alveolar process

ALVEOLAR BONE IN HEALTH
www.indiandentalacademy.com

“Bone is defined as a hard, rigid form of
connective tissue constituting most of the
skeleton of vertebrates, composed chiefly of
calcium salts”
“Alveolus is defined as the cavity or socket
of the jaw in to which the roots of the teeth
are embedded”

Development and growth of
bone
• The process of bone formation is called
osteogenesis.
• 3 phases :
-Primary osteoid tissue
-Secondary osteoid tissue
-Calcificationwww.indiandentalacademy.com

Osteogenesis occurs by two
mechanisms:
1. Endochondral
2. Intramembranous

ENDOCHONDRAL /INDIRECT BONE FORMATION
• Bone formation is preceded by formation of
cartilage which is later replaced by bone
(Horton,1990)
• Head of mandible, ends of long bones,
vertebrae, ribs and base of skull.

ENDOCHONDRAL / INDIRECT BONE
FORMATION

INTRA MEMBRANOUS / DIRECT BONE
FORMATION
• Bone develops directly
within the soft tissue
• Maxilla and Body of
mandible

Functional adaptation of bone.
- Wolffs law of
transformation.(Julius Wolff)
- Osteophytes.
Reaction of bone to pressure and
tension.(Schwartz 1932)

Alveolar Bone is the portion of the maxilla &
mandible that forms and supports the tooth
sockets (Alveoli).
As stated by
-Landsberger,1911.
-Schroeder,1911.

Near the end of the 2nd month of
fetal life, mandible and maxilla
form a groove that is opened
toward the surface of the oral
cavity.
As tooth germ starts to develop,
bony septa form gradually. The
alveolar process starts developing
strictly during tooth eruption.
DEVELOPMENT

The parts of the alveolar bone
1.Alveolar bone proper.
2. Supporting alveolar bone
 Cortical plates
 Spongy bone

Alveolar Bone Proper
• The thin lamella of bone that surrounds the root of the
tooth and gives attachment to the principal fibers of the
PDL.
• Bundle bone {Stein and weinmann,1925}

• Histologically –Cribriform plate or Lamina
cribrosa.
• Radiologically-Lamina dura.
(Goldman,1957)

SUPPORTING ALVEOLAR BONE
Surrounds the alveolar bone
proper and gives additional
support.
It consists of
•cortical plates
•spongiosa

Cortical Plates
• Consists of compact bone and forms the outer &
inner plates of the alveolar processes
• They are thinner in Maxilla than in Mandible
• In Maxilla, outer cortical plate is perforated by
many small openings through which blood &
lymph vessels pass
• Thickest in molar & premolar region of lower jaw
esp. on the buccal aspectwww.indiandentalacademy.com

Spongy / Cancellous Bone
• Spongy bone fills the area between the cortical plates and
the alveolar bone proper
• More common in Maxilla
• Found mainly in the inter-radicular & inter-dental spaces
and in limited amounts facially or lingually except in the
palate
• In the region of the anterior teeth of both jaws no spongy
bone is found and the cortical plate is fused with the
alveolar bone proper www.indiandentalacademy.com

INTERDENTAL SEPTUM
 Consists of cancellous bone bordered by the socket wall cribriform plates of
neighboring teeth and the facial and lingual cortical plates.
 Cribriform plate carries the nutrient canals Zuckerkandl & Hirschfield.
The alveolar crest is 0.75 and 1.49 mm
below the level of the CEJ.
(Gargiulo et al,1961)

Gross Bone Histology
Histologically the mature or adult bones, whether
compact or trabecular are composed of microscopic
layers or lamellae.
Three types of layering are recognized:
• Circumferential
• Concentric
• Interstitial

1. Circumferential: Encloses the entire adult
bone, forming its outer perimeter
2. Concentric: Makes up the bulk of compact
bone & forms the basic metabolic unit of bone -
the Osteon
osteocyte
Haversian canal
canaliculi

