BIOMECHANICS IN DENTAL IMPLANTS-(Dr.RAMAKRISHNA).ppt

biomechanics of implant

2. BIOMECHANICS IN
DENTAL IMPLANTS
PRESENTED BY
Dr. RAMAKRISHNA
Pg student
Dept of prosthodontics
(26-11-07)

3. CONTENTS
•Introduction
•Definitions
•Rationale in the field of dental implants
•Classification Of implant biomechanics
•Types of loads applied on implants
•Basic mechanical properties of matter
•Forces
•Components of forces
•Analysis of forces
•Characteristics of forces

4. •Stress
•Methods to analyze stresses
•Factors controlling stresses
•Deformation and strain
•Stress-strain relationship
•Impact loads
•Force delivery and failure mechanisms
•Torque /moment loads
•Clinical moment arms
•Fatigue failure
•Moment of inertia
•Diffences in tooth and implant biomechanics
•Conclusion
•references

5. INTRODUCTION

6. INTRODUCTION
•The discipline of bioengineering, which applies
engineering principles to living systems, has
unfolded a new era in diagnosis, treatment
planning and rehabilitation in patient care.
•One aspect of this field, Biomechanics concerns
the response of biological tissues to applied
loads.
•Thus my presentation deals with fundamental
concepts and principles of dental Biomechanics
as they relate to long-term success of dental
implants and restorative procedures.

7. DEFINITIONS

8. DEFINITIONS
ACCORDING TO GPT- 8
•DENTAL BIOMECHANICS is defined as the
relationship between the biologic behavior of oral
structures and the physical influence of a dental
restoration.
•BIOMECHANICS is the application of mechanical
laws to living structures, specially the locomotor
system of the body.

9. OTHER DEFINITIONS
•Biomechanics is the scientific study of the load-
force relationships of a biomaterial in the oral
cavity. (Ralph Mc Kinney).
•The study of biology from the functional
viewpoint.

10. RATIONALE OF
BIOMECHANICS IN
THE FIELD OF DENTAL
IMPLANTS

11. RATIONALE OF BIOMECHANICS
•First, to know the loading (bite forces) exerted on the
prosthesis.
•Secondly, to know the distribution of the applied forces
to the implants and teeth supporting the prosthesis.
•Thirdly, to see that the forces on each implant must
be delivered safely to the bony tissues in order to
prevent failure of any part of the system, including the
prosthesis, the supporting implants and the biological
tissues.

12. TYPES OF IMPLANT
BIOMECHANICS

13. CLASSIFICATION OF IMPLANT
BIOMECHANICS
•According to WEINBERG, they are classified as
–REACTIVE BIOMECHANICS
–THERAPEUTIC BIOMECHANICS

14. REACTIVEBIOMECHANICS
–It deals with
biomechanical factors
that are of destructive
nature to the implants.
THERAPEUTIC BIOMECHANICS
–It is the clinical process of
altering each biomechanical
factor to reduce the
cumulative response causing
implant overload.

15. LOADS APPLIED ON
IMPLANTS

16. WHAT ARE LOADS APPLIED TO
DENTAL IMPLANTS?
•Occlusal loads during function.
•passive loads like those applied to implants during healing
stage because of mandibular flexure, contact with first stage
cover screw and/or second stage- permucosal extension.
•Horizontal loads like perioral forces of tongue and circumoral
musculature.
•Forces due to application of non- passive prostheses to
implant bodies.
•Forces due to para functional oral habits or tongue thrust.

17. BASIC MECHANICAL
PROPERTIES OF
MATTER

18. BASIC MECHANICAL PROPERTIES
•Basic units of mechanics that are used to provide
the tools for consistent description and
understanding of physiologic and non
physiologic loads are as follows:
–Mass
–Force
–Weight

19. •Mass is the degree of gravitational attraction the
body of matter experiences.
–Units – metric(SI)system - Kg
English system - lbm
•Force was described by Newton in 1687 (in
Newton’s law of motion)
Newton's second law, states that the acceleration of
a body is inversely proportional to its mass and
directly proportional to the force that caused the
acceleration.
A α f \ m Therefore, F = ma

20. •Where, F=force (newtons)
m=mass (kilograms)
a=acceleration (m/s
2
)

•The gravitational constant (a=9.8m/s2) in the
above equation is approximately same at every
location on Earth, therefore mass (kg) is the
determining factor in establishing the magnitude
of static load.
•Weight is the gravitational force acting on an
object at a Specified location.
Weight and Force therefore can be expressed by
the same units, newtons (N) or pound force (Ibf)

21. FORCES

22. FORCES
•Forces acting on dental implants are referred to as
vector quantities; that is, they possess both
magnitude and direction.
•A force applied to a dental implant is rarely
directed absolutely longitudinally along a single
axis.

