Introduction:

The human salivary glands are important organs of the oral cavity that

produce saliva, an essential fluid required for normal speech, taste,

mastication, swallowing and digestion.

The salivary glands are exocrine glands whose reactions flow into the oral

cavity. Exocrine- those glands with a duct system to tansport secretion from

the glands.

Embryological development:

- The development of glanudular tissue involves interactions of the

epithelium with the underlying mesenchyme to form the functional

part of the gland.

- All salivary glands follow a similar development pattern

- The first sign of a gland during fetal life is the appearance of an

epithelial bud formed at a specific location in the oral cavity by the

growth of a bud of oral epithelium into the underluing

ectomesenchyme

- The epithelial bud grows into an extensively branched system of cords

of cells or solid epithelial cords of cells and later develop lumen and

ducts.

- Epithelial ingrowth ultimately forms the parenchyma of the salivary

gland and ectomesenchyme differentiates to form the supporting

connective tissue.

The epithelial cord proliferates rapidly and develops berry-like

swellings/terminal bulbs, which form the future secretory acini.

The next stage is characterized by the canalization of epithelial cord to

form ducts and lumen- Two theories have been proposed to explain

the mechanism of canalization:

1. Different rates of cell proliferation between outer and inner layers

of epithelial cord.

2. Fluid secretion by duct cells-increases hydrostatic pressure and

produces a lumen within the cord.

The final morphological stage of salivary gland development is the

cytodifferentiation of functional acini and intercalated ducts.

Microscopic Structure:

The structure of a salivary gland comprises of a series of secretory

units (acinar cells). They cluster around a central lumen and are

supported by Myoepithelial cells.

The acinus comprises the terminal or secretary end piece of the gland

situated farthest from the oral cavity. From each acinus the secretions

pass to a series of interconnected ducts and then through the major

salivary duct into the oral cavity.

The terminal secretory units/salivary gland acini are of three types-

serous, mucous or mixed.

a. Serous cells:

A typical serous cell is pyramidal in shape. It has a broad base resting on

a thin basal lamina and a narrow apex, which borders on the lumen. A

serous acinus is composed of numerous such wedge-shaped / pyramid

shaped cells arranged around a very small lumen and is usually not

visible at the light microscopic level.

Spherical nucleus is located towards the base of the cell. They have

abundant RER, Secretary granules and golgi apparatus and thus are

specialized for synthesis, storage and secretion of proteins.

Secretary granules are located / accumulated in the apical cytoplasm and

the RER and golgi apparatus are present in the basal portion of the

cytoplasm

The lateral surface between adjacent serous cells demonstrates a

junctional complex. A typical junctional complex comprises of a triad of

- Zonula Ocdudens (tight junction)

- Zonula adherens (Intermediate junction)

- Macula Adherens (desmosome)

These junctions serve 2 functions:

- Holds the cells together

- Prevents leakage of the lumen contents into the intercellular spaces

Several finger like branches of the lumen extend / radiates in a

serpentine pattern between adjacent serous cells – these are called

intercellular canaliculi. They increase total secretory surface area.

These may extend almost to the basal lamina surrounding the acinus.

Lysosome cells containing potent hydrolytic enzymes may be

occasionally seen.Their function is to destroy foreign material taken up

by cells or to remove worn out portions of cell organelles themselves.

b. Mucous cells:

Mucous cells are triangular or pyramidal in shape.

The flattened or oval nucleus is present at the base of the cell.

In routine histologic preparations, the apex of cell appears empty

except for thin stands of cytoplasm that forms a trabecular network.

At the electron microscopic level, the mucous cell is seen to be filled

with pale, irregular shaped granules containing mucins- called mucous

droplets.

These are usually large than the serous granules.

The RER and mitochondria are limited to a thin band cytoplasm near

the base and lateral parts of the cell.

Abundant golgi bodies are present and they play an important role by

adding large amount of carbohydrates to the secretion.

Thus, the secretary products of mucous cells differs from serous cells in

2 aspects:

- They have little or no enzymatic activity and serves mainly in

lubrication and protection of oral tissues.

- Carbohydrate to protein ratio is greater.

c. Myoepithelial cells:

They are stellate shaped cells that lie between the basal lamina and acinar

cells. They have numerous branching cytoplasmic processes that

interdigitate around the acini and ducts.The body of the cell is small with

a flattened nucleus.

