This document discusses biomechanics considerations for implant treatment planning and prosthesis design. It emphasizes controlling occlusal factors like cusp angles and occlusal table width to reduce cantilever effects and implant overload. Custom abutments are highlighted as a way to control these factors. The importance of proper implant positioning and attachment of implants to natural teeth with rigid rather than semi-precision attachments is also stressed.

1. 8b. Biomechanics and Treatment
Planning (cont’d)
John Beumer III DDS, MS
Division of Advanced Prosthodontics, Biomaterials and
Hospital Dentistry, UCLA
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2. Custom abutments and the width of
Note the buccal angulation of the
implants. Custom abutments can
be used to minimize the width of
the occlusal table.

3. Custom abutments and the width
of the occlusal table
*Note lingual
set screw
channels

4. Custom Abutments
Final prosthesis with ideal occlusal width.

5. Misalignment of Implants - Custom abutments
The implants placed in the right mandible
were inclined towards the lingual

6. Misalignment of Implants - Custom abutments
This technique permits the clinician to control two key occlusal factors –
width of the occlusal table, and the cusp angles. Result: Reduced load
magnification and less chance of implant overload.

7. Misalignment of Implants - Custom
Note width of the
occlusal table
*Note size of the embrasures
between the implants and the
implants and the dentition.

8. Connecting Implants to Natural Dentition
How do you minimize cantilever forces?
Semiprecision (nonrigid) vs rigid attachments

9. Connecting Implants toto anterior abutment
Natural Dentition
Posterior implant attached
Loads applied in the pontic area
Rigid attachment Nonrigid attachment
Nishimura et al, 1999

10. Connecting Implants to Natural Dentition
Rigid vs non rigid attachments
No difference as long as the nonrigid (semi-
precision) attachments remain fully seated

11. Semi-precision Attachments
Problems
v Intrusion of the natural tooth
leading to:
v Cantilever affect
v Load magnification
v Resorptive remodeling response
v Bone loss (arrows)
Semi-precision
attachment

12. Semi-precision attachments
Intrusion of the natural tooth abutment predisposes to
This phenomenon leads to load magnification and in selected
patients, bone loss around the implant adjacent to the cantilever.

13. Semi-precision attachments
Intrusion of the natural tooth abutment
l Eleven
years after delivery the patient noticed the premolar
began to intrude. Exam revealed that the screw retaining the
molar had become loose, hence the rotation of this crown.

14. Rigid Attachments*
Screw retained tube
lock attachment
*Shared support

15. Rigid Attachments*
Screw retained tube lock attachment
*Shared support

16. Rigid Attachment Systems*
Cement retained
with copings
*Shared support

17. Occlusal Anatomy and Biomechanics
• Narrow occlusal table
• Flat cusp angles
• Lingualize or buccalize

18. Occlusal Anatomy and Biomechanics
v Narrow occlusal table
Goal: Reduce the cantilever effect

19. Diagnostic Waxup
The prosthesis dictates the number and position of
the implants. Therefore, a diagnostic waxup should
be performed on even the simplest of cases.
Implants should be placed in tooth positions
Implants should be placed so that occlusal loads can be
directed axially
Proximal positions should be avoided

20. Implant Placement
v Perpendicular to the occlusal
plane
v Tooth positions
v Avoid proximal positions
v Screw access channel should
exit in the central fossa

21. Advantages of Proper Implant
Positioning
l Proper emergence profiles can be
developed
l Space available interproximally for
hygiene access (arrow)
l Control of occlusal anatomy (narrowed
occlusal table and flat cusp angles)
l Occlusal loads delivered axially
l Abutment selection simplified

22. Magnitude of the occlusal load is
controlled by:
v Biting forces during normal function
v Biting forces during para-function
v Buccal-lingual width of occlusal table*
v Cusp angles*
v Presence and length of cantilevers*
v Angulation of the implants relative to the
occlusal plane*
*Factors controlled by the clinician.

23. Strategies to Avoid Implant Overload
and Mechanical Failures
Edentulous patients – Implant Supported Restorations*
v Avoid excessive cantilever length in implant supported*
restorations ( limited to 2 times A-P spread in the
mandible and ½ times A-P spread in the maxilla).
v When planning for implant supported restorations place
adequate numbers of implants (minimum number - 4 in
the mandible, 6 in the maxilla).
When these conditions cannot be met overlay dentures with
implant assisted tissue bar designs* are recommended.
*In an implant supported prosthesis all the forces of occlusion are
born by the implants whereas in an implant assisted prosthesis,
the occlusal forces are shared between the implants and the
denture bearing areas.

24. Strategies to Avoid Implant Overload and
Mechanical Failures
Posterior quadrants of partially edentulous patients
v Place implants perpendicular to the occlusal plane (Note that the
occlusal plane is not flat – Curve of Wilson, Curve of Spee)
v When in doubt, always add the third implant
v Avoid use of cantilevers in linear configurations
v If required to attach to natural dentition, do so with a rigid
attachment system
v Control the occlusal factors (cusp angles, width of the occlusal
table)
v Avoid use of short implants (less than 10 mm)
v Avoid use of implant diameters of less than 4 mm
When these conditions cannot be met conventional
removable partial dentures are recommended

25. Pertinent Dental History Findings
Bruxism
Chronic bruxism predisposes to:
a) Implant fractures
b) Fracture of retaining screws
c) Implant overload with resorption of bone around
the implant
Note: The 3.75 mm diameter screw shaped implant is
particularly prone to fracture in such patients.

