1.Dr. Vibhuti Singh Gopal

2. INDEX Introduction of bone Bone composition - Composition of bone & bone matrix - Cells of bone Classification of bone - Type of bone Structure of bone Mechanism of bone formation - Intamambranous ossification - Endochondral ossification 3. Bone is one of the hardest substances of the body. Bone is a dynamic tissue that constantly changes shape in relation to the stresses placed on it. 4. Pressures applied to bone lead to its resorption, whereas tension applied to it results in development of new bone. Applying these facts, the orthodontist is able to remodel the bone of the dental arches by moving and straightening the teeth to correct malocclusion. 5. Bone Composition 6. COMPOSITION OF BONE MATRIX 1. INORGANIC CRYSTALS 2. ORGANIC MATRIX 7. INORGANIC CRYSTALS About 70% of the matrix of bone is made of inorganic salts, principally salts of calcium and phosphate. These salts are deposited as flat crystal plates of hydroxyapatites,which have a variable ratio of calcium and phosphorus. 8. Many other ions ,particularly fluoride, magnesium, sodium, potassium, and carbonate absorb on to the hydroxyapatite crystals but do not themselves seem to be incorporated into bone as crystals. Inorganic crystals give bone its compressional strength. Provide much of the bones stiffness and resistance to pressing or squeezing forces. 9. Organic matrix give bone its tensile strength About 30% of matrix of bone made up of organic matrix. 90% of organic matrix is made up of collagen fibers. ORGANIC MATRIX 10. The collagen fibers are arranged in lines of tensional force for each bone and are surrounded by a homogeneous ground substance containing:- hyaluronic acid sialic acid combined with various proteins and mucopolysaccharides. 11. Collagen gives bone its characteristic flexibility and contributes to its ability to resist pulling and stretching forces With aging, collagen is lost progressively and bone becomes more brittle 12. Water Bone consists of much smaller proportion of water than other body parts 13. Cells of Bone Osteoprogenitor cells Osteoblasts Osteocytes Osteoclasts. 14. Osteoprogenitor Cells These cells are unspecialized stem cell derived from embryonic mesenchyme . They are the only cells to undergo cell division; the resulting cell develop into osteoblast. 15. Osteogenic cells are found along the inner portion of the periosteum,in the endosteum,and in the canals with in bone that contain blood vessels. Most active during the period of intense bone growth. 16. Under certain conditions of low oxygen tension, these cells may differentiate into chondrogenic [cartilage forming]cells. 17. OSTEOBLASTS Derived from osteoprogenitor cells . Located on the surface of the bone in a sheet-like arrangement of cuboidal to columnar cells . 18. Osteoblasts exocytose their secretory products, each cell surrounds itself with the bone matrix. When this occurs, the imprisoned cell is referred to as an osteocyte, and the space it occupies is known as a lacuna. 19. Most of the bone matrix becomes calcified Osteoblasts as well as osteocytes are always separated from the calcified substance by a thin, noncalcified layer known as the osteoid (uncalcified bone matrix). 20. OSTEOCYTES Mature bone cells derived from osteoblasts that became trapped in their lacunae. Radiating out in all directions from the lacunae are narrow, tunnel like spaces (canaliculi) that contain cytoplasmic processes of the osteocyte. 21. Processes make contact with similar processes of neighboring osteocytes, forming gap junctions through which ions and small molecules can move between the cells. Canaliculi also contain extracellular fluid carrying nutrients and metabolites that nourish the osteocytes. 22. OSTEOCLASTS Osteoclast are huge cells derived from the fusion of as many as 50 monocytes and are concentrated in the endosteum. On the side of the cell that faces the bone surface, the osteoclasts plasma membrane is deeply folded into a ruffled border. 23. Cell releases powerful lysosomal enzymes and acids that digest the protein and mineral components of the underlying bone matrix. 