ALVEOLAR BONE1

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Presentation Transcript

ALVEOLAR BONE : 

ALVEOLAR BONE DR SUNNY JAIN

CONTENTS : 

CONTENTS INTRODUCTION. CLASSIFICATION. COMPOSITION. FUNCTIONS. VASCULAR, LYMPHATICS AND NERVE SUPPLY. PARTS OF THE ALVEOLAR PROCESS. DEVELOPMENT. GROSS HISTOLOGY OF BONE. CELLS OF BONE. BONE REMODELLING AND RESORPTION.

Slide 3: 

PROSTHODONTIC CONSIDERATIONS. PATHOLOGICAL FATE OF ALVEOLAR BONE. AGE CHANGES IN BONE. REVIEW OF LITERATURE. REFERENCES.

INTRODUCTION : 

INTRODUCTION Bone is a metabolically active organ, composed of both mineral and organic phases. Exquisitely designed for its role as the load bearing structure of the body, it is formed from a combination of dense, compact and cancellous (trabecular) bone that is reinforced at points of stress.

Slide 5: 

Alveolar bone is a specialised part of the maxillary and mandibular bones that forms the primary support structure for teeth. Although fundamentally comparable to other bone tissues in the body, alveolar bone is subjected to continous and rapid remodeling associated with tooth eruption and subsequently , the functional demands of mastication.

Slide 6: 

I. Depending on gross appearance Long bones Flat bones Short bones Irregular bones Pneumatic bone CLASSIFICATION OF BONE.

Slide 7: 

II. Depending upon the maturity/ histology of bone Mature bone Immature bone Woven bone Coarsely fibered bundle bone

Slide 8: 

III. Bone can also be classified as Both are lamellar bone Compact/ dense bone Spongy bone/ trabaecular bone/ cancellous bone

COMPOSITION OF ALVEOLAR BONE : 

COMPOSITION OF ALVEOLAR BONE Bone Inorganic (67 %) Organic (33%) Hydroxyapatite Magnesium Trace elements-nickel, iron. Collagen 28% Non- collagenous proteins 5% Osteonectin, Osteocalcin, Phosphoproteins & proteoglycans Type I

Slide 10: 

FUNCTIONS. The bone holds the tooth firmly in position to masticate and, for the lower jaw, transmits the muscle-powered movements of the body of the mandible. Adapts the strength and orientation of attachment to varying load. Helps to move the teeth for better occlusion. Supplies vessels for the PDL & cementum. Houses & protects developing permanent teeth while suppporting primary teeth. Organizes successive eruptions of primary & secondary teeth. Important reservoir for minerals.

Boundaries : 

Boundaries Anatomically: No distinct boundary Certain areas -Alveolar bone fused with basal bone Anterior maxillary region- palatine process fuses with the oral plate of alveolar process Posterior Mandibular region.

VASCULAR, LYMPHATICS AND NERVE SUPPLY : 

VASCULAR, LYMPHATICS AND NERVE SUPPLY Blood Supply : inferior and superior alveolar arteries of maxilla & mandible. Lymphatics drainage : submandibular lymph nodes. Nerve supply : branches from anterior , middle and posterior superior alveolar nerve innervate alveolar bone of maxilla & branches from the the inferior alveolar nerve innervate the mandible.

Slide 13: 

GROSS APPEARANCE OF ALVEOLAR BONE.

Slide 14: 

The cortex of the basal bone of either mandible or maxilla continues around the alveolar process as either the outer (OCP) or the inner (ICP) cortical plate. The alveolar bone of these outer and inner plates is composed of hard, lamellar (arranged in thin plates) bone. A - Alveolus B B - Basal Bone

Slide 15: 

“Alveolar Bone is that part of maxilla and mandible that forms and supports the teeth”

Slide 16: 

Alveolar Bone forms the bony sockets of the jaw bones in which the roots of the natural teeth are suspended by the attachment of the periodontal ligament fibers (“Gomphosis” - Greek “Bolting together”). Some alveolar bone is formed during tooth development, but the majority of alveolar bone formation occurs during tooth eruption.

Slide 17: 

The presence of alveolar bone in the jaw bones is totally dependent on the roots of the natural teeth; without the teeth the alveolar bone need not exist.

