overview on alveolar bone

1. Alveolar bone
Shashi Kant Chaudhary
JRII
Dept of Periodntology & Oral Implantology
Seminar

2. Content
 Introduction
 Development
 Gross histology
 Cellular components
 Regulation of bone metabolism
 Alveolar process
 Alveolar bone modeling and remodeling
 Conclusion
 References

3. Introduction
 Bone is a complex organ composed of multiple specialized tissues
(osseous, periosteum/endosteum, and bone marrow) that act
synergistically and serve multiple functions
 Bone is a living tissue, which makes up the body skeleton and is
one of the hardest structures of the animal body.
 A specialized connective tissue composed of organic and
inorganic elements that mineralizes

4. Classification
Based on shape :
Long Short Flat
Irregular
bones

5. Based on development
Endochondral bones
Intramembranous
bones.

6. Based on microscopic structure
Mature
bone
compact bone
cancellous
bone
Immature
bone.

7. Development
 During embryogenesis, the skeleton forms by either a
direct or indirect ossification process
 Although histologically one bone is no different from
another, bone formation occurs by three main
mechanisms:
Intramembranous
Endochondral and
Sutural

8. Intramembranous bone formation
 Intramembranous bone formation occurs directly within
mesenchyme
 Eg. mandible, maxilla, skull, clavicle
 Mesenchymal progenitor cells condensate and undergo
direct differentiation into osteoblasts, a process known as
intramembranous osteogenesis.

9. 1. Formation of bone matrix in fibrous
membrane
2. Formation of woven bone
3. Appositional growth mechanism and
formation of compact bone
4. Formation of osteon

11. ENDOCHONDRAL BONE FORMATION
 The mandibular condyle, the long bones and vertebrae form
initially through a cartilage template, which serves as an
anlage that is gradually replaced by bone.
 The cartilage‐dependent bone formation and growth process
is known as endochondral osteogenesis (Ranly 2000)

13. Sutural bone growth
 Bone forms along suture margins
 Found in skull
 Fibrous joints between bones
 Allow only limited movement
 Helps skull and face to accommodate growing
organs like eyes and brain

14. COMPOSITION OF BONE
 Bone is a connective tissue composed of cells, fibers and
ground substance.

15. Inorganic components
 The inorganic part is made of bone minerals
 Hydrated calcium and phosphate in the form of
hydroxyapatite crystals [3Ca3(PO4)2(OH)2] are the
principal inorganic constituent
 Ions present are calcium phosphate, hydroxyl and
carbonate.
 Citrate, magnesium, sodium, potassium, fluoride, iron,
zinc, copper, aluminum, lead, strontium, silicon and boron
are present in small quantities

16. Organic components
 The organic matrix is known as osteoid
 Made – collagen(90%) and noncollagenous proteins
 Type I collagen (> 95%) is the principal collagen, type V
collagen (< 5%)
 Alveolar bone :- type I, type V, type III and type XII
collagen, (Type XII expressed under mechanical strain)
 Sharpey’s fibers:- type III with type I collagen.

17. Noncollagenous proteins
 10% of the total organic content of bone matrix
 Most are endogenous proteins produced by bone
cells, while some like albumin are derived from other
sources such as blood
 Noncollagenous Proteins are

18. • first noncollagenous protein to be recognized (less than 15%
of the noncollagenous bone protein)
• Also known as bone Gla protein as it contains the amino acid
γ-carboxy glutamic acid.
• Is a glycoprotein secreted by osteoblasts and regulated by
vitamin D3 and parathyroid hormone.
• Carboxy terminal acts as a chemoattractant to osteoclast
precursors, suggesting a role in bone resorption
• Involved in bone calcification as it is a calcium binding protein
Osteocalcin

19. • Previously termed as bone sialoproteins I and II
• Heavily glycosylated and phosphorylated with high levels of
acidic amino acids.
• Glutamic acid is predominant in bone sialoprotein
• Aspartate is predominant in osteopontin.
• Bone sialoprotein-function in the initiation of mineral crystal
formation& transcription is suppressed by vitamin D3
• osteopontin is a potent inhibitor of hydroxyapatite crystal
growth & transcription is strongly upregulated by vitamin D3,
• TGF-β family members and glucocorticoids- stimulate
expression of both protein
Osteopontin & Bone sialoprotein