Earlier, was called ‘basket cell’ as its appearance resembles a basket

surrounding the secretory unit.

Morphologically, these cells resemble smooth muscle cells in that they

have several parallel microfilaments and proteins like actin and myosin.

Function: Myoepithelial cell processes wrap around portions of the duct

system and when they contact, they squeeze or expel the secretions from

the acinus and the associated duct system and secretions moves towards

the oral cavity.

Histology of Duct System:

The duct system differs / varies in each of the major salivary glands.

Duct system has 2 main structural parts:

DUCT SYSTEM

Intralobular ducts Interlobular portion

Intercalated Striated (Secretory) Excretory ducts

The intralobular ducts join large interlobular ducts. The interlobular ducts

join to form a lobar duct – which drains a lobe of the gland.

The lobar ducts join to form the interlobar duct – which runs in the

connective tissue between lobes and is continued as the main excretory or

terminal duct.

a. Intercalated ducts:

The interrelated ducts are the smallest ducts within a lobule and they connect

the terminal secretory unit to next larger duct the striated duct.

They are lined by a single layer of low cuboidal cells and contain few

secretory granules, some RER, mitochondria, a round / oval centrally placed

nucleus.

The lateral membranes of adjacent cells are joined apically by junctional

complexes. The secretory granules in intercalated duct cells contribute to the

2 antibacterial proteins lysozyme and lactoferrin present in saliva.

These ducts are longest in parotid, intermediate in submandibular and

shortest in sublingual glands.

b. Striated ducts:

They are located between the intercalated and excretory duct is also known

as secretory or salivary duct.

They are lined by tall columnar epithelial cells with large spherical

central/eccentrically placed nuclei and distinctly eosinophilic cytoplasm.

The term ‘striated’ refers to the light microscopic appearance of the basal

cytoplasm. Well-developed striations are present perpendicular to the base

of the cells. This appearance results from in folding of the basal plasma

membrane which procedure cytoplasmic rows that contain numerous

mitochondria.

A few RER, golgi apparatus, lysosomes, bundles of cytoplasmic filaments

are also present.Due to the structure of striated duct cells they are actively

involved in water and electrolyte transport.

The striated ducts are followed by the large excretory ducts.The epithelium

of these ducts gradually become pseudostratified columnar with occasional

goblet cells and surface cilia and the epithelium of the main duct gradually

becomes stratified as it merges with that of the oral cavity.

All the water content present in saliva is derived from interstitial fluid which

occurs at the terminal secretory units or acini.

No active transport of water occurs in the ducts as the striated and excretory

ducts are relatively impermeable to water.

CONNECTIVE TISSUE CELLS:

Connective tissue forms the capsule and septa of salivary glands and

surrounds ducts and acini. Also contains fibroblasts, macrophages and

lymphocytes.

CLASSIFICATION OF SALIVARY GLANDS: They are classified in

two main ways:

1) Based on size and location:

Major- Parotid

Submandibular

Sublingual

Minor-Lingual

Buccal/Labial

Glossopalatine

2) Based on the nature of secretion:

Serous-Parotid

Mucous-Glossopalatine

Mixed-Submandibular & sublingual

a) Serous secretion – contains water, enzymes salts and organic ions, is

watery and thin.

b) Mucous – Ropey and thick, rich in polysaccharides and contains

some non-enzymatic proteins.

SALIVAIntroduction:

Saliva plays an important role in oral health monitoring, regulating and

maintaining the integrity of oral hard tissues and some soft tissues.

There’s an old axiom, which states “You never miss the water till the well

runs dry.” This is especially true for saliva as the importance of saliva is

realized only by patients who lack it (xerostomia)

As, the lack of saliva causes dryness of mouth, altered taste, failed speech,

trouble with chewing, dental caries, bad breath, burning tongue, heartburn

etc.

saliva is a complex mixture of fluids which is derived from major and minor

salivary glands and GCF(gingival crevicular fluid). It also contains a high

population of bacteria, desquamated epithelial cells, residues of food and

drink.

The term ‘whole saliva’ refers to the combined fluids present in the mouth.

