direct retainers: clasp designs

1. By
Dr Vijyanta Suman

2.  INTRODUCTION
 DEFINITIONS
 CLASSIFICATION
 COMPONENTS
 IDEAL REQUIREMENTS OF DIRECT RETAINER
 FACTORS DETERMINING RETENTION
 DIRECT RETAINER SELECTION
 DIFFERENT TYPES OF CLASPS
 SPECIALIZED RETAINERS
 ESTHETIC RETAINERS
 CONCLUSION
 REFERENCES 2

3. 3
The term retention refers to resistance to dislodgement of
the prosthesis in an occlusal direction.
INTRODUCTION…
Ideal retention will retain the RPD against reasonable dislodging
forces without placing undue strain on the abutment teeth or the
components of the clasp assembly

4. 4
RETENTION - that quality inherent in the dental prosthesis acting
to resist forces of dislodgement along the path of placement
DIRECT RETENTION - retention obtained in a partial removable
dental prosthesis by use of clasps or attachments that resist
removal from the abutment teeth
HEIGHT OF CONTOUR : line encircling a tooth and designating
its greatest circumference at a selected axial position determined
by a dental surveyor
DEFINITIONS…
Keith J. Ferro, Editor and Chairman, Glossary of Prosthodontic Terms. 9th
Edition. JPD. May 2017;117:e75

5. CLASSIFICATION
Stewart’s clinical removable prosthodontics.4th
edition.2008.p63

6. INTRA CORONAL RETAINERS
• PROPOSED BY DR HERMAN E S CHAYES IN 1906.
• CAST OR ATTACHED WITHIN THE CONTOURS OF NATURAL
TEETH(ABUTMENT). KEYWAY AND KEY…..OPPOSING VERTICAL WALLS
PROVIDES RETENTION. RETENTION IS ACHIEVED BY FRICTIONAL
RESISTANCE.
• 1. PRECISION ATTACHMENT
• MANUFACTURED BY HIGH PRECISION TECHNIQUE AND INSTRUMENTS
• 2. SEMI PRECISION ATTACHMENT
• LESS INTIMATE CONTACT BETWEEN MATRIX AND PATRIX COMPONENT.

8. EXTRACORONAL ATTACHMENT
• First proposed by Henry H boos in 1900 later modified by
Ewing F Roach in 1908
• Retention from mechanical resistance
• Permit vertical movement during occlusal loading
• Minimize potentially damaging forces to abutment
• Stress breaking or stress directing effects

9. SELECTION OF ATTACHMENT
• Selection requires evaluation of 3 factors: location, retention and
available space
• The advantage of the intracoronal attachment is that the forces
exerted by the prosthesis are applied more closely to the long axis of
the tooth. intracoronal attachments are nonresilient and may require
double abutting or splinting of the adjacent teeth
• A clinical crown of greater than 4 mm is required with a similar
faciolingual width
• Extracoronal attachments have resilient attributes, attachment
alignment is not as critical thus advantage of multiple paths of
placement for the prosthesis

10. RETENTIVE CLASP ASSEMBLY
• FORCES ACTING TO DISLODGE A REMOVABLE PARTIAL
DENTURE TYPICALLY OCCUR PERPENDICULAR TO THE
OCCLUSAL PLANE
• TO MOST EFFECTIVELY RESIST DISLODGING FORCES,
ABUTMENTS MUST PROVIDE UNDERCUT AXIAL SURFACES
WHEN THE DENTAL ARCH IS ORIENTED WITH THE OCCLUSAL

12. GENERAL CONSIDERATIONS
• PROTHERO CONE THEORY 1916
• KENNEDY (1928) - HEIGHT OF CONTOUR
• IT REPRESENTS THE GREATEST AXIAL DIAMETER OF THE
CLINICAL CROWN WHEN VIEWED ALONG THE PROPOSED
PATH OF INSERTION.
• DEVAN 1955 - SUPRABULGE
INFRABULGE

