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Alveolar bone

This document provides an overview of alveolar bone, including its development, histology, cellular components, and remodeling. It begins with a brief introduction to bone classification and composition. Key points include that alveolar bone forms via intramembranous ossification, and is composed of inorganic minerals and organic collagen fibers. It contains two main cell types - osteoblasts, which build bone, and osteoclasts, which resorb bone. Alveolar bone is continually modeled and remodeled throughout life to adapt to forces.

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Alveolar bone Shashi Kant Chaudhary JRII Dept of Periodntology & Oral Implantology Seminar
Content  Introduction  Development  Gross histology  Cellular components  Regulation of bone metabolism  Alveolar process  Alveolar bone modeling and remodeling  Conclusion  References
Introduction  Bone is a complex organ composed of multiple specialized tissues (osseous, periosteum/endosteum, and bone marrow) that act synergistically and serve multiple functions  Bone is a living tissue, which makes up the body skeleton and is one of the hardest structures of the animal body.  A specialized connective tissue composed of organic and inorganic elements that mineralizes
Classification Based on shape : Long Short Flat Irregular bones
Based on development Endochondral bones Intramembranous bones.
Based on microscopic structure Mature bone compact bone cancellous bone Immature bone.
Development  During embryogenesis, the skeleton forms by either a direct or indirect ossification process  Although histologically one bone is no different from another, bone formation occurs by three main mechanisms: Intramembranous Endochondral and Sutural
Intramembranous bone formation  Intramembranous bone formation occurs directly within mesenchyme  Eg. mandible, maxilla, skull, clavicle  Mesenchymal progenitor cells condensate and undergo direct differentiation into osteoblasts, a process known as intramembranous osteogenesis.
1. Formation of bone matrix in fibrous membrane 2. Formation of woven bone 3. Appositional growth mechanism and formation of compact bone 4. Formation of osteon
ENDOCHONDRAL BONE FORMATION  The mandibular condyle, the long bones and vertebrae form initially through a cartilage template, which serves as an anlage that is gradually replaced by bone.  The cartilage‐dependent bone formation and growth process is known as endochondral osteogenesis (Ranly 2000)
Sutural bone growth  Bone forms along suture margins  Found in skull  Fibrous joints between bones  Allow only limited movement  Helps skull and face to accommodate growing organs like eyes and brain
COMPOSITION OF BONE  Bone is a connective tissue composed of cells, fibers and ground substance.
Inorganic components  The inorganic part is made of bone minerals  Hydrated calcium and phosphate in the form of hydroxyapatite crystals [3Ca3(PO4)2(OH)2] are the principal inorganic constituent  Ions present are calcium phosphate, hydroxyl and carbonate.  Citrate, magnesium, sodium, potassium, fluoride, iron, zinc, copper, aluminum, lead, strontium, silicon and boron are present in small quantities
Organic components  The organic matrix is known as osteoid  Made – collagen(90%) and noncollagenous proteins  Type I collagen (> 95%) is the principal collagen, type V collagen (< 5%)  Alveolar bone :- type I, type V, type III and type XII collagen, (Type XII expressed under mechanical strain)  Sharpey’s fibers:- type III with type I collagen.
Noncollagenous proteins  10% of the total organic content of bone matrix  Most are endogenous proteins produced by bone cells, while some like albumin are derived from other sources such as blood  Noncollagenous Proteins are
• first noncollagenous protein to be recognized (less than 15% of the noncollagenous bone protein) • Also known as bone Gla protein as it contains the amino acid γ-carboxy glutamic acid. • Is a glycoprotein secreted by osteoblasts and regulated by vitamin D3 and parathyroid hormone. • Carboxy terminal acts as a chemoattractant to osteoclast precursors, suggesting a role in bone resorption • Involved in bone calcification as it is a calcium binding protein Osteocalcin
• Previously termed as bone sialoproteins I and II • Heavily glycosylated and phosphorylated with high levels of acidic amino acids. • Glutamic acid is predominant in bone sialoprotein • Aspartate is predominant in osteopontin. • Bone sialoprotein-function in the initiation of mineral crystal formation& transcription is suppressed by vitamin D3 • osteopontin is a potent inhibitor of hydroxyapatite crystal growth & transcription is strongly upregulated by vitamin D3, • TGF-β family members and glucocorticoids- stimulate expression of both protein Osteopontin & Bone sialoprotein
• 25% of noncollagenous proteins • Bound to collagen and hydroxyapatite crystals • Secreted calcium binding glycoprotein, that interacts with extracellular matrix molecules. • May play a role in the regulation of cell adhesion, proliferation and modulation of cytokine activity, and in initiating hydroxyapatite crystal formation. Osteonectin
• A large chondroitin sulfate proteoglycan, two small proteoglycans, biglycan and decorin (chondroitin sulfate proteoglycan I and II respectively) • Decorin and biglycan comprise < 10% & decreases with maturation of bone. Proteoglycans • More prominent in developing bone and has been mineralized to pericellular areas. • The precise function unknown, but similar to decorin, it can bind TGF-β and extracellular matrix macromolecules, including collagen, and thereby regulate fibrillogenesis. Biglycan • Binds mainly within the gap region of collagen fibrils and decorates the fibril surface. Decorin
• Components of demineralized bone and dentin matrix. • Regulate the cellular response to TGF-β Lysyl oxidase & tyrosine rich acidic matrix proteins (TRAMP) • A critical enzyme for collagen crosslinking. Lysyl oxidase • Also known as dermatopontin, binds decorin and TGF-β, TRAMP
• Not secreted by osteoblasts but regulate mineralization. • Matrix Gla protein is a mineral binding ECM protein secreted by vascular smooth muscle cells and chondrocytes that prevent mineralization in vascular tissues and cartilage. • The absence of α2HS glycoprotein, which is produced by the liver, compromises the inhibition of apatite formation by serum. Procollagen peptides, thrombospondin, fibronectin, vitronectin and alkaline phosphatase are the other proteins found in bone. Also contains proteases, protease inhibitors and a variety of cytokines secreted by osteoblasts, that regulate cell metabolism. These cells secrete several members of bone morphogenetic proteins (BMP) superfamily, including BMP-2, BMP-7, TGF-β, insulin like growth factors (IGF-I and IGF-II), platelet derived growth factor (PDGF) and fibroblast growth factor (FGF). IGF-I, PDGF and TGF-β increase the rapidity of bone formation and bone repair.
