JSS ACADEMY OF HIGHER EDUCATION & RESEARCH

JSS Dental College & Hospital

15-01-2023 Department of Prosthodontics 1

JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital

DIRECT RETAINERS

15-01-2023 Department of Prosthodontics 2

 CONTENTS
1. DEFINITION
2. CLASSIFICATION
3. RETENTIVE CLASP ASSEMBLIES
4. PROTHERO CONE THEORY
5. DEVAN CONCEPT
6. STRUCTURE OF CLASP ASSEMBLY
7. REQUIREMENTS OF CLASP ASSEMBLY
8. CIRCUMFERENTIAL CLASPS
9. BAR CLASPS, RPI CLASP, RPA CLASP
10.INTRACORONAL ATTACHMENTS
11.EXTRACORONAL ATTACHMENTS
12.NON METAL CLASP DENTURES.
15-01-2023 Department of Prosthodontics
3
JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital DEFINITION:
DIRECT RETAINER: That component of a removable partial denture
used to retain and prevent dislodgment, consisting of a clasp
assembly or precision attachment – GPT9

CLASP: The component of the clasp assembly that engages a portion

of the tooth surface and either enters an undercut for retention or
remains entirely above the height of contour to act as a reciprocating
element; generally it is used to stabilize and retain a removable partial
denture. –GPT9
CLASP ASSEMBLY: The part of a removable partial denture that acts as
a direct retainer and/or stabilizer for a prosthesis by partially
encompassing or contacting an abutment tooth – GPT9
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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
DIRECT
RETAINERS

INTRA- EXTRA-
CORONAL CORONAL

RETENTIVE
PRECISION SEMIPRECISION
CLASP ATTACHMENTS
ATTACHMENTS ATTACHMENTS
ASSEMBLIES

SUPRABULGE INFRABULGE

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
RETENTIVE CLASP ASSEMBLIES

• Most common
• Given by Dr W. G. A.Bonwill’s in 1899

DESIGN: influenced by
 the path of insertion and removal for the prosthesis,
 and the height of contour for each abutment.

Upon insertion,
• the clasp should contact the axial surface,
• flex till the height of contour is reached
• and then return to passive state after seating

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JSS ACADEMY OFPROTHERO
HIGHER EDUCATION
CONE & RESEARCH
THEORY
JSS Dental College & Hospital
In 1916, Prothero introduced the “Cone theory” of clinical crown anatomy
and provided a conceptual basis for mechanical retention.

• Contours of a clinical crown • The height of contour is at the junction

resemble two cones sharing a of the occlusal and cervical
common base. convergence.
• The line formed at the junction • It represents the greatest axial diameter
of these cones represents the of the clinical crown when viewed
greatest diameter of the tooth along the proposed path of insertion.

- Height of contour, a term first used by Dr Edward Kennedy in 1928.

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 DEEDUCATION
JSS ACADEMY OF HIGHER VAN CONCEPT
& RESEARCH
JSS Dental College & Hospital
M. M. DeVan introduced the terms Suprabulge and Infrabulge, As an
application of Prothero’s cone theory.

SUPRABULGE: The portion of an

abutment that converges toward the
occlusal or incisal surface is considered
the suprabulge aspect of the Abutment

INFRABULGE: The portion of the clinical

crown that converges apically from the
height of contour is considered the
infrabulge aspect of the abutment.
Infrabulge locations are designated as
undercut relative to the height of
contour.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSSBased
Dentalon De Van’s
College Concept, two basic categories of retentive clasp
& Hospital
assemblies were given.
1. Circumferential, Suprabulge direct retainers or Akers clasp after
Dr Polk E. Akers.
2. Vertical projection, Bar-type, Infrabulge direct retainers or Roach
clasp after Dr F. Ewing Roach.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
Structure
JSS Dental College & Hospital of a clasp assembly
1. A Rest
2. A Retentive arm,
3. A Reciprocal element,
4. One or more minor connectors

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 REST:
JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
• The component of a clasp that provides vertical support for the
prosthesis is called a rest.
• The portion of the abutment prepared to receive the rest is a rest
seat.
rests serve to
1. Resist displacement of the prosthesis toward the supporting tissues
2. Transmit functional forces parallel to the long axes of the
abutments.

