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BONE
BY
DR. KRITI TREHAN
1st MDS
12/9/17
1. Introduction
2. Classification
3. Composition
4. Histology
5. Formation
6. Resorption
7. Remodeling
8. Alveolar process and Alveolar bone
9. Clinical implications
10. Systemic Disorders affecting Bone
11. References
CONTENTS
WHAT IS BONE
• Bone is essentially a highly vascular, living,
constantly changing mineralized connective
tissue.
• It is remarkable for its hardness, resilience and
regenerative capacity, as well as its
characteristic growth mechanisms.
• It is the basic unit of human skeleton.
FUNCTIONS
CLASSIFICATION
DEVELOPMENT
• ENDOCHONDRAL
• INTRAMEMBRANO
US
SHAPE
•LONG
•SHORT
•FLAT
•IRREGULAR
•SESAMOID
STRUCTURE
•MICROSCOPIC
WOVEN
LAMELLAR
•MACROSCOPIC
COMPACT
SPONGY
A TYPICAL LONG BONE
COMPOSITION
•Minerals- Hydroxyapatite crystals
•Amorphous Calcium phosphate
• Mg, Na, K ,Fl Zn,Cu – smaller quantity
INORGANIC CONTENT
•Collagen ( Type I >95% primarily),TYPE V
ORGANIC CONTENT
•Osteocalcin/ bone gla protein
•Osteopontin
•Bone sialoprotein
•Other proteins- osteonectin,
dermatopontin and proteoglycans
NON-COLLAGENOUS PROTEINS
HISTOLOGY
All bones consist of :
1.Outer compact bone
2.Inner medullary cavity
(cancellous/trabecular bone + red/yellow
marrow)
Periosteum
The outer surface of most
bone is covered by a layer of
condensed fibrous tissue, the
periosteum which contains cells
capable of converting into osteoprogenitor
cells and osteoblasts.
Endosteum
Is a thin vascular connective layer that
lines the inner surface of the bony tissue
that forms the medullary cavity of long
bones.
Compact Bone
• This type of bone is ivory-like and dense in texture without cavities.
• Forms the thick-walled tube of the shaft (or diaphysis) of long bones,
which surrounds the marrow cavity (or medullary cavity). A thin layer
of compact bone also covers the epiphyses of long bones.
• It consists mainly of haversian systems or secondary osteons
• Contains blood vessels, lymphatic vessels, nerves, and osteocytes
along with the calcified matrix.
•Haversian Systems
•The basic metabolic unit of compact bone also called osteons
•Volkmann's canals
•Are oblique canals running at right angles to the long axis of bone.
•Contain the neurovascular bundle and connect the haversian canals
with each other and also with the medullary cavity .
•Lamellae
•Concentric - surrounding each Haversian canal
•Interstitial - bony plates that fill in between the haversian systems.
•Circumferential – Circumferential lamellae are circular lamellae that
line the external surface of the cortex adjacent to the periosteum and
line the inner surface of the cortex next to the endosteum. There are
more outer than inner circumferential lamellae.
•Lacunae
These are small spaces between the lamellae , each containing a bone
cell called osteocyte.
•Canaliculli
These are fine radiating channels which
connect the lacunae with each other and central haversian canal
SPONGY BONE
• Spongy bone (anatomic term)/ Trabecular bone
(radiographic term)/ Cancellous bone (histologic term)
• They have the same cells and intercellular matrix but
differ in the arrangement of the components. These are
poorly organized tissue in contrast to compact bone and
contains more spaces as compared to compact bone.
• Trabeculae aligned in path of tensile and compressive
stresses to provide maximal resistance to occlusal forces
with minimum bone substance (Glickman et al 1970)
HEMOPOIETIC TISSUE IN BONES
•Red marrow is present in young bone.
•It contains stem cells of both fibroblast/mesenchymal and blood
lineage .
•It is found within cavities of spongy bone of long bones and diploe of
flat bones.
•Yellow marrow is present in old bone.
•Characterized by loss of hemopoietic potential and increased
accumulation of fat cells.
BONE CELLS
OSTEOBLASTS
Osteoblasts are mononucleated cells
responsible for the secretion and synthesis
of the organic constituents of bone matrix.
These cells are derived from
osteoprogenitor cells of mesenchymal
origin.
• Basophilic, plump cuboidal / slightly
elongated cells.
• These cells are found on the forming
surfaces of growing or remodelling bone.
• The most active secretory cells in
bone.
Produce--
• Type I collagen
• Noncollagenous bone proteins like Sialoprotein, Osteopontin,
Osteonectin
• Growth factors –BMP, Transforming growth factor, insulin like growth
factor, platelet derived growth factor, fibroblastic growth factor.
•Express and release alkaline phosphatase, which has been shown to be
closely associated with new bone formation and has been recognized
as a reliable indicator of osteoblast function.
• In addition, it has a controlling influence in activating Osteoclasts. It
contains receptors for the parathyroid hormone,vitamin D3,estrogen
and regulates the osteoclastic response to these hormones.
OSTEOCYTES
• Osteocytes are ‘entrapped’ osteoblasts within bone .
•Osteocytes occupy spaces (lacunae) in bone called
osteocytic lacuane.
•No. of osteocytes depends on the rapidity of bone
formation. More the rapidity more the cells per unit
volume.
•Osteocytes have an extensive network of cell
processes or extensions and through these channels
osteocytes maintain contact with adjacent osteocytes
and osteoblasts .
OSTEOCLASTS
•Osteoclast is a type of bone cell that removes bone tissue by removing the
mineralized matrix of bone.
•These are large cells with 15-20 closely packed nuclei and acidophilic
cytoplasm.
•Lie in Howship’s lacunae.
• Osteoclasts produce a number of
enzymes, chief among them acid
phosphatase, that dissolve both
the organic collagen and the
inorganic calcium and phosphorus
of the bone.
• The side of the cell closest to the bone contains many small projections
(microvilli) that extend into the bone’s surface, forming a ruffled, or
brush, border that is the cell’s active region. .
MICROSCOPIC ORGANIZATION
OF BONE
With regard to matrix arrangement, bone tissue
can be divided into the following categories:
Woven bone (primary bone tissue) - This is
immature bone, in which collagen fibers are
arranged in irregular random arrays and
contain smaller amounts of mineral
substance and a higher proportion of
osteocytes than lamellar bone; woven bone is
temporary and is eventually converted to
lamellar bone.
Lamellar bone (secondary bone tissue) - This
is mature bone with collagen fibers that are
arranged in lamellae. Lamellae in compact
bone are concentrically organized around a
vascular canal, termed a haversian canals.
BONE FORMATION
• The process of bone formation is called osteogenesis .
1. Endochondral bone formation
2. Intramembranous bone formation
INTRAMEMBRANOUS FORMATION
ALVEOLAR PROCESS
• The alveolar process is that portion of the maxilla and
mandible that forms and supports the sockets of the
teeth.
• Proper development of the alveolar process is
dependent on tooth eruption and its maintenance on
tooth retention. When teeth fail to develop (e.g.
anodontia), the alveolar process fails to form.
• When all teeth are extracted, most of the alveolar
process becomes involuted, leaving basal bone as the
major constituent of the jawbone. The remaining
jawbone, therefore, is much reduced in height.
