 hello everyone welcome back to another session in dentistry and more today's topic is periodontal ligament. periodontal ligament is one of the four component of periodontium. so periodontium is a structure which supports the tooth so it includes two hard tissues and two soft tissues. hard tissues are cementum and alveolar board. soft tissues are ginjeva and periodontal ligament. ginjeva we are already covered. so today's session is about periodontal ligament. so let's get into the details of periodontal ligament. so periodontal ligament the name itself gives an idea. peri means around and don't means tooth. so the structures which is around the tooth. so the ligament which is surrounding the tooth is periodontal ligament. so as I mentioned it is one of the four components of periodontium. so it is defined as the periodontal ligament is a connective tissue that surrounds the root and connects it to the bone. okay so this orange color is periodontal ligament. so it is a connective tissue that surrounds the root and connects it to bone. so it starts from root to the bone and it communicates with the marrow spaces through vascular channels in the bone. so it is something or it is a connective tissue which surrounds the root and connects it to the bone. it is given by carenza and it has got many names. the synonyms include periodontal membrane, alveolar dental ligament, desmodont, peri-symen, gum forces or dental periosteum. so this is a very important essay in dental histology. so this is a very frequently asked essay and there are lots of short notes will be asked from this chapter. so you might get a question like explain about gum forces and write about its principal fibers or draw a neat picture and explain about its structure function. so you might be knowing the complete answer of periodontal ligament but you might not be knowing that gum forces is periodontal ligament. so always make sure that you remember all these names such as periodontal membrane, alveolar dental ligament because it connects alveolar bone and tooth, desmodont, peri-symen because it covers the symptom, gum forces and dental periosteum. so these are the synonyms of periodontal ligament. now let's see the extension of periodontal membrane. so this is the periodontal membrane I have drawn in orange color lines. so it extends from coronal direction it is continuous with lamina property of gingiva. so you will be knowing what is lamina property of gingiva because in the gingiva session we had well covered the connective tissue part of gingiva. so this is the this pink color is the connective tissue part of gingiva. so it is continues with or it is associated with lamina property of gingiva at the coronal side. so this is the crown part this is a road part. so we say this is the coronal side this is a apical side okay. so on coronal side it is continuous with lamina property and it is demarcated by the alveolar crest fiber. so here it is alveolar crest fiber because this is a bone. this is a tip of the bone on us alveolar crest. so such fibers are demarcating this coronal extension of periodontal ligament and at the root apex it merges with the dental pulp okay. so at the root apex see this is the root apex and this pink color is a pulp. so at the root apex it merges with the dental pulp and it ranges in width from 0.15 to 0.38 mm. so 0.15 to 0.38 mm is the width of periodontal ligament. this is the width 0.15 to 0.38. so next is the shape of periodontal ligament. so it is thinnest around the middle third of the root okay. so this is a root portion. so this is middle portion it is thinnest around the middle portion or middle third of the root with an R-glass appearance. this is an R-glass appearance. it is broadened at the coronal and apical side but it is thinnest at the middle third of root okay. so this is a coronal third. this is the middle third. this is apical third. so it is thinnest at the middle third. so it looks like an R-glass with widened coronal and apical third. and we have a radio opaque boundaries of periodontal ligament. so when we take a x-ray so we can see an empty space. so periodontal ligament will be shown in x-ray as radio loosened area that means it is completely black. so there is no structure within it. so the x-ray will not produce any image. so it will be very black in color which is known as radio loosened. but it has two white borders which is known as radio opaque borders. so what are those white borders? one is alveolar bone and other one is a cementum. so it is outlined by alveolar bone and cementum. so in radiograph it looks like a radio loosened area with radio opaque boundaries. so it is between cementum. this is cementum and alveolar bone. so these are the mineralized structures. so it will appear as radio opaque or white areas. so it appears as black area between two white lines that is radio loosened area between radio opaque lines. so the average width changes based on the age around 10 to 15 years. it is around 0.21 mm and 30 to 50 30 to 50.21 mm in 10 to 15 years and 0.18 mm around 30 to 50 years and it is around 0.15. so as the age increases the width of this perirondal ligament decreases and also it changes according to time of eruption at function or hyper function. time of eruption it is around 0.1 to 0.5. it is very highest. at function it is around 0.2 to 0.3. this one 0.15 to 0.3. but hyper function it again reduces. now let's move on to the development of perirondal ligament. so how does it develop? so we have seen a develops from dental follicles. hope you remember our bell stage advanced bell stage of tooth formation. we have what stage gap stage bell stage. we have learned dentine and pulp develops from dental papilla and cementum perirondal ligament alveolar bone develops from dental follicle or dental sac. so it is developed from dental follicle. so what happens? it begins with root formation and prior to the tooth eruption. so at later bell stage when amelogenesis and dentino genesis are well advanced