Alveolar bone By Professor Mohamad Helal

Alveolar Bone
Professor Dr Mohamad Helal
Professor Of Oral Biology
Mansoura

• Bone is a dynamic
structure that is
adapting constantly to
its environment and
they are essential
elements for
locomotion, antigravity
support and life
sustaining functions
such as mastication

Based on
location
CLASSIFICATION OF BONES
Axial
skeleton
Appendicular
skeleton
8
0
12
6
+
20
6

Alveolar Bone
 BONE is a specialized connective tissue that is
mainly characterized by its mineralized organic
matrix.
 Similar to bone elsewhere, it also provides for
muscle attachement.
 The alveolar process is the portion of maxilla and
mandible that forms and support the tooth socket.
 It forms when tooth erupts to provide the osseous
attachment to the forming periodontal ligament; it
disappears gradually after the tooth is lost.

Alveolar Bone
• It is the mineralized connective tissue that supports
and protects the teeth
• The most important property of bone is its ‘plasticity’,
allowing it to remodel according to the functional
demands during movement.
• the basic unit of bone is the osteon (Haversian system)
and have five main types of bone cell

COMPOSITION OF BONE
By weight
Inorganic (67%) Cells
1.Ostoblasts
2.Osteoclasts
3.Osteocytes
4.Bone lining cells

2/3-
INORGANIC
MATTERIALS
1/3
ORGANIC
MATTERIALS
Hydroxyapatite crystals
Formed from calciumminerals
and phosphate along with
hydroxyl, carbonate, citrate
•Mg, Na, K ,Fl , –
smaller quantity
• 90% Collagen (primarily
Type I)
• 11-12% Noncollagenous
proteins-
• Osteocalcin
• Osteonectin
• BMP
• Sialoprotein
• Phosphoproteins
• Proteoglycan
COMPOSITION OF BONE

MAXILLA/MANDIBLE
ALVEOLAR
PROCESS
ALVEOLAR
BONE
PROPER
BUNDLE
BONE
LAMELLAR
BONE
INNER &
OUTER
CORTICAL
PLATES
TRABECULAR
BONE or
(cancellous)
INTERDENTAL
SEPTA
INTERRADIC
ULAR
SEPTA
BASAL
BONE
GROSS
MORPHOLOGY

• Outer alveolar
plate
• Inner alveolar
plate
• Interdental
septum
• Interradicular
septum
GROSS
MORPHOLOGY

`
CRIBRIFORM PLATE
• Cribriform plate (anatomic
term)/ Lamina dura
(radiographic term)/ Bundle
bone (histologic term)
• Cribriform plate thickness- 0.1
to 0.5mm
• External alveolar plate
thickness – 1.5 to 3mm around
posterior teeth, highly variable
around anterior teeth

Alveolar process is continuous
with basal bone of maxilla
and mandible
Arbitrarily the root apices
delineate the alveolar bone
from basal bone
INNER & OUTER CORTICAL
PLATES

CLASSIFICATION OF BONE
BASED ON Development:
•Endochondral bone
•Intramembranous bone
•Sutural bone
BASED ON Maturation:
• WOVEN BONE
• IMMATURE BONE
• MATURE BONE
So, Can classified in turn to:
•Compact (cortical) bone
•Cancellous (spongy) bone
• According to hsitological types:
• 1- Lamellar bone
• 2-Non lamellar bone
• 3- Bundle bone

Bone formation is preceded by
formation of cartilage which is
later replaced by bone.
Occurs in extremities of all
long bones, in vertebrae, in ribs,
in articular extremities of the
mandible and the base of skull.
Endochondral bone

•Bone develops directly within
the soft connective tissue.
•Occurs in Maxilla and Body of
mandible, cranial vault and
midshaft of long bones.
INTRA MEMBRANOUS /
DIRECT BONE FORMATION

•Bone forms along suture margins
•Not seen in relation to alveolar
bone.
•Occurs in skull, fibrous joints.
•Helps skull and face to
accommodate growing organs
like brain.
SUTURAL BONE
GROWTH

Bone
Outer compact bone
Central medullary cavity
(Trabacular / Spongy /
Cancellous bone)
BONE HISTOLOGY

COMPACT (CORTICAL) BONE
• Composed of dense and concentrically
arranged bony trabeculae or lamella.
• More solid with fewer cavities.
• Found external to spongy bone
• Presence of Haversian system or Osteon.

