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Good morning

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Alveolar bone in health

Guided by:-Dr. Anita PanchalDr. Sachin K.Dr. Bhaumik NanavatiDr. Rahul ShahDr. Mansi Pathak

Presented by:-GANESH NAIRFY PG

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Contents:• Introduction• Definition• Development of alveolar bone• Classification of Alveolar bone• Gross morphology• Osseous topography• Cells and intercellular matrix• Blood and Nerve supply• Periosteum and Endosteum• Bone resorption• Bone remodelling

• Markers of bone turnover• Orders of alveolar ridge

resorption• Age changes • Conclusion• References

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Introduction:-

• The alveolar bone is the portion of the maxilla and mandible which forms and supports the tooth socket.

• Since alveolar processes develop and undergo remodelling with tooth formation and eruption, they are tooth dependent bony structures.

• Therefore the size, shape, location and function of teeth determine their morphology.

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Definition:-

• The alveolar bone is the portion of the maxilla and mandible which forms and supports the tooth socket.

• Carranza 10th edition

• The alveolar process supports to alveoli, and consists of cortical bone, cancellous trabeculae, and the alveolar bone proper.

• Glossary of perio terms 2001

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Development of alveolar bone:

• Maxilla & mandible develop-- 1st branchial arch or mandibular arch.

• The maxilla forms within the maxillary process & mandible forms within the fused mandibular processes of mandibular arch.

• Both jaw bones start as small centres of intramembraneous ossification around stomodeum

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Both maxilla and mandible develop

intramembranously.

8th week in utero.

Alveolar process develops from the dental follicle during

eruption of tooth

Bell stage-- developing bone becomes closely related

The size of the alveolus is dependent upon the size of

the growing tooth germ.

Resorption - inner wall of the alveolus Deposition -outer

wall.

The developing teeth lie in a trough of bone -Tooth Crypt.

Teeth separated from each other by the development of

interdental septa.

With the onset of root formation, interradicular bone develops in multirooted teeth.

When a deciduous tooth is shed, its alveolar bone is

resorbed.

Alveolar process gradually incorporated into maxillary or

mandibular body.

Permanent tooth moves into place,

developing its own alveolar bone from its

own follicle.

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Classification of alveolar bone:

BASED ON THE FUNCTIONAL ADAPTATION

Alveolar bone proper

Supporting alveolar bone

KEVITTS CLASSIFICATION

Hypocalcemic Normal Hypercalcemic

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RADIOGRAPHIC APPEARANCE

Type I Type II

HISTOLOGICALLY

MATURE

COMPACT

CANCELLOUS

IMMATURE WOVEN BONE

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• Linlow in 1970– CLASS I BONE STRUCTURE: this ideal bone type consists of

evenly spaced trabeculae with small cancellated spaces– CLASS II BONE STRUCTURE: this bone has slightly larger

cancellated spaces with less uniformity of the osseous pattern– CLASS III: BONE STRUCTURE: large marrow filled spaces exists

between bone trabeculae• LEKHOLM AND ZARB IN 1985

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• MISCH BONE DENSITY CLASSIFICATION:– D1: bone is primarily dense cortical bone– D2: bone has dense to porous cortical bone on the crest and,

within the bone, has coarse trabecular bone– D3: have thinner porous cortical crest and fine trabecular region

next to the implant– D4: bone has almost no crestal cortical bone. The fine trabecular

bone composes almost all of the total volume of the bone next to the implant

– D5: a very soft bone, with incomplete mineralization and large intertrabecular spaces. Often immature bone in developing sinus grafts.

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GROSS MORPHOLOGY:

• Outer alveolar plate

• Inner alveolar plate

• Interdental septum

• Interradicular septum

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Inner and Outer cortical plates

• Alveolar process is continuous

with basal bone of maxilla and

mandible

• Arbitrarily the root apices

delineate the alveolar bone

from basal bone

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• Cribriform plate (anatomic term)/ Lamina dura (radiographic term)/ Bundle bone (histologic term)

• Cribriform plate thickness- 0.1 to 0.5mm

• External alveolar plate thickness – 1.5 to 3mm around posterior teeth, highly variable around anterior teeth

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INTERDENTAL SEPTUM• Bony partition that separate the adjacent alveoli• Coronally septa is thin and consists of only fused inner cortical

plates• Apically septa is thicker and contain intervening cancellous bone• Mesiodistal angulation of interdental septum is parallel to line

drawn between CEJ of approximating teeth (Ritchey et al, 1953)• If interdental space is narrow, septum may consist of only

cribriform plate• If roots are too close together, an irregular window can appear in

the bone between adjacent roots

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ALVEOLAR CREST• Formed when the inner and outer cortical plates meet• The margin is thin & knife edged in vestibular surfaces of anterior

and rounded/beaded in posterior teeth• Most prominent border of interdental septum• Runs roughly parallel to CEJ, 1-3mm apical to it, with greater

distance seen in older individuals– Ritchey & Orban 1953

• Average distance between CEJ & crest - 1.08mm• Increases with age - 2.81mm

– Gargiulo et al 1961

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INTERRADICULAR SEPTA

• The bone between the roots of multirooted teeth .

