Description of bone, types, classification, types of cells, functions of cells, Histological analysis, clinical implications

2. INTRODUCTION
 Bone is a living tissue, which makes up the body
skeleton and is one of the hardest structures of the
animal body.
 Bone or osseous tissue represents the highest
differentiation among supporting tissues.
 It possesses a certain degree of hardness and
elasticity.

3. FUNCTIONS
 It provides shape and support for the body.
 It provides site of attachment for tendons and muscles,
which are essential for locomotion.
 Protects vital organs of the body.
 Serves as a storage site for minerals.
 Provides the medium, the marrow for the development
and storage of blood cells.

4. CLASSIFICATION OF
BONESAccording to Orban’s 12th edition
ACC.TO SHAPE
• LONG BONES
• SHORT BONES
• FLAT BONES
• IRREGULAR
BONES
• SESAMOID
BONES
ENDOCHONDRAL
BONES
INTRAMEMBRANOUS
BONES
BASED ON
DEVELOPMENT
1) MATURE BONE:
A) COMPACT BONE
(CORTICAL/LAMELLAR)
B) CANCELLOUS BONE
(SPONGY)
2) IMMATURE/WOVEN
BONE
BASED ON
MICROSCOPIC
STRUCTURE

5. QUALITY 1 :
homogenous
compact bone
QUALITY 2 :
thick layer of
compact bone
surrounding a
core of dense
trabecular bone.
QUALITY 3: thin
layer of cortical
bone surrounding
dense trabecular
bone of favorable
strength.
QUALITY 4: thin
layer of cortical
bone surrounding
a core of low
density trabecular
bone.
CLASSIFICATION BY LEKHOLM AND ZARB,1985

6. MISCH BONE DENSITY CLASSIFICATION:

7. ANATOMY OF BONE

8. • THE SHAFT OR MAIN
PORTION OF THE BONE
DIAPHYSIS
• THE EXTREMETIES OR
ENDS OF THE BONEEPIPHYSIS
• THE REGION IN A MATURE
BONE WHERE DIAPHYSIS
JOIN EPIPHYSIS
METAPHYSIS
ARTICULAR
CARTILAGE
a thin layer of hyaline cartilage
covering the epiphysis where bone
forms a joint with another bone.

9. • The tissue covering the outer surface of bone. It
consists of two layers. The outer fibrous layer is
rich in blood vessels, lymphatic vessels, and
nerves that pass into the bone and inner layer is
composed of osteoblasts surrounded by
osteoprogenitor cells.
PERIOSTEUM
MEDULLARY
OR MARROW
CAVITY
The space within the diaphysis that contains the fatty
yellow marrow in adults. Yellow marrow consists
primarily of fat cells and a few scattered blood cells.
Thus, yellow marrow functions in fat storage.
• A layer of osteoprogenitor cells and
osteoblasts that lines medullary cavity
and also contains scattered osteoclasts
ENDOSTEUM

10. GROSS BONE
HISTOLOGY
 Characteristic of all bones
are a dense outer sheet of
compact bone and a
central, medullary cavity.
 In living bone the cavity is
filled with red or yellow
bone marrow that is
interrupted, particularly at
the extremities of long
bones, by a network of
bone trabeculae
(trabecular, cancellous,
or spongy bone are the
terms used to describe this
network ).

11. compact bone consists of
microscopic layers or
lamellae.
Three distinct types of
layering are recognized:
circumferential,
concentric, and
interstitial.
Circumferential lamellae
enclose the entire adult
bone, forming its outer and
inner perimeters.

12.  Concentric lamellae make up the bulk of compact bone and form the basic
metabolic unit of bone, the osteon (also called the haversian system).
 The osteon is a cylinder of bone, generally oriented parallel to the long axis
of the bone. In the center of each is a canal, the haversian canal, which is
lined by a single layer of bone cells that cover the bone surface; each canal
houses a capillary. Adjacent haversian canals are interconnected by
Volkmann canals, channels that, like haversian canals, contain blood
vessels, thus creating a rich vascular network throughout compact bone.

