 Introduction
 Bone Histology
 Cells and Intercellular Matrix
 Bone Development
 Remodelling
 Age Changes
 Clinical Considerations
 Conclusion
 References

 Bone- used to designate
both an organ and a
tissue
 Specialized mineralized
connective tissue

mineralised supporting tissue
act as a reservoir for ions
(especially calcium).
provide a framework for bone marrow
gives attachment to muscles
its "plasticity', allows it to remodel according to the
functional demand placed upon it.

 DEVELOPMENTALLY,
 Endochondral bone
 Intramembranous bone
 HISTOLOGICALLY, according to its density, mature bone can
be divided into;
 Compact (cortical) bone
 Cancellous (spongy) bone

 MICROSCOPICALLY:
 Lamellar bone
 Fibrous bone
LAMELLAR BONE:
 Most of the bones, whether compact or cancellous, are composed of
thin plates of bony tissues called lamellae.
 These are arranged in piles in a cancellous bone, but in concentric
cylinders (Haversian system or secondary osteon) in a compact bone.

FIBROUS BONE (WOVEN BONE):
 It is found in young fetal bone.
 Collagen fibers - more variable diameter
 Irregular orientation giving it matted appearance

 Alveolar process is dependent on the presence of teeth for its
development and maintenance.
 At the late bell stage, bony septa and bony bridge start to form,
and separate the individual tooth germs from another, keeping
individual tooth germs in clearly outlined bony compartment.
(BERKOVITZ)

 Initially, this bone forms a
thin egg shell of support,
termed as the ‘tooth crypt’,
around each tooth germ.

FIG. 9-5 A developing root shown by a
divergent apex around the dental
papilla (arrow), which is enclosed by
an opaque bony crypt.

 Relationship between
a deciduous tooth & its
accompanying
succedaneous tooth
detailing the formation
of the alveolar bone
- Scoh, Symonds 1974
12/85
AT BIRTH AT 7MONTHS
AT 2½YRS 7YRS

67 %
Inorganic
Hydroxyapatite
33% (organic)
28% 5 %
Collagen type Ӏ Non coll.
proteins
(ca10{po4}6{oh}2)

 Osteocalcin, Osteonectin, Bone morphogenic proteins,
Phosphoproteins and Proteoglycans
 Ground substance- Glycosaminoglycans, proteoglycans and
water
 Osteopontin, Bone Sialoprotein- cell adhesion proteins
(Mackie et al, 2003)

Osteocalcin (bone GLA protein)
 Found in bone matrix
 Expressed only by fully differentiated cells
 Specifically localized to developing bone
 Produced by osteoblasts and odontoblasts
 Role in bone formation

Osteopontin
 Glycosylated phosphoprotein
 Role in bone formation and resorption
 Synthetized by osteoblasts, osteoclasts, osteocytes, smooth
muscles and epithelial cells
 Role in cell adhesion
 Significant amounts at mineralizing front

Bone sialoprotein
 Structural protein of bone
 Restricted to mineralized tissues
 Secreted by osteoblasts

Osteonectin
 Glycoprotein bound to HA
 Calcium binding glycoprotein
 Synthesized by fibroblasts and role in wound healing

 Inorganic material- calcium, phosphate ,hydroxyl, carbonate,
citrate
 Trace amounts of sodium, magnesium and fluorine (Glimcher
1990)
 Hydroxyapetite crystals of ultramicroscopic size
 Enzymes like alkaline phosphatase, ATP and pyrophosphatase
 Parallel to collagen fibres and contribute to lamellar appearance
of bone

 Portion of maxilla and mandible that forms and supports the
tooth sockets (alveoli)
 Forms when tooth erupts to provide osseous attachment to
PDL
 Disappears gradually after tooth loss
 ‘Tooth dependent bony structure’ (Schroeder et al, 1991)

Transverse section
Longitudinal section

 Morphology determined by size, shape, function and location
of teeth
 Formed during fetal growth by intramembraneous ossification

Cancellous Bone
Compact Bone
Shelf like bone

Holds the tooth firmly in position during mastication
Aids in movement
Adapts to occlusal loads
Helps to move the teeth for better occlusion.
Functions of alveolar bone

Supplies vessels to the PDL.
Houses & protects developing permanent teeth while
supporting primary teeth.
Organizes successive eruptions of primary & secondary teeth.