CANCELLOUS or Trabecular (SPONGY) BONE
•Composed of bone trabeculae or spicules.
•Has a simple and less organized architecture.
•Has a lattice-work pattern with numerous small cavities.
•Found internal to compact bone.
•Has no Haversian system.

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

Compact or trabecular bone are histologically
identical in that they consist of microscopic
layers or lamellae.
Three types of layering:
1- Circumferencial lamellae.
2- Concentric lamellae.
3- Interstitial lamellae.

• Bone whether Compact or Trabecular are
deposited in layers, or lamellae, each lamella
being about 5µm thick.
Three distinct types of layering are recognised :
 Circumferential lamellae encloses the entire
adult bone, forming its outer and inner
perimeters.
 Concentric lamellae forms the bulk of compact
bone & forms the basic metabolic unit of bone –
The Osteon.
 Interstitial lamellae interspersed between adj
concentric lamellae and fills the spaces between
them.

The outer aspect of cortical bone is surrounded by a connectivetissue
membrane which has two layers.
The outer fibrous layer – Periosteum
The inner cellular layer - Endosteum

Periostium
• It is osteogenic outermost layer of compact bone
except articular surface
Function:
 Give attachement of Sharpey’s fibers acting as
medium of muscles and tendons.
 Performs a nutritive function for underlying bone
So its structure perform its function:
Consists of two layers:
• Outer layer: more fibrous with vuscular.
• Inner layer(Cambium)more cellular(osteoblast,
fibroblast, osteoclast, osteogenic cells)

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

Endosteum
• Thin high fibrocellular layer of C.T cover
medullary surfaces (Bone Marrow cavity) of
bone like inner layer of periosteum (Cambium).

Osteoid
• Any surface where active bone formation occurring
will be covered by a layer of newly deposited,
unmineralized, bone matrix called oseoid.
• 5-10 µm thickness.
• ↑ thickness in some diseases.

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

HISTOLOGICAL
COMPACT
CANCELLOUS
MATURE
IMMATURE
WOVEN
BONE

Coarse woven bone:
• Periosteum is very undulating
• Bone is very cellular and disorganized.
• ↑Vascularity.
• ↑Soft tissue content.

Young immature bone:
• Periosteal surface is less undulating.
• Less cellular and slightly more organized.
• Some primary small osteons are forming and
lamellae are not numerous and not well
delineated.
• Its endosteal surface is primarily for resorption.

Mature bone:
• Surface is less undulating.
• Tightly packed osteons create an organized
bone matrix.
• Fewer cells.
• Little loose C.T.

Immature bone/Non lamellar/Fibrous bone :
•These have more cells & fibers in them.
•These are first formed bone.
•In humans they are found only in fetus or in sockets
of alveolar bone, during fracture repair and sutures of
the skull.
•Also Known as Woven Bones.
Mature bone /Lamellar bone: The type of bone which
are composed of thin plates (lamellae) of bony tissue.
•Compact (cortical) bone
•Cancellous (spongy) bone

Type of Bone
• Lamellar Bone: compact and cancellous
• Non Lamellar Bone.
• Bundle Bone.

Lamellar bone
• Histologically , mature bone may be categorized as
compact (cortical) or cancellous (spongy) according
to its density.