24. The breakdown of bone extracellular matrix is termed resorption. It is part of the normal development, growth , maintenance and repair of bone. 25. Bone tissue can be classified in several ways:- Based on location Based on quality Based on the shape Texture Matrix Arrangement Maturity And developmental origin CLASSIFICATION OF BONE 26. 1- BASED ON LOCATION AXIAL SKELETON:- bones of skull, vertebral column, sternum and ribs APPENDICULAR SKELETON:-bone of the pectoral girdle, pelvic girdle, and limb. ACRAL SKELETON:-part of the appendicular skeleton Including bone of the hands and feet. 27. 2-Based on quality Classified in to four types, expressed as type I, II, III and VI ( D1, D2, D3, and D4) 28. D1 type bone D1 bone is composed of almost all cortical bone mass located primarily in the anterior mandible. Due to its density this type of bone has fewer intrinsic blood vessels and depends for a significant portion of nutrient and blood supply on the periosteum. 29. D2 type bone D2 bone is composed of a thick crestal layer of cortical bone and coarse trabecular bone underneath the cortical bone. This type of bone can mostly be found in the anterior and posterior mandible. 30. D3 type bone D3 bone is composed of a porous crestal layer of cortical bone and fine trabecular bone underneath the cortical bone. This type of bone can mostly be found in the anterior and posterior maxilla but also in the posterior mandible 31. D4 type bone D4 bone is composed of primarily fine trabecular bone and often the absence of cortical bone. This type of bone can mostly be found in the posterior maxilla and poses the greatest challenge in implant placement. 32. 3- According to shape of bone Almost all bones of the body can be classified into five main types based on shape: 1- Long 2- Short 3- Flat 4- Irregular 5- sesamoid 33. Long bone Long bone have greater length than width, consist of a shaft and a variable number of extremities, and slightly curve for strength. 34. Long bone consist mostly of compact bone tissue in their diaphyses but have considerable amount of spongy bone tissue in their epiphyses. 35. Long bones vary in size and include those in the 1. Thigh (femur) 2. Leg (tibia and fibula) 3. Arm (humerus), 4. Forearm (ulna and radius) 5. Fingers 6. Toe (phalanges). 36. SHORT BONE Short bone are somewhat cube shaped and nearly equal in length and width. They consist of spongy bone tissue except at surface,which has a thin layer of compact bone tissue. 37. Example of short bones are the 1. Carpal (wrist) bone 2. Tarsal (ankle)bones 38. FLAT BONE Flat bones are generally thin and composed of two nearly parallel plates of compact bone tissue enclosing a layer of spongy bone tissue. 39. Flat bones include the 1. Cranial bones, which protect the brain; 2. The sternum and ribs, which protect organs in the thorax and scapulae(shoulder blades) 40. IRREGULAR BONES Irregular bones have complex shapes. They vary in the spongy and compact bone present. Example : vertebrae, hip bones,and certain facial bones. 41. SESAMOID BONES Sesamoid bone develop in certain tendons where there is considerable friction, tension and physical stress such as palm and soles. They may vary in number from person to person, are not always completely ossified, and measure only in few millimeters in diameter. 42. 4-According to texture of bone According to the degree of porosity, bone can be classified into two general categories: Cortical bone (low porosity) Spongy or cancellous bone (high porosity) 43. Cancellous bone Compact Bone Porosity High (Low mineral content and high collagen) Low (High mineral content and low collagen) Structure Honey comb Compact Characteristic Provides more flexibility but is not as stress resistant Stiffer and can resist greater stress but less flexible Function Shock absorption due to its better ability to change shape are important Withstanding stress in body areas that are subject to higher impact loads Location e.g., vertebrae Long bones (e.g., bones of the arms and legs) 44. 5-According to matrix arrangement LAMELLAR BONE:- lamellar bone is mature bone with collegen fiber that are arranged in lamellae. 45. WOVEN BONE:-woven bone is immature bone , in which collegen fiber are arranged in irregular random arrays and contain smaller amount of mineral substance and higher proportion of osteocytes than lamellar bone. 46. 