Alveolar bone

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ALVEOLAR BONE Presented by- Dr. Rahul Ahirrao Junior Resident-1 Dept. of Prosthodontics


CONTENTS Introduction Function Composition Vascular, Lymphatic & Nerve supply Development Parts of alveolar process Gross histology of alveolar bone Remodelling and Resorption Age changes of alveolar bone Residual ridge resorption Pathological fate of alveolar bone Prosthodontic considerations References


INTRODUCTION Bone is a metabolically active organ, composed of both mineral and organic phases. Specially 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.

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


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 supporting primary teeth.

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Organizes successive eruptions of primary and permanent teeth. Important reservoir for minerals.


COMPOSITION OF ALVEOLAR BONE Alveolar bone Inorganic (67%) Organic(33%) Hydroxyapatite Magnesium Trace elements- nickel, iron. Collagen 28% Type 1 Non- collagenous proteins 5% Osteonectin , Osteocalcin , Phosphoproteins & Proteoglyacans .


VASCULAR, LYMPHATIC AND NERVE SUPPLY Blood supply: Inferior and superior alveolar arteries of maxilla & mandible. Lymphatic drainage: Submandibular lymph nodes. Nerve supply: Maxilla – anterior,middle and posterior branches of superior alveolar nerve. Mandible – branches from the inferior alveolar nerve.


DEVELOPMENT OF ALVEOLAR BONE The alveolar bone develops as the tooth develops. Initialy , 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 root of the tooth.

Dev.of alveolar process:

Dev.of alveolar process Forming Alveolar bone Horse-shoe shaped groove Formed by growth of facial and lingual plates At 1 st developing tooth germs lie in the groove Bony septa develop 8 th week in utero

Alv. Bone proper:

Alv . Bone proper Formed by the outermost cells of the dental follicle Bony matrix/ osteoid Differentiate into osteoblasts Some osteoblasts osteocytes Embedded Matrix Bone Calcifies

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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 alvelolar bone proper and they erupt from a position lingual or inter- radicular from a level within the basal bone” SCOTT-1968

Gross appearance of Alveolar bone:

Gross appearance of Alveolar bone

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 function:

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

Alveolar bone proper:

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

Supporting alveolar bone:

Supporting alveolar bone It surrounds the alveolar bone proper and gives support to the socket. 2 parts – a) Cortical plates – It consists of compact bone and form the outer and inner plates of the alveolar process. b) Spongy bone – It fills the area between these corticle plates and alveolar bone proper.

Spongy bone:

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 often seen 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.

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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/Alveolar septum:

Interdental /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 – contains 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

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.

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.

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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.


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


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

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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.

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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 Remodeling and Resorption:

Bone Remodeling and Resorption 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 changes in the initial bone architecture. It has been suggested that external demands such as load on bone tissue may initiate modeling .

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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 remodeling that occurs in order to allow replacement of old bone with new bone involves 2 processe - resorption and formation. Except during growth- there is a balance between bone formation and bone resorption .

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Bone remodelling takes place in- Tooth eruption Migration of teeth mesially Orthodontic tooth movement Changes in tooth position during mastication.

Dense bone remodelling:

Dense bone remodelling

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 .

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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 the bony changes in shape, resistance to forces, repair of wounds and Ca and PO4 homeostasis in the body.

Age changes of alveolar bone:

Age changes of alveolar bone In growing persons- bone formation overweighs bone resorption . In an adults- 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.

Residual ridge resorption (RRR):

Residual ridge resorption (RRR) Resiadual ridge resorption is chronic, progressive, irreversible, cumulative, multifactorial , biomechanical disease that results from a combination of anatomic, metabolic and mechanical determinants. After teeth loss, alveolar bone undergoes rapid remodeling , which results in bone loss.

Factors affecting bone resorption rate:

Factors affecting bone resorption rate Anatomical – size of ridge following extraction. - type of residual bone - type of mucoperiosteum - location with in oral cavity. Metabolic - Age - sex - diet - hormonal status Functional - Frequency,direction and amount of force applied to ridge. Prosthetic factor – type of denture base - forms and type of teeth - interocclusal distance

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Initiation of resorption is not completely known. It may be due to dying or dead osteocytes that stimulate the connective tissue, resulting in osteoclast’s in the area. Thomas, Stahl and Pedleton consider alveolar ridge resorption as normal biologic process that increases with age. Townsley in 1948 stated that bones have intrinsic growth pattern and it is possible that the alveolar bone may have a hereditory resorption pattern.

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In 1971, Atewood described RRR as “Major oral disease entity” characterised by loss of oral bone after the extraction of teeth. The size, shape and tolerance of residual ridges provides the basis of stability, retention and support of complete denture. According to Atwood D.A. – Class I – Pre-extraction. Class II – post-extraction : immediately following exfoliation of tooth with, the labial and lingual alveolar process remaining.

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3. Class III – High well rounded : The sharpe edges will be rounded OFF by the external osteoclastic activities leaving a high well rounded residual ridge. 4. Class IV – Knife edge : As resorption continues from both labial and lingual aspects the crest of ridge becomes increasingly narrow finally results in knife edge. 5. Class V – Low well rounded : The knife edge shortens and finally leaving low well rounded or flat ridge. 6 . Class VI – Depressed : Further resorption leaving only the thin cortical bone in lower border of body of maxilla.

