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Bone physiologynew /certified fixed orthodontic courses by Indian dental academy


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Bone physiologynew /certified fixed orthodontic courses by Indian dental academy

  1. 1. Bone Physiology INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. Contents • Introduction • Functions of bone • Structure of bone • Gross bone histology • Bone cells • Bone development • Nerve and blood supply of bone • Bone modeling and remodeling • Applied Clinical Aspect • Conclusion • References
  3. 3. INTRODUCTION: Bone is a specialized mineralized connective tissue consisting by weight of 33% organic matrix, 28% type I collagen, and 5% noncollagenous osteocalcin, bone proteins,including morphogenetic osteonectin, proteins, bone proteoglycan, and bone sialoprotein. This organic matrix is permeated by hydroxyapatite (CalO(P04)6(OH), which makes up the remaining 67% of bone.
  4. 4. Bone 67% Inorganic Hydroxyapatite 33% Organic 28% 5% Collagen Osteocalcin Sialoprotein Phosphoprotein Osteonectin Bone specific protein
  5. 5. Bone is extremely important to the dental practitioner, insofar as all his treatment procedures can be successful only if' the bony support remains intact. The success of orthodontic treatment is particularly dependent on the degree of stability that the underlying bone can maintain. Furthermore, there is a direct relation between the force required to move the teeth and the thickness of alveolar bone
  6. 6. FUNCTIONS OF BONE : 1. Support. The skeleton serves as the structural framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles. 2. Protection. The skeleton protects many internal organs from injury. For example, cranial bones protect the brain. 3. Assistance in movement. Because skeletal muscles attach to bones, when muscles contract, they pull on bones. Together, bones and muscles produce movement. 4. Mineral homeostasis. Bone tissue stores several minerals, especially calcium and phosphorus. On demand, bone releases minerals into the blood to maintain critical mineral balances (homeostasis) and to distribute the minerals to other parts of the body.
  7. 7. 5. Blood cell production. Within certain bones, a connective tissue called red bone marrow produces red blood cells, white blood cells, and platelets, a process called hemopoiesis. Red bone marrow consists of developing blood cells, adipocytes, fibroblasts, and macrophages within a network of reticular fibers. 6. Triglyceride storage. Triglycerides stored in the adipose cells of yellow bone marrow are an important chemical energy reserve. Yellow bone marrow consists mainly of adipose cells, which store Triglycerides, and a few blood cells. In the newborn, all bone marrow is red and is involved in hemopoiesis. With increasing age, much of the bone marrow changes from red to yellow.
  8. 8. STRUCTURE OF BONE: The structure of a bone may be analyzed by considering the parts of a long bone. A long bone is one that has greater lenght than width. A typical long bone consists of the following parts. 1. The diaphysis (= growing between) is bone's shaft or body-the long, cylindrical, main portion of bone. 2. The epiphyses (= growing over) are the distal and proximal ends of the bone.
  10. 10. 3. The metaphyses (sin is metaphysis) are the regions in a mature bone where the diaphysis joins the epiphyses. In a growing bone, each metaphysis includes an epiphyseal plate a layer of hyaline cartilage that allows the diaphysis of the bone to grow. 4. The articular cartilage is a thin layer of hyaline cartilage covering the epiphysis where the bone forms an articulating joint with another bone. Articular cartilage reduces friction, absorbs shock at freely movable joints. Because articular cartilage lacks a perichondrium, repair of damage is limited.
  11. 11. 5. The periosteum :(peri- = around) tough sheath of dense irregular connective tissue that sum the bone surface wherever it is not covered by articular cartilage. The periosteum contains bone-forming cells that enable growth in diameter or thickness, but not in length. It also assists in fracture repair, helps nourish bone tissue, serves as an attachment point for ligaments and tendons. 6. The medullary cavity (medulla- = marrow, pith) or marrow cavity is the space within the diaphysis that contains fatty yellow bone marrow in adults. 7. The endosteum (endo- = within) is a thin membrane that lines the medullary cavity. It contains a single layer of bone-forming cells and a small amount of connective tissue.