• Bone of foetus, callus of fracture, healing sockets.
• Irregular arrangement of collagen fs.
• ↑ number, size, irregular arrangement of
osteocytes.
• ↑ organic substance.
•  inorganic.
• Resorbed and replaced by lamellar bone .
Non Lamellar Bone

Bundle Bone
• Adjacent to periostium and PDL (tension areas).
• Its matrix pattern sharing between woven and
lamellar bone.
• Sharpey′s fibers.
• Their fibers arranged parallel to the bone surface
and at right angle to Sharpey′s fibers with
osteocytes between them.
•  number of fibers,  number of cells than woven
bone.
• ↑ calcium salts per unit area than woven bone.
• More radioopaque (lamina dura).

Resting Lines
• Present the
incremrntal pattern
of bone formation.
• Correspond to the
rest periods of th
successive formed
bone layers.
• Dark blue in dec.
H&E sections.
• Straight or slightly
undulated.

Reversal Lines
• The convexities towards
old resorbed bone.
• After osteoclastic activity,
new bone is laid down by
osteoblasts over the old
bone. Both bones are
separated by reversal lines.
• Dark blue in dec. H&E sec.
• Scalloped in shape.

Faint Lines
• Collagen fibers in every layer arranged parallel
to each other.
• Fibers of next layer change their direction with
45˚.
• It appeared Faint black by silver impregation.

HISTOLOGY
CELLS
OSTEOBLASTS
OSTEOCYTES
OSTEOGENIC CELLS
BONE LINING CELLS
OSTEOPROGENITOR
CELLS
OSTEOCLASTIC CELLS OSTEOCLASTS
MATRIX
COMPONEN
T
INORGANIC
CALCIUM HYDROXYL
APATITE CRYSTAL
ORGANIC
COLLAGEN
MATRIX
NON COLLAGENOUS
PROTEIN
OSTEOCALCIN
OSTEOPONTIN & BONE SIALOPROTEIN
OSTEONECTIN
PROTEOGLYCAN
LYSYL OXIDASE AND TYROSINE RICH ACIDIC
MATRIX PROTEINS (TRAMP)

OSTEOBLASTS
• During embryonic development, intramembranous bone of
the maxilla and mandible initially forms from osteoblasts
arising from condensing mesenchyme in the facial region
• The most active secretory cells in bone
• Basophilic, plump cuboidal / slightly
elongated cells.
• Rich in synthetic & secretory organelles-
rough endoplasmic reticulum, golgi
apparatus, secretory granules & microtubules
• Also contain other organelles associated with
cell metabolism- mitochondria & endosomal/
lysosomal elements & extensive cytoskeleton

Osteocytes
are
‘entrapped’
osteoblasts
within bone
Osteocytes
occupy spaces
(lacunae) in
bone and are
defined as cells
surrounded by
bone matrix.
Decreased
quantity of
synthetic and
secretory
organelles
Numerous and
extensive cell
processes that ramify
throughout the bone
in canaliculi and
make contact via gap
junctions with
processes extending
from other
osteocytes
Origin:
1-from osteoblastsr
2- bone lining cells at
the surface of the
bone
OSTEOCYTES

BONE LINING
CELLS
When bone surfaces are neither in the
formative nor resorptive phase, the
surface is completely lined by a layer
of flattened cells termed Bone lining
cells.
Regarded as
Postproliferative
osteoblasts.
Retain gap junctions with
osteocytes
Functions: control
mineral homeostasis &
endure bone vitality.

OSTEOPROGENITOR CELLS
• The stem cell population that
give rise to osteoblasts are
termed Osteoprogenitor cells.
• They are fibroblast-like cells,
with an elongated nucleus and a
few organelles.
• Their life cycle may involve upto
about eight cell divisions before
reaching the osteoblast stage.
• They reside in the layer of cells
beneath the osteoblast layer, in
the periosteal region, in the
periodontal ligament or in the
marrow spaces.