Three parts
1) External plate of cortical bone
2) Inner socket wall
3) Cancellous trabeculae (between two compact layers)-
function of support

 1) Circumferential lamellae (encloses entire adult bone and
forms the outer perimeter

 2) Concentric lamellae (make up bulk of compact bone and
forms the basic metabolic unit of bone, the osteon)
 3) Interstitial lamellae (inter-spread between adjacent concentric
lamellae and fill the spaces between them..actually fragments of
pre-existing concentric lamellae and can be of many shapes)

 Osteon –cylinder of bone parallel to
long axis of bone (structural and
metabolic units)
 Haversian canal –in centre of osteon,
lined by single layer of bone cells
 Each canal has a capillary

 Haversian canals
interconnected by Volkmann
canals
 System for dense bones like
cortical plates and alveolar
bone proper, where surface
vessels are unable to supply
blood

 Dense , lamellated bone – alveolar bone proper (contains
sharpeys fibers and circumferential lamellae)

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

 Bone adjacent to PDL that contain sharpeys fibers
 Contains higher calcium than other areas
 Many features in common with cementum layer on root
surface
 Collagen fibers larger in diameter, less numerous , less mature

 Localized within alveolar bone proper
 Sharpeys fibers completely calcified or partially calcified with
uncalcified core
 Not unique to jaw -occurs wherever ligaments and muscles
are attached
 Thickness of 100-200 microns
 High turnover rate

FIBER ARRANGEMENT IN ABP
 DOUBLE FIBRILLAR ORIENTATION:
 Extrinsic fibers- Sharpey’s fibers
 run perpendicular to bone surface
 produced by PDL fibroblast
 At their insertion in bone, they become mineralized, with their periphery
being hypermineralized than cores.
 Intrinsic fibers
 Laid down by osteoblasts between Sharpey’s fibers
 Irregularly arranged & less dense.

 Presence of trabeculae enclosing irregular marrow spaces
lined with a layer of thin, flattened endosteal cells
 Variation in trabeculae pattern depending upon occlusal forces
and genetically
 Matrix consists of irregularly arranged lamellae separated by
incremental and resorption lines

 Found in inter-radicular and inter-dental spaces
 Maxilla>mandible
 Trabeculae alligned in path of tensile and compressive stresses
to provide maximal resistance to occlusal forces with
minimum bone substance (Glickman et al 1970)
 in thickness and number with force

 Spongy bone (anatomic term)
 Trabecular bone (radiographic term)
 Cancellous bone (histologic term)

 Type 1: The interdental and interradicular trabeculae are regular
and horizontal in a ladder like arrangement.
 Type 2: Shows irregularly arranged numerous delicate
interdental and interradicular trabeculae

CORTICAL BONE SPONGY BONE
About 85% of bone About 15% of bone
Lesser turnover than spongy Higher turnover
Remodel about 3% of its mass
each year
remodel about 25% of its mass
each year
Mechanical/protective role More metabolic function

 Consists of cancellous bone
bordered by alveolar bone
proper of approximating
teeth and facial and lingual
cortical plates
 Narrow septa- only
cribriform plate
 Irregular window

 Study by Heins et al 1986
Area Cribriform
plate+cancell
ous bone
Only
cribriform
plate
Irregular
window
Maxillary
molars
66.6% 20.8% 12.5%
Mandibular
premolar and
molar
85% 15% 0%

 Mesiodistal angulation of IDS is parallel to line drawn
between CEJ of approximating teeth (Ritchey et al, 1953)
Shape and size of IDS depends on
1) Size and convexity of crowns of approximating teeth
2) Position of teeth
3) Degree of eruption

Crest of IDS located 1-2 mm apical to CEJ of adjacent teeth

Diagram of relation between CE junction of adjacent teeth shape of
crest of alveolar septa