  12. 12. Classification of bone
  13. 13. 1. Macroscopic appearance of cut surfaces Compact bone - the ivory surface layers of mature bone. Trabecular bone---the interior of mature bones (also termed cancellous or spongy bone). 2. Developmental origin Intramembranous (mesenchymal or dermal bone)formed by direct transformation of condensed mesenchyme. Intracartilaginous (cartilage or Endochondral bone)replacing a;preformed cartilage model. 3. Regions of long bones Diaphysis-intermediate region or shaft. Metaphysis---developing,juxta.epiphyseal regions of shaft. Epiphysis-extremity with a separate center of ossification.
  14. 14. 4. Organization of collagen fibers Woven bone (coarse-bundled bone), with an irregular collagen network-includes embryonic bone, isolated patches in adult bone, and repair tissue in fractures. Parallel-fibred bone-includes all forms of lamellar bone 5. General microstructure Non-lamellar bone-includes early woven bone and primary osteons. Lamellar bone-almost all mature bone. 6. Disposition of lamellae Circurnferentia/lamellae (primary lamellae): parallel to both periosteal and endosteal surfaces.
  15. 15. Osteonic lamellae (secondary lamellae) concentric lamellae around vascular canals of mature bone. Interstitial lamellae between osteons. 7. Types of osteon (Haversian system) Primary osteons-first formed, lamellar or non-lamellar osteons. Secondary osteons- concentric lamellae around vascular canals of mature bone. 8. General terms Surface bone-usually circumferential lamellae but may include woven and bundle (Sharpey or extrinsic fiber) bone. Interstitial bone-between osteons; often lamellar remnants of secondary osteons but may include woven or primary osteon fragments.
  16. 16. GROSS HISTOLOGY OF BONE: Bones have been classified as long or flat on the basis of their gross appearance. Long bones include the bones of the axial skeleton (e.g., tibia, femur, radius, ulna, and humerus). Flat bones include all the skull bones plus the sternum, scapula, and pelvis. Characteristic of all bones are a dense outer sheet of compact bone and a central medullary cavity. In living bone the cavity is filled with either red or yellow bone marrow.
  17. 17. Bone is not completely solid but has many small spaces between its cells and matrix components. Some spaces are channels for blood vessels that supply bone cells with nutrients. Other spaces are storage areas for red bone marrow. Depending on the size and distribution of the spaces, the regions of a bone may be categorized as compact or spongy Overall, about 80% of the skeleton is compact bone and 20% is spongy bone.
  18. 18. COMPACT BONE TISSUE: Compact bone tissue contains few spaces. It forms the external layer of all bones and makes up the bulk of the diaphysis of long bones. Compact bone tissue provides protection and support and resists the stresses produced by weight and movement. Compact bone tissue is arranged in units called osteons or Haversian systems Blood vessels, lymphatic vessels , and nerves from the periosteum penetrate the compact bone through transverse perforating (Volkmann's) canals. The vessels and nerves of the perforating canals connect with those of the medullary cavity, periosteum, and central (Haversian) canals.
  19. 19.
  20. 20. The central canals run longitudinally through the bone. Around the canals are concentric lamellae (rings of hard, calcified matrix). Between the lamellae are small spaces called lacunae (= little lakes;), which contain osteocytes. Radiating in all directions from the lacunae are tiny canaliculi (= small channels), which are filled with extra cellular fluid. Inside the canaliculi are slender fingerlike processes of osteocytes Neighboring osteocytes communicate via gap junctions. The canaliculi connect lacunae with one another and with the central canals.
  21. 21. Osteons in compact bone tissue are aligned in the same direction along lines of stress. In the shaft, for example, they are parallel to the long axis of the bone. As a result, the shaft of a long bone resists bending or fracturing even when considerable force is applied from either end. Compact bone tissue tends to be thickest in those parts of a bone where stresses are applied in relatively few directions. The lines of stress in a bone are not static. They change as a person learns to walk and in response to repeated strenuous physical activity, such as occurs when a person undertakes weight training. The lines of stress in a bone also can change because of fractures or physical deformity.