6- According to maturity of bone IMMATURE BONE:-immature bone is woven bone. MATURE BONE:-mature bone is characteristically lamellar bone . Almost all bone in adults are lamellar bone. 47. 7-According to developmental origin INTRAMEMBRANOUS BONE:-develops from direct transformation of condensed mesenchyme. Flat bone are formed in this way. INTRACARTILAGINOUS BONE:-forms by replacing a preformed cartilage model. Long bone are formed in this way. 48. Structure of a long bone Diaphysis Epiphysis Proximal Distal Periosteum Medullary cavity Articular cartilage Epyphyseal plates 49. 1. DIAPHYSIS:- (GROWING BETWEEN) is the bones shaft or body- the long,cylindrical ,main portion of the bone 2. EPIPHYSIS- Epiphysis are the distal and proximal ends of bone 50. 3- METAPHYSIS- are the regions in a mature bone where the diaphysis joins the epiphysis. In the growing bone each metaphysis includes an epiphysis plate 51. 4- ARTICULAR CARTILAGE is a thin layer of hyaline cartilage covering the part of the epiphysis where bone form an articulation with another bone. It reduce friction and absorb shock at freely movable joint. 52. 5- PERIOSTEUM- is a tough sheath of dense irregular connective tissue that surrounds the bone surface where it is not covered by articular cartilage. 53. 6-MEDULLARY CAVITY- is the space with in the diaphysis that contain fatty yellow bone marrow in adults 7-ENDOSTEUM- 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 54. MECHANISM OF BONE FORMATION Endochondral ossification Intramembranous ossification 55. Endochondral Ossification The replacement of cartilage by bone is called endocondral ossification. Almost all bone of the body are formed in this way, the process is best observed in long bone. 56. Endochondral Ossification It proceeds as follow:- 1. Development of the cartilage model. 2. Development of primary ossification center. 3. Development of secondary ossification center. 57. Endochondral Ossification Aggregation of mesenchymal cells Differentiation into condroblast. These condroblast lay down Hyaline cartilage. This is surrounded by a membrane-called perichondrium 58. Calcification of intercellular substance. Nutrition is cut off leading to cell death. Empty spaces are formed-primary areolae. . Blood vessel and osteogenic cells invade the calcified cartilaginous matrix. 59. This leaves a large empty space- secondary areolae. Osteogenic cells become osteoblast arrange themselves along the surface of these calcified matrix. Ostoblasts lay down osteoid, which later becomes calcified to form a lamellae of bone 60. INTRAMEMBRANOUS OSSIFICATION The flat bone of the skull and mandible are formed by intramembranous ossification. The soft spots that help the fetal skull pass through the birth canal later harden as they undergo intramenbranous ossification 61. INTRAMEMBRANOUS OSSIFICATION It occurs as follow:- 1- Development of ossification center 2- Calcification 3-Formation of trabeculae 4-Development of periosteum 62. Aggregation of mesenchymal cell at the site of bone formation. Some cells lay down bundles of collagen fibers. Some convert to osteoblasts. Osteoblast secrete a gelatanious matrix called osteoid. 63. Calcium salts are deposited into the osteoid. Now osteoblast move away from lamellae & new layer of osteoid is sectreted which also calcified. Some osteoblasts gets entrapped between two lamellae- ostocyte . 64. INDEX THE SKULL THE CRANIAL BONES OCCIPITAL BONE TWO PARIETAL BONE FRONTAL BONE TWO TEMPORAL BONE SPHENOIDAL BONE ETHMOIDAL BONE 65. THE FACIAL BONES TWO NASAL BONE TWO LACRIMAL BONE TWO ZYGOMATIC BONE TWO PALATINE BONE TWO INFERIOR NASAL CONCHA BONE TWO MAXILLA BONE VOMER BONE MANDIBLE BONE 66. The Skull The skull is supported on the summit of the vertebral column. skull consist an oval shape . Skull is wider in posterior than in front. Skull is composed of a series of flattened or irregular bones. 67. skull is divided into two parts: (1) the cranium, which lodges and protects the brain, consists of eight bones (2) the skeleton of the face, of fourteen bones 68. Skull consist of 22 bones OCCIPITAL TWO PARIETAL FRONTAL Cranium, 8 bones TWO TEMPORAL SPHENOIDAL ETHMOIDAL TWO NASAL TWO LACRIMAL Face, 14 bones TWO ZYGOMATIC TWO PALATINE TWO INFERIOR NASAL CONCHA TWO MAXILLA VOMER MANDIBLE 69. The Cranial Bones OCCIPITAL BONE TWO PARIETAL BONE FRONTAL BONE TWO TEMPORAL BONE SPHENOIDAL BONE ETHMOIDAL BONE 70. 