PRESENTED BY: GUIDED BY:

NAUSHEER PAGARKAR DR. SUREKHA BHEDASGAONKAR

II MDS PROF&HOD

DEPT. OF PERIODONTICS DEPT. OF PERIODONTICS

TYPES OF FIBERS IN THE PERIODONTAL

LIGAMENT

TYPES OF FIBERSARRANGEMENT OF THE PERIODONTAL COLLAGEN

FIBERSFIBER ARRANGEMENT IN TEETH OF LIMITED

GROWTHFIBER ARRANGEMENT IN CONTINOUSLY GROWING

TEETHFUNCTIONAL ADAPTATIONS OF THE COLLAGEN

FIBERS OF THE PDLCOLLAGEN CRIMPINGSHARPEY’S FIBERS

ARRANGEMENT AND FUNCTIONAL ADAPTATIONS OF THE ELASTIC FIBERS OF THE PDL

AGING OF THE FIBERS OF THE PDL

CONTENTS

Collagen of the PDL is mostly type I, with lesser amounts of type III, IV, V, VI, XII also present

I, III and V are banded collagens with characteristic periodicity of 67nm due to the staggered arrangement of molecules in the fibril

Collagen is divided into 2 main groupsFibril collagens(I,III,V)FACIT (fibril associated collages with interrupted

triple helices)FACIT collagens link the fibrillar collagen types

and organize the extracellular matrix

COLLAGEN FIBERS

Collagen fibril diameters of the PDL are relatively small with mean diameter of 45-55nm, in other CT such as tendon the diameter increases.

Studies correlate increase in diameter with maturation in CT, however due to the high turnover of the PDL collagen, the diameter of fibrils in the PDL is small

ELASTIC FIBER NETWORK

In many CT’s, the collagen fibers are closely associated with an elastic meshwork, either as a static elastic element or as a resilient material

3 components of the elastic system are recognisedOxytalanElauninElastin

ELASTIC FIBERS

Oxytalan fibers form a 3D network that extends from the cementum to the peripheral periodontal blood vessels

Occupy 3% of the PDLIn TEM, they appear similar to developing

elastin fibers and are composed of groups of microfilaments embedded within amorphous material

Similarities between microfibrils of oxytalan fibers and developing elastin fibers have led to conclusion that they are precursors of the elastin fibers

There is also a similarity between the ultrastructure of oxytalan microfibrils and fibrils of fibronectin, oxytalan is stained strongly by IHC stains for fibronectin

Oxtyalan fibers regulate vascular flow It has been suggested that oxytalan fibers

might play a role in fibroblast migration in the PDL

Elastin fibers are composed of a microfibrillar glycoprotein and amorphous elastin, which is a proteinaceous rubber

Elementary units are rod-like in shape

Black in 1887 described groups of principle fiber bundles arranged into gingival, crestal, horizontal,oblique and apical groups

Principal fiber bundles appear to branch into smaller bundles within ligament to form a continuous plexiform arrangement

Precise arrangement is debated, even though the majority of collagen fibers in PDL appear to be grouped together to form bundles

However the apparent disposition of fiber bundles has varied as per histological preparation

For example, the collagen fibers of the PDL appear as a random ‘indifferent fiber plexus’ when ground sections are examined under the SEM, however these cannot be correlated with either light microscopy or TEM

ARRANGEMENT OF PDL FIBERS

Hence now it is accepted that the ‘indifferent fiber plexus’ is an artifact produced by histologic processing

Correlation between LM, SEM,TEM is possible only in demineralized sections.

Human PDL appears to be a continuous band of fibrous tissue 100-150 µm in width.

Majority of collagen fibrils appear as bundles in both T.S and L.S, and SEM views suggest they pursue a wavy course.

Fibroblasts with extensive flattened cytoplasmic processes are present between bundles, intimate association between fibrils and cytoplasmic extensions of fibroblasts, thus facilitates remodeling by intracytoplasmic degradation.

Close to cementum the fiber bundles are 3-10µm, while close to the bone they are 10-12µm in diameter

Complex relationships between the networks of bundles may be investigated using polarising microscopy.In T.S, birefringence of collagen suggests that

predominance of radiating circumflex fibers that curve around neurovascular bundles

In L.S overlapping networks of anastomosing bundles are evident within the horizontal, apical, and oblique groups

Other authors (Kardos and Simpson, 1979) suggest that the PDL behaves like a thixotropic gel.

The theory proposes that till aging occurs only transseptal fibers of the gingiva are polymerized and remainder persist as a gel.

Application of force to such a system would cause change from gel to sol resulting in flow.

This theory is not accepted today, because then the fibers seen in histological specimens must be considered as artefacts and in a later study by Mashouf and Engel(1975), highly organized birefringent collagen fibers were found in rat PDL in fresh unmineralized sections

L.M and SEM studies have shown that PDL of mature teeth of limited growth is organized into 3 zones during development and eruption

However by the time functional occlusion is reached, the collagen fibers are organized as continuous bundles that insert into the alveolar bone and cementum as Sharpey’s fibers

Arranged into 3 zonesAlveolarMiddleCemental

Earlier it was accepted that the fibers of the middle zone were spliced to form an intermediate plexus, and that this arrangement facilitated remodelling of the PDL during tooth eruption

Now it has been regarded as artefact of processing because it forms a continuous branching network of fiber bundles in T.S rather than a plexus

FIBER ARRANGEMENT IN CONTINUOUSLY GROWING TEETH

Sloan et al in 1978 proposed a 3D structure of the PDL

Collagen fibers in inner and outer bundles are organised into round bundles

Alveolar zone bundles are larger than cemental zone bundles, these are arranged radially

In the middle zone, collagen fibrils are arranged into thin sheets that form a series of flattened compartments running along long axis

LM studies show that 3 fibrous zones are evident only in L.S, similarly in SEM L.S studies, homogenous appearance of middle zone is due to sheets of collagen lying in the section plane ( in T.S they are appear as bundles)

Using polarizing microscopy, Hindle (1967) determined that the collagen fibers in the middle zone were less mature than alveolar and cemental zones

In T.S, middle zone collagen appears as a network of birefringent bundles, while in L.S only patchy birefringence is seen.