SECRETION OF SALIVA:

Total volume- 500 750ml / day

Submandibular – 60%

Parotid – 30%

Sublingual- 3-5%

Minor salivary glands – 7%

These proportions vary with intensity and type of stimulation.

a) Under resting state – 0.3 ml / min- is the un-stimulated slow flow of saliva

that is present majority of time and is not associated with food ingestion.

b] On stimulation – 2.5 – 5.0ml / min (Can be acidic / mechanical

stimulation)

c) During sleep – flow is almost zero

COMPOSITION OF SALIVA:

Saliva is a dilute hypotonic fluid of over 99% of it being water.

Remaining 1% consists of dissolved organic and inorganic constituents.

INORGANIC CONSTITUNETS:

Saliva contains both cations and anions. The main cations are – Na, K along

with Ca and Mg. Anions are – Cl, HCO3 , Phosphate and trace amounts of

halides.

a) Na – 15mg/100ml

b) Potassium– 80mg

c) Calcium – 6mg

d) Phosphorus – 16.8

e) Chloride – 50mg

f) Fluoride (ppm) – 0.03

g) Bicarbonate – 6mg

h) Thiocyanate – 2mg

a) Salivary sodium concentration are highly flow dependant

In resting state – saliva has trace amount of sodium and conc increases

with salivary secretion due to less time available for reabsorption.

b) Potassium : Potassium level is independent of the secretory flow rate.

c)Calcium: Major part occurs in ionic form, part of it is bound to protein or

is in soluble complexes with carbonate phosphate lactate

d)Phosphate: Concentration decreases with increased flow rate.

e) Chloride – Passively reabsorbed along with sodium in the striated duct so

concentration is less than that of plasma.

e) Fluoride: content is directly proportional to dietary intake.

f) Bicarbonate: Is the principal salivary buffer concentration is low with

resting saliva but increase with glandular metabolic activity.

g) Thiocyanate: Present in saliva at higher concentration than in serum,

possess bacteriostatic properties.

h) Hydrogen ion: Normal pH of saliva – 6-7 slightly acidic.

pH range – 5-6 (peak flow)

ORGANIC CONSTITUNETS:

I) PROTEINS: consists only 3% of protein concentration present in plasma

i.e, about 200 mg/100ml.

Includes salivary enzymes,immunoglobulins, antibacterial factors,mucous

glycoproteins (mucins) & other polypeptides.

a) Salivary enzymes:

i) Alpha amylase(ptyalin): is a glyco-protein, major digestive enzyme of

saliva.

In parotid saliva – 60- 120mg / 100ml

In submandibular saliva – 25mg / 100ml

These is very little amylase activity in sublingual and minor glandular

secretions. The enzyme hydrolyses the alpha 1,4 glycosidic bond

between glucose units & producing maltose as end products.Chloride is

required a co- factor.

ii) Lysozyme: is an antibacterial enzyme. Concentration is greater in sub

mandibular saliva than in parotid.

Mechanism of action– acts on B(1;4) bond between N – acetyl muramic acid

and N-acetyl glucosamine in the gram +ve bacterial cell wall- causing

microbial death.

iii) Peroxidase system : includes lacto peroxide, Thiocyanate and hydrogen

peroxide. This system inhibits growth and acid production of several

microorganisms like streptococcus, lacto bacilli, fungi and enteric bacteria.

iv) Kallikrein: Causes functional vasodialation inorder to supply an actively

secreting gland.

v) Dextranases: Impaired oral hygiene or over consumption of sucrose /

fermentable carbohydrates, supports growth of organisms producing

dextranses.

vi) Invertase: High invertase activity is associated with increase lactobacillus

and streptoccus in plaque due to poor oral hygiene.

vii) Miscellaneous Enzymes:Acid phosphatase, cholinesterase, ribonuclease,

Lipase, Proteases, carboxypeptidases, urease, aminopeptidase etc.

b) Immuno globulins:

- Secretory Ig A is the predominant immunoglobulin- 20mg / 100ml.

IgG and IgM present in low amounts. JgA inhibits bacterial colonization.

c)Other antibacterial factors:

Sialoperoxidase,

Lactoferrin -An iron binding protein removes free iron from saliva –

depletes supply of iron required for bacterial growth.

d) Glycoproteins: Mucous glycoproteins (MG1 & MG2), proline-rich

proteins.