13. RETENTIVE CLASP ASSEMBLIES
14
Circumferential or
Aker’s or suprabulge Bar type or vertical
projection
or infrabulge or Roach
clasp

14. BASIC PARTS OF A CLASP
ASSEMBLY

16. • THE RIGID CLASP SHOULDER (S)
• THE RELATIVELY FLEXIBLE MIDSECTION OF THE CLASP
ARM (M)
• .THE FLEXIBLE CLASP TERMINUS (T)

17. REQUIREMENTS OF A CLASP ASSEMBLY
18
Retention
Support
Stability
Reciprocation
Encirclement
Passivity

18. 19
RETENTION:
1.Only the retentive 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

19. 20
4.The reciprocal element must contact the abutment
slightly before the retentive

20. 21
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

21. 22
Factors affecting The AMOUNT OF RETENTION
provided by a clasp assembly :
TYPE OF CLASP used
FLEXIBILITY of the retentive arm
LOCATION OF THE RETENTIVE TERMINAL in
the prescribed undercut

22. 23
Type of clasp used: Infrabulge Vs Suprabulge
Infrabulge clasp requires that the retentive arm be "pushed"
over the height of contour.
• Suprabulge clasp is "pulled" over the height of contour.

23. 24
FLEXIBILITY
Anusavice defines maximum flexibility as the strain occurring when a
material is stressed to its proportional limit.
Maximum flexibility of a retentive clasp arm may be defined as the
greatest amount of displacement that can occur without causing
permanent deformation of the clasp arm.

24. FLEXIBILITY OF THE CLASP ARM
DEPENDS ON ITS
25
Length
Cross-
sectional form
Cross-
sectional
diameter
Longitudinal
taper
Clasp
curvature
Metallurgical
characteristics
of the alloy

25. 26
LENGTH
Flexibility  as Length 
Flexibility is directly proportional to L3
Increasing the length and thus the flexibility, reduces
the horizontal stresses imparted to the abutment tooth
during insertion and withdrawal.

26. CROSS SECTIONAL DIAMETER
• Flexibility as Diameter
• THE AVERAGE DIAMETER TO BE CONSIDERED IS AT A POINT
MIDWAY BETWEEN ITS ORIGIN AND ITS TERMINAL END
• THICKNESS OF THE CLASP ARM IN THE BUCCOLINGUAL
DIRECTION IS TO BE CONSIDERED RATHER THAN THE WIDTH
IN THE OCCLUSO-GINGIVAL DIRECTION 27

27. 28
TAPER:
• A uniformly tapered clasp is more flexible than a
nontapered clasp of the same proximal dimensions
• To achieve the ideal uniform taper for optimal retentive
clasp arm flexibility, the cross-sectional dimensions at
the shoulder of the clasp should be twice the cross-
sectional dimensions at the clasp terminus

28. 29
.
CROSS-SECTIONAL FORM
A circular cross-sectional clasp form imparts
omnidirectional flexure, while a half-round form
allows only bidirectional flexure

29. 30
Curvature of a clasp in more than one spatial plane reduces the clasp's
flexibility.
When contouring a wrought-wire clasp arm, the operator should
ensure that the clasp arm remains in a single plane of space.
Multiple bends, especially those placing the clasp arm in multiple
planes of space, may produce permanent deformation of the
microstructure and lead to increased rigidity.
CURVATURE OF A CLASP

30. 31
METALLURGICAL PROPERTIES OF AN ALLOY
• Modulus of elasticity and flexibility are inversely related.
• MOE: Base metal alloys > cast gold > wrought gold wires
• Wrought wire is produced by drawing a cast metal through a
die. This process produces elongation of the alloy’s crystalline
microstructure
• The elongated crystalline structure of wrought wire imparts
greater flexibility than a conventional crystalline structure
• Wrought wire clasps should be soldered not casted (as far from

31. 32
The retentive terminal: flexible:- low modulus of elasticity.
The reciprocal elements: stiff and unyielding :- high modulus of
elasticity.
A clasp of the same cross-section is stiffer in cobalt-chrome than
in cast gold.

