-Bone is highly vascular, living, constantly changing, mineralized connective tissue.-Sesamoid bone are the bones embedded within tendon. Found in hand, knee and foot. Eg patella.-They act to protect the tendon and increase its mechanical effect.
-Supports soft tissues and provide attachment for tendons of most skeletal muscles.-Bone protects many internal organs from injury eg. Skull protect brain.-Red bone marrow (medulla ossiumrubra) consist mainly of hematopoietic tissue. Found mainly in flat bones.-Yellow bone marrow (medulla ossiumflava) : consist mainly of adipose cells which stores triglycerides, which body use as a last reservior in cases of extreme starvation.
Flat bones- skull, sternum, pelvis and ribs.Long bones- bones of limbs.Irregular bones- face bone and vertebral column.Short bones- bones of hands and feets such as phalanges, metacarpals and metatarsals.Accessory or supernumerary bone- extra bone that develop in additional ossification centers failed to fuse with main parts during development. These bones may be mistaken for bone chips or fractures.
epiphysis – its is the region between the growth or growth plate scar and the expanded end of bone, covered by articular cartilage. It is present at both the ends of bone except clavical, ribs, phalanges proximal end, proximal first and distal second through fifth meta carpals and pfads through fifth metatarsals.Carpal, tarsal bones and patella are also called epiphysioid bones and are developmentally equivalent to epiphysis of long bones.Metaphysis – this region is a comman site for many primary bone tumors and similar lesions.Diaphysis – located in the region between metaphyses.Physis – seperates epiphysis from metaphysis. It is zone of endochodral ossification.
-Endosteum is made up of loose irregular connective tissue, with osteoblast and osteoclast. It is highly vascular condensation of areolar tissue lining various medullary spaces.Long b ones include- femora, tibiae and fibulae of the legs; humeri, radii and ulnae of the arms; metacarpals and metatarsals of hands and feet;phalanges of fingers and toes and the clavicals or the collar bone, mandible.
Forms cortex or outer shell of most bones.Present between osteogenic layer of periosteum and spongy bone.Chifly consist of calcium phosphate and type 1 collagen.. These are arranged in concentric circles around central haversian canal.
It is primary anatomical and functional unit of cortical bone.Osteon- consist of concentric layers of lamellae of compact bone tissue that surrounds a central canal, Haversian canal, which contains blood and nerve supply to bone.The boundry of the osteon is CEMENT LINE.Osteons are connected to each other and the periosteum bye oblique channels called volkman’s canals or perforating canals.
Also known as cancellous boas compared to compact bone it has higher surface area, is less dense, softer, weaker and less stiff.Found in ends of long bones, proximal to joints and within the interior of vertebrae.
- The alveolar process contains a region of compact bone adjacent to the periodontal ligament called lamina dura- It is stated that in the posterior maxilla; the trabeculae are typically thin, and numerous, forming a fine, granular, dense pattern, and the marrow spaces are consequently slightly larger than the anterior region of the maxilla and relatively numerous. In the posterior mandible, the periradiculartrabeculae are somewhat thicker than in the maxilla resulting in a coarser pattern and they are relatively larger than the trabeculae in the anterior region of the mandible. The trabecular plates in the mandible are also fewer than in the maxilla and marrow spaces are correspondingly larger
It is also an pathologic tissue in adults, except in few places such as near the suture of the flat bones of skull, tooth sockets.
In diagram - One small and 1 large plasma cell in top left frame. 2 osteoblasts in top right frame, 1 osteoblast in lower frame.cuboidal and columnar in shape with a central nucleus.found on the bone surface. osteoblasts come from the poorly differentiated mesenchymal cell of the internal osteogenic layer of periosteum and the bone marrowThey have receptors for hormones such as vitamin D, estrogen, and parathyroid hormone. secrete factors that activate osteoclasts (RANK-ligand) secrete PHEX, a protein that helps to regulate the amount of phosphate excreted by the kidney. Procollagen molecules are produced bythe ribosomes and extruded into extracellular space , proteolysis and polymerization within the extracellular space results in formation of collagen fibrils. - Combination of thes extracellular and intracellular events leads to production of osteoid seam.
osteocyte, mature bone cells, a star shaped cellOsteocytes have an average half life of 25 years, they do not divide, and they are derived from osteoprogenitors, some of which differentiate into active osteoblastsCells contain a nucleus and a thin ring piece of cytoplasm. space that an osteocyte occupies is called a lacuna Osteocytes are networked to each other via long cytoplasmic extensions that occupy tiny canals called canaliculi, which are used for exchange of nutrients and waste through gap junctions-These have also been show to act as mechanosensoryreceptars regulating the bones response to stress and mechanical load.