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JSS ACADEMY
RETENTIVE OF HIGHER EDUCATION & RESEARCH
ARM:
JSS Dental College & Hospital
A retentive arm is the only portion of a removable partial denture that
contacts the surface of an abutment apical to the height of contour

• A suprabulge clasp arm • An infrabulge clasp arm

approaches the undercut region approaches the undercut
of an abutment from an occlusal region from an apical
or incisal direction direction
• Parts are, Shoulder, midsection • Parts are Approach arm and
and terminus terminus

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JSS ACADEMYARM:
RECIPROCAL OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
The component of a clasp assembly that braces an abutment during
prosthesis insertion and removal is called a reciprocal element

The reciprocal element may be

• a cast clasp,
• a lingual plate,
• a combination of mesial and distal minor connectors.

The reciprocal element

must contact the
abutment tooth at or
occlusal to the height of
contour.

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JSS ACADEMY
PURPOSE OF HIGHER ARM:
OF RECIPROCAL EDUCATION & RESEARCH
As the retentive arm passes over the
JSS Dental
height College & itHospital
of contour, displays a slight amount of flexure.
• This flexure places lateral stress on the abutment.
• If this stress is not counteracted, it may cause lateral displacement of
the abutment and significant damage to the supporting
periodontium.
• To prevent these effects, a rigid reciprocal element must be used.
• The reciprocal element should be placed on the tooth surface
opposite the retentive arm

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JSS ACADEMY
MINOR OF HIGHER EDUCATION & RESEARCH
CONNECTOR:
JSS Dental College & Hospital
It may serve as :
1. a guiding plate to direct insertion and removal of the RPD,
2. a reciprocal element to counteract non-axial forces produced by a
retentive clasp,
3. an approach arm for an infrabulge clasp.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
Requirements
JSS Dental College & Hospital of a clasp assembly

All clasp assemblies must be designed so that they satisfy the following
six requirements:
1. RETENTION
2. SUPPORT
3. STABILITY
4. RECIPROCATION
5. ENCIRCLEMENT
6. PASSIVITY.

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 1.EDUCATION
JSS ACADEMY OF HIGHER RETENTION& RESEARCH
JSS Dental College & Hospital
Retention is the quality of the clasp assembly that resists forces acting to
dislodge components away from the supporting tissues.

1. Only the clasp terminus should

engage the prescribed undercut.
2. The accompanying rest must
provide support so the clasp
terminus is maintained in an
optimal location.
3. The minor connector must be
sufficiently rigid to ensure proper
stability and function of parts of
the clasp assembly.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS
4. Dental College & Hospital
The reciprocal element must contact the
abutment slightly before the retentive
element contacts the tooth, and it must
maintain contact until the prosthesis is
fully seated to protect the abutment from
potentially destructive lateral forces.

5. Components must provide sufficient

encirclement to prevent movement of the
abutment away from the associated clasp
assembly, otherwise retention will be lost.

6. Indirect retainers must resist forces acting

to dislodge the prosthesis from its fully
seated position (these forces may result
from the actions of sticky foods, gravity,
etc).

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JSS ACADEMY OF HIGHER EDUCATION
CLASP & RESEARCH
FLEXIBILITY
JSS Dental College & Hospital

Dr K. J. Anusavice defines maximum flexibility as the strain occurring

when a material is stressed to its proportional limit.
The flexibility of the retentive clasp arm may be influenced by
1. Length
2. Cross-sectional form
3. Cross-sectional diameter
4. Longitudinal taper
5. Clasp curvature
6. Metallurgical characteristics of
the alloy.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
This is represented by a mathematical formula of Uniform
JSS Dental College & Hospital
Cantilever Beam

Where D = deflection, L = length, E = modulus of elasticity, w = beam

width, and t = beam thickness, P = applied force

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
LENGTH:
JSS Dental College & Hospital

• Increasing the length of a clasp arm produces a significant increase

in flexibility.
• By increasing the flexibility of the clasp, the horizontal stresses
imparted to an abutment during placement, withdrawal, and
movement of the prosthesis may be reduced.
• Nevertheless, the flexibility should not be so great that the
retentive characteristics of the clasp are lost.

CLASP WIDTH AND THICKNESS:

• Beam thickness has a much greater effect upon deflection than

does beam width.
• A width to thickness ratio of 2:1 is said to be optimal for half-round
cast clasps.
• Altering the clasp length is a more efficient method of increasing
clasp flexibility than is altering clasp diameter.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS TAPER:
Dental College & Hospital
• A uniformly tapered clasp is twice as flexible as a nontapered
clasp of the same proximal dimensions.