• It is composed of an outer and inner cortical plate of
compact bone that enclose the spongiosa, a
compartment composed of spongy bone .
GROSS MORPHOLOGY
MAXILLA/
MANDIBLE
ALVEOLAR
PROCESS
ALVEOLAR
BONE PROPER
BUNDLE
BONE
LAMELLAR
BONE
SUPPORTING
ALVEOLAR
BONE
BASAL BONE
INNER &
OUTER
CORTICAL
PLATES
SPONGY
BONE
ALVEOLAR BONE PROPER
• The alveolar bone proper consists partly of lamellated bone and partly of
bundle bone and is about 0.1 - 0.4 mm thick.
• It surrounds the root of the tooth and gives attachment to principal fibres of
the pdl.
LAMELLATED BONE
o The deeper portion of the alveolar bone proper is made of haversian system
(osteons).
o Each osteons has a blood vessel in a haversian canal and is surrounded by
concentric lamellae .
o Some lamellae of this bone are arranged roughly prallel to the surface of the
adjacent marrow spaces, whereas others form haversian systems.
BUNDLE BONE
oThe lamellated bone is
covered by areas of bundle
bone .
oIt is that bone in which the
principal fibres of the
periodontal ligament are
anchored.
oIt is characterized by
scarcity of fibrils in the
intercellular substance.
o Bundle bone is formed in
areas of recent bone
apposition. Lines of rest are
seen in bundle bone.
oRadiographically, it is also referred to as the lamina dura because of
increased radiopacity,which is due to the presence of thick bone without
trabeculations.
• The alveolar bone proper , which forms the inner wall of the socket is
perforated by many openings that carry branches of the interalveolar
nerves and blood vessels into the pdl and is therefore called the
cribiform plate.
•Bone between the teeth is called interdental septum and is composed
entirely of cribiform plate.
SUPPORTING ALVEOLAR
BONE
Cortical plate
• It consists of compact bone and form the outer and inner plates of the
alveolar processes.
• Bone underlying the gingiva is the cortical plate, both cribiform plate
and cortical plate are compact bone separated by spongy bone.
Spongy bone
• It fills the area between the cortical plates and the alveolar bone
proper.
• The trabeculae of the spongy bone butress the functionl forces to which the
alveolar bone proper is exposed.
• Radiographically, spongiosa can be classified into two main types.
 Type 1: The interdental and interradicular trabeculae are regular and
horizontal in a ladder like arrangement. (more often in mandible)
 Type2: Shows irregularly arranged numerous delicate interdental and
interradicular trabeculae. (more often in maxilla)
AGE CHANGES IN BONE
• Alveolar sockets appear jagged and uneven.
• The marrow spaces have fatty infiltration
• The alveolar process in edentulous jaws decrease in size.
• The distance between crest of the alveolar bone and CEJ increases with
age.
• Internal trabecular arrangement is more open, which indicate bone loss.
• Houses the roots of teeth.
• Anchors the roots of teeth to the alveoli, which is achieved by
insertion of sharpey’s fibres into the alveolar bone proper.
• Helps to move the teeth for better occlusion.
• Helps to absorb and distribute occlusal forces generated during tooth
contact.
• Supplies vessels to periodontal ligament.
• Houses and protects developing permanent teeth.
FUNCTIONS OF ALVEOLAR
BONE
BLOOD 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
LYMPHATIC DRAINAGE
•Submandibular lymph nodes
BONE RESORPTION
•Bone resorption is removal of mineral and organic components of bone
under the action of osteolytic cells, of which the most important is the
osteoclast.
SEQUENCE OF EVENTS OF BONE RESORPTION
First phase - Formation of osteoclast progenitors in the hematopoietic
tissues.
Second phase - Activation of osteoclasts at the surface of mineralized
bone.
Third phase – Involves Activated osteoclasts resorbing the bone.
ALTERATIONS IN THE OSTEOCLAST
Immediately before the resorption event, the osteoclasts undergo changes which
faciliate bone resorption. The two distinct altertions are
1. Ruffled border
2. Sealing zone at the plasma membrane.
 These changes occur only in the region of the cell that is next to the bone surface.
 Sealing zone serves to attach the osteoclasts very closely to the surafce of bone and
creates an islolated microenviroment for the resorption to take place.
 The attachment of osteoclasts to the
sealing zone is due to the presence of
cell membrane proteins
integrins,especially αVβ3 which binds
to specific amino acids sequences
present in proteins of the bone matrix,
namely, RGD.
REMOVAL OF HYDROXYAPATITE
• Dissolution of mineral phase by the action of HCl.
• The protons for the acid arise from the activity of cytoplasmic carbonic anhydrase II which is
synthesised in the osteoclast.
•Protons are released by an ATP consuming proton pump which is an absolute must for normal
bone resorption.
DEGRADATION OF ORGANIC MATRIX
•Next step involves the digestion of organic components of matrix by proteolytic enzymes which
are synthesized in ostoclasts,namely, CATHEPSIN –K and MMP-9. As a result visbile
depression or Howship’s lacunae is excavated into the bone.
REMOVAL OF DEGRADATION PRODUCTS FROM LACUNAE
•Once liberated from bone , free organic and inorganic particles of bone matrix
are packed in membrane bound vesicles within cytoplasm of osteoclast.
•These vesicles and their contents pass across the cell and fuse with FSD
(Function secretory domain) a specialized region of basal membrane.
•The vesicles are released by
exocytosis into the
extracellular space away
from bone.
•Following resoprtion
osteoclasts undergo
apoptosis , which provides a
mechanism for limiting
resorptive activity.
During this phase bone is formed along the periosteal surface and
destroyed along the endosteal surface
.
BONE REMODELLING
• Bone remodelling is performed by clusters of osteoclasts and
osteoblasts arranged within temporary anatomical structures called
Basic Multicellular Units (BMUs).
• Traversing and casing the BMU is a canopy of cells that creates a
bone-remodelling compartment.
The status of bone represents the net result of a balance between the two
processes.
‘Coupling’ of bone resorption and formation.
An active BMU consists of a leading front of osteoclasts and
osteoblasts occupy the tail portion of the BMU
–
• The leading edge
of resorption
Cutting
cone
• Osteoblasts
secrete osteoid
Filling
cone
The main functions of remodeling are-
To prevent the accumulation of damaged and fatigued bone by regenerating new
bone.
To allow bone to respond to changes in mechanical forces.
To facilitate mineral homeostasis.
STRUCTURAL LINES IN BONE
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.
Mediators of bone remodelling
Parathyroid Hormone
Calcitonin
• Estrogen
• Vitamin D3
• Growth hormones
• IL -1
• TNF α and β
• Prostaglandins
• BMPs
• Bacterial products
Clinical implications of Alveolar bone in
Complete dentures
EDENTULOUS INTRAORAL BONY CHANGES
•Anatomic changes will invariably take place within the alveolar
processes of the jaws following dental extractions.
• When the teeth are present, the pressures exerted are transmitted in the
form of tension to the bone by the periodontal membrane. This type of
stress is acceptable for the alveolar bone.
•Once the teeth are extracted, the load is not directed to the entire bone,
but is applied only its surface. Alveolar bone can only tolerate this
compression to a certain extent.
• The long-term effect of dentures over bone is the atrophy of the
residual alveolar ridge or what Atwood calls reduction of residual ridges
(RRR).