13. Interstitial lamellae are interspersed between adjacent
concentric lamellae and fill the spaces between them.

15. Surrounding the outer aspect of every compact bone is
connective tissue membrane, the Periosteum, which has two
layers.
The outer layer of the periosteum consists of a dense, irregular
connective tissue termed the fibrous layer. The inner layer of
the periosteum, next to the bone surface, consists of bone
cells, their precursors, and a rich microvascular supply.
The internal surfaces of compact and cancellous bone are
covered by Endosteum.
However, this layer is not well demarcated and consists of
loose connective tissue containing osteogenic cells and that
physically separates the bone surface from the marrow within.
The periosteal surface of bone is more active in bone formation
than the endosteal one.

16. CANCELLOUS BONE/TRABECULAR
BONE /SPONGY BONE:
 Looks like poorly organized tissue in
contrast to compact bone.
 Does not contain any true osteon.
 Consists of long, slender spicules
called as trabeculae.
 Marrow spaces are large.
 Trabeculae are oriented along the
lines of stress to withstand the
forces applied to bone.
 Osteocytes in trabeculae receive
nourishment directly from blood
circulating through marrow cavities
 It makes up most of the bone
tissue of short, flat and irregular
bones and most of epiphysis of long
bones.

17. COMPOSITION OF BONE
CELLS
OSTEOPROGENITOR CELLS
OSTEOBLAST CELLS
OSTEOCYTES
OSTEOCLAST CELLS
ORGANIC PART
33%-35%
 COLLAGEN: 88-90% TYPE 1
 NON COLLAGEN:10-11%
A)GYLCOPROTEINS 6-9%
B)PROTEOGLYCANS 8%
C)SIALOPROTEINS 35%
D)LIPIDS 4%
INORGANIC PART
65-67%
 CALCIUM & PHOSPHATE
 MAGNESIUM
 TRACE ELEMENTS: Nickel, iron,
Fluoride, cadmium, zinc,
magnesium

18. ORGANIC MATRIX
 It is known as OSTEOID and is made of collagen and non
collagenous proteins.
 COLLAGEN is the major organic component in mineralized bone
tissues.
 Type I collagen (>95%) is the major organic component in
mineralized bone and together with type V collagen (<5%) forms
heterotypic fiber bundles that provide the basic structural integrity
of CT.
 Alveolar bone contains type I, V, III and XII collagen.
 Type I, V and XII collagens are expressed by osteoblasts.

19. NON COLLAGENOUS PROTEINS
 Comprise remaining 10% of the total organic content of bone
matrix.
1) OSTEOCALCIN
 Represents less than 15% of the
non collagenous bone protein
 the first non collagenous
proteins to be recognized.
 Also known as BONE GLA
PROTEIN as it contains the
amino acid ɣ-carboxyl glutamic
acid.

20. 2) OSTEOPONTIN AND BONE SIALOPROTEIN
 Previously termed as bone
sialoproteins I and II respectively.
 Glutamic acid is predominant in
bone sialoprotein aspartate in
osteopontin.
 BSP is restricted to mineralizing
tissues whereas osteopontin has a
more generalized distribution.
 Bone sialoprotein is thought to
function in initiation of mineral
crystal formation in vivo. In
contrast, osteopontin is a potent
inhibitor of hydroxyapatite crystal
growth.

21. 3) OSTEONECTIN
 Comprises about 25% of non collagenous proteins.
 Bound to hydroxyapatite crystals.
 also known as secreted protein, acidic and rich in cysteine
[SPARC]).
 It is a secreted calcium binding glycoprotein, that interacts with
extracellular matrix molecules.
 It may play a role in the regulation of cell adhesion and
proliferation and modulation
of cytokine activity.

22. 4) PROTEOGLYCANS
 Also present in the bone matrix
 A large chondroitin sulfate proteoglycan has been
extracted from the non mineralized bone matrix, while
two small proteoglycans, Biglycan and decorin
(chondroitin sulfate proteoglycan I and II resp.) have
been found in EDTA extracts of bone.
 Decorin and Biglycan comprise <10% of the non
collagenous proteins in bone, but this decreases with
maturation of bone.
 Decorin binds mainly within the gap region of collagen
fibrils and decorates the fibril surface.

