RPI AND RPA SYSTEM IN CAST PARTIAL DENTURE

1. Dr. Kaushik Kr. Pandey
MDS

2.  A properly designed removable partial denture offers
excellent retention, function, comfort & esthetics
 The retention of a removable prosthesis is a unique
concern, as the direction of forces trying to unseat a
prosthesis can be towards, across or away from the
tissues

3. Support
Stabilization
Retention
Buccal view

4.  Removable partial prosthodontic therapy involves a
multidisciplinary clinical approach with each situation
presenting its unique features.

5.  Direct retainer-Extracoronal
 Aker’s clasp
 Roach clasp

6.  Various extracoronal clasp assemblies have been
designed for abutment teeth adjacent to a distal-
extension ridge - allow rotation of a removable
partial denture base toward tissue without torquing
the clasped tooth.’

7.  There are two schools of thought,
RPI concept
RPA concept

8. As such there is no evidence
which advocates the use of one
over the other, it entirely
depends upon the clinical situation

10. Kratochvil-(1963)
 popularized the proximal plate/ mesio-occlusal
rest/I-bar (RPI) design.
Krol-(1973)
 modified the proximal plate, naming the system
“The RPI bar clasp design.”

11. (1) more esthetically acceptable,
(2) tooth coverage is minimal
(3)the retainer disengages when unfavorable forces
are applied
(4) adequate retention is available with minimum
undercuts.

12. Original design is
credited to
Kratochvil (1963)
The Krol’s system lays emphasis on
stress control with minimal tooth
coverage & minimal gingival coverage

13. R:- REST ; mesio-occlusal rest
P:- PROXIMAL PLATE ; engages distal guiding
plane
I:- I-BAR

14. I- BAR
Proximal
plate

15. LINGUAL VIEW

16.  In RPI system (distal extension) the most distal rests
placed on mesial aspect of abutment .
 Helps to verticalize the forces of occlusion on denture
bearing mucosa.
 Mesial rest directs tipping forces on the abutment mesially
-move the abutment tooth into firm contact with the
support of anterior teeth.

17.  Covers the guide plane from marginal ridges to
tooth tissue junction and extend onto attached
gingiva for 2mm.
•Horizontal stability
•Reunites and stabilize the arch
•Increased retention
•Protect the tooth-tissue junction –preventing
food impaction
•Provides reciprocation
•Distribution of occlusal forces throughout
arch.

18. I BAR
 An I – bar is an extra coronal, infrabulge
removable partial denture component-
 tapering smoothly from its origin to its rounded
tip, flexible, & usually provides retention.
T.Berg.I-Bar : Myth and Countermyth. DCNA;28:1984

19. FEATURES:RPI
 The design minimizes
torquing forces
 Directs occlusal loads parallel
to the long axes of abutments
during rotational movement of
the removable partial denture

20.  Covers minimum of tooth structure
 Shows less metal than other clasps

21. Is useful for both tooth supported & distal extension
removable partial dentures

22.  I-Bar along with the rest and proximal plate
provides stabilization through ENCIRCLEMENT
( more than 180˚ coverage in the greatest
circumference of the tooth )

23. The
Location Of
The Rest
The
Design Of The
Minor Connector
(Proximal Plate)
As It Relates To
The Guiding
Plane
The Location
Of The
Retentive Arm

24. Distobuccal
Buttressing
stabilization

26. Greatest
mesiodistal
prominenece

28. Mesiobuccal

30. KRATOCHVIL’S DESIGN KROL’S
DESIGN
1. Covers entire length of proximal
surface
1mm of gingival portion of guide
plane
2. More stability Comparatively less stability
3. Less retention More retention
4. More forces on abutment Less forces on abutment
5. More tooth preparation for guiding
plane
Less tooth preparation
6. In function, abutment tooth
loaded more than edentulous
ridge
In function, more forces are
transferred to edentulous ridge
7. I-Bar on disto-buccal surface of
abutment
Mesio-buccal surface of abutment

31.  In cases of insufficient vestibular depth,
where placement of the I – bar 4 mm away
from the gingival margin would not be
possible
4mm

32.  Where there is an extensive tissue undercut
below the abutment, as excessive relief for
the approach arm will be uncomfortable for
the patient

33.  Sometimes due to length of the approach arm of the
retentive I – bar, the flexibility of the retentive arm
results in a compromised retention
 On recall examinations the clasp arms are found to
be distorted & permanently sprung away from the
tooth

34.  Since there is no convenient component in the
RPI removable partial dentures to grasp with
fingernail for its removal, it can pose real
problem for patients with arthritis or other
physical disabilities
Eliason CM. RPA clasp design for
removable partial dentures. J
Prosthet Dent. 1983; 49 (1): 25 – 27

35.  Relief of clasp components, where it crosses the
gingival border is crucial & in case this relief is
insufficient, it leads to gingival inflammation &
its sequels

37.  The RPA clasp ( rest, proximal plate & Aker’s
Clasp) was developed at the University Of Pacific
School Of Dentistry

38.  In RPA - the difference lies in the clasp arm, which arises
from the superior surface of the proximal plate & extends
around the tooth to engage the mesial undercut .
 The mesial rest & proximal plate are designed identical to
those of the RPI clasp
 The difference in the retentive arm.

