Principles of RPD designing

1. Principles of
Removable Partial
Denture Design

2. Introduction
Removable partial dentures by design are intended to be
placed into and removed from the mouth.
The forces occurring with removable prosthesis function
can be widely distributed and directed, and their effect can
be minimized by appropriate design of the removable
partial denture

3.  The strategy of selecting component parts for a
partial denture to help control the movement of the
prosthesis under functional load has been
highlighted as a method to consider for logical
partial denture design.
 The requirements for movement control are
generally functions of whether the prosthesis will
be tooth supported or tooth-tissue Supported.

4.  Colonel Arthur H. Schmidt (1953) introduced 5
basic principles in designing of Removable Partial
Denture :-
1. Dentist must have a working knowledge of both the
mechanical and biological factors included in R.P.D
design and construction.
2. Any plan of restoration must be based on complete
examination and diagnosis of individual patient.
3. The dentist not the technician should correlate the
pertinent factors and recommend a proper plan of
treatment.
4. A R.P.D should restore form and function without
injury to the tissue.
5. A R.P.D is a form of treatment ,not a care.

5. Difference in Prosthesis support
All forces against fixed partial denture are directed down long axis of abutment
teeth (arrows).
Tooth-supported, or Class III, removable partial denture, like fixed partial denture, is
supported by abutments. Most forces against it are transmitted down long axis of abutment
teeth (arrows). However, limited movement, including a tendency to lift in function, is possible.

6.  Of all partial dentures, an all-tooth-supported, or Class III,
partial denture can best resist forces because it, like the
fixed partial denture, is supported by abutment teeth
 1 A, Kennedy Class I partially edentulous arch. Major support for denture bases must come from
residual ridges, tooth support from occlusal rests being effective only at anterior portion of each
base. B, Kennedy Class III, mod 1, partially edentulous arch, which provides total tooth support for
prosthesis. Removable partial denture made for this arch is totally supported by rests on properly
prepared occlusal rest seats on four abutment teeth.
 Classes I, II, and IV removable partial dentures are
subjected to greater stresses because their support is a
combination of tooth and soft tissue

7.  A removable partial
denture in the mouth can
perform the action of two
simple machines, the lever
and the inclined plane
 If the lever rests against
its support and a weight is
applied at another point,
rotation or movement will
occur around the support.
The support is known as
the fulcrum, and
movement takes place
around the fulcrum.

8.  There are three types of levers, first-, second-,
and third-class, and each magnifies or disguises
the force to a different degree
Top, first-class lever. Fulcrum is in center, resistance is at one end,
and effort, or force, is at opposite end. This is most efficient and
easily controlled lever.
Center, second-class lever with fulcrum at one end, effort at
opposite end, and resistance in center. This type is seen as indirect
retention in removable partial dentures.
Bottom, third-class lever with fulcrum at one end, resistance at
opposite, and effort in center. This class is not encountered in
partial dentures.

9.  The inclined plane is the other simple machine to
be concerned with. Forces against the inclined
plane may result in deflection of that which is
applying the force or may result in movement to
the inclined plane. Neither of these results is
desirable.
 It is in distal extension removable partial dentures
that the type of prosthesis controlling stress is
important.
 The all tooth-supported partial denture is rarely
subjected to induced stresses, because leverage-
type forces are not involved and there are no
fulcrums around which the partial denture may
rotate. Inclined planes are also not a factor when
the partial denture is tooth supported.

10.  The distal extension partial denture, on the other
hand, is subjected to rotation around three
principal fulcrums
Horizontal fulcrum line passing
between two principal abutment
teeth controls rotational motion
of denture toward or away from
supporting ridge.
Second rotational fulcrum
extends from occlusal rest on
terminal abutment posteriorly
along crest of residual ridge. This
fulcrum controls rocking, or side-
to-side, movement that takes
place over crest of ridge. In a
Class I arch there are two such
fulcrums.

11. Third fulcrum is vertical and is located in mid-line lingual to anterior
teeth. It controls movement of denture in horizontal plane.

