Removable partial denture design principle... Biomechanics, action of force and movements of RPD

1. Principles of Removable Partial
Denture Design According to
Kennedy Classification
Presented By-
Dr. Ha-Meem Fattaha
Department of Prosthodontics
Sapporo Dental College & Hospital

2. Learning Objectives:
• To formulate denture design according to individual
patient’s oral condition and Kennedy classification.
• To obtain a thorough knowledge of mechanical and
biological factors involving RPD design.
• To prevent any harm to remaining oral structures.
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3. Introduction:
Designing a removable partial denture can be considered
similar to the classic, multifaceted design problem in
conventional engineering. It is important for clinicians
who provide removable partial denture to understand the
possible movements of denture during function.
Thorough knowledge about design principle helps to
provide useful, functional removable partial denture by
understand how to maximize every opportunity for
providing and maintaining a stable prosthesis.
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4. Kennedy Classification:
Kennedy class- I : Bilateral
free end saddle
Kennedy class- II : Unilateral
free end saddle
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5. Kennedy Classification:
Kennedy class- III : Unilateral
bounded saddle
Kennedy class- IV : Single ,
anterior bounded saddle
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6. RPD Classification :
According to support, RPD can be classified as-
• Tissue supported :
Kennedy class i & ii dentures
• Tooth- tissue supported :
Kennedy i & ii dentures
• Tooth supported :
Kennedy class iii & iv dentures
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7. To be successful, how a RPD design should be?
Successful
RPD
Harmless
Simple Comfortable
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8. Essentials of partial denture design :
Design of a partial denture framework should be
developed based on following concepts-
• Where the prosthesis is supported?
• How the support is connected?
• How the prosthesis is connected?
• How the retention and support are connected?
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9. Tooth supported RPD:
To develop the design , determination of support of the
denture is necessary. Following factors of the abutment
tooth must considered-
1. Periodontal health
2. Morphology of crown and root
3. Crown-root ratio
4. Bone index area
5. Location of the tooth in the arch
6. Length of edentulous span
7. The opposing dentition
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10. Tooth-tissue supported RPD:
In tooth- tissue supported partial denture, attention should
be given both in -
• Abutment tooth
• Edentulous ridge areas
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11. Edentulous ridge area:
In evaluating the potential support available from these
areas, consideration must be given to-
1. The quality of the residual ridge
2. The extent to which the residual ridge is covered by
denture base
3. The type and accuracy of the impression registration
4. The design characteristics of the partial denture
framework
5. The anticipated occlusal load
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12. A, The longer the edentulous area covered by the denture base, the greater the
potential lever action on the abutment teeth.
B. The flat ridge will provide good support, poor stability.
C. The sharp spiny ridge will provide poor support, poor to fair stability.
D. Displaceable tissue on the ridge will provide poor support and poor stability.
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13. What is biomechanics?
Biomechanics basically deals with application of
mechanical principles to biological tissues.
According to GPT, Biomechanics is an application of the
principles of engineering design as implemented in living
organism.
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14. Why dentist should know this?
In the oral cavity one would find a number of sources of
stress generation. However when a dentist try to create
an artificial replacement of that natural component which
is lost, he should know the possible movements of the
prosthesis during function. Should be able to logically
design the component parts of RPD to control these
movements, prevent harm to the remaining oral
structures and make it fully functional and adaptable.
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15. Forces are prime biomechanical concern.
… WHY?
RPD are objects that move when placed in function. It has
to be in a state in which opposing forces or influences
are balanced. Keeping in mind “Perpetual preservation
of what is remaining is more important than meticulous
replacement of what is lost”, forces should be given
major consideration while designing a partial denture.
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16. Considerations related to force:
Goal:
Minimize the
destructive
force
1.
Magnitude
of force
2.
Direction
of force
3.
Duration
4.
Frequency
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17. How to balance effects of force:
Forces
can be
minimized
by
Selection
of design
Selection
of
abutment
tooth
Location of
components
of RPD
Development
of
harmonious
occlusion
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18. Forces acting on RPD:
The forces acting on appliance can be vast in magnitude
and direction. They can be broadly categorized as –
1. Vertical force
- Displacing force
- Dislodging force
2. Horizontal force
3. Torsional force
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19. Vertical force:
• Displacing stress:
Those force which transmits along the long axis of the
teeth in a crown to apex direction and also on the ridge
mucosa, are known as displacing force. These are least
harmful if within physiologic limit.
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20. • Dislodging force:
These are forces which tend to lift the partial denture
form its rest position.
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21. Horizontal force
They originate as a component of rhythmic chewing.
These forces are effective in lateral and anterior-
posterior direction. These lateral forces are most
damaging.
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22. Torsional force:
It is a combination of vertical and horizontal force. Torsion
is noted most frequently where a long segment acts
upon the first abutment it engages. Where the ridge
mucosa has higher resiliency, torque is higher. Torque
applies rotation about a fixed point.
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23. Rotational movements of RPD:
Movements of RPD does not occur singularly. All occur at
the same time. Gross movement of the denture may be
small but potential damage to the abutment tooth may
be large.
The greatest movement possible found in the tooth-tissue
supported prosthesis which is rotation.
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24. When a force is placed on the distal extension base, the
framework will rotate in relation to the three cranial
planes.
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25. How this movements can be prevented?
Rotation around vertical axis:
Resisted by-
• Reciprocal clasp arms
• Minor connectors
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26. How this movements can be prevented?
Rotation around longitudinal axis:
Resisted by-
• Rigidity of major and minor
connector and their ability to resist
torque.
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27. How this movements can be prevented?
Rotation around horizontal axis:
Resisted by-
• Action of retentive clasp
arms on terminal abutments.
• Action of stabilizing
minor connectors
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28. Problems of free end saddle:
As in free end saddles edentulous ridge must bears some
part of masticatory load, ridge resorption can occur.
On the other hand, the abutment tooth is subjected to
torques which may lead to premature break down of its
supporting bone.
That’s why formulating treatment plan of free end saddle
dentures are more difficult.
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29. Treatment of free end edentulous area:
Following methods can be used to overcome problems
with free end saddle dentures-
1.Reducing the load by -
i)Using canines and premolar instead of premolars
and molars.
ii)Using narrow teeth.
iii)Leaving a tooth off the saddle.
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30. 2. Distributing the load between teeth and ridges.
i) By varying the connection between clasp and saddle-
-Stress breaking
-Combining rigid connector and gingivally approaching
clasp
-Combining rigid connector and occlusally approaching
clasp
ii) By anterior placement of occlusal rest.
iii) By mucocompression.
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31. 3. Distributing the load widely.
i) Over more than one abutment tooth on each side.
ii) Over the maximal area of edentulous ridge.
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32. Treatment of tooth bounded edentulous
area:
Horizontal forces acting on Kennedy class-iii prosthesis
may lead to instability of the denture. Following
measures can be taken to avoid this problem-
1. Provision of lingual and buccal cusp contacts.
2. Use of wide occlusal rests.
3. Provision of adequate bracing.
4. Provision of adequate retention.
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33. Conclusion:
All of the previous slides discuss factors that influence
retention, stability and resistance form of partial denture.
These should be considered during designing RPD to
provide best service and function of the prosthesis.
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34. References:
• Partial Dentures ( Fourth Edition)
By John Osborne,George Alexander Lammie
• McCracken’s Removable Partial Proshodontics
( Eleventh Edition)
By Alan B. Carr, Glen P. MacGivney, Devid T. Brown
• Textbook of Prosthodontics
By Deepak Nallaswamy
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