41. In RPA - Akers, or circumferential clasp arm-
 arises from the superior portion of the proximal
plate and extends around the tooth to engage the
mesial undercut.

42.  retentive arm coming off
the proximal plate above
the survey line -crossing
the survey line in the
middle of the tooth to
engage the undercut- vital
releasing capability will
be lost.
IMPROPERLY DESIGNED RPAASSEMBLY

43.  The rigid bracing portion
of the arm is not able to
move toward the gingival-
the fulcrum point will in
effect be moved toward the
distal surface of the tooth

44.  The components anterior
to the fulcrum point will
now lift in function.
 When occlusal pressure is
placed -the mesial rest
will lift out of its seat-the
retentive arm will engage
the undercut-torquing the
tooth distally.

45.  This is the same kind of force- destructive to an
abutment tooth -when a conventional Akers clasp
is used.

46. REQUIREMENTS :-
A normal tooth
alignment is needed
The survey line in
approximately middle
of the tooth
RPA –PROPER
DESIGN

47.  Abutment should provide undercuts on mesial or
distal aspects of the facial surface
LABIAL VIEW LINGUAL VIEW

48.  There must be at least a 0.01 inch undercut
mesially.
 A rest seat is placed on the mesio-occlusal surface
of the tooth .
 guiding plane prepared on the distal surface.

49.  The distal half of the facial
surface as well as the surface
under the guiding plane are
blocked out.

50.  In waxup- the superior border of the retentive arm
is placed on the survey line from the proximal
plate to the middle of the tooth- then drops down
to engage the necessary undercut for proper
retention

51.  After casting - the rigid
portion of the clasp arm
will contact the tooth
only along its superior
border at the level of the
survey line.

52. Advantage :-
In occlusal load -
 the retentive arm can move into the undercut
because of the relief under its rigid section and
release from the abutment tooth

53.  The freedom of the movement -
verified in the mouth with pressure-indicating
material under the clasp arm -digital pressure
applied to the denture bases.

54. •Easiest clasp to make & repair
•Less food retention
•Best for tooth supported partial
dentures
•Derives excellent support,
bracing & retention
•Easy removal of the appliance
ADVANTAGES OF RPA OVER
THE RPI CLASP ASSEMBLIES

55. DISADVANTAGES:
Covers a larger tooth surface area

56. Decalcification of tooth structure

57.  If placed more occlusally, can lead to a
premature contact

59. RPI CONCEPT
Kroll in 1973 RPA CONCEPT
PACIFIC SCHOOL OF DENTISTRY
MESIAL REST,
PROXIMAL
PLATE & I –
BAR CLASP
REST,
PROXIMAL
PLATE &
AKER’S CLASP
INFRABULGE
(GINGIVALLY
APPROACHING)
SUPRABULGE
(OCCLUSALLY
APPROACHING
EXTENSIVE
TOOTH
COVERAGE
MINIMAL
TOOTH
COVERAGE

60. RPI CONCEPT
Kroll in 1973
RPA CONCEPT
PACIFIC SCHOOL OF DENTISTRY
SHOWS LESS
METAL – IS
MORE ESTHETIC
MORE METAL
IS VISIBLE
AVOIDS CONTACT
WITH THE LINGUAL
SURFACE OF THE
ABUTMENT TOOTH
RECIPROCAL /
STABILIZING ARM
CONTACTS THE
LINGUAL SURFACE
INDICATIONS : TOOTH
SUPPORTED & DISTAL
EXTENSION
REMOVABLE PARTIAL
DENTURES
INDICATIONS : TOOTH
SUPPORTED PARTAIL
DENTURES, TIPPED
ABUTMENTS & TISSUE
IMPINGEMENTS
CONTRAINDICATIONS :
INSUFFICIENT VESTIBULAR
DEPTH, SOFT TISSUE
UNDERCUTS & TILTED
TEETH
CONTRAINDICA
TIONS : WHERE
ESTHETICS IS A
PRIME
CONCERN

61.  The RPA design has been discussed as an
alternative to the RPI design. With its mesial rest
and special retentive arm design, it gives essentially
the same kind of tooth release that the RPI clasp
provides.

62.  Davenport J.C., Basker R.M., Heath J.R. and Ralph J.P. : A color atlas of removable partial dentures.
 Stewart K.L., Rudd K.D. and Kuebker W.A. : Clinical Removable partial prosthodontics.
 Mc crakens removable partial prostodontics
 Advanced removable partial denture : james brudbvik
 Miller and Grasso: Removable partial prosthodontics.
 Charls M. Eliason. RPA clasp design for distal-extension removable partial dentures.JPD: january 1983 volume 49
number 1
 Eliason CM. RPA clasp design for removable partial dentures. J Prosthet Dent. 1983; 49 (1): 25 – 27
 T.Berg.I-Bar : Myth and Countermyth. DCNA;28:1984
 Kratochvil, F. J.: Influence of occlusal rest position and clasp design on movement of abutment teeth , J Prosthet
Dent 13:114, 1963
 Benson and Spolsky:A clinical evaluation of removable partial dentures with I-bar retainers. Part I, J Prosthet
Dent;41:1979