Alveolar Bone's Relevance in Prosthodontics

ALVEOLARALVEOLAR
BONEBONE
ITS RELEVANCE INITS RELEVANCE IN
PROSTHODONTICSPROSTHODONTICS
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

TABLE OF CONTENTS
 Definition.
 Development.
 Composition and Structure.
 Residual Ridge resorption.
 Alveolar Bone from a Removable denture point
of view.
 Alveolar Bone from a Fixed Prosthodontic point
of view.
 Alveolar Bone from Implantology point of view.
 Pathological Fate of Alveolar Bone.
 References.

DEFINITION
That part of the mandible and the maxilla in
which the teeth are located is referred to as the
ALVEOLAR PROCESS.
The alveoli that support the teeth are found
within the alveolar process, and the bone lining the
alveoli is called the ALVEOLAR BONE PROPER or
BUNDLE BONE.

THE FACE OF A SIX-WEEK-OLD EMBRYO
The two mandibular processes (A) fuse in the midline to
form the tissues of the lower jaw. The mandibular and
maxillary (B) processes meet at the angles of the mouth,
thus defining its outline.
From the corners of the mouth, the
maxillary processes grow inwards
beneath the lateral nasal processes (C)
towards the medial nasal processes (D)
of the upper lip. Between the merging
maxillary and the lateral nasal
processes lie the naso-optic furrows (E).www.indiandentalacademy.com

THE APPEARANCE OF THE DEVELOPING
JAWS OF A HUMAN FOETUS
(14 weeks intra-uterine)
A:Body of mandible
B:Ramus of the
mandible
C:Secondary condylar
cartilage
D:Secondary coronoid
cartilage
E:Frontal bone
F:Parietal bone
G:Occipital bone
H:Squamous portion
of temporal bone
I:Maxilla. www.indiandentalacademy.com

CONTRIBUTIONS TO THE ADULT FACE
FROM THE EMBRYONIC FACIAL
PROCESSES.
A: Maxillary process.
B: Mandibular process.
C: Medial nasal process.
D: Lateral nasal process.

POST NATAL DEVELOPMENT OF THEPOST NATAL DEVELOPMENT OF THE
MANDIBLEMANDIBLE
Mandible at birth (A), at six years (B), and in
an adult (C). The ratio of body to ramus is
greater at birth than in the adult, indicating a
proportional increase with time in the
development of the ramus. At birth, there is
no distinct chin and two halves of the
mandible are separated at the mandibular
symphysis. Ossification of symphysis is
complete during the second year and the two
halves of the mandible
uniting to form a single
bone. The chin becomes
most prominent after
puberty. www.indiandentalacademy.com

CELLS OF BONE
Osteoprogenitor cells
Osteoblast cells.
Osteocytes
Osteoclast cells.
COMPOSITION OF BONE

ORGANIC PART – 33% - 35%
 Collagen – 88% - 90% (Type – I)
 Non collagen – 10% - 11%.
 Glycoproteins – 6% - 9% (Mono, Di, Poly
and Oligosaccharides).
 Proteoglycanes – 0.8% (sulfated and Non
sulfated)
 Sialoproteins – 0.35%
 Lipids – 0.4%

INORGANIC PART – 65% - 67%
 Calcium & Phosphates – 95%
(Hydroxyapatite Crystals – Ca10(Po4)6 (OH)2)
 Magnesium
 Trace elements – Nickel, Iron, Fluoride,
Cadmium, Magnesium, Zinc and
Molybdenum.

Osteoblasts are uninucleated cells that synthesize both
collagenous and noncollagenous bone protein. They are
responsible for mineralization and are derived from a
multipotent mesenchymal cell. They constitute a cellular
layer over the forming bone surface. When bone is no longer
forming, the surface osteoblasts become inactive and are
termed lining cells(bone maintenance).
Osteoblasts exhibit high levels of
alkaline phosphate on the outer
surface of their plasma membranes.
OSTEOBLASTSOSTEOBLASTS