Precursors (blood monocytes) circulate in the blood and bone marrow. formed from fusion of the precursors. happens when RANK receptors on the osteoclast precursors are activated by the RANK-ligand which was secreted by osteoblasts. Osteoprotegerin (OPG) is a factor in the marrow which also binds RANK-ligand, so it can help to regulate the osteoclast activation. After they finish resorbing bone, they undergo apoptosis (programmed cell death, sometimes called 'cell suicide'). This process is regulated by proteins from other cells.
Nerve supply: Hilton’s law: according to this law nerve supplying a muscle will aslo supply the underlying bone.Most of the nerves coming to bone are sympathetic(activate fight or flight response) and vasomotor(causing or regulating dilation or constriction of blood vessels) in function.Some nerves are sensory and are distributed to the articular ends and the periosteum
At periphery of cartilage mesenchymal cells continue to proliferate and differentiate. Called as appositiona growth.In interstitial growth cell proliferation and synthesis of new matrix between chondrocytes occur.
Begin to form at epiphyseal ends.By similar process , as in development of primary ossification center , trabecular bone and marrow space are formed at these ends..
Zone of resting cartilage- cells separated by abundant extracellular matrix and have less tendancy to proliferate.Zone of proliferating cartilage- chondroblast divide actively forms groups and actively synthesize the matrixUpperZone of hypertrophic cartilage- increased vacuolation of cells. Matrix synthesis increased 3 fold compared to proliferative zone.
bone in a healthy person or animal will adapt to the loads under which it is placed.If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading. The internal architecture of the trabeculae undergoes adaptive changes, followed by secondary changes to the external cortical portion of the bone,perhaps becoming thicker as a result. The inverse is true as well: if the loading on a bone decreases, the bone will become weaker due to turnover, it is less metabolically costly to maintain and there is no stimulus for continued remodeling that is required to maintain bone mass.
It is refinement of wolfs law.Mechanostat is model describing bone growth and bone loss.
Bennighof studied the natural line of stress in skull by piercing small holes into fresh skulls.When skull were dried he observed holes assumed a linear form in the direction of bony trabeculae these were called benninghoff’s line or trajectories.It indicates direction of functional stresses
Canine lines run superiorly by the sides of piriform aperture and crest of nasal bone to frontal boneZygomatic lines runs inferiorly along the orbit,superiorly along the lateral wall of orbit,runs along the zygomatic arch.In mandible it radiates from beneath the teeth in the alveolar process & join common stress pillar that terminates in condyle.Lower border and mylohyoid ridges are other prominent buttresses of mandible.
Insulin-like growth factors (IGFs): These growth factors are produced by osteoblastic cells in response to several bone active hormones, such as parathyroid hormone and estrogens, or BMPs. Growth factorsBone morphogenetic proteins (BMPs): BMPs are produced in the bone or bone marrow. They bind to BMP receptors that are on mesenchymal stem cells within the bone marrow. This causes the cells to produce Cbfa 1, which is a factor that activates the DNA so proteins can be made -- a process known as gene transcription. When Cbfa 1 activates the genes, the cells differentiate into mature osteoblasts. Without Cbfa 1, the cells would turn into fat cells instead!IGFs accumulate in the bone matrix and are released during the process of bone remodeling by osteoclastsCytokinesInterleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor (TNF) family of cytokines: These factors are produced by osteoblastic cells in response to systemic hormones or other cytokines. IL-6 can cause: * Bone marrow stem cells to differentiate into pre-osteoclasts * Changes in proliferation and differentiation of osteoblasts * Inhibition of apoptosis of osteoblastsRANKL (RANK-ligand) is a cytokine that stays on the surface of osteoblast-related cells.