20. • 25% of noncollagenous proteins
• Bound to collagen and hydroxyapatite crystals
• Secreted calcium binding glycoprotein, that
interacts with extracellular matrix molecules.
• May play a role in the regulation of cell adhesion,
proliferation and modulation of cytokine activity, and
in initiating hydroxyapatite crystal formation.
Osteonectin

21. • A large chondroitin sulfate proteoglycan, two small
proteoglycans, biglycan and decorin (chondroitin sulfate
proteoglycan I and II respectively)
• Decorin and biglycan comprise < 10% & decreases with maturation
of bone.
Proteoglycans
• More prominent in developing bone and has been mineralized to
pericellular areas.
• The precise function unknown, but similar to decorin, it can bind
TGF-β and extracellular matrix macromolecules, including collagen,
and thereby regulate fibrillogenesis.
Biglycan
• Binds mainly within the gap region of collagen fibrils and decorates
the fibril surface.
Decorin

22. • Components of demineralized bone and dentin
matrix.
• Regulate the cellular response to TGF-β
Lysyl oxidase & tyrosine rich acidic
matrix proteins (TRAMP)
• A critical enzyme for collagen crosslinking.
Lysyl oxidase
• Also known as dermatopontin, binds decorin
and TGF-β,
TRAMP

23. • Not secreted by osteoblasts but regulate mineralization.
• Matrix Gla protein is a mineral binding ECM protein secreted
by vascular smooth muscle cells and chondrocytes that
prevent mineralization in vascular tissues and cartilage.
• The absence of α2HS glycoprotein, which is produced by the
liver, compromises the inhibition of apatite formation by
serum.
Procollagen peptides, thrombospondin, fibronectin, vitronectin and alkaline
phosphatase are the other proteins found in bone.
Also contains proteases, protease inhibitors and a variety of cytokines secreted by
osteoblasts, that regulate cell metabolism.
These cells secrete several members of bone morphogenetic proteins (BMP)
superfamily, including BMP-2, BMP-7, TGF-β, insulin like growth factors (IGF-I and
IGF-II), platelet derived growth factor (PDGF) and fibroblast growth factor (FGF). IGF-I,
PDGF and TGF-β increase the rapidity of bone formation and bone repair.

24. BONE HISTOLOGY
 All mature bones have a dense outer
sheet of compact bone and a central
medullary cavity
 The cavity is filled with red or yellow
bone marrow
 Cavity shows a network of bone
trabeculae. (Trabecular, spongy or
cancellous bone are the terms used to
describe this network)

25. Compact bone
 The outer aspect of compact bone is surrounded by a
condensed fibrocollagen layer, the periosteum
 Two layers:
An outer layer which is a dense, irregular connective tissue
termed fibrous layer
An inner osteogenic layer, next to the bone surface consisting
of bone cells, their precursors and a rich vascular supply

27.  The inner surface of compact and
cancellous bone are covered by a thin
cellular layer called endosteum.
 Quiescent osteoblasts and
osteoprogenitor cells are present on the
endosteal surfaces.
 Act as reservoir of new bone forming
cells for remodeling or repair

28.  Mature or adult bones, whether compact or trabecular,
are histologically identical in that they consist of
microscopic layers or lamellae
Three distinct types of layering are recognized:
Circumferential Concentric Interstitial

30. Circumferential lamellae
 At the periosteal and endosteal
surfaces, the lamellae are arranged in
parallel layers surrounding the bony
surface and are called circumferential
lamellae
 Circumferential lamellae enclose the
entire adult bone, forming its outer
and inner perimeters

