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Introduction Structure of alveolar bone Development Chemical composition Bone histology Bone remodeling Age changes The alveolar process is that part of the jaw bones in which teeth are found defined as the part of maxilla or mandible that forms and supports the socket of the teeth in which the teeth are anchored Houses the roots of teeth Anchors the roots of teeth to the alveoli, which is achieved by the insertion of sharpey’s fibers into the alveolar bone proper It furnishes a media for attachment of periodontal ligament Supplies vessels to PDL Helps to absorb and distribute occlusal forces generated during tooth contact Houses and protects developing permanent teeth, while supporting primary teeth Organises eruption of primary and permanent teeth For its development & maintenance Morphology of Alv. Bone depends on Size Shape position of teeth If teeth are lost, Alv bone undergoes atrophy If teeth congenitally missing – Alv. Bone not developed Two Parts: Alveolar Bone proper: Thin lamellated bone that surrounds the root of the tooth Gives attachment to the PDL Fibres Supporting alveolar Bone: Surrounds the alveolar bone Proper Gives support to the socket That lines the socket Forms the inner wall Thickness- 0.1 to 0.5mm Two Parts: Bundle bone Lamellated bone Lamellated Bone Bundle bone Cribriform plate Lamina Dura Immature bone Undergoes continous remodelling Tooth PL Histologic Name Provides attachment to PDL fibres Bundles of Principle fibres are inserted as- Sharpey’s fibres Anatomical name Inner wall of the socket is perforated by many openings- carry branches of the interalveolar nerves and bld vessels nto PDL Holes/canals – Volkman’s Canals Radiologic name Alv bone –appears as radiopaque line Due to overlapping effect of X-Rays Periodontal and periapical pathologies In histological sections, the layer of cribriform plate appears to stain more intensely The bundle bone is the most important part -tooth support important structure in the radiographic interpretation of periodontal and periapical pathologies. Two Parts Cortical Bone/plate Spongiosa Compact bone Forms inner &outer plates of the alveolar process Variations: Maxilla –thinner Mandible -Thicker Premolar, Molar region – Thicker Anterior region -Thin Buccal cortical plate – Thinner Lingual Cortical plate -Thick Relation to Local anaesthesia maxilla perforated by many openings Infiltration is sufficient Mandible Dense cortical plate Nerve Blocks required The cortical plate consists of surface layers of lamellar bone supported by compact Haversian system The outer surfaces of these cortical plates are covered by periosteum different types of lamellae - circumferential, concentric and interstitial lamellae The cortical plates are continuous with the compact bones of the maxilla and mandibular body The cortical plates are continuous with the compact bones of the maxilla and mandibular body. The cortical plate and the alveolar bone proper meet at the alveolar crest located usually 1.5 to 2mm below the level of cemento-enamel junction of the tooth. Fills the area between the cortical plates and the alveolar bone proper cancellous bone It is composed of irregular interlacing bony trabeculae, each consisting of one or more lamellae with osteocytes enclosed in lacunae The inter trabecular spaces - filled with yellow marrow rich in adipose cells or sometimes red or haemopoietic marrow Type I Trabeculae – Regular Horizontal Thick Ladderlike Mandible Trajectorial pattern Along lines of stress Type II Irregular Fine/Delicate No specific arrangement thin Maxila No trajectory pattern’\,More marrow space Zuckerkandl &Herschfeld Interdental &Interradicular septum Contain –BV, lymph vessels and nerves Appear as radioluscent linera shadows Parallel to long axis of tooth 2nd month of fetal life, the maxilla and mandible forms a groove that is open toward the surface of the oral cavity Alveolar bone is formed during fetal growth by intramembraneous ossification As the developing tooth germs reach the bell stage, developing bone becomes closely related to the tooth germ to form the alveolus The size of the alveolus - the size of the growing tooth germ Resorption - inner wall of the alveolus Deposition - outer wall the teeth become separated from each other by development of inter dental septa the onset of root formation- interradicular bone develops in multi rooted teeth Bone is mineralized connective tissue By weight 60% inorganic material, 25% organic material 15% water By volume 36% of bone is composed of inorganic material, 36% organic material 28% water Inorganic component - carbonated, hydroxyl apatite small plates Organic matrix – (90%)collagen &(10%)Non collagenous proteins collagen -type I collagen, type III and type V collagen osteoblasts Non collagenous proteins- proteoglycans glycoproteins(osteocalcin, osteonectin,osteopontin,alopsolein, thrombopondin and fibronectin ) All bones have dense outer sheet of compact bone & central medullary cavity. Medullary cavity – Red or yellow bone marrow & network of bone trabaculae. Compact bone has 2 surfaces: a) Periosteum(outer aspect): Fibrocollagen layer, which is divided into 2 layers Outer - irregular connective tissue, fibrous layer Inner - consist of bone cells, their precursor and rich vascular supply. b) Endosteum – inner surface covered by a thin cellular layer present in both compact & cancellous bone. histologically, both the