1.The Occipital Bone The occipital bone , situated at the back and lower part of the cranium. It is trapezoid in shape . It is pierced by a large oval aperture the foramen magnum through which the cranial cavity communicates with the vertebral canal. 71. OSSIFICATION The planum occipital of the squama is developed in membrane and may remain separate throughout life when it constitutes the interparietal bone. The rest of the bone is develop in cartilage. 72. The planum nuchale of the squama is ossified from two centers, which appear about the seventh week of fetal life and soon unite to form a single piece. Union of the upper and lower portions of the squama takes place in the third month of fetal life 73. An occasional center (Kerckring) appears in the posterior margin of the foramen magnum during the fifth month. Each of the lateral parts begins to ossify from a single center during the eighth week of fetal life. 74. About the fourth year the squama and the two lateral portions unite. About the sixth year the bone consists of a single piece. Between the eighteenth and twenty-fifth years the occipital and sphenoid become united, forming a single bone. 75. 2. The Parietal Bone The parietal bones form by their union to the sides and roof of the cranium. Each bone is irregularly quadrilateral in form, and has two surfaces, four borders, and four angles. 76. sagittal region occipital angle Frontal angle the parietal lobe superior temporal line occipital region frontal margin lower temporal line mastoid angle wedge angle scaly edge 77. Ossification. The parietal bone is ossified in membrane from a single center which appears at the parietal eminence about the eighth week of fetal life. Ossification gradually extends in a radial manner from the center toward the margins of the bone 78. The angles are consequently the parts last formed. 79. The Frontal Bone The frontal bone resembles a cockle-shell in form, and consists of two portions- 1. vertical portion 2. squama Corresponding with the region of the forehead and an orbital or horizontal portion, which enters into the formation of the roofs of the orbital and nasal cavities. 80. Ossification The frontal bone is ossified in membrane from two primary centers 1. One for each half, which appear toward the end of the second month of fetal life 2. One above each supraorbital margin 81. From each of these centers ossification extends upward to form the corresponding half of the squama, and backward to form the orbital plate. The spine is ossified from a pair of secondary centers, on either side of the middle line; similar centers appear in the nasal part and zygomatic processes. 82. The Temporal Bone The temporal bones are situated at the sides and base of the skull. Each consists of five parts- 1. Squama 2. Petrous 3. Mastoid 4. Tympanic parts 5. Styloid process. 83. Ossification.- The temporal bone is ossified from eight centers- 1. One for the squama including the zygomatic process. 2. One for the tympanic part. 3. Four for the petrous and mastoid parts. 4. Two for the styloid process. 84. Just before the close of fetal life the temporal bone consists of three principal parts: 1. The squama is ossified in membrane from a single nucleus, which appears near the root of the zygomatic process about the second month. 85. 2. The petromastoid part is developed from four centers- Protic Opisthotic Pterotic epiotic which make their appearance in the cartilaginous ear capsule about the fifth or sixth month. 86. 3.The tympanic ring is an incomplete circle, In the concavity of which is a groove The tympanic sulcus for the attachment of the circumference of the tympanic membrane. This ring expands to form the tympanic part, and is ossified in membrane from a single center which appears about the third month . 87. The Sphenoid Bone The sphenoid bone is situated at the base of the skull in front of the temporals and basilar part of the occipital. 88. Ossification. Until the seventh or eighth month of fetal life the body of the sphenoid consists of two parts 1- One in front of the tuberculum sella the presphenoid, with which the small wings are continuous. 2- The other, comprising the sella turcica and dorsum sella, the postsphenoid,which are associated with the great wings, and pterygoid processes. 