23. Three dominant clinical loading axes that can exist
in implant dentistry :-
–1.Mesio-distal
–2.Facio-lingual
–3.Occluso-apical

24. Components of Forces (Vector Resolution)
•A single occlusal contact most commonly result
in a three-dimensional occlusal force.
•The process by which three-dimensional forces
are broken down into their component parts is
referred to as vector resolution

25. ANALYSIS OF FORCES
•CARTESIAN coordinate axes
•FORMULAE:
•F = Fx
2
+ Fy
2
+ Fz
2
•Cos
2
x + Cos
2
 y + Cos
2
 z = 1
•Vector addition : More than one
force
• FR = F1 + F2 + F3

26. CHARACTERISTICS OF FORCES
•Forces may be described by
–magnitude,
–duration,
–direction,
–type, and
–magnification factors.

27. 1. MAGNITUDE OF FORCES
•Typical maximum bite force magnitudes exhibited by adults
are affected by age, sex, degree of edentulism, bite location
and especially parafunction.
•Craig, 1980
– Molar - 390 – 880N
– Canine - 453N
– Incisor - 222N
– Parafunction -1000Psi
•Colaizzi, 1984
– Complete denture - 77 – 196N

•Carlsson & Haraldson, 1985
– Denture with implant - 48 – 412N

28. 2.DURATION OF FORCES
•Mastication - 9mt/day with 20 to 30 psi
•Swallowing - 20mt/day with 3 to 5 psi

29. 3.TYPES OF FORCES
•Forces may be described
as
–Compressive forces
attempt to push masses
toward each other.
–Tensile forces pull
objects apart.
–Shear forces on implants
cause sliding forces.

30. •Compressive forces tend to maintain the integrity
of a bone-to-implant interface, where as tensile
and shear forces tend to disrupt such an interface.
•Shear forces are most destructive to implants and
bone when compared with other load modalities.
•Compressive forces, in general, are best
accommodated by the complete implant-
prosthesis system and should be dominant forces
for implant success.

31. •Cortical bone is strongest in compression
and weakest in shear.
•According to Cowin (1989)
• cortical Bone - Strongest -Compression
- 30% weaker - tension
- 65% weakest – shear

32. 4. DIRECTION OF FORCES
On centric vertical contact
Axial load Angle load
Greater compressive Greater tensile & shear
stress stress

33. 5. MAGNIFYING FACTORS

•Includes,
– Extreme angulation
– Cantilevers
– Crown height
– Parafunction
– Bone density
•Crown height - Increase in 1mm – 20%
increase in torque.

34. STRESS

35. STRESS
•The manner in which a force is distributed over a surface is
referred to as mechanical stress. Thus stress is defined by
the familiar relation:
σ = F/A
•Where, σ=stress (psi ; pa), F=force (newtons ; lbf), A=area
(sq.inches ; sq.meters)
•The internal stresses that develop in an implant system and
surrounding biologic tissues have a significant influence on
the long-term longevity of the implants in vivo.
•As a general rule of thumb, a goal of treatment planning
should be to both minimize and evenly distribute
mechanical stress in the implant system and the
contiguous bone.