BONE HISTOLOGY  All mature bones have a dense outer sheet of compact bone and a central medullary cavity  The cavity is filled with red or yellow bone marrow  Cavity shows a network of bone trabeculae. (Trabecular, spongy or cancellous bone are the terms used to describe this network)
Compact bone  The outer aspect of compact bone is surrounded by a condensed fibrocollagen layer, the periosteum  Two layers: An outer layer which is a dense, irregular connective tissue termed fibrous layer An inner osteogenic layer, next to the bone surface consisting of bone cells, their precursors and a rich vascular supply
 The inner surface of compact and cancellous bone are covered by a thin cellular layer called endosteum.  Quiescent osteoblasts and osteoprogenitor cells are present on the endosteal surfaces.  Act as reservoir of new bone forming cells for remodeling or repair
 Mature or adult bones, whether compact or trabecular, are histologically identical in that they consist of microscopic layers or lamellae Three distinct types of layering are recognized: Circumferential Concentric Interstitial
Circumferential lamellae  At the periosteal and endosteal surfaces, the lamellae are arranged in parallel layers surrounding the bony surface and are called circumferential lamellae  Circumferential lamellae enclose the entire adult bone, forming its outer and inner perimeters
Concentric lamellae  Deep to the circumferential lamellae, the lamellae are arranged as small concentric layers around a central vascular canal.  Haversian (vascular) canal (about 50 μ in diameter) and the concentric lamellae together is known as the osteon or haversian system  Concentric lamellae make up the bulk of compact bone and form the basic metabolic unit of bone, the osteon  up to 20 concentric lamellae within each osteon
 The osteon is a cylinder of bone, generally oriented parallel to the long axis of the bone.  Adjacent haversian canals are interconnected by Volkmann canals; these channels, like haversian canals, contain blood vessels, thus creating a rich vascular network throughout compact bone
Interstitial lamellae  Interspersed between adjacent concentric lamellae and fill the spaces between them  Are actually fragments of preexisting concentric lamellae from osteons created during remodeling that can take a multitude of shapes
Spongy bone  Spongy bone and compact bone have the same cells and intercellular matrix, but differ in the arrangement of components.  Looks like a poorly organized tissue  Consists of large slender spicules called trabeculae. (up to 50 μm thick)  The trabeculae are oriented along lines of stress to withstand the forces applied to bone  The trabeculae surround the marrow spaces from where they derive their nutrition through diffusion
Bone marrow  The bone marrow consists of hematopoietic tissue islands, stromal cells, and adipose cells surrounded by vascular sinuses interspersed within a meshwork of trabecular bone  Two Types Red marrow:- consists mainly of hematopoetic tissue Yellow marrow:-mainly made up of adipocytes.  At birth, all bone marrow is red with age it is converted to the yellow type
Bone cells Two cell lineages are present in bone, each with specific functions: Osteogenic cells Osteoprogenitors Preosteoblasts Osteoblasts Osteocytes Bone lining cells Osteoclasts
Osteoprogenitor cells  They are long, thin stem cell population  Derived from mesenchyme  Unspecialized stem cells  Undergo mitosis and develop into osteoblasts  Found on inner surface of periosteum and endosteum
Osteoblast  Mononucleated cells, basophilic, plump cuboidal or slightly flattened cells  Found on surfaces of growing or remodeling bone  Abundant and well developed protein synthetic organelles (rough endoplasmic reticulum)  Are fully differentiated cells and lack the capacity for migration and proliferation  Produce the organic matrix of bone (Osteoid)
Formation Osteoprogenitor cells express transcription factors cbfa1/Runx-2 and osterix which are essential for osteoblast differentiation Mesenchymal progenitor cells, driven by the expression of a gene known as Indian hedgehog (Ihh) The IOPCs represent mesenchymal cells present in other organs and tissues that may differentiate into bone forming cells when stimulated DOPCs are present in the bone marrow, endosteum and periosteum and differentiate into osteoblasts Divided into two types Determined osteogenic precursor cells (DOPCs) and Inducible osteogenic precursor cells (IOPCs) Derived from undifferentiated pluripotent mesenchymal stem cells
Functions Formation of new bone Regulation of bone remodeling and mineral metabolism Mineralization of osteoid Secrete small amounts of type V collagen, osteonectin, osteopontin, RANKL, osteoprotegerin, proteoglycans, latent proteases and factors including BMPs Exhibit high levels of alkaline phosphatase used as a cytochemical marker to distinguish preosteoblasts from fibroblasts Express receptors for hormones involved in the regulation of osteoblast differentiation
Fate of osteoblasts At the end of bone forming phase, osteoblasts can have one of four different fates 1. Become embedded in the bone as osteocytes 2. Transform into inactive osteoblasts and become bone lining cells 3. Undergo apoptosis 4. Transdifferentiate into cells that deposit chondroid or chondroid bone.
Bone lining cells  Once osteoblasts have completed their function, they are either entrapped in the bone matrix and become osteocytes or remain on the surface as lining cells  These cells cover most, but not all quiescent bone surfaces in the adult skeleton.  Together with osteocytes, bone forming cells and their connecting cell processes appear to form an extensive homeostatic network of cells capable of regulating plasma calcium concentration.
Osteocytes  As osteoblasts form bone, some become trapped in the matrix they secrete, whether mineralized or unmineralized; these cells then are called osteocytes  The number of osteoblasts that become osteocytes varies depending on the rapidity of bone formation;  Embryonic (woven) bone and repair bone have more osteocytes than does lamellar bone  Osteocytes are stellate‐shaped cells that are embedded within the mineralized bone matrix in spaces known as osteoctic lacunae
 Osteocyte cytoplasmic projections (known as dendrites)extend through cylindrical encased compartments referred as canaliculi  Osteocytes maintain contact with adjacent osteocytes, osteoblasts or lining cells on the bone surfaces  The osteocyte network is therefore an extracellular and intracellular communication channel that is sensitive to shear stress as the result of mechanical stimuli and bone deformation
 Osteocytes translate mechanical signals into biochemical mediators that will assist with the orchestration of anabolic and catabolic events within bone Canalicular–lacunar system arrangement allows osteocytes to 1. Participate in the regulation of blood calcium homeostasis and 2. Sense mechanical loading and transmit this information to other cells within the bone to further orchestrate osteoblast and osteoclast function (Burger et al. 1995; Marotti 2000).
 Failure of any part of this interconnecting system results in hypermineralization (sclerosis) and death of the bone.  Later may be resorbed and replaced during the process of bone turnover
Four schemes have been proposed to explain how an osteoblast could get trapped within bone matrix Osteoblasts are unpolarized and lay down bone in all directions, i.e. the cells become trapped in their own secretions. Individual osteoblasts are polarized, but those within same generation are polarized differently to those in adjacent layers. As a result, bone is deposited in all directions &osteoblasts become trapped. Osteoblasts of each generation are polarized in the same direction. One generation buries the preceding one in bone matrix. Within one generation, some osteoblasts slow down rate of bone deposition or stop laying down bone, so that they become trapped by the secretion of their neighboring cells.
Osteoclast  Greek words for “bone and broken”.  Specialized multinucleated cells(approx 40–100 μm in diameter with 15 to 20 nuclei)  Lie in resorption bays called Howship’s lacunae  Variable in shape due to their motility  Tartrate resistant acid phosphatase within its cytoplasmic vesicles and vacuoles which distinguishes it from multinucleated giant cells.  Adjacent to the tissue surface cell membrane of the osteoclast form ruffled border
 At the periphery of this border, the plasma membrane is apposed closely to the bone surface, and the adjacent cytoplasm, devoid of cell organelles, is enriched in actin, vinculin, and talin This is clear or sealing zone
Formation of osteoclast  Derived from hemopoietic cells of monocyte macrophage lineage.  The differentiation into osteoclasts - involving cell–cell interaction with osteoblast stromal cells  Formation of osteoclast requires the presence of RANK ligand (receptor activator of nuclear factor κB) and M-CSF (macrophage colony stimulating factor).- produced by stromal cells and osteoblasts direct contact of these cells and osteoclast precursors.
 M-CSF act on receptor on osteoclast precursors c-Fms (colony stimulating factor 1 receptor) and provides signals for proliferation  RANKL binds to RANK on surface of M-CSF triggered osteoclast precursors into multinucleated giant cells, their differentiation into mature osteoclasts, their attachment to bone surface and their activation to resorb bone.
