 So alveolar bone part 2, in this session we will be dealing about cells and matrix component of alveolar bone. So we have basically two types of cell that is osteogenic and osteoplastic. Osteogenic as the name suggests it is creating cells and osteoclastic it is destroying cells. Osteogenic cells are osteoblasts, osteocyte, bone lining cells and bone progenitor cells. Whereas the osteoclastic basically just the osteoclasts and in matrix component we have inorganic and organic. In inorganic we have calcium hydroxy, appetite crystals. In organic we have collagen matrix and non-collagenous proteins. In non-collagenous proteins we have osteocalcin, osteopontin and bone silo protein, osteonectin, proteoglycans etc. So the commonly asked questions are osteoclast, osteoblast. So we will start with osteoblast. So during embryonic development the intram-embrane is born of the maxilla and mandible. It forms from osteoblast arising from condensing mesenchym in the facial region. So it is a most active secretory cells in bone. So it has basophilic cuboidal elongated cells which is rich in synthetic and secretory organelles such as rough endoplasmic reticulum, Golgi apparatus, granules, microtubules and it produces basically typhoon collagen and non-cancelous bond proteins like silo protein, osteopontin, osteonectin and also growth factors also it will produce which express and release alkaline phosphatase. So alkaline phosphatase is very much important in bone formation, alkaline phosphatase. So alkaline phosphatase activity has been recognized as a reliable indicator of osteoblast function and osteocytes. So I will just give you a cycle of formation. This is osteoprogenator cell which is a very primitive one, then osteoblast, later osteocyte and finally osteoclast. So these three are osteogenic cell but this is osteoclastic cell. So osteocyte is nothing but cells which is entrapped like osteoblast which is entrapped within bone are known as osteocytes. So the entrapped osteoblast, so osteoblast we learned, so the entrapped osteoblast is known as osteocyte. So if this osteoblast is entrapped within bone that is osteocyte which will be having canalic ligament and they occupy in spaces known as lacunae in bone and defined as cells surrounded by bone matrix. Now we have bone lining cells. When bone surface are neither in the formative nor in the resopty phase the surface is completely lined by a layer of flattened cell which is known as bone lining cell which is regarded as post proliferative osteoblast. So these bone lining cells are present when osteoblast and osteoclast activities are not there on the bone surface. Now the osteoprozenator cell these are actually cells which produces osteoblast. So they are fibroblasts like cells with an elongated nucleus and few organelles. Whereas osteoclast we have learned this in detail about osteoclast in our previous sessions. So osteoclast originate from hematopoietic tissue, fusion of mononuclear cells to form a multi-nucleated giant cell. This is a multi-nucleated giant cell. I have told you about this is a ruffled border and there will be a clear zone. So it is very large it can have 5 to 50 nuclei which is active on less than one percentage of bone surface. It lie in house ships lacunae, acedophilic cytoplasm and there will be ruffled border. So there will be ruffled border phasing the bone because hydrolytic enzymes are secreted and it has increased surface area. So wherever this resorption happens the border will be in this shape ruffled border and multi-nucleated giant cell will be there and there will be a clear zone apart from it. So that is osteoclast. This is a commonly as short note. Osteoclast and osteoblast can be osteocyte and osteoprogenator cell also can be a short note. So osteoclast are the periphery of ruffled border. The plasma membrane is more than closely opposed to bone surface and the adjacent cytoplasm is devoid of cell organelles which is rich in actin and talin proteins associated with cell adhesion. This region is known as clear zone. So this is a ruffled border and this is a clear zone. So clear zone is the adjacent cytoplasm which is not having any cell organelles. So this clear zone creates an isolated microenvironment in which resorption can take place. So clear zone is also important. So severe osteoclast excavating a large area of bone which is the leading edge of resorption is termed as cutting con and released cytokines stimulate stem cells to differentiate into osteoblast. So these osteoblasts secrete osteoid which is known as filling con. So cutting con and filling con are the cutting con wherever this resorption happens is cutting con and when the deposition happens that is filling con. So always bone formation is a continuous process resorption and