1. 8a. Biomechanics and Treatment
Planning
John Beumer III DDS, MS
Division of Advanced Prosthodontics, Biomaterials and
Hospital Dentistry, UCLA
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2. Implant Biomechanics and
Treatment Planning
Why should we be concerned with
implant biomechanics when we develop
a plan of treatment?
Because if we are not, we risk implant
overload and prosthesis failures such
as fracture and screw loosening.
Implant overload can lead to bone loss around
implants and eventually implant failure.

3. Is it possible to overload the bone anchoring an
osseointegrated implant?
Bone is a dynamic structure. Excessive loads lead to a
resorptive remodeling response
! Hoshaw et al (1994) observed a resorptive remodeling of the
bone around implants subjected to excessive axial loads
(300N). Bone loss was observed at the crest around the
neck of the implant and in the zone of bone adjacent to the
body of the implant
! Brunski et al, 2000 J Oral Maxillofac Implants - Consensus
! Isador’s studies (1996, 1997) using a monkey model
presented data that was consistent with the hypothesis
proposed by Hoshaw and her colleagues.
! Recent studies by Myamoto et al (1998, 2000, 2008) have
reconfirmed Hoshaw and Brunski’s original hypothesis

4. Do the new surfaces reduce the risk Courtesy C Stanford
of Implant Overload?
v Excessive occlusal loads
v Resulting microdamage
(fractures, cracks, and
delaminations)
v Resorption remodeling
response of bone
v Increased porosity of bone in
the interface zone secondary
to remodeling
v Vicious cycle of continued
loading, more microdamage,
more porosity until failure

5. Implant Biomechanics
! What is the load bearing capacity of
osseointegrated implant supported restorations?
! Is the load carrying capacity of implant prostheses
influenced by the quality of the bone sites?
! What factors control the magnitude of the loads
that are delivered through the implant into the
surrounding bone?
! What loads should implant borne restorations be
designed to resist?

6. Implant Biomechanics
Karnak The Great Wall Pont de Gard
You must over engineer your implant restorations, particularly
when restoring posterior quadrants with linear configurations in
order achieve predictable long term results.

7. Implant Biomechanics
LOAD BEARING CAPACITY ANTICIPATED LOAD
1. Quality of bone site (Affected by)
2. Quality of bone ! Occlusal factors
Cusp angles
implant interface
Width of occlusal table
3. Implant microsurfaces Guidance type
! Machined vs Anterior guidance
microrough vs Group function
nano-enhanced ! Cantilever forces
surfaces Connection to natural
4. Implant dentition
! Number and Size of occlusal table
Arrangement Cantilevered prostheses
Linear vs Curvilinear ! Parafunctional habits
! Length and diameter (bruxism)
! Angulation ! Brachycephalics

8. Load bearing capacity
Implant number and arrangement
l Both the number and arrangement
of implants affect the load carrying
capacity of any particular implant
supported restoration.
l Curvilinear arrangements carry
withstand more load than linear
arrangements

9. Load bearing capacity
Linear vs Curvilinear
Curvilinear arrangements have the
greatest load bearing capacity.

10. Load bearing capacity
Linear vs Curvilinear
v Curvilinear arrangements such as seen in this
patient are very predictable
v This PFM fixed prosthesis is 8 years post insertion.
Occlusion: Group function

11. Load bearing capacity
Linear vs Curvilinear
Linear configurations restoring the cuspid region, such as the
patient on the right, are unpredictable, whereas curvilinear implant
arrangements such as shown on the left are very predictable.
Predictable Not predictable

12. Load bearing capacity
Linear vs Curvilinear
v The
central incisor sites were the most favorable
implant sites. Therefore:
! They were extracted and implants placed into these sites
v Result:
! More favorable biomechanics and predictability
Courtesy Dr. R. Faulkner

13. Load bearing capacity
Linear vs Curvilinear
v Centrals extracted
! Note the horizontal
dimension of the central
incisor sites
v Implants inserted
Courtesy Dr. R. Faulkner

14. Load bearing capacity
Linear vs Curvilinear
Courtesy Dr. R. Faulkner

15. Load bearing capacity
Linear vs Curvilinear
v Completedprosthesis
v Biomechanics are favorable
Courtesy Dr. R. Faulkner

16. Load bearing capacity
Implant number and arrangement
v Anterior – Posterior Spread
In the edentulous mandible,
curvilinear arrangements such as
this one have the greatest load
bearing capacity. The cantilever
length can be double the A-P
spread but not exceeding 20 mm.