 Osteoprotegerin (OPG) recognizes RANKL, and blocks the interaction between RANK and RANKL, leading to an inhibition of osteoclast differentiation and activation  Cbfa1 contributes to the expression of OPG
Regulation of osteoblast • PTH is secreted in response to a hypocalcemic signal in order to regulate calcium homeostasis by promoting bone resorption, Role of parathormone (PTH) • Stimulates synthesis of osteocalcin and osteopontin by osteoblasts and suppresses collagen production • Bone resorption at high concentrations (pharmacological) and support bone formation at low (physiologic) concentrations. Vitamin D3 • Required for attaining normal bone mass mediated by IGF-I. Growth hormone
• Targets osteoblast & stimulates bone formation & mineralization Insulin • A subgroup of the TGF- β superfamily. • Initiate osteoblastogenesis from uncommitted progenitor cells. • BMPs 2, 4 and 6 direct the pluripotent cells to commit to an osteoblastic pathway Bone morphogenetic proteins • Promote differentiation of osteoblasts & bone matrix formation • Prolonged treatment with glucocorticoids results in bone loss Glucocorticoids • Promoting osteogenesis. • It acts as a potent mitogen for all cells of mesenchymal origin PDGF (platelet derived growth factor)
• Early stage to recruit & stimulate osteoprogenitor cells to proliferate, providing a pool of early osteoblasts • Later stages of osteoblast blocks differentiation and mineralization. TGF-β • Increase proliferation and stimulating mature osteoblast function IGF I and II (insulin like growth factors) • Play a critical role in angiogenesis and mesenchymal cell mitogenesis FGF-2 is expressed by osteoblasts- bone formation FGF (fibroblast growth factors)
Regulation of osteoclast • Suppresses the production of bone resorbing cytokines including IL-1 & IL-6 • Estrogen deficiency results bone resorption by increasing osteoclast activity Estrogen • Vitamin D3 promotes the differentiation of osteoclasts from monocyte macrophage stem cell precursors - enhanced osteoclastic bone resorption • PTH binds to osteoblasts and induces the production of M-CSF and RANKL- - stimulate the maturation and action of osteoclasts. Vitamin D3 and parathyroid hormone (PTH) • Inhibits proliferation and differentiation of osteoclast precursors. • Reduces the dimension of ruffled border & dissociation into monocytic cells. Calcitonin
• Suppress bone resorption via injury to osteoclasts when they solubilize bisphosphonate contaminated bone without consistent reduction in osteoclast numbers Bisphosphonates • Mediators of bone resorption and can also influence bone formation • Induce osteoclast formation through increased expression of RANKL on the surface of immature osteoblasts and stromal cells PGE2 (Prostaglandins of E series) • Stimulates differentiation of osteoclast progenitors into osteoclasts TNFα • An inhibitor of osteoclast formation OCIL (osteoclast inhibitory lectin) • Inhibit proliferation and differentiation of committed precursors into mature osteoclasts. TGF-β and interferon-γ
Structural lines in bones • The site of change from bone resorption to bone formation is represented by a scalloped outline • Rich in sialoproteiin & osteopontin Reversal line or cementing line • Rythmic deposition of bone with periods of relative quiescence seen as parallel vertical lines Resting line
ALVEOLAR BONE The alveolar process is defined as that part of the maxilla and the mandible that forms and supports the sockets of the teeth. –Orbans The alveolar bone is constituted strictly of the ALVEOLAR PROCESS which is firmly attached to the basal bone of the jaws – Tencate The alveolar process is the portion of the maxilla and mandible that forms and supports the tooth sockets (alveoli). – Carranza
Functions of alveolar bone  Houses the roots of teeth  Anchors the roots of teeth to the alveoli, achieved by the insertion of Sharpey’s fibers into the alveolar bone proper.  Helps to move the teeth for better occlusion  Helps to absorb & distribute occlusal forces  Supplies vessels to periodontal ligament.  Houses & protects developing permanent teeth, while supporting primary teeth.  Organizes eruption of primary and permanent teeth.
DEVELOPMENT OF ALVEOLAR PROCESS  At the end of 2nd month of fetal life, the maxilla as well as mandible forms a groove that open to surface of oral cavity  Tooth germs contained in these groove (alveolar vessels & nerve)  Alveolar process consists of bone which is formed both by cells from the dental follicle (alveolar bone proper) & cells which are independent of tooth development
Permanent tooth moves into place, developing its own alveolar bone from its own follicle When a deciduous tooth is shed, its alveolar bone is resorbed. Alveolar process gradually incorporated into maxillary or mandibular body. With the onset of root formation - interradicular bone develops in multirooted teeth. Teeth separated from each other by the development of interdental septa. The developing teeth lie in a trough of bone -Tooth Crypt. Resorption - inner wall of the alveolus/ Deposition -outer wall. Alveolar process develops from the dental follicle during eruption of tooth size of the alveolus is dependent upon the size of the growing tooth germ.
STRUCTURE OF THE ALVEOLAR BONE  Anatomically, no distinct boundary exists between the body of the maxilla or the mandible and alveolar processes.  As a result of its adaptation to function, two parts of the alveolar process can be distinguished, The alveolar bone proper and The supporting alveolar bone
Alveolar bone Supporting alveolar bone Cortical plate Spongy bone Alveolar bone proper
Alveolar bone proper  Consists partly of lamellated & partly of bundle bone  About 0.1–0.4 mm thick.  Surrounds the root of the tooth and gives attachment to principal fibers of the periodontal ligament
Lamellated bone  Contains osteons each of which has a blood Vessel in a haversian canal.  Blood vessel is surrounded by concentric Lamellae to form osteon.  Some lamellae of the lamellated Bone are arranged roughly parallel to the surface of the Adjacent marrow spaces, whereas others form haversian systems.
Bundle bone  Bone in which the principal fibers of the periodontal ligament are anchored  The term ‘bundle’ because, the bundles of the principal fibers continue into the bone as Sharpey’s fibers  Characterized by the scarcity of the fibrils in the intercellular substance and arranged at right angles to Sharpey’s fibers  Contains fewer fibrils than does lamellated bone
 Sharpey’s fibers are mineralized at the periphery and have a larger diameter.  These fibers are less numerous than the corresponding fiber bundles in the cementum
 Radiographically, it is also referred to as the lamina dura, because, of increased radiopacity, which is due to the presence of thick bone without trabeculations
 The alveolar bone proper, which forms the inner wall of the socket is perforated by many openings that carry branches of the interalveolar nerves and blood vessels into the periodontal ligament, and it is therefore called the cribriform plate
 Bone between the teeth is called interdental septum  Composed entirely of cribriform plate.  The interdental and interradicular septa contain the perforating canals of Zuckerkandl and Hirschfeld (nutrient canals) which house the interdental and interradicular arteries, veins, lymph vessels and nerves
Supporting alveolar bone Consists of two parts Cortical plates Spongy bone
Cortical plates  Consist of compact bone and form the outer and inner plates of the alveolar processes  Continuous with the compact layers of the maxillary and mandibular body  Thinner in the maxilla, than in the mandible  Thickest in the premolar and molar region on buccal side of the lower jaw  The supporting bone usually very thin in anterior teeth region of both jaws – no spongy bone
 Histologically, the cortical plates consist of longitudinal lamellae and haversian systems.  In the lower jaw, circumferential or basic lamellae reach from the body of the mandible into the cortical plates
Spongy bone  Spongy bone fills the area between the cortical plates and the alveolar bone proper  Contains trabeculae of lamellar bone- surrounded by marrow that is rich in adipocytes and pluripotent mesenchymal cells  The trabeculae contain osteocytes in the interior and osteoblasts or osteoclasts on the surface  Trabeculae buttress the functional forces to which alveolar bone proper is exposed
Classification of the spongiosa (radiographically ) Type I the interdental and interradicular trabeculae are regular and horizontal in a ladder like arrangement - most often in the mandible Type II shows irregularly arranged, numerous, delicate interdental and interradicular trabeculae more common in the maxilla
lnterdental Septum  The interdental septum consists of cancellous bone and cortical plates  If the interdental space is narrow, the septum may consist of only lamina dura (between mandibular 2ndpremolars and 1stmolars consists of only lamina dura in 15% cases)  If roots are too close together, an irregular "window" can appear in the bone between adjacent roots
 The mesiodistal angulation of the crest of the interdental septum usually parallels a line drawn between the cemento-enamel junctions of the approximating teeth  The distance between the crest of the alveolar bone and the CEJ in young adults varies between 0.75 and 1.49 mm (average, 1.08 mm)  This distance increases with age to an average of 2.81 mm
Osseous topography  Normally conforms to the prominence of the roots  The height and thickness of the facial and lingual bony plates are affected by the alignment of the teeth, by the angulation of the root to the bone, and by occlusal forces
Fenestrations and Dehiscences  Isolated areas in which the root is denuded of bone and the root surface is covered only by periosteum and overlying gingiva are termed as fenestrations  In these instances the marginal bone is intact  When the denuded areas extend through the marginal bone, the defect is called a dehiscence  Fenestration and dehiscence are important, because they may complicate the outcome of periodontal surgery.