31. Concentric lamellae
 Deep to the circumferential lamellae, the lamellae are
arranged as small concentric layers around a central
vascular canal.
 Haversian (vascular) canal (about 50 μ in diameter) and the
concentric lamellae together is known as the osteon or
haversian system
 Concentric lamellae make up the bulk of compact bone and
form the basic metabolic unit of bone, the osteon
 up to 20 concentric lamellae within each osteon

32.  The osteon is a cylinder of bone,
generally oriented parallel to the
long axis of the bone.
 Adjacent haversian canals are
interconnected by Volkmann
canals; these channels, like
haversian canals, contain blood
vessels, thus creating a rich
vascular network throughout
compact bone

33. Interstitial lamellae
 Interspersed between adjacent
concentric lamellae and fill the spaces
between them
 Are actually fragments of preexisting
concentric lamellae from osteons
created during remodeling that can
take a multitude of shapes

34. Spongy bone
 Spongy bone and compact bone have the same cells and
intercellular matrix, but differ in the arrangement of
components.
 Looks like a poorly organized tissue
 Consists of large slender spicules called trabeculae. (up to
50 μm thick)
 The trabeculae are oriented along lines of stress to
withstand the forces applied to bone
 The trabeculae surround the marrow spaces from where
they derive their nutrition through diffusion

35. Bone marrow
 The bone marrow consists of hematopoietic tissue
islands, stromal cells, and adipose cells surrounded by
vascular sinuses interspersed within a meshwork of
trabecular bone
 Two Types
Red marrow:- consists mainly of hematopoetic tissue
Yellow marrow:-mainly made up of adipocytes.
 At birth, all bone marrow is red with age it is converted
to the yellow type

36. Bone cells
Two cell lineages are present in bone, each with specific
functions:
Osteogenic cells
Osteoprogenitors
Preosteoblasts
Osteoblasts
Osteocytes
Bone lining cells
Osteoclasts

38. Osteoprogenitor cells
 They are long, thin stem cell population
 Derived from mesenchyme
 Unspecialized stem cells
 Undergo mitosis and develop into osteoblasts
 Found on inner surface of periosteum and endosteum

39. Osteoblast
 Mononucleated cells, basophilic, plump cuboidal or
slightly flattened cells
 Found on surfaces of growing or remodeling bone
 Abundant and well developed protein synthetic organelles
(rough endoplasmic reticulum)
 Are fully differentiated cells and lack the capacity for
migration and proliferation
 Produce the organic matrix of bone (Osteoid)

40. Formation
Osteoprogenitor cells express transcription factors cbfa1/Runx-2 and osterix which are
essential for osteoblast differentiation
Mesenchymal progenitor cells, driven by the expression of a gene known as Indian
hedgehog (Ihh)
The IOPCs represent mesenchymal cells present in other organs and tissues that may
differentiate into bone forming cells when stimulated
DOPCs are present in the bone marrow, endosteum and periosteum and differentiate
into osteoblasts
Divided into two types
Determined osteogenic precursor cells
(DOPCs) and
Inducible osteogenic precursor cells
(IOPCs)
Derived from undifferentiated pluripotent mesenchymal stem cells

42. Functions
Formation of new bone
Regulation of bone remodeling and mineral metabolism
Mineralization of osteoid
Secrete small amounts of type V collagen, osteonectin, osteopontin,
RANKL, osteoprotegerin, proteoglycans, latent proteases and
factors including BMPs
Exhibit high levels of alkaline phosphatase used as a cytochemical
marker to distinguish preosteoblasts from fibroblasts
Express receptors for hormones involved in the regulation of
osteoblast differentiation

43. Fate of osteoblasts
At the end of bone forming phase, osteoblasts can have
one of four different fates
1. Become embedded in the bone as osteocytes
2. Transform into inactive osteoblasts and become bone
lining cells
3. Undergo apoptosis
4. Transdifferentiate into cells that deposit chondroid or
chondroid bone.

44. Bone lining cells
 Once osteoblasts have completed their function, they are
either entrapped in the bone matrix and become
osteocytes or remain on the surface as lining cells
 These cells cover most, but not all quiescent bone
surfaces in the adult skeleton.
 Together with osteocytes, bone forming cells and their
connecting cell processes appear to form an extensive
homeostatic network of cells capable of regulating
plasma calcium concentration.