17. Load bearing capacity
Cantilever length relative to A-P spread
Relatively linear arrangements
combined with excessive
cantilever length such as shown
here are able to withstand less
occlusal load.
v Result
• Mechanical failures
• Implant overload
A-P
In this patient the result Spread
was recurrent fractures
of the prosthesis
retaining screws.

18. Excessive Cantilever forces
Implant Overload and Resorptive Remodeling
l If cantilevers are excessive however, they can lead to implant
overload and provoke a resorptive remodeling response of
bone around the distal implants.
In this patient a fixed edentulous bridge similar to the one
shown previously, was fabricated for this patient. However,
the cantilever extensions were in excess of 30 mm. Note the
bone loss around the distal implants particularly on the
patient’s left. Eventually this implant fractured.

19. Maxilla vs Mandible
Courtesy Dr. C. Stanford
The size and shape of the
trabeculae is different in the
mandible as compared to the
mandible and may be one of
the reasons why the load
carrying capacity of implant
supported prostheses restoring
posterior quadrants in the
mandible appears to be
superior to those in the maxilla.

20. Number of Implants per Unit Posterior Maxilla
When restoring posterior quadrants with implants we
are forced to use linear arrangements by anatomic
necessity. Therefore in most instances:
! One implant for
each dental unit.
! At least three
where possible in
extension areas.
*The third implant
dramatically improves the
biomechanics of the
restoration One dental unit = premolar

21. Number of Implants per Unit Posterior Maxilla
Curvilinear arrangements are favored over linear arrangements from a
biomechanical perspective. However, when restoring posterior quadrants
with implants we are forced to use linear arrangements by anatomic
necessity. Therefore in most instances:
! One implant for
each dental unit.
! At least three
where possible in *The third implant dramatically improves
extension areas. the biomechanics of the restoration

22. Number of Implants per Unit Posterior Maxilla
The distal implants failed 30 months after loading in
both these patients because of implant overload.

23. Number of Implants per Unit Posterior Maxilla
These implants failed 66 months after
loading because of implant overload.
Group function was used to restore this patient. Result:
Another problem:excessive lateral forces
! Application of Cusp angles too steep
! Implant failure
and the occlusion was tripodized

24. Number of Implants per Unit
Posterior Maxilla
Space allowed only two implants to be placed in
this patient. However, note anterior guidance.
Design the occlusion to minimize the delivery of nonaxial forces

25. Number of Implants per Unit
Posterior Maxilla
Only two implants were placed.
Note anterior guidance

26. Bone Augmentation – Horizontal Deficiencies
! Grafting bone defects with horizontal deficiencies
has been relatively predictable, particularly in the
anterior region.
! However, these implants are usually exposed to
minimal loads. In most patients the graft serves to
restore bone and soft tissue contours in order to
enhance the final esthetic result and idealize implant
position.
! Fixation of the graft is easy to accomplish
! The blood supply to graft is usually quite good

27. Bone Augmentation – Vertical Defects
Grafting vertical defects by adding bone on
top of the alveolar ridge, as shown here, is
much less predictable particularly in the
posterior quadrants.
Problems:
! Tension on the wound secondary to closure of
tissue flaps
! Poor blood supply
! Difficulty in achieving fixation
Result:
! Relapse (resorption) rate is 75%

28. Sinus Lift and Graft
Sinus
membrane
Bone graft
Bone of the residual
allveolar ridge
Advantages over only grafts
Resorption probably less than 25%
Challenge
Elevate the sinus membrane without perforation

29. Sinus Lift and Graft
! This procedure has been
reasonably predictable
although no good long term
followup studies are
available.
! Sources of graft material
include chin, ramus, and
iliac crest sometimes mixed
with bone substitutes.
! Best results with respect
to implant success rates
appear to obtained when
there is at least 4-5 mm of
residual ridge.