23.  Biglycan is more prominent in the developing bone and
has been mineralized to pericellular areas.
 It can bind to TGF-β and extracellular matrix
macromolecules including collagen, and thereby
regulate fibrillogenesis.

24. INORGANIC PART

25. BONE CELLS
1) OSTEOPROGENITOR CELLS
- derived from mesenchyme
- all connective tissue is derived.
- unspecialized stem cells
- undergo mitosis and develop into “osteoblasts”
- found on inner surface of periosteum and endosteum.

26. 2) OSTEOBLASTS
 They are mononucleated cells responsible for the synthesis and
secretion of the macromolecular organic constituents of bone
matrix.
 Derived from osteoprogenitor cells of mesenchymal origin, which
are present in the bone marrow and other connective tissues.
 Osteoblasts are basophillic, plump cuboidal or slightly elongated
cells.
 The cells are found on the forming surface of growing or
remodeling bone.
 They form a protein mixture known as osteoid (primarily type I
collagen), which mineralizes to become bone.

27.  Osteoblasts exhibit abundant and well developed protein
synthetic organelle. The intense cytoplasmic basophilia is due to
an abundance of RER.
 Nucleus is situated in the part of the cell that is farthest away
from the adjacent bone surface..
 Osteoblasts also contain prominent bundles of actin, myosin and
cytoskeletal proteins which are associated with maintainence of
cell shape, attachment and motility.
 They exhibit high level of alkaline phosphatase on outer surface
of plasma membrane-used as a cytochemical marker to
distinguish preosteoblasts from fibroblasts.
 Total alkaline phosphatase activity has been recognized as a
reliable indicator of osteoblasts function

28. Inducible
osteoprogenitor
cells
Determined
osteoprogenitor
cell

29. FUNCTIONS
 Formation of new bone via synthesis of various proteins and
polysaccharides.
 Regulation of bone remodeling and mineral metabolism.
 It plays significant role in the mineralisation of osteoid.
 Osteoblasts also secrete small amount of type V collagen,
osteonectin, osteopontin, RANKL, osteoprotegerin, proteoglycans,
proteases, growth factors etc.
 Osteoblasts recognize the resorptive signal and transmit it to the
osteoclast.
 RANKL is a membrane bound TNF related factors that is expressed
by osteoblast/stromal cells. The presence of RANKL is vital in
osteoclast differentiation.

30. OSTEOCYTES
 Cells of mature bone & lie in the lacunae of bone.
 Represents osteoblasts imprisoned in matrix during bone
formation.
 The number of osteoblasts that becomes osteocytes depends on the
rapidity of bone formation.
 Within the bone matrix, the osteocyte reduces in size, creating a
space around it called the osteocytic lacuna.
 The lacuna can appear ovoid or flattened

32.  Narrow extensions of these launae form channels called
canaliculi.
 Osteocytic processes are present within these canaliculi.
Osteoblasts communicate with osteocytes through
canaliculi

33. Osteon with osteocytes Osteocytes residing
in lacunae in bone

34.  At the distal end, these processes contact the processes of adjacent
cells, i.e other osteocytes through gap junctions.
 They also maintain contact with osteoblasts and bone lining cell on
the surface.
 The canaliculi penetrates the bone matrix and permit diffusion of
nutrients, gases and waste products between osteocytes and blood
vessels.
 This interconnecting system maintains the bone integrity and bone
vitality.
 Failure of the interconnecting system between osteocytes and
osteoblasts leads to sclerosis and death of bone.

35. Functions
Maintains the integrity of the lacunae and canaliculi.
Keep open the channels for diffusion of nutrients through
bone.
Play role in removal and deposition of matrix and of calcium
when required.
Old osteocytes retract their processes from the canaliculi, and
when dead, their lacunae and canaliculi may get plugged with
debris.
The death of osteocytes leads to resorption of the matrix by
osteoclasts.