26. Bruxism - Case Report
This is a five year followup x-ray of
a patient with an implant
supported fixed partial denture.
The patient was a heavy bruxer.
Six months later he presented
with significant bone loss around
both implants.
Closer exam revealed
both implants to be
fractured .

27. Bruxism -Case Report
This patient did well with this
implant supported fixed partial
denture for more than four years
(note 4 year followup x-ray).
However, soon thereafter, the
anterior implant fractured, the
bridge was removed and a
trephine used to remove the
implant.

28. Implant Fractures
vThe 3.75 mm diameter screw shaped implant is particularly
prone to fracture* when used to support fixed partial dentures in
posterior quadrants of partially dentulous patients. Note the
difference between the 4 mm implant on the right and the 3.75
mm implant on the left. .
vThe thickness of the wall of the 3.75 mm
screw shaped implant is only .4 mm.
vFracture rate for the 3.75 mm diameter
screw shaped implant has been reported
to be as high as 7% in 5 year followup
studies.
We therefore recommend that implants of
at least 4 mm in diameter be used in
posterior quadrants. 3.75 mm

29. Strategies for the Moderate Bruxer
a) Use a wider diameter implant
b) Add the third implant
c) Narrow the occlusal table
d) Flatten the cusp angles

30. Strategies for the Moderate Bruxer
Use of Wide Body Implants – 5 mm
Five mm diameter implants were used in this
patient. The risk of implant fracture, retaining
screw fracture and screw loosening is almost
eliminated. However, surgical placement is more
difficult and the implants are still subject to occlusal
overload in the chronic bruxer.

31. Restoration of the Cuspid Region
Less predictable
a) Lateral forces
b) Linear configurations

32. Restoration of the Cuspid Region
Patient presented with partial anodontia.
The lateral incisors, cuspids and
premolars were missing.
Linear configurations restoring the cuspid
region, such as the one in this patient, are
unpredictable

33. Restoring the Cuspid Region
Curvilinear arrangements such as in this patient
are more capable of withstanding lateral forces.

34. 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
Courtesy Dr. R. Faulkner
and predictability

35. Implants in the Maxillary Cuspid
Region Mutually Protected Occlusion
(Group Function)
Patient in right working position.
Note lateral guidance is provided
by the premolars and the central
incisor.
Result: Lateral forces on
the implants are
minimized. Courtesy Dr. M. Hamada

36. Anterior Guidance with Centric
Only Contact
Note: The cusp Result: Lateral
angles are flat forces on the
and the occlusal implants are
tables are minimized
narrow

37. Anterior Guidance with Centric Only Contact
Issues
v Linear configuration
v Posterior implants
in poor quality bone
v Posterior implants
shorter than desired
(10 mm)

38. Anterior Guidance with Centric Only Contact
Solution
v Anterior guidance with remaining
anterior dentition
v Note buccal lingual dimension of
occlusal tables (premolar sized)
v Posterior implant used for addition
support and stability
v Note proxy brush access

39. Anterior Guidance with Centric Only Contact

40. Implants in the Maxillary Cuspid Region
Mutually Protected Occlusion (Group Function)
Issues
v Insufficient number for the corner of
the arch
v Linear configuration with anterior
cantilever
v Slight labial-buccal angulation

41. Implants in the Maxillary Cuspid Region
Mutually Protected Occlusion (Group Function)
Angulation
v Addressed with milled customized abutments
milled to a three degree taper

42. Implants in the Maxillary Cuspid Region Mutually
Protected Occlusion (Group Function)
v Finished prosthesis
v Note the hygiene access
v Retention is by lingual set screws

43. Implants in the Maxillary Cuspid Region
Mutually Protected Occlusion (Group Function)
v Guidance in the left working position is accomplished by the
central incisor and the maxillary molars. The teeth restored
with implants are not in contact during excursion
v Lateral forces on the implants are minimized and the risk
overload is diminished.
v Remember, parafunctional habits are the most destructive

44. Restoring the Cuspids: Mutually Protected
Occlusion (Group Function)
Patient in right and left working position.
Note lateral guidance is provided by the
premolars and the central incisor.
Result: Lateral forces on
the implants are minimized.
Right working Left working

45. Restoring the corner of the arch :
Mutually protected occlusion
Group function
was used to
distribute lateral
loads as widely as
possible in order
to reduce the risk
of implant
overload

46. Restoration of the Cuspid Region
Errors made in this patient:
a) Insufficient number of
implants
b) Connection with natural
dentition made with semi-
precision attachment

47. Strategies to Avoid Implant Complications
Posterior quadrants of partially edentulous patients
Place implants
perpendicular to the
occlusal plane (Note that
the occlusal plane is not
flat – Curve of Wilson,
Curve of Spee)
Place implants in tooth
positions
When in doubt,
always add the third
implant
Avoid use of cantilevers in
linear configurations

48. Strategies to Avoid Implant Complications
Posterior quadrants of partially edentulous patients
If required to attach to
natural dentition, do so with a
rigid attachment system
Control the occlusal factors
(cusp angles, width of the
occlusal table)
Avoid use of
short implants
(less than 10 mm
Restore anterior
guidance

49. When these conditions cannot be met
conventional removable partial
Mastication efficiency of distal extension
RPD’s is equivalent to implant supported fixed
partial dentures.

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