30. Sinus Lift and Graft
This patient was restored following a sinus lift
and graft. Autogenous chin bone was used.
She is 10 years post treatment and doing well.
Note: Best results achieved when there is 4-5 mm
of normal bone over the sinus before the procedure

31. Sinus Lift and Graft
This patient was restored following a
bilateral sinus lift and graft. Freeze
dried bone was used to graft the left
maxillary sinus. The implants placed
in this graft failed 18 months following
delivery of the implant supported
fixed partial denture.

32. Distraction Osteogenesis
This procedure has been used successfully in other sites,
particularly the anterior maxilla and the mandibular body. Its
usefulness in the posterior maxilla is probably limited. The
relapse (resorption) rate is about 25% (Moy et al, 2005)
Osteotomy
Distracted
site
bone
Distraction
Distraction
apparatus apparatus

33. *Removable Partial Dentures*
Removable partial dentures properly designed and fabricated
provide the patient with masticatory function equivalent to that
obtained with an implant supported fixed partial dentures
(Kapur, et al, 1992) and this service should be offered to the
patient before grafting is considered.

34. Number of Implants per Unit
Posterior Mandible
Two is sufficient for most patients
Why? The trabecular bone is more dense
resulting in better bone anchorage

35. Number of Implants per Unit
Posterior Mandible
Three are recommended when:
v There is bone over the nerve for only short implants
v Bone quality is poor
v When restoring four dental units

36. Number of Implants per Unit
Posterior Mandible
Three implants were used to
restore four units in this patient

37. Posterior Mandible – Limiting Factors
v Inferior alveolar nerve(arrow)
v Insufficient bone over the nerve to permit
placement of a 10 mm or longer implant
v Uni-cortical anchorage (arrow)

38. Posterior Mandible – Limiting Factors
Many patients such as this one, present with moderate
to severe resorption precluding placement of implants
unless the inferior alveolar nerve displaced.

39. Displacement of the Inferior Alveolar Nerve
! This procedure enables placement of implants of sufficient length with
bicortical anchorage.
! Although the risk of nerve injury is relatively small the morbidities
associated with injury may be severe.
! Therefore, these issues must be thoroughly discussed with the patient
before proceeding with the procedure.

40. Crestal Augmentation
Augmentation of vertical defects in posterior mandibular quadrants with free
autogenous bone grafts (A) has been unpredictable. Following surgery the
relapse rate is about 75% and further bone loss is also seen after loading (B).
Why?
a) Tension on the wound upon closure
b) Poor blood supply
c) Difficulty is achieving proper fixation of the graft
A B
Presently, distraction osteogenesis is the only reasonably
predictable method for enhancing this site vertically.

41. Use of Short Wide Diameter
Implants in the Posterior Mandible
This practice has not been predictable. The short implants
are particularly prone to occlusal overload and bone loss. This
is a 5 year followup x-ray of two 6 mm diameter implants.

42. If implants of adequate length cannot be
used, consider removable partial dentures
Mastication efficiency of distal extension RPD’s is
equivalent to implant supported fixed partial dentures.

43. Connecting Implants to Natural Dentition
Semiprecision vs rigid attachments

44. Linear configurations
Over engineer your cases
! When in doubt add the 3rd
implant in posterior
quadrant cases.
! Minimize the length and
width of the occlusal table

45. Over-engineer your linear quadrant cases
v When in doubt re: the quality of
the implant site bone, history of
parafunction etc., add the third
implant
v Minimize the width of the
occlusal table

46. Over-engineer your linear quadrant cases
However there is a flaw in he design of this
case. What is it?
Note: The buccal-lingual dimension is excessive
v Minimize the width of the occlusal surfaces. They should
be no wider than a premolar

47. Staggered vs linear configuration in
posterior quadrants
Straight line implant configuration
1.5 mm 1.5 mm
1.5 mm
Staggered implant configuration
This has been studied using a photoelastic model
by Itoh, et al, 2003

48. Staggered vs linear configuration
Is it biomechanically more favorable?
Straight line implant configuration
1.5 mm 1.5 mm
1.5 mm
v Yes, particularly with specific
chewing cycles. Nonlinear
arrangements resist lateral forces Staggered implant configuration
more effectively
v Is the improvement clinically
significant? This is unknown Itoh and Caputo, et al 2003

49. Staggered vs linear configuration
Is it feasible in the posterior quadrants?
Straight line implant configuration
1.5 mm 1.5 mm
1.5 mm
Probably not. Inthe posterior
quadrants you can’t get enough Staggered implant configuration
stagger to make much of a
difference biomechanically. Itoh and Caputo, et al 2003