Residual alveolar ridge is the portion of the alveolar ridge and its soft
tissue covering which remains following the removal of or loss of teeth.
[GPT-8]
•The residual bony architecture of the maxilla and mandible undergoes a
life-long catabolic remodelling.
•The rate of reduction in size of the residual ridge following extractions
is maximum in the first 3-6 months and then gradually tapers off.
According to Atwood’s :
(JPD 1971 Vol.26)
Order 1 : Pre-extraction
Order 2 : Post-extraction
Order 3 : High, well rounded
Order 4 : Knife-edge
Order 5 : Low, well rounded
Order 6 : Depressed
ORDER 1 ORDER 2 ORDER 3
ORDER 4 ORDER 5 ORDER 6
CLASSIFICATION
TREATMENT AND
PREVENTION
•A thorough knowledge will provide the clinician with the additional
piece of information required for the selection of an adequate plan of
treatment.
• For certain types of atrophy, a combination of surgery and prosthetics is
required to provide a rapid solution for patients severely handicapped by
dentures.
•It will permit the selection of a technique of choice for the treatment,
based on knowledge about the condition of the remaining hard and soft
tissues.
•Most ideal is a high ridge with flat crest with parallel or nearly parallel
sides.
•Knife edge ridge or a ridge with multiple bony spicules offer the poorest
prognosis.
PROSTHETIC IMPLICATIONS OF
ALVEOLAR BONE IN FPD
•The contour of edentulous ridge should be carefully evaluated before a
fixed partial denture is undertaken.
•The ideal ridge height and width allows placement of a natural looking
pontic which facilitates maintenance of plaque-free environment.
•Loss of residual ridge contour may lead to unasthetic open gingival
embrasures, food impaction and percolation of saliva during speech.
Role of alveolar bone in implantology
ROLE OF ALVEOLAR BONE IN IMPLANTOLOGY
•Dental implants have become a predictable treatment option for
restoring missing teeth.
•The term bone quality is commonly used in implant treatment and
reports on implant success and failure. Bone quality encompasses factors
other than bone density such as skeletal size, the architecture and 3-
dimensional orientation of the trabeculea, and matrix properties
.
•Bone quality is not only a matter of mineral content, but also of
structure. It has been shown that the quality and quantity of bone
available at the implant site are very important local patient factors in
determining the success of dental implants (Drage et al., 2007; Lindh et
al., 2004). Therefore, it is important to know the bone quantity and
quality of the jaws when planning implant treatment.
MISCH BONE DENSITY CLASSIFICATION
• D1: Dense
cortical bone
• D2: Thick
dense to porous
cortical bone on
the crest and
coarse
trabecular bone
within.
D3: Thin
porous cortical
bone on crest
and fine
trabecular bone
within.
D4: Fine
trabecular bone
D5:Immature,
non-mineralized
bone
Bone classification schemes
related to implant dentistry
LEKHOLM AND ZARB IN 1985
QUALITY 1
• HOMOGENOUS
COMPACT BONE
QUALITY 2
• THICK LAYER
OF COMPACT
BONE
SURROUNDING
A COREOF
DENSE
TRABECULAR
BONE
QUALITY 3
• THIN LAYER OF
CORTICAL BONE
SURROUNDING
DENSE
TRABECULAR
BONE
QUALITY 4
• THIN LAYER OF
CORTICAL BONE
SURROUNDING
A CORE OF LOW
DENSITY
TABECULAR
BONE
•In the jaws, an implant placed in poor-quality bone with thin cortex and
low-density trabeculae (Quality IV by Lekholm and Zarb (1985)) has a
higher chance of failure compared with the other types of bones. This
low density bone is often found in the posterior maxilla and several
studies report higher implant failure rates in this region (Bryant, 1998;
Drage et al., 2007; Penarrocha et al., 2004).
•When compared to the maxilla, clinical reports have indicated a higher
survival rate for dental implants in the mandible, particularly in the
anterior region of the mandible, which has been associated with better
volume and density of the bone (Turkyilmaz et al., 2008).
OSSEOINTEGRATION
•American Academy of Implant Dentistry
defined it as “contact established without
interposition of non bone tissue between
normal remodeled bone and on implant
entailing a sustained transfer and distribution
of load from the implant to and within bone
tissue”.
•Osseointegration requires new bone
formation around the fixture. A process
resulting from remodeling within bone tissue.
•Osteoblastic and osteoclastic activity helps
maintain blood calcium without change in
quantity of bone.
SYSTEMIC DISORDERS
AFFECTING ALVEOLAR BONE
• Systemic disorders affect the entire body , so the
radiographic changes manifested in the jaws are generlized .
The general changes include :
1. A change in size and shape of the bone.
2. A change in the number ,size and shape of the trabeculae.
3. Altered thickness and density of cortical structures.
4. An increase or decrease in overall bone density.
•Metabolic disorders
• Osteoporosis
• Rickets and osteomalacia
• Osteopetrosis
• Hypophosphatasia
• Hypophosphatemia
• Renal osteodystrophy
Endocrine disorders:
•Hypo/Hyperparathyroidism
•Hyperpitutarism
•Hypo/Hyperthyroidism
•Diabetes mellitus
•Cushings syndrome
OSTEOPOROSIS
•Generalized decrease of bone mass and density.
•Imbalance occurs between bone formation and resorption.
•Decrease in bone formation result in changes in trabecular
architecture ,volume of trabecular bone, size and thickness of
individual trabeculae.
•Trabeculae are thin and indistinct
•(Diffuse granularity)
•Thinning of cortical boundaries
such as inferior mandibular cortex.
•Lamina dura may appear thinner.
RICKETS AND OSTEOMALACIA
•Inadequate serum calcium and phosphorus levels
• both abnormalities result from a defect in the normal activity of the
metabolites of Vitamin D, required for resorption of calcium in the
intestine. .
•Accumulation of osteoid in place of mineralized bone.
•RICKETS
oInferior mandibular border or the mandibular canal walls may be
thinned.
oCancellous bone trabeculae beco-
mes reduced in density, number,
thickness.
oLamina dura may be thinned
•OSTEOMALACIA
oGeneralized rarefaction of jaws
oCortical thinning
oSparse trabeculae
oLamina dura is thinned or lost
HYPOPHOSPHATASIA
•Due to defective production or function of alkaline phosphatase.
•Jaws: generalized radiolucency of maxilla and mandible.
• both cortical bone and lamina dura are thin.
•Alveolar bone is poorly calcified and may appear deficient.
•Both primary and permanent tooth have thin enamel, large pulp
chambers.
•Tooth is hypoplastic.
RENAL OSTEODYSTROPHY
•Renal rickets: bone changes result from chronic renal failure
•General: generalized decreased bone density and thinning of bony
cortices.
•Jaws: decrease in no of trabeculae, pattern is granular
•Loss of distinct lamina dura.
•Of interest is the occassional finding of an increase in bone density.
OSTEOPETROSIS
•Synonyms: albers –schonberg and marble bone disease
•Disorder of bone results from a defect in the differentiation and
function of osteoclasts
•Increased density bilaterally
•Internal aspect of bone is radio-opaque and lamina dura is lost.
•Entire bone is enlarged.
•Increased radio-opacity of jaws .