Osteoclast
• The multinucleated osteoclast (10-20
nuclei) is much larger cell (may be up to
100μm in diameter).
• Tartrate-resistant acid phosphotase
within its cytoplasmic vesicles and
vacuoles.
• Foamy esinophilic cytoplasm.
• Against bone surface, occupying shallow,
hollowed-out depression called
Howship´s lacunae.
• Foamy or striated appearance
• Life span is at least 10-14 days, after
which undergo apoptosis.

OSTEOCLAST
• Origin: from hematopoietic tissue
• Fusion of mononuclear cells
(blood derived monocytes) to
form a multinucleated cell
• Very large, 5-20 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

 At the periphery of the ruffled
border, the plasma membrane is
smooth and closely apposed to the
bone surface.
 The adjacent cytoplasm, devoid of
cell organelles,enriched in
actin,vinculin,and talin,proteins
associated with integrin mediated
cell adhesion. This region is called
the Clear (Sealing) zone.
 This zone, thus creates an isolated
micro environment in which
resorption can take place.

TEM:
• Ruffled border in contact with mineralized matrix (many
tightly packed microvilli).
• Numerous mitochondria.
• Multinucleation (division of nucleus or fusion of several
mononuclear cells) but may be mononucleated.
• Tightly arranged Golgi saccules.
• Clear zone attaches osteoclast to the mineralized surface.
• Primary lysosomes.

• Several osteoclasts excavating a large area of bone which
is the leading edge
of resorption is termed as the Cutting cone.
• Released cytokines[Bone Morphogenic Proteins & Insulin
like Growth Factor] stimulate stem cells to differentiate
into osteoblasts.
• These osteoblasts secrete osteoid known as Filling cone.

RANKL expressed on plasma membrane of stromal and
osteoblastic cells bind to RANK expressed on osteoclastic
progenitors to induce a signaling cascade leading to
differentiation and fusion of osteoclast precursor cells.
Osteoclast differentiation and activation is inhibited by
osteoprotegerin (OPG), which is a member of the TNF
receptor family and is secreted by osteoblastic cells

Bone Resorption
1. Removal of minerals
2. Desintegration of organic matrix
3. Transport of soluble
• Products to extracellular fluid or blood
vascular system(unknown mechanism).

ALVEOLAR BONE PROPER
• The alveolar bone proper is a thin layer of compact
bone.
• Continuation of the cortical plate and forms the tooth
socket.
• It surrounds the roots of the teeth and gives
attachment to the principal fibres of the Periodontal
ligament.
• Referred to as Cribriform plate -reflects a sieve-like
appearance produced by numerous vascular canals.
• Double Fibrilar Orientation

Sharpey’s fibres
• Called Bundle bone as numerous bundles of
pass into it from the Periodontal ligament.

• It appears as dense white line in radiographs-
Lamina dura.
• Break in continuity of lamina dura at the
proximal aspects of crest of interdental
septum has been considered as the earliest
radiographic change in periodontitis.

CANCELLOUS BONE
• Spongy bone (anatomic term)/ Trabecular bone
(radiographic term)/ Cancellous bone (histologic term)
• Presence of trabeculae enclosing irregular marrow spaces
lined with a layer of thin, flattened endosteal cells
• Matrix consists of irregularly arranged lamellae separated
by incremental and resorption lines
• Type 1: The interdental and interradicular trabeculae are
regular and horizontal in a ladder like arrangement.
• Type2: Shows irregularly arranged numerous
delicate interdental and interradicular trabeculae

INTERDENTAL SEPTUM
• Bony partition that separate the adjacent alveoli
• Coronally septa is thin and consists of only fused inner
cortical plates
• Apically septa is thicker and contain intervening
cancellous bone
• Mesiodistal angulation of interdental septum is parallel
to line drawn between CEJ of approximating teeth
• If interdental space is narrow, septum may consist of only
cribriform plate

Diagram of relation between CE junction of adjacent teeth shape of
crest of alveolar septa
If roots are too close together,
an irregular window can appear
in the bone between adjacent
roots