• The cross-sectional dimensions at the shoulder of the clasp

should be twice the cross-sectional dimensions at the clasp
terminus.

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JSS ACADEMY
CROSS OF HIGHER
SECTION FORM: EDUCATION & RESEARCH
JSS Dental College & Hospital
CIRCULAR CROSS SECTION HALF ROUND CROSS SECTION
omnidirectional flexure bidirectional flexure
permit dissipation of detrimental flexes in a plane that is
forces during functional perpendicular to the flat surface
movement of the prosthesis of the clasp. Therefore, stress
dissipation is somewhat limited
As a result, a retentive clasp with a circular cross-sectional form
provides better clasp flexibility.

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CURVATURE
JSS OFOF
ACADEMY A CLASP:
HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
• in more than one spatial plane reduces the clasp’s flexibility.
• Deflection of a curved beam is less than that of a straight beam of
similar length and material because curvature makes the beam more
rigid.
• When contouring a wrought-wire clasp arm, we should ensure that the
clasp arm remains in a single plane of space.

METALLURGICAL CHARACTERISTICS

• Alloys exhibiting higher elastic moduli exhibit greater stiffness, while

alloys displaying lower elastic moduli exhibit greater flexibility.
• CoCr – Higher elastic modulus, lower flexibility
• Gold alloys – Lower elastic modulus, Higher flexibility, Expensive
• An alternative would be Wrought-wire alloy .When increased
flexibility is required wrought-wire clasps should be attached to metal
frameworks using common soldering procedures.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital 2. SUPPORT

• Support is the quality of a clasp assembly that resists displacement

of a prosthesis in an apical direction.
• Primarily achieved through rests and rest seats.
• They aid in longevity of abutment tooth.

• A properly prepared rest seat and corresponding rest serve to:

1. resist displacement of the prosthesis toward the supporting
teeth and soft tissues, thereby ensuring that the clasp assembly
maintains its intended relation to the abutment
2. Transmit functional forces parallel to the long axes of the
abutments.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital 3. STABILITY

Stability is the quality of a clasp assembly that resists displacement of

a prosthesis in a horizontal direction.

The greatest contributions to stability come from:

1. The reciprocal element,
2. The shoulder(s) of a cast circumferential retentive clasp,
3. Vertically oriented minor connectors.

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 4. RECIPROCATION
JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital

Reciprocation is the quality of a clasp assembly that counteracts lateral

displacement of an abutment when the retentive clasp terminus passes
over the height of contour.

The reciprocal element may be

• a cast clasp
• lingual plating,
• or a combination of mesial and distal minor connectors.
Regardless of form, the reciprocal element must be rigid and must
contact the abutment tooth at or occlusal to the height of contour.

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JSS ACADEMY OF HIGHER
5. EDUCATION & RESEARCH
ENCIRCLEMENT
JSS Dental College & Hospital

• Encirclement is the characteristic of a clasp assembly that prevents

movement of an abutment away from the associated clasp assembly.
• Each clasp assembly must be designed to provide direct contact over
at least 180 degrees of the tooth’s circumference
• Encirclement may be continuous or discontinuous
• If discontinuous encirclement is planned, the clasp assembly must
contact the abutment tooth at three widely separated areas that
encompass more than half the tooth’s circumference.

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 6. PASSIVITY
JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
• Passivity is the quality of a clasp assembly that prevents the
transmission of adverse forces to the associated abutment when
the prosthesis is completely seated.
• The retentive arm should be activated only when dislodging forces
are applied to the removable partial denture.
• The clasp assembly will apply non-axial (ie, lateral) forces to the
abutment. This may result in discomfort, the potential for
unintended tooth movement, or premature failure of the retentive
arm due to metallurgical fatigue.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
CIRCUMFERENTIAL CLASP
JSS Dental College & Hospital
The cast circumferential clasp design was introduced by Dr N. B. Nesbitt
in 1916

ADVANTAGES:
1. Simplicity and ease of construction.
2. Excellent support, bracing, and retentive properties
3. Minimizes the entrapment of food and debris (Close adaptation to
tooth surface)
4. Design of choice for tooth supported prosthesis.
DISDVANTAGES:
1. Large amount of tooth surface that is covered by the clasp assembly
– Decalcification
2. Alters the gross morphology of the clinical crown – interferes with
food flow and Bolus elimination.
3. Ultimately may lead to damage to abutment tooth and
periodontium.
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JSS ACADEMY
Design rules. OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
1. C Clasp should originate from the framework above the height of
contour. The retentive arm should extend cervically and
circumferentially in a gently arcing manner. The terminus should
pass over the height of contour and enter the infrabulge portion of
the abutment. The reciprocal element should be located at or slightly
above the height of contour on the opposite surface of the tooth.