ALVEOLAR PROCESS. : 

ALVEOLAR PROCESS. Is the portion of the maxilla and mandible that forms and supports the tooth sockets (alveoli). It forms when the tooth erupts to provide the osseous attachment to the forming periodontal ligament and disappears gradually after the tooth is lost.

Depending on adaptation to functionAlveolar process : 

Depending on adaptation to functionAlveolar process Alveolar bone proper Supporting alveolar bone Cortical plates Spongy bone

Slide 20: 

Alveolar bone proper consists of a thin lamella of bone that surrounds the root of the tooth and gives attachment to principal fibres of the periodontal ligament.

Slide 21: 

Supporting alveolar bone surrounds the alveolar bone proper and gives support to the socket. 2 parts- cortical plates, which consists of compact bone and form the outer and inner plates of the alveolar processes. the spongy bone, which fills the area between these plates and the alveolar bone proper.

Slide 22: 

Spongy bone 2 types Type 1-the interdental and interradicular trabeculae are regular and horizontal in a ladder like arrangement often seen in mandible. Type 2- shows irregularly arranged, numerous, delicate interdental and interradicular trabeculae. more common in maxilla.

CRIBRIFORM PLATE : 

CRIBRIFORM PLATE Anatomical name Resembles a fine holed sieve Histologically, alveolar bone proper contains a series of openings through which neurovascular bundles link the periodontal ligament with the central component of alveolar bone i.e. the cancellous bone.

Slide 24: 

On the labial surfaces of anterior teeth, the outer cortical plate of alveolar bone is very thin and fused to the cribriform plate, and spongy bone is notably absent.

INTERDENTAL SEPTUM/ ALVEOLAR SEPTUM. : 

INTERDENTAL SEPTUM/ ALVEOLAR SEPTUM. Is that part of the alveolar process which separates the individual alveoli. Found between two teeth. Contains the perforating canals of Zuckerkandl and Hirschfeld (nutrient canals) which house the interdental and interradicular arteries, veins, lymph vessels and nerves.

Interradicular septum : 

Interradicular septum Situated between 2 roots. Alveolar bone not fused- contain spongiosa.

Bundle Bone : 

Bundle Bone Histologic Name Entity of alveolar bone proper. Provides attachment to PDL fibres. Bundles of Principal fibres are inserted as- Sharpey’s fibres.

LAMINA DURA : 

LAMINA DURA Radiologic term. Used to describe the radiopaque line representing the cribriform plate of the alveolus i.e. the alveolar bone proper.

Alveolar Crest : 

Alveolar Crest Rim of the alveolar socket. Most prominent border of interdental septum. Terminating close to and parallel with the contours of the cemento-enamel junction. Alveolus Rim Floor

Bone Development. : 

Bone Development. Occurs by 3 main mechanisms- Endochondral- cartilage replaced by bone. Intramembranous- occurs directly in mesenchyme. Sutural.

Endochondral bone formation. : 

Endochondral bone formation. Occurs at the extremities of all long bones, vertebrae, ribs and at the articular extremity of the mandible and base of the skull. Early embryonic development Condensation of mesenchymal cells Cartilage cells Formation of perichondrium around periphery Differentiate

Slide 32: 

As differentiation of cartilage cells proceed towards the metaphysis, the cells organise into longitudinal columns. 3 functionally different zones Zone of proliferation Zone of hypertrophy and maturation Zone of provisional mineralisation Cells constitute a source of new cells Broadest zone Increased hypertrophy Secretion of proteoglycans Matrix environment for mineral deposition breakdown Elaboration of matrix vesicles Matrix mineralization begins Formation of calcium phosphate phospholipid complexes Calcification of Longitudinal cartilage septa

Slide 33: 

ZONES/LAYERS OF THE GROWTH PLATE Expansion Osteoclasts stop the trabeculae from forever extending Erosion new bone on calcified cartilage

Slide 34: 

Cartilage is replaced by bone. There is no transformation of cartilage into bone

Intramembranous Ossification : 

Intramembranous Ossification Formation of the bone matrix within the fibrous membrane Osteoblasts begin to secrete osteoid; it is mineralized within a few days Trapped osteoblasts become osteocytes

Slide 36: 

Formation of an ossification center in the fibrous membrane Centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming the ossification center

Slide 37: 