• Both of them contain perforating canals of Zukerkandl & Hirschfeld [nutrient canals].

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OSSEOUS TOPOGRAPHY:• Normally: prominence of the

roots with the intervening vertical depressions that taper toward the margin.

• On the labial version: the margins of the labial bone is thinned to a knife edge & presents an accentuated arc in the direction of the apex.

• On the lingual version: the margins of the labial bone is blunt, rounded & horizontal rather than arcuate.

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Cells and Intercellular matrix:

• Osteoblasts:- are mononucleated cells responsible for the synthesis and secretion of macromolecular organic constituents of bone matrix.

• Basophilic, plump cuboidal / slightly elongated cells.• Rich in synthetic & secretory organelles- rough endoplasmic

reticulum, golgi apparatus, secretory granules & microtubules• Also contain other organelles associated with cell metabolism-

mitochondria & endosomal/ lysosomal elements & extensive cytoskeleton

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• In addition, it has a controlling influence in activating Osteoclasts. It contains receptors for the parathyroid hormone and regulates the osteoclastic response to this hormone.

• Periosteum also serves as an important reservoir of osteoblasts

OSTEOBLASTDOPCIOPCSTROMAL STEM CELLS

BMPGROWTH FACTORS

SYSTEMIC & BONE GF

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• Functions: Formation of new bone, regulation of bone remodelling and mineral metabolism.

• Osteoblast secrete type I collagen, osteocalcin and cfba-1 (osteoblast specific transcription factor), Type V collagen, osteonectin, Osteopontin, RANKL, Osteoprotegrin, proteoglycans, latent proteases and growth factors like BMP.

• Osteoblast exhibit high levels of alkaline phosphatase. • RANKL is membrane bound TNF related factor, expressed by

osteoblasts/stromal cells. It is important in differentiation of osteoclast. Cbfa1 regulates the expression of OPG (osteoprotegrin) which is a potent inhibitor of osteoclast.

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Osteocytes:• Haversian system (osteons) are internal mechanism that bring

vascular supply to the bones too thick to be supplied only by surface vessels.

• extend processes called canaliculi that radiate from the lacunae.• These canaliculi anastomose with each other in the matrix and help

in transfer of oxygen and nutrients to the osteocytes through the blood and remove metabolic waste products.

• They are found primarily in the outer cortical plates and alveolar bone proper.

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Osteoclast:

• Osteoclasts are large cells approximately 40-100 µm in diameter with 15-20 closely packed nuclei.

• Osteoclasts with more nuclei resorb more bone as compared to those with less nuclei.

• Cathepsin containing vesicles and vacuoles are present close to the ruffled border indicating resorptive activity of these cells.

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RANK, RANKL and OPG

• RANK (receptor activator of nuclear factor ĸB) is expressed by osteoclast precursor, a membrane bound TNF receptor recognizes RANKL through cell to cell interaction of osteoblast or stromal cells.

• Interaction between RANK and RANKL results in transduction signal in preosteoclast that activates NF-ĸB (nuclear factor- ĸB) through RANK to produce mature osteoclast.

• Osteoprotegrin (OPG) is a member of TNF receptor family which recognizes RANKL, and blocks the interaction between RANK and RANKL, leading to an inhibition of osteoclast differentiation and activation.

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Structural lines in bones:

• Reversal line or cementing line--The site of change from bone resorption to bone deposition is represented by a scalloped outline. -Rich in sialoprotein & osteopontin.

• Resting line – ⁻ Rhythmic deposition of bone

with periods of relative quiescence seen as parallel vertical lines.

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Inorganic component of bone:

• Bone consists of two thirds inorganic matter and one third organic matrix.

• The inorganic matter is composed principally of the minerals calcium and phosphate, along with hydroxyl, carbonate, citrate, and trace amounts of other such as sodium, magnesium and fluorine.

• The mineral salts are in the form of hydroxyapatite crystals of ultramicroscopic size and constitute approximately two thirds of the bone structure. Its Ca/P ratio is lesser as compared to the enamel.

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Organic components: COLLAGEN

• Collagen comprises the major (80–90%) organic component in mineralized bone tissues.

• Type I collagen (>95%) is the principal collagen in mineralized bone, together with Type V (<5%) collagen.