•Delayed eruption, loose tooth, malformed roots, missing tooth,
poorly calcified, more prone to caries.
•Lamina dura is thicker than normal
HYPERPARATHYROIDISM
•It is an endocrine abnormality in which there is an excess of
circulating PTH due to which there is increased bone remodelling and
serum calcium levels.
•Osteitis fibrosa generalisata(cystica): refers to pattern of generalised
rarefaction of bone.
•Bones appear quite radiolucent with thin cortices and hazy indistinct
trabeculae.
•Thinning of the cortical boundaries
•Density of the jaws is decreased
•The teeth stand out in contrast
to the radiolucent jaws,
•Normal trabecular pattern to
ground glass appearance.
•Trabeculae are numerous small
randomly oriented.
•Loss of lamina dura
HYPERPITUTARISM
• Results from hyperfunction of the anterior lobe of the pituitary
gland,which increases the production of the growth hormone.
• Enlargement of the jaws , most notably the mandible.
•Increase in the length of the dental
arches.
•The most profound growth occurs
in the condyle and ramus , often
resulting in class III skeletal
relationship.Thickness and height
of the alveolar process may
increase.
•Hypercementosis may be seen.
HYPERTHYROIDISM
•Excessive production of thyroid hormo
ne and increased level of thyroxine.
•Generalized decrease in bone density.
•Early eruption and premature loss of
primary teeth.
HYPOTHYROIDISM
•Synonyms; myxedema, cretinism
•In sufficient secretion of thyroxin
•Delayed eruption and short roots
•Thinning of lamina dura
•Maxilla and mandible are relatively
small
•External root resorption
REFERENCES
• Orban’s oral histology and embryology
• Contemporary Implant Dentistry, Carl E. Misch
• Prosthodontic Treatment for Edentulous
Patients, Boucher
• Oral Radiology: Principles and Interpretation, Stuart C.
White, Michael J. Pharoah
• Bone Quality Assessment for Dental Implants Ayse Gulsahi
Baskent University Faculty of Dentistry, Ankara, Turkey
Thank you

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BONE

  • 2. 1. Introduction 2. Classification 3. Composition 4. Histology 5. Formation 6. Resorption 7. Remodeling 8. Alveolar process and Alveolar bone 9. Clinical implications 10. Systemic Disorders affecting Bone 11. References CONTENTS
  • 3. WHAT IS BONE • Bone is essentially a highly vascular, living, constantly changing mineralized connective tissue. • It is remarkable for its hardness, resilience and regenerative capacity, as well as its characteristic growth mechanisms. • It is the basic unit of human skeleton.
  • 7.
  • 8. COMPOSITION •Minerals- Hydroxyapatite crystals •Amorphous Calcium phosphate • Mg, Na, K ,Fl Zn,Cu – smaller quantity INORGANIC CONTENT •Collagen ( Type I >95% primarily),TYPE V ORGANIC CONTENT •Osteocalcin/ bone gla protein •Osteopontin •Bone sialoprotein •Other proteins- osteonectin, dermatopontin and proteoglycans NON-COLLAGENOUS PROTEINS
  • 10. All bones consist of : 1.Outer compact bone 2.Inner medullary cavity (cancellous/trabecular bone + red/yellow marrow) Periosteum The outer surface of most bone is covered by a layer of condensed fibrous tissue, the periosteum which contains cells capable of converting into osteoprogenitor cells and osteoblasts. Endosteum Is a thin vascular connective layer that lines the inner surface of the bony tissue that forms the medullary cavity of long bones.
  • 11. Compact Bone • This type of bone is ivory-like and dense in texture without cavities. • Forms the thick-walled tube of the shaft (or diaphysis) of long bones, which surrounds the marrow cavity (or medullary cavity). A thin layer of compact bone also covers the epiphyses of long bones. • It consists mainly of haversian systems or secondary osteons • Contains blood vessels, lymphatic vessels, nerves, and osteocytes along with the calcified matrix.
  • 12. •Haversian Systems •The basic metabolic unit of compact bone also called osteons
  • 13. •Volkmann's canals •Are oblique canals running at right angles to the long axis of bone. •Contain the neurovascular bundle and connect the haversian canals with each other and also with the medullary cavity . •Lamellae •Concentric - surrounding each Haversian canal •Interstitial - bony plates that fill in between the haversian systems. •Circumferential – Circumferential lamellae are circular lamellae that line the external surface of the cortex adjacent to the periosteum and line the inner surface of the cortex next to the endosteum. There are more outer than inner circumferential lamellae. •Lacunae These are small spaces between the lamellae , each containing a bone cell called osteocyte. •Canaliculli These are fine radiating channels which connect the lacunae with each other and central haversian canal
  • 14. SPONGY BONE • Spongy bone (anatomic term)/ Trabecular bone (radiographic term)/ Cancellous bone (histologic term) • They have the same cells and intercellular matrix but differ in the arrangement of the components. These are poorly organized tissue in contrast to compact bone and contains more spaces as compared to compact bone. • Trabeculae aligned in path of tensile and compressive stresses to provide maximal resistance to occlusal forces with minimum bone substance (Glickman et al 1970)
  • 15. HEMOPOIETIC TISSUE IN BONES •Red marrow is present in young bone. •It contains stem cells of both fibroblast/mesenchymal and blood lineage . •It is found within cavities of spongy bone of long bones and diploe of flat bones. •Yellow marrow is present in old bone. •Characterized by loss of hemopoietic potential and increased accumulation of fat cells.
  • 16. BONE CELLS OSTEOBLASTS Osteoblasts are mononucleated cells responsible for the secretion and synthesis of the organic constituents of bone matrix. These cells are derived from osteoprogenitor cells of mesenchymal origin. • Basophilic, plump cuboidal / slightly elongated cells. • These cells are found on the forming surfaces of growing or remodelling bone. • The most active secretory cells in bone.
  • 17. Produce-- • Type I collagen • Noncollagenous bone proteins like Sialoprotein, Osteopontin, Osteonectin • Growth factors –BMP, Transforming growth factor, insulin like growth factor, platelet derived growth factor, fibroblastic growth factor. •Express and release alkaline phosphatase, which has been shown to be closely associated with new bone formation and has been recognized as a reliable indicator of osteoblast function. • In addition, it has a controlling influence in activating Osteoclasts. It contains receptors for the parathyroid hormone,vitamin D3,estrogen and regulates the osteoclastic response to these hormones.
  • 18. OSTEOCYTES • Osteocytes are ‘entrapped’ osteoblasts within bone . •Osteocytes occupy spaces (lacunae) in bone called osteocytic lacuane. •No. of osteocytes depends on the rapidity of bone formation. More the rapidity more the cells per unit volume. •Osteocytes have an extensive network of cell processes or extensions and through these channels osteocytes maintain contact with adjacent osteocytes and osteoblasts .
  • 19. OSTEOCLASTS •Osteoclast is a type of bone cell that removes bone tissue by removing the mineralized matrix of bone. •These are large cells with 15-20 closely packed nuclei and acidophilic cytoplasm. •Lie in Howship’s lacunae. • Osteoclasts produce a number of enzymes, chief among them acid phosphatase, that dissolve both the organic collagen and the inorganic calcium and phosphorus of the bone.