II) BLOOD GROUP SUBSTANCES

Blood group antigens are present in saliva & corresponds to the blood

groups A,B,AB, O

III) HORMONES: ‘Parotin’ facilitates calcification and maintains calcium

level.

‘Nerve growth factor’ affects growth and development of sympathetic nerve

fibers.

IV) Others include carbohydrates, lipids, N2, urea.

FACTORS AFFECTING SALIVARY FLOW RATE :

1. Diurnal Variation:

Protein concentration - high in the afternoon.

Na and Cl concentration – are high in early hours of morning.

Calcium concentration – is more at night

Ca and Po4 concentration- are stable during day

2. Duration of stimulus:

If glands are stimulated for longer than 3 mins- concentration of many

components is reduced.

3. Nature of stimulus: Difference in stimulus causes variations in salivary

composition

Eg: Salt stimulates a higher protein content. Sugar stimuli leads to increase

amylase content.

4. Dietary Factors:

Long term diet changes does not have a significant effect on salivary

composition .Glandular activity is influenced by mechanical factors –

eg- new denture insertion.

FUNCTIONS OF SALIVA:

1) Digestion:

Salivary amylase acts on polysaccharide starch (dextein) and glycogen

Maltose formed as the byproduct may be fermented by oral bacteria to

form acid. But the effect of this on caries initiation is still being studied.

Due to rapid ingestion of food ,digestion of starch continues in stomach.

2) Lubrication:

It keeps the hard and soft oral surfaces moist and helps in speech

mastication and swallowing.

Water and mucous glycoprotein constituents of saliva helps in bolus

formation and provides lubrication for movement of oral tissues against

each other.

saliva has viscoelastic properties, this can be demonstrated by the ability

to draw out a thread of saliva which is typical of a viscoelastic fluid-

called ‘Spinnbarkeit’ phenomenon.

3) Dilution and clearance:

Brings about dilution and clearance of substances introduced into mouth

by swallowing or spitting.Thus potentially harmful substances like sugars

and plaque acids are cleared.

4) Buffering:

The buffering systems of saliva are:

a) Bicarbonates – 85% total buffer capacity of saliva comes from the

bicarbonate system.

b) Phosphates

c) Protein mucin

d) Urea

As salivary flow increase during a meal – HCO3 concentration increases

which makes pH of oral fluids critical for survival of bacterial flora (thus

decreasing the production of acids from food plaque)

5) ANITIBACTERIAL EFECTS:

Is brought about by lysozymes, immunoglobulins IgA, IgM, IgG.

Non specific proteins like sialoperoxidase , lactoferrin, thyocyanate etc.

6) ANTI FUNGAL FUNCTION:

Is brought about by salivary mucin and histidine rich proteins (histatins)

7) PELLICLE & PLAQUE FORMATION:

Is formed by selective adsorption of salivary glycoproteins to the tooth

surface. Pellicle protects the teeth from chemical and mechanical insult

and also acts as a substrate for colonization of bacteria Plaque formation

also involves incorporation of salivary proteins, which helps in the synthesis

of intracellular glucans.

8) WATER BALANCE:

Dryness of mouth stimulates the thirst centre Individual consumes

more water.

During vomiting /dehydration/hyperapnoea Vasopressin is produced

increases water hormone re-absorption though striated ducts.

9) EXCRETORY FUNCTION:

Saliva serves as an important excretory route for several blood components

like urea, uric acid, ammonia and also lead, Hg, alkaloids, bismuth etc.

10) SALIVARY ANTICARIES ACTIVITY:

Several potential mechanisms are involved in the prevention of dental caries

by saliva.

1) Increased salivary flow leads to increase carbohydrate clearance from

the oral cavity.

2) Salivary components reduce acid formed in plaque by promotion of

less acidogenic plaque microorganisms / microorganisms that form

weaker acids on carbohydrate fermentation.

3) Salivary bicarbonates buffers acids formed by carbohydrate

fermentation .

4) Rate of glycolyis is increased by salivary urea / HCO3 faster

metabolism of carbohydrates. Thus there is decreased duration of

exposure of enamel to critical pH levels.

5) Presence of fluoride increases enamel resistance to decalcification

6) Promotes subsurface mineralization of carious lesion by calcium /

phosphate / fluoride ions.