In the center of each is a canal – “The Haversian
Canal” and each canal houses a capillary
Adjacent haversian canals are interconnected by
Volkmann canals. They contain blood vessels
thus creating rich vascular network throughout
compact bone

3. Interstitial:
They are interspersed between adjacent concentric lamellae
and fill the spaces between them. They are actually
preexisting concentric lamellae and can take a multitude of
shapes

Periosteum
• It is the connective tissue membrane that surrounds the
outer aspect of compact bone
• It has 2 layers- Outer & Inner
• Outer consists (fibrous)of dense irregular connective
tissue.
• Inner layer (cambian) is next to bone surface. It consists of
bone cells,their precursors and rich micro-vascular supply

Endosteum
• It is the cellular membrane that surrounds the
internal surface of compact and cancellous bone
• The periosteal surface of bone is more active in
bone formation than the endosteal one

Bone Cells
• Two cell lineages are present in bone each with specific
functions:
1. Osteogenic Cells: They form and maintain bone. They have a
variable morphology and include:
• Osteoprogenitors
• Preosteoblasts
• Osteoblasts
• Osteocytes
• Bone lining cells
2. Osteoclasts: Are bone resorbing & remodeling cellswww.indiandentalacademy.com

Osteoprogenitor cells
 The determined osteoprogenitor cells are responsible for
bone formation during embryogenesis.
 The inducible osteoprogenitor cells like pericytes arrive at
the injury focus about 3 to 5 days after injury .

Osteoblasts
• They are mononucleated cells, derived from mesenchymal stem
cells
• Ultra structure is characteristic of any actively secreting cell
with prominent Golgi apparatus, RER, mitochondria, nucleoli
and many secretory vesicles & vacuoles
• Are responsible for bone matrix synthesis and subsequent
mineralization of both collagenous & non-collagenous matrix of
bone

• The major constituents of this matrix are Type I & V
Collagen
• Are plump, cuboidal cells (when very active) or slightly
flattened cells
• The pre-osteoblasts & osteoblasts exhibit high level of
alkaline phosphatase on the outer surface of their plasma
membrane
• This enzyme is used as a cytochemical marker to
distinguish pre-osteoblasts from fibroblasts

Osteocytes
• Osteoblasts secrete the organic matrix of bone and is at
first devoid of mineral salts. At this stage it stains pink with
H&E stain and is called Osteoid tissue
• As Osteoblasts form bone some of the Osteoblasts get
entrapped within the matrix they secrete and are called as
Osteocytes
• The more rapid the bone volume, the more osteocytes are
present per unit volume.

• Space in matrix occupied by an osteocyte is called
as Osteocytic lacunae
• Narrow extensions of lacunae form cannaliculi
that have radiating osteocytic processes

Osteoclasts
• Are Bone resorbing cells
• Large, multi nucleated but can be small and mono nuclear
• Circulating monocytes are the precursor cells
• In a light microscope they appear to occupy bays in bone or
hollowed out depressions called as Howship’s Lacunae
• Cytoplasm exhibits numerous mitochondria and lysosomes,
abundant golgi saccules, free ribosomes but little RER

• Ruffled or striated border is a part of plasma membrane
lying adjacent to bone that is being resorbed – and is raised
in characteristic folds
• Clear zone is the zone of specialized membrane that
separates the ruffled membrane border from the rest of the
plasma membrane
• It is devoid of organelles

Chemical Composition of Bone
67% Inorganic 33% Organic
(Hydroxyapatite)
28% Collagen10%
Non Collagenous
proteins
BONE
Calcium and Phosphate with
hydroxyl, carbonate, citrate and
other trace ions like Na, Mg &
Fl.
Mineral salts are in the form of
hydroxyapatite crystals that
make approx. 2/3 rd of the
total bone structure
Type I collagen
(90%)
• Osteocalcin
• Osteonectin
• Bone Morphogenic proteins (BMP)
• Phosphoproteins
• Proteoglycans
• Bone sialoprotein
• Osteopontin
• Growth factors & Serum proteins