fenestrationdehiscence
• They occur more often on the facial bone than on the lingual, are more common on anterior teeth than on posterior teeth, and are frequently bilateral. • Prominent root contours, malposition, and labial protrusion of the root combined with a thin bony plate are predisposing factors.(Elliot JR,Bowers GM)
Bone formation  The osteo progenitor cells express transcription factors cbfa1/Runx2. cbfa1(osteoblast specific transcription factors) Osterix and b- catenin (maturation)  Osteoblast contains high level of alkaline phosphatase- liberated phosphate - initiation and progressive growth of bone mineral crystals  Cytoplasm is intensely basophilic, abundant and well developed protein synthetic organelles such as rough endoplasmic reticulum
 Procollagen and other organic proteins synthesized and transported to golgi complex by transfer vesicle  Golgi complex form secretory vesicles and secret extracellularly along the bone forming surface to form osteoid(prebone)  Osteoblasts produces Collagen type I, collagen type V and non collagenous protein such as bone sialoprotein and osteopontin- where they participate in regulating mineral deposition
BONE RESORPTION Sequence of events in resorptive process Attachment of osteoclasts to mineralized surface of bone Creation of a sealed acidic environment through action of the proton pump which demineralizes bone and expose organic matrix Degradation of the exposed organic matrix to its constituents amino acids by action of released enzymes such as acid phosphatase and cathepsin Sequestering of mineral ions and amino acids within the osteoclast Ten Cate AR
Role of TRAP in bone resorption( tartarate resistant acid phosphatase) latent inactive proenzyme-cysteine proteinases convert it into an active form Extracellular role: Regulate osteoclast adhesion to the bone Degrades the phosphoprotein-degradation of the bone matrix Liberate pyrophosphate (inhibitor)osteoclast migration Intracellular role:  Endocytosed vesicle & TRAP containing vesicle fuses to form functional secretory domain (FSD)
Extra cellular fate:  TRAP taken up into circulation from interstitial space  Bind with 2 macroglobulin  Loses binuclear iron centre and recycled  Free enzymes metabolized in liver & excreted through urine
Various bone resorbing factors A. Systemic factors: (a) Parathyroid hormone (b) Parathyroid related peptide (c) Vitamin D3 (d) Thyroid hormone B. Local factors: (a) Prostanoids (b) Lipoxygenase metabolites (c) Cytokines: IL – 1, IL – 4, TNF – α, TNF – β, IL – 6 C. Growth factors: (a) EGF (b) TGF – α (c) TGF − β (d) PDGF D. Bacterial factors: (a) Lipopolysaccharides (b) Capsular material (c) Peptidoglycans (d) Lipoteichoic acids.
Bone modeling  Bone modeling is defined as a change in the shape and architecture of the bone  It extends from embryonic bone development to the pre-adult period of human growth, which is continuous and covers a large surface  The ability of bone to adapt to mechanical loads is brought about by continuous bone resorption and bone formation  If these processes occur at different locations, the bone morphology is altered, Frost defined this as modeling (Frost, 1990a)
Bone remodeling  Bone remodeling is defined as a change without concomitant change in the shape and architecture of the bone  In a homeostatic equilibrium resorption and formation are balanced In that case old bone is continuously replaced by new tissue  This ensures that the mechanical integrity of the bone is maintained but it causes no global changes in morphology, Frost defined this as remodeling (Frost, 1990b)
 In a healthy individual, this turnover is in a steady state; that is, the amount of bone lost is balanced by bone formed.  Remodeling occurs in discrete, focal areas involving groups of cells called bone remodeling or basic multicellular units.
Activation Resorption ReversalFormation Resting The bone remodeling cycle
 As osteoclasts move through compact bone, they create a resorption channel. The leading edge of resorption is termed the cutting cone and is characterized by a scalloped array of resorption lacunae (Howship’s lacunae), each housing an osteoclast  Behind the cutting cone is a migration of mononucleated cells (macrophages and/or preosteoblasts) differentiate into osteoblasts, The entire area of the osteon where active bone formation occurs is termed the filling cone  When formation is complete, the haversian canal contains a central blood vessel and a layer of inactive osteoblasts, the lining cells that communicate by means of cell processes with the embedded osteocytes.
Remodeling of alveolar bone  Major pathway of bony changes in shape, resistance to forces, repair of wounds and calcium-phosphate homeostasis  Involves the co-ordination of activities of cells from two distinct lineages, the osteoblasts and the osteoclasts  A complex process involving hormone and local factors acting in autocrine and paracrine manner on generation and activity of differentiated bone cells
Coupling  It is interdependency of osteoblasts and osteoclasts in remodeling of the bone. Parathyroid hormone OSTEOBLASTS Interleukin 1 and 6 Releases leukemia inhibiting factor (LIF) Monocytes Multinucleated OSTEOCLASTS (Resorb bone) Bound to collagen OSTEOBLASTS (Deposits bone) Stimulates Release Stimulates Migrates into bone and coalasces Releases osteogenic substrates Stimulates differentiation of
Age changes In older individuals:  Alveolar sockets appear jagged and uneven.  The marrow spaces have fatty infiltration  The alveolar process in edentulous jaws decreases in size.  Loss of maxillary bone is accompanied by increase in size of the maxillary sinus.  Internal trabecular arrangement is more open, which indicates bone loss.  The distance between the crest of the alveolar bone and CEJ increases with age—approximately by 2.81 mm.
Conclusion  Bone is a mineralized connective tissue with a relatively flexible character and compressive strength  The property of plasticity allows it to be remodeled according to the functional demands placed on it.  In order to maintain stability and integrity of bone, it constantly undergoes remodeling.  About 10% of bone material is renewed each year.  This process is brought about by osteoclasts and osteoblasts.
References  Newman ,Takei , Klokkevold , Carranza ; Carranza's Clinical Periodontology ,10thedition,  Newman ,Takei , Klokkevold , Carranza; Carranza's Clinical Periodontology , 12th Edition.  Niklaus P. Lang , Jan Lindhe , Clinical Periodontology And Implant Dentistry ,6thedition  Orban's Oral Histology And Embryology , 13th Edition ,  Antonio Nancy, Ten Cate Oral Histology Development , Structure And Function , 8th edition
Thank you

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Alveolar bone

  • 1.
    Alveolar bone Shashi KantChaudhary JRII Dept of Periodntology & Oral Implantology Seminar
  • 2.
    Content  Introduction  Development Gross histology  Cellular components  Regulation of bone metabolism  Alveolar process  Alveolar bone modeling and remodeling  Conclusion  References
  • 3.
    Introduction  Bone isa complex organ composed of multiple specialized tissues (osseous, periosteum/endosteum, and bone marrow) that act synergistically and serve multiple functions  Bone is a living tissue, which makes up the body skeleton and is one of the hardest structures of the animal body.  A specialized connective tissue composed of organic and inorganic elements that mineralizes
  • 4.
    Classification Based on shape: Long Short Flat Irregular bones
  • 5.
    Based on development Endochondralbones Intramembranous bones.
  • 6.
    Based on microscopicstructure Mature bone compact bone cancellous bone Immature bone.
  • 7.
    Development  During embryogenesis,the skeleton forms by either a direct or indirect ossification process  Although histologically one bone is no different from another, bone formation occurs by three main mechanisms: Intramembranous Endochondral and Sutural
  • 8.
    Intramembranous bone formation Intramembranous bone formation occurs directly within mesenchyme  Eg. mandible, maxilla, skull, clavicle  Mesenchymal progenitor cells condensate and undergo direct differentiation into osteoblasts, a process known as intramembranous osteogenesis.
  • 9.
    1. Formation ofbone matrix in fibrous membrane 2. Formation of woven bone 3. Appositional growth mechanism and formation of compact bone 4. Formation of osteon
  • 11.
    ENDOCHONDRAL BONE FORMATION The mandibular condyle, the long bones and vertebrae form initially through a cartilage template, which serves as an anlage that is gradually replaced by bone.  The cartilage‐dependent bone formation and growth process is known as endochondral osteogenesis (Ranly 2000)
  • 13.
    Sutural bone growth Bone forms along suture margins  Found in skull  Fibrous joints between bones  Allow only limited movement  Helps skull and face to accommodate growing organs like eyes and brain
  • 14.
    COMPOSITION OF BONE Bone is a connective tissue composed of cells, fibers and ground substance.
  • 15.