12.  Robert B Potter , Ralph C Appleby, and Cliffton D Adams (1967) :
 Certain important biomechanical principles apply to the design of
all R.P.D, these are :-
 A modified T bar or I bar engaging the distobuccal retentive area
results in action similar to second class lever, when downward
pressure is applied to partial denture, the clasp tip will also have
downward movement thereby minimizing lateral stress on the
abutment tooth.
 Extra coronal retainers change the contour of abutment teeth.
 Lingual and palatal major connectors must be rigid to transmit
lateral stresses to other parts of the partial denture

13. Differentiation between two main types of
Removable Partial Denture
 It is clear that two distinctly different types of removable
partial dentures exist.
 Certain points of difference are present between the Kennedy
Class I and Class II types of partial dentures on the one hand
and the Class III type of partial denture on the other.
1. The first consideration is the manner in which each is
supported. The Class I type and the distal extension side of
the Class II type derive their primary support from the tissue
underlying the base and secondary support from the
abutment teeth
The Class III type derives all of its support from the
abutment teeth

14. 2- Second, for reasons directly related to the
manner of support, the method of impression
registration and jaw record required for each
type will vary.
3- Third, the need for some kind of indirect
retention exists in the distal extension type of
partial denture, whereas in the tooth-supported,
Class III type there is no extension base to lift
away from the supporting tissue because of the
action of sticky foods and movement of the
tissue of the mouth against borders of the
denture.
4- Fourth, the manner in which the distal extension
type of partial denture is supported often
necessitates the use of a base material that can
be relined to compensate for tissue changes.

15. Differences in Support
 The distal extension partial denture derives its major support from
the residual ridge with its fibrous connective tissue covering. The
length and contour of the residual ridge notably influence the
amount of available support and stability
A, The longer the edentulous area
covered by the denture base, the greater
the potential lever action on the abutment
teeth.
B, Flat ridge will provide good support,
poor stability.
C, Sharp spiny ridge will provide poor
support, poor to fair stability.
D, Displaceable tissue on ridge will
provide poor support and poor stability.

16. Impression Registration
 An impression registration for the fabrication of a
partial denture must fulfill the following two
requirements:
 The anatomic form and the relationship of the
remaining teeth in the dental arch and the
surrounding soft tissue must be recorded accurately
so that the denture will not exert pressure on those
structures beyond their physiological limits.
The elastic impression
materials,such as irreversible hydrocolloid (alginate),
mercaptan rubber base (Thiokol), silicone impression
materials (both condensation and addition reaction),
and the polyethers

17.  The supporting form of the soft tissue underlying
the distal extension base of the partial denture
should be recorded so that firm areas are used as
primary stress-bearing areas and readily
displaceable tissues are not overloaded.
 No single impression material can satisfactorily
fulfill both of the previously mentioned
requirements.
 Recording the anatomic form of both teeth and
supporting tissue will result in inadequate support
for the distal extension base.
 This is because the cast will not represent the
optimum coordinating forms, which necessitates
that the ridge be related to the teeth in a
supportive form.

18. Differences in Clasp Design
 A fifth point of difference between the
two main types of removable partial
dentures lies in their requirements for
direct retention

19.  The tooth-supported partial denture, being totally
supported by abutment teeth, is retained and stabilized
by a clasp at each end of each edentulous space
The only requirement of such clasps is
that they flex sufficiently during placement and removal of the
denture to pass over the height of contour of the teeth in
approaching or escaping from an undercut area,
Cast retentive arms are generally used for this purpose. These may
be either of the circumferential type, arising from the body of the
clasp and approaching the undercut from an occlusal direction, or
of the bar type, arising from the base of the denture and
approaching the undercut area from a gingival direction.

20.  In the combination tooth- and tissue-supported
removable partial dentures,
because of this tissue
ward movement, those elements of a clasp that
lie in an undercut area mesial to the fulcrum for a
distal extension (as is often seen with a distal
rest) must be able to flex sufficiently to dissipate
stresses that otherwise would be transmitted
directly to the abutment tooth as leverage

21. SURVEY LINES
 A survey line is a line produced on a cast by a surveyor marking
the greatest prominent of contour in relation to the planned path
of placement of a restoration. (GPT 7)
 The survey line marks the height of contour of the tooth.
 Blatterfein divided the buccal and lingual surfaces in to two
halves and described them as the near zone , the area which is
closer to the edentulous space and the far zone , the area away
from the edentulous space. The proximal surface can also be
described in the same manner.
 Survey lines can be classified as:
 HIGH SURVEY LINE
 MEDIUM SURVEY LINE
 LOW SURVEY LINE
 DIAGONAL SURVEY LINE