  22. 22. The areas between osteons contain interstitial lamellae, which also have lacunae with osteocytes and canaliculi. Interstitial lamellae are fragments of older osteons that have been partially destroyed during bone rebuilding or growth. Lamellae that encircle the bone just beneath the periosteum are called outer circumferential lamellae; those that encircle the medullary cavity are called inner circumferential lamellae.
  23. 23. SPONGY BONE TISSUE: In contrast to compact bone tissue, spongy bone tissue does not contain osteons. it consists of trabeculae an irregular latticework of thin columns of bone. The macroscopic spaces between the trabeculae of some bones are filled with red bone marrow. Within each trabecula are osteocytes that lie in lacunae. Radiating from the lacunae are canaliculi. Because osteocytes are located on the superficial surfaces of trabeculae, they receive nourishment directly from the blood circulating through the medullary cavities.
  24. 24.
  25. 25. Spongy bone tissue makes up most of the bone tissue of short, flat, and irregularly shaped bones. It also forms most of the epiphyses of long bones and a narrow rim around the medullary cavity of the diaphysis of long bones. At first glance, the structure of the osteons of compact bone tissue may appear to be highly organized, whereas the trabeculae of spongy bone tissue may appear to be far less well organized. However, the trabeculae in spongy bone tissue are precisely oriented along lines of stress, a characteristic that helps bones resist stresses and transfer force without breaking. Spongy bone tissue tends to be located where bones are not heavily stressed or where stresses are applied from many directions.
  26. 26. Spongy bone tissue is different from compact bone tissue in two respects. First, spongy bone tissue is light, which reduces the overall weight of a bone so that it moves more readily when pulled by a skeletal muscle. Second, the trabeculae of spongy bone tissue support and protect the red bone marrow. The spongy bone tissue in the hip bones, ribs, breastbone, back­bones, and the ends of long bones is the only site of red bone marrow and, thus, of hemopoiesis in adults.
  27. 27. BONE CELLS: In bone, separate cells are primarily responsible for the formation resorption,and maintenance of osteoarchitecture. 1. Osteogenic cells: Are un specialized stem cells derived from mesenchyme, the tissue from which all connective tissues are formed. They are the only bone cells to undergo cell division; the resulting daughter cells develop into osteoblasts. Osteogenic cells are found along the inner portion of the periosteum, in the endosteum, and in the canals within bone that contain blood vessels.
  28. 28. Osteoblast: Osteoblasts are uninucleated cells that synthesize both cartilaginous and noncollagenous bone proteins (the organic matrix, osteoid). They are responsible for mineralization and are derived from a multipotent mesenchymal cell. The osteoblast is generally considered to differentiate through a precursor cell, the preosteoblast. Preosteoblasts and, to a lesser extent, osteoblasts exhibit high levels of alkaline phosphatase on the outer surface of their plasma membranes. This enzyme, which is used experimentally as a cytochemical marker, distinguishes the osteoblast from the fibroblast. Functionally it is believed to cleave organically bound phosphate. The liberated phosphate likely contributes to the initiation and progressive growth bone mineral crystals.
  29. 29. osteoblast
  30. 30. Osteoblasts secrete, in addition to type I and type V collagen and small amounts of several noncollagenous proteins (some of which [the phosphoproteins] are critical to bone mineralization, a variety of cytokines). These autocrine or paracrine factors, which include growth factors, help regulate cell metabolism. A key factor in the rate of bone cell development is the elaboration by osteoblasts, their precursors, or both of a number of growth factors. Osteoblasts secrete several members of the bone morphogenetic protein (BMP) super family, including BMP2, BMP7, and transforming growth factor, in addition to the insulin­like growth factors (lGF­I and IGF­II), platelet­derived growth factor (pDGF­AA), and fibroblastic growth factor beta.
  31. 31. Under physiologic conditions that support resorption rather than formation, osteoblasts can be stimulated by lymphokines (e.g., interleukin 1, tumor necrosis factor alpha) and by prostaglandins (E2) to produce interleukin 6. Osteoblasts under the stimulation of interleukin 6 also produce their own hydrolytic enzymes that aid in destroying or modifying the unmineralized matrix or pericellular coating, thus freeing the osteoblast from its own secreted matrix. This dissociation may be critical during the initial phases of bone turnover and repair, when osteoblasts must be able to migrate and proliferate.