32. 33
Location of each retentive clasp
terminus relative to the height of
contour may be described in two
distinct dimensions:
(1)Mediolateral or horizontal
dimension
(2) Occluso-apical or vertical
dimension.
LOCATION OF RETENTIVE CLASP TERMINUS
The position of the retentive clasp terminus against the axial
surface of an abutment influences the retentive force
imparted by the clasp.

33. 34
While keeping all other clasp-
related factors constant,
positioning the clasp
terminus in a greater
horizontal undercut will result
in increased retentive force
a retentive clasp engaging an
abutment that possesses a
greater angle of cervical
convergence will possess
increased retentive force

34. 35
SUPPORT
• Support is the quality of a clasp assembly that resists
displacement of a prosthesis in an apical direction.
• Rest
• Elements that contact the abutment occlusal to the
height of contour (eg a reciprocal element or shoulder
of retentive clasp)
Stewart’s clinical removable prosthodontics.4th edition.2008.p75

35. 36
STABILITY
• quality of a clasp assembly that resists displacement of
a prosthesis in a horizontal direction
• Rigid framework components contacting vertically
oriented hard and soft tissues contribute to the stability
of a prosthesis
• eg- Reciprocal element, rigid portion of retentive clasp
arm, minor connectors and guide plates
Stewart’s clinical removable prosthodontics.4th
edition.2008.p63

36. 37
RECIPROCATION
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.
Lateral displacement of an abutment is potentially harmful to the
supporting periodontal tissues.
To negate these forces, a clasp assembly must include a rigid
component that resists lateral movement of the affected tooth.
This component is known as a Reciprocal element.

37. 38
The reciprocal element may be a cast clasp, lingual plating,
or a combination of mesial and distal minor connectors.

38. 39
ENCIRCLEMENT
Encirclement is the characteristic of a clasp assembly that
prevents movement of an abutment away from the
associated clasp assembly

39. 40
PASSIVITY
•quality of a clasp assembly that prevents the transmission of
adverse forces to the associated abutment when the prosthesis is
completely seated.
•A clasp assembly should be passive when fully seated. The
retentive arm should be activated only when dislodging forces are
applied to RPD
•If the clasp assembly is not fully seated, the retentive terminus
will not be positioned in its intended location. As a result, the
clasp assembly will apply non-axial forces to the abutment

40. Mc cracken’s Removable partial prosthodontics. 2016. 13th edition.
Elsevier. P67-93

41. 42
DIFFERENT TYPES OF CLASPS

42. SUPRABULGE OR CAST CIRCUMFERENTIAL OR
AKERS CLASP
INTRODUCED BY DR. N.B. NESBITT in 1916.
It is the design of choice for tooth-supported removable
partial dentures
• SIMPLICITY OF DESIGN
• EASY CONSTRUCTION
• PROVIDES EXCELLENT SUPPORT, BRACING AND
RETENTIVE PROPERTIES
• CLOSE ADAPTATION TO THE ABUTMENT AND, THEREFORE,
MINIMIZES THE ENTRAPMENT OF FOOD AND DEBRIS.
43
ADVANTAGES

43. 44
Disadvantages
If proper oral hygiene is not maintained, the underlying enamel is at
increased risk for decalcification.
cast circumferential clasp also alters the gross morphology of the
clinical crown
Difficulty in adjusting- half-round form prevents edgewise
adjustment.
Bending the clasp to increase retention has to be accomplished
exactly at the correct location.

44. 45
DESIGN RULES FOR CIRCUMFERENTIAL CLASP
Origin…
Direction..
Termination…
Position..
clasp should originate from the portion of frame work that
lies above the height of contour
Retentive terminus should always be directed occlusally
never towards gingiva
Clasp arm should always terminate at mesial or distal line
angle, never at mid facial or midlingual surface
Should be positioned as far apically on the abutment as is
practical.