7) Saliva promotes microbial clearance from oral cavity thus decreases

plaque formation.

CONTROL OF SECRETION:

Salivary glands differ from other glands as they are purely under nervous

control. Hormones can alter only composition but not its secretion.

Sympathetic nerve supply to glands causes release of secretory proteins like

amylase and vasoconstrictors.

Parasympathetic supply – Nerves innervate acinar cells duct cells, blood

vessels and myoepithelial cells , are secretomor and vasodialator.

FACTORS THAT CONTROL SECRETION:

a) Resting flow

During resting conditions ( no stimulation by ingestion of food), there is

continuous slow flow of saliva that keeps the mouth moist and lubricates

the mucous membrane.

This salivary flow is influenced by several factors like.

Circadian rhythm Flow peaks at approximately 5 pm in most

individuals. Flow decreases during night and sleep.

Hydration: If 8% of body water is lost cessation of salivary flow

occurs.The resultant drying of oral cavity is a feature of

thirst.Thirst and water intake are under hypothalamic control and

is not dependant on dryness.

Exercise and stress – Exerts inhibitory influences on the salivary

nuclei in hypothalamus causing dryness of mouth

b) Psychic flow:

A small increase in flow of saliva occurs on thought or sight of food .It

has been suggested that this may be due to momentary contraction of

myoepithelial elements – to express ready formed saliva into mouth

without increasing the overall amount of saliva formed.

c) Unconditional reflexes: Like masticatory movements sour or sweet taste

stimuli results in increase in salivary flow.

CLINICAL CONSIDERATIONS

Saliva provides an easily available non-invasive diagnostic medium for

a widening range of diseases and clinical situations.

The most common subjective complaint resulting from salivary gland

dysfunction is xerostomia (drymouth).

This causes difficulty in speech and mastication, mucositis / candidal

infection, atrophic changes in mucosa of tongue, rapid carious

destruction and periodontal disease.

Flow rates for whole saliva of less than 0.1/min (unstimulated) is

considered as abnormally low.

Causes:

-Local / systemic disease- fever, oral infections, diabetes etc

-Side effects of drugs- antihypertensives, antidepressants, antiparkinson

drugs etc

- Radiation therapy

- Emotional stress / anxiety

Treatment:

- Is focused on relief of symptoms

- Use of salivary substitutes

- If functional gland tissue is present-saliva can be stimulated by chewing

non-cariogenic foods like raw vegetables / gum

- Prevention of caries by fluoride therapy.

CONTENTS

1. INTRODUCTION

2. DEVELOPMENT

3. STRUCTURAL ELEMENTS

4. FUNCTIONS

5. CLINICAL CONSIDERATIONS

6. CONCLUSION

INTRODUCTION:

The periodontal ligament is the most fascinating, irreplaceable periodontal

tissue and represents one of the soft tissue components of the human

periodontium, the other being the gingiva.

The periodontium comprises of four connective tissues:

2 mineralized Connective tissues– Cementum and alveolar bone

2 fibrous Connective tissues – Periodontal ligament & lamina propria of

Gingiva

Definition: The PDL is the fibrous connective tissue that occupies the

periodontal space between the root of tooth or cementum and its bony

socket. It is also sometimes referred to by different names – periodontal

membrane, alveolo- dental ligament, desmodont ,pericementum, Gomphois

etc

At the cervical region of the tooth, above the alveolar crest, the PDL merges

with the gingival connective, tissue. At the root apex, PDL merges with the

pulp

SHAPE: Hour-glass shaped, being narrowest in the mid root region, near the

fulcrum about which the tooth moves.

THICKNESS: 0.15 – 0.38mm

Thickness decreases with age (0.21mm young adult)

(0.15mm old age)

It also depends on the functional state of the tissue.

Teeth in heavy function tend to have wider ligaments than non-functioning

teeth (unopposed or impacted teeth)

It is wider in primary teeth than in teeth permanent dentition

EVOLUTION:

In the ancestral reptiles, the teeth were ankylosed to the bone.

The evolutionary change from reptiles to mammals (more specifically

humans) replaces the ankylosis of tooth and bone to a ligamentous

suspension of the tooth .This is due to a radical change in the mode of

growth of mandible. In reptiles, the mandible is made by a series of bones

united by sutures and growth occurs at these sutures, Where as the

mammalian mandible consists of a single bone and growth occurs at the free

margins of alveolar process with the condylar cartilage serving as the most

important growth site.