  32. 32. The osteoblast and the lining cell support resorption through hydrolytic enzyme and interleukin6 production. Osteoprogenitor cells, preosteoblasts, and osteoblasts can undergo mitosis. Osteoblasts produce large amounts of type I collagen and small amounts of proteoglycans and glycoproteins. The osteoblast modifies the adjacent matrix by removal or modification of the proteoglycans or glycoproteins. The osteoblast initiates the mineralization of the matrix by secretion of several promoters or regulators of mineralization (primarily phosphoproteins) and by providing additional inorganic phosphate by the action of membrane bound alkaline phosphatase.
  33. 33. Osteocyte As osteoblasts secrete bone matrix, some of them become entrapped in lacunae and are then called osteocytes. The number of osteoblasts that become osteocytes varies depending on the rapidity of bone formation: The more rapid the formation, the more osteocytes are present per unit volume. After their formation, osteocytes gradually loose most of their matrix­synthesizing machinery and become reduced in size. The space in the matrix occupied by an Osteocyte is called the osteocytic lacuna. Narrow extensions of these lacunae form enclosed channels, or canaliculi, that house radiating osteocytic processes.
  34. 34. Thus osteocytes maintain contact with adjacent osteocytes and with the osteoblasts or lining cells on the bone surfaces ,the endosteum, periosteum, and Haversian canals. Failure of any part of this interconnecting system results in hyper­mineralization (sclerosis) and death of the bone. This non­vital bone is resorbed and replaced during the process of bone turnover The functions attributed to osteocytes are that (a) They probably maintain the integrity of the lacunae and canaliculi, and thus keep open the channels for diffusion of nutrition through bone (b) They play a role in removal or deposition of matrix and of calcium when required.
  35. 35. Osteoclast: Osteoclasts are multinucleated non­dividing cells that move around on bone surfaces, resorbing bone matrix from sites where it is either deteriorating or not needed. Compared to all other bone cells and their precursors, the multinucleated osteoclast is a much larger cell. Because of their size, osteoclasts can easily be identified under the light microscope; they are generally seen in a cluster rather than singly. The osteoclast is characterized cytochemically by possessing tartrate­resistant acid phosphatase enzyme within its cytoplasmic vesicles and vacuoles which distinguishes it from other giant cells and macrophages.
  36. 36. osteoclast
  37. 37. Typically osteoclasts are found against the bone surface, occupying shallow, hollowed-out depressions, called Howship’s lacunae that they themselves have created. At the sites of bone resorption the surface of an osteoclast shows many folds, which are described as a ruffled membrane. Removal of bone by osteoclasts involves demineralisation & removal of matrix. Bone removal can be stimulated by factors secreted by osteoblasts, by macrophages, or by lymphocytes. It is also stimulated by the parathyroid hormone. It is not certain whether osteoclasts are formed by fusion of several monocytes or by repeated division of the nucleus, without division of cytoplasm.
  38. 38. DEVELOPMENT OF BONE: The process by which bone forms is called ossification or osteogenesis. The "skeleton" of a human embryo is composed of loose fibrous connective tissue membranes and pieces of hyaline cartilage, which are shaped like bones and are the sites where ossification occurs. These embryonic tissues provide the template for subsequent ossification, which begins during the sixth or seventh week of embryonic development and follows one of two patterns. The two methods of bone formation involve 1. Intramembranous ossification 2. Endochondral ossification
  39. 39. Endochondral Bone Formation: Endochondral bone formation takes place when cartilage is replaced by bone. It occurs at the ends of all long bones, vertebrae, and ribs and at the head of the mandible and base of the skull. Early in embryonic development, there is condensation of mesenchymal cells. Cartilage cells differentiate from these mesenchymal cells, and a perichondrium forms around the periphery. Rapid growth of the cartilage anlage ensues-by interstitial growth within the core of the engage and by appositional growth through cell proliferation and matrix secretion within the expanding perichondrium.
