Indian Dental Academy: will be one of the most relevant and exciting
training center with best faculty and flexible training programs
for dental professionals who wish to advance in their dental
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implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic
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11. Deformation and strain-
Load application may induce deformation of
both implant and surrounding tissues.
Biological tissue interprets deformation and
it’s manifestations and responds with
remodeling.
Stress and strain relationship-The closer the
modulus of elasticity of the implant to the
bone, less the likelihood of relative motion at
the tissue to implant interface.
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12. It is more important to decrease stress in
softer bone because of greater elastic
difference and lower ultimate strength.
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13. IMPACT LOAD
When two bodies collide in a very small
interval of time, relatively large reaction forces
develop.
Such collisions are called impacts.
Example : occlusal loads.
Cause deformation of implants and
surrounding tissue.
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14. Impact loads can be decreased by-
- Using acrylic teeth – Skalak (JPD 1983 : 49;
843-49).
- Weiss advocated fibrous tissue to implant
interface for shock absorption.
- Use of intramobile element to lower the
stiffness than rest of the implant.
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15. Misch advocates acrylic provisional with
progressive occlusal loading to improve
Bone-Implant interface before final
restoration.
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16. FORCE DELIVARY AND FAILURE MECHANISM
Moment loads
Moment of force about a point tends to
produce rotation or bending about that point.
M = Force x perpendicular distance , from
the point of interest.
Also called torque or torsional load.
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18. Clinical moment arms and crestal bone
loss
Six moments may develop about the 3
clinical coordinate axes .
Such loads induce microrotation and stress
concentration at the crest of alveolar ridge –
implant – bone interface and leads to crestal
bone loss
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19. Three clinical moment arms exist in implant
dentistry, minimization of each is necessary to
prevent failure.
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21. Occlusal height moment arm
Acts as a moment arm for a force components
directed along faciolingual and mesiodistal axis
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22. Cantilever length moment arm
Large moments from vertical axis force
component is seen in prosthetic
environments designed with cantilevered
extensions or offset loads from rigid implants
Distal cantilever should not extend 2.5 x the
A-P distance under ideal conditions
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24. Occlusal width moment arm
Wide occlusal tables increase moment
arm for any offset occlusal loads
Faciolingual rotation can be reduced by
narrow occlusal tables and adjusting
occlusion to provide more centric contact
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25. Scientific rationale for dental implant design
Biomechanical load management Is
dependent on two factors:
- Character of the applied force
- Functional surface area over which the
load is dissipated
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26. Character of forces applied to dental
implants
Forces applied to dental implants may be
characterized in terms of five distinct factors,
namely:
- Magnitude
- Duration
- Type
- Direction
- Magnification
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27. Force magnitude
Physiologic constraints on design:
- After sustained period of edentulism……
- Careful treatment planning & appropriate
implant design selection.
Influence on biomaterial selection:
- Many biocompatible materials unable to
sustain the magnitude of parafunctional loads
imposed on dental implant.
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28. Clinical implant design failures related to
choice of biomaterial and force magnitude.
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29. Force duration
Physiologic constraints on design-
-Ideally the forces duration while eating and
swallowing is ≈ 30 min ∕ day.
-Bruxers and other parafunctional habit pt.
Influence on implant body design-
- Materials that are subjected to repetitive
loads are at greater risk of fatigue failure.
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31. How the implant and abutment resists,
fracture from bending forces -----
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32. Force type
Physiological constraints on design :
- Bone is strongest in compressive > tensile >
shear
- Endosteal implants load bone - implant
interface in pure shear, unless surface
features are incorporated in design to
transform shear loads to more resistant force
types
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33. Influence on Implant body design :
- As angulation of load increases stress around
the implant Increases particularly in the
vulnerable crestal region
- As a result all implants are designed for
placement perpendicular to the occlusal
plane
- The face of thread or plateau can change the
direction of load from prosthesis to abutment
connection, to a different force direction at the
bone
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35. Force magnification
Extreme angulation and parafunctional habits
exceed the capability of the dental implant
design to withstand physiological load
Cantilever crown heights are levers and force
magnifiers
Careful treatment planning and multiple
implants are indicated in case of force
magnification
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36. Surface area
Anatomical constraints on surface area
optimization-
Bone vol : external architecture of bone
- Width is greater in the posterior region
- In general 6 to 8mm bone is available in the
anterior region and 4mm implant is used
- 7mm width is available in the posterior
region and 5mm implant is used
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37. - Therefore implant width may increase as
amount of force magnification increases from
anterior to posterior region.