36. METHODS TO ANALYZE STRESS
•Stress analysis can be performed:-
1. Experimentally e.g. Stress-optical examination
2. Theoretically & mathematically with computer
simulation e.g. Finite-element method
1.Stress-optical examination
•Implant to be analyzed is embedded in synthetic
resin and stresses induced by loading are made
visible by polarized light.
•Disadvantages are:-
– Not possible in inhomogeneous structure of bone
– Limited optical resolution

37. •2. Finite-element method
•The structures to be examined are
subdivided into a finite number of
elements of similar size that can
be connected with each other at
corner points, i.e. nodes.
•The displacements and stresses
at each node caused by loading
can be calculated with a computer
program. (eg: NISA)

38. •Advantages are:-
•Allows inclusion of various materials with
differing material properties. Most importantly,
the inhomogeneous structure of bone, i.e. the
subdivision into cortical and cancellous bone,
can be taken into consideration.
•Allows three-dimensional visualization of the
calculated displacement and stresses

39. •Finite element analysis – Siegele 1989,
Chelland 1991
Determined the distribution and concentration of
strain and deformation within implant and stated
that force distribution to surrounding bone occurs
at crestal bone and level of third screw thread.

40. •Finite element analysis of implant loads reveals
•compress stresses =400 N/m
2
•Tensile and shear stresses=200 N/m
2

41. • The magnitude of stress is dependent on two variables:-
1. force magnitude and
2.cross-sectional area over which the force is dissipated.
•FORCE MAGNITUDE
• rarely be completely controlled by a dental practitioner.
• The magnitude of the force may be decreased by reducing the
significant "magnifiers of force“ :- cantilever length, offset
loads, and crown height.
• Night guards to decrease nocturnal parafunction, occlusal
materials that decrease impact force, and overdentures rather
than fixed prosthesis so they may be removed at night are
further examples of force reduction strategies.
Factors controlling stress

42. •Functional cross-sectional area is defined as that
surface that participates significantly in load bearing and
stress dissipation.

•It may be optimized by :-
1.Increasing the number of implants for a given edentulous
site, and
2.Selecting an implant geometry that has been carefully
designed to maximize functional cross-sectional area.
Functional surface area - magnitude of mechanical
stress

43. HOW DOES PEAK STRESSES OCCUR
AND WHAT IS THEIR SIGNIFICANCE?
•Peak stresses occur when the stress element is
positioned in particular orientation (or geometric
configuration) in which all shear stress
components are zero.
•Determination of peak normal stresses in a dental
implant system and tissues give valuable insights
regarding sites of potential implant fracture and
bony atrophy.

44. DEFORMATION AND
STRAIN

45. DEFORMATION AND STRAIN
•Strain is defined as the
change in length divided
by the original length.
•For tension and
compression, strain
expresses a lengthening
and a shortening of the
body respectively.
• In shear, the shape
change is expressed in
terms of a change in angle
of one part of the body
relative to the other.
Є = l –lo/lo = Δ l/lo

46. •The deformation and strain characteristics of the
materials used in implant dentistry may influence
interfacial tissues, ease of implant manufacture and
clinical longevity.
•Elongation (deformation) of biomaterials used for dental
implants range from 0% for aluminum oxide (Al2O3) to
up to 55% for annealed 316-L stainless steel.
•Poisson’s ratio: with in an elastic range the axial strain
and lateral strain due to a load are proportional to one
another.
• µ = lateral strain/axial strain

47. •The concept of strain is a parameter believed to
be a key mediator of bone activity.
•All materials (both biologic and nonbiologic) are
characterized by a maximum elongation possible
before permanent deformation or fracture results.

48. STRESS-STRAIN
RELATIONSHIP

49. SRESS-STRAIN RELATIONSHIP
•A relationship is needed between the applied
force (and stress) and the subsequent
deformation (and strain).
• If any elastic body is experimentally subjected
to an applied load, a load-vs.-deformation curve
may be generated.

50. •If the load values are divided by the surface area over
which they act and the change in the length by the original
length, a classic engineering stress-strain curve is
produced.
• Such a curve provides for the prediction of how much
strain will be experienced in a given material under an applied
load.
• The slope of the linear (elastic) portion of this curve is
referred to as the modulus of elasticity (E), and its value is
indicative of the stiffness of the material under study.

51. •The closer the modulus of elasticity of the implant
resembles that of the biologic tissues, the less the
likelihood of relative motion at the tissue-to-implant
interface.
•The cortical bone is atleast 5 times flexible than
titanium.
•The density of bone is not only related to the bone
strength, but also the modulus of elasticity
(stiffness).
•The stiffer the bone, the more rigid; the softer the
bone, the more flexible.