Parfit states that a fully developed BMU consists of a team of osteoclasts forming the cutting cone or hemicone, a team of osteoblast forming the closing cone, some boold vessels and associated connective tissue
The cutting head is stimulated by inflammatory cytokines produced by osteocytes in damagedbone (left). Preosteoclasts have RANK receptors that are bound and activated by RANKL, probably produced ormediated by T cells (lymphocytes) near the resorption front. Growth factors from resorbed bone (bottom)stimulate production of preosteoblasts, which then produce OPG to block the RANK receptors on osteoclasts;the latter then withdraw from the scalloped surface and degenerate. Relatively flat mononuclear cells (bottomcenter) form cementing substance to form a resorption arrest line. Osteoblasts (bottom right) produce newlamellar bone to fill the resorption cavity.
Regional accelerIt is an important reaction of bone Any regional noxious stimulus can evoke RAPMost of the active vital processes are accelerated like perfusion,growth of bone cartilage ,BMU turnover of woven & lamellar bone ,turnover of connective tissueWhen RAP fails to develop ,healing is delayed & infection progressesDuration of RAP is in the range of months to years
PRESENTED BY –
DR. PARAG S. DESHMUKH
Classification of bone
The Adult human skeleton has a total of 206 bones,
excluding the sesamoid bone.
Each bone constantly undergoes modeling during
life to help it adapt to changing biomechanical
forces as well as remodeling to remove old,
microdamaged bone and replaced it with new,
mechanically stronger bone to help preserve bone
Functions of Bone
Supports & protects soft tissues
Store minerals (Ca & P) – mineral homeostasis
Blood cell production (hemopoiesis) in red bone marrow.
Energy storage -- yellow bone marrow
Buffering action – buffers blood by
absorbing or releasing alkaline salts
Detoxification – Bones can store heavy metals
and foreign elements, removing them from
blood and reducing there effects on other
Bones are Classified based on shape and structure
Based on location
• Bones of skull, vertebral column, sternum
• Bones of pectoral griddle, pelvis gridle
• It‟s a part of appendicular skeleton and
includes bones of hands and feets.
Gross structure of long bones
Articular cartilage = covers joint surfaces,
reduces friction and absorbs shock
Epiphysis : End of long boes.
Metaphysis = area between epiphyses & diaphysis
includes epiphyseal plate in growing bones
Diaphysis = Shaft of long bones.
Medullary cavity = marrow cavity
Physis = epiphyseal growth plate
• Endosteum =
lining of marrow
• Periosteum = tough
membrane covering bone
Fibrous layer: Fibrous and
madeup of dense irregular CT
Osteogenic layer: contains
many osteoblasts & blood vessels
that nourishes bone
TYPES OF BONE TISSUE
on texture of cross
Compact bone(dense bone or
Spongy bone(trabecular bone,
Represents 80% of skeletal mass
• Has slower turnover rate and high resistance to bending and torsion
Contains series of adjacent and overlapping bulls eye formations
known as, haversian system or osteon.
Between each osteons are interstitial lamellae(concentric layer of
Haversian canals communicate with medullary cavity through spaces in spongy
bone and with the surface of bone by oblique or transverse channels called as
Located along the epiphyses of long bones
Site of Erythrocyte (RBC) formation
Collagen fibers are not arranged in concentric rings. But the lamellae form
rods called TRABACULAE. No Osteons or Haverian Systems are present.
Found in short, flat, irregular bones & epiphyses of long bones. Supports and
protect red bone marrow
It is less dense, more elastic and has a higher turnover rate
Trabeculae follows lines of stresses and can realign if the lines of stress
BASED ON MATRIX
(SECONDARY BONE TISSUE)
Matur bone with collagen fibers
that are arranged in lamellae
In spongy bone lamellae are
arranged parellel to each
In compact bone lamellae are
around vascular canal.
WOVEN BONE (PRIMARY
• It is immature bone, in which
collagen fibers are arranged in
regular random arrays and contain
smaller amounts of mineral
substance and higher proportion
of osteocytes than lamellar bone
• It is temporary bone.
• Eventually gets converted to
BASED ON MATURITY
IMMATURE BONE (Primary bone tissue)
It is woven bone.