    Inorganic components  Theinorganic part is made of bone minerals  Hydrated calcium and phosphate in the form of hydroxyapatite crystals [3Ca3(PO4)2(OH)2] are the principal inorganic constituent  Ions present are calcium phosphate, hydroxyl and carbonate.  Citrate, magnesium, sodium, potassium, fluoride, iron, zinc, copper, aluminum, lead, strontium, silicon and boron are present in small quantities
  • 16.
    Organic components  Theorganic matrix is known as osteoid  Made – collagen(90%) and noncollagenous proteins  Type I collagen (> 95%) is the principal collagen, type V collagen (< 5%)  Alveolar bone :- type I, type V, type III and type XII collagen, (Type XII expressed under mechanical strain)  Sharpey’s fibers:- type III with type I collagen.
  • 17.
    Noncollagenous proteins  10%of the total organic content of bone matrix  Most are endogenous proteins produced by bone cells, while some like albumin are derived from other sources such as blood  Noncollagenous Proteins are
  • 18.
    • first noncollagenousprotein to be recognized (less than 15% of the noncollagenous bone protein) • Also known as bone Gla protein as it contains the amino acid γ-carboxy glutamic acid. • Is a glycoprotein secreted by osteoblasts and regulated by vitamin D3 and parathyroid hormone. • Carboxy terminal acts as a chemoattractant to osteoclast precursors, suggesting a role in bone resorption • Involved in bone calcification as it is a calcium binding protein Osteocalcin
  • 19.
    • Previously termedas bone sialoproteins I and II • Heavily glycosylated and phosphorylated with high levels of acidic amino acids. • Glutamic acid is predominant in bone sialoprotein • Aspartate is predominant in osteopontin. • Bone sialoprotein-function in the initiation of mineral crystal formation& transcription is suppressed by vitamin D3 • osteopontin is a potent inhibitor of hydroxyapatite crystal growth & transcription is strongly upregulated by vitamin D3, • TGF-β family members and glucocorticoids- stimulate expression of both protein Osteopontin & Bone sialoprotein
  • 20.
    • 25% ofnoncollagenous proteins • Bound to collagen and hydroxyapatite crystals • Secreted calcium binding glycoprotein, that interacts with extracellular matrix molecules. • May play a role in the regulation of cell adhesion, proliferation and modulation of cytokine activity, and in initiating hydroxyapatite crystal formation. Osteonectin
  • 21.
    • A largechondroitin sulfate proteoglycan, two small proteoglycans, biglycan and decorin (chondroitin sulfate proteoglycan I and II respectively) • Decorin and biglycan comprise < 10% & decreases with maturation of bone. Proteoglycans • More prominent in developing bone and has been mineralized to pericellular areas. • The precise function unknown, but similar to decorin, it can bind TGF-β and extracellular matrix macromolecules, including collagen, and thereby regulate fibrillogenesis. Biglycan • Binds mainly within the gap region of collagen fibrils and decorates the fibril surface. Decorin
  • 22.
    • Components ofdemineralized bone and dentin matrix. • Regulate the cellular response to TGF-β Lysyl oxidase & tyrosine rich acidic matrix proteins (TRAMP) • A critical enzyme for collagen crosslinking. Lysyl oxidase • Also known as dermatopontin, binds decorin and TGF-β, TRAMP
  • 23.
    • Not secretedby osteoblasts but regulate mineralization. • Matrix Gla protein is a mineral binding ECM protein secreted by vascular smooth muscle cells and chondrocytes that prevent mineralization in vascular tissues and cartilage. • The absence of α2HS glycoprotein, which is produced by the liver, compromises the inhibition of apatite formation by serum. Procollagen peptides, thrombospondin, fibronectin, vitronectin and alkaline phosphatase are the other proteins found in bone. Also contains proteases, protease inhibitors and a variety of cytokines secreted by osteoblasts, that regulate cell metabolism. These cells secrete several members of bone morphogenetic proteins (BMP) superfamily, including BMP-2, BMP-7, TGF-β, insulin like growth factors (IGF-I and IGF-II), platelet derived growth factor (PDGF) and fibroblast growth factor (FGF). IGF-I, PDGF and TGF-β increase the rapidity of bone formation and bone repair.
  • 24.
    BONE HISTOLOGY  Allmature bones have a dense outer sheet of compact bone and a central medullary cavity  The cavity is filled with red or yellow bone marrow  Cavity shows a network of bone trabeculae. (Trabecular, spongy or cancellous bone are the terms used to describe this network)
  • 25.
    Compact bone  Theouter aspect of compact bone is surrounded by a condensed fibrocollagen layer, the periosteum  Two layers: An outer layer which is a dense, irregular connective tissue termed fibrous layer An inner osteogenic layer, next to the bone surface consisting of bone cells, their precursors and a rich vascular supply
  • 27.
     The innersurface of compact and cancellous bone are covered by a thin cellular layer called endosteum.  Quiescent osteoblasts and osteoprogenitor cells are present on the endosteal surfaces.  Act as reservoir of new bone forming cells for remodeling or repair
  • 28.
     Mature oradult bones, whether compact or trabecular, are histologically identical in that they consist of microscopic layers or lamellae Three distinct types of layering are recognized: Circumferential Concentric Interstitial
  • 30.
    Circumferential lamellae  Atthe periosteal and endosteal surfaces, the lamellae are arranged in parallel layers surrounding the bony surface and are called circumferential lamellae  Circumferential lamellae enclose the entire adult bone, forming its outer and inner perimeters
  • 31.
    Concentric lamellae  Deepto the circumferential lamellae, the lamellae are arranged as small concentric layers around a central vascular canal.  Haversian (vascular) canal (about 50 μ in diameter) and the concentric lamellae together is known as the osteon or haversian system  Concentric lamellae make up the bulk of compact bone and form the basic metabolic unit of bone, the osteon  up to 20 concentric lamellae within each osteon
  • 32.
     The osteonis a cylinder of bone, generally oriented parallel to the long axis of the bone.  Adjacent haversian canals are interconnected by Volkmann canals; these channels, like haversian canals, contain blood vessels, thus creating a rich vascular network throughout compact bone
  • 33.
    Interstitial lamellae  Interspersedbetween adjacent concentric lamellae and fill the spaces between them  Are actually fragments of preexisting concentric lamellae from osteons created during remodeling that can take a multitude of shapes
  • 34.
    Spongy bone  Spongybone and compact bone have the same cells and intercellular matrix, but differ in the arrangement of components.  Looks like a poorly organized tissue  Consists of large slender spicules called trabeculae. (up to 50 μm thick)  The trabeculae are oriented along lines of stress to withstand the forces applied to bone  The trabeculae surround the marrow spaces from where they derive their nutrition through diffusion
  • 35.
    Bone marrow  Thebone marrow consists of hematopoietic tissue islands, stromal cells, and adipose cells surrounded by vascular sinuses interspersed within a meshwork of trabecular bone  Two Types Red marrow:- consists mainly of hematopoetic tissue Yellow marrow:-mainly made up of adipocytes.  At birth, all bone marrow is red with age it is converted to the yellow type
  • 36.
    Bone cells Two celllineages are present in bone, each with specific functions: Osteogenic cells Osteoprogenitors Preosteoblasts Osteoblasts Osteocytes Bone lining cells Osteoclasts
  • 38.
    Osteoprogenitor cells  Theyare long, thin stem cell population  Derived from mesenchyme  Unspecialized stem cells  Undergo mitosis and develop into osteoblasts  Found on inner surface of periosteum and endosteum
  • 39.
    Osteoblast  Mononucleated cells,basophilic, plump cuboidal or slightly flattened cells  Found on surfaces of growing or remodeling bone  Abundant and well developed protein synthetic organelles (rough endoplasmic reticulum)  Are fully differentiated cells and lack the capacity for migration and proliferation  Produce the organic matrix of bone (Osteoid)
  • 40.
    Formation Osteoprogenitor cells expresstranscription factors cbfa1/Runx-2 and osterix which are essential for osteoblast differentiation Mesenchymal progenitor cells, driven by the expression of a gene known as Indian hedgehog (Ihh) The IOPCs represent mesenchymal cells present in other organs and tissues that may differentiate into bone forming cells when stimulated DOPCs are present in the bone marrow, endosteum and periosteum and differentiate into osteoblasts Divided into two types Determined osteogenic precursor cells (DOPCs) and Inducible osteogenic precursor cells (IOPCs) Derived from undifferentiated pluripotent mesenchymal stem cells
  • 42.