  • 20. • The side of the cell closest to the bone contains many small projections (microvilli) that extend into the bone’s surface, forming a ruffled, or brush, border that is the cell’s active region. .
  • 21. MICROSCOPIC ORGANIZATION OF BONE With regard to matrix arrangement, bone tissue can be divided into the following categories: Woven bone (primary bone tissue) - This is immature bone, in which collagen fibers are arranged in irregular random arrays and contain smaller amounts of mineral substance and a higher proportion of osteocytes than lamellar bone; woven bone is temporary and is eventually converted to lamellar bone. Lamellar bone (secondary bone tissue) - This is mature bone with collagen fibers that are arranged in lamellae. Lamellae in compact bone are concentrically organized around a vascular canal, termed a haversian canals.
  • 22. BONE FORMATION • The process of bone formation is called osteogenesis . 1. Endochondral bone formation 2. Intramembranous bone formation
  • 24. ALVEOLAR PROCESS • The alveolar process is that portion of the maxilla and mandible that forms and supports the sockets of the teeth. • Proper development of the alveolar process is dependent on tooth eruption and its maintenance on tooth retention. When teeth fail to develop (e.g. anodontia), the alveolar process fails to form. • When all teeth are extracted, most of the alveolar process becomes involuted, leaving basal bone as the major constituent of the jawbone. The remaining jawbone, therefore, is much reduced in height. • It is composed of an outer and inner cortical plate of compact bone that enclose the spongiosa, a compartment composed of spongy bone .
  • 26. ALVEOLAR BONE PROPER • The alveolar bone proper consists partly of lamellated bone and partly of bundle bone and is about 0.1 - 0.4 mm thick. • It surrounds the root of the tooth and gives attachment to principal fibres of the pdl. LAMELLATED BONE o The deeper portion of the alveolar bone proper is made of haversian system (osteons). o Each osteons has a blood vessel in a haversian canal and is surrounded by concentric lamellae . o Some lamellae of this bone are arranged roughly prallel to the surface of the adjacent marrow spaces, whereas others form haversian systems.
  • 27. BUNDLE BONE oThe lamellated bone is covered by areas of bundle bone . oIt is that bone in which the principal fibres of the periodontal ligament are anchored. oIt is characterized by scarcity of fibrils in the intercellular substance. o Bundle bone is formed in areas of recent bone apposition. Lines of rest are seen in bundle bone.
  • 28. oRadiographically, it is also referred to as the lamina dura because of increased radiopacity,which is due to the presence of thick bone without trabeculations. • The alveolar bone proper , which forms the inner wall of the socket is perforated by many openings that carry branches of the interalveolar nerves and blood vessels into the pdl and is therefore called the cribiform plate. •Bone between the teeth is called interdental septum and is composed entirely of cribiform plate.
  • 29. SUPPORTING ALVEOLAR BONE Cortical plate • It consists of compact bone and form the outer and inner plates of the alveolar processes. • Bone underlying the gingiva is the cortical plate, both cribiform plate and cortical plate are compact bone separated by spongy bone. Spongy bone • It fills the area between the cortical plates and the alveolar bone proper.
  • 30. • The trabeculae of the spongy bone butress the functionl forces to which the alveolar bone proper is exposed. • Radiographically, spongiosa can be classified into two main types.  Type 1: The interdental and interradicular trabeculae are regular and horizontal in a ladder like arrangement. (more often in mandible)  Type2: Shows irregularly arranged numerous delicate interdental and interradicular trabeculae. (more often in maxilla) AGE CHANGES IN BONE • Alveolar sockets appear jagged and uneven. • The marrow spaces have fatty infiltration • The alveolar process in edentulous jaws decrease in size. • The distance between crest of the alveolar bone and CEJ increases with age. • Internal trabecular arrangement is more open, which indicate bone loss.
  • 31. • Houses the roots of teeth. • Anchors the roots of teeth to the alveoli, which is achieved by insertion of sharpey’s fibres into the alveolar bone proper. • Helps to move the teeth for better occlusion. • Helps to absorb and distribute occlusal forces generated during tooth contact. • Supplies vessels to periodontal ligament. • Houses and protects developing permanent teeth. FUNCTIONS OF ALVEOLAR BONE
  • 32. BLOOD 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 LYMPHATIC DRAINAGE •Submandibular lymph nodes
  • 33. BONE RESORPTION •Bone resorption is removal of mineral and organic components of bone under the action of osteolytic cells, of which the most important is the osteoclast. SEQUENCE OF EVENTS OF BONE RESORPTION First phase - Formation of osteoclast progenitors in the hematopoietic tissues. Second phase - Activation of osteoclasts at the surface of mineralized bone. Third phase – Involves Activated osteoclasts resorbing the bone.
  • 34. ALTERATIONS IN THE OSTEOCLAST Immediately before the resorption event, the osteoclasts undergo changes which faciliate bone resorption. The two distinct altertions are 1. Ruffled border 2. Sealing zone at the plasma membrane.  These changes occur only in the region of the cell that is next to the bone surface.  Sealing zone serves to attach the osteoclasts very closely to the surafce of bone and creates an islolated microenviroment for the resorption to take place.  The attachment of osteoclasts to the sealing zone is due to the presence of cell membrane proteins integrins,especially αVβ3 which binds to specific amino acids sequences present in proteins of the bone matrix, namely, RGD.
  • 35. REMOVAL OF HYDROXYAPATITE • Dissolution of mineral phase by the action of HCl. • The protons for the acid arise from the activity of cytoplasmic carbonic anhydrase II which is synthesised in the osteoclast. •Protons are released by an ATP consuming proton pump which is an absolute must for normal bone resorption. DEGRADATION OF ORGANIC MATRIX •Next step involves the digestion of organic components of matrix by proteolytic enzymes which are synthesized in ostoclasts,namely, CATHEPSIN –K and MMP-9. As a result visbile depression or Howship’s lacunae is excavated into the bone.
  • 36. REMOVAL OF DEGRADATION PRODUCTS FROM LACUNAE •Once liberated from bone , free organic and inorganic particles of bone matrix are packed in membrane bound vesicles within cytoplasm of osteoclast. •These vesicles and their contents pass across the cell and fuse with FSD (Function secretory domain) a specialized region of basal membrane. •The vesicles are released by exocytosis into the extracellular space away from bone. •Following resoprtion osteoclasts undergo apoptosis , which provides a mechanism for limiting resorptive activity.
  • 37. During this phase bone is formed along the periosteal surface and destroyed along the endosteal surface . BONE REMODELLING • Bone remodelling is performed by clusters of osteoclasts and osteoblasts arranged within temporary anatomical structures called Basic Multicellular Units (BMUs). • Traversing and casing the BMU is a canopy of cells that creates a bone-remodelling compartment. The status of bone represents the net result of a balance between the two processes. ‘Coupling’ of bone resorption and formation.
  • 38.
  • 39. An active BMU consists of a leading front of osteoclasts and osteoblasts occupy the tail portion of the BMU – • The leading edge of resorption Cutting cone • Osteoblasts secrete osteoid Filling cone
  • 40. The main functions of remodeling are- To prevent the accumulation of damaged and fatigued bone by regenerating new bone. To allow bone to respond to changes in mechanical forces. To facilitate mineral homeostasis. STRUCTURAL LINES IN BONE 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.