45. 46
SIMPLE CIRCLET CLASP:
Most versatile and widely used design.
Clasp of choice: tooth supported rpds
usually originates on the proximal surface of an abutment adjacent to
an edentulous area, with the clasp arms projecting away from the
edentulous space.
Uncomplicated design and easy to repair

46. 47
Indication
When the available undercut is located
at the facial or lingual line angle
adjacent to an edentulous space (2nd
choice after Infrabulge clasp).
REVERSE CIRCLET/REVERSE APPROACH
distal extension base is loaded,
the posterior aspect of the prosthesis
moves toward the underlying tissues
the tip of the retentive clasp moves into an area of greater
undercut torsion stresses on the abutment are minimized and
rpd is retained

47. 48
• shoulder of a reverse circlet clasp originates from a
minor connector that must traverse the marginal
ridges of adjacent teeth
• Because a reverse circlet clasp crosses the facial surface from
mesial to distal, it is a poor choice from an esthetic viewpoint. As a
result, it is not the clasp of choice for canine and premolar
abutments

48. 49
MULTIPLE CIRCLET CLASP
two simple circlet clasps joined at the terminal aspects of
their reciprocal elements.
Indication:
When the principal abutment tooth is periodontally
compromised

49. 50
EMBRASURE CLASP/MODIFIED CRIB CLASP
Two simple circlet clasps joined at the body
An embrasure clasp is used when no
edentulous space exists at the clasp
assembly site.
Can be subrabulge or infrabulge type
Can be cast or wrought.

50. 51
RING CLASP
Indication – tipped molars
In most instances, the clasp originates from a mesial rest. traverses the
facial and distal surfaces of the tooth, remaining occlusal to the height
of contour. At the middle of the lingual surface, the clasp arm passes
apical to the height of contour and engages undercut at the mesiolingual
line angle.

51. 52
C-CLASP (REVERSE ACTION/ HAIRPIN/FISH-
HOOK CLASP)
Indication…
• when the retentive undercut lies adjacent to the edentulous span.
•Simple circlet clasp in which the retentive arm loops back to
engage an undercut apical to the point of origin.
•Two horizontal components of the retentive arm - occlusal portion
and apical portion
•3rd choice after infrabulge, reverse circlet for undercuts adjacent
to post edentulous space

52. 53
Limitations
• sufficient clinical crown height: Adequate space between the occlusal
and apical aspects of the retentive arm to provide access for metal
finishing procedures and to minimize food accumulation
• The occlusal aspect of the retentive arm also should not interfere
with the opposing teeth in maximum intercuspation.
• C-clasp design generally yields inadequate flexibility- resulting in
harmful non-axial forces
• Unesthetic (avoided on canine & premolars)

53. 54
ONLAY CLASP DESIGN
• An onlay clasp consists of a rest that covers the entire
occlusal surface and serves as the origin for buccal and
lingual clasp arms.
• This clasp design is indicated when the occlusal surface
of the abutment lies noticeably apical to the occlusal
plane.
• The onlay rest serves as a vertical stop and also aids in
the establishment of an acceptable occlusal plane.

54. 55
HALF-AND-HALF CLASP
•Consists of a cast buccal circumferential clasp arm
originating from the guide plate and a cast lingual
circumferential arm originating from the minor connector.
•Indicated for lingually inclined premolars.

55. 56
COMBINATION CLASP
Introduced by Dr. O.C.Applegate in 1965
Composed of a wrought wire retentive arm
and a cast metal reciprocal arm.
The combination clasp is most frequently
indicated on an 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.

56. 57
Advantages:
• Esthetic- increased flexibility allows the clasp tips to be placed in
deeper undercuts and closer to the gingiva
• Allows for greater adjustability.
Because of their round form, they
can be adjusted in any spatial plane.
Disadvantages:
• Additional laboratory procedure
• Increased potential for permanent deformation by the patient.

