Bone is a connective tissue
composed of ground substance,
cells and fibers.
A). Based on Morphology:
covered with a
thin layer of
Develop in areas
of pressure or
Morphologic classification :
a. Long bones
b. Short bones
c. Irregular bones
d. Flat bones
B). Based on Development:
Replacement of hyaline
cartilage with bony
e.g. bones of trunk and
Replacement of sheet
like connective tissue
with bony tissue
e.g. cranial & facial flat
bones of skull, mandible
C). Based on Microscopic Structure:
Mature Bone Immature Bone
-first formed bone
-rarely seen after
-seen in alveolar
bone & during
healing of fractures.
-irregular bony spikules
called ‘Trabeculae’ around
• Mineral Content
• Hydroxyapatite crystals with
carbonate content & low Ca/P
• Bone crystals as ‘leaf like’
structures aligned parallel to
• Narrow gaps between crystals
is associated with water and
• Organic Content
• Mainly type I collagen
• Also type V
• Alveolar bone = type I + type
III + type V + type XII
• Sharpeys fibres contain type
III with type I collagen
• Type III & type XII are
produced by fibroblasts during
production of periodontal
• Type I, V and XII are
expressed by osteoclasts.
Non Collagenous Proteins
-Has amino acid – gamma carboxy glutamic acid
-Demonstrated in alveolar bone
-Carboxy terminal is chemo-attractant to osteoclasts precursors.
-Present in alveolar bone
-Heavily glycosylated & phosphorylated
-Aspartate is predominant
-Inhibits hydroxyapatite crystal growth
3). Bone Sialoprotein:
-Glutamic acid is predominant
-Initiation of mineral crystal formation
-Calcium binding glycoprotein
• Circumferential lamellae
• Concentric lamellae
• Haversian canal
• Haversian canal + Concentric Lamellae = OSTEON
• Reversal Line: sharply delineated by cement lines which is highly
basophilic(due to rich content of glycoproteins & proteoglycans) and marks
the limit of bone erosion prior to osteon formation.
• Resting Line
• Volksmann canal connects the osteons and the periosteum.
• Lacunae containing osteocytes at the junction of lamellae
• Canaliculi radiating from lacunae; helps in exchange of nutrients and
wastes between lacunae (osteocytes).
• Interstitial lamellae: present between osteons; remnants of osteon, left
behind during remodelling.
Inner layer with bone cells with rich
Skeletal developmental anomaly of
the bone forming mesenchyme
that manifests as a defect in
osteoblastic differentiation &
• Non heridetary disorder of unknown cause.
• Can occur in any part of the skeleton but the
bones of skull, thigh, ribs, upper arms and pelvis
are most commonly involved.
• It is not a form of cancer.
• Most lesions are monostotic, asymptomatic &
identified incidentally & can be treated with
• Post zygotic mutation in GNAS 1 gene(20q.13.2)
• GNAS 1(Guanine Nucleotide Binding Protein- alpha
stimulating activity polypeptide)gene encodes a G-
protein that stimulates the production of cAMP.
• Continuous activation of G-protein leading to over
production cAMP in the affected tissues.
• Hyperfunctioning of the affected endocrine organs.
• Leading to
i. Precocious puberty
iii. GH & cortisol overproduction
iv. Increased proliferation of melanocytes resulting in
large Cafe-au-lait spots with irregular margins.
v. cAMP affects the differentiation of osteoblasts leading
to fibrous dysplasia
• Medullary bone is replaced by fibrous tissue which
appears radiolucent on radiographs-”Ground Glass
• Trabeculae of woven bone contains fluid filled cysts that
are embedded largely in collagenous fibrous matrix.
• Bony trabeculae are abnormally thin & irregular & often
described as “Chinese Characters”
• Fibrous Dyspalsia is characterised by “Shepherd’s
Crook” deformity which refers to coxa varus angulation
of proximal femur.
• Cause of transformation is not completely known,
however levels of transcription factor C-fos are raised
which leads to gene over expression & tumor formation.
• Monostotic: Involvement of a single bone.
• Polyostotic: Many bones are involved.
Most severe form is McCune Albright
• Four disease patterns are recognised:
iii. Craniofacial form
Age : 3-15 years
2/3 of patients with polyostotic disease are asymptomatic before
they are aged 10 years.
Monostotic patients as old as 20-30 years are asymptomatic.
Males and females are equally affected.
Clinical findings of increasing pain & an enlarging soft tissue
mass suggest malignant change.
Monostotic Fibrous Dysplasia
70-80% of the lesions.
Most frequently occurs in the ribs(28%),
femur(23%) and humerous in decreasing order of
The clinical term ‘Leontiasis Ossea’ has often been
applied to cases of fibrous dysplasia which affect the
maxilla or facial bones & give the patient a leonine
• Age: children & young adults.
• Sex: equally affects males &
• Painless swelling or bulging of
(usually involves labial/buccal
plate; when it involves
mandible, sometimes it causes a
protruberant excrescence of
• Malalignment, tipping of teeth
due to progressive expansile
nature of lesion & tenderness
• Mucosa over the lesion is
(Fibrous Dysplasia of maxilla is
a serious form of disease since it
has marked predilection for
occurrence in children & is
impossible to eradicate without
radical, mutilating surgery).
