PRINCIPLES OF RPD DESIGNING BY MC CRACKEN

1. PRINCIPLES OF DESIGNING FOR
KENNEDY’S CLASS III & CLASS
IV
DR LEENA TOMER

2. Contents
 Introduction
 Definition
 Basic Principles for RPD Design
 Biomechanical Considerations
 Various Factors Influencing Design
 Essentials of Partial Denture Design
 Factors which influence the magnitude of stress
to the abutment teeth
 Design considerations in control of stress

3. Contents
 Differences between Class III & other types of
Removable Partial Denture conditions
 Components of class III partial denture design
 Components of class IV partial denture design.
 Additional considerations influencing design
 Summary & Conclusion
 References

4. Introduction
 There is no aspect of dentistry that involves as much
variation and individual preference as designing
removable partial dentures.
 It has been calculated that there are 32,000 different
possible combination of design.
 This fact coupled with the lack of good longitudinal
studies has led many to design based on what they feel
comfortable.
 The completed design should serves as a blue print…….

5. Definition
 Class III : A unilateral
edentulous area with natural
teeth remaining both anterior
and posterior to it.
 Class IV : A single, but
bilateral (crossing the
midline), edentulous area
located anterior to the
remaining natural teeth.

6. Basic Principles of RPD Design
- Dr. A.H. Schmidt (1953)
 Dentist must have a working knowledge of both the
mechanical and the biological factors involved in RPD
design.
 Any plan of restoration must be based on a complete
examination and diagnosis of individual patient.
 The dentist not the technician should correlate the
pertinent factors and recommend a proper plan of
treatment.
 A removable partial denture should restore form and
function without injury to tissue.
 A RPD is a form of treatment not a cure.

7. Biomechanical Considerations
 “Common observation clearly indicates that the ability of
living things to tolerate force is largely dependent upon
the magnitude or intensity of the force.
- Maxwell
 In designing consideration of maintaining the health of
abutment teeth and residual ridges the direction,
duration and magnitude of force applied should be
considered.

8.  In designing RPD consideration should be given on
avoiding lever and inclined plane designs.
 There are 3 types of lever.
 First class
 Second class
 Third class
A lever system usually
magnifies the force applied.
Mechanical advantage =
Effort arm / Resistance arm

9.  Denture base of a distal extension partial denture will rotate in
relation to 3 cranial planes when force is directed on it.
 Even though the movements may be small there still exists
the potential for detrimental lever like imposed forces on
abutment teeth.

10.  Cantilever designs for distal extension cases should be
avoided and alternative designs to minimize the
destructive potential should be used.

11.  A tooth is apparently better able to tolerate vertically directed forces than
off vertical or near horizontal forces.
 Abutment tooth will tolerate off vertical forces better if these forces are as
near as possible to the horizontal axis of rotation.

12. Various factors influencing
Design
I. Arch relationship.
a. Occlusal relationship of remaining teeth.
b. Orientation of occlusal plane.
c. Space available for restoration of missing teeth.
d. Arch integrity.
e. Tooth morphology.
II. Type of major connector indicated, based on
existing and correctable situations.

13. III. If distal extension bases are involved then.
a. Need for indirect retention.
b. Clasp designs that will minimize forces directed
towards abutment teeth.
c. Type of base material for later rebasing.
IV. Materials to be used both for framework and for
the bases.
V.Type of replacement teeth to be used, influenced
by the opposing dentition.

14. VI. Need for abutment restoration which may
influence the type of clasp arms to be used.
VII. Patients past experience and reason for
making a new denture.
VIII. Response of oral structures to previous stress,
the amount of abutment support remaining.
IX. Method to be used for replacing single teeth
or missing anterior teeth.

15. Essentials of Partial
Denture Design
 Design should be systematically developed
and outlined on an accurate diagnostic cast.
 Step-1: Support.
 Tooth supported partial denture has the
support on prepared rest seat.The potential
support on an abutment can be evaluated by:
 Periodontal health.
 Crown and root morphology.
 Crown to root ratio.
 Bone index area.
 Location of the tooth in the arch.
 Relationship of the tooth to other support
units.
 Opposing dentition.