• The shape of the interdental bone is a function of the
tooth form and the embrasure width.
• The more tapered the tooth, the more pyramidal is the
bony form.
• The wider the embrasure, the more flattened is the
interdental bone mesiodistally and buccolingually

ALVEOLAR CREST
• Formed when the inner and outer
cortical plates meet
• The margin is thin & knife edged in
vestibular surfaces of anterior and
rounded/beaded in posterior teeth
• Most prominent border of
interdental septum

INTERRADICULAR SEPTA
• The bone between the roots of
multirooted teeth .
• Both of them contain
perforating canals of Zukerkandl &
Hirschfeld [nutrient canals].
BASAL BONE
• It is the osseous tissue of the
mandible and the maxilla except the
alveolar process.
• Anatomically, there is no distinct
boundary that exists between the
body of the maxilla / mandible and
their alveolar process.

Development Of Alveolar Bone:
From cells originating from Dental Follicle.
Peripheral layer called perifollicular
mesenchyme.
It has loose structure from it PDL and alveolar
bone develop.
The maxilla as well as the mandible form a
groove which opens towards oral cavity at the
end of the second month of fetal life .
These grooves contain tooth germs, alveolar
nerves and vessels.
Bony septa develop between the tooth germs.
Later on, a horizontal plate of bone separates
the mandibular canal from the dental crypt.

• The alveolar process develops only during the
eruption of teeth and it gradually diminishes in
height after the loss of teeth.
• A part of the alveolar process is included in the
maxillary and the mandibular body of edentulus
patients.

Alveolar
process
Supporting
alveolar bone
Cortical
plates
Inner(ling.)
Outer(labial,
buccal)
Supporting
spongiosa
Alveolar
bone proper
Bundle bone Lamellar
bone

Cross-section at midroot
level-maxilla
Cross-section at coronal third of root-
Mandible
Cross-section at apical third of
root- Mandible

• According to function, to which the
alveolar process adapts itself, it is
divided into two parts.

Supporting Alveolar Bone
Supporting alveolar bone is the bone that
surrounds the alveolar bone proper and gives
support to the socket.
Supporting bone is a dense cortical plate. It
covers the surface of the maxilla and the
mandible and supports the alveolar bone proper
.

Supporting Bone consists of:
A. Cortical plates. They consist of compact bone and
form the outer and inner plates of the alveolar
process.
B. Spongy bone. It is the bone which fills the space
between the outer and inner plates and the alveolar
bone proper.

Cortical plates
• Histologically, cortical plates contain
longitudinal lamellae and Haversian systems.
• In the lower jaw, circumferential lamellae
extend from body of the mandible into the
cortical plates.

• They are much thinner and more perforated
in maxilla than in mandible.
• The outer cortical plate is thinner than the
inner in anterior teeth area of both jaws
especially in maxilla.
• Outer and inner cortical plates may join
alveolar bone proper in anterior teeth at
alveolar crest ( spongiosa is absent).

Buccal cortical plate is thinner or absent at
upper post teeth (perforated by many
foramina contain blood and lymph).
 Buccal cortical plate is thick in lower posterior
teeth region.
The alveolar process is masked or fused with
basal bone as in anterior part of maxilla
palatally and oblique ridge of the mandible

Alveolar bone: Alveolar bone (AB) at the periphery of periodontal ligament
(PL) x30 (a) Alveolar bone proper, (b) Supporting alveolar bone, (C)
Cemenum

Spongy bone is the cancellous bone which supports
the alveolar bone proper. Heavy trabeculae with
bone marrow spaces are present in the spongy
bone. These bone marrow spaces contain blood
forming elements and osteogenic cells.
Lies between the cortical plates and alveolar bone
proper.
Continuous with the spongiosa of the jaws.
The marrow spaces contain fatty tissue and islets of
RBCs.