• Embryo and newborn,
• Ribs, sternum, vertebrae, skull, humerus
• Hemopoiesis
Red
hematopoietic
marrow
• Adult
• Red marrow foci found sometimes in
maxillary tuberosity, symphysis and angle
of ramus
• Storage of energy
Yellow fatty
marrow

 Determined osteogenic precursor cells
 Inducible osteogenic precursor cells
 Muscles.
Friedenstein (1973) divided osteoprogenitor cells into:

 Produce organic matrix of bone
 Differentiated from pluripotent
follicle cells
 No decrease with age
 Uninuclear cells
 Secrets collagen as well as non
collagenous proteins
 Present on outer bone surface

 Have high levels of alkaline
phosphatase (this feature
distinguishes it from fibroblasts)
 Alkaline phosphatase believed
to cleave organically bound
phosphate and help in bone
growth
 Active-plump, cuboidal
 Inactive-flattened

 Secrete type Ӏ and V collagen,
variety of cytokines and several
members of BMP such as BMP-
2, BMP-7, TGF-ß, IGF-1, IGF-2
 BMP family helps in bone
formation and repair
 Under physiologic condition
which support resorption- release
of IL-6 and hydrolytic enzymes

 Enclosed within spaces
called lacunae within
calcified matrix
 Entrapped Osteoblasts
 Reduction in size and loss of
matrix synthesizing ability
after being entrapped
 Excess space-lacunae

 Extend processes into canaliculi
that radiate from lacunae
 Anastomosing system
 Bring O2 and nutrients to
osteocytes through blood and
remove metabolic waste products

 More rapid the bone formation-more osteoblasts get
entrapped – more osteocytes (eg- bone formed during repair)
 Osteolytic osteolysis- osteocytes capable of resorption

 Quiescent osteocytes:
 paucity of rER, diminished golgi apparatus
 An osmiophilic lamina representing mature calcified matrix is seen in close apposition to cell
membrane.
 Formative osteocyte:
 abundant rER & golgi apparatus
 evidence of osteoid in pericellular space within the lacuna.
 Resorptive osteocyte:
 Numerous ER & well developed golgi apparatus.
 The pericellular space is devoid of collagen fibrils & may contain a flocculent material
suggestive of breakdown product.
 ‘Osteocytic osteolysis’.

 Originate from hematopoietic tissue
 Fusion of mononuclear cells (blood
derived monocytes) to form a
multinucleated cell
 Very large, 5-50 nuclei
 Active on less than 1% of bone surface
 Mobile and capable of migrating

 Lie in Howships lacunae
 Acidophilic cytoplasm
 Active osteoclasts- ruffled
border facing bone
(hydrolytic enzymes are
secreted)
 Increases surface area

 Clear zone devoid of organelles
but rich in actin filament,
vinculin, talin (site of adhesion of
osteoclast to bone)
 Sealing zone
 Ruffled border-enzymes like
tartarate resistant acid
phosphatase, carbonic anhydrase,
proton pump ATP’s
Cathepsin containing
cytoplasmic vesicles near
ruffled border

1. Attachment of the osteoclast to mineralized bone surface
2. Creation of sealed acidic environment through action of proton
pump which demineralizes bone & exposes the organic matrix
3. Degradation of the exposed organic matrix to its constituent
amino acids by the action of released enzymes like acid
phosphatase & cathepsin
4. Sequestering of the mineral ions & amino acids within the
osteoclasts.
Tencate 1994- Described sequence of events of resorptive
process:

- When bone is no longer forming…..surface
osteoblasts become inactive ….. Lining cells.
- Thin flat nucleus, few cytoplasmic organelles
- Retain gap junctions with osteocytes….functions
to control mineral homeostasis & endure bone
vitality.