45. Osteocytes
 As osteoblasts form bone, some become trapped in the
matrix they secrete, whether mineralized or
unmineralized; these cells then are called osteocytes
 The number of osteoblasts that become osteocytes varies
depending on the rapidity of bone formation;
 Embryonic (woven) bone and repair bone have more
osteocytes than does lamellar bone
 Osteocytes are stellate‐shaped cells that are embedded
within the mineralized bone matrix in spaces known as
osteoctic lacunae

46.  Osteocyte cytoplasmic projections (known as
dendrites)extend through cylindrical encased
compartments referred as canaliculi
 Osteocytes maintain contact with adjacent osteocytes,
osteoblasts or lining cells on the bone surfaces
 The osteocyte network is therefore an extracellular and
intracellular communication channel that is sensitive to
shear stress as the result of mechanical stimuli and bone
deformation

48.  Osteocytes translate mechanical signals into biochemical
mediators that will assist with the orchestration of anabolic
and catabolic events within bone
Canalicular–lacunar system arrangement allows osteocytes to
1. Participate in the regulation of blood calcium homeostasis
and
2. Sense mechanical loading and transmit this information to
other cells within the bone to further orchestrate osteoblast
and osteoclast function (Burger et al. 1995; Marotti 2000).

49.  Failure of any part of this interconnecting system results
in hypermineralization (sclerosis) and death of the bone.
 Later may be resorbed and replaced during the process
of bone turnover

50. Four schemes have been proposed to explain how an osteoblast could get
trapped within bone matrix
Osteoblasts are unpolarized and lay down bone in all
directions, i.e. the cells become trapped in their own
secretions.
Individual osteoblasts are polarized, but those within same
generation are polarized differently to those in adjacent
layers. As a result, bone is deposited in all directions
&osteoblasts become trapped.
Osteoblasts of each generation are polarized in the
same direction. One generation buries the preceding
one in bone matrix.
Within one generation, some osteoblasts slow down
rate of bone deposition or stop laying down bone, so
that they become trapped by the secretion of their
neighboring cells.

51. Osteoclast
 Greek words for “bone and broken”.
 Specialized multinucleated cells(approx 40–100 μm in
diameter with 15 to 20 nuclei)
 Lie in resorption bays called Howship’s lacunae
 Variable in shape due to their motility
 Tartrate resistant acid phosphatase within its cytoplasmic
vesicles and vacuoles which distinguishes it from
multinucleated giant cells.
 Adjacent to the tissue surface cell membrane of the
osteoclast form ruffled border

52.  At the periphery of this border, the plasma membrane is
apposed closely to the bone surface, and the adjacent
cytoplasm, devoid of cell organelles, is enriched in actin,
vinculin, and talin This is clear or sealing zone

53. Formation of osteoclast
 Derived from hemopoietic cells of monocyte macrophage
lineage.
 The differentiation into osteoclasts - involving cell–cell
interaction with osteoblast stromal cells
 Formation of osteoclast requires the presence of RANK
ligand (receptor activator of nuclear factor κB) and M-CSF
(macrophage colony stimulating factor).- produced by
stromal cells and osteoblasts direct contact of these cells
and osteoclast precursors.

54.  M-CSF act on receptor on osteoclast precursors c-Fms
(colony stimulating factor 1 receptor) and provides
signals for proliferation
 RANKL binds to RANK on surface of M-CSF triggered
osteoclast precursors into multinucleated giant cells, their
differentiation into mature osteoclasts, their attachment
to bone surface and their activation to resorb bone.