2. The retentive terminus should be directed occlusally, never toward

the gingiva.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
3. Clasp arm should terminate at the mesial line angle or distal line angle
JSS Dental College & Hospital
of the abutment, never at the midfacial or midlingual surfaces.

4. The retentive arm should be positioned as far apically on the

abutment as is practical. But it should not Impinge on the gingiva.

5. A cast circumferential clasp should not be used to engage

(a) The mesiofacial surface of an abutment adjacent to a
posterior edentulous space or
(b) The distofacial surface of an abutment adjacent to an
extensive anterior edentulous space.

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JSS ACADEMY
1. SIMPLE OFCLASP
CIRCLET HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital

Undercut located on the proximal surface of the abutment tooth away

from edentulous space.

ADVANTAGES:
 The simple circlet clasp design is versatile and widely used.
 Fulfills the design requirements of support, stability, reciprocation,
encirclement, and passivity
 Easy to construct and relatively simple to repair

LIMITATIONS:
Difficulty in adjustment - can be adjusted
only in a buccolingual Direction
Deprive the adjacent gingival tissues of
physiologic Stimulation – Tooth coverage

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JSS2.ACADEMY OF HIGHER
REVERSE CIRCLET EDUCATION & RESEARCH
CLASP
JSS Dental College & Hospital
• Undercut is located at the facial or lingual line angle adjacent to
an edentulous space.
• Infrabulge clasps are ideal in these situations but if it is
contraindicated, reverse circlet clasp can be used.

LIMITATION
 Difficult to provide adequate room for clasp components without
removing a significant amount of tooth structure from the abutments.
 Cannot be used for canine and premolar abutments.

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JSS ACADEMYCIRCLET
3. MULTIPLE OF HIGHER EDUCATION & RESEARCH
CLASP:
JSS Dental College & Hospital
A multiple circlet clasp design involves two simple circlet clasps joined
at the terminal aspects of their reciprocal elements

INDICATION:
 When the principal abutment tooth is periodontally compromised –
stress distribution btw multiple teeth.

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JSS ACADEMY OF
4. EMBRASURE HIGHER EDUCATION & RESEARCH
CLASP:
JSS Dental College & Hospital
An embrasure clasp is essentially two simple circlets joined at their
bodies

INDICATION:
 Used on the side of the arch where there is no edentulous space
LIMITATION:
 Adequate Tooth preparation should be done. Otherwise it will lead to
fatigue failure of the clasp.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
5. RING CLASP
JSS Dental College & Hospital

A ring clasp assembly is used to engage a

mesiolingual undercut on this mandibular
second molar abutment that has tipped
mesially and lingually following loss of the
first molar
To provide additional support for the
long clasp arm of a ring clasp assembly, a
facial bracing arm may be incorporated.

LIMITATION:
 Excessive tooth coverage –
Demineralisation.
 Susceptible to distortion and fracture.
 Difficult to correct and repair.

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6. FISHHOOK
JSS ACADEMYOR
OFHAIRPIN
HIGHERCLASP:
EDUCATION & RESEARCH
JSS Dental College & Hospital
• A Simple Circlet clasp in which the retentive arm loops back to engage
an undercut apical to the point of origin.
• the occlusal portion of the clasp arm should display consistent
dimensions, while the apical portion of the clasp arm should be gently
tapered.
INDICATION:
 Can be used as an alternative to Reverse circlet clasp when there is
insufficient occlusal clearance for reverse circlet clasp.
LIMITATIONS:
 Tooth should have sufficient vertical
height.
 Excessive tooth coverage
– Demineralisation
 Metal display – Unesthetic
 Less Flexible – Non axial forces.

