Concepts new/ dental technician training online

• INTRODUCTION:
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

• In contrast with the Kratochvil’s basic design,
which necessitates heavy preparation, Krol
developed a modification that avoids tooth
preparation.

• The state emphasis in Krol’s system is stress
control with minimal tooth coverage and
minimal gingival coverage.

• The clasp system includes the three elements
of Kratochvil’s system: -
mesial rest,
proximal plate
and I-bar.
• Each element, however, has undergone
significant change to meet Krol’s criteria.

• In RPI system:
R = Rest
P = Proximal plate
I = I-bar

REST
• Rest preparations are less extensive in the RPI
system.
• The mesial rest extends only into the
triangular fossa, even in molar preparations,
and canine rests are often circular concave
depressions prepared in the mesial marginal
ridge

• Mesio occlusal rest with the minor connector
placed into the mesiolingual enbrassure, but
not contacting the adjacent tooth.

PROXIMAL PLATE:
• The proximal plate makes greatest departure
from Kratochvil’s design.
• The prepared guide plane is 2 to 3 mm high
occlusogingivally and the proximal plate
contacts only 1 mm of the gingival portion of
the guide plane

• . Relief is provided at the tooth – tissue
junction to allow the proximal plate to
disengage into the proximal undercut under
occlusal loading.

• This proximal plate, in conjunction with the
minor connector supporting the rest, provides
the stabilizing and reciprocal aspects of the
clasp assembly.

I – bar:
• The I-bar should be located in the gingival
thirds of the buccal or labial surface of the
abutment in a 0.001 inch undercut.
• The whole arm should be tapered into the
terminus, with no more than 2 mm of its tip
contacting abutment.

• The retentive tip contacts the tooth from the
undercut to the height of contour.
• This area of contact along with the rest and
proximal plate contact provides stabilization
through encirclement.
• The horizontal portion of the approach arm
must be located at least 4 mm from the
gingival margin and even farther if possible.

• There are three basic approaches to the
application of the RPI system.
• The location of the rest, the design of the
minor connector (proximal plate) as it relates
to the guiding plane, and the location of the
retentive arm are factors that influence how
this clasp system functions.

• All advocate the use of a rest located mesially
on the primary abutment tooth adjacent to
the extension base area.

I approach :
• This approach recommends that the guiding
plane and corresponding proximal plate minor
connector extend the entire length of the
proximal tooth surface, with physiological
tissue relief to eliminate impingement of the
free gingival margin

• Bar clasp assembly in which guiding plane
(GP) and corresponding proximal plate (PP)
extend entire length of proximal tooth surface
to contact greater surface area of guide plane
which directs functional forces in horizontal
direction , thus tooth {teeth} are loaded more
than edentulous ridge.

II approach:
• This approach suggests that the guiding plane
and corresponding proximal plate minor
connector extend from the marginal ridge to
the junction of the middle and gingival thirds
of the proximal tooth surface

• Both approaches recommend that the
retaining clasp arm be located in the gingival
third of the buccal or labial surface of the
abutment in a 0.001 inch undercut

• Bar clasp assembly in which guiding plane and
corresponding proximal plate extend from
marginal ridge to junction of middle and
gingival thirds of proximal tooth surface.
• This decrease amount of surface area contact
of proximal plate on guide plane more evenly
distributes functional force between tooth
and edentulous ridge

III approach:
• This approach favours a proximal plate minor
connector that contacts approximately 1mm
of the gingival portion of the guiding plane
and retentive clasp arm located in a 0.001 inch
undercut in the gingival third of the tooth at
the greatest prominence or to the mesial away
from the edentulous area

• Bar clasp assembly in which proximal plate
contacts approximately 1 mm of gingival portion
of guiding plane .
• During function, proximal plate and I-bar clasp
arm are designed to move in mesiogingival
direction, disengaging tooth. Lack of sustained
contact between proximal plate and guide plane
distributes more functional force to edentulous
ridge.
•

• Application of each approach is predicated on
the distribution of load to be applied to the
tooth and edentulous ridge.

• The stated purpose of reducing the proximal
plate is to improve gingival health by opening
up embrasure spaces as much as possible.

MODIFICATION TO RPI SYSTEM:
• Kroll in 1976 has given modification to RPI
system. That is
• RPA in which
R = rest
P = proximal plate
A = Akers clasp

contraindications for a bar- type clasp
 exaggerated buccal or lingual tilts,
 severe tissue undercut
 or a shallow buccal vestibule
 and the desirable undercut is located in the
gingival third of the tooth away from the
extension base area,
• this modification to RPI i.e., RPA should be
considered.

Tipped abutments
and tissue impingements are
• treated with RPA clasp.
• When Akers clasp arm is used, careful
attention is paid to relieve all undercuts
except at the retentive tip

The removable partial denture design:
british dental journal: vol-189; n0-7 pg-414
• In the study they concluded that there a plaque
accumulation in terms of quality and quantity on
alloplastic materials and there is some components are
leached into oral cavity from this alloplastic material
• And this will cause tissue injury
• This can be prevented with the equillibrium in 3
components
• 1- operator
• 2- patient
• 3- laboratory perosenell

10yr old eveluation of r.p.d’s ,survival rates
based in re treatment
j.p.d- vol-76: no-1, 1996
• In this survey 784 patients were given with
metal dentures and their feed back was taken
• In the survey it was found that
88% - with 96% of success
10 people died that is 8%
Remaining people didnt wear the r.p.d

A randomised clinical trial of 2 basic r.p.d’s-
comparision of masticatory efficiency-
j.p.d- 1997: 78; 15-21
• Statement of problem: there is no clinical data
about the functional efficiency of different
r.p.d designs.
• For this 118 patients were selected with
unilateral or bi lateral r.p.d’s
• Conclusion: despite some performance
difference at entry the mean performance
scores for the 2 different groups became
similar

conclusion
• Successful use of the system requires careful
analysis of each component for the function
that it provides and thoughtful execution of
the system in the abutment preparation and
precise fitting of framework

Thank you
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