synthesis -fibrillogenesis -crosslink placement

structure of type 1 collagen before quarter stagger parallel array appearance.

procollagen formation. specific amino acids assembled

Polypeptide chain formation 50% longer than the final molecules.

(presence of n- and c-terminal peptides) vital role in the synthesis but eventually deleted from the sequence.

Hydroxylation of the amino acids (proline and lysine)

Addition of sugar residues (glycosylation)

placement of disulphide bonds (facilitated by the n and c terminals)

well aligned triple helices formed

molecule transported to g. apparatus further remodelling of the c terminal occurs

procollagen moleculeprocollagen molecule.aligned in a non stagger formation

Fibrillogenesis process of alignment into crossbanded fibrils. - removal of entire c-terminal - partial removal of n-terminal

Initial 5 staggered unit aligned parallel (facilitated by the n-terminal)

final stagger (regular series of gaps)

final remnant of n-terminal deleted placement of few crosslinks. (stabler and chemically more insoluble)

.

Collagen fibril

collagen degradation.

Intracellular.Extracellular.

Intracellular collagen profiles provide the evidence. Tencate 1972

Schematic of intracellular collagen profiles

extracellular degradation.

…carried out via a group of enzymes called matrix metalloproteinases. (MMPs)

chief MMP : collagenase

jnitial cleaving of the fibril Further degradation requires

other enzymes.

Cells of the periodontal ligament. connective tissue cells, epithelial rest cells,

immune system cells, cells of neurovascular element. connective tissue cellsconnective tissue cells fibroblasts cementoblasts

osteoblasts

epithelial cellsepithelial cells rests cells of malassez defence cells.defence cells. neutrophils lymphocytes

mast cells, macrophages

Layer of cementoblasts lining cementum.

Layer of osteoblasts lining the alveolar bone

Cells close to alveolar bone

Cells in transverse section

Epithelial cellrests of malassez…Epithelial cellrests of malassez…-Remains of the hertwig’s epithelial root sheath-stain deeply, closely.-Apically and cervically more in numbers.-Stain for cytokeratins, proliferate when stimulatd to form periapical and lateral root cysts.

fibroblasts.

Originate from mesenchymal cells. -divide 50 times (embryonic tissue)

-about 20 times in the adult

- extracellular fibers.

collagen, elastin, (oxytalan, elaunin)

- ground substance.

contractility and motility,

determines and maintains the shape of the structures during embryogenesis.

“architect, builder and caretaker of the connective tissue…!”

fibroblast structure.

types

contractile elements

cells junctions

eruption and the hypothesis.

Stellate or irregular appearing fibroblast outline.

fibroblast…. (ultrastructural appearance)

structure. ( structure. ( Tencate 1977) - light microscope.

- lies alongside collagen fibers.

- shape.

nucleus stains better then cytoplasm.

ovoid and flat (Fullmer, 1967)

fusiform and elongated (Garant and Cho)

spindle shaped

stellate , irregular

pleomorphic (sem study, Roberts and Chamberlain)

-artefacts.

-lack of preferential orientation.

flattened ovoid discs, 30 micro m.

irregular outline ( cytoplasmic projections ) (shore et al 1981)

-resting cell.

flat ,dark staining , closed nucleus. scanty cytoplasm

-active cell.

low nuclear cytoplasmic ratio pale staining open type of nucleus. abundant cytoplasm. complement of organelles.

why is shape of a fibroblast significant….? contractility and motility hypothesis of eruption. (melcher and beertsen 1979 ) “fibroblasts move occlusally at the rate equal to that of eruption”

….tractional forces generated by fibroblasts. morphology…? invivo- rounded in vitro- elongated.

inactive or resting cell.

Resting cell

Active cell

functionally…

synthesis and secretion.

contractility motility and tractional forces.

in vitro.. ( collagen gels, plastic )

organize a fibrous network.

generate significant forces.

-thin, polarized, highly motile.

-microtubules, microfilaments.

-crenulated nuclei, gap junctions.

….myofibroblasts?

but… none of these features are seen in pdl fibroblast.

chief function: synthesize and secrete proteins and degradation. but… cytoskeleton of a fibroblast contains… microtubules. long , gently curving cylindrical structures .(major protien tubulin) average diameter 240 nm. microfilaments. 80 nm , actin myosin, intracellular muscles. intermediate filaments. vimentin, maintain cellular junctions

Attributes of a cell with contractile and motile properties….

manifestation..?manifestation..? 1) “crawls” ( motility ) 2) remains stationary ( contractile forces ) migration . -chemotactic stimuli. (from bone and cementum) -cytoskeleton. -surface integrins.

Microfilaments.

Microtubules.

…. Associated with…

polarity of the cell

-nucleus at the trailing edge

-golgi and centriole at the leading edge.( matrix secreted at the leading edge.)

movement though matrix helps align the fibers.fibroblasts and cell junctions.

( no contact.)

type of junctional arrangement.

( desmosome 20 nm )

desmosomes and eruption….?

periodontal ligament : unusually high numbers of cell to cell contacts.

Generate eruptive forces

desmosomes

Transmitted via

Shore et al 1981…High numbers of desmosomes located adjacent to enamel related connective tissue hence ….. Desmosomes may not play a role in generating eruptive forces.

fibroblasts and tooth eruption

melcher and beertsen 1977. motility and contractility hypothesis of tooth eruption.

( microtubules and microfilaments )

Extension of cell processes

motilitymotility contractilitycontractility

Movement of the tooth in occlusal direction

In vitro studies.

Incorporation of fibroblasts in a 3 dimensional collagen gels- contraction of the gelBellows et al 1981 1)

2) placement of fragments of tooth and dentine– movement. Bellows et al 1982

colchicine (antimicrotubular drug)

Disruption of microtubule- microfilament

Contraction inhibited.

Morphology of the fibroblast in vivo.. More of the secretory function in vitro.. Contractility

2 types of connective tissues in an erupting tooth. enamel related . tooth related connective tissue.( periodontal ligament proper ) fibroblast morphology stays the same…..

thank u…!