the internal and external lamina. so we know that the internal and external lamina when the stratum intermedium collapses the outer enamel epithelium and inner enamel epithelium approximates and it becomes two layer cells two layer epithelium with outer enamel and inner enamel epithelium. so it forms or it the cervical loop of enamel organ it becomes bent and makes this double layered epithelial root sheath and this root sheath which proliferates epically and forms a future root and forms a future root. okay so this is how it forms outer enamel epithelium inner enamel epithelium it bends at root portion or the cervical portion and it proliferates epically. so you know what is epically towards the root epically and forms a future root. so what happens? there will be hard wicks epithelial root sheath at advance bell stage which covers the root area. so this root sheath is continuous so this root sheath is continuous so it loses its structural integrity and forms the remnants which is known as epithelial rest of molasses. so epithelial rest of molasses forms. so once epithelial rest of molasses forms what happens there will be connective tissue. so there will be the connective tissue. okay this is all let it be connective tissue of dandelion follicle. so from dandelion follicle the connective tissue cells from dandelion follicle migrate to the newly formed root of dentine. so it will be like this. so the remnants gives the entrance gives the pathway of proliferation towards the root dentine. okay before it was a hard wicks epithelial root sheath. this is hard wicks epithelial root sheath. it was a continuous layer after that it loses its structural integrity. so the dandelion follicle which is present outside continuous proliferation happens and it goes between the epithelial rest of molasses and forms a peridontal ligament. so that is how it forms and dandelion follicle cell basically produces fibroblast cementoblast and osteoblast. this is collagen, this is cementum and this is bone. okay collagen is a principal fiber of peridontal ligament. so ultimately dandelion follicle give rise to peridontal ligament, cementum and alveolar bone. so asteroid formation continues cells in the peri follicle animation give rise to there will be active synthesis of collagen fibers and this collagen fibers assemble and it forms as a bundle on the bone and cemental surface. okay so it becomes bundles. so from the dental follicle there will be active synthesis and this fibers will be formed and it will be attached to cementum and bone. so this is how it happens this is alveolar bone proper this is a peridontal ligament space and this is a root cementum. so as the growth happens this is a root cemental area this is the alveolar bone area there will be a continuous proliferation mitosis happens and ultimately it joins and it become peridontal ligament. so we have a mature peridontal ligament three areas that is bone, bone related region, bone related region and the middle region and the cementum related region. the bone related region is basically very rich in cells and the middle zone is fewer cells with thinner collagen fibers and the cemental related region which is then some ordered collagen fibers are present. so bone related region associated with alveolar bone proper middle region it is thinner and thick bundles of fibers are seen in cemental region because this is a tooth area this is a bone area see this is a tooth this is a bone so this is the picture i have showing here just the opposite here it is a cementum is a alveolar bone but here it is alveolar bone here is a cementum so this is just expanded picture is okay if i draw this picture it will be like this so this is how it forms this is the enlarged this is enlarged version of this area but only thing you need to think opposite this is alveolar bone this is root but here it is a root this is the alveolar bone okay so that is how it forms you can see the various formation when the tooth erupts where this is covered within the ginger so there is little bit of periodontal ligament formation as the tooth erupts there will be more and more periodontal ligament formation when it is completely replete the bundles will be formed and principal fibers will be completely around the root so what are the functional changes happens in periodontal ligament so the basically periodontal ligament is always subjected to change when there is increased functional limit the width may increase as much 50 percentage of the present width because more function more functional limit more stress it need to bear so it will increase its width 50 up to 50 percentage it can increase and fiber bundles also increase in thickness when there is a increased functional demand well when functional demand decreases the narrowing of periodontal ligament and decrease in number and thickness of fibers happens so it can modify itself based on the functional changes so that's the beginning part of periodontal ligament i've explained to you about its extension its shape and the in detail about the development so you need to study properly about the tooth formation that is butt stage cap stage and bell stage then only it is easy to understand if you don't know that chapter properly it's very difficult because you need to know what is hudwig's epithelial rest of hudwig epithelial root sheath and epithelial rest of molasses and how this collagen fibers starting from dental follicle to the cement demand bond so it is a very important chapter because this is commonly asked essay question so the short notes might be hudwig's epithelial root sheath epithelial cell rest of molasses so all these might come as short notes so next thing is the structural elements that is cells and extracellular elements so this is the introduction part development extension shapes and how the periodontal ligament changed according to the functional demands now we move on to the structure the cells and extracellular elements of periodontal ligament thank you