50. Implants in Compromised Sites
Can we use shorter implants?
! Posterior maxilla
! Posterior mandible over the
inferior alveolar nerve in partially
edentulous patients
! Craniofacial application
Theoretically perhaps.
However we need well
designed clinical
outcome studies to
determine predictability

51. Length and diameter of Implants
Avoid the use of implants less than 10 mm in length and
4mm in diameter when restoring posterior quadrants.
v Short implants, such as this 7 mm
screw shaped implant, demonstrate
unfavorable stress distribution
patterns as seen in this study
performed with finite element
analysis. Longer implants distribute
stresses more favorably.
v Given the bone anchorage
achieved with modern surfaces,
failures are most likely to occur in the
Cho et al, 1993 trabecular bone

52. Length and diameter of Implants
• Two year followup data from Moy and Sze,’93
• Note the high failure rates with the 7 mm and
10 mm implants in the posterior maxilla.

53. Implant length vs diameter
Does increasing the
diameter compensate for
the lack of sufficient
length?
Using a photoelastic model,
Caputo et al, 2002 attempted
to determine whether
increasing the diameter of the
implant or increasing the length
of the implant had a significant
impact on stress distribution.
They concluded that:

54. Implant length vs diameter
! Most equitable load transfer
with axially directed loads.
! Under comparable loading
conditions, the stresses
transferred by the wide
diameter implant were only
slightly lower than the same
length narrow implant.
! For implants tested,
increased length was more
important than diameter in
Axial Buccal
Lingual
load load
stress reduction.
load
Caputo et al,2002

55. Implant length vs width
These data appear to have clinical significance. In our clinical
experience length is more important than width. Short wide
diameter implants appear to be susceptible to overload when used
in linear configurations such as shown here.
2 years
5 years
Cho,In Ho et
al, 1992

56. Ideal Implant Diameter
4-5 mm in diameter
! Less than 4 mm the rate of implant
fracture is unacceptably high
! Implants
3.75 mm in diameter have a 5-7%
fracture rate
! More than 5 mm the higher the
failure rate.
! Implants
6 mm in diameter have a 20%
failure rate
! Implants 4-5 mm in diameter have a less than
5% failure rate

57. Implant Angulation – Posterior vs Anterior
v Implants in the posterior
quadrants should be placed
so that occlusal loads can be
directed axially in the
posterior quadrants.
v In the anterior region, anatomic
necessity precludes implant
placement perpendicular to the
occlusal plane. However, the
forces used to incise the bolus are
only about ¼ of those used
posteriorly to masticate the bolus.
For this and other reasons implant
overload is rarely seen in the
anterior regions.

58. Implant angulation
v Nonaxial loads result in load magnification. Kinni et al
(1987), using photoelastic analysis and Cho et al (1993),
using finite element analysis, demonstrated that nonaxial
loads concentrated potentially clinically significant stresses
around the neck and at the tip of the implant.
Cho,In Ho et al, 1992

59. Biomechanics – Partially Edentulous Patients
Nonaxial loads and implant overload in posterior
quadrants
v Because of the curve of Spee and the distal angulation of the implants, the
occlusal loads (arrow) are nonaxial. Note the bone loss around the implants.
Linear configurations in the posterior region, such as in this patient, are
particularly vulnerable to the effects of nonaxial loading, particularly
brachycephalic individuals.

60. Cantilever forces
Cantilever forces are potentially detrimental particularly when
applied to implants with a linear configuration and single implants
placed in posterior quadrants.
! The longer the
cantilever the greater the
load magnification and
the more stress
concentrated in the bone
anchoring neck of the
distal implant.
! Note the dramatic
increase in stresses
associated with the 20
mm cantilever as
opposed to the 5 mm
one.

61. Cantilever forces
Cantilever
section
They are well tolerated when
implant supported
restorations are used to
restore the edentulous
mandible, so long as:
l The cantilevered section is
within a reasonable limit
l The implants are arranged in a
reasonable arc of curvature.
l Rigid frameworks with cross
arch stabilization are used

62. Excessive Cantilever forces
Implant Overload and Resorptive Remodeling
l If they are excessive however, they can lead to
implant overload and provoke a resorptive remodeling
response of bone around the distal implants.
In this patient a fixed edentulous bridge similar to the one
shown previously, was fabricated for this patient. However,
the cantilever extensions were in excess of 30 mm. Note the
bone loss around the distal implants particularly on the
patient’s left. Eventually this implant fractured.