55.  Osteoprotegerin (OPG) recognizes RANKL, and blocks
the interaction between RANK and RANKL, leading to an
inhibition of osteoclast differentiation and activation
 Cbfa1 contributes to the expression of OPG

56. Regulation of osteoblast
• PTH is secreted in response to a hypocalcemic signal in order to
regulate calcium homeostasis by promoting bone resorption,
Role of parathormone (PTH)
• Stimulates synthesis of osteocalcin and osteopontin by osteoblasts
and suppresses collagen production
• Bone resorption at high concentrations (pharmacological) and
support bone formation at low (physiologic) concentrations.
Vitamin D3
• Required for attaining normal bone mass mediated by IGF-I.
Growth hormone

57. • Targets osteoblast & stimulates bone formation & mineralization
Insulin
• A subgroup of the TGF- β superfamily.
• Initiate osteoblastogenesis from uncommitted progenitor cells.
• BMPs 2, 4 and 6 direct the pluripotent cells to commit to an
osteoblastic pathway
Bone morphogenetic proteins
• Promote differentiation of osteoblasts & bone matrix formation
• Prolonged treatment with glucocorticoids results in bone loss
Glucocorticoids
• Promoting osteogenesis.
• It acts as a potent mitogen for all cells of mesenchymal origin
PDGF (platelet derived growth factor)

58. • Early stage to recruit & stimulate osteoprogenitor cells to
proliferate, providing a pool of early osteoblasts
• Later stages of osteoblast blocks differentiation and
mineralization.
TGF-β
• Increase proliferation and stimulating mature osteoblast
function
IGF I and II (insulin like growth factors)
• Play a critical role in angiogenesis and mesenchymal cell
mitogenesis FGF-2 is expressed by osteoblasts- bone
formation
FGF (fibroblast growth factors)

59. Regulation of osteoclast
• Suppresses the production of bone resorbing cytokines including IL-1 & IL-6
• Estrogen deficiency results bone resorption by increasing osteoclast activity
Estrogen
• Vitamin D3 promotes the differentiation of osteoclasts from monocyte
macrophage stem cell precursors - enhanced osteoclastic bone resorption
• PTH binds to osteoblasts and induces the production of M-CSF and RANKL-
- stimulate the maturation and action of osteoclasts.
Vitamin D3 and parathyroid hormone (PTH)
• Inhibits proliferation and differentiation of osteoclast precursors.
• Reduces the dimension of ruffled border & dissociation into monocytic cells.
Calcitonin

60. • Suppress bone resorption via injury to osteoclasts when they solubilize
bisphosphonate contaminated bone without consistent reduction in
osteoclast numbers
Bisphosphonates
• Mediators of bone resorption and can also influence bone formation
• Induce osteoclast formation through increased expression of RANKL on the
surface of immature osteoblasts and stromal cells
PGE2 (Prostaglandins of E series)
• Stimulates differentiation of osteoclast progenitors into osteoclasts
TNFα
• An inhibitor of osteoclast formation
OCIL (osteoclast inhibitory lectin)
• Inhibit proliferation and differentiation of committed precursors into mature
osteoclasts.
TGF-β and interferon-γ

61. Structural lines in bones
• The site of change from bone
resorption to bone formation is
represented by a scalloped outline
• Rich in sialoproteiin & osteopontin
Reversal
line or
cementing
line
• Rythmic deposition of bone with
periods of relative quiescence
seen as parallel vertical lines
Resting line

62. ALVEOLAR BONE
The alveolar process is defined as that part of the maxilla and
the mandible that forms and supports the sockets of the
teeth. –Orbans
The alveolar bone is constituted strictly of the ALVEOLAR
PROCESS which is firmly attached to the basal bone of the
jaws – Tencate
The alveolar process is the portion of the maxilla and
mandible that forms and supports the tooth sockets (alveoli).
– Carranza

63. Functions of alveolar bone
 Houses the roots of teeth
 Anchors the roots of teeth to the alveoli, achieved by the
insertion of Sharpey’s fibers into the alveolar bone proper.
 Helps to move the teeth for better occlusion
 Helps to absorb & distribute occlusal forces
 Supplies vessels to periodontal ligament.
 Houses & protects developing permanent teeth, while
supporting primary teeth.
 Organizes eruption of primary and permanent teeth.