16.  Tooth tissue supported partial denture
equitable support must come from the
edentulous ridge areas which can be
evaluated by:
 The quality of residual ridge.
 The extent to which the residual ridge will
be covered by the denture base.
 Type and accuracy of the impression
registration.
 The accuracy of denture base.
 The design characteristics of the
component parts of the partial denture
framework.
 The anticipated occlusal load.

17.  Denture base areas adjacent to abutment teeth are primarily tooth supported.
 Locating rest and designing minor connectors that are adjacent to the edentulous
areas to contact the guiding planes so that they disperse the functional load
equitably.

18.  Step-2:
 To connect the tooth and tissue support units.
 By major and minor connectors.
 Major connectors should be rigid.
 Minor connectors arising from the major connectors
should transfer functional stress to each abutment
through its connection with the rests.

19.  Step-3:
 To determine how the partial denture is to be
retained.
 Successful clasp design should-
 Avoid direct transmission of tipping or torquing forces to the
abutment.
 Correct positioning of component parts on abutment tooth
surface.
 Provide retention against reasonable dislodging forces.
 Be compatible with undercut location, esthetic desires of
patient.
 Undercut location is the most important factor in
selecting a clasp.
 Design should have provision for indirect retention.

20.  Step-4:
 Connect the retention units to the support units
should be rigidly attached.
 Step-5:
 Outline and join the edentulous area to the
already established design components.

21. Factors which influence the
magnitude of the stress transmitted
to abutment tooth. Length of edentulous span
 Form of residual ridge
 Type of mucosal covering
 Type of clasp
 Design of clasp
 Construction of clasp
 Amount of clasp surface in contact with the tooth
 Type of abutment tooth surface
 Harmony of the occlusion
 Type of opposing occlusion
 Areas of base to which load is applied

22. Design consideration in the
control of stressI. Retention as a means of stress control
Any retention supplied by units of the
prosthesis other than clasps reduces the
amount of retention clasps have to provide
 Adhesion
 Atmospheric pressure
 Frictional contact
 Neuromuscular control

23. II. Clasp positioning
Leverages can be controlled entirely by means
of clasps, if there are sufficient abutment teeth.
 Quadrilateral configuration
 Tripod configuration
III. Other factors in stress control
 Clasp design
 Indirect retention
 Functional basing
 Harmonious intercuspation
 Size and coverage of the base
 Accuracy of adaptation of the base

24. Differences between Class III & Other
types of RPD Condition
1. Manner of support.
2. Method of impression registration.
3. Need for some kind of indirect retention.
4. Use of a base material that can be relined.
5. Differences in clasp design.

25. Components of Class III partial
denture design
A) Direct retention:
1. Prosthesis are entirely tooth borne, the
transmission of harmful forces to the abutment
and ridges can be minimized
2. Positions of the retentive undercuts are not
critical.
B) Clasps:
1. Quadrilateral positioning is
considered ideal.
2. Tooth & soft tissue contours,
esthetics should be considered.
3. Reciprocal elements must be rigid.

26. C) Rests:
1. Should be positioned adjacent to the
edentulous space.
2. Should support major connectors and lingual
plating.
D) Indirect retention
Usually not required
E) Major and minor connector
1. Must be rigid and should not impinge on
gingival tissues
Usually a palatal strap is used, if modification
spaces are present anteroposterior bar can be

27. 2. Minor connectors should be positioned to enhance
comfort, cleanliness and placement of artificial teeth.
F) Occlusion:
1. Maximum intercuspation should coincide centric relation
2. Harmonious occlusion should be established
3. Prosthetic teeth should be selected and placed to
minimize stresses on the prosthesis
G) Denture bases:
1. Functional impressions are not required
2. Coverage of the residual ridge should be determined by
appearance, comfort and avoidance of food impaction.

28. Components of Class IV partial
denture design
Fixed partial denture is contraindicated for the
following reasons:
1. Ridge resorption may necessitate the addition
of an anterior flange.
2. The condition of abutments may not suitable
for bridge support.
3. The length of the dentulous span may put more
strain on the abutments.