  40. 40. As differentiation of cartilage cells proceeds toward the metaphysis, the cells organize themselves roughly into longitudinal columns. The longitudinal columns of cells can be subdivided into three functionally different zones: - the zone of proliferation, - the zone of hypertrophy and maturation, and - the zone of provisional mineralization. - In the zone of proliferation, the cells (which are small and somewhat flattened) primarily constitute a source of new cells. The zone of hypertrophy and maturation is the broadest zone
  41. 41. In the early stages of hypertrophy, the chondroblasts secrete mainly type II collagen that forms the primary structural component of the longitudinal matrix septa. As hypertrophy proceeds, mostly proteoglycans are secreted. As the chondroblast reaches maximum size, it secretes type X collagen, chondrocalcin, and bone sialoprotein, which together with partial proteoglycans breakdown; create a matrix environment with the potential to mineralise.
  42. 42.
  43. 43. Endochondral Ossification : The essential steps in the formation of bone by endochondral ossification are:    At the site where the bone is to be formed, the mesenchymal cells become closely packed to form a mesenchymal condensation. Some mesenchymal cells become chondroblasts and lay down hyaline cartilage. The intercellular substances between the enlarged cartilage cells become calcified under the influence of alkaline phosphatase, which is secreted by the cartilage cells. The nutrition to the cells is thus cut off and they die, leaving behind empty spaces called areolae.
  44. 44.     Some blood vessels of the perichondrium now invade the cartilaginous matrix. They are accompanied by osteoprogenitor cells. This mass of vessels and cells is called the periosteal bud. It eats away much of the calcified matrix forming the walls of the primary areolae, and thus creates large cavities called secondary areolae, also called medullary spaces. The walls of secondary areolae are formed by thin layers of calcified matrix that have not been dissolved. The osteoprogenitor cells become osteoblasts and arrange themselves along the surfaces of these bars, or plates, of calcified matrix. These osteoblasts now lay down a layer of ossein fibrils embedded in a gelatinous ground substance, exactly as in the intramembranous ossification. This osteoid is calcified and a lamellus of bone is formed.
  45. 45.  Osteoblasts now lay down another layer of the first lamellus. This is also calcified. Thus two lamellae of the bone are formed. Some osteoblasts that get caught between the two lamellae become osteocytes .  As more lamellae are laid down bony trabeculae are formed. It may be noted that the process of bone formation in endochondral ossification is exactly the same as in intramembranous ossification.  In this way formation of new cartilage keeps the pace with the loss due to replacement by bone. The total effect is that the ossifying cartilage progressively increases in size.
  46. 46. Intramembranous Bone Formation: Intramembranous bone formation occurs directly within the mesenchyme. Bone develops directly within the soft connective tissue rather than on a cartilaginous model. As vascularity increases at these sites of condensed mesenchyme, osteoblasts differentiate and begin to produce bone matrix de novo. This occurs at multiple sites within each bone of the cranial vault, maxilla, body of the mandible and mid-shaft of long bones. Once begun, intramembranous bone formation proceeds at an extremely rapid rate. This first embryonic bone is termed coarse-fibred woven bone and at first, the woven bone takes the form of radiating spicules, but progressively the spicules fuse into thin bony plates.
  47. 47. Intramembranous ossification: The various stages in intramembranous ossification are as follows.  At the site where the membrane bone is to be formed, the mesenchymal cells become densely packed (a mesenchymal condensation is formed.)  The region becomes highly vascular.  Some of the mesenchymal cells lay down bundles of collagen fibres in the mesenchymal condensation. In this way a membrane is formed. Some mesenchymal cells (possibly those that had earlier laid down the collagen fibres) enlarge and acquire a basophilic cytoplasm, and may now be called osteoblasts.
  48. 48.   Under the influence of osteoblasts, calcium salts are deposited in osteoid. As soon as this happens the layer of osteoid can be said to have become one lamellus of bone. Over this lamellus, another layer of osteoid is laid down by osteoblasts. The osteoblasts move away from the lamellus to line the new layer of osteoid. However, some of them get caught between the lamellus and the osteoid. The osteoid is now ossified to form another lamellus. The cells trapped between the two lamellae become osteocytes.