compact and the trabecular bone consists of lamellae Three types of lamellae : circumferential concentric interstitial lamellae In spongy bone the lamellae are apposed to each other to form trabeculae The trabeculae - 50 microns thick aligned along the lines of stress to withstand the force applied to the bone In young bone the marrow - red In old bone, the marrow - yellow a.Ostegenenic cells derived - mesenchymal(ectomesenchymal) stem cells, osteoprogenitors, preosteoblasts, osteoblasts and osteocytes form and maintain the bone b.Osteoclasts resorb bone derived _ monocytes macrophages form part of hematopoietic system Bone forming cells & are found on the outer surface of the bone Produce organic matrix of bone(osteoid) The matrix is deposited around the cell bodies Periosteum serves as an important reservoir of osteoblasts mononucleated cells mesenchymal origin a layer of cuboidal cells on the surface of bone bone formation is taking place a prominent, round nucleus located at the basal end & cytoplasm contain rich synthetic organelles synthetic cells of the bone secretion of the organic matrix of bone i.e. osteoid and also in process of mineralization of matrix controlling influence in activating osteoclasts OSTEOBLASTS Formation of new bone Regulation & control of bone remodeling Regulation & control of mineral metabolism Important role in mineralization of osteoid Once osteoblasts have completed their function, they are either entrapped in bone matrix & become osteocytes or remain on the surface as lining cells surfaces of the adult skeleton contain only few cell organelles They are regarded as post proliferative osteoblasts protect the bone from resorptive activity of osteoclasts They can be reactivated to form osteoblasts Entrapped osteoblasts cells Usually about 15% of osteoblasts become embedded in the organic matrix as osteocytes Approximately 25,000 osteocytes can be seen per cubic mm of bone Woven bone show more osteocytes than lamellar bone Osteocytes are present within the lacunae Narrow extensions of these lacunae form channels – canaliculi Osteocytic processes are present within these canaliculi Through this canaliculae, osteocytes maintain contact with adjacent osteocytes, osteoblasts and lining cells Osteocytes are regarded as the main mechanoreceptors of bone Osteocytes are thought to be capable of taking part in bone resorption -osteocytic osteolysis OSTEOCYTES Osteoclast Cells that resorb bone by removing the mineralized matrix of bone Multinucleated cells (10-20) , can be mononucleated Origin: Circulating monocytes or macrophage easily seen under light microscope The cell body is irregularly oval and may show many branching processes. Location: Howships lacunae the size -100microns in diameter Location: Howships lacunae Arrangement –usually in clusters Content: Abundant golgi, mitochondria, lysosomes but little RER. Acid phosphatase Function – resorb bone The life span of osteoclasts is thought to be about 10-14 days The cell membrane of the osteoclast that lies adjacent to resorbing bone surface - number of deep folds that form the ruffled -large surface area for the resorptive process The cytoplasm adjacent to the ruffled border is devoid of cell organelle but contains numerous contractile actin microfilaments -clear zone clear zone or sealing zone serve to attach the cell very closely to the surface of bone and create a microenvironment in which resorption can take place without diffusion of the hydrolytic enzymes produced by the cell into adjacent tissue. 1. 2. 3. 4. 5. 6. 7. Osteoprotegerin Estrogen Vitamin D3 & parathyroid hormone Calcitonin TNF-β & interferon-γ Osteoclast inhibitory lectin biophosphonates Initially, the mineral phase is removed and later the organic matrix A sealed acidic microenvironment is created in the resorption lacunae which dissolves the mineral crystals in bone and exposes the organic matrix The process by which the over all size and shape of bone is established -bone remodeling Extends from embryonic bone development to the preadult period of human growth Bone is laid down rhythmically; there are periods of active deposition and quiescence which result in formation of regular parallel incremental lines, called resting lines The resting lines are formed in periods of relative quiescence (rest period) Simultaneous with bone deposition bone is resorbed along the endosteal surface at focal points During the growing phase of a child- bone deposition & resorption - increase in bone mass During adult phase- the amount of bone deposition bone resorption - bone mass is more or less constant In old age and in diseases like osteoporosis bone deposition is generally less when compared to resorption therefore there is an overall decrease in bone mass The replacement of old bone, by new bone bone turn over In rapidly growing children bone turn over 30-100%. The rate of bone turn over decreases in adults The rate of cortical bone turn over- 5% per year trabecular bone and endosteal surface of cortical bone - 15% per year The old and new bone is separated by a distinct curved hematoxiphilic line with its convexity facing the old bone. These lines are called - reversal lines indicators of continuous remodeling of bone As age advances alv.bone facing PDL becomes irregular Osteoporotic changes Decreased metabolic rate, vascularity, healing capacity Cancellous bone becomes dense with coarse trabecular pattern Teeth are lost- undergoes gradual atrophy