Formation of the woven bone and the periosteum Accumulating osteoid forms a network which encloses local blood vessels Vascularized mesenchyme forms on the external face of woven bone to become periosteum

Slide 38: 

Bone collar of compact bone forms Trabeculae just deep to the periosteum thicken, forming a woven collar which is later replaced with mature lamellar bone Spongy bone persists internally and its vascular tissue becomes red marrow

Slide 39: 

ENDOCHONDRAL vs INTRAMEMBRANOUS OSSIFICATION Spine, ribs, limb bones, and the cranial base form first from mesenchyme as small pieces of hyaline cartilage, which is mostly replaced by bone Jaw, facial bones, and the clavicles start as mesenchyme, which turns directly into osteoblasts & bone ENDOCHONDRAL INTRA-MEMBRANOUS

Sutural bone growth. : 

Sutural bone growth. Sutures are the fibrous joints between bones. Function -permit the skull and face to accommodate growing organs. Sutures have same osteogenic potential as periosteum and connects 2 periosteal surfaces. Osteogenic layer-cambium Inner layer- capsule.

DEVELOPMENT OF ALVEOLAR BONE. : 

The Alveolar bone develops as the tooth develops. Initially, bone forms a thin eggshell of support, the bony crypt, around each tooth germ. Gradually, as the roots grow and lengthen, the alveolar bone keeps pace with the elongating erupting tooth and maintains relationship with each tooth root. DEVELOPMENT OF ALVEOLAR BONE.

Slide 42: 

Dev. Of alv. Process….8th week in utero Forming alv. bone Horse - shoe shaped groove Formed by growth of facial & lingual plates At 1st developing tooth germs lie in the groove Bony septa develop

Slide 43: 

Alv. Bone proper …… formed by the outermost cells of the dental follicle Differentiate into osteoblasts Bony matrix / osteoid Some osteoblasts embedded osteocytes Matrix calcifies Bone

Slide 44: 

The development of the alveolar process and the alveolar bone proper must wait till the completion of the resorption of the roots and alveolar socket of deciduous teeth. “germs of the permanent teeth develop in deep seated crypts completely enclosed by bone, excluding alveolar bone proper and they erupt from a position lingual or interradicular from a level within the basal bone”-SCOTT-1968.

Gross histology of bone : 

Gross histology of bone Characteristic of all bones are a dense outer sheet of compact bone and a central medullary cavity. In living bone the cavity is filled with either red or yellow bone marrow. The marrow cavity is interrupted, particularly at the ends of long bones, by a network of bone trabeculae (cancellous or spongy bone). Whether compact or trabecular, it consists of microscopic lamellae, 3 distinct types of lamellae are found – Circumferential, Concentric and Interstitial.

Slide 46: 

Circumferential lamellae enclose the entire adult bone, forming its outer perimeter. Concentric lamellae make up the bulk of compact bone and form the basic metabolic unit of bone, the osteon. Interstitial lamellae are interspersed between adjacent concentric lamellae and fill the spaces between them.

An Osteon : 

An Osteon Each osteon is a group of hollow tubes of bone matrix Each matrix tube is a lamella Collagen fibers in each layer run in opposite directions-resists torsion stresses.

Slide 48: 

In the center of each osteon is a canal, the Haversian canal which is lined by a single layer of bone cells that cover the bone surface, each canal houses a capillary. Adjacent haversian canals are interconnected by Volkmann canals (channels that contain blood vessels).

Slide 49: 

Surrounding every compact bone is an osteogenic (bone forming) connective tissue membrane, the periosteum – consists of two layers. Inner layer next to the bone surface consist of bone cells, their precursors and rich microvascular supply. Outer layer termed as fibrous layer due to presence of dense, irregular connective tissue.

Slide 50: 

Both the internal surfaces of compact bone and cancellous bone are covered by a single layer of bone cells, the endosteum, which physically seperates the bone surface from the bone marrow within.

LAMELLAR BONE : 

LAMELLAR BONE

WOVEN BONE. : 

WOVEN BONE. Newly formed bone does not have a lamellar structure. The collagen fibres are present in bundles that run in different directions. Because of this interlacing of fibres, it is termed as woven bone.

BONE CELLS. : 

BONE CELLS. Responsible for the formation, resorption and maintenance of osteoarchitecture. OSTEOGENIC CELLS- which form and maintain bone. They include osteoprogenitors, preosteoblasts, osteoblasts, osteocytes and bone lining cells. OSTEOCLASTS- which resorb bone.

