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PRESENTED BY: JUHI SAINI MDS IST PROF

INTRODUCTION According to Orbans . . . The alveolar bone is defined as that

part of the MAXILLA & MANDIBLE that forms & supports the sockets of the teeth. According to Tencate . . . The alveolar bone is constituted

strictly of the ALVEOLAR PROCESS which is firmly attached to the basal bone of the jaws.

BASED ON DEVELOPMENT

ENDOCHONDRAL

INTRAMEMBRANOUS

1.COMPACT (CORTICAL) BASED ON THEIR MICROSCOPIC STRUCTURE MATURE 2.CANCELLOUS (SPONGY) 2.IMMATURE (WOVEN)

ALVEOLAR BONEThe part of the maxilla or mandible that supports and protects the teeth is known as alveolar bone.

Alveolar bone functions as a mineralised supporting tissue, giving attachment to muscles, providing a framework for bone marrow, and acting as a reservoir for ions (especially calcium).

One of the most important biological properties of bone is its "plasticity', allowing it to remodel according to the functional demands placed upon it. Alveolar bone is dependant on the presence of teeth for its development and maintenance. Where teeth are congenitally absent (as in anodontia), alveolar bone is poorly developed. Alveolar bone requires functional stimuli to maintain bone mass. Thus, following tooth extraction, it atrophies.

STRUCTURE OF ALVEOLAR BONEThe maxilla and mandible of the adult human can be subdivided into two portions: (a) The alveolar process that involves in housing the roots of erupted teeth and (b) The basal body that does not involve in housing the roots.

Cortical plate Supporting alveolar bone Spongy bone Alveolar bone proper

Alveolar bone

As a result of its functional adaptation, two parts of the alveolar process can be distinguished. The FIRST consists of thin lamellae of bone that surrounds the root of the tooth and gives attachment to the principal fibers of periodontal ligament. This is ALVEOLAR BONE PROPER. The SECOND part is the bone, which surrounds the alveolar bone proper and gives support to the socket. This has been called SUPPORTING ALVEOLAR BONE

SUPPORTING ALVEOLAR BONE

1.CORTICAL PLATE, which consists of

2.SPONGY BONE, which fills area between these

compact bone and forms outer and inner plates of alveolar processes.

plates and alveolar bone proper, also known as cancellous bone.

ALVEOLAR BONE ROLESIt holds tooth firmly in position to masticate. Adapts the strength to varying load. Helps to move the teeth in better occlusion. Houses and protects developing permanent tooth germs while supporting the teeth. Supplies vessels for PDL and cementum.

Together with root cementum and periodontal membrane, the alveolar bone constitutes the attachment apparatus of the teeth. The main function is to distribute and reabsorb forces generated by forces of mastication and other tooth contacts .

CORTICAL PLATESCortical plates are continous with compact layer of the maxillary and mandibular body, and are generally much thinner in maxilla than in mandible. They are thickest in the premolar and molar regions of the lower jaw, especially on buccal side.

In the maxilla the outer cortical plate is perforated by many small openings through which blood and lymph vessels pass.

In the region of the anterior teeth of both the jaws, the supporting bone is usually very thin. No spongy / cancellous bone is found here, and the cortical plate is fused with the alveolar bone proper. In such areas, notably in premolars and molar regions of the maxilla, defects of the outer alveolar wall are fairly common. Histologically, cortical plates consist of longitudinal lamellae and haversian system. I In the lower jaw, circumferential or basic lamellae reach the body of the mandible into the cortical plates.

INTERDENTAL SEPTA Interdental septa consist of cancellous bone bordered by the

socket wall cribriform plates of approximating teeth and facial and lingual cortical plates. The interdental septa are bony partition that separate adjacent

alveoli coronally at cervical region, the septa are thinner and here the cortical plates are fused and cancellous bone is frequently missing.

The mesiodistal and faciolingual dimension and shape of the

interdental septum are governed by the size and convexity of the crowns of the approximating teeth , as well as by the position of the teeth in the jaw and their degree of eruption.(Ritchey B, Orban) The interdental and interradicular septa contain the perforating

canals of Zuckerkandl and Hirschfeld which house interdental or interradicular arteries, veins, lymph vesels and nerves.

SPONGY / CANCELLOUS BONE

It fills the area between the cortical plates and the ABP.

Radiographic studies permit the classification of spongiosa of the alveolar process into two main types; Type 1: The interdental and interradicular trabeculae are regular and horizontal in a ladder like arrangement. Seen most commonly in the mandible.

Type 2:

Shows irregularly arranged numerous delicate interdental and interradicular trabeculae. Although, functionally satisfactory, lacks a distinct trajectory pattern which seems to be compensated by greater number of trabeculae in any given area. This type of arrangement is more common in maxilla.