  • 41. Mediators of bone remodelling Parathyroid Hormone Calcitonin • Estrogen • Vitamin D3 • Growth hormones • IL -1 • TNF α and β • Prostaglandins • BMPs • Bacterial products
  • 42. Clinical implications of Alveolar bone in Complete dentures EDENTULOUS INTRAORAL BONY CHANGES •Anatomic changes will invariably take place within the alveolar processes of the jaws following dental extractions. • When the teeth are present, the pressures exerted are transmitted in the form of tension to the bone by the periodontal membrane. This type of stress is acceptable for the alveolar bone. •Once the teeth are extracted, the load is not directed to the entire bone, but is applied only its surface. Alveolar bone can only tolerate this compression to a certain extent. • The long-term effect of dentures over bone is the atrophy of the residual alveolar ridge or what Atwood calls reduction of residual ridges (RRR).
  • 43. Residual alveolar ridge is the portion of the alveolar ridge and its soft tissue covering which remains following the removal of or loss of teeth. [GPT-8] •The residual bony architecture of the maxilla and mandible undergoes a life-long catabolic remodelling. •The rate of reduction in size of the residual ridge following extractions is maximum in the first 3-6 months and then gradually tapers off.
  • 44. According to Atwood’s : (JPD 1971 Vol.26) Order 1 : Pre-extraction Order 2 : Post-extraction Order 3 : High, well rounded Order 4 : Knife-edge Order 5 : Low, well rounded Order 6 : Depressed ORDER 1 ORDER 2 ORDER 3 ORDER 4 ORDER 5 ORDER 6 CLASSIFICATION
  • 45. TREATMENT AND PREVENTION •A thorough knowledge will provide the clinician with the additional piece of information required for the selection of an adequate plan of treatment. • For certain types of atrophy, a combination of surgery and prosthetics is required to provide a rapid solution for patients severely handicapped by dentures. •It will permit the selection of a technique of choice for the treatment, based on knowledge about the condition of the remaining hard and soft tissues. •Most ideal is a high ridge with flat crest with parallel or nearly parallel sides. •Knife edge ridge or a ridge with multiple bony spicules offer the poorest prognosis.
  • 46. PROSTHETIC IMPLICATIONS OF ALVEOLAR BONE IN FPD •The contour of edentulous ridge should be carefully evaluated before a fixed partial denture is undertaken. •The ideal ridge height and width allows placement of a natural looking pontic which facilitates maintenance of plaque-free environment. •Loss of residual ridge contour may lead to unasthetic open gingival embrasures, food impaction and percolation of saliva during speech.
  • 47. Role of alveolar bone in implantology ROLE OF ALVEOLAR BONE IN IMPLANTOLOGY •Dental implants have become a predictable treatment option for restoring missing teeth. •The term bone quality is commonly used in implant treatment and reports on implant success and failure. Bone quality encompasses factors other than bone density such as skeletal size, the architecture and 3- dimensional orientation of the trabeculea, and matrix properties . •Bone quality is not only a matter of mineral content, but also of structure. It has been shown that the quality and quantity of bone available at the implant site are very important local patient factors in determining the success of dental implants (Drage et al., 2007; Lindh et al., 2004). Therefore, it is important to know the bone quantity and quality of the jaws when planning implant treatment.
  • 48. MISCH BONE DENSITY CLASSIFICATION • D1: Dense cortical bone • D2: Thick dense to porous cortical bone on the crest and coarse trabecular bone within. D3: Thin porous cortical bone on crest and fine trabecular bone within. D4: Fine trabecular bone D5:Immature, non-mineralized bone Bone classification schemes related to implant dentistry
  • 49. LEKHOLM AND ZARB IN 1985 QUALITY 1 • HOMOGENOUS COMPACT BONE QUALITY 2 • THICK LAYER OF COMPACT BONE SURROUNDING A COREOF DENSE TRABECULAR BONE QUALITY 3 • THIN LAYER OF CORTICAL BONE SURROUNDING DENSE TRABECULAR BONE QUALITY 4 • THIN LAYER OF CORTICAL BONE SURROUNDING A CORE OF LOW DENSITY TABECULAR BONE
  • 50. •In the jaws, an implant placed in poor-quality bone with thin cortex and low-density trabeculae (Quality IV by Lekholm and Zarb (1985)) has a higher chance of failure compared with the other types of bones. This low density bone is often found in the posterior maxilla and several studies report higher implant failure rates in this region (Bryant, 1998; Drage et al., 2007; Penarrocha et al., 2004). •When compared to the maxilla, clinical reports have indicated a higher survival rate for dental implants in the mandible, particularly in the anterior region of the mandible, which has been associated with better volume and density of the bone (Turkyilmaz et al., 2008).
  • 51. OSSEOINTEGRATION •American Academy of Implant Dentistry defined it as “contact established without interposition of non bone tissue between normal remodeled bone and on implant entailing a sustained transfer and distribution of load from the implant to and within bone tissue”. •Osseointegration requires new bone formation around the fixture. A process resulting from remodeling within bone tissue. •Osteoblastic and osteoclastic activity helps maintain blood calcium without change in quantity of bone.
  • 52. SYSTEMIC DISORDERS AFFECTING ALVEOLAR BONE • Systemic disorders affect the entire body , so the radiographic changes manifested in the jaws are generlized . The general changes include : 1. A change in size and shape of the bone. 2. A change in the number ,size and shape of the trabeculae. 3. Altered thickness and density of cortical structures. 4. An increase or decrease in overall bone density.
  • 53. •Metabolic disorders • Osteoporosis • Rickets and osteomalacia • Osteopetrosis • Hypophosphatasia • Hypophosphatemia • Renal osteodystrophy Endocrine disorders: •Hypo/Hyperparathyroidism •Hyperpitutarism •Hypo/Hyperthyroidism •Diabetes mellitus •Cushings syndrome
  • 54. OSTEOPOROSIS •Generalized decrease of bone mass and density. •Imbalance occurs between bone formation and resorption. •Decrease in bone formation result in changes in trabecular architecture ,volume of trabecular bone, size and thickness of individual trabeculae. •Trabeculae are thin and indistinct •(Diffuse granularity) •Thinning of cortical boundaries such as inferior mandibular cortex. •Lamina dura may appear thinner.
  • 55. RICKETS AND OSTEOMALACIA •Inadequate serum calcium and phosphorus levels • both abnormalities result from a defect in the normal activity of the metabolites of Vitamin D, required for resorption of calcium in the intestine. . •Accumulation of osteoid in place of mineralized bone. •RICKETS oInferior mandibular border or the mandibular canal walls may be thinned. oCancellous bone trabeculae beco- mes reduced in density, number, thickness. oLamina dura may be thinned •OSTEOMALACIA oGeneralized rarefaction of jaws oCortical thinning oSparse trabeculae oLamina dura is thinned or lost
  • 56. HYPOPHOSPHATASIA •Due to defective production or function of alkaline phosphatase. •Jaws: generalized radiolucency of maxilla and mandible. • both cortical bone and lamina dura are thin. •Alveolar bone is poorly calcified and may appear deficient. •Both primary and permanent tooth have thin enamel, large pulp chambers. •Tooth is hypoplastic.