52. •HOOKE’S LAW:
the relationship between stress and strain is
given by a formula
σ = EЄ
In stress

 In stiffness difference

 Relative motion

Interface is more
affected
Viscoelastic bone can stay in
contact with more rigid titanium
more predictably when the stress
is low

53. •Once a particular implant system (i.e., a
specific biomaterial) is selected, the only
way to control the strain is to control the
applied stress or change the density of
bone around the implant.

54. IMPACT LOADS

55. •When two bodies collide in a very small interval of
time (fractions of a second), relatively large forces
develop. Such a collision is described as impact.

•In dental implant systems subjected to occlusal
impact loads, deformation may occur in the
prosthetic restoration, in the implant itself, or in the
interfacial tissue.

•
IMPACT LOADS

56. •The higher the impact load, the greater the risk
of implant and bridge failure and bone fracture.
•Rigidly fixed implants generates a higher impact
force than a natural tooth with its periodontal
ligament.

•Various methods have been proposed to address
the issue of reducing implant loads.

57. •Skalak suggested the use of acrylic teeth in
conjunction with osteointegrated fixtures
•Weiss has proposed that a fibrous tissue-to-implant
interface provides for physiologic shock absorption in
the same manner as by a functioning periodontal
ligament.
•one implant design has attempted to incorporate
shock absorption capability in the design itself, by the
use of an "intramobile element" of lower stiffness
compared with the rest of the implant.
•Misch advocates an acrylic provisional restoration
with a progressive occlusal loading to improve the
bone-to-implant interface before the final restoration,
occlusal design, and masticatory loads are distributed
to the system.

58. FOUR CLINICAL VARIANTS
WITH IMPLANT LOADING
•Includes
• Cuspal inclination
• Implant inclination
• Horizontal Implant
Offset
• Apical Implant
Offset

59. REACTIVE BIOMECHANICS
•Cuspal Inclination
•Increase in 10° 
increased 30% torque
•Implant Inclination
•Increase in 10° 
Increased 5% torque

60. REACTIVE BIOMECHANICS
•Horizontal Implant
Offset
•Increase in 1mm 
increased 15% torque
•Apical Implant Offset
•Increase in 1mm 
Increased 5% torque

61. THERAPEUTIC BIOMECHANICS
•CUSPAL INCLINATION: Reduction in cuspal
inclination by 10
0
causes 30% less torque, as the
resultant line of force is shifted towards the center
of rotation of implant.

62. THERAPEUTIC BIOMECHANICS
•IN IMPLANT INCLINATION: REDUCTION OF
IMPLANT INCLINATION BY 10
0
REDUCES TORQUE
BY 5%

63. THERAPEUTIC BIOMECHANICS
•IN HORIZONTAL OFFSET: reduction of horizontal
offset by 1mm results in reduction of torque
by15%. This can be done by
•1. By changing the position of implants
•2. using angled abutments with out changing the
position of implants
•3. using cross occlusion
•4. modifying the occlusal contacts

64. 1.Reduction of horizontal offset and torque
by changing the position of implant
•before •after

65. 2. By changing the abutment angulation
•before •after

66. 3.By establishing cross occlusion

68. 4. By modifying the occlusal contacts
(in posteriors)
•before •after

69. By modifying incisal contacts
(in anteriors)
•before •after

70. FORCE DELIVERY AND
FAILURE MECHANISMS

71. FORCE DELIVERY AND FAILURE
MECHANISMS
•The manner in which the forces are applied to implant
restoration in oral environment dictates the likelihood of
system failure.
•Fatigue failure of implant or prosthesis occurs due to
low magnitude forces being repeatedly applied over
along period of time.
•Stress concentration and ultimately failure may develop
due to insufficient cross-sectional area to dissipate high
magnitude forces.
•If a force is applied applied some distance away from a
weak link in implant or prosthesis bending failure results
from moment loads.

72. TORQUE

73. Torque/bending loads/moment loads
•Product of inclined
resultant line of force
and distance from
center of rotation.

Torque =Force x Distance

•Longer the distance
arm or force arm or
moment arm, greater
is the torque.

74. •Center of rotation for natural tooth is at -Apical
1/3rd
•Chelland, 1991
Implant - First to third screw level.