36. OSTEOCLASTS
 Bone resorbing cells derived
from hematopoetic cells of
monocyte-macrophage lineage.
 The word osteoclast is derived
from the Greek words for
“bone and broken”.
 Osteoclasts lie in resorption bay
called Howship’s lacunae.
 These are large cells approx.
40-100µm in diameter with 15
to 20 closely packed nuclei.

37.  Under EM, multinucleated osteoclasts exhibit a unique set of
morphologic characteristics.
 Adjacent to the tissue surface, the multinucleated osteoclast cell
membrane is thrown into a myriad of deep folds that form a ruffled
border.
 The cytoplasm of the osteoclast shows
acid phosphatase containing vesicles
and vacuole.
 Mitochondria are extensive and distributed throughout the
cytoplasm, except below the ruffled border.
 Cathepsin containing vesicles and vacuoles are present close to the
ruffled border indicating resorptive activity of these cells.

39. FOUR TYPES OF BONE
CELLS

41. Alveolar Process:
It may be defined as that part of maxilla
and the mandible that forms and
supports the sockets of the teeth.
Functions Of Alveolar Bone:
Houses the roots of teeth.
Anchors the roots of teeth to alveoli,
which is achieved by the insertion of
Helps to absorb and distribute occlusal forces generated during
tooth contact.
Supplies vessels to PDL.
Houses and protects developing permanent teeth, while supporting
primary teeth.
Organises eruption of primary and permanent teeth.
Helps to move the teeth for better occlusion.
sharpey’s fibers into the alveolar bone proper.

42. STRUCTURE OF ALVEOLAR BONE
 As a result of its adaptation to
function, two parts of the
alveolar process can be
distinguished-
1) The first part consists of a thin
lamella of bone that surrounds
the root of the tooth and gives
attachment to principal fibers of
the periodontal ligament. This is
the ALVEOLAR BONE
PROPER.
2) The second part is the bone that
surrounds the alveolar bone
proper and gives support to the
socket. This is called as the
SUPPORTING
ALVEOLAR BONE.

43. ALVEOLAR BONE
PROPER
The alveolar bone proper consists partly of lamellated and partly of
bundle bone.
LAMELLATED BONE:
Some lamellae of the lamellated bone are arranged roughly parallel
to the surface of adjacent marrow spaces, whereas others form
haversian systems.
BUNDLE BONE:
 It is the bone in which the principal fibers of PDL are anchored.
 The term ‘bundle’ was chosen because the bundles of the principal
fibers continue into the bone as Sharpey’s fibers.

44.  It contains fewer fibrils than does the lamellated bone and therefore
appears dark in routine H&E stained sections.
 In some areas, alveolar bone proper consists mainly of bundle bone.

45.  Radiographically, alveolar bone proper is called as LAMINA
DURA, because, of increased radiopacity, which is due to the
presence of thick bone without trabeculations, that X-rays must
penetrate and not to any increased mineral content.
 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 it is
therefore called as the CRIBRIFORM PLATE.
 Bone between the teeth is called as INTERDENTAL SEPTUM and
is 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.

47. SUPPORTING ALVEOLAR BONE
It consists of two parts:
1)Cortical plates 2)Spongy bone

48. CORTICAL PLATES
Consist of compact bone
and form the outer and
inner plates of alveolar
processes.
The cortical plates,
continuous with the
compact layers of
maxillary and mandibular
body, are much thinner in
the maxilla than in the
mandible.

51. They are thickest in the premolar and molar region of the lower
jaw, especially on the buccal side.
In the maxilla, outer cortical plate is perforated by many small
openings through which blood and lymph vessels pass.
In the lower jaw, cortical bone of the alveolar process is dense.
In the region of anterior teeth of both jaws, supporting bone is
usually very thin.
No spongy bone is found here and cortical bone is fused with the
alveolar bone proper.
 Histologically, cortical plates consist of longitudinal lamellae and
haversian systems.

52.  The thickness of the cortical plate varies significantly from tooth to
tooth throughout the arches.
MANDIBLE: The labial and buccal cortical plate is generally
considerably thicker than the lingual plate, except in the incisor
region,
MAXILLA: The palatal cortical plate is usually thicker than the facial
plate.
 Bone underlying the gingiva is the cortical plate.
 Both cribriform plate and cortical plate are compact bone separated
by spongy bone.