OSTEOPROGENITOR CELLS. : 

OSTEOPROGENITOR CELLS. These are stem cells of mesenchymal origin that can proliferate and convert themselves into osteoblasts whenever there is need for bone formation. They resemble fibroblast in appearance.

Osteoblasts. : 

Osteoblasts. Arise from pluripotent stem cells. Mononucleated cells that synthesize collagenous and noncollagenous bone matrix proteins which accumulates as an uncalcified matrix called osteoid that acts as a scaffold for the deposition of the apatite crystals of bone. Exhibit high levels of alkaline phosphatase on the outer surface of plasma membrane.

Slide 57: 

Osteoblasts form membrane over the bony surface along with adjacent cells to control mineral homeostasis and bone viability. Produce type I and type V collagen, Phosphoproteins, cytokines, growth factors, and proteases which degrade and remodel the matrix. Secrete BMP superfamily including BMP-2 and BMP-7 in addition to the IGF-1 and IGF-2, PDGF and FGF. These combinations are used to speed healing and bone growth.

OSTEOCYTES. : 

OSTEOCYTES. As osteoblasts secrete bone, some of them become entrapped within the bone- osteocytes. More rapid bone formation –more osteocytes present per unit volume. Space in the matrix occupied by an osteocyte- osteocytic lacunae. Narrow extensions of these lacunae form canaliculi, that house radiating osteocytic processes.

osteocyte Gap junction osteoblast Osteocyte-osteoblast complex Through these channels osteocytes maintain contact with adjacent osteocytes and with the osteoblasts. This osteocyte-osteoblast complex maintain mineralised bone matrix integrity and vitality and prevent hypermineralisation of bone by pumping calcium into the blood stream. It moves calcium and inorganic phosphate in and out of mineral pool.

Slide 61: 

OSTEOCLAST* Multinucleated Ruffled border agitating released enzymes & acid Eaten-out hole is a Howship’s lacuna Sealing ring of tight attachment to bone Eosinophilic Large cell

Slide 62: 

Characterized cytochemically by possessing tartrate resistant acid phosphatase within its cytoplasmic vesicles. At the periphery of ruffled border, plasma memrane is apposed closely to the bone surface and the adjacent cytoplasm is enriched in fibrillar contractile proteins. This clear or sealing zone attaches the cells to the mineralized surface and isolates a microenvironment between them and the bone surface.

Slide 63: 

BONE LINING CELLS When bone is no longer forming…..surface osteoblasts become inactive ….. Lining cells. Thin flat nucleus, few cytoplasmic organelles.. Mitochondria, ribosomes & isolated profiles of rough ER. Retain gap junctions with osteocytes….functions to control mineral homeostasis & endure bone vitality.

Slide 64: 

Once bone has formed, the new mineralized tissue starts to be reshaped and renewed by the processes of resorption and apposition modeling and remodeling. Modeling…… a process that allows a change in the initial bone architecture. It has been suggested that external demands such as load on bone tissue may initiate modeling. Bone Remodeling and Resorption

Slide 65: 

Remodeling …. represents a change that occurs within the mineralized bone without a concomitant alteration of the architecture of the tissue. Is the major pathway of bony changes in shape, resistance to forces, repair of wounds, and Ca and PO4 homeostasis in the body.

Slide 66: 

During bone formation remodeling enables the substitution of the primary bone (woven bone), which has low load bearing capacity, with lamellar bone which is more resistant to load. Bone remodelling that occurs in order to allow replacement of old bone with new bone involves 2 processes – resorption and formation. Except during growth….a balance between bone formation and resorption

Slide 67: 

Bone remodeling takes place in : Tooth eruption Migration of teeth mesially Orthodontic tooth movement Changes in tooth position during mastication

Bone Resorption : 

Bone Resorption Is the removal of mineral and organic components of the extracellular matrix of bone under the action of osteolytic cells i.e. osteoclasts.

Slide 70: 

3 steps: -Formation of the osteoclast progenitors in the haematopoietic tissues followed by their vascular dissemination & generation of resting preosteoblasts and osteoclasts. -Osteoclast activation at the surface of mineralized bone. -Resorption of bone by activated osteoclasts.