DEVELOPMENT:

The periodontal ligament is derived from the dental follicle /

dental sac proper. The dental sac is clearly defined in the bell stage of

the tooth germ. It is made up of an inner cell rich fibrous layer which

encapsulates the entire tooth germ and an outer loosely constructed

layer.

- It begins with root formation and always occurs in connection with

the prior disintegration of Hertwig’s epithelial root sheath and the

simultaneous appearance of cementum..

- The inner layer gives origin to cementum while the alveolar bone and

Pdl arise in the outer layer.

- The formation of the Pdl occurs after the disintegration and separation

of hertwig’s epithelial root sheath following root formation and these

separated epithelial cells from the surface of the forming root dentin

later become the epithelial cell rests of malassez in the pdl.

- The tooth germ lies deep within its bony crypt and the borders of it

extend far occlusally over the tooth germ.

- The fibroblasts derived from dental follicle form the collagen fiber

bundle, one end of which gets embedded in the newly formed

cementum, while the remainder extends occlusally within the walls of

the bony compartment.

- Thus the fibre bundles of pdl are at first oriented parallel with the long

axis of tooth and run from cementum in an occlusal direction and only

later are remodeled with their usual orientation

- Pdl formation proceeds in a coronal to apical sequence as the root

grows

- The fibre bundles that insert into the crest of the alveolar bone

(alveolar crest fibres) are formed first followed by the horizontal

fibres (stretch horizontally in the coronal part of the pdl) and oblique

fibres (cementoalveolar fibre bundles that run obliquely towards the

apex) and finally the apical fibre bundles.

STRUCTURAL ELEMENTS OF PERIODONTAL LIGAMENT:

PDL

Cells Extra Cellular Substance

Synthetic Resorptive Progenitor Fibers Ground Substance

Cells Cells Cells

Osteoblast Osteoclasts Collagen

Fibroblast Fibroblasts Oxytalan

Cementoblast Cewmentoclasts

- Synthetic cells like fibroblasts, osteoblasts cementoblasts in various

stages of differentiation are present.

- Fibroblasts represent the most numerous cell type and are oriented

parallel to collagen fibres bundles

- They are actively involved in secreting extra cellular substances and

hence have a large nucleus, abundant cytoplasm, RER, Golgibodies

mitochondria and other cell organelles.

- Resorptive cells: Osteoclasts are large multinucleated giant cells

derived from circulating monocytes, located within superficial bone

cavities howship lacunae

- brings about resorption of bone in 2 stages- removal of mineral from

bony margin & disintegration of organic matrix by the acid

phosphatase enzyme.

-Ruffled /striated border is seen in presence of active osteoclasts.

Ruffled border is separated from the rest of the plasma membrane by a

specialized membrane devoid of organelles-‘clear zone’.

Osteoclast and osteoblasts are seen normally in a functioning Pdl –and

responsible for remodeling of bone, thus bring about functional

changes in position of teeth by removal and deposition of bone.

Cementoclasts resemble osteoclasts in morphology and function.

Fibroblasts in the C.T of Pdl are capable of both synthesis and

resorption of collagen fibers during remodeling of Pdl.

Progenitor cells: are cells with a capacity to divide or undergo mitotic

division when stimulated appropriately to replace the cells lost due to

death or trauma.

- Are located predominantly in the vicinity of blood vessel.

Epithelial rests of malassez: are remnants of hertwigs epithelial root

sheath found close to cementum parallel to the surface of root.

Continuous layer of epithelial on the surface of newly formed root

dentin, disintegrates or breaks into strands or island – epithelial rests

of malassez.

EXTRACELLULAR SUBSTANCE:

- The fibres of PDL predominantly consist of collagen and oxytalan

fibres

- The fiber apparatus is made up partly by fibre bundles in an orderly

arrangement running from alveolar bone to cementum called the

principal fibers and partly by loose fibres which mostly surrounded

the blood vessels and nerves (elastic fibres)

a) Collagen fibers: Collagen is a high molecular wt protein to which a

small number of sugars are attached.

- PDL is made up of type I collagen mainly and a smaller portion of

type III collagen (20%)

- A collagen fibril is approximately 40-70nm thick with cross striations

at intervals of 64nm.