75. MOMENT ARMS

76. CLINICAL MOMENT ARMS – THEIR
SIGNIFICANCE
A total of six moments (rotations) may develop
about the three clinical coordinate axes.
Clinical moment
arms

77. •Such moment loads induce microrotations and
stress concentrations at the crest of the
alveolar ridge at the implant-to-tissue interface,
which leads to crestal bone loss.
•Three "clinical moment arms" exist in implant
dentistry:-
– Occlusal height,
– Cantilever length, and
– Occlusal width.
•Minimization of each of these moment arms is
necessary to prevent unretained restorations,
fracture of components, crestal bone loss,
and/or complete implant system failure

78. THREE CLINICAL MOMENT
ARMS IN IMPLANT DENTISTRY

79. 1.OCCLUSAL HEIGHT- MOMENT ARM
Occlusal height serves as the moment arm for
force components directed along the
faciolingual axis as well as along the
mesiodistal axis.

80. •Moment of a force along the vertical axis is not
affected by the occlusal height because there is
no effective moment arm. Offset occlusal contacts
or lateral loads, however, will introduce significant
moment arms.

81. 2.CANTILEVER LENGTH- MOMENT ARM
•Large moments may develop from vertical axis force
components in cantilever extensions or offset loads
from rigidly fixed implants.

82. A lingual force component may also induce a
twisting moment about the implant neck axis if
applied through a cantilever length.

83. •An implant with a cantilevers extending1 cm, 2 cm,
and 3 cm has significant ranges of moment loads.
• A 100-N force applied directly over the implant does
not induce a moment load or torque because no
rotational forces are applied through an offset
distance.
•This same 100-N force applied 1 cm from the implant
results in a 100 N-cm moment load.
•Similarly, if the load is applied 2 cm from the implant,
a 200 N-cm torque is applied to the implant-bone
region, and 3 cm results in a 300 N-cm moment load.
•(Implant abutments are typically tightened with less
than or equal to 30 N-cm of torque).

84. •The distance from the center of the most anterior implant to
the distal of each posterior implant is called the antero -
posterior (AP) distance.

•The greater the A - P distance, the smaller the resultant load
on the implant system from cantilevered forces, because of
the stabilizing effect of the antero- posterior distance.
•Clinical experiences suggest that the distal cantilever
should not extend 2.5 times the A-P distance under ideal
conditions.

85. •A square arch form
involves smaller A-P
distances between
splinted implants and
should have smaller
length cantilevers.
•A tapered arch form
has largest distance
between anterior and
posterior implants and
may have longest
cantilever design.
ARCH FORMS AND CANTILVERS

86. •Tapering arch form is favorable for anterior implants with
posterior cantilevers.
•Square arch form is preferred when canine and posterior
implants are used to support anterior cantilevers in either
arch.
•Ovoid arch form has qualities of both tapered and square
arches.
•Patients with severe bruxism should not be restored with
any cantilevers

87. 3.OCCLUSAL WIDTH-MOMENT ARM
•Wide occlusal tables increase the moment arm
for any offset occlusal loads.
•Faciolingual tipping (rotation) can be
significantly reduced by narrowing the occlusal
tables and/or adjusting the occlusion to provide
more centric contacts.

88. FATIGUE FAILURE

89. FATIGUE FAILURE
•Characterized by dynamic, cyclic loading.

• Depends on FATIGUE FACTORS like –
 Biomaterial


Geometry
 Force magnitude
 Number of cycles

90. 1. Biomaterial
–Fatigue failure occurs above endurance level of
biomaterial.
–Stress level below which an implant biomaterial
can be loaded indefinitely is referred as
endurance limit.
–Ti alloy exhibits high endurance limit compared to
CP Ti.

91. 2. Implant geometry
•Resist bending & torsional load and ultimately
fatigue failure.
• Related to thickness of implant or metal.
•A material 2 times thicker in wall thickness – 16
times stronger

92. 3. force magnitude:
•lesser the load, lesser fatigue failure.
•forces can be reduced by
–Careful consideration of arch position (more
loads in posterior region than anterior region)
–Increasing surface area available
–Elimination of torque

93. •4. Number Of Loading Cycles
•Loading cycles should be reduced
to reduce fatigue failure.
• Eliminate parafunctional habit.
• Reduce occlusal contacts.