• In addition, both type III and XII collagens are also present.• The expression of type XII collagen in alveolar bone is related to

mechanical strain.• Type I,V & XII are expressed by osteoblasts• Type III & some type XII collagen appear to be produced by

fibroblasts during formation of periodontal ligament

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Osteocalcin:• First non collagenous protein to be recognized.• Found in bone matrix and specifically localizes to developing bone • It is regulated by Vitamin D3 and Parathyroid hormone.• The carboxy terminal segment of osteocalcin acts as a

chemoattractant to osteoclast precursors, suggesting a role in bone resorption.

• It is also believed to be involved in bone calcification as it is a calcium binding protein.

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Osteopontin and bone sialoprotein• They were previously termed as Bone sialoproteins I and II.• Bone sialoprotein is thought to function in the initiation of mineral

crystal formation in vivo.• Osteopontin is a potent inhibitor of hydroxyapatite crystal growth.• Osteopontin transcription is strongly upregulated by Vitamin D3

whereas Bone sialoprotein transcription is suppressed by Vitamin D3.

• It could play a role in the regulation of cell adhesion and proliferation, and in the modulation of cytokine activity

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Osteonectin:• It is predominantly bound to hydroxyapatite crystals.• Also termed as SPARC (secreted proteins & acidic rich in cysteins) &

BM-40• SPARC, which has also been characterized in basement membranes

as BM40, is a secreted calcium-binding glycoprotein that interacts with a range of extracellular matrix molecules.

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PROTEOGLYCANS

• Chondroitin sulfate proteoglycan.• Two small proteoglycans, Biglycan (chondroitin sulfate proteoglycan

I) and Decorin (chondroitin sulfate proteoglycan II).• These regulate collagen synthesis.

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Byglycan• Byglycan is more prominent in developing bone and has

mineralised to pericellular areas • Its precise function is not known,but it can bind TGF-β and

extracellular matrix macromolecules including collagen and thereby regulate fibrillogenesisDecorin

• Binds mainly with in the gap region of collagen fibrils and as suggested by its name, decorates fibril surface

• The primary calcification in bones as reported to follow removal of decorin and the fusion of collagen fibrils

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Blood and nerve supply:

• Vascular supply: – Derived from inferior and superior alveolar

arteries of maxilla and mandible, venous drainage accompanies the arterial supply

• Nerve supply:– Branches from anterior, middle and posterior

superior alveolar nerves for maxilla and branches from inferior alveolar nerve for mandible

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Periosteum & Endosteum:

• The alveolar bone is surrounded by a condensed fibrocollagen layer, the periosteum which has two layers:– outer layer which is dense, irregular connective tissue termed

fibrous layer and– inner layer next to the bone surface consisting of bone cells,

their precursors and a rich vascular supply.ENDOSTEUM:

– It contains marrow spaces which are filled with either red marrow in young bones and yellow marrow in old bones.

– Red marrow is found in spongy cavity of long bones and diploe of flat bones.

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Bone reorption:

• Sequence of bone resorption: • First phase involves formation of osteoclast progenitors in the

hemopoietic tissues, followed by their vascular dissemation and the generation of resting proosteoclasts and osteoclast in the bone itself.

• Second phase consists of activation of the osteoclasts at the surface of mineralized bone. Osteoblasts play a major role by retracting, to expose the mineral to the osteoclast and releasing factor that activates these cells.

• Third phase involves the activated osteoclast resorbing the bone.

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• Ten cate described the sequence of events of bone resorption as follows:

1. Attachment of osteoclasts to mineralized surface of bone.2. Creation of a sealed acidic environment through action of proton

pump, which demineralises bone and exposes the organic matrix.3. Degradation of the exposed organic matrix to its constituent

amino acid by the action of released enzymes such as acid phosphatase and cathepsin.

4. Sequestering of mineral ions and amino acids within the osteoclast.

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Alteration in the osteoclast:

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Removal of hydroxyapatite:

• the initial involves the action of dissolution of the mineral phase by the action of HCl.

• The proton of the acid arise from the activity of cytoplasmic carbonic anhydrase II, which is sythetised by the osteoclast.

• The protons are then released across the ruffled border into the resorption zone by an ATP consuming proton pump.

• This leads to pH fall to 2.5-3.0 in the osteoclast resorption space.

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Degradation of the organic matrix:• Proteolytic enzymes are synthesized by the osteoclasts, namely,

cathepsin-K and MMP-9, these are produced in the rough endoplasmic reticulum and transferred across the ruffled border into the sealed environment, creating extracellular lysosomes.