Reversal Phase : 

Reversal Phase After the maximum eroded depth has been achieved by the osteoclasts, there is a reversal phase that lasts for 9 days. Hypothesis- Since the osteoclasts has a limited life span….cell probably undergoes apoptosis following an extensive episode of resorptive activity. Secondly, the accumulation of calcium directly controls osteoclast activity. A third possibility is that the release of related peptides from the matrix during the resorption process……… inactivates osteoclasts and osteoblasts.

PROSTHODONTIC CONSIDERATIONS. : 

PROSTHODONTIC CONSIDERATIONS.

ALVEOLAR BONE (FROM COMPLETE DENTURE POINT OF VIEW) : 

ALVEOLAR BONE (FROM COMPLETE DENTURE POINT OF VIEW)

Slide 74: 

Edentulous bony anatomy include: Profound bone loss

Slide 75: 

Slow, progressive thinning of the jaw bones

Slide 76: 

Remodeling changes occur in the mandible that account for the typical edentulous facial anatomy. The overall length of the mandible does not decrease but may in fact increase as new bone is added to the mental protuberance, thus accentuating the chin point.

EDENTULOUS INTRAORAL BONY CHANGES : 

EDENTULOUS INTRAORAL BONY CHANGES The loss of teeth means not only the loss of the clinical crown but also the supporting tissues, the periodontal ligament and alveolar bone. When the alveolar bone is lost, the resultant residual ridge is progressively resorbed throughout the life of the individual (Atwood, 1971).

Slide 78: 

There is an anterior displacement of the mandible (protrusive position) because of residual ridge reduction, mandibular rotation (Change in the angulation of the body relative to the mandibular ramus), and deposition of bone in the mental region. Reduction in the residual ridges occurs in an inferior direction in the molar and premolar areas, but in both an inferior and lingual direction in the incisor region. There is generalized thinning of the anterior and posterior aspects of the mandibular ramus.

ALVEOLAR RIDGES : 

ALVEOLAR RIDGES Developmental Structure: The individual variation in bone size and its degree of calcification. The size of the natural teeth: Large teeth are usually supported by bulky ridges, small teeth by narrow ridges. The alveolar ridges vary greatly in size and shape and their form is dependent on the following factors:

Slide 80: 

The amount of bone lost prior to the extraction of the teeth: Periodontal disease results in the destruction of the alveolar process. If the natural teeth are retained until gross alveolar loss has occurred the resultant alveolar ridges will be narrow and shallow. The amount of alveolar process removed during the extraction of the teeth: During extraction the buccal alveolar plate is fractured and removed with the tooth.

Slide 81: 

The rate and degree of resorption: During the first six weeks after the extraction of the teeth the rate of resorption is rapid. During the second six weeks it begins to slow down. At the end of three months,the immediate post-extraction resorption is complete and thereafter it continues throughout life. The effect of previous dentures: ill-fitting dentures, or dentures occluding with isolated groups of natural teeth, may cause rapid resorption of the alveolar process in the areas where they cause excessive load or lateral stress.

MAXILLARY DENTURE-BEARING AREA : 

MAXILLARY DENTURE-BEARING AREA Well-developed but not abnormally thick ridges and a palate with a moderate vault. This is a favorable formation because: The center of the palate presents an almost flat horizontal area and this will aid adhesion. The roomy sulcus allows for the development of a good peripheral seal. The well-developed ridges resist lateral and antero-posterior movement of the denture.

Slide 83: 

High V-shaped palate usually associated with thick bulky ridges. This may be an unfavorable formation because: The forces of adhesion and cohesion are not at right angles to the surface when counteracting the normal displacing forces of gravity and so peripheral seal is essential.

Flat palate with small ridges and shallow sulci. : 

Flat palate with small ridges and shallow sulci. This may be an unfavorable formation because: The ill-developed or resorbed ridges do not resist lateral and antero-posterior movement of the denture. The sulci being shallow do not form a good peripheral seal, unless the width of the denture periphery is adequate.

Ridges exhibiting undercut areas. : 

Ridges exhibiting undercut areas. These are unfavorable because: frequently the flanges of the denture need to be trimmed in order to be able to insert it and this may reduce the effectiveness of the peripheral seal.