57. INFRABULGE CLASP
(VERTICAL PROJECTION/ROACH/BAR TYPE
CLASP) 58

58. 59
This design was introduced in early 1900s but received
popularity by Dr. F Ewing Roach in 1930.
• Minimal tooth contact and minimal distortion of normal tooth
contours
• Improved esthetics
• Increased retention (push action)
• Decreased torque forces applied to terminal abutments in
extension RPDs

59. 60
• They cannot be used in the presence of soft tissue undercuts, a
shallow vestibule or high frenal attachments.
• Bracing action provided by bar clasps is considerably less than
that provided by cast circumferential clasps
• The bar clasp will not totally disengage in certain distal extension
cases (where the undercut is located on the distofacial surface
of the terminal abutment).
• Appearance may be adversely affected if the smile line is high
enough to expose the approach arm as it crosses the gingiva.
DISADVANTAGE
S

60. 61
DESIGN RULES FOR INFRABULGE CLASPS:
• Approach arm should not impinge the soft tissues.
• Tissue surface smooth and well polished.
• Approach arm should cross the free gingival margin at 90 degrees.
• To optimize flexibility the approach arm should be uniformly
tapered from its origin to the clasp terminus.
• Clasp terminus should be positioned as far apically on the
abutment as is practical.

61. 62
TYPES OF INFRABULGE CLASPS:
• T- clasp
• Modified T – clasp
• Y- clasp
• I clasp

62. 63
T – Clasp
• This clasp design is often used in Kennedy Class
I or Class II partially edentulous situations
when an undercut is located adjacent to the
edentulous area (distofacial aspect of
abutment)
• Upon loading, the retentive tip moves apically
and mesially. This transmits a relatively small,
mesially directed force to the abutment. The
mesially directed force is well tolerated as a
result of sound contact with the adjacent
natural tooth.

63. 64
if the only available
undercut is located on
the mesiofacial aspect
of the most posterior
abutment.
Never be used in a
Kennedy Class I or
Class II partially
edentulous
As prosthesis rotation occurs, the retentive terminus of the T-clasp moves
occlusally, engaging the abutment. Clasp engagement places occlusally directed
stress on the abutment. This stress is not counteracted, resulting in potentially
harmful force being delivered to the abutment

64. 65
Modified T-clasp design:
The modified T-clasp is essentially a T-clasp that lacks
the nonretentive, horizontal projection.
More esthetic than T-clasp.

65. 66
Y – Clasp:
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 surface.

66. I- bar clasp
• The clasp arm contacts the abutment surface over an area
that extends from the measured undercut to the height of
contour.
• the contact area between the clasp and the abutment is 2.0
to 3.0 mm in height and 1.5 to 2.0 mm in width.
• The approach arm has a half-round, cross-sectional geometry
and is characterized by a gradual and uniform taper
throughout its length.

67. CLASP DESIGN PHILOSOPHIES
• RPI
• RPA CLASPS
• RPL CLASPS
• VRHR CLASPS
• RPH CLASPS
• DEVAN CLASP
• MGR CLASPS

68. 69
In 1963, Kratochvil introduced I-bar design philosophy.
Consists of
•A mesial rest,
• Long distal proximal plate
• I- bar retentive element
• claimed that the resultant clasp design minimized
torquing forces and directed occlusal loads parallel to the
long axes of abutments

69. • As the distance from the rotational center (rest) to
the denture base is increased, the associated radius
becomes larger, and the accompanying
arc becomes more linear.
• Hence anterior placement of rests helps direct the
forces vertically onto the bearing tissues beneath the
extension bases.
WHY MESIAL REST ?
"buttressing" effect

70. 71
Proximal plates:
extend from marginal ridge to tooth-tissue junction
This configuration
• Improved stabilization
• Improved retentive characteristics by limiting the path of insertion
and removal
• Protects the tooth-tissue junction by reducing food impaction
between the tooth and the proximal plate
• Provides reciprocation during insertion and removal of the prosthesis
• Distributes occlusal forces throughout the arch