• Cathepsin-K is the most important enzyme in bone resorption.• It is a collagenolytic papainlike cysteine protease expressed in

osteoclasts. Cathepsin-K degrades major amount of type I collagen and other non collagenous proteins, which have been demineralised by the acidic environment of the resorptive zone.

• MMP-9 is believed to be required for osteoclast migration. MMP-13 is proposed to be involved in bone resorption and osteoclast differentiation.

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Removal of the degradation product from the lacunae: • Once liberated from the bone, free organic and inorganic particles

of the bone matrix are taken in or endocytosed from the resorption lacunae, across the ruffled border, into the osteoclast.

• These are then packed into membrane bound vesicles. • These vesicles and their contents pass across the cell and fuse with

the FSD (functional secretory domain) a specialised region of the basal membrane. Then the vesicles are released via exocytosis.

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Mediators of bone resorption:stimulators

• IL-1• IL-6• TNF• PTH• PTHrP• PGE2• M-CSF• RANK• RANKL• Vitamin D3

Inhibitors

• IFN-ɣ• OPG• Estrogens• Androgens• Calcitonin• Cyclosporin

Modified by McCauley LK, Koh-Paige Aj, Chen H, et al: Endocrinology, 142:1975,2001.

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Bone Remodelling:-• Remodelling is a major pathway of bony change in shape, resistance

to forces, repair of wounds, and calcium and phosphate homeostatsis in the body.

• Bone remodelling involves the coordination of activities of cells from different lineages, the osteoblasts and the osteoclasts.

• Regulation of bone remodelling is a complex process involving hormones and local factors acting on autocrine and a paracrine manner on the generation and activity of differentiated bone cells.

• Eg of some hormones which influence remodelling are PTH,calcitonin, IL-1, IL-6, LIT(Leukemia Inhibiting factor).

• The interdependency of osteoblasts and osteoclasts in remodelling is called coupling.

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Factors influencing bone remodelling:• Local influences

– Functional requirements– Age related changes in bone cells

• Systemic influences– Hormones (PTH, vit D, calcitonin)

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Role of PTH:

Decrease in blood Ca

Detected by receptors on chief

cellsof parathyroid gland

Release of PTH

Stimulate osteoblasts

to release IL-1 and IL-6

Stimulates monocytes

to migrate to area

Monocytes coalesces to form

multinucleated osteoclasts in

presence of LIF-

Bone resorption

Release of Ca ions from

hydroxyapetite crystals

Normal blood calcium levels

PTH secretion stopped by feedback

mechanism

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Mediators of bone remodelling:

BONE RESORBERS :• Parathyroid Hormone• Vitamin D3 • Cytokines• IL -1• IL-6• TNF α and β • Colony stimulating factors• Prostaglandins and other

arachidonic acid metabolites • RANKL/ OPG-L / TRANCE • Bacterial products

BONE PROTECTORS :• Calcitonin • Bisphosphonates• Statins• Osteoprotegerin• Interferon gamma • Glucocorticoids• Indomethacin/Aspirin• IL-1 receptor antagonist• Estrogen• Leptin

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Markers of bone turnover:• Bone formation (serum markers):– Alkaline phosphatase– Osteocalcin– Procollagen 1 extension peptide

• Bone resorption (urinary markers):– Urine calcium– Urine hydroxy proline– Collagen crosslink fragments– Urine N-telopeptide– Urine C- telopeptide– Urine total pyridinoline– Urine free deoxypyridinoline

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Orders of alveolar ridge resorption:• The pattern of resorprtion is different in maxilla and mandible. • The alveolar ridge resorbs downwards and outward in the mandible,

whereas, in the maxilla the resorption of is upwards and inwards. • The end result is that over the period of time maxillary arch become

progressively smaller, whereas the mandibular arch becomes wider.• Six orders of mandibular alveolar ridge resorption:-

– Order I Preextraction– Order II Postextraction– Order III High, well round– Order IV Knife Edge– Order V Low, well round– Order VI Depressed

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AGE CHANGES

• Similar to those occurring in remainder of skeletal system• Osteoporosis with ageing• Decreased vascularity • Reduction in metabolic rate and healing capacity(implants,

extraction sockets, bone grafts)• Bone resorption may be increased or decreased • More irregular periodontal surface

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Conclusion:

• The alveolar processes develop and undergo remodeling with the tooth formation and eruption- Tooth dependent bony structure.

• Although its constantly changing its internal organization, it retains the same form from childhood through adult life.

• The coupling of bone resorption with bone formation constitutes one of the fundamental principles by which bone is remodeled throughout its life.

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References:

• Orban’s Oral Histology and Embryology: 12th edition• Carranza’s Clinical Periodontology: 10th edition• Clinical Periodontology and Implantology: 6th edition• Complete denture Prosthodontics: 2nd edition

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