64. DEVELOPMENT OF ALVEOLAR PROCESS
 At the end of 2nd month of fetal life,
the maxilla as well as mandible forms
a groove that open to surface of oral
cavity
 Tooth germs contained in these
groove (alveolar vessels & nerve)
 Alveolar process consists of bone
which is formed both by cells from the
dental follicle (alveolar bone proper) &
cells which are independent of tooth
development

65. Permanent tooth moves into place, developing its own alveolar bone from its own
follicle
When a deciduous tooth is shed, its alveolar bone is resorbed. Alveolar process
gradually incorporated into maxillary or mandibular body.
With the onset of root formation - interradicular bone develops in multirooted
teeth.
Teeth separated from each other by the development of interdental septa.
The developing teeth lie in a trough of bone -Tooth Crypt.
Resorption - inner wall of the alveolus/ Deposition -outer wall.
Alveolar process develops from the dental follicle during eruption of tooth size of
the alveolus is dependent upon the size of the growing tooth germ.

66. STRUCTURE OF THE ALVEOLAR BONE
 Anatomically, no distinct boundary
exists between the body of the maxilla
or the mandible and alveolar
processes.
 As a result of its adaptation to function,
two parts of the alveolar process can
be distinguished,
The alveolar bone proper and
The supporting alveolar bone

67. Alveolar bone
Supporting
alveolar bone
Cortical plate
Spongy bone
Alveolar bone
proper

69. Alveolar bone proper
 Consists partly of lamellated & partly of bundle bone
 About 0.1–0.4 mm thick.
 Surrounds the root of the tooth and gives attachment to
principal fibers of the periodontal ligament

70. Lamellated bone
 Contains osteons each of which has a
blood Vessel in a haversian canal.
 Blood vessel is surrounded by concentric
Lamellae to form osteon.
 Some lamellae of the lamellated Bone are
arranged roughly parallel to the surface of
the Adjacent marrow spaces, whereas
others form haversian systems.

71. Bundle bone
 Bone in which the principal fibers of the periodontal
ligament are anchored
 The term ‘bundle’ because, the bundles of the principal
fibers continue into the bone as Sharpey’s fibers
 Characterized by the scarcity of the fibrils in the
intercellular substance and arranged at right angles to
Sharpey’s fibers
 Contains fewer fibrils than does lamellated bone

72.  Sharpey’s fibers are mineralized at
the periphery and have a larger
diameter.
 These fibers are less numerous
than the corresponding fiber
bundles in the cementum

73.  Radiographically, it is also referred
to as the lamina dura, because, of
increased radiopacity, which is due
to the presence of thick bone
without trabeculations

74.  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 periodontal ligament, and it is therefore called
the cribriform plate

75.  Bone between the teeth is called interdental septum
 Composed entirely of cribriform plate.
 The interdental and interradicular septa contain the
perforating canals of Zuckerkandl and Hirschfeld (nutrient
canals) which house the interdental and interradicular
arteries, veins, lymph vessels and nerves

76. Supporting alveolar bone
Consists of two
parts
Cortical
plates
Spongy
bone

77. Cortical plates
 Consist of compact bone and form the outer and inner
plates of the alveolar processes
 Continuous with the compact layers of the maxillary
and mandibular body
 Thinner in the maxilla, than in the mandible
 Thickest in the premolar and molar region on buccal
side of the lower jaw
 The supporting bone usually very thin in anterior teeth
region of both jaws – no spongy bone

78.  Histologically, the cortical plates consist of longitudinal
lamellae and haversian systems.
 In the lower jaw, circumferential or basic lamellae reach
from the body of the mandible into the cortical plates

79. Spongy bone
 Spongy bone fills the area between the cortical plates
and the alveolar bone proper
 Contains trabeculae of lamellar bone- surrounded by
marrow that is rich in adipocytes and pluripotent
mesenchymal cells
 The trabeculae contain osteocytes in the interior and
osteoblasts or osteoclasts on the surface
 Trabeculae buttress the functional forces to which
alveolar bone proper is exposed