Wide variations occur in trabecular pattern which is affected by

occlusal forces. Maxilla has more cancellous bone than mandible.

BUNDLE BONE (LAMINA DURA) AND CRIBRIFORM PLATE Bundle bone is the part of alveolar bone, into which the

extrinsic collagen fiber bundles of the PDL insert.(Weinman JP,sicher H) The ABP appears as an opaque line called LAMINA DURA. The apparent density is due to thick bone without trabeculations that x-ray must penetrate and not due to any increase in mineral content. The alveolar bone is perforated by many openings through which the blood vessels, lymphatics and nerves of PDL pass. It is referred to as cribriform plate because of perforation.

OSSEOUS TOPOGRAPHY The bony contour normally conforms to the prominence of the

roots,with intervening vertical depressions that taper towards the margin. On teeth in labial version ,the margin of the labial bone is located farther apically. On teeth in lingual version,facial bone is thicker than normal. The bone margin is located farther apically on the roots which forms relatively acute angles with the alveolar bone(Hirschfeld I).

HAVERSIAN SYSTEMCircumferential lamellae Concentric lamellae Interstitial lamellae

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. The osteon is a cylinder of bone, generally oriented parallel to the long axis of the bone. In the center of each 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.

OSTEONPRIMARY OSTEONS Recently formed osteons that

SECONDARY OSTEONS They become partially

have not remodelled.

become

resorbed and replaced by adjacent osteons, which is indicative of old bone.

Interstitial lamellae are interspersed between adjacent concentric lamellae and fill the spaces between them. They are actually fragments of preexisting concentric lamellae .

PERIOSTEUM AND ENDOSTEUM Tissue covering outer surface of bone is termed Periosteum,

where as tissue lining the internal bone cavities is called Endosteum. The periosteum consists of an inner layer composed of osteoblasts surrounded by osteoprogenitor cells, which have the potential to differentiate into osteoblasts, and an outer layer rich in blood vessels and nerves and composed of collagen fibers and fibroblasts. The endosteum is composed of a single layer of connective tissue. The inner layer is the osteogenic layer, and the outer layer is the fibrous layer.

RADIOGRAPHIC FEATURES LAMINA DURA The tooth sockets are bounded by a thin radiopaque layer of

dense bone. Its name, lamina dura ("hard layer"), is derived from its radiographic appearance. Its radiographic appearance is caused by the fact that the x-ray beam passes tangentially through the thickness of the thin bony wall many times, which results in its observed attenuation.

ALVEOLAR CREST The gingival margin of the alveolar process that extends

between the teeth is apparent on radiographs as a radiopaque line, the alveolar crest. The level of this bony crest is considered normal when it is not more than 1.5 mm from the cementoenamel junction of the adjacent teeth.

CANCELLOUS BONE It is composed of thin radiopaque plates and rods (trabec-ulae) surrounding many small radiolucent pockets of marrow. The trabeculae in the anterior maxilla are typically thin and numerous, forming a fine, granular, dense pattern, and the marrow spaces are consequently small and relatively numerous. In the posterior maxilla the trabecular pattern is usually quite similar to that in the anterior maxilla, although the marrow spaces may be slightly larger.

CANCELLOUS BONE In the anterior mandible the trabeculae are somewhat thicker than in the maxilla, resulting in a coarser pattern, with trabecular plates that are oriented more horizontally. The trabecular plates are also fewer than in the maxilla, and the marrow spaces are correspondingly larger. In the posterior mandible the periradicular trabeculae and marrow spaces may be comparable to those in the anterior mandible but are usually somewhat larger.

COMPOSITION OF BONE

The

organic matrix consists mainly of collagen type I(Muhlemann HR,Zander HA),with small amounts of noncollagenous proteins such as osteocalcin ,osteonectin,phosphoproteins,and proteoglycans.

NON COLLAGENOUS PROTEINS They constitute the remaining 10%of the total organic content of bone matrix. osteocalcin is the first noncollagenous protein to be recognized and represents less than 15%of the noncollagenous protein. osteopontin and bone sialoprotein were previously termed as bone sialoproteins I and II respectively. glutamic acid is predominant in bone sialoprotein and aspartate is predominant in osteopontin.

BONE CELLSOSTEOBLASTS These are mononucleated cells that synthesize collagenous &

non - collagenous bone matrix proteins.It exhibits a high level of alkaline phosphatase on their outer plasma membrane. The osteoblast secretes the organic matrix of bone, which

initially is represented by an unmineralised layer known as OSTEOID, about 5-10 um thick.