  • 57. RENAL OSTEODYSTROPHY •Renal rickets: bone changes result from chronic renal failure •General: generalized decreased bone density and thinning of bony cortices. •Jaws: decrease in no of trabeculae, pattern is granular •Loss of distinct lamina dura. •Of interest is the occassional finding of an increase in bone density.
  • 58. OSTEOPETROSIS •Synonyms: albers –schonberg and marble bone disease •Disorder of bone results from a defect in the differentiation and function of osteoclasts •Increased density bilaterally •Internal aspect of bone is radio-opaque and lamina dura is lost. •Entire bone is enlarged. •Increased radio-opacity of jaws . •Delayed eruption, loose tooth, malformed roots, missing tooth, poorly calcified, more prone to caries. •Lamina dura is thicker than normal
  • 59. HYPERPARATHYROIDISM •It is an endocrine abnormality in which there is an excess of circulating PTH due to which there is increased bone remodelling and serum calcium levels. •Osteitis fibrosa generalisata(cystica): refers to pattern of generalised rarefaction of bone. •Bones appear quite radiolucent with thin cortices and hazy indistinct trabeculae. •Thinning of the cortical boundaries •Density of the jaws is decreased •The teeth stand out in contrast to the radiolucent jaws, •Normal trabecular pattern to ground glass appearance. •Trabeculae are numerous small randomly oriented. •Loss of lamina dura
  • 60. HYPERPITUTARISM • Results from hyperfunction of the anterior lobe of the pituitary gland,which increases the production of the growth hormone. • Enlargement of the jaws , most notably the mandible. •Increase in the length of the dental arches. •The most profound growth occurs in the condyle and ramus , often resulting in class III skeletal relationship.Thickness and height of the alveolar process may increase. •Hypercementosis may be seen.
  • 61. HYPERTHYROIDISM •Excessive production of thyroid hormo ne and increased level of thyroxine. •Generalized decrease in bone density. •Early eruption and premature loss of primary teeth. HYPOTHYROIDISM •Synonyms; myxedema, cretinism •In sufficient secretion of thyroxin •Delayed eruption and short roots •Thinning of lamina dura •Maxilla and mandible are relatively small •External root resorption
  • 62. REFERENCES • Orban’s oral histology and embryology • Contemporary Implant Dentistry, Carl E. Misch • Prosthodontic Treatment for Edentulous Patients, Boucher • Oral Radiology: Principles and Interpretation, Stuart C. White, Michael J. Pharoah • Bone Quality Assessment for Dental Implants Ayse Gulsahi Baskent University Faculty of Dentistry, Ankara, Turkey

Editor's Notes

  1. Bone is a dynamic structure that is adapting constantly to its environment
  2. These bones are longer than they are wider. A Typical long bone has a tubular shaft which is also called as diphysis. It is made up of compact bone at the periphery surrounding a central medullary cavity which contains yellow marrow. The two bulky ends of long bones are called epiphyses which are made of copmactt bone at the periphery and spongy bone at the center. Each epiphysis meets the diaphysis at the metaphysis, the narrow area that contains the epiphyseal plate (growth plate), WHICH IS A layer of hyaline (transparent) cartilage in a growing bone. When the bone stops growing in early adulthood (approximately 18–21 years), the cartilage is replaced by osseous tissue and the epiphyseal plate becomes an epiphyseal line. The articular surface of the epiphyses is covered with hyaline cartilage, which provides a cushioning effect to the opposing bone ends during joint movements and absorbs atress. The medullary cavity has a delicate membranous lining called the endosteum. where bone growth, repair, and remodeling occur. The outer surface of the bone is covered with a fibrous membrane called the periosteum.The periosteum contains blood vessels, nerves, and lymphatic vessels that nourish compact bone. Long Bones Support Weight and Facilitate Movement
  3. Short bones are almost of equal length and width. They consist of spongy bone which is covered by a thin layer of compact bone and are joined by multiple articulations. It allows for increased flexibilitty , decreased mass but no sacrifice in strength.  short bones provide stability and some movement.These include bones of wrist(carpals) and ankles(tarsals). Flat bones- these are thin,flat,curved. In these types of bones spongy bone is present between upper and lower layer of compact bone. Spongy bones includes bones of sternum,ribs,scapula and bones that form roof of the skull. Flat Bones Protect Internal Organs. Irregular bones vary in shape and structure and are notched or with ridges. therefore do not fit into any other category (flat, short, long, or sesamoid). They often have a fairly complex shape, which helps protect internal organs. For example, the vertebrae, irregular bones of the vertebral column, protect the spinal cord. The irregular bones of the pelvis (pubis, ilium, and ischium) protect organs in the pelvic cavity and mandible. Sesamoid bones are bones embedded in tendons. These small, round bones are commonly found in the tendons of the hands, knees, and feet. Sesamoid bones function to protect tendons from stress and wear. The patella, commonly referred to as the kneecap, is an example of a sesamoid bone.
  4. BONE IS A CONNECTIVE
  5. Say whats in slide
  6. . It is made up of concentric bony layers or lamellae disposed around a central channel containing blood vessels, lymphatic and nerves. These neurovascular channels are known as canals of havers or haversian canals , and with their concentric lamellae form haversian systems. There may be upto 20 concentric lamellae in each osteon Function of volkma’s canal:transmit blood vessl from periosteum to deeper osteons
  7. Spongy bones have the same cells and intercellular matrix but differ in the arrangement of the components. These are poorly organized tiisue in contrast to compact bone .trabeculae are arrnged prallel to the lines of stress to withstand the forces applied to bone.
  8. In adults red bone marrow is primarily found in the flat bones such as pelvic girdle and the sternum.skull,vertebrae
  9. After Mesenchymal origin , say which are present in the bone marrow and other connective tissues. Periosteum also serves as a reservoir especially in childhood. Growth,after skeletal fratures or in bone forming tumors.
  10. Osteoblats produce the osteoid and as these cells form the bone matrix they get entapped within the matrix they secrete and are called osteocytes. Embryonic or repair bone show more oesteocytes. And also transduce signals that affect the cells involved in bone remodeling to maintain bone integrity and vitality.
  11. Osteoclasts with more nuclei resorb more bone than osteoclasts with few nuclei.
  12. Bone formation also known as osteogenesis is a process by which bone tissue replaces embryonic connective tissue . From childhood to adulthood ossification lengthens and thickens the bone. Intramembranous bone formation is the direct formation of bone within highly vascular sheets of condensed primitive mesenchyme. This process occurs in the flat bones of the skull and clavicles. It begins towrads the end of the 2nd month of gestation. The first step to formation of intramembranous bone is An ossification center appears in the fibrous connective tissue membrane- at the site where a bone will develop, there is initially loose mesenchyme, which appears as widely separareted , pale staining stellate cells with interconnecting cytoplasmic processes..(slide picture) these osteoblasts (slide picture). As the osteoblasts secrete osteoid the cells become trapped within the bone and becoem osteocytes. formation of woven bone- the first formed mass of newly formed bonw is an irregular shaped spicule which gradullay lengthen to form trabeculae, these trabeculae enclose local blood vessels and the early membrane bone is called woven bone.. 4. the new layers of bone matrix are deposited on pre exisiting bone surfaces thus showing an appositional growth, which results in a build up of bone tissue one layer at a time. As layers of bone tissue build up, the trabeculae just deep to the periosteum thicken and the soft tissue spaces gets narrowed. This process converts cancellous bone to compact bone. ENDOCHONDRAL This type of ossification involves the replacement of a cartilagenous model by bone and occurs at the extremities of all long bones,ribs,vertebrae base of the skull, articular extremity of the mandible. This process involves the following steps. Formation of cartlagenous model: at the site where a limb will emerge, the embryo shows outgrowth af mesoderm. The mesenchymal cells in this site condense, differentiate into chondroblasts and form the cartilage matrix, resulting in the development of a hyaline cartilage model. This process begins late in the 2nd month of development.