89. The greater part of the bone is ossified in cartilage. There are fourteen centers in all, Six for the presphenoid Eight for the postsphenoid. 90. Presphenoid. About the ninth week of fetal life an ossific center appears for each of the small wings (orbitosphenoids) just lateral to the optic foramen. The sphenoidal concha are each developed from a center which makes its appearance about the fifth month. At birth they consist of small triangular lamina, 91. And in the third year that they become hollowed out and cone shaped About the fourth year they fuse with the labyrinths of the ethmoid And between the ninth and twelfth years they unite with the sphenoid. 92. Postsphenoid. The first ossific nuclei for the great wings are -- alisphenoids One makes its appearance in each wing between the foramen rotundum and foramen ovale about the eighth week. The orbital plate and that part of the sphenoid which is found in the temporal fossa, as well as the lateral pterygoid plate, are ossified in membrane . 93. The presphenoid is united to the postsphenoid about the eighth month and at birth the bone is in three pieces- A central, consisting of the body and small wings, and Two lateral, each comprising a great wing and pterygoid process 94. 6. Ethmoid bone The ethmoid bone is exceedingly light and spongy, and cubical in shape. It is situated at the anterior part of the base of the cranium, between the two orbits, at the roof of the nose, and contributes to each of these cavities. It consists of four parts: Cribriform plate Perpendicular plate Two lateral masses 95. Ossification. The ethmoid is ossified in the cartilage of the nasal capsule by three centers: - one for the perpendicular plate, and one for each labyrinth. The labyrinths are first developed, At birth, the bone consists of the two labyrinths, which are small and ill-developed. 96. During the first year after birth the perpendicular plate and crista galli begin to ossify from a single center and are joined to the labyrinths about the beginning of the second year. The cribriform plate is ossified partly from the perpendicular plate and partly from the labyrinths. The development of the ethmoidal cells begins during fetal life. 97. The Facial Bones. TWO NASAL TWO LACRIMAL TWO ZYGOMATIC TWO PALATINE TWO INFERIOR NASAL CONCHA TWO MAXILLA VOMER MANDIBLE 98. The Nasal Bones The nasal bones are two small oblong bones. Varying in size and form in different individuals. They are placed side by side at the middle and upper part of the face, and form, by their junction, the bridge of the nose . 99. Ossification. Each bone is ossified from one center, which appears at the beginning of the third month of fetal life in the membrane overlying the front part of the cartilaginous nasal capsule 100. The Maxilla (Upper Jaw) The maxilla are the largest bones of the face and form upper jaw by their union. 101. Each assists in forming the boundaries of three cavities- The roof of the mouth The floor and lateral wall of the nose The floor of the orbit 102. It also enters into the formation of two fossa- The infratemporal The pterygopalatine Two fissures- The inferior orbital Pterygomaxillary. 103. Ossification. The maxilla is ossified in membrane It is ossified from two centers only One for the maxilla proper One for the premaxilla These centers appear during the sixth week of fetal life and unite in the beginning of the third month. But the suture between the two portions persists on the palate until nearly middle life. 104. The maxilla was formerly described as ossifying from six centers- Orbitonasal Zygomatic Palatine Premaxillary Nasal Infravomerine 105. The Lacrimal Bone The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders 106. Ossification. The lacrimal is ossified from a single center, Which appears about the twelfth week in the membrane covering the cartilaginous nasal capsule 107. The Zygomatic Bone The zygomatic bone is small and quadrangular, and is situated at the upper and lateral part of the face: It forms the prominence of the cheek. Part of the lateral wall Floor of the orbit Parts of the temporal and infratemporal fossa. 