22. HIGH SURVEY LINE PASSES FROM THE OCCLUSAL
THIRD IN THE NEAR ZONE TO THE OCCLUSAL THIRD
IN THE FAR ZONE.UNDERCUT WILL BE DEEP-
A WROUGHT WIRE CLASP WHICH IS MORE FLEXIBLE
SHOULD BE USED.
MEDIUM SURVEY LINE PASSES FROM THE
OCCLUSAL THIRD IN THE NEAR ZONE TO THE
MIDDLE THIRD IN THE FAR ZONE. AKER’S OR
ROACH CLASP IS USED.
LOW SURVEY LINE IS CLOSER TO
THE CERVICAL THIRD OF THE
TOOTH IN BOTH NEAR AND FAR
ZONE. A MODIFIED T- CLASP IS
USED.
DIAGONAL SURVEY LINE RUNS FROM OCCLUSAL
THIRD IN THE NEAR ZONE TO CERVICAL THIRD OF
FAR ZONE.A REVERSE CIRCLET CLASP IS USED.

23. Clasp Design
 Circumferential Cast Clasp
 The conventional circumferential cast clasp originating from a
distal occlusal rest on the terminal abutment tooth and
engaging a mesio buccal retentive undercut should not be used
on a distal extension removable partial denture.
 The terminal of this clasp reacts to movement of the denture
base toward the tissue by placing a distal tipping, or torquing,
force on the abutment tooth
 This particular force is the most destructive force a retentive
clasp can exert. This clasping concept must be avoided at all
costs.

24.  The reverse circlet, a cast circumferential clasp that
approaches a distobuccal undercut from the mesial
surface of a terminal abutment tooth, is acceptable
 The effect on the abutment tooth is reversed from that
of the conventional circumferential clasp.
 As an occlusal load is applied to the denture base, the
retentive terminal moves further gingivally into the
undercut area and loses contact with the abutment
tooth. In this manner torque is not transmitted to the
abutment tooth
A reverse circlet clasp, approaching a
distobuccal undercut from mesial occlusal
surface, may be acceptable for a distal
extension partial denture. As denture base
moves toward the tissue, retentive clasp tip
will tend to move into an area of greater
undercut (arrow). This action releases
torquing forces that can damage an
abutment tooth

25. Vertical Projection, or Bar, Clasp
 The vertical projection, or bar, clasp is used on the terminal
abutment tooth on a distal extension partial denture when the
retentive undercut is located on the distobuccal surface.
 It is never indicated when the tooth has a mesiobuccal undercut.
 The bar clasp functions in a manner similar to the reverse
circumferential clasp.
 As the denture base is loaded toward the tissue, the retentive tip
of the T clasp rotates gingivally to release the stress being
transmitted to the abutment tooth
The vertical projection T Clasp releases
torsional stress on terminal abutment
tooth. This releasing action is accomplished
when retentive clasp tip rotates gingivally
into a greater undercut as tissueward
forces are applied to denture base
(arrows). Rotation takes place around
distal occlusal rest.

26.  One school of thought on the philosophy of removable partial
denture design has advocated omitting the distal occlusal rest from
the terminal abutment in favor of a mesial rest when a bar clasp is
used.
 advantage claimed for moving the occlusal rest more anteriorly is
that the lever arm (the distance from the rest to the denture base)
is increased, which causes the force directed toward the residual
ridge to be more vertical and thus better tolerated by the ridge
One advantage claimed for eliminating distal occlusal
rest (A) and placing a mesial rest more anteriorly
(B) is that lever arm, represented by distance from
rest to denture base, is increased.
This increase in length makes rotational action
caused by up-and-down movement of denture base
in function more vertical.
A vertical force is better tolerated by ridge than is a
horizontal oblique force.