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A. Tallgren in 1972 stated that means reduction in lower anterior ridge height is approximately four times as great as that of upper ridge. Tallgren stated that RRR  1⁄damping effect of the mucosa

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Clayton F. Parkinson in 1978 stated that Arch width of maxilla is less than mandible in molar region by 6-7 mm. Alveolar resorption rate is highest in early stages of edentulism and slows with loss of bone, longevity of edentulsm and the attendant wearing dentures. Winkler observed that RRR  Anatomic factor⁄Time + Bone resorption factore⁄Bone formation factors + Force factors⁄Damping Effects

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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 alveolar ridges. Tooth displacement, failure of eruption, impaired mastication and speech difficulties.

Fibrous dysplasia:

Fibrous dysplasia Painless enlargement of the affected bone. Teeth remains firm but may be displaced. Radiographic feature-”ground glass appearance”.


Osteosarcoma Common symptoms- Swelling Pain Loosening of teeth Paresthesia


Chondrosarcoma Symptoms- painless mass or swelling Loosening of teeth

Paget’s desease (osteitis deformans):

Paget’s desease ( osteitis deformans ) Results in enlargement of the middle third of the face. Lion like facial deformity- leontiasis ossea . Grossly enlarged alveolar ridge-causes spacing of the teeth.

Cleidicranial dysplasia:

Cleidicranial dysplasia Characteristic feature- Narrow high arched palate. Prolonged retention of deciduous teeth. Delay or failure of eruption of permanent teeth.


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’.

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Characterized by enlargement of the jaws. Radiographically - Loss of lamina dura surrounding the roots of the teeth, Ground glass appearance i.e. decreased 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 Marked increased in bone density Bone marrow is replaced by dense bone Tooth eruption is always delayed.


Osteoporosis Osteoporosis is a systemic disease in the elderly. Shows a decreased 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.

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Edentulous bony anatomy include: Profound bone loss

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Slow ,progressive thinning of the jaw bones

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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)

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There is an anterior displacement of the mandible (protrusive position) because of residual ridge reduction, mandibular rotation(changes in the angulation of the body relative to the mandibular ramus ), and deposition of bone in the mental region. Reduction in the residual ridge 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 The alveolar ridge vary greatly in size and shape and their form is dependent on the following factors: Developmental structure : The individual variation in bone size and its degree of calcification. The size of the natural teeth : Large teeth are usually suppoerted by bulky ridge, small teeth by narrow ridges.

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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.

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5. The rate and degree of resorption : During the 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 there after it continues throughout life. 6. The effect of previous dentures : ill-fitting 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 favourable 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.

High V-shaped palate usually associated with thick bulky ridges:

High V-shaped palate usually associated with thick bulky ridges This may be an unfavourable formation because: The forces of adhesion are not at right angles to the surfaces 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 unfavourable 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 favourable formation because: The 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 undercut pain and soreness will result and if it is eased, food will lodge under the denture. The easing of the peripheral 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 unfavourable because: The pressure of the denture during clenching and mastication on the sharp ridge will cause pain. Adhesion and cohesive forces are negligible.

Flat and atrophic ridges:

Flat and atrophic ridges These are unfavourable 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 contact.

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ALVEOLAR BONE (From fixed partial denture point of view)

Residual ridge contour:

Residual ridge contour The edentulous areas where a fixed prosthesis is to be provided may be overlooked during the treatment planning phase. Unfortunate, 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.

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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.

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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.

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

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

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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. 1. 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.

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

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

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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.

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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 implant of 4.0mm crestal diameter usually require more than 5.0mm of bone width to ensure sufficient bone thickness and blood supply around the implant for predictable survival. These diamensions provide more than 0.5mm 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 from implants of 4.0mm crestal diameter usually require a minimum mesio -distal length of 7mm.

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 ridge and wider root from implants a modification upto 30 degree can 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 size or shape 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.

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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.

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

Misch bone density classification:

Misch bone density classification D1 Dense cortical bone D2 Thick dense to porous cortical bone on crest and coarse trabecular bone within D3 Thin porous cortical bone on crest and fine trabecular bone within D4 Fine trabecular bone D5 Immature,nonmineralised bone

Anatomic location of bone density types (% occurence):

Anatomic location of bone density types (% occurence ) Bone Anterior Maxilla Posterior maxilla Anterio Mandible Posterior Mandible D1 0% 0% 6% 3% D2 25% 10% 66% 50% D3 65% 50% 25% 46% D4 10% 40% 3% 1%

Radiographic bone density:

Radiographic bone density CT scan can determine bone density precisely. Each CT image has pixel and each pixel has a CT number ( Housefield unit). Higher the housefield unit, denser the tissue. D1 >1250 Housefield units D2 850-1250 Housefield units D3 350-850 Housefield units D4 150-350 Housefield units D5 <150 Housefield units


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

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Book of Oral Histology (6 th edition) Tencate . Complete Denture Prosthodontics (3 rd edition) J.J.Sharry . Oral and Maxillofacial Pathology (2 nd edition) Neville.

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