Salivary glands and saliva

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Salivary glands and saliva

  1. 1. 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.
  2. 2. 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.
  3. 3. 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.
  4. 4. 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:
  5. 5. 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
  6. 6. 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
  7. 7. 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
  8. 8. 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.
  9. 9. SALIVA Introduction: 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.
  10. 10. 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
  11. 11. 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.
  12. 12. 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.
  13. 13. 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
  14. 14. 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.
  15. 15. 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)
  16. 16. 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.
  17. 17. 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.
  18. 18. 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
  19. 19.  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.
  20. 20. CONTENTS 1. INTRODUCTION 2. DEVELOPMENT 3. STRUCTURAL ELEMENTS 4. FUNCTIONS 5. CLINICAL CONSIDERATIONS 6. CONCLUSION
  21. 21. 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
  22. 22. 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.
  23. 23. - 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.
  24. 24. 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.
  25. 25. 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
  26. 26. 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
  27. 27. - 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
  28. 28. - 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).
  29. 29. - 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.
  30. 30. 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.
  31. 31. 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
  32. 32. - 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
  33. 33. - 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

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