71. KROL’S RPI SYSTEM(1973)
Krol was in agreement with kratochvil’s basic design but opposed his
extensive tooth preparation.
Modified the design: less tooth alteration- minimal coverage
• Rest preparations are less extensive(only into the triangula
The I-bar terminus is pod shaped to allow additional
tooth contact, and the vertical portion of the clasp arm
assumes a more mesial position to achieve efficient
reciprocation from the smaller proximal plate

72. 73
Proximal Plate
The superior edge of the proximal plate is located at the bottom of the
prepared guide plane which should be at the junction of occlusal 1/3
and middle 1/3 of the proximal surface. The remainder of the proximal
plate lies below the guide plane.
The proximal plate extends lingually just far enough so that the
distance between the minor connector and proximal plate is less than
the mesiodistal width of the tooth .

73. VERTICAL RECIPROCAL ARM HORIZONTAL
RETENTIVE ARM
GRASSO IN 1980
 A DISTAL OCCLUSAL REST SUPPORTED BY A MINOR CONNECTOR.
 A LINGUAL VERTICAL RECIPROCAL COMPONENT ORIGINATING
FROM THE MAJOR CONNECTOR.
 A HORIZONTAL RETENTIVE ARM ATTACHED TO EITHER THE
MAJOR CONNECTOR OR THE RETENTION LATTICE WORK
VRHR Clasp
Grasso JE: A new removable partial denture clasp assembly. J Prosthet
Dent 1980;43:618-621

74. 75
RPA CLASP (REST-PROXIMAL PLATE-
AKERS CLASP):
•Consists of a mesial rest, a proximal plate, and a circumferential
retentive arm originating from the proximal plate.
•Retentive arm may cast or wrought wire.
•The RPA clasp has been recommended for extension RPDs when the
use of a bar clasp is contraindicated.
Eliason CM. RPA clasp design for distal extension removable partial
dentures. JPD.1983;49:25-27

75. RPL CLASP (one half t type-bar
clasp/modified t-bar)
• The i-bar is replaced by an L-shaped direct
retainer and engages the distobuccal undercut in
extension bases
• The L-bar frees itself from the abutment tooth
when rotation of the denture occurs around the
mesio-occlusal rest
• Located more distally on the buccal surface, the l-
bar is more esthetically acceptable.
76
Ben-Ur Z, Aviv I, Cardash HS. A modified direct retainer design for distal
extension reovable partial denture. J Prosthet Dent 1988;60(3):324-44

76. Aim: the functional load exerts with RPI and RPL
direct retainer in bilateral distal extension
there is a significant difference between RPI and
RPL direct retainer design, the occlusal load
concentrated at edentulous area either RPI or
RPL direct retainer, and the occlusal load
distribution between the first premolar and
edentulous area are more uniform on RPI direct
retainer design.
Dahlia S,et.al RPI and RPL clasp masticatory load distribution in lower free
end denture case with photoeslastic methods. Padjadjaran Journal of
Dentistry 2007, 18(1):34-45

77. Nazarova E. Taylor TD. The RPH Clasp Assembly: A Simple Alternative to Traditional
Designs. Journal of Prosthodontics.2012;20:331–333(ACP 2011)
RPH Clasp Assembly
Mesial rest
Proximal plate
Horizontal retentive arm: horizontal retentive arm
touches the abutment tooth only at its retentive tip
Advantages:
• Retains stress breaking concept of
RPI
• can be used in case of soft tissue
undercut, limited vestibular space,
high frenal attachment
• More esthetic

78. It is made more flexible than the usual clasp arm
Also known as infrabulge or mirror view clasp
Uses proximal undercut .
Two occlusal rests are used on each abutment.
DE VAN CLASP

79. 80
SPECIALIZED RETAINERS
ODDO HINGE CLASP
Indication: labially inclined anterior abutment with height of contour
very near the incisal edge(deep undercuts)
Rigid cast clasp arm hinged at the point of attachment to the
denture base and is held in contact with the tooth by a clip or spring
lock
The hinge is opened, the prosthesis seated, and the hinge closed.
Donald A Cameron; Mervyn F Lyons. Properties of a custom-made
hinge clasp compared with a conventional circumferential clasp. JPD.
1996;75(3):326–331

80. DIRECT RETAINERS IN THE ESTHETIC ZONE
81
Aras MA et al. Direct retainers: Esthetic solutions in the smile
zone.JIPS.2005;5:4-9
Hidden
clasps/internally
braced clasps
Masking of the
clasps with resins
and composites
Metal-free
clasps.