- Each of these fibrils is surrounded by a mucopolysaccharide shell

- Several such fibrils become arranged parallel to one another to form a

fibril bundle or called collagen fiber.

Based on their functional orientation the collagen fiber bundles can be

classified into 5 principal groups running in different directions in

different parts of Pdl.

1. Alveolar crest fibres:

- Run obliquely from supra alveolar cementum apically to crest of

alveolar bone apically to crest of alveolar bone, resists vertical and

intrusive force.

2. Horizontal fibers: lies apical to the level of alveolar bone crest (at the

entrance into Pdl space), runs horizontally across the ligament at right

angles to root bone surfaces/long axis tooth from cementum to

alveolar bone proper.

- Resists horizontal and tipping force.

3. Oblique fibers: These constitute the most numerous group and the

main attachment of the tooth. They occupy about the middle two

thirds of the entire Pdl space

- run obliquely in coronal direction from root cementum to alveolar

bone proper.

- The fibres progressively change direction and coronally merge with

horizontal fibres and apically with apical fibres.

- resist vertical and intrusive force

4. Apical Fibers:

Irregularly arranged and radiates from the apical region of the root to

the surrounding bone.

-resists vertical force.

5. Inter radicular fibers:

-Occurs on multi rooted teeth within bi and trifurcations

-irregularly arranged, fanning out from the cementum across the

ligament to the crest of the interradicular septum.

Sharpey’s fibers:

Collagen fiber bundles are anchored in cementum at one end of

periodontal space and into alveolar bone on the other.

- The (terminal portions) segments of the periodontal fiber bundles

embedded within these hard tissues are called sharpey’s fibers.

- They do not extend in a straight line but have a wavy course.

Intermediate Plexus:

- Is a zone of loose, not well-oriented collagen fibers in the center of the

periodontal space.

- Within this zone, the fiber bundles radiating out from bone and

cementum inter wine into a lattice work – intermediate plexus

- Earlier it was believed that this zone persisted after tooth eruption and

was the site of rapid remodeling of fibers necessary for tooth

movement.

- It is presently concluded / believed to be just an artifact arising out of

the plane of section.

- In the median section, the sheets of collagen lie in the section plane

and are not cut transversely and hence do not resemble bundles as

they do in transverse section.

- Within the completely formed pdl of erupted functioning teeth an

intermediate plexus no longer exists.

b) Oxytalan Fibers: 3%

- Resembles immature elastic fibers ultra structurally. The orientation

of oxytalan fibers is different from collagen fibers. Oxytalan fibers

and collagen bundles interweave at right angles to each other.

- They form a three–dimensional meshwork that extends from

cementum / bone to the periapical periodontal blood vessels.

- Due to its close relationship to periodontal b.v they are considered to

be a part of a mechanoreceptor system which regulates vascular flow

according to functional tooth movement

Blood vessels / Nerves /Lymphatics:

- are discrete structures present in the C.T of Pdl.

- Pdl is heavily vascularized due to the high oxygen requirements of

the densely fibrous and cellular Pdl (Superior and Inferior alveolar art

branches).

- Branches from the dental artery just before it enters the apical

foramen

- Branches from gingival vessels

Lymphatic vessels :

- follow the path of b.v and leaves the Pdl through gingival tissue,

alveolar mucosa / bone or apically.

Nerves:

-are associated with blood vessels

-Pdl can register 2 types of sensation pain and pressure.

FUNCTIONS OF PDL:

1. Formative

2. Physical

3. Nutritional

4. Sensory

1. Formative: The cells of Pdl participate in the formation and

resorption of cementum and alveolar bone during

- Orthodontic tooth movement

- Repair following trauma / injury

- Accommodation of occlusal forces

Pdl is constantly undergoing remodeling. Old cells and fibres are

broken down and replaced by new ones.

Collagen turnover in Pdl is fastest than all connective tissues in the

body. It is greatest at the apical and crestal regions.

2) Physical: Functions include-

a) Transmission of occlusal forces to alveolar bone:

- The arrangement of principle fibers is similar to a suspensory bridge /

Hammock. When an axial force is applied to tooth the oblique fibres

alter their wavy course, assume their full length / straighten and

sustain a major part of the axial force and transmit to alveolar bone

causing an elastic deformation of bony socket.