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JSS ACADEMY
7. ONLAY OF: HIGHER EDUCATION & RESEARCH
CLASP
JSS Dental College & Hospital
An onlay clasp consists of a rest that covers the entire occlusal surface
and serves as the origin for buccal and lingual clasp arms.
INDICATION:
the occlusal surface of the abutment lies noticeably apical to the occlusal
plane.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital

ADVANTAGES:
 Serves as a vertical stop
 Aids in the establishment of an acceptable occlusal plane
DISADVANTAGES:
 Causes maximun tooth coverage and is most prone to caries.
 If opposing natural teeth, the clasp should have a layer of Acrylic /
Gold to prevent wearing away of the teeth.
 Should only be considered when fixed restoration of the teeth is not
possible.
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JSS ACADEMY OF HIGHER
8. COMBINATION CLASP: EDUCATION & RESEARCH
JSS Dental College & Hospital
• Introduced In 1965, Dr O.C. Applegate.
• It consists of an occlusal rest, a cast metal reciprocal arm, and a
wrought-wire retentive arm.
INDICATION:
Abutment adjacent to a Kennedy Class I or Class II posterior Edentulous
area when the usable undercut is located at the mesiofacial line angle of
the most posterior abutment.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
ADVANTAGES:
JSS Dental College & Hospital
 Omnidirectional flexure allows the clasp to flex in all planes and can
minimize the transfer of potentially harmful forces to the abutment
 Kinder to Distal extension abutment.
 Can also be used in a greater undercut because of better flexibility.
 Minimal Tooth coverage, more esthetic.

LIMITATIONS:
 Excessive Laboratory procedure
 More prone to damage
 Does not possess the stabilizing/ bracing qualities of other
circumferential clasps.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
INFRABULGE CLASPS
JSS Dental College & Hospital

• Introduced by Dr F. Ewing Roach in 1930.

• An infrabulge clasp approaches the undercut region of an abutment
from an apical direction
• Flexibility of the infrabulge clasp is controlled by the taper and length
of the approach arm.

ADVANTAGES:
 exhibits a “push” type of retention that is more effective than the
“pull” retention associated with a suprabulge clasp.
 More esthetic

LIMITATIONS:
 Minimal Horizontal stability - additional bracing and stabilizing units
may be required.
 More prone to accumulation of food debris

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JSS ACADEMY
DESIGN OF HIGHER EDUCATION & RESEARCH
RULES:
JSS Dental College & Hospital
1. Approach arm should not impinge on soft tissues
2. Approach arm should cross perpendicular to the free gingival
margin.
3. Approach arm should never be designed to “bridge” an area of soft
tissue undercut

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JSS ACADEMY
DESIGN OF HIGHER EDUCATION & RESEARCH
RULES:
JSS Dental College & Hospital
4. Approach arm should be uniformly tapered from its origin to the
clasp terminus.
5. Clasp terminus should be positioned as far apically on the abutment
as is practical.
6. Minor connector that attaches the occlusal rest to the framework
should be rigid and should contribute to the overall bracing and
stabilization characteristics of the prosthesis.

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1. T-CLASP:
JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
DESIGN:
• Originates from framework adjacent to edentulous space, extends
horizontally. The approack arm then takes a 90 degree bend to
contact the abutment at the height of contour.
• From this point, two horizontal projections arise. The projection
towards the edentulous area passes over the height of contour and
enters a undercut. The second projection extends in the opposite
direction and remains occlusal/incisal to the height of contour.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
INDICATION:
 Used in Kennedy Class I or Class II partially edentulous situations when
an undercut is located adjacent to the edentulous area.
CONTRAINDICATIONS:
 Mesiofacial undercut
 Height of contour located occlusally

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JSS ACADEMY
2. MODIFIED OF HIGHER
T CLASP : EDUCATION & RESEARCH
JSS Dental College & Hospital
• Non retentive arm of T clasp is not present
• Improves esthetics – can be given in canine and premolars.

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JSS
3. Y-ACADEMY
CLASP OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
A Y-clasp is formed when the approach arm terminates in the cervical
third of the abutment, while the mesial and distal projections are
positioned near the occlusal/incisal surface.

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4. I BAR
JSS CLASP OF HIGHER EDUCATION & RESEARCH
ACADEMY
JSS Dental College & Hospital

• Placed at or mesial to the midfacial prominence of the abutment.