• Forms the main bulk of interdental and interradicular
alveolar septa. These septa contain perforating
canals (Zuckerkandle and Hirschfield nutrient
canals).
• Canals of Zuckerkandl and Hirschfeld (Nutrient
canals) are present in the interradicular and
interdental septa. These canals carry the interdental
and interradicular arteries, veins, lymph vessels and
nerves.
• At alveolar crest spongiosa may be absent.

Spongiosa of the alveolar process is divided into
two main types on the basis of radiographic
studies. In both types, there is variation in
thickness of trabeculae and size of marrow
spaces.

Radiographic Types of spongy supporting alveolar bone:
It depend on the direction of occlusion force loading
Type- I :
 The interdental and interradicular trabeculae are
regular and horizontal in a ladder like form.
 Mostly present in the mandible and is suitable for the
trajectory pattern of spongy bone.
From the apex of mandibular molars trabeculae may
sometimes radiate in a distal direction from the fundus
of the socket.

Type-II :
 The interdental and interradicular trabeculae are
irregularly arranged and are numerous and delicate.
No distinct trajectory pattern but it is compensated by
more number of the trabeculae per square
centimeter.
 The type II arrangement is mostly present in maxilla.
Radiating trabeculae are not prominent in maxilla as
the maxillary sinus and the nasal cavity are close to
the roots of the molars.

Alveolar bone proper surrounds the root of the
tooth and gives attachment to the principal
fibers of the periodontal ligament. It is a thin
lamella of bone.
Forms the inner wall of the socket. Perforated by
many foramina (called cribriform plate).
Alveolar Bone Proper

Principal fiber bundles embedded in the
alveolar bone proper are the Sharpey's fibers.
This bone which lines the socket in which
Sharpey's fibers are embedded is known as
bundle bone.

Histologically; the alveolar bone proper is formed by:
1- Bundle bone: form the
inner most layer of
alveolar bone proper
(cribriform plate-
lamina dura).

2-Lamellated bone: next to bundle bone.
Consists of thick layer of compact bone
composed of minute osteon arranged
parallel to bone spongiosa.

Anatomy of the cortical plates
 The cortical plates, continuous with the compact layers of the
maxillay and mandibular body are generally much thinner in the
maxilla than in the mandible.
 They are thickest in the premolar and molar regions of the lower
jaw especially on the buccal side.
 In the premolar and molar region of the maxilla, defect of the
outer wall of the cortical plate is fairly common, because it is
perforated by many small openings through which blood vessels
and lymph vessels pass. Such defects where periodontal tissues
and covering mucosa fuse, do not impair the firm attachment
and function of the teeth.

In the maxilla the outer cortical plate is perforated by
many small openings through which blood and
lymph vessels pass.
In the lower jaw the cortical bone of alveolar process
is dense.
In the region of anterior teeth of both jaws the
supporting bone usually is very thin and no spongy
bone is found here and the cortical plate is fused
with the alveolar bone proper.

Fenestration:
some bone present in the
most coronal portion
Dehiscence:
the bone coverage
is missing at the
coronal portion of the
roots
Dr. FatinAwartani

The shape of alveolar septa in x-ray is dependent
on the position of adjacent teeth. If neighboring
teeth are inclined, therefore, the alveolar crest is
oblique.
When the teeth are tipped mesially, then CEJ of
M. tooth is situated in a more occlusal plane than
that of D. tooth and the alveolar crest slopes
distally.

Age changes
•  water content→ ↑ brittleness.
• Widening of marrow spaces and thinning of trabeculae of
supporting spongiosa.
• Marrow is transformed into fatty marrow except in condylar
head, mandibular angle and maxillary tuberosity.
• Distal sloping of the crest of alveolar septa in premolar and
molar regions.
• Resorbed after loss of teeth.
• Approximation of maxillary sinus floor.
• Mental foramen becomes closer to the upper border of the
mandible.

• Bone is biologically a highly plastic tissue.
• Where bone is covered by vascularized CT., it is
exceedingly sensetive to pressure, where
tension acts generally as a stimulus to new bone
production.
• Bone is resorbed on the side of pressure and
apposed on the side of tension.
• ↑cAMP in cells on the pressure side.