 Both are layers of differentiated osteogenic connective tissue
 Periosteum covers outer surface of bone and endosteum lines
the internal bone cavities
 Bundles of collagen fibres from outer layer penetrate bone and
bind periosteum to bone
 Endosteum composed of a single layer of osteoblasts with
some connective tissue

• Rich in blood vessels, nerves
• Contains collagen fibres and
fibroblasts
• Fibrous periosteum
Outer
layer(fibrous)
• Composed of osteoblasts and
osteoprogenitor cells
• Cellular periosteum
Inner layer
(osteogenic)

 Medium through which muscles, tendons and
ligaments are attached to bone
 Nutritive function to the bone
 Osteoprogenitor cells – Important role during
development and repair after fracture
 Fibrous layer- acts as limiting membrane
(exostoses in cases of periosteal tear)

1) Endochondral bone formation
2) Intramembranous bone formation
3) Sutural bone formation

 Cartilage replaced by bone
 Shape of cartilage resembles miniature
version of bone to be formed
 At end of long bones, vertebrae, ribs,
head of mandible and base of skull
 Condensation of mesenchymal cells

 Perichondrium at the periphery
 Rapid growth of cartilage
 Cartilage replaced by bone gradually
by osteoblasts at periphery

 Occurs directly within mesenchyme
 Bone develops directly within the soft connective tissue
 Vascularity increases and osteoblasts differentiate and lay
down bone
 Occurs at multiple sites (primary ossification center)

 Ossification centers grow radially
 Cranial vault, maxilla, body of mandible and mid shafts of long
bones
 Proceeds at extremely rapid rate
 Woven bone formed first in form of radiating spikules which
ultimately fuse to form plates
 Transition of woven bone to lamellar bone

 Mesenchymal condensation
followed by increase in
vascularity
 Some mesenchymal cells lay
down collagen fibre bundles
forming a membrane

 Some differentiate into osteoblasts and lay down osteoid
Which then gets calcified
Mineralization always lags behind the production of bone matrix

 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

Vascular supply
Derived from inferior and superior alveolar arteries of maxilla and
mandible
Lymphatic drainage
Submandibular lymph nodes
Nerve supply
Branches from anterior, middle and posterior superior alveolar
nerves for maxilla and branches from inferior alveolar nerve for
mandible

 Bone contour follows root prominence
 Intervening vertical depressions that taper
towards margin
Height of facial/lingual plates affected by
1) Allignment of teeth
2) Angulation of root to bone
3) Occlusal force

Normally: prominence of the roots
with the intervening vertical
depressions that taper toward the
margin.
On the labial version: the margins
of the labial bone is thinned to a
knife edge & presents an
accentuated arc in the direction of
the apex.
On the lingual version: the
margins of the labial bone is blunt
& rounded & horizontal rather
than arcuate.

 Buttressing bone- adaptive mechanism against occlusal force
(thickened cervical portion of alveolar plate)

 Fenestration- Isolated areas in
which root is denuded of bone
and root surface covered only
by periosteum and overlying
gingiva
 Dehiscence- Denuded area
extends through marginal bone

 Facial > lingual
 Anteriors > posteriors
 Frequently bilateral
 20% of all teeth affected
 Caused due to malposition, root prominence, labial protrusion
and a thin cortical plate
 Can complicate procedure and outcome of periodontal surgery

 Least stable of periodontal tissues
 Structure in a constant state of flux
• Functional requirements
• Age related changes in
bone cells
Local
influences
• Hormones (PTH, vit D,
calcitonin)Systemic
influences

 Remodeling is the major pathway of bone
changes in
 shape,
 resistance to forces,
 repair of wounds, and
 calcium and phosphate homeostasis in the body.
REMODELING

 Regulation of bone remodelling is a complex process
involving hormones and local factors acting in a autocrine and
paracrine manner on the generation and activity of
differentiated bone cells – Sodek et al 2000
 Bone-99% of body calcium ions
 Major source of calcium release when blood Ca
 Monitored by parathyroid gland

Decrease in blood Ca
Detected by receptors on chief cells
of parathyroid gland
Release of PTH
Stimulate osteoblasts
to release IL-1 and IL-6
Stimulates monocytes
to migrate to area
Monocytes coalesces to form
multinucleated osteoclasts in
presence of LIF-
Leukemia inhibiting factor
released by osteoblasts
Bone resorption
Release of Ca ions
from hydroxyapetite
crystals
Normal blood calcium levels
PTH secretion stopped by
feedback mechanism
Organic matrix resorbed
with hydroxyapetite
Collagen breakdown
Release of organic substrate which
are covalently bound to collagen
Stimulates differentiation Bone deposition