53. Cross section of mandibular alveolar process where
buccal cortical plate thicker than lingual in the
posterior region

54. Palatal plate is thicker than the labial/buccal plate
in maxilla
Arrows denote that the walls of the socket are lined
by the cortical bone

55. SPONGY BONE
Fills the area between the cortical plates and the alveolar bone
proper.
 It occupies most of the
interdental septa but only a
relatively small portion of the
buccal and palatal bone
plates.
 It contains bone trabeculae,
the architecture and size of
which are determined
- partly genetically and
- partly the result of the
forces to which the teeth are
exposed during function.

56.  The cancellous trabecular bone is commonly referred to as
“SPONGIOSA”.
 The study of radiographs permits the classification of the
spongiosa of the alveolar process into two main types:
SPONGIOSA
TYPE I:
The interdental and
interradicular
trabeculae are regular
and horizontal in a
ladder-like arrangement.
TYPE II:
Irregularly arranged,
numerous, delicate
interdental and inter
radicular trabeculae.

57. The interdental and
interradicular trabeculae are
regular and horizontal in a
LADDER-LIKE
ARRANGEMENT
TYPE I:
Irregularly
arranged,
numerous,
trabeculae
TYPE II:

58.  Both types show a variation in the thickness of
trabeculae and size of the marrow spaces.
 The architecture of type I is seen most often in the
mandible and fits well into the general idea of a
trajectory pattern of spongy bone.
 Type II although evidently functionally satisfactory,
lacks a distinct trajectory pattern. This arrangement is
more common in the maxilla.

59.  In addition, the jaw bones
consist of the BASAL
BONE, which is the
portion of the jaw located
apically but unrelated to
the teeth.
 The alveolar process is
divisible into separate
areas on an anatomic
basis, but it functions as a
unit, with all parts
interrelated in the support
of the teeth.

60.  If the interdental space is narrow, the septum may consist of only
the cribriform plate.
 For Eg:
Heins PJ et al (1986) reported in their study that the space between
the mandibular second premolars and first molars consisted of
cribriform plate and cancellous bone in 85% of the cases and only
cribriform in the remaining 15%.
INTERDENTAL
SEPTUM
 It consists of cancellous bone
bordered by the socket wall
cribriform plates of
approximating teeth and facial
and lingual cortical plates.

61.  If the roots are close together, an irregular “window” can appear
in the bone between adjacent roots.
Boneless window between two
adjoining roots

62. CREST OF THE ALVEOLAR SEPTA
The shape of the outlines of
the alveolar septa in the
roentgenogram is dependant
on the position of the
adjacent teeth.
In a healthy mouth, the
distance between the CEJ and
the free border o the alveolar
bone proper is fairly constant.
If the neighbouring teeth are
inclined, therefore the
alveolar crest is oblique.

63.  The distances between the crest of the alveolar bone and the CEJ
in young adults varies between 0.75 and 1.49mm(avg. 1.08mm).
 This distance increases with age to an average of 2.81mm
(Gargiulo AW et al 1961)
CEJ TO CREST
Cortical bone and alveolar
bone meet at the alveolar
crest usually 1.5 to 2 mm
below the level of CEJ on the
tooth it surrounds.

64. BONE DEVELOPMENT:
 All bone is of mesodermal in origin.
 The process of bone formation is called as
ossification.
 It begins around 6th-7th week of embryonic life and
continuous throughout adulthood.
 There are 2 different ways of bone development-
 Intramembranous ossification
 Endochondral ossification

65. INTRAMEMBRANOUS OSSIFICATION:
 Bone is formed directly with in soft connective tissue rather than
on cartilaginous model.
 Sites where this type of
ossification occur
include-
 Bones of vault of skull
 Maxilla
 Body of mandible
 Mid-shaft of long bones
 clavicle

66. 1) Formation of matrix within
fibrous membrane:
At the sites of bone development,
there is loose mesenchyme
The mesenchymal cells proliferate
and condense into compact nodules.
Cells in center become round and
basophilic with thick interconnecting
processes
These differentiate into osteoblasts
which secrete organic matrix which
calcifies soon.
First small mass of newly formed
bone is irregularly shaped spicule.