This is explained by the spatial distribution of collagen fibers of the middle zone if arranged into sheets because highly oriented collagen fibers would only produce measurable birefringence if transversely sectioned.

An L.S would include several sheets or parts of sheets of varying orientation, thus producing patchy birefringence

Minns (1973) showed that internal orientation of collagen fibers in the C.T influences mechanical properties of the tissue, and that collagenous bundles could best resist axial forces

The arrangement of the majority of the PDL collagen fiber groups into horizontal and obliquely directed groups is thus adapted to resist such axial forces

The overlapping arrangement of the bundle networks seen in SEM could also be of importance in resisting rotational forces

This complex 3D arrangement means that some bundles would always be placed in tension irrespective of direction of force

FUNCTIONAL ADAPTATIONS OF THE COLLAGEN FIBERS

Thus the PDL is able to resist the compressive forces

When subjected to rotational and intrusive forces, some fiber groups will be in tension

Tension Compression

COLLAGEN CRIMPINGCollagenous tissues

exhibit a quantifiable periodicity of structure on a variable scale; this has been described as a crimp.

In the polarizing microscope, crimping can be recognized by a regular banding of dark lines across a collagenous bundle when its axis lies perpendicular to the polarizer.

Some authors say that the crimping might also be due to the microanatomical arrangement of the collagenous sheets and bundles in addition to the zigzag arrangement of collagen fibrils

Viidik (1980) suggested that the waveform is sinusoidal and unlikely to be present in vivo.

However TEM,SEM and polarizing microscope studies show that there is indeed a crimped arrangement.

Crimping confers certain mechanical properties on the PDL.

Straightening out of the crimp enables the ligament to absorb impact tensile loads without extending collagen fibrils and without generating heat( Trelstad & Silver,1981)

It has been suggested that the fibroblast processes in developing collagenous tissues plays a role in the crimped arrangement.

Hence it may be an important feature in tooth eruption

At the insertions, collagen bundles of the PDL are embedded into cementum and alveolar bone in a manner similar to tendon inserting into bone i.e. in the form of Sharpey’s fibers.

Orientation in alveolar bone is similar to adjacent PDL bundles, however it is different in the cementum.

2 types of Sharpey’s fibers existIntrinsicExtrinsic

SHARPEYS FIBERS

• Dreyfuss & Frank reported that most of the Sharpey’s fibers that insert into alveolar bone have unmineralized cores, and are separated from each other by lamellar bone fibers

• IHC studies show that Sharpey’s fibers are enclosed within a sheath of collagen type III, this collagen confers elasticity on the fibers and also prevents mineralization

Where the fibers insert obliquely, the bone surface exhibits a stepped appearance mineralization occurs at right angles to axis of the fiber.

Mineralized periphery of fibers mech advantage for axial forces while mineralization at right angles to fibers suggests that Sharpeys fibers are subjected to tensional forces

Maximum strength to the mineral-collagen interface which is weakest part of fiber bundle

Elastin fibers dampen lateral masticatory stresses, also in this case the low modulus and long range reversible extensibility of elastin is more important than resilience.

However studies previously reported that only oxytalan is present in the PDL of humans, it has a specific role in stabilizing the tooth in certain functional situations.

Oxytalan and collagen bundles of the PDL appear to interweave at right angles to each other in a manner similar to the elastic ligaments.

Later on studies proved that oxytalan fibers can act in the same way as elastin fibers as they are straightened during forced extrusion

ARRANGEMENT AND FUNCTIONAL ADAPTATIONS OF ELASTIC FIBERS

Thus there must be an attachment of oxytalan fibers directly to collagen or indirectly to the blood vessels

This has been proven in human premolar teeth, in which the largest apico-occlusal oxytalan fibers are linked to laterally anastamosing minor fibers that in turn insert into cementum and CT around neurovasculature

Qualitative studies of aged PDL showDecreased cellularityIncreased collagen fibrosisFiber groups appear to be broader and more

highly organizedFiber bundles appear thickerSporadic mineralization of fibers was also seen

Other studies(Grant 1973) reported apparent decrease in number of PDL fibers in human post mortem tissues and aged primates.Increased size of interstitial spaces also noticedDecreased collagen content decreased

cellularity+multinucleated fibroblasts

AGING OF THE PERIODONTAL FIBERS

Severson et al (1978) found that alveolar bone in older adults was jagged and uneven and an irregular insertion of fibers was seen.

Also cementum was thicker and cemental surface was irregular.

Thus irregularity of fiber insertions, replacement of interstitial tissues with fat cells suggests that structural organization of PD degenerates with age.

However many of the age related changes are also noticed during the early stages of periodontal disease, hence more studies are required to know more about the same

The Periodontal Ligament in Health and Disease, Berkowitz

Clinical Periodontology, 10th edition, Carranza.

Clinical Periodontology and Implant Dentistry, 4th edition, Lindhe.

REFERENCES