- On the contrary bone height usually decreases
from anterior mandible, compared with the
anterior maxilla, the posterior mandible, to the
least in the edentulous posterior maxilla
- Hence as occlusal force increases bone height
and vol decreases
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38. Bone quality : internal architecture of bone
- four distinctly different bone density
classifications exist within the max and mand
- Greater failure rate has been documented in
porous bone compared with dense bone
- Additional implants or implants with greater
surface area have to be used in porous bone
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39. Functional surface area forces vs. Total
surface area-
For a given bone vol, implant surface area
must be optimized for functional loads
FSA: defined as the area that actively
serves to dissipate compressive and tensile
non shear loads through the I-B interface
and provides initial stability of the implant
following its surgical placement
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40. Functional thread surface area: portion of
the thread that participates in compressive
load transmission under the action of a axial
or near axial occlusal load
Total surface area : may Include a passive
area that does not participate in load transfer
Example : plasma spray coatings have 600%
more TSA but less than 30% is actually
exposed to the bone
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41. Since most stress to the I-B interface Is in the
crestal 1/2 of the implant, the crestal zone is
most important to distribute stresses
appropriately
Design variables in SA optimization
Implant macrogeometry
Implant width
Thread geometry
Implant length
Crest module configuration
Apical design considerationswww.indiandentalacademy.com
42. Implant macro geometry
Smooth sided cylindric implants provide
surgical ease however B-I interface is
subjected to significantly large shear
conditions
Smooth sided , tapered implants allows for a
component of compressive load to be
delivered to bone B-I interface depending on
the degree of taper
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43. Threaded implants with circular cross section
provide ease of surgical placement and allow
for >FSA optimization to transfer
compressive forces to the B-I interface
Also gives initial rigid fixation to limit micro
movement during healing
Smooth sided cylinder depends on coating
our micro structure for load transmission to
bone
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44. Implant width
Over the years implants have gradually
Increased in width
Scientific principle being > the width greater
the surface area
4mm implants have 33% > SA than 3mm
implants
Largest the width better the emergence
profile of the crownwww.indiandentalacademy.com
45. Crestal bone anatomy limits implants to <
5.5mm except in limited situations
Thus implant design innovations in crestal
region are required to provide increase in
FSA in this vulnerable region
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46. Thread geometry
FSA for unit length of the implant may be
modified by varying three geometric
parameters of implant
- Thread pitch
- Thread shape
- Thread depth
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47. Thread pitch is defined as the distance
measured parallel with its axis between
adjacent thread forms ( for V type threads ),
for the number of threads per unit length in
the same axial plane and on the same side of
the axis
Smaller / finer pitch : more threads on the
Implant body for given unit length and thus
greater surface area per unit length
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49. Thread shape:
• V shaped
• Square
• Buttress
- Dental implant applications dictates the
need for a thread shape optimized for a
long-term function ( load transmission )
under occlusal intrusive ( opposite of pull
out ) load directions
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51. The square thread provides an optimum
surface area for intrusive & compressive load
transmission
Shear loading most detrimental to bone
Shear force on V thread face its ten times
greater than on square thread
Buttress has similar shear component as V
under occlusal load
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52. Thread depth : refers to the distance between
the major and minor diameter of the thread
It may be varied for the length of the implant
to increase FSA in the region of highest
stress, example : crestal region
Reverse taper leads to a dramatic increase in
functional surface area at the crest of the
bone where stresses are highest
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54. Implant length
As length of the implant increases so does the
overall total surface area
Once I-B interface is formed excessively long
implants do not receive stress transmission to
the apical region and are not needed
D3, D4 bone in the posterior region have less
available bone height
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55. Nerve repositioning is cited as an acceptable
clinical treatment to facilitate longer implants
in the posterior mandible
Maxillary sinus grafts done for posterior
maxilla
Longer implants have been suggested to
provide greater stability under lateral loading
stress generated by lateral load can be
dissipated by implant in the range of 10 -15
mm length compared with implant of 20-30
mm length
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56. Crest module configuration
Crest module of implant body is the
transosteal region from implant body and is
characterized as a region of high
concentration of mechanical stress
Many crest modules have been designed to
reduce plaque accumulation once bone loss
has occurred
However design of crest module contributes
to crestal bone losswww.indiandentalacademy.com
59. Angulated crest module > 20° with surface
texture that increases bone contact causes
slightly beneficial cumbersome stress to
adjacent bone and decreased bone loss
Crest module should be slightly larger than
outer thread diameter
Crest module height is often 2 mm
A polished collar of minimum height should be
designed on the superior portion just below
the prosthesis platform (0.5 mm)
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60. Apical design considerations
Most root form implants are circular in cross
section
Around cross section does not resist shear
forces
As a result anti - rotational feature is
incorporated in apical region of implant body
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62. Another anti - rotational feature flat sides or
gross along the body or apical the region of
the implant body
When bone grows against flat end it is kept
under compression with rotational loads ,
thus apical end must be flat than pointed
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63. Surface coatings
Titanium plasma spray ( TPS )
- Implant body may be covered with a porous
coating , two materials commonly used for this
purpose titanium and hydroxyapatite
- Both are plasma sprayed on to implant body
- TPS increases B-I surface area and acts
similar to three dimensional surface rates may
stimulate adhesion osteogenesis
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64. - There is 600% increase in total surface area
- FSA increases by 25 to 30% which is
significant
- Improved initial fixation of implant is seen
specially in softer bone
Hydroxyapatite coatings :
- Similar roughness as TPS and increase FSA
- Direct bonding to bone which is of greater
strength
- Enhanced gap healing in hydroxyapatite
coating is seen
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65. Advantages of surface coatings:
- Increased surface area
- Increased roughness for initial stabilization
- Stronger B-I interface
Additional advantages of HA over TPS
- Faster healing of B-I interface
- Increased gap healing between B & HA
- Stronger interface than in TPS
- Less corrosion of metalwww.indiandentalacademy.com
66. Disadvantages of surface coatings :
- Coatings may be damaged when being
inserted in dense bone
- Increased surface roughness with the risk of
bacterial contamination when present above
bone
- HA : increased plaque retention when exposed
- Increased costs
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67. Contemporary implant dentistry – Carl E. Misch , 2nd
edition
Dental materials – Philips 11th
edition
Fundamentals of implant dentistry, Weiss and Weiss
Implants in restorative dentistry, Scortsessi
Journal of dental education vol 52 no 12 pg 755,
1988
Jpd 1985 : 54; 410-14
Jpd 1983 : 49; 843-49
Atlas of oral imlantology – Crennin
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