OSTEOCYTES As the osteoblasts form the bone matrix ,they get entrapped

within the matrix they secrete ,and are called osteocytes. Embryonic bone and repair bone ,show more osteocytes as they they are formed rapidly.within the bone matrix ,the osteocyte reduces in size ,creating a space around it ,called the osteocytic lacuna. Narrow extensions of these lacunae form channels called canaliculi. Osteocytic processes are present within these canaliculi.

BONE CELLS

BONE LINING CELLS When bone surfaces are neither in the formative nor resorptive

phase, the bone surface is completely lined by a layer of flattened cells termed bone-lining cells. These show little sign of synthetic activity as evidenced by their

organelle content. They are regarded as post prolifcrative osteoblasts. By covering the surface of bone, they protect it from any

resorptive activity from osteoclasts.

OSTEOPROGENITOR CELLS The cells that eventually give rise to osteoblasts are termed

osteoprogenitor cells ( FRIEDENSTEIN ). They reside in the layer of cells beneath the osteoblast layer in

the periosteal region, in the periodontal ligament, or in the marrow spaces.

osteoprogenitor cells

Determined osteogenic precursor cells

Inducible osteogenic precursor cells

OSTEOCLASTS Osteoclasts are the cells responsible for bone resorption. They

are derived from haemopoietic cells of the monocyte/ macrophage lineage by fusion of mononuclear precursors. (Bernard GW) Resorbing surfaces of alveolar bone show resorption concavities (Howship's lacunae), in which lie the multinucleated osteoclasts. Characteristically, osteoclasts may be up to 100 um in diameter and have on average 10-20 nuclei.

That part of the cell that lies adjacent to bone, and where

rcsorption is occurring, often has a foamy, striated appearance at the light microscope level (the so-called 'ruffled border'). A useful marker for osteoclasts is tartarate-resistant acid phosphatase. At the ultrastructural level, the ruffled border is composed of many tightly packed microvilli adjacent to the bone surface. This border provides a large surface area for the resorptive process.

PHYSIOLOGICAL REMODELLING The ability of the alveolar bone to remodel rapidly facilitates

positional adaptation of teeth in response to functional forces and in the physiological drift of teeth that occurs with the development of jaw bones. Bone remodeling involves the co-ordination of activities of cells , the osteoblasts and the osteoclasts, which form and resorb the mineralized connective tissues of bone, respectively. (Sodek J)

BONE REMODELLING

BONE FORMATION It involves the proliferation and differentiation of stromal stem

cells along an osteogenic pathway that leads to the formation of osteoblasts. The alkaline phosphatase and collagen I expression are characteristic of the osteogenic lineage .

BONE RESORPTION Tencate described the resorptive process : Attachment of osteoclasts to the mineralized surface of bone. Creation of a sealed acidic environment through the action of

the proton pump, which demineralizes bone and exposes the organic matrix. Degradation of exposed organic matrix by the action of released enzymes, such as acid phosphatase and cathepsin B. Sequestering of mineral ions and amino acids within the osteoclast.

BLOOD SUPPLY Maxilla receives blood Mandible receives blood

supply from superior alveolar artery .

supply from alveolar artery.

inferior

VENOUS DRAINAGE It accompanies arterial supply. Venules receive blood via abundant capillary network, there are

also AV anastomoses that bypass the capillaries. More frequently in apical and interradicular region .

LYMPHATIC DRAINAGE

Those draining region just beneath the JE pass into PDL and

accompany blood vessels into periapical region(Box KF). From there they pass through alveolar bone to inferior dental canal in mandible or infraorbital canal in maxilla and then to submaxillary lymphnodes.

IMPLANT BONE INTERFACE Osseointegration:

when the bone is in intimate but not ultrastructural contact with implant.

Fibrosseous

integration, in which soft tissues such as fibers and/or cells, are interposed between the two surfaces.

PATHWAYS OF INFLAMMATION Inflammation extends along

the collagen fiber bundles & follows the course of blood vessels, through the loosely arranged tissues around them in to alveolar bone.

Facially & lingually, inflammation spreads along the outer periosteal surface of the bone and penetrates into the marrow through the vessel channels in the outer cortex.

Once inflammation reaches the bone, it spreads into the marrow spaces and replaces the marrow with: -a leukocytic and fluid exudate -new blood vessels -proliferating fibroblasts Resorption precedes from within the marrow cavities, causing thinning of the surrounding bony trabeculae &enlargement of marrow spaces, followed by destruction of bone and reduction in bone height.

