2INTRODUCTION Periodontal ligament is an integral part of periodontium. The periodontium is an attachment apparatus of the teeth. It is a connective tissue organ, which is covered by epithelium on top surface.Teeth are attached to the bone of the jaws by periodontium.
3The periodontal ligament is a soft, fibrous specialized connective tissue which is present in the periodontal space, which is situated between the cementum of root of the tooth and the bone forming the socket wall.The periodontal ligament extends coronally up to the most apical part of connective tissue of gingiva.Because the collagen fibers are attached to the cementum and alveolar bone, the ligament provides soft tissue continuity between the mineralized connective tissues of periodontium.
4Other terms which were previously used for periodontal ligament are:- DesmondontGomphosisPericementumDental PeriosteumAlveolodental ligamentPeriodontal membrane
5STRUCTUREThe periodontal ligament has the shape of an “HOUR GLASS” and is narrowest at the midroot level.The width of periodontal ligament is approximately mm.
7SYNTHETIC CELLS The characteristic of synthetic cells are: Should be actively synthesizing ribosomes.Increase in the complement rough endoplasmic reticulum and golgi apparatus.Large open faced or vesicular nucleus with prominent nucleoli.
8OSTEOBLASTSThe osteoblasts covers the periodontal surface of alveolar bone. Alveolar bone constitute a modified endosteum and not a periosteum. A periosteum comprises at least two distinct layers:1. Inner – CELLULAR LAYER2. Outer – FIBROUS LAYERA cellular, but not an outer fibrous layer is present on the periodontal surface of alveolar bone.
9Function: Osteoblasts help in the synthesis of alveolar bone.
10FIBROBLASTSFibroblasts are the most common cells in periodontal ligament. They constitute about 65% of total population.They appear as ovoid or elongated cells with pseudopodia like process.They consist of subtypes with distinct phenotypes and found to synthesize higher quantities of chondroitin sulphate and lesser quantities of heparin sulphate and hyaluronic acid.
11FUNCTION: PRODUCTION OF VARIOUS TYPES OF FIBERS & IS ALSO INSTRUMENTAL IN THE SYNTHESIS OF CONNECTIVE TISSUE MATRIX.
12The fibroblast is stellate shaped cell which produces: 1. COLLAGEN FIBERS2. RETICULIN FIBERS3. OXYTALAN FIBERSVarious stages in the production of collagen fibers are as follows:The first molecule released by fibroblasts is tropocollagen which contains three polypeptide chains intertwined to form helix. Tropocollagen molecules are aggregated longitudinally to form protofibrils, which are subsequently laterally arranged parallel to form collagen fibrils.
13Importantly in inflammatory situations such as those associated with periodontal diseases, an increased expression of matrix metalloproteinase's occurs that aggressively destroys collagen.Thus attractive therapies for controlling tissue destruction may include host-modulators that have the capacity to inhibit metalloproteinases.
14The damaged periodontal fibers are replaced and remodeled by newly formed fibers. The “RENEWAL CAPABILITY” is an important characteristic of periodontal ligament.
15CEMENTOBLASTSCementoblasts synthesize collagen and protein polysaccharides, which make up the organic matrix of cementum.After some cementum has been laid down, its mineralization begins with the help of calcium and phosphate ions.Sharpey’s fibers
16RESORPTIVE CELLS OSTEOCLASTS Resorb bone.The surface of an osteoclasts which is in contact with bone has a ruffled border.Resorption occurs in two stages:The mineral is removed at bone margins and then exposed organic matrix disintegrates. The osteoclasts demineralise the inorganic part as well as disintegrates the organic matrix.
18FIBROBLASTS Fibroblasts are capable of both synthesis and resorption. They exhibit lysosomes, which contain collagen fragments undergoing digestion.The presence of collagen resorbing fibroblasts in a normal functioning periodontal ligament indicates resorption of fibers occurring during remodeling of periodontal ligament.
19CEMENTOCLASTSCementoclasts are found in periodontal ligament but not remodeled like alveolar bone and periodontal ligament.These are found on the surface of cementum.
20PROGENITOR CELLSProgenitor cells are the undifferentiated mesenchymal cells, which have the capacity to undergo mitotic division and replace the differentiated cells dying at the end of their life span.These cells are located in perivascular region and have a small close faced nucleus and little cytoplasm.When cell division occurs, one of the daughter cells differentiate into functional type of connective tissue cells. The other remaining cells retain their capacity to divide.
21EPITHELIAL CELL RESTS OF MALASSEZ These cells are the remnants of the epithelium of Hertwig’s Epithelial Root Sheath and are found close to cementum.These cells exhibit monofilaments and are attached to each other by desmosomes.The epithelia cells are isolated from connective tissue by a basal lamina.