80. Classification of the spongiosa (radiographically )
Type I the interdental and interradicular
trabeculae are regular and horizontal in a ladder
like arrangement - most often in the mandible
Type II shows irregularly arranged, numerous,
delicate interdental and interradicular
trabeculae more common in the maxilla

81. lnterdental Septum
 The interdental septum consists of
cancellous bone and cortical plates
 If the interdental space is narrow, the
septum may consist of only lamina dura
(between mandibular 2ndpremolars
and 1stmolars consists of only lamina
dura in 15% cases)
 If roots are too close together, an
irregular "window" can appear in the
bone between adjacent roots

82.  The mesiodistal angulation of the
crest of the interdental septum
usually parallels a line drawn
between the cemento-enamel
junctions of the approximating
teeth
 The distance between the crest of
the alveolar bone and the CEJ in
young adults varies between 0.75
and 1.49 mm (average, 1.08 mm)
 This distance increases with age to
an average of 2.81 mm

83. Osseous topography
 Normally conforms to the
prominence of the roots
 The height and thickness of the
facial and lingual bony plates are
affected by the alignment of the
teeth, by the angulation of the
root to the bone, and by occlusal
forces

84. Fenestrations and Dehiscences
 Isolated areas in which the root is denuded of bone and
the root surface is covered only by periosteum and
overlying gingiva are termed as fenestrations
 In these instances the marginal bone is intact
 When the denuded areas extend through the marginal
bone, the defect is called a dehiscence
 Fenestration and dehiscence are important, because they
may complicate the outcome of periodontal surgery.

85. fenestrationdehiscence

86. • 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)

87. Bone formation
 The osteo progenitor cells express transcription factors
cbfa1/Runx2. cbfa1(osteoblast specific transcription
factors) Osterix and b- catenin (maturation)
 Osteoblast contains high level of alkaline phosphatase-
liberated phosphate - initiation and progressive growth
of bone mineral crystals
 Cytoplasm is intensely basophilic, abundant and well
developed protein synthetic organelles such as rough
endoplasmic reticulum

88.  Procollagen and other organic proteins synthesized and
transported to golgi complex by transfer vesicle
 Golgi complex form secretory vesicles and secret
extracellularly along the bone forming surface to form
osteoid(prebone)
 Osteoblasts produces Collagen type I, collagen type V
and non collagenous protein such as bone sialoprotein
and osteopontin- where they participate in regulating
mineral deposition

89. BONE RESORPTION
Sequence of events in resorptive process
Attachment of osteoclasts to mineralized surface of bone
Creation of a sealed acidic environment through action of the proton pump
which demineralizes bone and expose organic matrix
Degradation of the exposed organic matrix to its constituents amino acids by
action of released enzymes such as acid phosphatase and cathepsin
Sequestering of mineral ions and amino acids within the osteoclast
Ten Cate AR

90. Role of TRAP in bone resorption( tartarate
resistant acid phosphatase)
latent inactive proenzyme-cysteine proteinases convert it
into an active form
Extracellular role:
Regulate osteoclast adhesion to the bone
Degrades the phosphoprotein-degradation of the bone
matrix
Liberate pyrophosphate (inhibitor)osteoclast migration
Intracellular role:
 Endocytosed vesicle & TRAP containing vesicle fuses to
form functional secretory domain (FSD)

91. Extra cellular fate:
 TRAP taken up into circulation from interstitial space
 Bind with 2 macroglobulin
 Loses binuclear iron centre and recycled
 Free enzymes metabolized in liver & excreted through
urine

92. Various bone resorbing factors
A. Systemic factors:
(a) Parathyroid hormone
(b) Parathyroid related peptide
(c) Vitamin D3
(d) Thyroid hormone
B. Local factors:
(a) Prostanoids
(b) Lipoxygenase metabolites
(c) Cytokines: IL – 1, IL – 4, TNF – α,
TNF – β, IL – 6
C. Growth factors:
(a) EGF
(b) TGF – α
(c) TGF − β
(d) PDGF
D. Bacterial factors:
(a) Lipopolysaccharides
(b) Capsular material
(c) Peptidoglycans
(d) Lipoteichoic acids.