Other enzymes that participate in there activity are
ATPase and pyrophosphates. Osteoblasts secrete, in
addition to type I and type V collagen and small amounts
of several noncollagenous proteins, a variety of cytokines.
Osteoblasts under the stimulation of interleukin 6
also produce their own hydrolytic enzymes that aid in
destroying or modifying the unmineralized matrix. Thus
freeing the osteoblast from its own secreted matrix.
The hormones most important in
bone metabolism are parathyroid
hormone. 1,25 dihydroxyvitamin
D, calcitonin, estrogen, and the
glucocorticoids,which have a
influence on osteoblasts.www.indiandentalacademy.com

As osteoblasts secrete bone matrix, some of them
become entrapped in lacunae and are then called osteocytes.
The number of osteoblasts that become osteocytes varies
depending on the rapidity of bone formation. The more
rapid the formation, a more osteocytes are present per unit
volume.
OSTEOCYTE
As a general rule,
embryonic bone and repair bone
have more osteocytes than does
lamellar bone. www.indiandentalacademy.com

Osteocytes gradually lose most of their matrix
synthesizing machinery and become reduced in size.
The space in the matrix occupied by an osteocyte is
called the osteocytic lacuna. Narrow extensions of these
or canaliculi, that form radiating osteocytic processes
maintain contact with adjacent osteocytes and
osteoblasts the endosteum, periosteum, and Haversian
canals.
Failure of any part of this inter connecting system
result in hyper mineralization (sclerosis) and death of the
bone.

OSTEOCLAST
Compared to all other bone cells and their
precursors, the multinucleated osteoclast is a much larger
cell. Because of their size, it can be identified under the
light microscopy, generally seen in a cluster rather than
singly. The osteoclast is characterized by acid phosphatase
within its cytoplasmic vesicles and vacuoles, which
distinguishes it from other giant cells and macrophages.
Typically osteoclasts are found
against the bone surface occupying
shallow, hollowed out depressions,
called Howship’s lacunae.www.indiandentalacademy.com

Isolates a micro environment between them and the bone
surface. The cell organelles consist of many nuclei, each
surrounded by multiple Golgi complexes, an array of
mitochondria and free polysomes, a rough endoplasmic
reticulum, many coated transport vesicles, and numerous
vacuolar structures. Osteoclast are also rich in lysosomal
enzymes.
Adjacent to the tissue
surface, their cell membrane is
thrown into a myriad of deep
folds that form a brush border.
This clear or “sealing” zone
attached the cells to the
mineralized surface.

TThus the sequence of resorptive events is considered to
be
11. Attachment of osteoclasts to the mineralized surface of
bone.
C2. Creation of a sealed acidic environment through action
of the proton pump, which demineralizes bone and
exposes the organic matrix.
D3. Degradation of this exposed organic matrix to its
constituent amino acids by the action of released
enzymes.
4. Uptake of mineral ions and
amino acids by the cell.

CLASSIFICATION OF BONE
Bones are organs because they are
functionally related groups of tissues and each
bone has a unique form and function.
Macroscopically, osseous structure is classified
according to density as Compact or Trabecular
bone. But practically, bone mass is actually a
combination of Fine Trabeculae, Coarse
Trabeculae, Porous Compacta and Dense
Compacta. Microscopically bones are
composed of Woven bone, Lamellar bone,
Bundle bone and Composite bone.

Woven bone
• Highly cellular.
• Formed rapidly (30-50 µm/ day or more) in
response to growth or injury.
• Low mineral content.
• Random fiber orientation and minimal
strength.
• Stabilize unloaded Endosseous implants
during initial healing.

Lamellar bone
• Principle load bearing tissue of adult
skeleton.
• Predominant component of mature cortical
and trabecular bone.
• Formed relatively slowly (<1 µm/ day).
• Densely mineralized and highly organized
matrix.

Bundle bone
• Characteristic of ligament and tendon
attachments along bone-forming
surfaces.
• Sharpey’s fibers from adjacent
connective tissue insert directly into
bone.
• Bundle bone is formed adjacent to the
periodontal ligament of natural teeth.

Composite bone
• High quality lamellar bone deposited
on a woven bone matrix.
• Got adequate strength for load
bearing.
• Important in achieving stabilization of
an implant during the rigid integration
process.