MANDIBULAR DENTURE-BEARING AREA : 

MANDIBULAR DENTURE-BEARING AREA Broad and well developed ridges. This is a favorable formation because: It provides a large area on which to rest the denture and prevents lateral and anteroposterior movement. The surface presented for adhesion is as large as it can ever be in a lower jaw. The lingual, labial and buccal sulci are satisfactory for developing a close peripheral seal.

Ridges exhibiting undercut areas. : 

Ridges exhibiting undercut areas. These are unfavorable because: If the denture is not eased away from the undercuts pain and soreness will result and if it is eased, food will lodge under the denture. The easing of the periphery will reduce the surface area of mucosal contact and will affect the peripheral seal adversely.

Well developed but narrow or knife like ridges : 

Well developed but narrow or knife like ridges These are unfavorable because: The pressure of the denture during clenching and mastication on the sharp ridge will cause pain. Adhesive and cohesive forces are negligible

Flat and atrophic ridges. : 

Flat and atrophic ridges. These are unfavorable because: No resistance is offered to anteroposterior or lateral movements. Frequently found to have resorbed to the level of attachments of the mylohyoid, genioglossus and buccinator muscles and if the denture base is made sufficiently narrow so as not to encroach on these structures, its area is too small for the denture to function correctly. When the area is increased to encroach on the muscles they may move the dentures when they contract.

ALVEOLAR BONE (FROM FIXED PARTIAL DENTURE POINT OF VIEW) : 

ALVEOLAR BONE (FROM FIXED PARTIAL DENTURE POINT OF VIEW)

Slide 91: 

The edentulous areas where a fixed prosthesis is to be provided may be overlooked during the treatment planning phase. Unfortunately, any deficiency or potential problem that may arise during the fabrication of a pontic is often identified only after the teeth have been prepared or even when the master cast is ready. RESIDUAL RIDGE CONTOUR

Slide 92: 

Proper preparation includes a careful analysis of the critical dimensions of the edentulous areas: Mesiodistal width. Buccolingual diameter. Occlusocervical distance. Location of the residual ridge.

Slide 93: 

The contour of the edentulous ridge should be carefully evaluated during the treatment planning phase. An ideally shaped ridge has a smooth, regular surface of attached gingiva, which facilitates maintenance of a plaque-free environment. Its height and width should allow placement of a pontic that appears to emerge from the ridge and mimics the appearance of the neighboring teeth. Facially, it must be free of frenum attachment and of adequate facial height to sustain the appearance of interdental papillae.

Slide 94: 

Siebert has classified residual ridge deformities into three categories: Class I defects- faciolingual loss of tissue width with normal ridge height. Class II defects- loss of ridge height with normal ridge width. Class III defects- a combination of loss in both dimensions.

Slide 95: 

Loss of residual ridge contour may lead to unesthetic open gingival embrasures (“Black triangles”), food impaction, and percolation of saliva during speech.

Slide 96: 

Surgical Modification Although residual ridge width may be augmented with hard tissue grafts, this is usually not indicated unless the edentulous site is to receive an implant. Roll technique uses soft tissue from the lingual side of the edentulous site. The epithelium is removed, and the tissue is thinned and rolled back, thereby thickening the facial aspect of the residual ridge.

Slide 97: 

Pouches may be prepared in the facial aspect of the residual ridge, into which subepithelial or submucosal grafts may be inserted.

Slide 98: 

Interpositional graft is a wedge-shaped connective tissue graft which is inserted into a pouch preparation on the facial aspect of the residual ridge.

ALVEOLAR BONE FROM IMPLANTOLOGY POINT OF VIEW : 

ALVEOLAR BONE FROM IMPLANTOLOGY POINT OF VIEW

AVAILABLE BONE : 

AVAILABLE BONE Available bone describes the amount of bone in the edentulous area considered for implantation and is measured in: Height. Width. Length Angulation. Crown-Implant body ratio.

AVAILABLE BONE HEIGHT : 

AVAILABLE BONE HEIGHT The height of available bone is measured from the crest of the edentulous ridge to the opposing landmark, such as maxillary sinus, mandibular canal, maxillary nares, inferior border of the mandible, maxillary canine eminence region etc.

Slide 102: 

The minimum height of the available bone for endosteal implants is in part related to the density of the bone. The more dense bone may accommodate a shorter implant. The minimum bone height for a predictable long-term endosteal implant survival is 10mm.

