principles of removable partial denture design

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2. Presented by
Dr.Abbasi Begum .M
PG dept. of Prosthodontics
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3. 1. Introduction
2. Biomechanics of RPD.
3. Biomechanical considerations.
4. Possible type of movement taking place.
5. Differences in design between tooth supported and tissue
supported prosthesis.
6. Factors contributing to amount of stress transmitted to the
abutment.
7. Design considerations of prosthesis to control stress
8. conclusion
9. Reference.
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5.  1. A thorough, general examination of the mouth with
roentgenograms.
 2. A thorough prophylaxis, and the treatment of, and
removal of all questionable teeth.
 3. The repair of all carious lesions.
 4. Obtaining a preliminary impression and study casts
and articulating them.
 5. Drawing a tentative design on study casts, preparing
occlusal rests and teeth by grinding.
Planning and designing removable partial dentures-
Colonel Arthur H. Schmidt -JPD-November 1953Volume 3, Issue
6, Pages 783–806
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6.  6. Obtaining an accurate impression after all teeth are
prepared.
 7. Remembering that the basis for all successful partial
dentures is summed up in the words

 Plan—Design—Construct.
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7.  The principles for removable partial denture design
were first expounded by A.H. Schmidt in 1956
1. The dentist must have a thorough knowledge of
both the mechanical and biologic factors involved
in removable partial denture design
2. The treatment plan must be based on a complete
examination and diagnosis of the individual patient
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8. 3.The dentist must correlate the pertinent factors and
determine a proper plan of treatment.
4.A removable partial denture should restore form and
function without injury to the remaining oral
structure.
For example in restoring occlusion, the prosthesis
should also restore a normal or desirable facial contour
and not impede the normal movement of the tongue
and other tissues.
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9.  Forces due to a removable restoration can be widely
distributed, directed and minimized by
 the selection
 Design
 The location of components of removable partial
denture and
 By developing a harmonious occlusion
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10. Why is it important to
understand the
biomechanics?????????
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11.  Removable partial denture  forces in oral
cavity.
 causes movement of various component of
the RPD.
 So its important to understand the
movements taking place on these
components and logically help design them
in order to control the movements taking
place in them.
 what are the types of movements taking
place in the oral cavity????
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12. Sagittal plane
Horizontal plane
Frontal plane.
Stewart-clinical removable partial prosthodontics-3rd edition
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14.  Designing of an rpd is based on both biological and
mechanical considerations.
 Most of us dentist consider the mechanical aspects but it is
also important to understand the biological aspect.
 Biological aspects :-
1. whether tooth used for support can bear the loads
falling on it.
2. The type of underlying mucosa.
 The resistance to load from a tooth is based on the amount
of force falling on it, the duration of force and direction of
force applied.
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15. 1. A RPD  lever, mainly distal extension.
 Based on the type of lever the forces applied on the
abutment teeth varies.
 The lever has the potentiality to increase the
forces falling on the tooth.
2. Cantilever type design rpd should be avoided.
3. Tooth tends to withstand vertical forces than non
vertical forces because of the number of pdl fibres
involved.
4. An abutment tooth will withstand non vertical forces
if the forces are applied as close to the horizontal axis
of rotation.
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16. The Inclined Plane
In this system, two objects share an interface that forms an
acute angle with the horizontal plane.
Application of vertical power (P) causes the objects to move in
opposite directions 16

17.  consist of a fulcrum (F) about which the lever rotates, a
power source (P) that mobilizes the lever to do work,
and a resistance (R) to which the lever does work.
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18.  Fulcrum is
Fulcrum is placed between effort and load
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20. The most efficient lever The most inefficient
lever is a third-class
lever
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21.  When externally loaded, a distal extension removable
partial denture may function as a first-class lever.
 A fulcrum (F) exists near the rest seat. The power that
activates the lever results from occlusal loading (L) of
the extension base.
 As the lever functions, aspects of the prosthesis
anterior to the fulcrum will move in a superior
direction
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22.  Forces arising from three principal fulcrums
principal fulcrum line-
A horizontal fulcrum line
 Rotational movement around this fulcrum line
is the greatest in magnitude
 but , not necessarily the most damaging.
 Resultant force on the abutment teeth - mesio-
apical or disco-apical
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23.  A second fulcrum line - in the sagittal plane and
extends through the occlusal rest on the terminal
abutment and along the crest of the residual ridge on
one side of the arch
 This fulcrum line controls the rotational movements
of the denture in the frontal plane
 easier to control
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24.  The third fulcrum- located in the vicinity of the
midline, just lingual to the anterior teeth
 Oriented vertically and controls rotational movement
in the horizontal plane
 Forces can be extremely damaging
 Significant attention during the design process.
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25. Tooth supported
 Class III,class IV
 Derive support from teeth
 The movement potential is
less because the teeth
provide resistance to
functional loading.
 single universal design can
be followed for teeth
supported prosthesis
 The denture base is made
up of metal bases.
Tissue supported
 Seen in classI and classIIcases.
 Tissue  maximum amount of
support (tissue provides primary
support and teeth provide
secondary support).
 Too much tissue movement
because of the dynamic state of
the tissue.
 Multiple complex design have to
followed.
 Denture base  acrylic resin
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26. 1) Length of edentulous span:-
2) Quality of ridge support
3) Clasp flexibility
4) Clasp design
5) Length of the clasp
6) Material used for clasp construction
7) Surface characteristics of an alloy
8) Occlusal harmony:-
Stewart-clinical removable partial prosthodontics-3rd
edition
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27. Longer edentulous span
longer denture base
greater force transmitted
to abutment teeth
Retain a Posterior abutment to serve as vertical
support, even as an overdenture abutment
Improved patient service
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28. Broad ridges with parallel sides
longer flanges
stabilize the denture against lateral forces.
A) Form of residual ridge
 Better support by ridge less stress on abutment teeth
 Large well formed ridges  less stress on abutment
 Small thin, knife like ridges are very poor.
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29.  Influences magnitude of stresses transmitted to
abutment teeth.
 Healthy mucosa capable of bearing greater functional
loads
 Soft, flabby, displaceable
mucosa
 little vertical support of
denture
 allows excessive movement
of denture
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30. 30