Mature bone(Secondary bone tissue)
It is charectiristically lamellar bone
Almost all bone in adults are lamellar bone
Histology of Bone Tissue
Bone: CT of widely-spaced cells separated by matrix
Matrix = 25% water, 25% collagen fibers, & 50%
crystallized mineral salts
4 types of cells in bone :
Contains inorganic mineral salts & protein
- mostly hydroxyapatite( calcium phosphate )
- some calcium carbonate, K, Mg
- collagen fibers
Mineral salts deposited in a framework of collagen fibers
- calcification(=mineralization gives bone hardness
- collagen fibers give bone great tensile strength
Osteoblasts, osteocytes, osteoclasts
Other organic molecules
calcium and phosphorus keep bone rigid
Bone stores minerals and ions for body
Non – collagenous organic
Osteonectin – Phosphorylated glycoprotein secreted by
osteoblasts, binds to collagen & hydroxyappatite, play a role
in hydroxy appatite crystallization.
Osteocalcin – Glycoprotein synthesized by osteoblasts, binds
hydroxyappatite & Ca, used as a marker of new bone
Bone proteoglycans biglycan & decorin may bind
transforming growth factor–β (TGF-β).
Bone sialoproteins, osteopontin & thrombospondin mediate
osteoclast adhesion to bone surfaces via binding to
Bone matrix also contains many growth factors,
proteases & protease inhibitors which are secreted by
osteoblasts, often in a latent form.
Transforming growth factor-β (TGF-β), secreted by
osteoclasts as well as osteoblasts, is activated in the
acid conditions of the ruffled border zone of the
osteoclast, & may be a coupling factor for new bone
formation at resorption site.
Osteoprogenitor or Osteogenic cells
small, spindle shaped
present on all nonresorbing surfaces in
lacunae within bone.
processes into small
give rise to osteoblasts in
chondroblasts in avascular
constituents of bone
aid in calcification
smaller and less basophilic
keeps bone matrix in
release calcium ions
from bone matrix when
Have a ruffled
border and a
clear zone on
move around on
digestion by acid
uptake of digested
. It is a process of formation of bone and it
includes proliferation of collagen and
ground substance with subsequent
deposition of calcium salts.
It is the direct laying down of bone into the
primitive connective tissue(Mesenchym).
It results in formation of cranial bones of the skull
and the clavicles
All bones formed this way are flat bones
It is also an important process during natural
healing of bone fractures
Results in the formation of all of the rest of
Begins in the second month of
Uses hyaline cartilage “bones” as models
for bone construction
Requires breakdown of hyaline cartilage
prior to ossification
1. Development of
cartilage model of bone
There is an aggregation of
Mesenchymal cells differentiate into
These chondroblast secret hyaline
2. Growth of Cartilage
Cartilage grows by both :
interstitial (mostly in length)
Appositional(mostly in width)
Sometimes during growth of cartilage model some of
Inner perichondral cells gives rise to osteoblast instead of
chondroblast (as a result fomer perichondrium is now
called the periosteum).
Newly formed osteoblast secret osteoid forming bone
collar around cartilage model.
3. Development of Primary
Chondrocytes differentiate and become hypertrophic.
Then it deposits mineralized matrix.
Cartilage calcification is initiated by matrix vesicles
Calcified matrix is partially resorbed by osteoclast.
After resorption osteoblast differentiate into this area
forming woven bone layer.
Blood vessels enter in this area.
And penetrate bone to allow seeding of bone marrow.