108. Ossification. The zygomatic bone is generally described as ossifying from three centers One for the malar Two for the orbital portion These appear about the eighth week and fuse about the fifth month of fetal life. 109. The Palatine Bone The palatine bone is situated at the back part of the nasal cavity between the maxilla and the pterygoid process of the sphenoid . 110. It contributes to the walls of three cavities: 1-The floor and lateral wall of the nasal cavity 2-The roof of the mouth 3-The floor of the orbit It enters into the formation of two fossa- 1-The pterygopalatine 2- pterygoid fossa One fissure- 1- Inferior orbital fissure. 111. Ossification. The palatine bone is ossified in membrane from a single center Which makes its appearance about the sixth or eighth week of fetal life at the angle of junction of the two parts of the bone. From this point ossification spreads- Medialward to the horizontal part Downward into the pyramidal process Upward into the vertical part. 112. The Inferior Nasal Concha The inferior nasal concha extends horizontally along the lateral wall of the nasal cavity and consists of a lamina of spongy bone. It has two surfaces, two borders, and two extremities. 113. Ossification. The inferior nasal concha is ossified from a single center, which appears about the fifth month of fetal life in the lateral wall of the cartilaginous nasal capsule. 114. The Vomer The vomer is situated in the median plane but its anterior portion is frequently bent to one or other side It is thin, somewhat quadrilateral in shape, and forms the hinder and lower part of the nasal septum 115. Ossification At an early period the septum of the nose consists of a plate of cartilage, the ethmovomerine cartilage The postero-superior part of this cartilage is ossified to form the perpendicular plate of the ethmoid Its antero-inferior portion persists as the septal cartilage 116. While the vomer is ossified in the membrane covering its postero-inferior part. Two ossific centers, one on either side of the middle line, appear about the eighth week of fetal life in this part of the membrane, and hence the vomer consists primarily of two lamella. About the third month these unite below, and thus a deep groove is formed in which the cartilage is lodged. 117. The Mandible (Lower Jaw) The mandible the largest and strongest bone of the face, serves for the reception of the lower teeth. It consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, which unite with the ends of the body nearly at right angles. 118. Ossification. The mandible is ossified in the fibrous membrane covering the outer surfaces of Meckels cartilages. These cartilages form the cartilaginous bar of the mandibular arch and are two in number, a right and a left. Their proximal or cranial ends are connected with the ear capsules, and their distal extremities are joined to one another at the symphysis by mesodermal tissue. 119. They run forward immediately below the condyles and then, bending downward, lie in a groove near the lower border of the bone In front of the canine tooth they incline upward to the symphysis. 120. Ossification takes place in the membrane covering the outer surface of the ventral end of Meckels cartilage And each half of the bone is formed from a single center which appears, near the mental foramen, About the sixth week of fetal life. 121. By the tenth week the portion of Meckels cartilage which lies below and behind the incisor teeth is surrounded and invaded by the membrane bone. Somewhat later, accessory nuclei of cartilage make their appearance, 122. A wedge-shaped nucleus in the condyloid process and extending downward through the ramus; A small strip along the anterior border of the coronoid process; And smaller nuclei in the front part of both alveolar walls and along the front of the lower border of the bone. 123. The Hyoid Bone The hyoid bone is shaped like a horseshoe And is suspended from the tips of the styloid processes of the temporal bones by the stylohyoid ligaments. It consists of five segments- a body, two greater cornua, and two lesser cornua. 124. Ossification. The hyoid is ossified from six centers:- Two for the body, One for each cornu. Ossification commences in the greater cornua toward the end of fetal life, In the body shortly afterward In the lesser cornua during the first or second year after birth. 125. THANKS