Alveolar Bone forms the bony sockets of the jaw
bones in which the roots of the natural teeth are
suspended by the attachment of the periodontal
ligament fibers (“Gomphosis” - Greek “Bolting
together). Some alveolar bone is formed during tooth
development, but the majority of alveolar bonethe majority of alveolar bone
formation occurs during tooth eruption.formation occurs during tooth eruption.

The presence of alveolar bone in the jaw
bones is totally dependent on the roots of the
natural teeth; without the teeth the alveolar bone
need not exist.

ERUPTION OF TEETH AND
ALVEOLAR BONE
The teeth move within the jaws throughout the life
and these movements include:
1. Pre-eruptive Movement
2. Eruptive (“Break Out”) Movement
a) Pre-functional Eruption
b) Functional Eruption
# Active eruption
# Passive eruption

THEORIES OF ERUPTION
1. Bone remodeling.
2. Growth of the root.
3. Hydrostatic pressure.
4. Traction via the periodontal ligament.

There is no sharp line or suture which
differentiates alveolar bone from the
surrounding basal bone of either the mandible
or the maxilla. There is no morphologic or
biochemical distinction between the two types
of bone.

Several morphologic
features can be distinguished
within the alveolar bone. The
cortex of the basal bone of
either mandible or maxilla
continues around the alveolar
process as either the outer
(OCP) or the inner (ICP)
cortical plate. The alveolar
bone of these outer and inner
plates is composed of hard,
lamellar (arranged in thin
plates) bone.
A - Alveolus
B B - Basal Bonewww.indiandentalacademy.com

Numerous blood vessels and
nerve fibers pass through the
cribriform plate, providing unlimited
access between the alveolar bone
and tissues of the periodontal
ligament.
The actual tooth socket, is composed of a
slightly different type of hard bone called the
“cribriform (sieve like) plate”.

The cribriform plate itself is made up of two
types of bony layers:
The Hard, lamellar type.
Bundle Bone oriented toward the
periodontal ligament and thick enough to
anchor the periodontal fibers within it.

The periodontal fibers
visible in the bundle bone
are termed “Sharpey’s
Fibers”. The fibers of the
periodontal ligament
function like a miniature
shock absorber system
that acts to dissipate the
forces of occlusion
through the trabecular
pattern of the alveolar
bone.www.indiandentalacademy.com

The cribriform plate (alveolar bone proper)
forms the sockets, or alveoli, around each single-
or multiple- rooted tooth and follows the
configuration of the root(s) with precision, leaving
only a small space of less than 0.2 mm between
the root and bone occupied by the suspensory
periodontal ligament. Between the alveoli of
adjacent teeth, the alveolar bone forms an
interdental septum composed of adjacent cribriform
plates and at times interposed spongy bone. The
roots of multirooted teeth are separated from one
another by interradicular septum, and are
composed of adjacent cribriform plates and spongy
bone between them.www.indiandentalacademy.com

When viewed with a dental radiograph (IOPA),
the cribriform plate surrounding each tooth root
appears as a dense white line called the “Lamina
dura”. We might assume that the alveolar bone
surrounding the tooth is denser or more highly
calcified than the other bone.
But this is not clearly the
case and is a radiographic
artifact based on the
geometry of the cribriform
plate.

Between the cortical and cribriform plates of the
alveolar bone, another type of bone termed “Spongy
Bone” may be present. This spongy bone contains
small amounts of bony trabeculae (supporting
beams) surrounded by bone marrow that is of either
the RED (forming blood - in young adults) or
YELLOW (fatty - in older individuals). The response
of the alveolar bone to occlusal forces transmitted by
the tension of the periodontal fiber bundles is to form
a trabecular pattern that is both parallel and
perpendicular to the functional forces applied.

On the labial surfaces
of anterior teeth, the
outer cortical plate of
alveolar bone is very
thin and fused to the
cribriform plate, and
spongy bone is notably
absent.

Alveolar bone is a plastic tissue, able to respond
and adapt to both functional occlusal forces and
changes in tooth position. E.g. “mesial drift”, which
is a nonpathologic, slow mesial tooth migration due
to enamel wear between the contact areas of some
or all adjacent natural teeth. For this changes to
occur in each alveoli of the teeth, both Osteoblasts
and Osteoclasts must be active.
Throughout the life of the individual, age-related
tooth wear, changes in occlusal loading and
pathologic changes in the teeth and supporting
tissues keep the trabecular pattern of alveolar bone
in a constant state of remodeling activity.