• Adaptation of bone to function:
• ↑ functional force→formation of new bone.
• function →volume of supporting bone.

• During healing of fractures or extraction wounds
embryonic bone is formed (radiolucent), which
only later is replaced by mature bone.
• The visibility in radiographs lags 2-3ws behind
actual formation of new bone.

• Periodontal disease:
• Both horizontal and vertical bone resorption
occurs.
• Endotoxins by G-ve bacteria of
plaque→↑cAMP→↑osteoclastic activity.
• Lymphocytes→OAF→↑cAMP→↑osteoclastic
activity and osteoblastic activity at the target
site.

• Synthetic materials that replace bone tissue lost.
Non resorbable hydroxyapatite.
Resorbable tricalcium phosphate.
• If root portion is retained in the alveolar process,
this structure does not undergo a noticeable
reduction in its height.

• In trauma or malignant disease, the need for
larger amounts of bone may require
additional techniques. Requirements may be
met by either autologous bone grafts,
allografts or xenografts, typically BioOssbovine
bone chips.

• The possible role of oxygen tension on
osteoclast activity may help provide an
explanation for the loss of bone that is seen to
accompany many clinical conditions where the
blood supply is compromised and hypoxia is
encountered, such as following inflammation,
radiation damage, fractures and ageing.

 Among important bioactive molecules implicated in this
resorption process are cytokines and prostaglandins, as well as
protons (as inflamed tissue is generally acidic).
 As differences exist between the collagen and the ground
substance of bone and periodontal ligament, analysis of their
breakdown products in the local serum exudates contributing
to gingival crevicular fluid may provide a marker to distinguish
those patients who are more at risk of losing alveolar bone.
 Levels of such molecules will also be found to increase when
crevicular fluid is analysed in patients undergoing orthodontic
tooth movement.

This is a bone disorder characterized by a low bone mass but of
normal constitution.
It particularly affects trabecular bone, which has a higher
turnover rate than compact bone, and predisposes the patient to
spontaneous or low trauma energy level fractures as, once lost, the
bone mass is not usually replaced.
 Vulnerable sites include the neck of the femur and the lumbar
vertebrae.
Osteoporosis

• Osteoporosis can be age related and particularly
affects postmenopausal women, but is of less
importance for the jaws, which have
comparatively small amounts of cancellous bone
and therefore more mineralized tissue per unit
volume than many other parts of the skeleton
• The precise cause of osteoporosis is not known,
although a number of factors, including sex
hormone (particularly oestrogen) deficiency,
lack of mechanical loading and glucocorticoid
excess, have been identified.

 Analyses of various molecules in the blood and/or
urine are also of importance in diagnosing conditions
affecting the turnover rate of bone.
These moleculesi nclude calcium, parathormone,
acid phosphatase, alkaline phosphatase. In addition,
collagen type I cross-linked N-terminals result from
the proteolytic cleavage caused by osteoclasts and
their levels in serum or urine are indicative of
turnover rates, as are the levels of hydroxyproline and
hydroxlylysine .

• An analogous condition in rodents prevents
teeth from erupting because of the inability to
resorbe the overlying bone. The cause of one
such condition is a lack of osteoclasts of M-
CSF.
• If the missing factor is replaced, osteoclasts
can be switched on to allow alveolar bone
resorption and normal eruption.

Distraction osteogenesis:
 Is undertaken to allow length augmentation by
the sustained addition of new woven bone at
the fracture site, formed under tension. When
adequate length has been achieved, the two
bone ends are immobilized for some weeks to
allow the woven bone callus to be reinforced and
ultimately replaced by mature dense lamellar
bone.
For success the original periosteum and blood
supply must be retained.

Osteotomy sites for distraction osteogenesis

Alveolar bone By Professor Mohamad Helal

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Alveolar bone By Professor Mohamad Helal