RADIUS OF ACTION Page & Schroeder- range of effectiveness of dental plaque to

induce loss of bone is within about 1.5 to 2.5 mm. Large defects exceeding a distance of 2.5 mm from the tooth surface may be caused by the presence of bacteria in the tissues.(Carranza ,Saglie R,Newman MG)

OSTEOGENESIS This occurs when osteoblasts &the precursor osteoblasts are transplanted with graft material into the defects. In these , they may estabilish centres of bone formation. OSTEOCONDUCTION This occurs when non vital implant material serves as a scaffold for the ingrowth of precursor osteoblasts into the defect that is followed by gradual resorption of implant material. OSTEOINDUCTION This process involves new bone formation by the differentiation of local uncommitted cells into bone forming cells under the influence of one or more inducing agents.

CLINICAL IMPLICATIONS FENESTRATIONS &

DEHISCENCE Fenestrations are the isolated area in which the root is denuded of bone & root surface is covered by periosteum & gingiva. Dehiscence is when denuded area extends through the marginal bone.

FENESTRATION

DEHISCENCE

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)

PATTERNS OF BONE DESTRUCTIONHORIZONTAL BONE LOSS Bone is reduced in height. Bone margin remains

perpendicular to tooth surface.

VERTICAL BONE LOSS Vertical or angular defects

are those that occur in an oblique direction, leaving a hollowed out thorough in the bone along side the root, the base of the defect is located apical to the surrounding bone.

Angular defects are classified as follows: Three wall bony defects Two wall bony defects One wall bony defects

VERTICAL BONE LOSS

OSSEOUS CRATERS Osseous

craters are concavities in the crest of the interdental bone confined within the facial and lingual walls. Craters have been found to be made up about one third of all defects and about two thirds of all mandibular defects. (Melcher AH)

BUTTRESSING BONE FORMATION Bone formation sometimes occurs in an attempt to buttress

bony trabeculae weakened by resorption. When it occurs within the jaw, it is termed as central buttressing bone formation. When it occurs on the external surface, it is known as peripheral buttressing bone formation.(Glickman I) The latter may cause bulging of the bone contour, termed lipping.

BULBOUS BONY CONTOURS These are bony

enlargements caused by exostoses, adaptation to function, or buttressing bone formation.

REVERSE ARCHITECTURE These defects are produced

by loss of interdental bone, including the facial and/or lingual plates, without concomitant loss of radicular bone, thereby reversing the normal architecture. Such defects are more common in the maxilla. (Neilson JI)

LEDGES Ledges are plateau-like

bone margins caused by resorption of thickened bony plates.

FURCATION The

term furcation involvement refers to the invasion of the bifurcation and trifurcation of multirooted teeth by periodontal disease.

The mandibular first molars

are the most sites.(Larato DC)

common

TRAUMA FROM OCCLUSION When occlusal forces exceed the adaptive capacity of the tissue,

tissue injury results. The resultant injury is termed trauma from occlusion. An occlusion that produces such injury is called a traumatic occlusion. Widening of the marginal periodontal ligament space, a narrowing of the interproximal alveolar bone, and a shelf-like thickening of the alveolar margin. Although trauma from occlusion does not alter the inflammatory process, it changes the architecture of the area around the inflamed site.

SYSTEMIC DISORDERS CAUSING BONE LOSS Osteoporosis post menopausal Hyperparathyroidism Brown s tumour Leukemia

Langerhans cell histiocytosis

AGE RELATED CHANGESMore irregular periodontal surface of bone. Less regular insertion of collagen fibres. Diminished vascularity Increasing number of interstitial lamellae

Fewer cells in the osteogenic layerDecreased trabeculation Osteoporosis

CLINICAL CONSIDERATIONS Extremely

sensitive to pressure and tension. Enables Orthodontic tooth movement. Adaptation of the bone to function is qualitative as well as quantitative. Increase in the functional forces leads to the formation of the new bone, decrease in the functional forces leads to the decrease in the volume of the bone.

During healing of the fracture immature type of the bone is

formed,characterized by the greater number, size and irregular arrangement of the osteocytes than are found in mature bone.

In periodontal destruction both vertical & horizontal type of the

bone loss can be seen & is related to the bacterial plaque and pocket formation.

Synthetic materials,including non resorbable hydroxyapatite &

resorbable tricalcium phosphate, used for the ridge augmentation & for filling the bone defects produced by the periodontal diseases. Alveolar bone of the maxilla & mandible develops for the

support of the teeth, when teeth are lost it undergoes gradual atrophy.

CONCLUSION The basic understanding of the structure of alveolar bone &

remodeling in response to various stimuli can help us to better understand the progression of periodontal disease. Progressive loss of bone is difficult to control, once lost it is

very difficult to repair or regenerate.