• The tip of the retentive clasp contacts the abutment tooth at the
height of contour for an area of 2-3 mm in height and 1.5 to 2 mm in
width.
• As prosthesis rotation occurs, the retentive terminus moves mesially,
thus disengaging from the abutment.
• Used in Class I or class II applications
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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
ADVANTAGES:
JSS Dental College & Hospital
 Food accumulation is minimized because tooth contours are not
significantly altered.
 The clasp terminus disengages from the tooth when an occlusal load
is applied to the adjacent distal extension base.
 Because the approach arm does not contact the abutment, lateral
forces are minimized.

DISADVANTAGES:
 Minimal tooth contact
 Small clasp terminus.
 Less Horizontal Stability, Retention.
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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
RPI CLASP:
JSS Dental College & Hospital
Kratochvil in 1963 developed the early clasp assembly which consisted of three
separate units connected to each other only through the framework.
They were
• The mesial occlusal rest,
• A distal guide plate and an
• I-bar retainer.

He preferred a full length guide plane that is subsequently relieved in the mouth
to prevent torque or binding.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental
Krol College
in 1973 & Hospital
made certain modifications in the design of the proximal
plate and named it the RPI bar clasp design.

• He had a 2-3mm of contact of the tooth with the guide plane, the
section below this point being relieved and he felt that the V
shaped space that is left underneath was not as detrimental as the
possible restriction of rotation.
• Mesial rest was minimally prepared
• The I bar clasp was more mesially positioned to compensate for the
smaller proximal plate.

LIMITATIONS:
• Less vestibule Depth
• Potential Food Impaction
• Lingually Tilted Tooth

15-01-2023 Department of Prosthodontics 53

JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
RPA
JSS CLASPS
Dental College & Hospital

The rest, proximal plate, Aker’s clasp was developed and described by
Eliason in 1983

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
DIRECT
RETAINERS

INTRA- EXTRA-
CORONAL CORONAL

RETENTIVE
PRECISION SEMIPRECISION
CLASP ATTACHMENTS
ATTACHMENTS ATTACHMENTS
ASSEMBLIES

SUPRABULGE INFRABULGE

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
INTRACORONAL
JSS Dental College & Hospital ATTACHMENTS:

• Introduced by Herman E. S. Chayes in 1906.

• Intracoronal attachment reduces nonaxial loading and diminishes
rotational movement of the abutment during occlusal loading
• It Consists of Patrix/Flange And Matrix/Slot

CHEYES ATTACHMENT
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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
DESIGN:
JSS Dental College & Hospital
retention depends largely on the surface area of the two parts of
attachment in contact.
This surface area can be increased by
- Increasing area of cross section
- Increasing the extent of the attachment occlusogingavally

• T shaped
• H Shaped
• Circular

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
FRICTION
JSS Dental College & Hospital FIT
ATTACHMENTS WITH
ADJUSTMENT
• Constant insertion and removal of the prosthesis will cause the
attachment to wear. Hence some kind of adjustment is required to
tighten it once again.
• Mostly they can be tightened with a scalpel or blade. But some types
of attachments may be complicated and they will have manufacturers
instructions which will have to be followed.

STERN G/A ATTACHMENT CRISMANI ATTACHMENT

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital MC COLLUMS ATTACHMENT
It is paired. The slit should face
laterally

T – GESCHIEBE 123
It is cast along with a
bracing arm.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSSAUXILLARY
Dental College & Hospital
ATTACHMENTS:
• Since the size of the attachment is determined by the size of the
tooth, shorter teeth need auxillary retention for sufficient coverage
• Still a minimum of 4mm vertical height of the abutment is required.

SPRING LOADED PLUNGER

IN MATRIX – SCHATZMAN STERN GINGIVAL LATCH
SERIES ATTACHMENT

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JSS ACADEMY OF HIGHER
FACTORS EDUCATION
AFFECTING & RESEARCH
AUXILLARY ATTACHMENTS
JSS Dental College & Hospital
1. BULK : Any bulk in the matrix part of the attachment defeats
its purpose. Hence any auxillary attachments is given in the Patrix

2. ADJUSTMENT: Any spring loaded attachment should be

replaced in 6 months or yearly interval. Hence, proper access for
adjustment should be given.

3. RETENTION MECHANISM : Most of the fractures if attachment

occurs during adjustment. Sturdy attachment must be selected.
Spring loaded attachments are most sensitive to food impaction.

4. TRIMMING THE ATTACHMENT: Any interference in the

occlusal aspect will cause breakage of the attachment.