• lesions extend locally to involve
maxillary sinus, zygomatic
process & floor of orbit & base of
• Bulging of canine fossa
• Extreme prominence of
• Marked facial deformity
• Has 3 basic patterns:
i. Small, unilocular/large, multilocular with well
circumscribed border containing a network of fine
ii. Increased trabeculations render the lesion more
iii. Many delicate trabeculations-Ground Glass or peau
d’ orange appearance; it is not well circumscribed
and blends into adjacent normal bone.
• In all types, cortical plate is thinned because of
expansile nature of growth.
• Lesion is fibrous composed of proliferating
fibroblasts in compact stroma of interlacing
• Irregular bony trabeculae are scattered
throughout the lesion without any definite
pattern- ‘Chinese Character’ shaped.
• Trabeculae are of coarse, woven bone.
• Surgical removal of lesion.
• Lesions with type III radiographic findings
should be block resected.
• Malignant transformation into osteosarcoma.
Mc Cune Albright Syndrome
Polyostotic Fibrous Dysplasia
Defined as association of polyostotic
fibrous dysplasia, precocious puberty,
café-au-lait spots & other
endocrinopathies due to hyperactivity
various endocrine glands.
• Post zygotic activation mutation of GS alpha
gene in affected tissues.
• GS alpha subunit is a component of G-protein
complex, which couples hormone receptors to
Adenylyl Cyclase (intracellular second
messenger) in a submembrane site.
• Precocious puberty associated with the condition is gonadotrophin-
• Gonadotrophin-McCune Albright Syndrome
• Some severely affected patients may present with associated
hepatic, cardiac and GI dysfunction.
• Cutaneous pigmentation is the most common extraskeletal
manifestation & is ipsilateral to side of bony lesions.
• Café-au-lait spots are related to amount of melanin in basal cells
• Pigmentation may occur at birth & may precede the development of
skeletal & endocrine abnormalities.
• Areas of fibrous metaplasia within flat and tubular
• Progressively expanding fibrous lesion of bone
• Concentric expansion in an outward direction within
the medullary bone.
• Well-defined, non-encapsulated.
• Lesions are rich in spindle shaped fibroblasts with a
swirled appearance within the marrow space.
• Mild cases: surgical radiation
• Severe cases: X-ray radiation
• Prognosis depends on the degree of skeletal
• Malignant transformation into osteosarcoma
can also occur.
Most common fibro-osseous lesion
which occurs in tooth bearing
areas of the jaws.
• Periodontal origin; or
• Defect in extraligamentary bone remodelling
that maybe triggered by local factors or possibly
by hormonal imbalance.
• Based on clinical and radiographic features, it is
divided into three groups:
i. Focal cemento-osseus dysplasia
ii. Periapical cemento-osseus dysplasia
iii. Florid cemento-osseus dysplasia
Focal Cemento-Osseus Dysplasia
• Exhibits a single site of involvement.
• Most commonly in black females with a
predilection for 3-6 decade.
• Posterior mandible is the commonest site.
• Usually asymptomatic with a positive vitality
test of the affected teeth.
• Most of the lesions are smaller than 1.5cm in
• Lesions vary from being completely radiolucent to
densely radiopaque with a thin peripheral
• Most common is a mixed radiolucent and
• Well defined lesion with a slightly irregular border.
• Occurs in both dentulous and edentulous areas.
Periapical Cemento-Osseus Lesions
• Also called as ‘Cementoma’,
‘Fibrocementoma’, ‘Periapical Fibro
• Teeth associated with lesion is invariably vital.
• Involves periapical region of anterior mandible.
• Generally occurs between 30-50 yrs of age.
• Early lesions appear as circumscribed areas of
radiolucency involving periapical areas of tooth.
• Mature lesions create a mixed radiolucent and a
• Periodontal ligament is intact.
• There is no fusion to the teeth.
Florid Cemento-Osseus Lesions
• Most clinically extensive form of cemento-osseus dysplasia,
thus the term – ‘Florid’.
• Common in black females with marked predilection for
middle aged to older adults.
• Multifocal involvement, not limited to anterior areas.
• May involve all the 4 quadrants.
• Dull pain and an alveolar sinus tract maybe present.
• Some degree of expansion maybe seen.
• Bilateral and symmetric involvement.
• Initially, lesion is predominantly radiolucent,
with time, becomes mixed and then
predominantly radiopaque with a thin
• Maybe totally radiopaque and blend with
adjacent normal appearing bone.
• Both, edentulous and dentulous areas are
• All 3 variants present a similar histopathologic picture.
• Tissue consist of fragments of cellular mesenchyme
composed of spindle shaped fibroblasts and collagen fibres
with numerous blood vessels.
• Free hemorrhage is typically noted interspersed
throughout the lesion.
• Within the fibrous connective tissue background is a
mixture of woven bone, lamellar bone & cementum like
• As the lesions mature and become more sclerotic, the ratio
of fibrous connective tissue to mineralised material
• With maturation, the bony trabeculae become thick,
curvilinear structures that have been said to resemble the
shape of ‘ginger roots’.
• For asymptomatic patients: regular recall
examinations with prophylaxis and
reinforcement of good home hygiene care.
• For symptomatic patients:
• Sequestration of sclerotic cement like masses
and is followed by healing.
• Saucerisation of dead bone.