- When horizontal or tipping force is applied there are 2 phases of tooth

movement one within the confines of pdl and the second resulting in

displacement of alveolar bone with increasing force.

b) Attachment of teeth to the Jaws

c) Maintenance of gingival tissue location to the teeth.

d) Resistance to the impact of occlusal forces (shock absorption)

3) Sensory: Pdl is abundantly supplied by sensory nerve fibers – provides a

very effective mechanism of response to proprioceptive stimuli (pressure).

The sensing of pressure is extremely refined. The lightest of tooth contacts

and the smallest of particles between the contact surfaces are registered.

This is crucial to the neuromuscular control

of masticatory function and helps in protecting the tooth and its supporting

structures from effects of excessively vigorous masticatory movements.

4) Nutritive:

It provides nutrients for the cementum, alveolar bone and gingiva by its

component, blood vessels as well as provides lymphatic drainage.

CLINICAL CONSIDERATIONS:

Pdl is a suspensory ligament and its main role is to support the tooth

in the bony socket. The thickness of the ligament varies in different

individuals and also in different teeth in the same individual.

As the tooth depends on the Pdl for support during function, the Pdl

depends on stimulation from occlusal forces to maintain its structure.

Within physiological limits, increased function is accommodated by

increasing principal fiber size, sharpey’s fiber thickness and number –

thus increasing the width of Pdl as a whole. When function is

diminished / absent, the Pdl is thinned and component principal fibers

become disorganized. This change should necessarily be considered in

dentistry – If a tooth has remained out of function for a long time, it is

unable to take the sudden load of restoration. Some time must be allowed

for the readaptation of tissues to the new functional demands:

Trauma can result from excessive abnormal occlusal function / premature

contact from high crown orthodontic forces/ pulpal injury that leads to

periapical changes. Overinstrumentation during root canal therapy causes

profuse periapical hemorrhage age and dissemination of dentin particles

hemorrhage age and dissemination of dentin particles beyond the apical

foramina.

- Periapical Pdl response to endodontic materials depends on the texture

of the filling and its chemical composition

- When the filling material projecting from the apex is hard and

compact, it tends to become encapsulated when it is less compact, the

filling material is resorbed more rapidly.

- But more serve inflammation occurs if the overfilled mass is not

compact.

- Overfilling – destruction / compression thermo basis of apical vessels

– infraction of pdl – necrosis of apical pdl or infiltration of neut– and

macrophages and giant cells abscess granules formation.

- Necrosis was most extensive with zinc-oxide eugenol and cements

- Resorbable pastes like iodoform produces mild neutrophilic

inflammatory reaction.

- All these reactions are teansient. Newly formed fibrotic tissue replaces

necrotic pdl

- Untreated Gingivitis / Periodontities can extends to pdl endo treatment

followed by perio

- Vitc deficiency – balance between synthesis and resorption of

collagen fibres of pdl resorption increased resorption of collagen and

decreased synthesis and replacement loss of attachment between bone

and tooth – loss of tooth

5) Following replantation of avulsed teeth – replacement / inflammatory

resorption.

- Minor areas of Pdl damage – repaired from adjacent vital ligament –

by causing root surface resorption and repair with new cementum

- If dentin is damages and infected

- Inflammatory resorption occurs with of both root and bone

and replaced tissue

- More extensive Pdl damage – resulted in healing with rapid

osteogenesis - of periodontal space – ankylasis

- Thus prognosis of a replanted tooth depends on the viability of its Pdl

and on a minimum delay before replantation.

CONCLUSION:

The periodontal is a complex field of study with enormous literature

available thro extensive research studies Pdl as connective tissue adopted to

perform several specialized functions should be given its due importance by the

clinician.

The morphologic and functional variations of periodontitis and also the changes

associated with age must be clearly understood by the clinician for any treatment

rendered to be effective

STRUCTURAL ELEMENTS OF PERIODONTAL LIGAMENT:

PDL

Cells Extra Cellular Substance

Synthetic Resorptive Progenitor Fibers Ground Substance

Cells Cells Cells

Collagen

Osteoblast Osteoclasts Oxytalan

Fibroblast Fibroblasts

Cementoblast Cementoclasts