AVAILABLE BONE WIDTH : 

AVAILABLE BONE WIDTH Width is measured between the facial and lingual plates at the crest of the potential implant site. The crest is supported by a wider base. The root form implants of 4.0 mm crestal diameter usually require more than 5.0 mm of bone width to ensure sufficient bone thickness and blood supply around the implant for predictable survival. These dimensions provide more than 0.5 mm bone on each side of the implant at the crest.

AVAILABLE BONE LENGTH : 

AVAILABLE BONE LENGTH The mesio-distal length of available bone in an edentulous area is often limited by adjacent teeth or implants. The root form implants of 4.0 mm crestal diameter usually require a minimum mesio-distal length of 7 mm.

AVAILABLE BONE ANGULATION : 

AVAILABLE BONE ANGULATION Ideally the bone angulation should be such that the long axis of the implant can be placed parallel to the long axis of the restoration. In edentulous areas with wide ridge, and wider root form implants a modification upto 30 degrees can be achieved.

CROWN-IMPLANT BODY RATIO : 

CROWN-IMPLANT BODY RATIO The crown height is measured from the occlusal or incisal plane to the crest of the ridge and the endosteal implant height from the crest of the ridge to its apex. The greater the crown height, the greater the lever arm with any lateral force.

DIVISIONS OF AVAILABLE BONE : 

DIVISIONS OF AVAILABLE BONE Division A (Abundant Bone) Division B (Barely Sufficient Bone) Division C (Compromised Bone) Division D (Deficient Bone)

VARIABLE BONE DENSITY- WHY? : 

VARIABLE BONE DENSITY- WHY? Cortical and trabecular bone are constantly modified by either Modeling or Remodeling. In Bone modeling there is independent sites of formation and resorption and results in the change of the shape or size of bone. In Bone remodeling the resorption and formation are at the same site that replaces previously existing bone and primarily affects the internal turnover of bone.

Slide 109: 

These adaptive phenomena of modeling and remodeling of bone have been associated with the alteration of the mechanical stress environment within the host bone. MacMillan and Parfitt noted that Bone is most dense around the teeth. Density of bone around the crest region is more compared to the regions around the apices. Generalized trabecular bone loss occurs in regions around a tooth from a decrease in mechanical stress.

Slide 110: 

Frost reported a model of four zones for compact bone as it is related to mechanical adaptation to stress Pathologic overload zone Mild overload zone Adapted window zone Acute disuse window zone

MISCH BONE DENSITY CLASSIFICATION : 

MISCH BONE DENSITY CLASSIFICATION

ANATOMIC LOCATION OF BONE DENSITY TYPES (% OCCURRENCE) : 

ANATOMIC LOCATION OF BONE DENSITY TYPES (% OCCURRENCE)

RADIOGRAPHIC BONE DENSITY : 

RADIOGRAPHIC BONE DENSITY CT scan can determine bone density precisely. Each CT image has pixels and each pixel has a CT number (Housefield unit). Higher the Housefield unit, denser the tissue.

FATE OF ALVEOLAR BONE : 

FATE OF ALVEOLAR BONE PATHOLOGICAL

HISTIOCYTOSIS X : 

HISTIOCYTOSIS X Bone lesion appears as sharply “Punched-out” lytic defect, often with irregular margins. The posterior mandible is the most common site. Mild dull pain is commonly present. Alveolar bone involvement leads to severe horizontal bone loss.

CHERUBISM : 

Widening and distortion of the alveolar ridges. Tooth displacement, failure of eruption, impaired mastication and speech difficulties. CHERUBISM

FIBROUS DYSPLASIA : 

FIBROUS DYSPLASIA Painless enlargement of the affected bone. Teeth remain firm but may be displaced. Radiographic feature- ‘ground glass appearance’.

OSTEOSARCOMA : 

OSTEOSARCOMA Common symptoms- Swelling Pain Loosening of teeth Paresthesia.

CHONDROSARCOMA : 

CHONDROSARCOMA Symptoms-painless mass or swelling-loosening of teeth.

OSTEITIS DEFORMANS (Paget’s Disease) : 

OSTEITIS DEFORMANS (Paget’s Disease) Results in enlargement of the middle third of the face. Lion like facial deformity-leontiasis ossea. Grossly enlarged alveolar ridges-causes spacing of the teeth.