27. Combination Clasp
 When a mesiobuccal undercut exists on an abutment
tooth adjacent to a distal extension edentulous ridge,
the combination clasp can be employed to reduce the
stress transmitted to the abutment tooth.
 Wrought alloy wire, by virtue of its internal structure,
is more flexible than a cast clasp.
 It can flex in any spatial plane, whereas a cast clasp
flexes in the horizontal plane only.
 The wrought wire retentive arm has a stress-breaking
action that can absorb torsional stress in both the
vertical and horizontal planes.

28. ESSENTIALS OF PARTIAL DENTURE
DESIGN
 To develop the design, it is first necessary to determine how the
partial denture is to be supported
 In an entirely tooth-supported partial denture the potential
support an abutment tooth can provide, consideration should be
given to:
 (1) periodontal health
 (2) crown and root morphologies
 (3) crown-to-root ratio
 (4) bone index area (how the tooth has responded to previous
stress)
 (5) location of the tooth in the arch
 (6) relationship of the tooth to other support units (length of
edentulous span)
 (7) the opposing dentition.

29.  In a tooth- and tissue-supported partial
denture consideration must be given to:
 (1) the quality of the residual ridge, which includes
contour, quality of the supporting bone and quality
of the supporting mucosa
 (2) the extent to which the residual ridge will be
covered by the denture base
 (3) the type and accuracy of the impression
registration;
 (4) the accuracy of the denture base;
 (5) the design characteristics of the component
parts of the partial denture framework
 (6) the anticipated occlusal load.

30.  The second step in systematically developing the
design for any removable partial denture is to
connect the tooth and tissue support units
 Major connectors must be rigid so that forces
applied to any portion of the denture can be
effectively distributed to the supporting
structures.
 Minor connectors arising from the major
connector make it possible to transfer functional
stress to each abutment tooth through its
connection to the corresponding rest and also to
transfer the effect of the retainers, rests, and
stabilizing components to the remainder of the
denture and throughout the dental arch

31.  The third step is to determine how the removable
partial denture is to be retained.
 Retention is accomplished by mechanical
retaining elements (clasps), The key to selecting
a successful clasp design for any given situation
is to choose one that will:
 (1) avoid direct transmission of tipping or
torquing forces to the abutment
 (2) accommodate the basic principles of clasp
design
 (3) provide retention against reasonable
dislodging forces
 (4) be compatible with undercut location, tissue
contour, and esthetic desires of the patient.

32.  The fourth step is to connect the
retention units to the support units. If
direct and indirect retainers are to
function as designed, each must be
rigidly attached to the major connector.
 The fifth and last step in this systematic
approach to design is to outline and
join the edentulous area to the already
established design components.

33. Controlling Stress by Design
Considerations
 Forces of Adhesion and Cohesion
To secure the maximum
possible retention through the use of the forces
of adhesion and cohesion, the denture base
should cover the maximum area of available
support and must be accurately adapted to the
underlying mucosa
To enhance quality of
retention through
adhesion and cohesion,
denture base (arrows]
must fit edentulous ridge
accurately and must
cover maximum area of
available support

34. Frictional Control
 The partial denture should be designed so that
guide planes are created on as many teeth as
possible
 Term guiding plane is defined as two or more
parallel, vertical surfaces of abutment teeth, so
shaped to direct a prosthesis during placement
and removal.
. Development of guide planes on
proximal surfaces of teeth adjacent
to edentulous spaces will increase
retention of partial denture by
frictional contact. These guide planes
may be created in enamel surfaces

35. Quadrilateral Configuration
 The quadrilateral configuration is indicated most
often for Class III arches particularly when there is a
modification space on the opposite side of the arch.
 A retentive clasp should be positioned on each
abutment tooth adjacent to the edentulous spaces.
This results in the denture being confined within the
outline of the four clasps, and leverage on the
denture is effectively neutralized.

36. Tripod Configuration
 Tripod clasping is used primarily for Class II
arches. If there is a modification space on the
dentulous side, the teeth anterior and posterior
to the space are clasped to bring about the tripod
configuration.
 This design is not as effective as the quadrilateral
configuration, but is most effective in neutralizing
leverage in the Class II situation.

37. Bilateral Configuration
 most removable partial dentures fall into the
bilateral distal extension group, or Class I
 the single retentive clasp on each side of the arch
should be located near the center of the dental
arch or denture bearing area.
 In the bilateral configuration the clasps exert
little neutralizing effect on the leverage-induced
stresses generated by the denture base.