CLASSIFICATION OF RESIDUAL RIDGE
RESORPTION
According to Branemark et al in 1985, ridges
were classified on the basis of bone quantitybone quantity and
bone qualitybone quality by radiographic means
BONE QUANTITYBONE QUANTITY
Class A : Most of the alveolar bone is present.
Class B : Moderate residual ridge resorption occurs.
Class C : Advanced residual ridge resorption occurs.
Class D:Moderate resorption of the basal bone is
present.
Class E : Extreme resorption of the basal bone.

BONE QUALITYBONE QUALITY
Class 1: Almost the entire jaw is composed of
homogenous compact bone.
Class 2: A thick layer of compact bone surrounds a
core of dense trabecular bone.
Class 3: A thin layer of cortical bone surrounds a core
of dense trabecular bone.
Class 4: A thin layer of cortical bone surrounds a core
of low density trabecular bone.

ATWOODS CLASSIFICATION
Order I: pre-extraction.
Order II: post extraction.
Order III: high, well rounded.
Order IV: knife edge.
Order V: low, well rounded.
Order VI: depressed.

CLASSIFICATION ACCORDING TO THE
MANDIBULAR CANAL RESORPTION
RADIOGRAPHICALLY
Grade 0: the crest of the residual ridge above both
the mental foramen and the mandibular canal.
Grade I: the crest of residual ridge above both the
mandibular canal and the mental foramen at the top
of the residual ridge with or without a partially
resorbed ridge.
Grade II: the superior border of the mandibular canal
at the top of the residual ridge and the mental
foramen with or without a partially resorbed border.

MERCIER’S CLASSIFICATION
Group I: High Crestal muscles and non resorbed ridge.
Group II: Painful atrophic ridge.
Group III: Absence of residual ridge.

ZELTSER’S CLASSIFICAIONZELTSER’S CLASSIFICAION
Group 1: high muscle attachment and minimal
residual ridge resorption
Group 2: severe residual ridge resorption with pain.
Group 3: absence of residual ridge.
Group 4: severe resorption of basal bone.

MISCH’S CLASSIFICATIONMISCH’S CLASSIFICATION
(based on bone density)(based on bone density)
D1: dense cortical bone
D2: thick dense to porous cortical bone on the crest
and coarse trabecular bone within.
D3: thin porous cortical bone on crest and fine
trabecular bone within.
D4: fine trabecular bone
D5: immature, non-mineralized bone.

CLASSIFICATION ACCORDING TO THECLASSIFICATION ACCORDING TO THE
AMERICAN COLLEGE OFAMERICAN COLLEGE OF
PROSTHODONTISTS:PROSTHODONTISTS:
Based on bone height (mandible only)Based on bone height (mandible only)
Type I: Residual bone height of 21mm or greater
measured at the least vertical height of the mandible.
Type II: Residual bone height of 16-20mm measured
at the least vertical height of the mandible.
Type III: Residual alveolar bone height of 11-15mm
measured at the least vertical height of the mandible.
Type IV: Residual alveolar bone height of 10mm or
less measured at the least vertical height of the
mandible. www.indiandentalacademy.com

ALVEOLAR BONE
(FROM COMPLETE DENTURE POINT OF VIEW)

EDENTULOUS INTRAORALEDENTULOUS INTRAORAL
BONY CHANGESBONY CHANGES
The loss of teeth means not only the loss of
the clinical crown but also the supporting
tissues, the periodontal ligament and alveolar
bone. When the alveolar bone is lost, the
resultant residual ridge is progressively resorbed
throughout the life of the individual (Atwood,
1971).

It is critical to successful dental practice that
the dentist understands the anatomy of the mouth
in both the dentulous and edentulous states and
the results of that transition in the individual.
Edentulous bony anatomy include:
Profound bone loss

Slow, progressive thinning of the jaw bones

Remodeling changes occur in the mandible that
account for the typical edentulous facial anatomy.
 The overall length of the mandible does not
decrease but may in fact increase as new bone is
added to the mental protuberance, thus
accentuating the chin point.