94. MOMENT OF INERTIA

95. MOMENT OF INERTIA
•It is important property of cylindrical
implant design because of its connection
with the analysis of bending and torsion.
•The bending stress in a cylinder is given by
σ = My/I
Where M = moment (N- cm),
y = distance from the neutral axis of
bending (cm), and
I = moment of inertia (cm
4
)

96. DIFFERENCES
BETWEEN TOOTH AND
IMPLANT
BIOMECHANICS

97. DIFFERENCES IN BIOMECHANICS
•NATURAL TOOTH
•Has PDL
•Shows flexion
•Stresses distributed to
surrounding bone
•Shows micro-movement
(0.5 µm)
•IMPLANT
•Has osseointegrated bone
•Is rigid or stiff
•Stress concentrated at the
crest of bone near third
screw level
•Shows micron movement
(0.1 µm)

98. •Elastic modulus similar to
bone
•Surrounding bone formed
at childhood
•Increased magnitude of
forces produces warning
signs like occlusal trauma,
wear facets, sensitivity,
mobility etc..
•5 -10 times different from
bone, therefore when same
load that is applied on tooth
is is applied on implant,
incresed stress seen and
concentrates at crestal bone
level.
•Bone formed rapidly and
intensely
•No warning signs seen.
direct bone fracture results
on increasing magnitude of
forces.

99. DIFFERENTIAL MOBILITY
•Qualitative difference between
the flexion of periodontal
ligament and stiffness of
osseointegration.
•Micro movement
Natural teeth with good bone will
move laterally
approximately 0.5mm
measured occlusally.
•Micron Movement – (Weinberg,
Rangert, 1994)
Implant can move laterally
0.1mm or less
measured
occlusally.

100. CLINICAL
APPLICATION OF
BIOMECHANICS

101. BIOMECHANICS OF FORCE DISTRIBUTION IN
MULTIPLE IMPLANT PROSTHESIS
Splinting
 Natural tooth – Periodontal ligament – forced distribution
 Implant – stiff – no force distribution and only
concentration at crestal bone

102. FORCE DISTRIBUTION IN COMBINED PROSTHESIS
 Supported by both natural teeth and implants
 Mode of attachment
 Flexible
 Stiff
 Flexible – internal attachment
 Stiff – when terminal abutments are
implants

103. FLEXIBLE ATTACHMENT
 Tooth supported prosthesis – Female attachment
 Implant supported prosthesis – Screw retained
Flexion Occurs
Not Deleterious

104. STIFF ATTACHMENT
 Natural tooth – permanently cemented substructure
telescopic crown
 Implant supported prosthesis – over crown, coping with
temporary cement
Tend to Loosen
To eliminate, permanent cementation rather than fixed
retrievability

105. DIAGNOSTIC FACTORS IN COMBINED PROSTHESIS
Standard Prosthesis design
Internal attachment placed in distal of natural tooth
Differential mobility
Natural tooth cannot support implant
Increase in lever arm
Increase Torque

106. Recommended Prosthesis Design
One cantilever pontic from each segment
Flexible internal attachment
Drifting apart of segment
Decreased Torque

107. COMPLETE EDENTULISM AND BIOMECHANICS
 Screw loosening not common these patients
Implant placed across and around arch
Cross splinting
Lateral forces –Vertical force
Tripodism
Excellent resistance to bending

108. Staggered Implant Offset – Rangert 1993
Staggered buccal and lingual offset
Tripod Effect
Compensates torque
Implant placed 1.5mm bucal and lingual from centre
line to achieve Tripodism.