38. MAJOR AND MINOR CONNECTORS
Major connectors : The part of the partial
removable denture prosthesis that joins the
components of one side of the arch to those on
the opposite side.(GPT7)
 Major connectors should be rigid necessary to
provide proper distribution of forces to and
from the supporting components
 Minor connectors : The connecting link between
the major connector or base of a partial
removable denture prosthesis and the other
units of the prosthesis such as the clasp
assembly , indirect retainers ,occlusal rests or
cingulum rests. (GPT 7)

39. Major Connector
In the mandibular arch the lingual plate
major connector that is properly supported
by rests can aid in the distribution of
functional stresses to the remaining teeth
Major connector, in this case anterior
lingual plate, can help control functional
stresses on remaining teeth. By contacting
a number of teeth, major connector
reduces amount of force transmitted to
each tooth. Major connector must be
supported by rests at each end of anterior
span
In the maxillary arch the use of a
broad palatal major connector that
contacts several of the remaining
natural teeth through lingual plating
can distribute stress over a large
area

40. Minor Connector
 The most intimate tooth-to-partial denture contact
takes place between the minor connector joining
the clasp assembly to the major connector and the
guiding planes on the abutment tooth surfaces
 This close metal-to-enamel contact serves two
purposes:-
1. First, it offers horizontal stability to the partial
denture against lateral forces on the prosthesis.
The tooth with its supporting bone helps dissipate
these displacing stresses,
2. Second, through the contact of the minor
connector and the abutment tooth, the tooth
receives stabilization against lateral stresses.

41. DIRECT RETAINERS FOR TOOTH-
SUPPORTED PARTIAL DENTURES
DIRECT RETAINER : is that component of a partial
removable dental prosthesis used to retain and
prevent dislodgement, consisting of a clasp
assemble and precision attachment. (GPT 7)
Clasp assembly:
The part of the removable dental prosthesis that acts
as a direct retainer and or a stabilizer for a
prosthesis by partially encompassing or
contacting an abutment tooth.(GPT 7)
Precision attachment :
An interlocking device ,one component of which is
fixed to an abutment or abutments and the other
is integrated to a removable dental prosthesis in
order to stabilize and/or to retain it. (GPT 7)
KEY AND KEYWAYS

42. functions:
A. To retain the prosthesis against reasonable dislodging forces
without damage to the abutment teeth and
B. To aid in resisting any tendency of the denture to be displaced in a
horizontal plane.
 The prosthesis cannot move tissueward as the rest supports the
retentive components of the clasp assembly.
 There should be no movement away from the tissue and therefore
no rotation about a fulcrum because a direct retainer secures the
retentive component.
 Intracoronal (frictional) retainers are ideal for tooth-supported
restorations and offer esthetic advantages that are not possible
with extracoronal (clasp) retainers.
DALBO EXTRACORONAL ATTACHMENT

43.  The clasp retainer must not impinge on
gingival tissue and must not exert
excessive torque on the abutment tooth
during placement and removal.
 It must be located the least distance into
the tooth undercut for adequate retention,
and it must be designed with a minimum of
bulk and tooth contact.
 The bar clasp arm should be used only
when the area for retention lies close to
the gingival margin of the tooth.
 With an excessive tissue undercut, re
contouring the abutment and using some
type of circumferential direct retainer is
advisable.
Circumferential clasp
Occlusal view of bar clasp

44. DIRECT RETAINERS FOR DISTAL
EXTENSION PARTIAL DENTURES
 The retainer should retain the
prosthesis, and also be able to flex
or disengage when the denture base
moves tissueward under function.
Thus the retainer may act as a
stress-breaker.
 The clasp arm must be freely
flexible in any direction, as dictated
by the stresses applied.
 Round, tapered clasp forms offer
advantages of greater and more
universal flexibility, less tooth
contact, and better esthetics.

45.  Allison. G. James (1955) :-
 Explained stress breakers which automatically return the saddle
to rest position following displacement.
 Basic principle involved is that portion of appliance directly
attached to the abutment teeth, the anterior part of palatal
casting shall be rigid, and with minimum motion possible allowed
between it and the abutment.
 The saddles will be attached to this rigid portion by a narrow
isthmus in the saddle casting as close as feasible to the midline of
the palatal appliance.