CLEIDOCRANIAL DYSPLASIA : 

CLEIDOCRANIAL DYSPLASIA Characteristic features- Narrow high arched palate, prolonged retention of deciduous teeth delay or failure of eruption of permanent teeth.

HYPERPARATHYROIDISM : 

HYPERPARATHYROIDISM Increased production of parathyroid hormone results in a generalized disorder of calcium, phosphate and bone metabolism. Patients have the classic triad of signs and symptoms- ‘Stones, Bones and Abdominal Groans’

Characterized by enlargement of the jaws.Radiographically,- loss of lamina dura surrounding the roots of the teeth-ground glass appearance i.e. decrease in trabecular density and blurring of the normal trabecular pattern. : 

Characterized by enlargement of the jaws.Radiographically,- loss of lamina dura surrounding the roots of the teeth-ground glass appearance i.e. decrease in trabecular density and blurring of the normal trabecular pattern.

OSTEOGENESIS IMPERFECTA. : 

OSTEOGENESIS IMPERFECTA. Clinical features- Opalescent dentin Due to maxillary hypoplasia, increased prevalence of class III malocclusion.

OSTEOPETROSIS : 

OSTEOPETROSIS Marked increase in bone density Bone marrow is replaced by dense bone Tooth eruption is always delayed.

Slide 126: 

Osteoporosis is a systemic disease in the elderly. Shows a decrease in the skeletal mass without alteration in the chemical composition of bone. Loss of the spongy spicules of bone that support the weight bearing parts of the skeleton can be seen in radiographs of regions of the skeleton that bear heavy loads. In edentulous patients, reduction of the residual ridge is important factor in affecting denture support, retention, stability, and masticatory function. OSTEOPOROSIS

AGE CHANGES IN BONE. : 

AGE CHANGES IN BONE. In growing persons- bone formation overweighs bone resorption. In an adult the two processes are in equilibrium. In the aged, the resorption may not be compensated by production of bone resulting in osteoporosis. It is difficult to separate age changes from bone changes.

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Jowsey(1960) by microradiographic studies showed that young persons have a high degree of both bone formation and resorption. In young adults, there is little of both, while in persons over 70 years of age, as much as 25 percent of bone may be engaged in resorptive processes. Reifenstein(1950) stated that ‘osteoporosis in some degree may be normal after menopause’. REVIEW OF LITERATURE.

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Ortman(1962) stated that ‘it is not improbable that the ridge may show resorption in connection with a generalized osteoporosis’. Some authors (Thomas,1946; Pendleton,1940) consider ridge resorption a normal biologic process that increases with advancing age. There is no definitive evidence indicating that resorption is inevitable in the aged and many elderly patients have excellent alveolar ridges even though they may be veteran denture wearers.

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Bones have an intrinsic growth pattern (Townsley,1948) and it is possible that bone may have a hereditary resorption pattern. Factors such as hormones, vitamins, pressure, age and heredity may influence ridge resorption. Consideration of these factors and prevention of excessive alveolar resorption will aid in the success of prosthodontic treatment.

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Bone is a very active organ. In an adult it is continuously renewed and capable of complete repair. The process involves the dissolution of existing mineral content with resorption of the extracellular matrix and formation of the new matrix. The process of bone resorption and bone formation is very carefully regulated by both systemic hormones and local factors. The density of available bone in an edentulous site is a determining factor in treatment planing , surgical approach, healing time , implant design, and initial progressive loading during prosthetic reconstruction.

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Essentials of Complete Denture Prosthodontics (2nd edition) Sheldon Winkler. Contemporary Implant Dentistry (2nd edition) Carl E. Misch. Boucher’s Prosthodontic Treatment for Edentulous Patients (11th edition) George A. Zarb Fundamentals of Fixed Prosthodontics (3rd edition) Herbert T. Shillingburg Textbook of Human Histology(4th edition) Inderbir Singh References

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Book of Oral Histology(6th edition) Tencate Complete Denture Prosthodontics(3rd edition) John J Sharry Orban’s Oral Histology and Embryology(11th edition) S.N.Bhaskar Oral and Maxillofacial Pathology(2nd edition) Neville Colour Atlas and Textbook of Oral Anatomy Berkovitz

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