  49. 49.
  50. 50. Blood and nerve supply of bone: Bone is richly supplied with blood. Blood vessels, which are especially abundant in portions of bone containing red bone marrow, pass into bones from the periosteum. Periosteal arteries accompanied by nerves enter the diaphysis through many perforating (Volkmann's) canals and supply the periosteum and outer part of the compact bone Near the center of the diaphysis, a large nutrient artery passes through a hole in the compact bone called the nutrient foramen. On entering the medullary cavity, the nutrient artery divides into proximal and distal branches that supply both the inner part of compact bone tissue of the diaphysis and the spongy bone tissue and red marrow as far as the epiphyseal plates (or lines).
  51. 51.
  52. 52. Veins that carry blood away from long bones are evident in three places: (1) One or two nutrient veins accompany the nutrient artery in the diaphysis; (2) Numerous epiphyseal veins and metaphyseal veins exit with their respective arteries in the epiphyses; and (3) Many small periosteal veins exit with their respective arteries in the periosteum. Nerves accompany the blood vessels that supply bones. The periosteum is rich in sensory nerves, some of which carry pain sensations. These nerves are especially sensitive to tearing or tension, which explains the severe pain resulting from a fracture or a bone tumor.
  53. 53. Modeling and remodeling Both trabecular and cortical bones grow, adapt and turnover by means two mechanisms In bone modeling:-independent sites of resorption and formation change the form of a bone In remodeling:- a specific, coupled sequence of resorption and formation occurs to replace previously existed bone the biomechanical response to tooth movement involves an integrated array of bone modeling and remodeling. Bone modeling is the dominant process of facial growth and adaptation to applied loads such as head gear,RME and functional appliances Modeling changes can be seen on cephalometric tracing but remodeling changes are only apparent at the microscopic levels
  54. 54. Both modeling and remodeling are controlled by an interaction of metabolic and mechanical signals  Bone modeling is directly under the integrated biomechanical control of functional applied loads and under harmonal influence particularly during periods of growth and aging.  Remodeling response to metabolic mediators such as PTH and estrogen is by varying the rate of bone turnover.  Bone scans with 99te biphosphate [bone marker] indicated that the alveolar processes, but not the basilar mandible, have a high remodeling rate.
  55. 55. Control factors for bone modeling  Mechanical:( peak load in micro strain) disuse atrophy : less than 200 %deformation 10-4 bone maintenance: 200-2500 physiologic hypertrophy:2500-4000 pathologic overload:above 4000  Endocrine :bone metabolic harmones :PTH, Vit.D, calcitonin growth harmones : somatotropin, IGF I & II sex steroids : testosterone & estrogen
  56. 56. Control factors for bone remodeling  Mechanical :Less than 1000 % deformation 10-4 : more bone remodeling More than 2000 % deformation 10-4 : less bone remodeling  Metabolic :PTH : increased activation frequency estrogen : decreased activation frequency
  57. 57.      Effect of hormones: During childhood the most important hormone that stimulates bone growth are the insulin like growth factor which is produced by bone tissue it is inturn stimulated by human growth hormone. At puberty the hormones known as sex steroids i.e estrogen and androgens secreted by the adrenal glands. They are responsible for the sudden growth spurt that occurs during the teenage years.
  58. 58. Parathyroid Hormone has a direct action on adult bone. It is responsible for maintenance of blood calcium level (10 to 12 mg%). It has four main sites of action 1.Kidney: Tubular reabsorption of calcium from the glomerular filtrate and decrease in resorption of phosphate. 2.Bone: Stimulates osteoclastic activity and increases resorption of bone leading to increased liberation of calcium and phosphate. 3.Intestine: It increases absorption of calcium from diet. 4.Lactating Mammary Glands: It acts to decrease calcium secretion.