    Functions Formation of newbone Regulation of bone remodeling and mineral metabolism Mineralization of osteoid Secrete small amounts of type V collagen, osteonectin, osteopontin, RANKL, osteoprotegerin, proteoglycans, latent proteases and factors including BMPs Exhibit high levels of alkaline phosphatase used as a cytochemical marker to distinguish preosteoblasts from fibroblasts Express receptors for hormones involved in the regulation of osteoblast differentiation
  • 43.
    Fate of osteoblasts Atthe end of bone forming phase, osteoblasts can have one of four different fates 1. Become embedded in the bone as osteocytes 2. Transform into inactive osteoblasts and become bone lining cells 3. Undergo apoptosis 4. Transdifferentiate into cells that deposit chondroid or chondroid bone.
  • 44.
    Bone lining cells Once osteoblasts have completed their function, they are either entrapped in the bone matrix and become osteocytes or remain on the surface as lining cells  These cells cover most, but not all quiescent bone surfaces in the adult skeleton.  Together with osteocytes, bone forming cells and their connecting cell processes appear to form an extensive homeostatic network of cells capable of regulating plasma calcium concentration.
  • 45.
    Osteocytes  As osteoblastsform bone, some become trapped in the matrix they secrete, whether mineralized or unmineralized; these cells then are called osteocytes  The number of osteoblasts that become osteocytes varies depending on the rapidity of bone formation;  Embryonic (woven) bone and repair bone have more osteocytes than does lamellar bone  Osteocytes are stellate‐shaped cells that are embedded within the mineralized bone matrix in spaces known as osteoctic lacunae
  • 46.
     Osteocyte cytoplasmicprojections (known as dendrites)extend through cylindrical encased compartments referred as canaliculi  Osteocytes maintain contact with adjacent osteocytes, osteoblasts or lining cells on the bone surfaces  The osteocyte network is therefore an extracellular and intracellular communication channel that is sensitive to shear stress as the result of mechanical stimuli and bone deformation
  • 48.
     Osteocytes translatemechanical signals into biochemical mediators that will assist with the orchestration of anabolic and catabolic events within bone Canalicular–lacunar system arrangement allows osteocytes to 1. Participate in the regulation of blood calcium homeostasis and 2. Sense mechanical loading and transmit this information to other cells within the bone to further orchestrate osteoblast and osteoclast function (Burger et al. 1995; Marotti 2000).
  • 49.
     Failure ofany part of this interconnecting system results in hypermineralization (sclerosis) and death of the bone.  Later may be resorbed and replaced during the process of bone turnover
  • 50.
    Four schemes havebeen proposed to explain how an osteoblast could get trapped within bone matrix Osteoblasts are unpolarized and lay down bone in all directions, i.e. the cells become trapped in their own secretions. Individual osteoblasts are polarized, but those within same generation are polarized differently to those in adjacent layers. As a result, bone is deposited in all directions &osteoblasts become trapped. Osteoblasts of each generation are polarized in the same direction. One generation buries the preceding one in bone matrix. Within one generation, some osteoblasts slow down rate of bone deposition or stop laying down bone, so that they become trapped by the secretion of their neighboring cells.
  • 51.
    Osteoclast  Greek wordsfor “bone and broken”.  Specialized multinucleated cells(approx 40–100 μm in diameter with 15 to 20 nuclei)  Lie in resorption bays called Howship’s lacunae  Variable in shape due to their motility  Tartrate resistant acid phosphatase within its cytoplasmic vesicles and vacuoles which distinguishes it from multinucleated giant cells.  Adjacent to the tissue surface cell membrane of the osteoclast form ruffled border
  • 52.
     At theperiphery of this border, the plasma membrane is apposed closely to the bone surface, and the adjacent cytoplasm, devoid of cell organelles, is enriched in actin, vinculin, and talin This is clear or sealing zone
  • 53.
    Formation of osteoclast Derived from hemopoietic cells of monocyte macrophage lineage.  The differentiation into osteoclasts - involving cell–cell interaction with osteoblast stromal cells  Formation of osteoclast requires the presence of RANK ligand (receptor activator of nuclear factor κB) and M-CSF (macrophage colony stimulating factor).- produced by stromal cells and osteoblasts direct contact of these cells and osteoclast precursors.
  • 54.
     M-CSF acton receptor on osteoclast precursors c-Fms (colony stimulating factor 1 receptor) and provides signals for proliferation  RANKL binds to RANK on surface of M-CSF triggered osteoclast precursors into multinucleated giant cells, their differentiation into mature osteoclasts, their attachment to bone surface and their activation to resorb bone.
  • 55.
     Osteoprotegerin (OPG)recognizes RANKL, and blocks the interaction between RANK and RANKL, leading to an inhibition of osteoclast differentiation and activation  Cbfa1 contributes to the expression of OPG
  • 56.
    Regulation of osteoblast •PTH is secreted in response to a hypocalcemic signal in order to regulate calcium homeostasis by promoting bone resorption, Role of parathormone (PTH) • Stimulates synthesis of osteocalcin and osteopontin by osteoblasts and suppresses collagen production • Bone resorption at high concentrations (pharmacological) and support bone formation at low (physiologic) concentrations. Vitamin D3 • Required for attaining normal bone mass mediated by IGF-I. Growth hormone
  • 57.
    • Targets osteoblast& stimulates bone formation & mineralization Insulin • A subgroup of the TGF- β superfamily. • Initiate osteoblastogenesis from uncommitted progenitor cells. • BMPs 2, 4 and 6 direct the pluripotent cells to commit to an osteoblastic pathway Bone morphogenetic proteins • Promote differentiation of osteoblasts & bone matrix formation • Prolonged treatment with glucocorticoids results in bone loss Glucocorticoids • Promoting osteogenesis. • It acts as a potent mitogen for all cells of mesenchymal origin PDGF (platelet derived growth factor)
  • 58.
    • Early stageto recruit & stimulate osteoprogenitor cells to proliferate, providing a pool of early osteoblasts • Later stages of osteoblast blocks differentiation and mineralization. TGF-β • Increase proliferation and stimulating mature osteoblast function IGF I and II (insulin like growth factors) • Play a critical role in angiogenesis and mesenchymal cell mitogenesis FGF-2 is expressed by osteoblasts- bone formation FGF (fibroblast growth factors)
  • 59.
    Regulation of osteoclast •Suppresses the production of bone resorbing cytokines including IL-1 & IL-6 • Estrogen deficiency results bone resorption by increasing osteoclast activity Estrogen • Vitamin D3 promotes the differentiation of osteoclasts from monocyte macrophage stem cell precursors - enhanced osteoclastic bone resorption • PTH binds to osteoblasts and induces the production of M-CSF and RANKL- - stimulate the maturation and action of osteoclasts. Vitamin D3 and parathyroid hormone (PTH) • Inhibits proliferation and differentiation of osteoclast precursors. • Reduces the dimension of ruffled border & dissociation into monocytic cells. Calcitonin
  • 60.
    • Suppress boneresorption via injury to osteoclasts when they solubilize bisphosphonate contaminated bone without consistent reduction in osteoclast numbers Bisphosphonates • Mediators of bone resorption and can also influence bone formation • Induce osteoclast formation through increased expression of RANKL on the surface of immature osteoblasts and stromal cells PGE2 (Prostaglandins of E series) • Stimulates differentiation of osteoclast progenitors into osteoclasts TNFα • An inhibitor of osteoclast formation OCIL (osteoclast inhibitory lectin) • Inhibit proliferation and differentiation of committed precursors into mature osteoclasts. TGF-β and interferon-γ
  • 61.
    Structural lines inbones • The site of change from bone resorption to bone formation is represented by a scalloped outline • Rich in sialoproteiin & osteopontin Reversal line or cementing line • Rythmic deposition of bone with periods of relative quiescence seen as parallel vertical lines Resting line
  • 62.