5. PLAQUE CONTROL: Should be straightforward to clean.

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JSS ACADEMY OF HIGHER
FRICTION FITEDUCATION & RESEARCH
ATTACHMENTS WITHOUT
JSS Dental College & Hospital
ADJUSTMENT

Round cross sectioned

Attachments are used in the
anterior abutments.

Beyeler attachment Is more

often used in posterior
abutments – More contact
area.

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JSS ACADEMY OF HIGHER APPLICATIONS:
EDUCATION & RESEARCH
JSS Dental College & Hospital
1. BILATERAL DENTURES
Major connector of the prosthesis provides cross arch stability. The
attachment substitutes the clasp arm, rest and reciprocal arm.
ADVANTAGES:
1. Appearance.
2. Retention unaffected by crown contour.
3. Reduced bulk.
4. Stability.
5. Elimination of food stagnation.
6. Non axial Stresses on abutment teeth minimised.
LIMITATIONS:
1. Preparation of Abutment teeth
2. Cost and time
3. Crown length and pulp size
4. Construction of attachment is Technique sensitive.

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JSS
2.ACADEMY OF DENTURES.
UNILATERAL HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
• Small tooth supported edentulous areas where a flange is required
for support or appearance.

ADVANTAGES:
• A clasp retained denture needs undercut on both buccal and
lingual aspect of the tooth.
• And if the size of the denture is too small – inadvertently swallow
the dentures.
• Hence Major connector is necessary in a clasp retained prosthesis.
• Another ideal alternative would be Fixed prosthesis.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
SEMI PRECISION ATTACHMENTS:

Louis Blatterfein in 1969 gave three aspects of rest

seat preparation.

I. OCCLUSAL ASPECT
1. Circular
2. Dovetail
3. Mortise
4. Rectangular

II. PROXIMAL WALLS

1. Parallel
2. Tapering – not
more than 5
degrees
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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
III. GINGIVAL FLOOR
1. Flat
2. Mortise
3. Thompsons dowel

Advantages:
 Versatility for clinical situations - employing various rest seat
outline forms.
 Variation in tooth size and shapes are easily accommodated.
 Better crown contour compared to prefabricated type
Disadvantages:
 Long term wear is more –Based on alloy.
 No standardization of sizing.
 Greater degree of laboratory skill and attention in detail.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
EXTRACORONAL
JSS Dental College & Hospital ATTACHMENTS
• Introduced to dentistry in the early 1900s by Henry P. Boos and
later modified by F. Ewing Roach,

• Provides a
1. Rigid,
2. Movable, or
3. Resilient connection between an abutment and a
removable partial denture

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSSAdvantages:
Dental College & Hospital
• No alteration of contour of the abutment crown.
• Can be used in short abutment teeth
• Greater freedom in the design
• Ease of insertion and removal

Disadvantages (Wolf RE 1980):

• Lack of occlusal stability
• Bulky
• Rebasing problems
• Improper control of force distribution
• Encroachment on the gingival papilla use of mini
attachment

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
RIGIDCollege
JSS Dental EXTRACORONAL
& Hospital ATTACHMENTS

• Roach / Ball and tube

• Ball and pin
• Stabilex
• Conex
• Scott attachment

Roach attachment Ball and pin attachment

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
STABILEX:

ADVANTAGES:
Superior mechanical retention – supported by
pins which can be screwed in.

DISADVANTAGES:
Bulky – takes up more mesiodistal space
Plaque control

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSSCONEX:
Dental College & Hospital
ADVANTAGES
• It is similar to stabilex except that it takes lesser
mesiodistal space.
• Both frictional and mechanical retention.

DISADVANTAGES:
• Plaque control

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSSSCOTT
DentalATTACHMENT:
College & Hospital

It has a removable telescopic crown on a

tapered connector.
• It can be rigid or allow an axio
rotational joint.
• Easy to clean and maintain

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
RESILIENT
JSS Dental College EXTRACORONAL
& Hospital ATTACHMENT:

Stress breaker compensates

for tissue resiliency and
reduces stress transmitted to
abutment tooth.

DALBO ATTACHMENT ADVANTAGES

They incorporate a tilt preventing
device
Resistance to both lateral and distal
displacing forces.
TYPES:
Shoulder Dalbo
Spring retained Dalbo
Miniaturised Dalbo
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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
Springs as stress breakers
JSS Dental College & Hospital

It is critical to change the springs every 6 months.

