Transcript BONE DENSITY A key determinant in clinical implant success

BONE DENSITY
A key determinant
in clinical implant
success
ROHIT YADAV
J.R III
INTRODUCTION
External as well as internal architecture of bone is
important for clinical implant success .
External architecture is described as AVAILABLE
BONE VOLUME, and internal bone architecture
is described in terms of BONE QUALITY or BONE
DENSITY.

Bone density(bone mineral density) is a
medical term normally referring to the
amount of mineral matter per squre
centimeter of bones.
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Determining factor in treatment planning,
implant design, surgical approach, healing
time, and initial progressive bone loading.
The range of implant success documented should be
considered in terms of the location concerned, as
different regions of the jaws have different bone
conditions i.e. bone volume and density.
Higher implant success are well documented in denser
bony regions as compared to less denser locations.
But this doesn't mean that clinical implant
success cannot be achieved in regions
with less dense bones. Factors from initial
treatment planning to loading protocols
have to be addressed carefully in these
conditions.
ETIOLOGY OF VARIABLE BONE DENSITY
As per the WOLFF’S LAW ( 1892) “ Every change in
the form or function of bones or of their function
alone is followed by certain definite changes in their
internal architecture and equally definite alterations
in the external conformation, in accordance with
mathematical laws.
Bone is an organ that changes in relation to no. of
variable factors including hormones, vitamins, and
mechanical factors.
Macmilllan & Parfitt reported the variation
of trabeculae in the alveolar regionMandible - force absorption unit
Maxilla - force distribution unit
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Cortical and trabecular bone are modified constantly
by modelling and remodelling.
MODELING - has independent sites for formation and
resorption and results in change in shape or size of
bone.
REMODELING – is resorption and formation at the
same site that replaces existing bone and primarlily
affects the internal turnover of the bone, including next
to the endosteal implants.
Bone modeling and remodeling are primarily
controlled by mechanical strain.
Bone density evolves as a result of mechanical
deformation from strain .Bone was found to be most
dense around teeth and more dense around the
teeth at the crest compared to the regions around
apex.
 Decrease in bone density –
- occurs after tooth loss
- occurs after loss of
opposing occlusal contacts
- related to the time of edentulism, original density,
muscular attachments, flexure and torsion of
mandible, parafunction ,hormonal influences
and systemic conditions.
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Frost has modeled 4 zones for cortical bone related to
mechanical adaptation to strain before spontaneous
fracture.
ACUTE DISUSE WINDOW
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The bone density decreases and disuse atrophy
occurs, as modeling for new bone is inhibited and
remodeling is stimulated, resulting in net loss of the
bone.
The microstrain levels are 0 to 50 microstrains.
ADAPTED WINDOW ( Physiologic loading zone)
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Represents the equilibrium of modeling and
remodeling and bone conditions are maintained in this
level.
Steady state levels are maintained and regarded as
homeostatic window of health.
Histologically it is primarily lamellar or load bearing
bone type.
Microstrain levels are 50 to 1500 microstrains.
The ideal desired zone around the implants.
MILD OVERLOAD WINDOW
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The microstrain levels are 1500 to 3000 microstrains.
This zone corresponds to bone modeling stimulation
and remodeling inhibition leading to decrease in bone
density and strength.
Histologically this zone corresponds to woven or repair
bone type.

Overloaded implants may have this type of
bone around them, when the bone get
damaged due to slight overload conditions
and then tries to repair itself.