    ALVEOLAR BONE The alveolarprocess is defined as that part of the maxilla and the mandible that forms and supports the sockets of the teeth. –Orbans The alveolar bone is constituted strictly of the ALVEOLAR PROCESS which is firmly attached to the basal bone of the jaws – Tencate The alveolar process is the portion of the maxilla and mandible that forms and supports the tooth sockets (alveoli). – Carranza
  • 63.
    Functions of alveolarbone  Houses the roots of teeth  Anchors the roots of teeth to the alveoli, achieved by the insertion of Sharpey’s fibers into the alveolar bone proper.  Helps to move the teeth for better occlusion  Helps to absorb & distribute occlusal forces  Supplies vessels to periodontal ligament.  Houses & protects developing permanent teeth, while supporting primary teeth.  Organizes eruption of primary and permanent teeth.
  • 64.
    DEVELOPMENT OF ALVEOLARPROCESS  At the end of 2nd month of fetal life, the maxilla as well as mandible forms a groove that open to surface of oral cavity  Tooth germs contained in these groove (alveolar vessels & nerve)  Alveolar process consists of bone which is formed both by cells from the dental follicle (alveolar bone proper) & cells which are independent of tooth development
  • 65.
    Permanent tooth movesinto place, developing its own alveolar bone from its own follicle When a deciduous tooth is shed, its alveolar bone is resorbed. Alveolar process gradually incorporated into maxillary or mandibular body. With the onset of root formation - interradicular bone develops in multirooted teeth. Teeth separated from each other by the development of interdental septa. The developing teeth lie in a trough of bone -Tooth Crypt. Resorption - inner wall of the alveolus/ Deposition -outer wall. Alveolar process develops from the dental follicle during eruption of tooth size of the alveolus is dependent upon the size of the growing tooth germ.
  • 66.
    STRUCTURE OF THEALVEOLAR BONE  Anatomically, no distinct boundary exists between the body of the maxilla or the mandible and alveolar processes.  As a result of its adaptation to function, two parts of the alveolar process can be distinguished, The alveolar bone proper and The supporting alveolar bone
  • 67.
    Alveolar bone Supporting alveolar bone Corticalplate Spongy bone Alveolar bone proper
  • 69.
    Alveolar bone proper Consists partly of lamellated & partly of bundle bone  About 0.1–0.4 mm thick.  Surrounds the root of the tooth and gives attachment to principal fibers of the periodontal ligament
  • 70.
    Lamellated bone  Containsosteons each of which has a blood Vessel in a haversian canal.  Blood vessel is surrounded by concentric Lamellae to form osteon.  Some lamellae of the lamellated Bone are arranged roughly parallel to the surface of the Adjacent marrow spaces, whereas others form haversian systems.
  • 71.
    Bundle bone  Bonein which the principal fibers of the periodontal ligament are anchored  The term ‘bundle’ because, the bundles of the principal fibers continue into the bone as Sharpey’s fibers  Characterized by the scarcity of the fibrils in the intercellular substance and arranged at right angles to Sharpey’s fibers  Contains fewer fibrils than does lamellated bone
  • 72.
     Sharpey’s fibersare mineralized at the periphery and have a larger diameter.  These fibers are less numerous than the corresponding fiber bundles in the cementum
  • 73.
     Radiographically, itis also referred to as the lamina dura, because, of increased radiopacity, which is due to the presence of thick bone without trabeculations
  • 74.
     The alveolarbone proper, which forms the inner wall of the socket is perforated by many openings that carry branches of the interalveolar nerves and blood vessels into the periodontal ligament, and it is therefore called the cribriform plate
  • 75.
     Bone betweenthe teeth is called interdental septum  Composed entirely of cribriform plate.  The interdental and interradicular septa contain the perforating canals of Zuckerkandl and Hirschfeld (nutrient canals) which house the interdental and interradicular arteries, veins, lymph vessels and nerves
  • 76.
    Supporting alveolar bone Consistsof two parts Cortical plates Spongy bone
  • 77.
    Cortical plates  Consistof compact bone and form the outer and inner plates of the alveolar processes  Continuous with the compact layers of the maxillary and mandibular body  Thinner in the maxilla, than in the mandible  Thickest in the premolar and molar region on buccal side of the lower jaw  The supporting bone usually very thin in anterior teeth region of both jaws – no spongy bone
  • 78.
     Histologically, thecortical plates consist of longitudinal lamellae and haversian systems.  In the lower jaw, circumferential or basic lamellae reach from the body of the mandible into the cortical plates
  • 79.
    Spongy bone  Spongybone fills the area between the cortical plates and the alveolar bone proper  Contains trabeculae of lamellar bone- surrounded by marrow that is rich in adipocytes and pluripotent mesenchymal cells  The trabeculae contain osteocytes in the interior and osteoblasts or osteoclasts on the surface  Trabeculae buttress the functional forces to which alveolar bone proper is exposed
  • 80.
    Classification of thespongiosa (radiographically ) Type I the interdental and interradicular trabeculae are regular and horizontal in a ladder like arrangement - most often in the mandible Type II shows irregularly arranged, numerous, delicate interdental and interradicular trabeculae more common in the maxilla
  • 81.
    lnterdental Septum  Theinterdental septum consists of cancellous bone and cortical plates  If the interdental space is narrow, the septum may consist of only lamina dura (between mandibular 2ndpremolars and 1stmolars consists of only lamina dura in 15% cases)  If roots are too close together, an irregular "window" can appear in the bone between adjacent roots
  • 82.
     The mesiodistalangulation of the crest of the interdental septum usually parallels a line drawn between the cemento-enamel junctions of the approximating teeth  The distance between the crest of the alveolar bone and the CEJ in young adults varies between 0.75 and 1.49 mm (average, 1.08 mm)  This distance increases with age to an average of 2.81 mm
  • 83.
    Osseous topography  Normallyconforms to the prominence of the roots  The height and thickness of the facial and lingual bony plates are affected by the alignment of the teeth, by the angulation of the root to the bone, and by occlusal forces
  • 84.
    Fenestrations and Dehiscences Isolated areas in which the root is denuded of bone and the root surface is covered only by periosteum and overlying gingiva are termed as fenestrations  In these instances the marginal bone is intact  When the denuded areas extend through the marginal bone, the defect is called a dehiscence  Fenestration and dehiscence are important, because they may complicate the outcome of periodontal surgery.
  • 85.
  • 86.
    • They occurmore often on the facial bone than on the lingual, are more common on anterior teeth than on posterior teeth, and are frequently bilateral. • Prominent root contours, malposition, and labial protrusion of the root combined with a thin bony plate are predisposing factors.(Elliot JR,Bowers GM)
  • 87.
    Bone formation  Theosteo progenitor cells express transcription factors cbfa1/Runx2. cbfa1(osteoblast specific transcription factors) Osterix and b- catenin (maturation)  Osteoblast contains high level of alkaline phosphatase- liberated phosphate - initiation and progressive growth of bone mineral crystals  Cytoplasm is intensely basophilic, abundant and well developed protein synthetic organelles such as rough endoplasmic reticulum
  • 88.
     Procollagen andother organic proteins synthesized and transported to golgi complex by transfer vesicle  Golgi complex form secretory vesicles and secret extracellularly along the bone forming surface to form osteoid(prebone)  Osteoblasts produces Collagen type I, collagen type V and non collagenous protein such as bone sialoprotein and osteopontin- where they participate in regulating mineral deposition
  • 89.
    BONE RESORPTION Sequence ofevents in resorptive process Attachment of osteoclasts to mineralized surface of bone Creation of a sealed acidic environment through action of the proton pump which demineralizes bone and expose organic matrix Degradation of the exposed organic matrix to its constituents amino acids by action of released enzymes such as acid phosphatase and cathepsin Sequestering of mineral ions and amino acids within the osteoclast Ten Cate AR
  • 90.
    Role of TRAPin bone resorption( tartarate resistant acid phosphatase) latent inactive proenzyme-cysteine proteinases convert it into an active form Extracellular role: Regulate osteoclast adhesion to the bone Degrades the phosphoprotein-degradation of the bone matrix Liberate pyrophosphate (inhibitor)osteoclast migration Intracellular role:  Endocytosed vesicle & TRAP containing vesicle fuses to form functional secretory domain (FSD)
  • 91.