67. 2) Formation of Woven Bone
Bony spicules lengthen into longer anastomosing structures called as
Trabeculae
These extend in radial pattern and enclose local blood vessels
This early membrane bone is called as WOVEN BONE.
External to woven bone, there is condensation of mesenchyme called as
PERIOSTEUM.

68. 3) Appositional growth mechanism and formation of compact bone:
Osteoblasts and osteogenic cells cover the spicules and bony trabeculae.
These osteogenic cells proliferate in a vascular environment to give rise to
osteoblasts.
These cells deposit new layers of bone matrix on preexisting bone surfaces.
This is Appositional growth and it results in the build up of bone tissue one layer
at a time.
As the trabeculae increase in width due to appositional growth, neighbouring
capillaries are incorporated to provide nutrition to osteocytes in deeper layers.
New bone is deposited on some surfaces and resorbed on the other. This
continued appositional growth and remodeling of trabeculae convert the
cancellous bone into compact bone
Cancellous bone is in the central part and vascular tissue in the cancellous bone
differentiates into red marrow.

69. 4) Formation of Osteon:
As cancellous bone gets converted
into compact bone
No. of narrow canals are formed and
lined by osteogenic cells
These canals enclose vessels that
were present in soft tissue spaces of
cancellous network.
The consecutive lamellae of bone
become added to the bony walls of
spaces in cancellous bone.
This is called as OSTEON.
This is primitive osteon as they are
short compared to those in long
bones.

70. ENDOCHONDRAL BONE FORMATION:
 Most bones are formed in this manner only.
 Bone formation is preceded by formation of cartilaginous model
that closely resembles the bone to be formed.
 This cartilage is subsequently replaced by bone.
 Bones formed in this manner are called as CARTILAGE BONES.
 It occurs at the ends of all long bones, vertebrae, ribs , articular
extremity of mandible and base of skull

71.  Mesenchymal condensation
occurs at the site of bone
formation.
 Some mesenchymal cells
become CHONDROBLAST
and lay down hyaline
cartilage.
 Mesenchymal cells on the
surface of cartilage form a
membrane called
PERICHONDRIUM .
 This membrane is vascular
and contains osteogenic cells.
 Developing carilage model assumes the shape of bone to be
formed.

72.  At the midshaft of the diaphysis
the perichondrium becomes a
PERIOSTEUM through the
development of osteoprogenitor
cells and osteoblasts.
 The osteoblasts produce a
COLLAR OF BONE by
intramembranous ossification.
Calcium salts are deposited in the
enlarging cartilage model.

73.  Blood vessels grow through the
periosteum and bone collar, carrying
osteoprogenitor cells within them. These
cells establish a PRIMARY (OR
DIAPHYSEAL) OSSIFICATION
CENTER.
 Bony trabeculae spread out from the
primary ossification center to occupy the
entire diaphysis, linking up with the
previously formed bone collar, which
now forms the cortical bone of the
diaphysis. At this stage the terminal club-
shaped epiphyses are still composed of
cartilage.
 At about term, secondary or epiphyseal
ossification centers are established in the
center of each epiphysis by the ingrowth
along with blood vessels of mesenchymal
cells, which become osteoprogenitor cells
and osteoblasts.

74. REGULATIONOF BONE FORMATION:
PARATHYROID
HARMONE
regulates the serum calcium level by stimulating
bone resorption.
VITAMIN D3
• Stimulates bone resorption & is essential for normal
bone growth & development.
• It stimulates the synthesis of osteocalcin &
osteopontin by osteoblastic cells while suppressing
collagen production.
INSULIN
• Directly stimulates bone matrix formation and
mineralization
• Indirectly affects bone formation through stimulation
of insulin like growth factor I produced in the liver

75. GROWTH HORMONE helps in attaining normal bone
mass.
GLUCOCORTICOIDS
• Promote differentation of osteoblasts
and stimulate bone matrix
formation.
• Prolonged treatment results in bone
loss which is due to inhibition of
calcium absorption & depletion of
osteogenic precursor cells.
BONE MORPHOGENIC
PROTEIN (BMP)
induces chondrogenic & osteogenic
differentiation in undifferentiated
mesenchymal cells.
INSULIN GROWTH
FACTORS (IGF I and II)
Stimulate proliferation of osteoblast
precursors.