 There is an anterior displacement of the
mandible (protrusive position) because of
residual ridge reduction, mandibular rotation
(Change in the angulation of the body relative to
the mandibular ramus), and deposition of bone
in the mental region.
 Reduction in the residual ridges occurs in an
inferior direction in the molar and premolar
areas, but in both an inferior and lingual
direction in the incisor region.
 There is generalized thinning of the anterior and
posterior aspects of the mandibular ramus.

ALVEOLAR RIDGES
1. Developmental Structure: The individual
variation in bone size and its degree of
calcification.
2. The size of the natural teeth: The teeth like the
bone show wide variation in size. Large teeth are
usually supported by bulky ridges, small teeth by
narrow ones.
The alveolar ridges vary greatly in size and
shape and their ultimate form is dependent on the
following factors:

3. The amount of bone lost prior to the extraction
of the teeth: Periodontal disease is a chronic
inflammation of the supporting structures of the
teeth and results in the destruction of the alveolar
process. If the natural teeth are retained until
gross alveolar loss has occurred the resultant
alveolar ridges will be narrow and shallow.
4. The amount of alveolar process removed
during the extraction of the teeth: During
extraction with forceps the buccal alveolar plate is
sometimes fractured and removed with the tooth.
The commonest sites for this occurrence are the
upper and lower canine and first molar regions.
When teeth are removed by surgical dissection
some alveolar is always destroyed.

5. The rate and degree of resorption: During the
first six weeks after the extraction of the teeth the
rate of resorption is rapid. During the second six
weeks it is fast but begins to slow down. At the
end of three months, on average, the immediate
post-extraction resorption is complete and
thereafter it continues throughout life at an ever-
decreasing pace.
6. The effect of previous dentures: ill-fitting
dentures, or dentures occluding with isolated
groups of natural teeth, may cause rapid
resorption of the alveolar process in the areas
where they cause excessive load or lateral stress.

MAXILLARY DENTURE-BEARING AREA
Well-developed but not abnormally thick ridges
and a palate with a moderate vault.
This is a favorable formation because:
 The center of the palate presents an almost flat
horizontal area and this will aid adhesion.
 The roomy sulcus allows for the development of
a good peripheral seal.
 The well-developed ridges resist lateral and
antero-posterior movement of the denture.www.indiandentalacademy.com

High V-shaped palate usually associated
with thick bulky ridges.
This may be an unfavorableunfavorable formation because:
 The forces of adhesion and cohesion are not at right
angles to the surface when counteracting the normal
displacing forces of gravity and so peripheral seal is
essential.

Flat palate with small ridges and shallow
sulci.
This may be an unfavorable formation because:
 The ill-developed or resorbed ridges do not resist
lateral and antero-posterior movement of the
denture.
 The sulci being shallow do not form a good
peripheral seal, unless the width of the denture
periphery is adequate.www.indiandentalacademy.com

Ridges exhibiting undercut areas.
These are unfavorable because:
 frequently the flanges of the denture need to be
trimmed in order to be able to insert it and this
may reduce the effectiveness of the peripheral
seal.

MANDIBULAR DENTURE-BEARING AREA
Broad and well developed ridges.
This is a favorable formation because:
 It provides a large area on which to rest the denture
and prevents lateral and anteroposterior
movement.
 The surface presented for adhesion is as large as it
can ever be in a lower jaw.
 The lingual, labial and buccal sulci are satisfactory
for developing a close peripheral seal.www.indiandentalacademy.com

Ridges exhibiting undercut areas.
 If the denture is not eased away from the undercuts
pain and soreness will result and if it is eased, food
will lodge under the denture.
 The easing of the periphery will reduce the surface
area of mucosal contact and will affect the
peripheral seal adversely.www.indiandentalacademy.com

Well developed but narrow or knife like ridges
 The pressure of the denture during clenching and
mastication on the sharp ridge will cause pain.
 Adhesive and cohesive forces are negligible

Flat and atrophic ridges.
 No resistance is offered to anteroposterior or
lateral movements.
 Frequently found to have resorbed to the level of
attachments of the mylohyoid, genioglossus and
buccinator muscles and if the denture base is
made sufficiently narrow not to encroach on
these structures, its area is too small for the
denture to function correctly.
 When the area is increased to encroach on the
muscles they may move the dentures when they
contract. www.indiandentalacademy.com