4. Development of the
Medullary ( Marrow) Cavity
Osteoblasts deposit matrix
over calcified cartilage
form trabeculae of spongy
Osteoclasts form medullary
5) Development of Secondary
Formation of Articular Cartilage &
• Cartilage on epiphyses remains as
• Epiphyseal (growth) plate also remains
4 Zones of Epiphyseal Plate:
Zone of resting cartilage
Zone of proliferating cartilage
Zone of hypertrophic cartilage
Zone of calcified cartilage
Zone of resting cartilage
anchors growth plate to bone
Zone of proliferating cartilage
rapid cell division (stacked coins)
Zone of hypertrophic cartilage
cells enlarge & remain in columns
Zone of calcified cartilage
thin zone of mostly dead cells
osteoclasts remove matrix
osteoblasts & capillaries build bone over
Factors Affecting Bone
Nutrition: need adequate levels of minerals
- Ca & P for bone growth
- vitamin C for collagen synthesis
- vitamins K & B12 for protein synthesis
Need adequate levels of specific hormones
- insulinlike growth factor ( IGF) needed during childhood
- promotes cell division at epiphyseal plate
- also need hGH, thyroid (T3 & T4) , & insulin
- sex hormones needed at puberty (estrogen &
- stimulate growth & male/female skeletal modifications
orthodontists as craniofacial bone
specialist and hence torough
knowledge about bone
physiology will help us to treat
patients more effectively and
Wolff's law is a theory developed by the German anatomist
and surgeon Julius Wolff (1836–1902) in the 19th century
that states that
Bone reacts to mechanical functional stress through an
adaptive process resulting in a change of its external and
internal architecture to better withstand this stress.
If loading on a particular bone increases, the bone will
remodel itself over a period of time to become stronger to
withstand greatest strength with least amount of material
The remodeling of bone in response to loading is
achieved via mechanotransduction, a process through
which forces or other mechanical signals are
converted to biochemical signals in cellular signaling.
The specific effects on bone structure depends on the
duration, magnitude and rate of loading, and it has
been found that only cyclic loading can induce bone
When loaded, fluid flows away from areas of high
compressive loading in the bone matrix
Osteocytes are the most abundant cells in bone and
are also the most sensitive to such fluid flow caused by
Upon sensing a load, osteocytes regulate bone
remodeling by signaling to other cells with signaling
molecules or direct contact
Additionally, osteoprogenitor cells, which may
differentiate into osteoblasts or osteoclasts, are also
mechanosensors and may differentiate one way or
another depending on the loading condition.[
Weightlifters often display increases
in bone density in response to their training.
Martial artists who strike objects with
increasing intensity (e.g., repeated elbow
strikes), display increases in bone density in
the striking area. This process is
termed cortical remodeling
Frost’s Mechanostat Concept
According to the Mechanostat, bone growth and
bone loss is stimulated by the local mechanical elastic
deformation of bone. The reason for the elastic
deformation of bone is the peak forces caused by
The Adaptation of bone according to the maximum
forces is considered to be a lifelong process. Hence
bone adapts its mechanical properties according to
the needed mechanical function – bone mass, bone
geometry and hence bone strength is adapted
according to the every-day usage / needs.
Frost’s Mechanostat Concept
Strain : Deformation per unit length.
It is a dimensionless parameter that is expressed as percent strain or
For instance, when a bone of 100 mm in length is elongated by 2 mm, the
associated strain is expressed as 2% strain, 0.02 strain, or 20,000 micro strain.
Ultimate strength of bone=25000µ£=2.5%
Benninghoff’s Stress Trajectories
It states that lines of orientation of bony
trabeculae corresponds to the pathways of
maximal pressure and tension that bony
trabeculae are thicker in the region where the
stress is greater.
In Maxilla – frontonasal buttress, malar Zygomatic
In Mandible - Condyle, Gonial angles, Coronoid process
Modeling & Remodeling
The modern physiologic concept of bone remodeling is
largely attributed to Harold Frost.
He differentiate Bone “modeling”(change in shape, size,
and position of bones)
Bone “remodeling”(coupled turnover sequence)
Modeling & Remodeling
Both trabecular & cortical bone grow, adapt & turn over
by means of these two fundamentally distinct
Changes the shape,
size, or position of
bones in response to
Independent site of
resorption & formation
change the form of a
Physiologic term for
It is a coupled
sequence of catabolic
and anabolic events to
homeostasis and repair
/ renew aged or
internal turnover of a
without a change in its
Modeling & Remodeling
form of a bone
An example of this process long
bone increases in length and
Bone modeling occurs during
birth to adulthood and is
responsible for gain in skeletal
mass and changes in skeletal
Dominant process of
facial growth &
adaptation to applied
loads such as
head gear, RPE,
Changes can be seen on
the ceph tracings.
After peak bone mass has been
becomes the final common
pathway by which bone mass is
adjusted throughout adult life.