29. Essentials of Design:
A. Movement of removable partial denture for
Kennedy Class IV arches and the stresses
transmitted are unlike those seen in other
classes.
B. Esthetic and phonetic requirements may place
teeth anterior to the ridge crest resulting in
tipping and rotational forces to the abutment.

30. Guidelines should be observed to minimize these stresses:
 Preserve the hard and soft tissue components of anterior
edentulous ridge
 A central incisor or other tooth can be retained to serve as an
intermediate or an overdenture abutment which minimizes
the rotation.
 A quadrilateral configuration of direct retainers is ideal.

31. C. Rests
1. Should be located anteriorly &
posteriorly in a quadrilateral
configuration.
2. Should be placed immediately
adjacent to the edentulous area.
D. Clasps
1. Posterior embrasure clasps eliminate
the need for anterior clasps in some
cases
2. If more retention is needed anterior
clasps can be added, directed from
the distal surface of the tooth to
terminate mesially

32. E. Connector
1. The major connector should be rigid
2. Horseshoe type major connector can be
utilized
3. Anteroposterior bar can be used if
increased rigidity is required.
F. Indirect retention
Should be located as far posterior to
the fulcrum line.
G. Functional impressions may be indicated if
edentulous area is extensive.

33.  Newton JP, Quinn DM (1989): Described a
technique in which acrylic resin extensions from
the labial surface of the anterior tissue base of
Kennedy Class IV RPD are used as retentive
elements to minimize motion around the axis of
rotation.The labial rests, formed by extending
the base material act as guiding planes and also
improve esthetics by covering the interdental
spaces.

34. Additional Considerations
Influencing Design1. Splint bar for denture support
Ordinarily support for replacing anterior teeth is given by placing rests on
adjacent teeth.When the edentulous span is large:
• An anterior splint bar may be attached to the abutment teeth so that
splinting occurs.
• Length of the span influences the size of the splint bar
• Positioned anteroposteriorly just lingual to the residual ridge to allow the
esthetic arrangement of artificial teeth

35. 2. Internal clip attachment
• Provides support and retention from the connecting bar
• Cast bar should rest lightly above the tissue
• Nylon clips are embedded in the overlying resin denture base
• Provides support, stability and retention for anterior
modification area.

36. Summary
 Retention should not be the prime objective of design
instead, efficiency, esthetics, comfort and
preservation should be taken care.
 Simplest type of clasp and connector that will
accomplish design objective should be employed.
 Tooth support should be exploited to the extent that
it is available.
 No parts should impinge on free gingival margin.
 All connectors must be rigid.
 Principle of indirect retention should be employed
when feasible.
 Harmonious occlusion should be developed.
 The base of the partial denture should be constructed
from a functional impression.

37. Conclusion
 The important factor is that basic principles of designing are
not violated.
 Retainer choice, rest placement, connector design are all
critical factors. However, the fact remains that adequate
time must be spent in proper diagnosis and devising a
workable treatment plan in terms of patients prosthetic
needs and expectations.
 Once this is achieved the rather mechanical tasks of laying
out the nuts and bolts of RPD design can be carried out to
ensure that our patients receive the full benefit of our
knowledge and skills.

38. References
 McCracken’s : Removable Partial Prosthodontics. 11th
edition, Mosby.
 Stewart’s : Clinical Removable Partial Prosthodontics. 3rd
edition, Quintessence.
 Ernest L. Miller, Joseph E. Grasso : Removable partial
prosthodontics. 2nd edition, SansTache.
 David M.Watt, MacGregor : Designing Partial Dentures:
Wright.
 Davenport : A ColorAtlas of Removable Partial Dentures.
Wolfe.

39.  Robert L. De Franco : Designing Removable Partial
Dentures. DCNA 1984; 28: 307-325.
 Arthur H. Schmidt : Planning and Designing Removable
Partial Denture. JPD 1953; 3: 783-806.
 Gordon E. King: Dual path Design for Removable Partial
Dentures. JPD 1978; 39: 392-395.
 Arthur R. Frechette: Partial Denture Planning with
Special Reference to Stress Distribution. JPD 1951; 1: 711-
724.
 William L. McCracken: Contemporary Partial Denture
Designs. JPD 1958; 8: 71-84.

40. Thank You