The woven bone is definitely weaker than
the more mature lamellar bone
PATHOLOGIC OVERLOAD WINDOW
The microstrain levels are >3000 microstrains.
 Spontaneous fracture occurs at 20,000 to
30,000 microstrains.that means the pathologic
overload zone begins at 20-40% of ultimate
fracture strength.
 The only type of bone present is woven in
nature
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Initial crestal bone loss evident after
implant placement shows this type of
overload zone.
Different zones just described are basically
of cortical bone and varies according to
bone density i.e all levels have lower
values for corresponding lower densities of
bones.
MISCH - BONE DENSITY CLASSIFICATION
BONE
DENSITY
DESCRIPTION
TACTILE
SENSES
COMMON
LOCATION
D1
Dense cortical
Oak or
Maple
Anterior mandible
D2
Porous cortical and coarse
trabecular
White pine
or spruce
wood
Ant – post
mandible.
Ant. Maxilla.
D3
Porous cortical (thin) and
fine trabecular.
Balsa wood
Ant.- post.
Maxilla.
Post. Mandible.
D4
Fine trabecular
Styrofrom
Posterior maxilla
ANATOMICAL LOACTION OF BONE DENSITY
TYPES IN PERCENTAGE
BONE
ANT. MAXILLA
POST MAXILLA
ANT.
MANDIBLE
POST MAND.
D1
0
0
6
3
D2
25
10
66
50
D3
65
50
25
46
D4
10
40
3
1
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Bone density D2 is most common density
observed in mandible as a whole, with anterior
mandible showing D2 bone 2/3rd of times.
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Single-tooth or two-tooth partially edentulous
span almost always have D2 bone.
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As far as D1 bone is concerned it is found
mainly in mandible ( anterior > posterior
regions).
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D3 bone is common in maxilla, more than
half of the patient have D3 bone in upper
arch, mainly in anterior maxilla.
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D4 bone is mostly found in posterior maxilla
especially in molar region.
RADIOGRAPHIC BONE DENSITY
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COMPUTERIZED TOMOGRAPHY
Bone density can be determined precisely by using
computerized tomograms (CT)
CT produces axial images of the patient's anatomy,
perpendicular to the long axis of the body. Each CT
axial image has 260,000 pixels, and each pixel has a
CT no. called HOUNSFIELD UNIT, related to the
density of the tissue .
Higher the no. of Hounsfield unit / CT no. , higher the
density.
Bone density is different in crestal region as compared
to apical region, and it is the crestal density ( i.e.
creatal 7 – 10 mm ) which is important to treatment
protocol.
COMPUTED TOMOGRAPHY DETERMINATION
OF BONE DENSITY
D1
> 1250 HOUNSFIED UNIT
D2
850 – 1250 HOUNSFIED UNIT
D3
350 – 850 HOUNSFIED UNIT
D4
150 – 350 HOUNSFIED UNIT
D5
< 150 HOUNSFIED UNIT
As far as panoramic radiographs or periapical
radiographs are concerned , they are not
reliable sources as lateral cortical plate obsure
the trabecular bone density.
 In addition to this little diffrences between
different bone types are difficult to assess , esp.
between D2 and D3.
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BONE STRENGTH AND DENSITY
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Bone density is
directly related to the
strength of the bone
before microfracture,
i.e ultimate fracture
strength.
D1 bone is found to
be 10 times stronger
to D4 bone.
D2 bone is 47 to 68%
greater than D3 bone.
Elastic modulus and density
Relate to the stiffness of material.
Elastic modulus of bone is more flaxible
than titanium.
The difference between the two materials
may create microstrain condition of
pathologic overload and cause implant
failure.
INFLUENCE OF BONE DENSITY ON LOAD
TRANSFER
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The mechanical distribution of stress occurs
primarily where bone is in direct contact to the
implant. Smaller the area of bone contact with the
implant , greater the overall stress.
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Initial bone density is thus important, not only for
initial immobilization of the implant during healing
but also for the wide distribution of stress to the
bone.
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Bone density influences the amount of contacting
bone with the implant surface, at both the 1st and 2nd
stages.
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For areas with lesser bone density like posterior
mandible greater implant surface area is required to
obtain a similar amount of bone implant contact ( as
compared to greater bone densities).
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For same amount of load applied ,as the bone density
decrease the amount of crestal stress increases , with
increase in of penetrence of stress towards the apical
end.
TREATMENT PLANNING FACTORS
REALTED TO VARIED BONE DENSITIES.
Bone density is implant treatment modifier in
many ways –
-Prosthetic factors
-Implant size
-Implant design
-Implant surface
condition
-Implant number
Prosthetic factors
As bone density decreases , the strength of the bone
decreases , and to reduce microfracture of the bone
the stress to the bone should be reduced.
Prosthesis design factors for less dense bones (D3/ D4)
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Shortened cantilever length.
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Narrower occlusal table.
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Preventing offset loading.
To minimize wearing time RP-4
restorations can be provided instead of
fixed restorations.
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RP-5 restorations help to transfer some
load to soft tissue sparing the implants.
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Night or occlusal / guards to prevent
parafunctional forces on implant system.
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Implant size
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Width of the implant also decrease the stress by
increasing the surface area, which may also reduce
the required implant length.
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For every .5mm increase in width , increase in surface
area is between 10- 15 %.
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Also greatest stresses are concentrated at the crestal
region of implant, width is more important than implant
length. E.g. D4 bone requires wider implants than D1
or D2 bone.
Implant length is also important for initial
fixation of the implants .
 However after complete healing, implant length
is not of much importance as much of the
stresses are concentrated at the crestal region.
 The minimum implant length are –
D1 --- 10mm
D2 --- 12mm
D3 --- 14mm
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For D4 bones, implants with greatest surface
area should be used.
E.g. classic V thread screw design has 30 %
more surface area than cylindrical implants.
 The no. as well as the depth of the threads
also influences the total surface area of the
implants.
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Greater the no. of threads, greater the functional
surface area at the time of immediate load
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Surface Coatings on the implants help to
increase surface area and thus total bone
contact.
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Hydroxypatite coating are strongly
recommended in D4 implants as they have
shown to increase short term survival rates.
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In long term total mechanical loads transfer to
the implants are more critical than surface
coatings.
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Finally as far as the loading protocols are
concerned, progressive loading is
recommended for softer bones which allows
bone to accommodate according to functional
loads..
Over time progressive loading changes the
amount and density of the bone- implant
contact.