76. THYROID HORMONE
Helps in endochondral bone
formation through its action on
cartilage formation.
FIBROBLAST GROWTH
FACTORS
FGF affects bone formation
through proliferation of osteo
progenitor cells and promotion
of osteogeneic differentiation
PLATLET DERIVED
GROWTH FACTOR
Has similar effects to FGF in
promoting osteogenesis.

77. BONE RESORPTION
Attachment of osteoclasts to mineralized bone surface.
Creation of sealed acidic microenvironment through proton pump.
Demineralizes the bone and exposes the matrix
Degradation of exposed matrix by action of released enzymes like Acid
phosphatase and Cathepsin B.
Degraded material undergoes Endocytosis at the ruffled border.
Translocation of degradation products in transport vesicles and
extracellular release of contents on opposite side of ruffled border
(TRANSCYTOSIS).
Ten Cate described the sequence of events in the resorptive process
as follows:

78. BONE REMODELING
 Bone is a highly dynamic connective tissue with a capacity for
continuous remodeling.
 The two principal cell types osteoclast and osteoblast are the
major effectors in the turnover of bone matrix.
 At any given time, the process of bone synthesis and bone
breakdown go on simultaneously.
 This phenomenon is called ‘COUPLING’ of bone resorption and
formation.

79. WHAT HAPPENS DURING BONE
REMODELING:
Osteoclasts tunnel into surface of bone.
In haversian canals, closest to the surface, osteoclasts travel
along a vessel, resorb the haversian lamellae, and a part of
circumferential lamellae, and form a resorption tunnel or
cutting cone.
After sometime resorption ceases and osteoclasts are
replaced by osteoblasts.
These osteoblasts lay down a new set of haversian lamellae,
encircling a vessel upon a reversal line.

80. The entire area of osteon, where active formation occurs is
termed the filling cone.
The osteoblasts get entrapped in new bone are called
osteocytes.
Fragments of lamellae from old bone haversian systems are
left behind as interstitial lamellae.
This cement line is a thin layer of glycoproteins comprising
bone sialoprotein and osteopontin, that acts as a cohesive
mineralized layer between the old bone and new bone to be
secreted.

83. Response to Mechanical Stress
 Wolff’s law – a bone grows or remodels in response to the forces
or demands placed upon it

84.  The gingival margin normally follows the alveolar margin
morphology.
 FENESTRATION AND DEHISCENCE
 Isolated areas in which root is denuded of bone and covered by
only periosteum and gingiva – Fenestration (intact marginal
bone).
 Denuded area extends through the marginal bone –
Dehiscence
 Common on the facial than lingual aspect and more common
on anterior teeth than posterior teeth.
 Predisposing factors – prominent root contours, malposition,
labial protrusion of roots, thin bony plate
 May complicate the outcome of periodontal surgery
CLINICAL CONSIDERATIONS:

86. 1)GENETIC DISEASES:
 Osteogenesis imperfecta( abnormal collagen
maturation)
 Osteopetrosis (sclerotic, fragile & dense bone)
 Achondroplasia (failure of normal cartilage
proliferation)
 Infantile cortical hyperostosis(cortical thickening)
 Marfan syndrome(collagen is abnormally soluble)
PATHOLOGIES OF BONE

87. Osteogenesis imperfecta:
 Osteogenesis imperfecta heritable disorders
charaterised by impairment of collagen
maturation.
 Disorder arises from mutation in one of two
genes that guide formation of type 1 collagen.
 Abnormal collagen maturation results in bone
with thin cortex, fine trabeculation and
diffuse osteoporosis.