DIETARY GUIDELINES FOR PATIENTS AT
RISK OF LOSING BONE
Maintain a high daily calcium intake
Obtain four servings of low fat dairy foods or obtain
equivalent amounts of calcium from green gram,
canned fish.
Take calcium supplements if dietary intake is low

Prevent negative calcium balance
Limit daily alcohol (2 glasses) and caffeine (2
cups) intake
Consume about 6 ounces of protein from
meat, poultry and fish
Use small amounts of processed foods high in
sodium

Obtain 4000 I.U of Vitamin D daily
•Spend 15 minutes in the sun 3 times a week
•Choose a multivitamin or calcium supplement
that contains 4000 I.U of Vitamin D.
Discuss calcium or drug interactions that interface
with calcium bioavailability with the physician

ALVEOLAR BONE
(FROM FIXED PARTIAL DENTURE POINT OF VIEW)

The edentulous areas where a fixed prosthesis is
to be provided may be overlooked during the
treatment planning phase. Unfortunately, any
deficiency or potential problem that may arise
during the fabrication of a pontic is often identified
only after the teeth have been prepared or even
when the master cast is ready to be sent to the
laboratory.
RESIDUAL RIDGE CONTOUR

Proper preparation includes a careful
analysis of the critical dimensions of the
edentulous areas:
Mesiodistal width.Mesiodistal width.
Buccolingual diameter.Buccolingual diameter.
Occlusocervical distance.Occlusocervical distance.
Location of the residual ridge.Location of the residual ridge.

The contour of the edentulous ridge should be
carefully evaluated during the treatment
planning phase. An ideally shaped ridge has a
smooth, regular surface of attached gingiva,
which facilitates maintenance of a plaque-free
environment. Its height and width should allow
placement of a pontic that appears to emerge
from the ridge and mimics the appearance of the
neighboring teeth. Facially, it must be free of
frenum attachment and of adequate facial height
to sustain the appearance of interdental papillae.

SiebertSiebert has classified residual ridge
deformities into three categories:
1. Class I defects- faciolingual loss of tissue
width with normal ridge height.
2. Class II defects- loss of ridge height with
normal ridge width.
3. Class III defects- a combination of loss in
both dimensions.

Loss of residual ridge contour may lead to
unesthetic open gingival embrasures (“Black
triangles”), food impaction, and percolation of
saliva during speech.

Surgical Modification
Although residual ridge width may be
augmented with hard tissue grafts, this is
usually not indicated unless the
edentulous site is to receive an implant.
1. Roll technique uses soft tissue from the
lingual side of the edentulous site. The
epithelium is removed, and the tissue is
thinned and rolled back, thereby
thickening the facial aspect of the
residual ridge.

2. Pouches may be prepared in the facial
aspect of the residual ridge, into which
subepithelial or submucosal grafts may
be inserted.

3. Interpositional graft is a wedge-shaped
connective tissue graft which is inserted
into a pouch preparation on the facial
aspect of the residual ridge.

ALVEOLAR BONE
FROM IMPLANTOLOGY POINT OF VIEW

AVAILABLE BONE
Available bone describes the amount of bone in the
edentulous area considered for implantation and is
measured in: Height.
Width.
Length
Angulation.
Crown-Implant body ratio.

AVAILABLE BONE HEIGHT
The height of available bone is measured
from the crest of the edentulous ridge to the
opposing landmark, such as maxillary sinus,
mandibular canal, maxillary nares, inferior
border of the mandible, maxillary canine
eminence region etc.

The minimum height of the available bone
for endosteal implants is in part related to the
density of the bone. The more dense bone may
accommodate a shorter implant. The minimum
bone height for a predictable long-term endosteal
implant survival is 10mm.

AVAILABLE BONE WIDTH
Width is measured between the facial and
lingual plates at the crest of the potential implant site.
The crest is supported by a wider base. The root
form implants of 4.0 mm crestal diameter usually
require more than 5.0 mm of bone width to ensure
sufficient bone thickness and blood supply around
the implant for predictable survival. These
dimensions provide more than 0.5 mm bone on each
side of the implant at the crest.