A replacement spring slightly too

long would have a tendency to lift
the base away from the mucosa.

If a spring loses its resiliency and

becomes de formed, damaging
loads can be applied to the
gingivae and to the mucosa distal
to the abutments.

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
Hinges
JSS as stress
Dental College breakers:
& Hospital

COMPLICATION:
1. The hinges should be aligned with sagittal plane to prevent jamming of the
hinges during rotation.
2. The hinges should be aligned with the midline of the ridges so that no
buccal or lingual movement of the base accompanies rotation.

Divergencies upto 20 degrees will cause no problem.

More than 60 degrees will cause stress in the abutment tooth.

LIMITATIONS:
• Plaque control
• Lingual Bulge
• Uneven edentulous span

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
BAR College
JSS Dental ATTACHMENTS
& Hospital

These attachments can be attached to:

• Metal coping
• Implants
Bar attachments can be:
1. Single sleeve / Multiple sleeve
2. Round / oval / U shaped in cross
section
DOLDER BAR: HADER BAR:
• Provides vertical and Resin sleeves
rotational movement
• Egg shaped
• Open sided sleeve

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital
ACKERMANN BAR: ADVANTAGES:
Circular cross section • Rigidly splint the teeth
• Provides good retention, stability
and support
• Provides cross arch stabilization
• Positioned close to the alveolar
bone (exhibit less leverage)

DISADVANTAGES:
• Bulk of bar
• Plaque accumulation
• Wearing
• Soldering procedure
• Manual dexterity

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College NON METAL
& Hospital CLASP DENTURES

• They are usually Flexible in nature

• They may or may not be fabricated with metal framework

MATERIALS
• Polyamide – Valplast, Lucitone
FRS
• Polyester
• Polycarbonate

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College NON METAL
& Hospital CLASP DENTURES
INDICATIONS CONTRAINDICATIONS
• Allergy to metallic components • Few remaining natural teeth –
of RPD • Short anatomical Crown of
• Torus abutment - Excessive stress on the
• Obturators clasp
• Patients with Repeated fracture
of dentures DISADVANTAGES
• Xerostomia • Intrusion of clasp into marginal
• May be used in distal extension gingiva causing periodontal
problems
ADVANTAGES: • Displacement caused by their
• Esthetics and comfort flexible bases on the supporting
• Temporary for implants – tissues can lead to lesions to the
reduced occlusal overload and coating fibromucosa and even
better tissue response acceleration of alveolar ridge
resorption
• Loss of polish

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS HIGH
DentalPERFORMANCE POLYMERS
College & Hospital

• Polyethyl ether ketone

• Polyether ketoneketone

PEEK: Better fexibility of its clasps

compared with CoCr allows it to engage
deeper undercuts.

Sheffield Design Clasp -

clasping assembly to
engage both above and
below the survey line,
providing support and
retention

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital

CONCLUSION:
Direct retainers play a very vital part in the construction of an
RPD. Knowledge of its components, design and knowing where
and how to provide the prosthesis through proper case
selection will make the prosthesis a success

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
REFERENCES
JSS Dental College & Hospital
1. Stewart – 4th edition
2. Mc Craken 13th edition
3. Preskiel Volime 1 Prescision attachments in prosthodontics.
4. Mendoza-Carrasco I, Hotta J, Sugio CYC, Procópio ALF, Urban VM,
Mosquim V, Foratori-Junior GA, Soares S, Neppelenbroek KH.
Nonmetal clasp dentures: What is the evidence about their use? J
Indian Prosthodont Soc. 2020 Jul-Sep;20(3):278-284. doi:
10.4103/jips.jips_459_19. Epub 2020 Jul 17. PMID: 33223697; PMCID:
PMC7654199
5. Fueki, Kenji, et al. "Clinical application of removable partial dentures
using thermoplastic resin—Part I: Definition and indication of non-
metal clasp dentures." Journal of prosthodontic research 58.1 (2014):
3-10.
6. Bural, C., Geckili, O. (2016). Direct and Indirect Retainers. In: Şakar, O.
(eds) Removable Partial Dentures. Springer, Cham.
https://doi.org/10.1007/978-3-319-20556-4_11

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JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
JSS Dental College & Hospital

THANK YOU!

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