22Periodontal ligament showing epithelial cell rests of malassez, indicated by arrows.
23MAST CELLSMast cells are small round or oval. These cells are characterized by numerous cytoplasm, which mask its small, indistinct nucleus.The diameter of mast cells is about 12 to 15 microns.The granules contain heparin and histamine. The release of histamine into the extracellular compartment causes proliferation of the endothelial and mesenchymal cells.Degranulate in response to antigen- antibody formation on their surface.
25MACROPHAGESMacrophages are derived from blood monocytes and are present near the blood vessels.These cells have a horse-shoe shaped or kidney shaped nucleus with peripheral chromatin and cytoplasm contain phagocytosed material.Macrophages help in phagocytosing dead cells and secreting growth factor, which help to regulate the proliferation of adjacent fibroblasts.
27EXTRACELLULAR SUBSTANCE Extra cellular substance comprises the following:1. Fibers a) Collagen b) Oxytalan2. Ground Substance a) Proteoglycans b) Glycoproteins
28PERIODONTAL FIBERSThe most important element of periodontal ligament has principal fibers, the principal fibers are collagenous in nature and a arranged in bundles and follow a wavy course.Collagen is a high molecular weight protein.Collagen macromolecules are rod like and are arranged in form of fibrils. Fibrils are packed side by side to form fibers.Vitamin C help in formation and repair of collagen.
29Half life of collagen fibers is between 3 to 23 days and collagen imparts a unique combination of flexibility and strength to tissue.
30TYPES OF PERIODONTAL LIGAMENT FIBERS 1. TRANSEPTAL GROUP These fibers extend interproximally over alveolar bone crest and are embedded in the cementum of adjacent teeth.They are reconstructed even after the destruction of alveolar bone resulting from periodontal disease.These fibers may be considered as belonging to the gingiva because they do not have osseous attachment.
32ALVEOLAR CREST GROUPThese fibers extend obliquely from the cementum just beneath the junctional epithelium to alveolar crest.Fibers also run from the cementum over the alveolar crest and to fibrous layer of periosteum covering alveolar bone.The alveolar crest fibers prevent extrusion of tooth and resist lateral tooth movements.The incision of these fibers during periodontal surgery does not increase tooth mobility unless significant attachment loss has occurred.
333. HORIZONTAL GROUPHorizontal fibers extend at right angles to long axis of tooth from the cementum to alveolar bone.4. OBLIQUE GROUPOblique fibers, the largest group in periodontal ligament, extend from cementum in a coronal direction obliquely to bone. They bear the brunt of vertical masticatory stresses and transfer them into tension on the alveolar bone.5. APICAL GROUPThe apical fibers radiate in a rather irregular manner from the cementum to bone at apical region of the socket. They do not occur on incompletely formed roots.
34INTER-RADICULAR FIBERS The interradicular fibers fan out from the cementum to the tooth in furcation areas of multirooted teeth.The remodeling of fibers take place in intermediate plexus. This allows adjustments in the ligament, which accommodate small movements of tooth.
35OXYTALAN FIBERSThese are immature elastic fibers restricted to walls of blood vessels and are oriented in an axial direction.The function is to support the bloods vessels in the periodontal ligament.
36STRUCTURES PRESENT IN THE CONNECTIVE TISSUE BLOOD VESSELSMain blood supply is from superior and inferior alveolar arteries. The blood vessels are derived from the following:1. BRANCHES FROM APICAL VESSELS Vessels supplying the pulp.2. BRANCHES FROM INTRA-ALVEOLAR VESSELS:- Vessels run horizontally and penetrate the alveolar bone to enter into the periodontal ligament.
373. BRANCHES FROM GINGIVAL VESSELS:- The arterioles and capillaries ramify and form a rich network. Rich vascular plexus is found at the apex and in cervical part of ligament.
38NERVE SUPPLYNerves found in ligament pass through foramina in alveolar bone.The nerves are the branches of second and third division of fifth cranial nerve (trigeminal nerve) and follow same path as blood vessels.These nerve fibers provide sense of touch, pressure, pain and proprioception during mastication.
39CEMENTICLESCementicles are small calcified bodies present in the periodontal ligament.They may form into large calcified bodies and fuse within cementum or remain free.These are found in old age.The degenerated epithelial cells form a nidus for calcification.
40FUNCTIONS PHYSICAL FUNCTION Provision of soft tissue ‘casing” in order to protect the vessels and nerves from injury due to mechanical forces.Transmission of occlusal forces to bone.Depending on type of force applied, axial force when applied causes stretching of oblique fibers of periodontal ligament.