46. INDIRECT RETAINERS
Indirect retainers :are the components of the partial
removable dental prosthesis that assists the
direct retainers in preventing displacement of
the distal extension denture by functioning
through lever action on the opposite side of the
fulcrum line when the denture base moves away
from the tissues in pure rotation around the
fulcrum line. (GPT 7)
It must be placed as far anterior from the
fulcrum line.
It must be placed on a rest seat prepared on an
abutment tooth that is capable of withstanding
the forces placed on it.

47. PLACEMENT OF INDIRECT RETAINERS IN A PARTIALLY EDENTULOUS ARCH
A
C
E
G
B
D
F
H

48. Indirect retainer cannot function
effectively on an inclined tooth surface,
nor on a single weak incisor tooth
,either a canine or premolar tooth
should be used for the support of an
indirect retainer.
Function :
A. Restrict movement of a distal extension
base away from the basal seat tissue.
B. Support for major connectors.

49. ADDITIONAL CONSIDERATIONS
INFLUENCING DESIGN
 Use of a Splint Bar for Denture Support
 when the edentulous span is too large to ensure
adequate support from the adjacent teeth,
 An anterior splint bar may be attached to the
adjacent abutment teeth in such a manner that fixed
splinting of the abutment teeth results, with a
smooth, contoured bar resting lightly on the gingival
tissue to support the removable partial denture
A, Splint bar attached to double
abutments on either side of
arch.
. B and C, Denture framework
designed to fit and be supported
by splint bar.

50. Lower canines and lateral incisors splinted together with splint
bar. Longevity of these teeth is greatly enhanced by splinting,
and enhanced stability of the removable partial denture is
provided.
Tissue surfaces are minimally contacted by rounded form of
lower portion of bar. Anterior and posterior slopes of splint bar
must be compatible with path of placement of denture.

51. Internal Clip Attachment
 The internal clip attachment differs from the
splint bar in that the internal clip attachment
provides both support and retention from the
connecting bar
Canines have been endodontically
treated and are splinted together with
round, straight connecting bar, slightly
elevated from residual ridge. Retaining
left molar as abutment will
immeasurably contribute to stability of
removable partial denture.
B, Tissue surface of completed
mandibular restoration containing
internal clip attachment.

52. Overlay Abutment as Support for a Denture
Base
 Every consideration should be directed to
preventing the need for a distal extension
removable partial denture.
 In many instances it is possible to salvage the
roots and a portion of the crown of a badly
broken-down molar through endodontic
treatment.

53. Use of a Component Partial to Gain
Support
 A component partial is a removable partial
denture in which the framework is designed and
fabricated in separate parts. The tooth support
and tissue supported components are individually
fabricated, and the two are joined with a high
impact acrylic resin to become a single, rigid
functioning unit
A, Design of component part removable
partial denture.
B, Tooth support component individually
fabricated and fit to the master cast.
C, Tissue support component individually
fabricated and fit to the master cast.
D, Tooth and tissue support components
assembled on cast.
E, Components joined with high-impact
resin.

54. EXAMPLES OF SYSTEMATIC APPROACH
TO DESIGN
 Class III Removable Partial Denture
 Removable partial denture in maxillary Class III,
Mod 1 arch. Design consists of single palatal
connecting a single tooth space to a 2-tooth space.
The impression for such modification spaces does
not require tissues to be captured in a supportive
form. A palatal strap major connector is less bulky
and for most patients would be more comfortable
than a thicker bar design.

55. Kennedy Class II Removable Partial
Dentures
 The Kennedy Class II partial denture actually
may be a combination of both tissue-supported
and tooth supported restorations. The distal
extension base must have adequate tissue
support, whereas tooth-supported bases
elsewhere in the arch may be made to fit the
anatomic form of the underlying ridge

56. Bibliography
 Stewart : Clinical Removable Partial
Prosthodontics,second edition ,Ishiyaku
European American publishers.
 Carr, McGivney, Brown: McCracken’s
Removable Partial Prosthodontics, eleventh
edition ,Mosby publishers.
 Applegate : Essentials of Removable Partial
Denture Prosthesis., saunders Company.