MATRIX
ORGANIC MATRIX
• Collagen(28%)
- Type I (Rao et al ,1979)
- Type V (Bronckers et al,1986),
- Type III (Wang et al,1980) &
- Type XII collagen are also present

Non-collagenous Proteins – 10%
• GAG’s : chondroitin sulfate,
dermatan sulfate
keratan sulfate
heparin sulfate
• Lysyl oxidase & TRAMP
Categorised as GAGs and Glycoproteins

PROTEOGLYCANS
BIGLYCAN
DECORIN

• Glycoproteins:
osteonectin
thrombospondin
osteopontin
bone sialoprotein
osteocalcin

OSTEOCALCIN (bone gla protein )
• First non collageneous bone protein to be characterized.
• 15% of non collagenous protein
• Role in mineral maturation and bone resorption
• Acts as a chemo attractant to osteoclast precursors
(Mundy et al,1983)

BONE SIALOPROTEIN
• Bone sialoproteins I & II (Franzen et al,1985)
• Expressed in alveolar bone (Chen et al,1991)
• Glutamic acid is predominant in Bone sialoprotein
• Play role in . hydroxyapatite binding
. cell attachment
. activation of cell signaling pathways

OSTEOPONTIN
Osteopontin plays a role in bone resorption by inhibiting
hydroxyapatite crystal growth (Golberg et al,1995)
Mediates cell attachment
Aspartate is predominant

SPARC/OSTEONECTIN
• SPARC comprises 25% of the non-collagenous proteins.
• Calcium-binding glycoprotein,interacts with
extracellular matrix molecules (Sodek et al,1992)
• Associated with rapidly remodelling tissues

INORGANIC MATRIX
• Constitutes 2/3rd of the bone matrix
• Composed of calcium, phosphate ,hydroxyl, carbonate, citrate
(Glimcher,1990)
• Trace amounts of sodium , magnesium , fluorine
• Mineral salts in the form of hydroxyapatite crystals

Blood Supply
Arterial Supply:
Derived from inferior and superior alveolar arteries to
the mandible and maxilla
Venous drainage
Accompanies the arterial supply. Arterio-venous
anastomoses seen mostly in apical & inter-radicular
regions
Lymphatic drainage:
Lymphatic channels pass through alveolar bone to inf.
dental canal in mand. Or inf.orbital canal in maxilla
then to submaxillary lymph nodes.www.indiandentalacademy.com

Bone Remodeling
• Bone is constantly undergoing remodelling in
which resorption of bone is followed by a phase of
formation.
• In adults-Balance (Frost,1964)
• Involves sequential, coupled actions by osteoclasts
and osteoblasts
• It does not change the shape and size of bone
• It removes a portion of old bone & replaces it with
new bone

• It affects the height, contour and density of bone.
• Basic multicellular units (FROST,1991)
• Bone turn over (Charles et al,1987; Erickson et
al,1986)
• SITES
-adjacent to the PDL
-periosteum of the facial and lingual
plates
-endosteum of the marrow spaces

Regulation Of Bone Remodeling
• Complex process involving hormones and local factors,
which affects cells of both osteoblast and osteoclast cell
lineage and exert their influence on the:
-replication of undifferentiated cells
-recruitment of cells
-the differentiated functions of cells

Hormones that regulate bone remodelling
• Polypeptide hormones
• Parathyroid hormone
• Calcitonin
• Insulin
• Growth hormones
• 1,25 dihydroxyvitamin D3
• Glucocorticoids
• Sex steroids
• Thyroid hormones

Growth factors that regulate bone
remodelling
• Insulin like growth factor 1,2 (Lean et al,1996)
• Transforming growth factor-b 1,2 (Martin and
Ng,1994)
• Fibroblast growth factors
• Platelet derived growth factors
• Cytokines
• Tumor necrosing factor
• Colony stimulating factor