Take place at the
same time, but
apparent only at the
seen in bone scans and /or
Modeling & Remodeling
Where bone strains
exceed bone's modeling
modeling can switch on
to strengthen the bone.
whereas when bone strains stay
below a lower threshold range,
disuse-mode remodeling can turn on
to reduce whole bone strength by
removing some trabecular and
Growth factors that regulate bone
Insulin – like growth factors (IGF) I & II
Transforming growth factor –b (TGF – b)
superfamily, including the bone
morphogenetic proteins (BMPs)
Fibroblast growth factors (FGF)
Selected cytokines of the interleukin (IL),
tumour necrosis factor (TNF), & colony –
stimulating factor (CSF) families
It provides a way for the body to alter the
balance of essential minerals by increasing
or decreasing the concentration of these in
It provides a mechanism for the skeleton to
adapt to its mechanical environment
reducing risk to fracture
Basic multi-cellular unit
The process of bone resorption and formation are closely
linked within discrete temporary anatomic structures called
as „basic metabolizing units‟(by Frost)later called as basic
They are readily present in cortical bone but there are
evidence for the same concept in cancellous bone.
The cellular components of a BMU maintains the same
spatial & temporal relationship to each other while moving
through or across the bone.
REMODELING IN CORTICAL
Axially oriented cutting & filing cones are the mechanism underlying
internal remodeling of dense compact bone.
The cutting/filling cone has a head of osteoclasts that cuts through
the bone & a tail of osteoblasts that forms a new secondary osteon.
10 osteoclasts dig a circular tunnel
osteoblasts that fill the tunnel .
It requires about 29 days to create resorption cavity (200-250µm in
diameter) and 134 days to refill it .
Remodeling rate 2%-10% per year.
followed by thousands of
REMODELING IN TRABECULAR
Due to much larger surface to volume ratio it is more actively
remodeled than cortical bone, with remodeling rate 10 times
In trabecular bone 151days ; remodeling here is surface event.
Here osteoclasts digging a trench rather than tunnel and
resulting structure that is formed is called a
cutting/filling cone .
Remodeling rate 20%-30% per year.
Hemi cutting/filling cone in showing the mechanism
for coupling bone resorption to formation
Summary of remodelling process
Micro cracks in bone causes
Release of inflammatory cytokines cells(prostaglandins,interleukin)
&exposure of mineralised collagen to extracellular fluid
T- cells produce RANKL which induces osteoclasts histogenesis
RANKL stimulates preosteoclasts from circulatory blood through RANKL receptors to form
Bone resorption takes place
Growth factors are produced & they stimulate preosteoclasts to produce OPG
Mononuclear cells coat the irregular or scalloped resorbing surface with cementing surface
Perivascular cells migrate & differentiate to preosteoblast
Osteoblasts form new bone
Control of Remodeling
Two control loops regulate bone remodeling
Homeostasis in the blood (negative feedback)
Hormonal mechanism maintains calcium
Mechanical and gravitational forces acting on the
Rising blood Ca2+ levels trigger the thyroid to release
Calcitonin inhibits bone resorption and stimulates calcium
salt deposit in bone
Falling blood Ca2+ levels signal the parathyroid glands to
release parathyroid hormone (PTH)
PTH signals osteoclasts to degrade bone matrix and release
Ca2+ into the blood
Fracture & Repair of Bone
Healing is faster in bone (vascular) than in cartilage
Repair is still slow due to BV damage
- closed reduction: restore pieces to normal position by
- open reduction: realignment during surgery
Aging & Bone Tissue
The loss of Ca+2 from bone
may result in osteoporosis
rapid in women age 40-45
( when estrogen levels decrease )
begins after age 60 in men
Decreased rate of protein
less collagen production
less growth hormone
brittle bones more likely to
Bone physiologic concepts have important clinical
applications in orthodontics & dentofacial
A detailed knowledge of the dynamic nature of bone
physiology is important for successful orthodontic
Mechanical adaptation of bone to forces used in
Orthodontics is the physiologic basis of Orthodontics
and dento-facial orthopedics.
Physiology- Robert M. Berne Fifth Edition
• Anatomy- gray’s anatomy
• Craniofacial growth- Sridhar premkumar
• Wikipedia, the free encyclopedia