  13. As a result of adaptation to function alveolar process is further distinguised into alveolar bone proper andd supprting alveolar bone.
  14. The term bundle was chosen ,because, the bundles of principal fibres continue into the bone as sharpey;s fibres.
  15. The cortical plates , continously with the compact layers of the maxillary and mandibular body, are generally much thinner in the maxilla, they are thickest in the premolar, molar regions of the lower jaw on the buccal side.
  16. Inferior alveoar nerve a branch of mandibular nerve which is itself the 3rd branch of the trigeminal nerve Psa braanch of maxillary nerve
  17. Immediately before the resorption event, the osteoclasts undergo changes by assuming a polarity of structure and function. The two distinct altertions are: Development of a Ruffled border Sealing zone at the plasma membrane. These changes occur only in the region of the cell that is next to the bone surface.The ruffled border consists of many infoldings which results in finger like projections and is the active part of the cell. At the periphery of ruffled border, the plasma membrane is smooth and apposed closely to the bone surface. This region is called the clear sealing zone.
  18. After the following alterations in the osteoclasts dissolution of mineral phase begins This is carried out by the action of hcl. The protons for the acid arise from the activity of cytoplasmic carbonic anhydrase II which is synthesised in the osteoclast. Protons are released across the ruffled border int the resoprtion zone by an ATP consuming proton pump. This leads to a fall in ph to 2.5-3.0 in the osteoclast resorption spaace the proton pump is an absolute requirement for normal bone resorption.
  19. Afte the degradation of both mineral and organic contents
  20. Bone remodelling is performed by clusters of bone resorbing osteoclasts and bone forming osteoblasts arranged within temporary anatomical structures called Basic Multicellular Units (BMUs). The process by which overall shape and size of bones is established
  21. Bone remodelling is a cellular mechanism behing bone turnover. It renews the bone piece by piece and thus ensureses correction of microdamage and enables the regulation of mineral homeostasis. Activation stage: the cells of the osteoblast lineage interact with the hemopoetic cells to initiate osteoclast formation. This stage of remodelling involves detection of an initiating remodelling signal. This signal can be in the form of mechanical strain on the bone or hormonal action on bone in response to systemic changes in homeostasis. Resorption stage:in this stage osteoblasts respond to signals generated by osteocytes and recruit osteoclast precursors to the remodelling site. In addition to the recruitment osteoblast also expresses M-csf, RANKL and MMP;s which promotes differentiation and survival of osteoclast precursors and mmps help to degrade the unmineralized osteoid that lines the bone surface and exposes rgd sites within mineralized bone. The osteoclasts tunnels into the surafce of the bone and travel along a vessel resorb the haverain lamellae and a part of circumferentil lamellae and form a resorption yunnel or a cutting cone. Reversal stage : the resorption stage is followed by reversal phase, comprising the differentiation of osteoblast precursor and discontinuation of resorption by osteoclast apoptosis. A mononuclear cel of undetermined cell lineage removes the collagen remenants in howships lacuna eand prepares the bone surface for osteoblast mediated bone formation. in the next stage , avtivated osteoblasts lay down new bone material, until the resorbed bone is entirely replaced by new one.. The entire area os osteon where active formation occurs is called the filling cone.for bone to assume its final form hydroxyapattite is incorporated into this newly deposied bone.
  22. BONE RESORBERS : Parathyroid Hormone:PTH affects bone cell function, may alter bone remodeling, and cause bone loss. PTH acts on both bone-resorbing cells (osteoclasts) and bone-forming cells (osteoblasts). When administered continuously, it increases osteoclastic bone resorption and suppresses bone formation. When administered in low dose intermittently, it stimulate bone formation, a response that has been called the anabolic effect of PTH CALCITONIN : Reduces calcium levels by inhibiting the ctivity of osteoclasts And by decreasing renal cell reabsorption of calcium and phosphate Vitamin D3 : IT FAVORS BONE RESORPTION BY INCREASING Osteoclast number and activity,Ruffled border size, Clear-zone volume ESTROGENS: favors bone formation by increasing the number and function of osteoblats. Growth hormones : act directly on osteoblasts tsimulating their activity and increasing the synthesis of collagen, osteocalcin, and alkaline phosphate IL -1 does not have a direct action and act via osteoblast. It inhibits the apoptosis of osteoclasts and has a direct promotional effect on osteoclast formation. TNF α and β stimulate bone resorption and believed to inhibit bone collagen and non collagenous protein synthesis. Prostaglandins and other arachidonic acid metabolites Bmps : most important factors for osteoblast differntiataion. Bacterial products
  23. Proximity of the alveolar bone to sinus cavities or major nerves (mandibular nerve) may create problems during tooth extraction or surgical interventions.
  24. Anatomic changes will invariably take place within the alveolar processes of the jaws following dental extractions. When the teeth are present, the pressures exerted on these structures during contraction of the masticatory muscles are transmitted in the form of tension to the bone by the periodontal membrane. This type of stress is acceptable for the alveolar bone and may even serve as a stimulus for alveolar bone remodeling. Once the teeth are extracted, the whole distribution of forces is changed. The load is not directed to the entire bone, but is applied only on its surface. Alveolar bone can only tolerate this compression to a certain extent. The long-term effect of dentures over bone is the atrophy of the residual alveolar ridge or what Atwood4 calls reduction of residual ridges (RRR). Residual alveolar ridge atrophy: Classifiication and influence of facial morphology Paul Mercier, D.D.S., F.R.C.D.(C),* and Roger Lafontant, M.D.** St. Mary’s Hospital Center, Montreal, Quebec, Can
  25. Proper design of dentures and maintenance Diet counselling Preprosthetic surgery Immediate dentures Overdentures
  26. Contemporary fixed prosthodontics , roseinstein
  27. Before suggesting implants as a possible teatment option we need to evaluate certain parameteres of alveolar bone , bone height bone width bone depth andbone quality. Bone length is the mesiodistal dimension, width is the bucolingual dimension and depth is the length from the crest to the nearest limiting landmark. Bone density is a key determinant in implant impanning.
  28. It occurs with the aging process of bone and can be considered a normal variation of normal (primary )
  29. Calcium and p are required for normal calcification of bone and teeth.
  30. Alakaline phospatase is required for normal mineralization of osteoid.(autosomal dominant) Hypophosphatasia results in teeth with thin enamel, thin root dentin and large pulp chambers
  31. This panoramic image reveals areas of radiolucency corresponding to loss of bone mass, loss of distinct lamina dura, and a sclerotic bone pattern around the roots of the teeth.
  32. The jaws are usually osteoporotic nad in extreme cases remarkably radiolucent
  33. Delayed closing of the epiphysis with production of numerous wormian bones.