 ‘COUPLING’ refers to interdependency of osteoclasts and
osteoblasts in remodelling
Bone multicellular unit (BMU)
Reversal line

POTENTIALTHERAPEUTIC STRATEGIES TOTREAT BONE
RESORPTION

 Similar to those occurring in remainder of skeletal system
 Osteoporosis with ageing
 Decreased vascularity
 Reduction in metabolic rate and healing capacity(implants,
extraction sockets, bone grafts)
 Bone resorption may be increased or decreased
 More irregular periodontal surface

 Thinning of cortical plates
 Rarification of bone
 Reduction in no of trabeculae
 Lacunar resorption more prominent
 Susceptibility to fracture
 Thickening of collagen fibers
 Decrease in water content

- Gingival margins …follows the contour of alveolar process.
Abnormalities such as ledges, exostosis & tori…reflect on
gingiva.
- Areas of fenestrations & dehiscence - partial thickness flap.

- Process of bone remodeling - in orthodontic treatment.
- Knowledge of the various factors regulating bone formation
has resulted in their use for regeneration of bone.

 Buccal-lingual/palatal ridge resorption
during first 3 months after extraction
about 30%... Reaching 50% at the end of
1 year (Schropp et al , 2003)
 Resorption more pronounced at buccal
than lingual/palatal aspect of ridge
leading to shift of center of ridge towards
lingual/palatal side

 Socket preservation

Classification (Lekhom and Zarb- 1985)
 4 bone qualities for the anterior regions of the jaw bone:
 Quality1, Quality 2, Quality 3, Quality 4

Misch Bone Density Classification
 D1-dense cortical
 D2-porus cortical and coarse trabecular
 D3-porus cortical and fine trabecular
 D4-fine trabecular

 Local response to a noxious stimulus.
 A process by which tissue forms faster than the normal regional
regeneration process.
- Frost et al, 1983
 By enhancing the various healing stages, this phenomena makes the
healing process occur 2 – 10 times faster than normal physiologic
healing.
 RAP begins within a few days of injury, typically peaks at 1 - 2
months, usually lasts 4 months in bone, & may take 6 - >24 months
to subside.

 Duration & intensity of RAP α type & amount of stimulus & the
site where it was produced.
 Noxious stimuli of sufficient magnitude: can evoke RAP.
 Fractures
 Mechanical abuses
 Noninfectious inflammatory injuries: dental implant procedures
 Bone grafting surgeries
 Internal fixation procedures
 Mucoperiosteal surgery

 Injury to bone: Pathologic process
 Arthrofibrosis
 Neuropathic soft tissue problems
 Rheumatoid phenomena
 Secondary osteoporosis
 Excessice heat
RAP is delayed / not initiated.
Formation of biologically delayed union / nonunion.

 RAP does not result in a change in bone volume.
 Restricted to bone remodelling.
 More evident in cortical bone.
 Usually accompanied by a systemic response: Systemic
Acceleratory Phenomena
 Biochemical agents also appear to facilitate the RAP.
 PG E1
 Bisphosphonate

 Inadequate RAP is associated with:
 DM
 Peripheral neuropathies
 Regional sensory denervation
 Severe radiation damage
 Severe malnutrition

Thus a sound knowledge of bone anatomy,
histology and physiology, will help the clinician in
diagnosing and treatment planning, and lead to a
favorable outcome of surgical procedures
performed

 Carranza’s Clinical Periodontology- 10th edition
 Clinical Periodontology and Implant Dentistry- Jan Lindhe-
5th edition
 Contemporary Implant Dentistry- Carl Misch- 3rd edition
 Orban’s Oral Histology and Embryology- 11th edition
 Structure of Periodontal Tissues in Health and Disease-
Periodontology 2000, vol 40, 2006, 11-28

Thank you