ROLE OF PARATHYROID HORMONE
• Bone contains 99% of body’s Ca ions & is a major source of
Ca release when Ca level in blood falls
Dec. in blood Ca is mediated by receptors on chief cells of
Parathyroid gland
Releases parathyroid hormone which stimulates osteoblasts
to release interleukin 1 & 6

• Stimulates monocytes to migrate in to bone area
• Leukemia inhibiting factor secreted by osteoblasts
coalesces with monocytes in to multinucleated osteoclasts
• Resorbs bone releasing Ca ions from blood
• Breakdown of collagen from organic matrix releases
osteogenic substrates
• Stimulates differentiation of osteoblasts which ultimately
deposit bone
• This interdependency of osteoblasts & osteoclasts in
remodeling is called coupling (Parfitt,1982)www.indiandentalacademy.com

Vitamin D and bone physiology
• Features observed in vit.D defeciency.
-Dec. absorption of Ca and Phosphorus.
-Blood Ca – Normal
-Blood phosphorus-Depressed
-Increased excretion of phosphorus
-Enlarged Parathyroid glands
-Prevention of calcification of osseous
structures.

Parathyroid hormone and
Vit D

BONE RESORPTION
Recruitmentand dissemination
ofosteoclastprogenitorcells
Suda et al 1996 cell cellinteraction
Proliferateand differentiateintoosteoclasts
Melkelet al 1992 proteolytic enzymes
Preparationofbonesurface
Lakkaorpeietal 1991 VITRONECTINFACTOR

Recognition of extra cellular
Bone matrix proteins
Osteoclast polarization [Clear zone, Ruffledborder ]
Martin and Ng 1994 Local factors
Fuller et al1991 Osteoblast
Osteoclast activation
Laotiala1994 H + ions
Hill et al 1993 Proteolyticenzymes
Bone resorption
Arrest of osteoclast activitywww.indiandentalacademy.com

FACTORS ASSOCIATED WITH BONE
RESORPTION
• Interleukin 1
• Interleukin 6
• Tumor necrosis factor and Lymphotoxin
• Gamma interferon
• Colony stimulating factor
• Prostaglandins
• Sex steroids

BONE FORMATION
Proliferationofmesenchymalcells
Osteoblast precursor cells
Chemotactic attraction to site
Differentiation to mature osteoblast
Formation of matrix
Mineralization www.indiandentalacademy.com

Factors associated with bone
formation
• Platelet derived growth factor
• Heparin derived growth factor
• Acidic and Basic fibroblast growth factors
• Insulin like growth factors
• Transforming growth factors
• Bone morphogenic proteins

Stage 1- Activation: Pre-Osteoclasts are
stimulated and differentiate under the
influence of cytokines and growth factors
into mature active Osteoclasts
Stage 2 - Resorption: Osteoclasts digest
mineral matrix (old bone)
Stage 3 - Reversal: End of resorption
Stage 4- Formation: Osteoblasts
synthesize new bone matrix
Stage 5- Quiescence: Osteoblasts become
resting bone lining cells on the newly
formed bone surface www.indiandentalacademy.com

BONE TURNOVER (Charles et al,1987;
Erickson et al,1986)
AMT. OF
RESORPTION
AMT. OF
FORMATION
BONE
ACTIVATION
FREQUENCY

• Rapidly growing children -30-100%
• Cortical bone-5% per year
• Trabecular bone-15% per year

BONE HEALING
• Healing of bone tissue includes both regeneration
and repair depending on the type of injury.
Healing of a wound has 4 phases:
a)Blood clotting
b)Wound cleansing
c)Tissue formation
d)Tissue modelling and remodelling

OSSEOUS TOPOGRAPHY

FENESTRATION AND DEHISCENCE

CONCLUSION
Together with the root cementum and the
periodontal ligament ,the alveolar bone
constitutes the attachment apparatus of the
teeth.
So , it is mandatory to know the basic biology
of this very important structure.

alveolar process

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