88. Osteopetrosis(Albers-Schonberg disease;Marble bone
disease)
 Osteopetrosis is characterised by a marked
increase in bone density resulting from a defect
in remodelling caused by failure of normal
osteoclast function.
 number of osteoclasts is increased
however,because of their failure to function
normally,bone is not resorbed

89. Cleidocranial dysplasia:
 Best known for its dental and
clavicular abnormalities.
 Disorder of bone caused by a
defect in CBFA1 gene of
chromosome 6p21.this gene
guides osteoblastic differentiation
and appropirate bone formation.
 Muscles associated with abnormal
clavicles are underdeveloped.
 patient’s neck appears long,
 shoulders narrow and drooped.
 Patients tend to be short statured
and have large heads with
pronounced frontal and parietal
bossing.

90. METABOLIC BONE DISEASE:
 Deficiency of vitamin D
in early childhood may
lead to decreased
absorption of calcium and
phosphorus.
 Skeleton is poorly
developed because of
defective calcifications in
growing bones.
RICKETS:

91. HYPER PARATHYROIDISM:
 Execessive secretion of Parathormone from
parathyroid gland causes hyper parathyroidism
 Clinical Features
 Bone fractures are common in hyperthyroidism.
 Cyst like spaces in jaw bone .
 Radiographic Features
Multiple, well defined, unilocular or multilocular
radiolucent areas are seen in jaw bone.

93. GROUND GLASS
RADIOGRAPHIC
APPEARANCE SEEN:

94. DISEASES OF UNKNOWN
ORIGIN
 PAGETS DISEASE/OSTEITIS DEFORMANS
It is the disease of bone in which excessive , rapid and purposeless
resorption and replacement occurs, particularly in elderly patients.
Etiology
unknown but it is presumed that the disease is due to
 Inflammation
 Viral infection
 Circulatory disturbances.

95. Oral Manifestations
Maxilla is more frequently affected
and enlarged.
In extreme cases maxilla enlarges
and results in leontiasis ossea.
There is hypercementosis of teeth.
Cotton wool appearance of jaw bone

96. FIBROUS
DYSPLASIA
 It is the disease of unknown
etiology characterized by
replacement of normal bone
with fibrous tissues that have
tendency to spontaneous
ossification or regression
coinciding with sketetal
maturation .
 It results from a postzygotic
mutation in GNAS 1(guanine
nucleotide binding protein, a
stimulating activity
polypeptide 1 gene)
Irregular shaped trabeculae
resembling chinese letter :

97. Clinical features:
MONOSTOTIC FIBROUS
DYSPLASIA OF JAWS:
 Limited to single bone.
 Painless swelling of affected
area.
 Growth is slow.
 Maxilla involved more than
mandible
POLYOSTOTIC FIBROUS
DYSPLASIA:
 More than one bone affected.
 When disease seen with café-
au-lait(coffee with milk)
pigmentation, process termed as
jaffe-Lichtenstein syndrome.
 When café au lait pigmentation
alongwith endocrinopathies like
sexual precocity, pituitary
adenoma or hyperthyroidism is
present then its known as
McCune-Albright syndrome.
 Increased serum alkaline phosphatase level is seen in both.

98. Apert syndrome:
 More common in ASIANS.
 Cranostenosis resulting in acrocephaly, brachycephaly,
large late closing fontanels, Gaping midline defect, shallow
orbits, depressed nasal bridge with parrot beak appearance.
 Polydactyly, syndactyly with fusion of 2nd ,3rd,4th digits (mitten
hands and sock feet)
 Prominent mandible, high arched palate, bifid uvula, cleft
palate, anterior crowding, malocclusion, delayed and ectopic
eruption, shovel shaped incisors and supernumerary teeth.

100. BIBLIOGRAPHY
Tencate’s oral histology 7th edition.
Orban’s oral histology and embryology 12th edition
Carranza’s clinical periodontology 11th edition.
Contemporary implant dentistry 3rd edition.
Clinical Periodontology and Implant Dentistry 4th
edition
Linde 4th edition.