31.  More flexible the retentive arm of clasp  less stress
to abutment tooth
 Wrought-wire retentive clasp Class I and Class II
applications
 It has tendency to produce very high amount of lateral
stress.
 But not indicated in cases with poor ridges as it cannot
with stand lateral stresses leading to heavy stresses on
the ridges.
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32. Clasp design
Clasp should be passive once framework seated
completely
It should be such that it doesn't apply force on the
teeth while it is seated on the teeth.
So complete seating of prosthesis is mandatory.
Reciprocal arm should designed that it lies above
the height of contour.
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33. Length of clasp
Increase in length
Increased flexibility
•Doubling the length of a clasp
will increase its flexibility fivefold
•Clasp length may be increased
by using a curved, rather than
straight, course on an
abutment tooth
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34. Material
•Co cr alloys based clasp apply more force on the
abutment teeth than gold based alloy.
•So thinner diameter co cr clasp can be used to
reduce the amount of force applied.
Surface characteristics of an
alloy
Gold crowns  more resistance to clasp than enamel.
Abutment restored with gold experiences more forces than
intact enamel.
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35. 8. Occlusal harmony:-
It plays an important role.
Deflective contacts should be avoided.
Prosthesis opposing natural dentition face more
forces than from a natural dentition.
Occlusal force should be directed to middle of
residual alveolar ridge  closer to the abutment.
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36. Ideally, the occlusal load should be applied in the
center of the denture-bearing area, both
anteropostenorly and faciolingually.
The second premolar and first molar regions
represent the best areas for the application of the
masticatory loads.
Artificial teeth should be arranged so that the
bulk of the masticatory forces are applied in these
areas
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37.  Direct retention
Retentive clasp arm -Responsible for transmitting
most of the destructive forces to the abutments
 So retentive clasp arm should provide adequate retention with least
forces.
 This can be done by providing retention from other components of
denture.
 the support and stability of the prosthesis also may be improved.
 Other components that provide additional retention are:-
 Adhesion cohesion.
 Frictional grip.
 Neuromuscular control.
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38.  Clasp position :-
 Often, the spatial distribution of retentive clasps
is more important to retention than the number
of clasps.
 The following configurations can be followed
while determining clasp position.
1. Quadrilateral configuration:- it is used in
class 3 situation with modification space.
2. Tripodal configuration:- class 2
modification 1
3. Bilateral configuration
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39. 1. Quadrilateral configuration:-
 Class 3 with modification space.
 Clasp assembly on both abutment teeth
adjacent to edentulous space.
 In case of absence of modification space
clasp assembly anteriorly and posteriorly
are given on the dentulous opposite arch.
2. Tripodal configuration:-
 Class 2 with modification space.
 Clasp present adjustment to the
edentulous space.
 On the modification space side clasp on
both the abutment teeth.
 If modification is absent clasp placed as far
anteriorly and posteriorly on the teeth.
 Not as effective as quadrilateral
configuration but better in class 2 cases.
3. bilateral configuration:-
 Class 1 situations.
 Provides least stress reduction.
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40. CLASP DESIGN:-
Cast circumferential clasp:-
•Class 2 and class 1 cases clasp assembly
involving disto occlusal rest and retentive tip
involving mesiofacial undercut is prevented.
•Terminal end of such clasp  tipping forces on
the abutment teeth.
•A clasp that originates from the mesioocclusal
rest and engages the distofacial undercut or a
reverse circulate clasp should be used.
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41. Vertical projection clasp:-
•T clasp or modified t clasp can be used on an
abutment adjacent to the distal extension space.
•It is used when the a distofacial undercut is seen
on the abutment.
•It is not indicated in case of mesiofacial
undercut.
•I clasp is better used involving mesiofacial
undercut and mesioocclusal rest seat.
•It doesn’t apply any stress on teeth.
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42. 42