AVAILABLE BONE LENGTH
The mesio-distal length of available bone in
an edentulous area is often limited by adjacent
teeth or implants. The root form implants of 4.0
mm crestal diameter usually require a minimum
mesio-distal length of 7 mm.

AVAILABLE BONE ANGULATION
Ideally the bone angulation should be such
that the long axis of the implant can be placed
parallel to the long axis of the Prosthodontic
restoration. In edentulous areas with wide ridge,
and wider root form implants a modification upto
30 degrees can be achieved.

CROWN-IMPLANT BODY RATIO
The crown height is measured from the
occlusal or incisal plane to the crest of the ridge
and the endosteal implant height from the crest
of the ridge to its apex. The greater the crown
height, the greater the lever arm with any lateral
force.

DIVISIONSDIVISIONS
OFOF
AVAILABLE BONEAVAILABLE BONE
 Division A (Abundant Bone)
 Division B (Barely Sufficient Bone)
 Division C (Compromised Bone)
 Division D (Deficient Bone)

Division A
(Abundant Bone)
# >10-13mm height
# >5mm width
# >7mm mesio-distal length
# <30o
angulation between occlusal
plane and implant body
# Crown/Implant ratio <1

Division B
(Barely Sufficient Bone)
# 2.5-5mm width
# >10-13mm height
# >12mm mesio-distal length
# <20o
angulation between implant
body and occlusal plane.
# Crown/Implant ratio <1

Division C
(Compromised Bone)
# Unfavorable in: Width (C-w)
Height (C-h)
# >30o
Angulation between occlusal plane
and implant body.
# Crown/Implant ratio >1

Division D
(Deficient Bone)
# Severe atrophy
# Basal bone loss
# Flat maxilla
# Pencil thin mandible.

VARIABLE BONE DENSITY- WHY?
Cortical and trabecular bone are constantly modified
by either ModelingModeling or Remodeling.Remodeling.
In bonebone modelingmodeling there is independent sites of
formation and resorption and results in the change of
the shape or size of bone.
In bonebone remodelingremodeling the resorption and formation
are at the same site that replaces previously existing
bone and primarily affects the internal turnover of
bone. www.indiandentalacademy.com

These adaptive phenomena of modeling and
remodeling of bone have been associated with the
alteration of the mechanical stress environmentalteration of the mechanical stress environment
within the host bone.within the host bone.
MacMillanMacMillan and ParfittParfitt noted that
Bone is most dense around the teeth (Cribriform
Plate).
Density of bone around the crest region is more
compared to the regions around the apices.
Generalized trabecular bone loss occurs in
regions around a tooth from a decrease in
mechanical stress.www.indiandentalacademy.com

FrostFrost reported a model of four zones for compact
bone as it is related to mechanical adaptation to
stress
Pathologic overload zone
Mild overload zone
Adapted window zone
Acute disuse window zone

ACUTE DISUSE WINDOW ZONE
The bone loses mineral density, and disuse
atrophy occurs because modeling for new
bone is inhibited and remodeling is
stimulated, with a gradual net loss of bone.
0 - 50 Microstrain
This phenomenon is also seen in
microgravity environments in outer space.

ADAPTED WINDOW ZONE
Represents an equilibrium of modeling &
remodeling, and bone conditions are
maintained at this level.
Bone remains in a steady state.
Histologically – Lamellar or load-bearing
bone.
50-1500 microstrain ideally desired around
and endosteal implant.

MILD OVERLOAD ZONE
Bone modeling stimulation and remodeling
inhibition.
Bone density and strength may eventually
decrease.
Histologically – Woven or repair bone.
Low density bone resulting from overloaded
implant
1500-3000 microstrainwww.indiandentalacademy.com

PATHOLOGIC OVERLOAD ZONE
The bone resorb and only woven bone
formation is seen because of sustained
repair.
Microstrain greater than 3000.
Cortical fracture takes place at 10000-20000
microstrain
 The crestal bone loss often evidenced
during early implant loading is a result of the
bone in the pathologic overload zone

MISCH BONE DENSITY
CLASSIFICATION
D1 Dense cortical bone
D2 Thick dense to porous cortical bone on
crest and coarse trabecular bone within
D3 Thin porous cortical bone on crest and
fine trabecular bone within
D4 Fine trabecular bone
D5 Immature, nonmineralized bone