63. Excessive Cantilever forces
Implant Overload and Resorptive Remodeling
Case Report
This tissue bar uses nonresilient attachments in the distal with a
long cantilever anteriorly and is therefore an implant supported
design. The implants were exposed to tipping forces magnifying
the occlusal loads, in turn leading to a resorptive remodeling
response of the bone around the implants and eventually loss of
the implants.

64. Excessive Cantilever forces
Implant Overload and Resorptive Remodeling
Cantilever
Cantilever
Overlay Dentures in Edentulous Maxilla
! During the eighties, tissue bar designs using four implants, such as the
one above, were commonly used at UCLA to retain overlay dentures. Hader
bar attachments were used anteriorly and in the extension areas.
! Such designs result in most of the posterior occlusal forces borne by the
implants and therefore are implant supported.
! The followup data (collected by the author from his private patients)
indicated significant bone loss and implant failures of the distal implants as
shown in the following table.

65. Excessive Cantilever forces
Implant Overload and Resorptive Remodeling
Cantilever Cantilever
Overlay Dentures in Edentulous Maxilla
Four implanted supported overlay dentures with nonresilient
(Hader) attachments (arrows) and distal cantilevers
Patients # Implants Followup Failures Position Time of
of failed failure
implants
10 40 5-12 yrs. 4 all distal 39-73 mths.
***Failures were attributed to implant overload, with its
resultant loss of bone around the implants

66. Cantilever forces
Implant Overload and Resorptive Remodeling
l Implant Assisted Design – 4 implants
When implant tissue bars with resilient attachments
connected to the distal portion of the bar (ERA type in
this patient) were used in the maxilla the failures after
loading were completely eliminated.

67. Cantilevers and Linear Configurations in
Posterior Quadrants
Mesial and distal cantilevers
l They are particularly detrimental and are therefore
contraindicated when using linear configurations to restore
posterior quadrants. They cause load magnification and
overload the bone around the implant adjacent to the
cantilever.

68. Cantilevers – Implant Overload
l Note the bone loss around the dental implants
adjacent to the cantilever.
Restorations designed in this
fashion have a poor prognosis.

69. Cantilevers – Implant Overload

70. Avoid buccal, lingual and cantilevers
The occlusal tables are
excessively wide in this
case. Buccal and lingual
cantilever forces may
lead in selected patients
to:
Prosthesis failures
• Porcelain fractures
• Screw fractures
Implant overload and
bone loss

71. Occlusal Anatomy and Biomechanics
v Narrow occlusal table
Goal: Reduce the buccal - lingual cantilever effect

72. Avoid buccal and lingual cantilevers
The occlusal table must be narrowed
to avoid buccal and lingual cantilevers.
Molars should be no wider than
premolars as shown in these two
examples.

73. Solitary implants restoring single molars –
Cantilever effect
A B
When the food bolus is applied to the marginal ridge (B), the
restoration is easily tipped because the crown is supported by
such a narrow platform.
Result: Cantilever forces lead to screw loosening, implant
fracture and overload the bone anchoring the implant.

74. Solitary implants restoring single molars
Cantilever effect
Fracture
Implant fractured after 30 months of function

75. Single tooth restorations in the molar
region – Cantilever effect
Mesial cantilever
4 mm
diameter
implant
This implant was too short and too narrow to
withstand occlusal loads and bone loss caused by
the resorptive remodeling response led to its loss.

76. Single Tooth Restorations Distal
Extension Defects

77. Distal Extension Defects

78. Restoration of single molar sites - Solutions
Eliminate the cantilever by using
! Wide diameter
! Multiple implants
In this patient a wide diameter implant was used to
restore the first molar.

79. Restoration of single molar sites
In this patient, two 4 mm diameter implant were used to
restore the first molar. The width of the occlusal table was
limited to the width of the
natural premolar,
thereby elimating any
possible buccal or
lingual cantilevers.
Custom abutment Lingual set screw

80. Restoration of single molar sites
Note:
! Hygiene access for proxy brush
! Note width of occlusal table

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