109. Weinberg 1996
In maxilla, lingual offset - increased 24% torque
Buccal offset - Decrease 24% torque
Maxilla - Tripod –increase in 24% torque
Maxilla- As far as bucally
Mandibular - Tripodism

110. WIDER IMPLANTS
Developed by Dr.Burton Langer
Advantages
 Increase in surface area
 Limited bone height
 Upon removal of failed standard size implant
 Wider implant - Larger size – tighter joint

overall strength increases

111. BONE DENSITY AND BIOMECHANICS
Density ∞ Strength
∞ Amount of contact with implant
∞ Distribution and dissipation of
force
Misch 1995
FEM study – stress contour is different for each bone
density.
With same load
D1 - Crestal stress and lesser magnitude
D2 - Greater crestal stress and along implant
body
D4 - Greatest stress and farther apically

112. Implant Number
Increase in number  Increase in functional
loading area
Implant Macrogeometry
Length
 D1 - 10mm
 D2 - 12mm
 D3 - 14mm with V-shaped thread screw
Density decreased  Length increased

113. SINGLE TOOTH IMPLANT AND BIOMECHANICS
 Requires good bone support
 Control of occlusal lever parallel to long axis
 Access for oral hygiene

114. When space exceeds 12mm
When space less than 12mm

115. Cantilever Prosthesis and Biomechanics
 It result in greater torque with distal abutment as fulcrum.
 May be compared with Class I lever arm.
 May extend anterior than posterior to reduce the amount
of force
It depends on stress factors
 Parafunction
 Crown height
 Impact width
 Implant Number

116. Sufficient bone height exist to place long implant,
Avoid contact on central incisors during protrusion, labial
excursion and maximum intercuspation
CANTILEVER FIXED PARTIAL DENTURE

117.  Group function - lateral movement
 Avoid loading on canine
 Lateral guidance provided by central and lateral incisor

118. Three implants placed with
2
nd
premolar as cantilever

119. IMPLANT DESIGN & BIOMECHANICS
Ti alloy offers best biomechanical strength & biocompatibility
Bending fracture resistance factor:-

Wall thickness = (outer radius)4_ (inner radius)4
If outer diameter increases by 1mm & inner diameter unchanged
33% increase in bending fracture resistance
If inner diameter decreases by 1mm & outer diameter unchanged


20% increase in bending fracture resistance

120. 1. Shape

THREAD GEOMETRY
V-shaped
Buttress
Square
shaped

121. 1. THREAD PITCH 2. THREAD DEPTH
THREAD GEOMETRY

122. IMPLANT MACROGEOMETRY
Smooth sided cylindrical implants – subjected to shear
forces.
Smooth sided tapered implants – places compressive
load at interface.
Greater the taper – greater the compressive load
delivery.
Taper cannot be greater than 30 degree.

123. Implant width
•Increase in implant width – increases functional surface
area of implant.
•Increase in 1mm width – increase in 33% of functional
surface area.

124. Implant length
Increase in length –Bicortical stabilization
Maximum stress generated by lateral load can be
dissipated by Implants in the range of 10-15mm
Softer the bone –greater length or width
Sinus grafting & nerve re-positioning to place greater
implant length
Longer implants are not necessarily better.

125. Crestal module design
Smooth parallel sided crest –shear stress
Larger diameter than outer thread diameter
-Prevents bacterial ingress
-Initial stability
-Increase in surface area
Angled crest module less than 20 degree-
-Increase in bone contact area
-Beneficial compressive load

126. Apical Design
Round cross-section do not resist torsional load
Incorporation of anti –rotational feature

- Vent\ hole- bone grow the hole
- Resist torsion
- Flat side\groove - bone grow against
- places bone in compression

127. Surface Coating

-Titanium plasma spray
-Hydoxyapatite coating
•Advantages
-Increase in surface area
-Roughness for initial stability
-Stronger bone – implant interface
•Disadvantages

-Flaking and scaling upon insertion
-Plaque retention
-Bacteria and nidus for infection
-Increased cost

128. CONCLUSION

129. CONCLUSION
•The most common complications in implant-related
reconstruction are related to biomechanical
conditions.
•The manifestation of biomechanical loads on dental
implants (moments, stress, and strain) controls the
long-term health of the bone-to-implant interface.
•Thus a thorough Knowledge of basic biomechanical
principles is required for the dentists doing implant
treatment.

130. REFERENCES

131. REFERENCES
Dental implant prosthetics - Carl E.Misch
Osseointegration and occlusal rehabilitation- Sumiya
Hobo
Atlas of tooth & implant supported prosthesis-
lawrence a. weinberg
Endosteal Dental Implants -Ralf V McKinney JrRalf V McKinney Jr
Endosseous implants- Georg WatzekGeorg Watzek