93. Bone modeling
 Bone modeling is defined as a change in the shape and
architecture of the bone
 It extends from embryonic bone development to the
pre-adult period of human growth, which is continuous
and covers a large surface
 The ability of bone to adapt to mechanical loads is
brought about by continuous bone resorption and bone
formation
 If these processes occur at different locations, the bone
morphology is altered, Frost defined this as modeling
(Frost, 1990a)

94. Bone remodeling
 Bone remodeling is defined as a change without
concomitant change in the shape and architecture of the
bone
 In a homeostatic equilibrium resorption and formation are
balanced In that case old bone is continuously replaced
by new tissue
 This ensures that the mechanical integrity of the bone is
maintained but it causes no global changes in
morphology, Frost defined this as remodeling (Frost,
1990b)

95.  In a healthy individual, this turnover is in a steady state;
that is, the amount of bone lost is balanced by bone
formed.
 Remodeling occurs in discrete, focal areas involving
groups of cells called bone remodeling or basic
multicellular units.

96. Activation
Resorption
ReversalFormation
Resting
The bone remodeling cycle

98.  As osteoclasts move through compact bone, they create a
resorption channel. The leading edge of resorption is termed
the cutting cone and is characterized by a scalloped array of
resorption lacunae (Howship’s lacunae), each housing an
osteoclast
 Behind the cutting cone is a migration of mononucleated cells
(macrophages and/or preosteoblasts) differentiate into
osteoblasts, The entire area of the osteon where active bone
formation occurs is termed the filling cone
 When formation is complete, the haversian canal contains a
central blood vessel and a layer of inactive osteoblasts, the
lining cells that communicate by means of cell processes with
the embedded osteocytes.

100. Remodeling of alveolar bone
 Major pathway of bony changes in shape, resistance to
forces, repair of wounds and calcium-phosphate
homeostasis
 Involves the co-ordination of activities of cells from two
distinct lineages, the osteoblasts and the osteoclasts
 A complex process involving hormone and local factors
acting in autocrine and paracrine manner on generation
and activity of differentiated bone cells

101. Coupling
 It is interdependency of osteoblasts and osteoclasts in
remodeling of the bone.
Parathyroid hormone
OSTEOBLASTS
Interleukin 1 and 6
Releases leukemia
inhibiting factor
(LIF)
Monocytes
Multinucleated
OSTEOCLASTS
(Resorb bone)
Bound to collagen
OSTEOBLASTS
(Deposits bone)
Stimulates
Release Stimulates
Migrates into bone and coalasces
Releases osteogenic substrates
Stimulates differentiation of

102. Age changes
In older individuals:
 Alveolar sockets appear jagged and uneven.
 The marrow spaces have fatty infiltration
 The alveolar process in edentulous jaws decreases in size.
 Loss of maxillary bone is accompanied by increase in size of the
maxillary sinus.
 Internal trabecular arrangement is more open, which indicates
bone loss.
 The distance between the crest of the alveolar bone and CEJ
increases with age—approximately by 2.81 mm.

103. Conclusion
 Bone is a mineralized connective tissue with a relatively
flexible character and compressive strength
 The property of plasticity allows it to be remodeled
according to the functional demands placed on it.
 In order to maintain stability and integrity of bone, it
constantly undergoes remodeling.
 About 10% of bone material is renewed each year.
 This process is brought about by osteoclasts and
osteoblasts.

104. References
 Newman ,Takei , Klokkevold , Carranza ; Carranza's Clinical
Periodontology ,10thedition,
 Newman ,Takei , Klokkevold , Carranza; Carranza's Clinical
Periodontology , 12th Edition.
 Niklaus P. Lang , Jan Lindhe , Clinical Periodontology And Implant
Dentistry ,6thedition
 Orban's Oral Histology And Embryology , 13th Edition ,
 Antonio Nancy, Ten Cate Oral Histology Development , Structure
And Function , 8th edition

105. Thank you