43. Combination clasp:-
Used when a distal extension is presented with a
mesiofacial undercut.
Flex more and in multiple spatial planes..
Combination of both cast and wrought wire is used.
Wrought wire is used as the retentive arm and cast metal
is used as the reciprocal arm
More flexible and produces less stress on the abutment.
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44.  Splinting two or more teeth increases the periodontal
ligament area and distributes applied loads more
effectively
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45.  Loss of periodontal attachment has occurred
 Abutment tooth - tapered root or short roots to the
extent that there is not an acceptable amount of
periodontal ligament attachment present
 The joining of two such teeth by crowns will produce
an acceptable multirooted abutment tooth
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46.  Splinting  removable prosthesis
 Not done if fixed splinting is possible.
 The splinting consists of clasping more than one tooth on
each side of the arch and using additional rests for
increased support.
 All clasps need not to be retentive.
 Prepared guiding planes may provide additional horizontal
stability.
 Results in decreased mobility.
 Cross arch stabilization
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47.  Swing-Lock partial denture, can be used to splint teeth
effectively
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48.  Helps resist rotation and/or displacement of a
removable partial denture
 The indirect retainer is essential in the design of Class
I and Class II removable partial dentures
 The indirect retainer or retainers must be
positioned as far anterior to the fulcrum line as possible
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49.  not as critical in a Class I arch
 Required- modification space on the tooth-supported
side of the arch, abutment teeth on both sides of the
space should be rested .
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50.  Class III situation usually doesn’t need a indirect
retainer as there is no lever effect.
 Class IV situation it just opposite to the class I
situation with indirect retainer present as far
posteriorly as possible.
 Auxiliary rests
Mesio-occlusal rests on the first
premolars serve to support this long
lingual plate major connector
Auxiliary rests
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51.  Smoothly functioning occlusion in harmony with TMJ &
neuromusculature-minimize the load transferred to the
teeth and soft tissues.
 The contacts of the remaining natural teeth should be
the same whether the removable partial denture is in
mouth or not.
 The number of teeth replacing the natural teeth should
be reduced to decrease the amount of force falling on
the ridge.
 Artificial posterior teeth should have sharp cusp with
low incline plane in order to increase the cutting
efficiency and prevent horizontal interferences force.
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52.  The denture base should extend as much denture bearing
area as possible in order to dissipate the forces falling on
the prosthesis.
 Denture flanges should be as long as possible.
 Maxillary denture base extend  maxillary tuberosity.
 Mandibular denture base  retromolar pad.
 Overextension of denture base should be avoided.
 Accurate adaptation of denture base is necessary for proper
retention of denture base.
 The external polished surface of the denture should be
contoured properly in order to aid in retention of the
dentures.
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53. Major connectors
 A major connector  maximum coverage area  dissipate
the occlusal forces falling on it.
 In maxilla a palatal full coverage major connector is more
preferred as it contacts all the remaining teeth with a
lingual plate thus helps in dissipating the forces.
 In mandible the lingual plate major connector Is most
preferred because it covers the whole lingual surface of
anterior teeth.
 Thus distributing the forces to all the teeth.
 It is particularly helpful in splinting periodontally
weakened teeth.
 It also provides rigidity and cross arch stabilization.
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54. Minor connector
 The minor connector connecting the guide plane to
the major connector plays a very important role in
dissipating functional stresses. Because of its close
adaptation to the abutment teeth.
 This minor connector helps in two major functions.
 It provides a single path of insertion.
 Improved stability by providing increased resistance to
horizontally directed forces
 Additional guide planes can be incorporated on
other teeth to help dissipate the lateral stresses
falling on the single tooth.
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55.  Rest seats are essential as they transmit force
vertically along the long axis of the teeth.
 rest seats prevent formation of any lateral stresses.
 Rest seats should be designed in such a way that
they are less than 90 degrees to the path of
insertion.
 Thus helping the rest seat to grab the tooth
securely and prevent its migration.
 Occlusal rest seats should be rounded and some
amount of space should be present between the
rest and rest seat to allow free movement as a
movement of ball and socket joint.
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56.  The principles of surveying, the significance of the
survey line, the relation of the clasp to the survey line,
and the opportunity presented by tilting the cast to
control the location of undercuts are basic factors
which will enable the prosthodontist to solve any
removable partial denture problem
 Thorough understanding and application of these
these basic principles will lead to a successful
treatment outcome .
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57.  Mc crackens removal partial denture. 11th edition.
 Stewarts clinical removable prosthodontics. 3rd edition
 Beumer J, Curtis TA, Firtell DN. Maxillofacial
rehabilitation, prosthodotics and surgical
considerations.
 Planning and designing removable partial
dentures-Colonel Arthur H. Schmidt -JPD-
November 1953Volume 3, Issue 6, Pages 783–806
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