deposition will occur in a bone. That's how it is remodeled throughout the life. So cutting con is a osteoclastic activity creating a edge which is resorbed and the other side when cytokines are released and there will be osteoid deposition which is known as filling con. So cutting con and filling con. So cutting con there will be osteoclast activity and filling con there will be osteoblast activity. So that's about osteoclast and osteoblast. So two more things we need to learn is reversal line and resting line. So these are important what is reversal line and what is resting line. So this all can be asked as short note. So reversal line or also known as cementing line. So reversal line or cementing line which is a site of change from bone resorption to bone deposition is represented by a scalloped outline which is rich in silo protein and osteopontane. So reversal line you can say it is corresponding with filling con where the osteoblast are deposit the new bone or steoid. So this is known as reversal line or cementing line that is the site of change from bone resorption to bone deposition. So before it was bone resorbed area so new bones will be added. So bone resorbed area will be like this ruffled border. So when there is bone deposition it will be shallow instead of ruffled border. So that is known as reversal line or cementing line. So the change of bone resorption to bone deposition. Now what is resting line. Resting line is rhythmic deposition of bone with periods of relative inactivity seen as parallel vertical lines. So there will be parallel vertical lines in bones when we take ground section of bone we can see parallel vertical lines. So there will be rhythmic deposition of bone it will be added layer by layer. But in between there will be a relative inactive phase which is seen as vertical parallel line that is known as resting line and reversal line is when deposition and resorption. Deposition happens previously resorbed area gives a scalloped area which is known as reversal or cementing line. So we have few age changes in bone just like any heart tissue we have seen that in cement the age changes and also we have seen in PDL also. So any tissue any living tissue will go through the age changes. So in bones it is similar to like what is occurring in skeletal system there will be osteoporosis with aging there will be decreased vascularity reduction and metabolic rate and healing capacity. So bone resorption may be increased and more irregular periodontal surface will be seen. And few variations in normal bone are fenestration, dacens, exostosis, buttressing bone formation or it is also known as slipping. So fenestration and dacens are removal of bone that is facial surface more involved fenestration is isolated loss of bone and dacens is a complete loss of facial bone. So this anterior tooth are more involved and frequently bilateral sometimes due to malposition and root prominence or labelled protrusion. So etiology could be excessive occlusion force. So this fenestration and dacens could be a short note. So next thing is exostosis, exostosis are outgrowth of bone of varied size and shape they can occur as small nodules, large nodules maybe sharp ridge or spike leg projection or any combination of the above. There is nodule small or large ridges or spike leg projections and buttressing bone formation or lipping is nothing but sometimes what happens is bone formation occurs in an attempt to buttress bony trabeculae which is weakened by resorption. So when it occurs within the jaw which is termed as central buttressing bone formation and when it is on the external surface which is known as peripheral buttressing bone formation. So this peripheral buttressing bone formation will cause bulging of the bone contour which is known as lipping. So that is attempt to buttress a bony trabeculae which is weakened by resorption. So that is bone buttressing. So that is all about normal variations and we have bone deformities horizontal and vertical. So vertical will be an angular bone loss horizontal will be evenly distributed misiodistral direction. So we are not going much into those things. So idea was to give a proper introduction about alveolar bone, the types of alveolar bone, its formation, its composition and little bit about its variation, bone deformities and age changes. So we finished our paradigm that is djunjeva, paradigm ligament, the soft tissues and cementum and alveolar bone are the heart tissues. So paradigm is nothing but which supports and surrounds the tooth. So djunjeva, paradigm ligament, cementum, alveolar bone are supporting structures of tooth. So we have many more topics coming up. We have to finish in amal, dentine and pulp. So I will come up with these topics in my next sessions. Thank you.