ANATOMIC LOCATION OF BONE
DENSITY TYPES (% OCCURRENCE)
BONE ANT:
MAXILLA
POST:
MAXILLA
ANT:
MANDIBLE
POST:
MANDIBLE
D1 0 0 6 3
D2 25 10 66 50
D3 65 50 25 46
D4 10 40 3 1

RADIOGRAPHIC BONE DENSITY
CT scan can determine bone density
precisely.
Each CT image has pixels and each pixel
has a CT number (Housefield unit). Higher
the Housefield unit, denser the tissue.
D1 >1250 Housefield units
D2 850-1250 Housefield units
D5 < 150 Housefield unitswww.indiandentalacademy.com

FATE OF ALVEOLAR
BONE
PATHOLOGICAL

HISTIOCYTOSIS X
Bone lesion appears as sharply “Punched-
out” lytic defect, often with irregular
margins.
The posterior mandible is the most
common site.
Mild dull pain is commonly present.
Alveolar bone involvement leads to severe
horizontal bone loss.

HISTIOCYTOSIS X

CHERUBISM
 Extensive maxillary involvement
may stretch the skin to expose
the sclera.
 Marked enlargement of maxilla
and multiple missing teeth

FIBROUS DYSPLASIA
Painless enlargement of the affected
bone.

OSTEOSARCOMA
Swelling, pain, loosening
of teeth, paresthesia are
common complaints

CHONDROSARCOMA

OSTEITIS DEFORMANS
(Paget’s Disease)
 Progressive, symmetric
maxillary enlargement
that may reach massive
proportions

CLEIDOCRANIAL DYSPLASIA
 Skull and clavicles are chief sites of disorder.
 Large head with bulging of frontal bone.
 Unusual mobility of shoulders.
 Narrow high arched palate, prolonged retention
of deciduous teeth and delay or failure of
eruption of permanent teeth.

CLEIDOCRANIAL DYSPLASIA

HYPERPARATHYROIDISM
Increased production of parathyroid
hormone results in a generalized disorder
of calcium, phosphate and bone
metabolism

OSTEOPETROSIS
Marked increase in bone density
Bone marrow is replaced by dense bone

OSTEOPOROSIS
Osteoporosis is a systemic disease in the elderly.
Osteoporosis shows a decrease in the skeletal mass
without alteration in the chemical composition of
bone. Loss of the spongy spicules of bone that
support the weight bearing parts of the skeleton can
be seen in radiographs of regions of the skeleton that
bear heavy loads, such as the vertebral column,
epiphysis of long bones, the mandible and the
fingers.
In edentulous patients, reduction of the residual ridge
is one of the most important factors affecting denture
support, retention, stability, and masticatory function.www.indiandentalacademy.com

SEVERITY OF OSTEOPOROSIS
JIKEI’S CLASSIFICATION
Class I – Horizontal trabeculae are decreased and
vertical trabeculae are prominent.
Class II – Decreasing of horizontal trabeculae is
more prominent and vertical trabeculae are sparse.
Class III – Horizontal trabeculae almost disappear
and vertical trabeculae are found to be indistinct.

REFERENCES
1. Human Oral Embryology and Histology.
I. A. Mjor & O. Fejerskov.
2. A Colour Atlas and Textbook Of Oral Anatomy.
B.K.B. Berkovitz.
3. An Introduction to Dental Anatomy & Esthetics.
Robert P. Renner.
4. Sicher & Dubrul’s Oral Anatomy (8th
Edition)
E. Lloyd Dubrul.
5. Dental Histology & Embryology.
Dr. A. N. Radhakrishnan.

6. Essentials of Complete Denture Prosthodontics (2nd
edition)
Sheldon Winkler.
7. Contemporary Implant Dentistry (2nd
edition)
Carl E. Misch.
8. Clinical Removable Partial Prosthodontics (2nd
edition)
Kenneth L. Stewart
9. Boucher’s Prosthodontic Treatment for Edentulous
Patients (11th
edition)
George A. Zarb
10. Fundamentals of Fixed Prosthodontics (3rd
edition)
Herbert T. Shillingburg

Alveolar Bone's Relevance in Prosthodontics

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