    Extra cellular fate: TRAP taken up into circulation from interstitial space  Bind with 2 macroglobulin  Loses binuclear iron centre and recycled  Free enzymes metabolized in liver & excreted through urine
  • 92.
    Various bone resorbingfactors A. Systemic factors: (a) Parathyroid hormone (b) Parathyroid related peptide (c) Vitamin D3 (d) Thyroid hormone B. Local factors: (a) Prostanoids (b) Lipoxygenase metabolites (c) Cytokines: IL – 1, IL – 4, TNF – α, TNF – β, IL – 6 C. Growth factors: (a) EGF (b) TGF – α (c) TGF − β (d) PDGF D. Bacterial factors: (a) Lipopolysaccharides (b) Capsular material (c) Peptidoglycans (d) Lipoteichoic acids.
  • 93.
    Bone modeling  Bonemodeling is defined as a change in the shape and architecture of the bone  It extends from embryonic bone development to the pre-adult period of human growth, which is continuous and covers a large surface  The ability of bone to adapt to mechanical loads is brought about by continuous bone resorption and bone formation  If these processes occur at different locations, the bone morphology is altered, Frost defined this as modeling (Frost, 1990a)
  • 94.
    Bone remodeling  Boneremodeling is defined as a change without concomitant change in the shape and architecture of the bone  In a homeostatic equilibrium resorption and formation are balanced In that case old bone is continuously replaced by new tissue  This ensures that the mechanical integrity of the bone is maintained but it causes no global changes in morphology, Frost defined this as remodeling (Frost, 1990b)
  • 95.
     In ahealthy individual, this turnover is in a steady state; that is, the amount of bone lost is balanced by bone formed.  Remodeling occurs in discrete, focal areas involving groups of cells called bone remodeling or basic multicellular units.
  • 96.
  • 98.
     As osteoclastsmove through compact bone, they create a resorption channel. The leading edge of resorption is termed the cutting cone and is characterized by a scalloped array of resorption lacunae (Howship’s lacunae), each housing an osteoclast  Behind the cutting cone is a migration of mononucleated cells (macrophages and/or preosteoblasts) differentiate into osteoblasts, The entire area of the osteon where active bone formation occurs is termed the filling cone  When formation is complete, the haversian canal contains a central blood vessel and a layer of inactive osteoblasts, the lining cells that communicate by means of cell processes with the embedded osteocytes.
  • 100.
    Remodeling of alveolarbone  Major pathway of bony changes in shape, resistance to forces, repair of wounds and calcium-phosphate homeostasis  Involves the co-ordination of activities of cells from two distinct lineages, the osteoblasts and the osteoclasts  A complex process involving hormone and local factors acting in autocrine and paracrine manner on generation and activity of differentiated bone cells
  • 101.
    Coupling  It isinterdependency of osteoblasts and osteoclasts in remodeling of the bone. Parathyroid hormone OSTEOBLASTS Interleukin 1 and 6 Releases leukemia inhibiting factor (LIF) Monocytes Multinucleated OSTEOCLASTS (Resorb bone) Bound to collagen OSTEOBLASTS (Deposits bone) Stimulates Release Stimulates Migrates into bone and coalasces Releases osteogenic substrates Stimulates differentiation of
  • 102.
    Age changes In olderindividuals:  Alveolar sockets appear jagged and uneven.  The marrow spaces have fatty infiltration  The alveolar process in edentulous jaws decreases in size.  Loss of maxillary bone is accompanied by increase in size of the maxillary sinus.  Internal trabecular arrangement is more open, which indicates bone loss.  The distance between the crest of the alveolar bone and CEJ increases with age—approximately by 2.81 mm.
  • 103.
    Conclusion  Bone isa mineralized connective tissue with a relatively flexible character and compressive strength  The property of plasticity allows it to be remodeled according to the functional demands placed on it.  In order to maintain stability and integrity of bone, it constantly undergoes remodeling.  About 10% of bone material is renewed each year.  This process is brought about by osteoclasts and osteoblasts.
  • 104.
    References  Newman ,Takei, Klokkevold , Carranza ; Carranza's Clinical Periodontology ,10thedition,  Newman ,Takei , Klokkevold , Carranza; Carranza's Clinical Periodontology , 12th Edition.  Niklaus P. Lang , Jan Lindhe , Clinical Periodontology And Implant Dentistry ,6thedition  Orban's Oral Histology And Embryology , 13th Edition ,  Antonio Nancy, Ten Cate Oral Histology Development , Structure And Function , 8th edition
  • 105.

Editor's Notes

  • #12 Intramembranous bone formation. A, Coarse woven bone. The bone is cellular and disorganized. B, Immature bone. The bone is less cellular and slightly more organized; some primary osteons are forming. C, Mature lamellar bone. The tightly packed osteons create an organized bone matrix; fewer cells and little loose connective tissue are apparent. As remodeling of the bone in its mature state takes place, the periosteal bone surface becomes more regular and eventually will be covered with circumferential lamellae.
  • #14 Endochondral bone formation. A, Chondroblasts develop in primitive mesenchyme and form an early perichondrium and cartilage model. B, The developing cartilage model assumes the shape of the bone to be formed, and a surrounding perichondrium becomes identifiable. C, At the midshaft of the diaphysis the perichondrium becomes a periosteum through the development of osteoprogenitor cells and osteoblasts, the osteoblasts producing a collar of bone by intramembranous ossification. Calcium salts are deposited in the enlarging cartilage model. D, Blood vessels grow through the periosteum and bone collar, carrying osteoprogenitor cells within them. These cells establish a primary (or diaphyseal) ossification center in the center of the diaphysis. E, Bony trabeculae spread out from the primary ossification center to occupy the entire diaphysis, linking up with the previously formed bone collar, which now forms the cortical bone of the diaphysis. At this stage the terminal club-shaped epiphyses are still composed of cartilage. F, At about term (the precise time varies between long bones), secondary or epiphyseal ossification centers are established in the center of each epiphysis by the ingrowth along with blood vessels of mesenchymal cells, which become osteoprogenitor cells and osteoblasts. (From Stevens A, Lowe J: Human histology, ed 3, London, 2005, Mosby Elsevier.)
  • #17 carbonate content and low Ca/P ratio than the pure hydroxyapatite
  • #18 Types III and XII collagen fibers:- fibroblast Types I, V and XII collagens are expressed by osteoblasts
  • #37 the body can convert yellow marrow back to red marrow to increase blood cell production
  • #53 Osteoclasts with many nuclei resorb more bone than osteoclasts with few nuclei
  • #56 RANKL belongs to the TNF (tumor necrosis factor) family RANK is homotrimeric TNF receptor family member
  • #57 Osteoprotegerin (OPG) is a member of the TNF receptor family and is expressed by osteoblasts
  • #78 X-rays must penetrate and not to any increased mineral content.
  • #84 cancellous component in maxilla is more than in the mandible
  • #100 The bone multicellular unit has one resorption front (left) characterized by the presence of osteoclasts (OC) and one formation front (right) characterized by the presence of osteoblasts (OB).
  • #102 Bone remodeling. The bone remodeling cycle involves a complex series of sequential steps that are highly regulated. The “activation” phase of remodeling is dependent on the effects of local and systemic factors on mesenchymal cells of the osteoblast lineage. These cells interact with hematopoietic precursors to form osteoclasts in the “resorption” phase. Subsequently, there is a “reversal” phase during which mononuclear cells are present on the bone surface. They may complete the resorption process and produce the signals that initiate bone formation. Finally, successive waves of mesenchymal cells differentiate into functional osteoblasts, which lay down matrix in the “formation” phase. (Source: McCauley & Nohutcu 2002. Reproduced from the American Academy of Periodontology.)
  • #103 osteoblasts, they deposit onto the resorbed bone surface a thin “coating” of noncollagenous matrix proteins termed the cement or reversal line. This layer is composed of at least bone sialoprotein and osteopontin and acts as a cohesive, mineralized layer between the old bone and the new bone that will be formed on top of the cement line by these same osteoblasts