81. HIDDEN CLASPS/INTERNALLY BRACED
CLASP DESIGN
GUIDING PLANES
• Guide planes may reduce or eliminate the need for
conventional clasp retention in tooth-borne rpds.
• Guide planes themselves serve to provide retention
• Indication: Kennedy class III
• Cingulum rest, retentive arm-lingual undercut
82

82. MESIAL GROOVE RECIPROCATION (MGR) CLASP
• 19 gauges round i-bar and retentive dimple
located at at distobuccal undercut on the tooth.
• Uses a mesial groove or rest or distal proximal
plate provides reciprocation
83

83. • MILLER IN 1972 designed a clasp to satisfy both the mechanical
and esthetic requirements without the shortcomings of the
internal attachment.
• The cingulum clasp has 2 lingual clasp arms.
ERNEST L. MILLER J.PROSTHET.DENT 1972
Cingulum clasp

84. SADDLE LOCK
• Eliminates facial clasp display while achieving
natural esthetics with superior stability and
retention.
• Eliminates facial clasps by using the available
mesial/distal concave surfaces of the abutment
teeth for retention instead of the buccal
undercuts
85
Aras MA et al. Direct retainers: Esthetic solutions in the smile zone.
JIPS.2005;5:4-9

85. MASKING THE DIRECT RETAINER
• COMPOSITE RESIN
• The difficulty of using acrylic/composite resin to
veneer rpd metals lies in the difference between their
abilities to flex and their coefficient of thermal
expansion.
• The less flexible the clasp, the more likelihood there is that
the bond will endure
• MACROMECHANICAL RETENTION
• MICROMECHANICAL RETENTION
86

86. METAL-FREE CLASPS
• OPTI•FLEX
• ACETYL RESIN CLASPS, METAL-FREE,
Lightweight partial dentures that
provide natural esthetics and a
comfortable fit can be designed
• opti•flex coating applied to metal clasps
87
Flexite Plus: flexible thermoplastic
material, monomer-free, virtually un-
breakable, lightweight, and impervious
to oral fluids.

87. OTHER ESTHETIC CLASPS …
• ESTHETI CLASP WIRE
• SMILE RITE PARTIALS
• ESTHETI-FLEX DUET
• FLEXITE PLUS CAST THERMOPLASTIC
• PROFLEX CLEAR WIRE CLASPS
• NATURAL FLEX

88. CONCLUSION
• Prosthesis design should be kept as
simple as the clinical situation permits
• Selection of the most appropriate clasp
assembly for a specific clinical situation
must be based on a variety of factors
• Correct design and principles should be
followed in order to achieve maximum
retention

89. REFERENCES
• Stewart’s clinical removable partial prosthodontics. 2008. 4th
edition
• Mc cracken’s Removable partial prosthodontics. 2016. 13th
edition. Elsevier. P67-93
• Grasso JE. A new removable partial denture clasp assembly.
j. prosthet. Dent. 1980.43:618-621.
• Ben-ur z, aviv i, cardash hs. a modified direct retainer
design for distal extension reovable partial denture. j
prosthet dent 1988;60(3):324-44
• Donald a cameron; mervyn f lyons. properties of a custom-
made hinge clasp compared with a conventional
circumferential clasp. jpd. 1996;75(3):326–331

90. • Extracoronal direct retainers for distal extension
rpds. jips. 2005; 5:65-71
• Arthur j. krol (1973). clasp design for extension-base
removable partial dentures. , 29(4), 408–415.
• Elena nazarova; thomas d. taylor (2012). the rph
clasp assembly: a simple alternative to traditional
designs. , 21(4)