  59. 59. The removal of osseous tissue during progressive tooth movement is directly related to 1) bone porosity 2) remodeling rate 3) resorption rate 4) osteoclast recruitment The osteoclast resorption rate is largely controlled by metabolic factors mainly the PARATHYRIOD HARMONE
  60. 60.      Effect of Vitamins on bone: Growth and maintenance of bone depends on adequate dietary intake of minerals and vitamins. Vitamin D: Hypervitaminosis: small overdose – Aberrant calcification in vessels in kidney may take place. Overdose in Excess – Generalized resorption changes may be seen. Hypovitaminosis: In avitaminosis the ingestion of large quantities of calcium will lead to formation of calcium phosphate in intestine.
  61. 61. Tuomo Kantomaa and Brian K. Hall in 1991 studied the importance of cAMP and Ca++ in mandibular condylar growth and adaptation and concluded that calcium is necessary for maturation of cell . Both calcium and cAMP play a major role in bone formation .
  62. 62. Vitamin A: Hypervitaminosis: Acute violent headaches, vomiting, irritability, and, occasionally, peeling of the skin. Chronic loss of appetite, itching, and painful swellings over the limbs, hyper-ostosis of the shafts of long bones. Hypovitaminosis: Affects: primarily the epithelial structures. In general, it is believed that over-all bone growth is retarded and that in the later stages of the disease, endochondral bone growth ceases entirely. Vitamin C: Hypovitaminosis: The pathologic findings in bone can be traced to the failure of collagen production. A decreased activity of fibro-blasts, osteoblasts, and odontoblasts, which ultimately affects collagen production
  63. 63. Methods used to study bones 1. Mineralized sections. 2. Polarized light 3. Fluorescent light 4. Micro-radiography 5. Auto radiography 6. Nuclear volume morphometry 7. Cell kinetics 8. Finite element modeling 9. microelectrodes
  64. 64. Clinical correlation :  1) Intermittent vs. continues mechanics tooth movement is directly proportional to no. of hours the force is applied. Even when motivation and co-operation are optimal,the effectiveness of therapy is in consistent. 2) Differential anchorage the density of alveolar bone and the cross sectional area of the roots in the plane perpendicular to the direction of tooth movement are primary consideration for assessing anchorage potential anchorage value: the volume of osseous tissue that must be resorbed for a tooth to move a given distance is its anchorage value
  65. 65. Mandibular molars are difficult to move when compared  to maxillary molars because   Thin cortices and trabecular bone of maxilla offer less resistance to resorption than the thick cortices and more coarse trabeculae.  The leading root of mandibular molars being translated mesially forms bone that is far more dense than the bone formed by translating maxillary molars
  66. 66. There is change in trabecular pattern of bone in maxilla and  mandible because  maxilla transforms most of its force to the cranium  the mandible is subjected to substantial torsion and flexure caused by muscle pull and masticatory function  Maxilla is loaded predominantly in compression and there is no major muscle attachment. 3)  Rate of Tooth movement  the rate of tooth movement is inversely proportional to bone density and the volume of bone resorbed. maximal rate of translation of mid-root area trough dense cortical bone is about 0.5 mm per month for the first few months; the rate then declines to 0.3mm per month until 1st molar site is closed
  67. 67. The 3 principle variables that determine rate of tooth movement are 1)Growth 2)bone density 3)type of tooth movement During growth period there is increase in tooth movement. Increase in density slow is the tooth movement and vicevesra. Bodily movement is difficult to produce when compared to tipping movement.
  68. 68. Conclusion: It is important to understand the details of the physiology of bone. It is especially necessary to remember that such factors as hormones, vitamins, age and probably heredity may influence the resorption of bone. The success of orthodontic treatment is dependent on  Amount of force applied  Reaction of bone to orthodontic forces  Ultimate stability of bone So it is necessary to apply optimal forces to particular type of bone to produce desired results and check for the stability of the bone once the treatment is complete.
  69. 69. References 1.Oral Histology: Development, structure and function: Ten Kate; 10th Ed 2.Fundamentals of anatomy and physiology: Tortora; 10th Ed 3. Orthodontics –principles and practice graber vanarsdall 3 rd edition 4. Principles and practice of Orthodontics by T.M.Graber-3rd edition 5. Contemporary Orthodontics by Proffit 6. Human physiology- Tortora 7. Guyton and Hall--Human physiology
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