41Transmission of this tensional force to alveolar bone encourages bone formation rather then bone resorption.But when horizontal or tipping force is applied, the tooth rotates around the axis.When a greater force is applied, displacement of facial and lingual plates may occur.The axis of rotation in a single rooted tooth is located in area between the apical and middle third of root.In multirooted tooth, axis of rotations is located at furcation area.
42C) Attaches the teeth to the bone. D) Maintains the gingival tissues in their proper relationship to the teeth.E) “Shock absorption” resists the impact of occlusal surfaces. Due to its property of shock absorption the teeth are slightly more mobile in early morning than in evening.
43Two theories have been explained for mechanism of tooth support. TENSIONAL THEORYVISCOELASTIC THEORY
44A. TENSIONAL THEORYAccording to it, principal fibers play a major role in supporting tooth and transmitting forces to bone.When forces are applied to tooth, principal fibers unfold and straighten and then transmit the forces to alveolar bone, causing elastic deformation of socket.
45A. Tooth in a resting state B A. Tooth in a resting state B. The periodontal ligament fibers are compressed in areas of pressure and stretched in area of tension.
46VISCOELASTIC THEORYAccording to it, the fluid movement largely controls the displacement of the tooth, with fibers playing a secondary role.When forces are transmitted to the tooth, the extracellular fluid is pushed from periodontal ligament into marrow spaces through the cribriform plate.After depletion of tissue fluids, the bundle fibers absorb the shock and tighten.This leads to blood vessel stenosis arterial lack pressure ballooning of vessels tissue replenishes with fluids.
472. FORMATIVE & REMODELLING FUNCTION Cells of the periodontal ligament have the capacity to control the synthesis and resorption of cementum, ligament and alveolar bone.Periodontal ligament undergoes constant remodeling, old cells and fibers are broken down and replaced by new ones.
483. NUTRITIONAL FUNCTIONBlood vessels of periodontal ligament provide nutrition to the cells of periodontium, because they contain various anabolites and other substances, which are required by cells of ligament.Compression of blood vessels (due to heavy forces applied on tooth) leads to necrosis of cells.Blood vessels also remove catabolites.
494. SENSORY FUNCTIONThe nerve bundles found in periodontal ligament, divide into single myelinated nerve, which later on lose their myelin sheath and end in one of the four types of nerve termination: 1. Free endings, carry pain sensations Ruffini like mechanoreceptors located in the apical area. 3. Meissener’s corpuscles are also mechanoreceptors located primarily in mid-root region Spindle like pressure endings, located mainly in apex.Pain sensation is transmitted by small diameter nerves, temperature by intermediate type; pressure by large myelinated fibers.
50HOMEOSTATIC MECHANISM The resorption and synthesis are controlled procedures.If there is a long term damage of periodontal ligament, which is not repaired, the bone is deposited in the periodontal space.This results in obliteration of space and ankylosis between bone and the tooth.The quality of tissue changes if balance between synthesis and resorption is disturbed.
51If there is deprivation of Vit If there is deprivation of Vit. C which are essential for collagen synthesis, resorption of collagen will continue.So there is progressive destruction and loss of extra cellular substance of ligament.This occurs more on bone side of ligament.Hence, loss of attachment between bone and tooth and at last, loss of tooth.
52CLINICAL CONSIDERATIONS The primary role of periodontal ligament is to support the tooth in the bony socket.The width of periodontal ligament varies from 0.15 to 0.38mm. The average width is: mm at 11 to 16 years of age mm at 32 to 50 years of age mm at to years of age.So, the width of periodontal ligament decreases as age advances.
53In the periodontal ligament, aging results in more number of elastic fibers and decrease in vascularity, mitotic activity, fibroplasia and in the number of collagen fibers and mucopolysaccharides.If gingivitis is not cured and supporting structure become involved, the disease is termed as periodontitis.There are few coccal cells and more motile rods and spirochetes in the diseased site than in the healthy site. The bacteria consists of gram-positive facultative rods and cocci in healthy site while in diseased site, gram-negative rods and anaerobes are more in number.
54Resorption and formation of both bone and periodontal ligament play an important role in orthodontic tooth movement. If tooth movement takes place, the compression of PDL is compensated by bone resorption whereas on tension side, apposition takes place.Periapical area of the tooth is the main pathologic site. Inflammation of the pulp reached to the apical periodontal ligament and replaces its fiber bundles with granulation tissue called as granuloma, which then progresses into apical cyst.
55Chronic periodontal disease can lead to infusion of microorganisms into the blood stream. The pressure receptors in ligament have a protective role. Apical blood vessels are protected from excessive compression by sensory apparatus of the teeth.The rate of mesial drift of tooth is related to health, dietary factor and age. It varies from 0.05 to 0.7mm per year.