This document discusses various types of clasps used for removable partial dentures and their design considerations. It describes intracoronal and extracoronal attachments as well as different clasp designs like Akers clasps, circumferential clasps, and back action clasps. Factors that influence clasp retention like undercut depth and shape are covered. Design principles for survey lines and preventing torquing forces on teeth with free-end saddles are also summarized.

1. RETENTION OFRETENTION OF
REMOVABLEREMOVABLE
PARTIALPARTIAL
DENTURESDENTURES

4. RETENTION OFRETENTION OF
REMOVABLE PARTIALREMOVABLE PARTIAL
DENTURESDENTURES
Dr. Amal Fathy KaddahDr. Amal Fathy Kaddah
Professor of Prosthodontic,Professor of Prosthodontic,
Faculty of Oral &Dental Medicine,Faculty of Oral &Dental Medicine,
Cairo UniversityCairo University

6. Retention
Physical Mechanical
Intracoronal attachment Extracoronal
Clasp retainer
Attachment
)The resistance to tissue away movement(
physiologic

7. Intracoronal attachmentsIntracoronal attachments

8. Extracoronal attachmentExtracoronal attachment

9. ExtracoronalExtracoronal
attachmentattachment

10. Clasp retainerClasp retainer
Retentive arm
Bracing arm
Occlusal
rest
Minor connector

11. DESIRABLE UNDERCUT
NON DESIRABLE UNDERCUT

12. REQUIREMENTS OF CLASPREQUIREMENTS OF CLASP
DESIGN.DESIGN.
Bracing arm better located
In the apical portion of the
Middle 1/3
Retentive arm better located
In the gingival 1/3 for better
esthetics & mechanics

13. UNDERCUT IS BETTER BE FOUND WITHIN THE
GINGIVAL1/3 For mechanical reasons
Post Is More Readily Removed by Application of Force Near Its Top
Than by Applying Same Force Nearer Ground Level

14. 180ENCIRCLING TOOTH
continuous intermittent
Tooth can't move horizontally away from the clasp

15. Each retentive terminal should be reciprocated as
retentive arm exerts some orthodontic movement
during placement and removal as it flexes about the
height of contour

16. Amount of retention depends onAmount of retention depends on
The greater the distance we go into the undercut the greater will be the retention
A- depth of undercut

17. B- flexibility of clasp arm
Increasing arm length increases the
flexibility ,thus decreasing the retention

18. Round clasps have universal
flexibility thus lowers the
retention than ½ round and flat
clasps
shape of the clasp

19. Degree of taper , retentive arm should be tapered in
two dimensions

20. C- Angle of cervical convergence

21. Occlusally approaching clasp Gingivally approaching clasp
Clasps according to way of approach
to undercut

23. 1-Akers clasp (circlet(
0.01 of an inch

24. 2-DOUBLE AKER (embrasure(

25. 3- Circumferential `C` Clasp3- Circumferential `C` Clasp

26. 4-R.P.A

27. 5- Multiple Clasp5- Multiple Clasp

28. 6-Extended arm clasp
Abutment has no undercut
Adjacent tooth has a reasonable undercut

29. 7- Half & Half clasp7- Half & Half clasp
 2 M.C., 2 O.R. & 22 M.C., 2 O.R. & 2
arms.arms.
 Mainly indicated forMainly indicated for
dual retentiondual retention
commonly incommonly in
unilateral cases.unilateral cases.

30. 7-RING CLASP7-RING CLASP
Provides unilateral bracing. Used for single tilted molars
More flexible than aker because it is one arm clasp.

31. 8-Back action clasp8-Back action clasp
 Single arm claspSingle arm clasp
 Minor connectorMinor connector
starts mesio-starts mesio-
linguallylingually
 It engages mesio-It engages mesio-
buccal undercut.buccal undercut.
 O.R. is locatedO.R. is located
distally.distally.
 Used in free endUsed in free end
saddle.saddle.

32. 99--Reverse Back action claspReverse Back action clasp
M.C.
originating
Mesio-
buccally
Retentive arm
engage
Mesio-lingual
undercut

33. Reverse Back actionReverse Back action
claspclasp
Back action claspBack action clasp

34. 1010--Mesio-Distal claspMesio-Distal clasp
•Used only in anterior teeth
•Depends on frictional resistance for retention

36. • A retentive clasp arm
• A rigid reciprocal clasp
arm
• An occlusal rest and a
minor connector The tip
of the retentive arm may
be in the form I, T, U, C or Y.
One
1- The I-bar clasp (Roach clasp arm):
The I - bar clasp consists of

37. T clasp
Modified T clasp
Different forms of gingivally approaching claspsDifferent forms of gingivally approaching clasps
I clasp

38. R.P.I
The base of the I bar
Should be 3mm away
From the gingival margin
Provides unilateral bracing.
Commonly used for tooth
mucosa borne partial
dentures. A retentive
clasp arm

39. Contraindications for the use of
gingivally approaching clasps

40. Devan clasp
•More esthetic due to interproximal position
•No distortion due to it`s proximity to denture border

42. Combination clasp
Gingivally app.
Retentive arm
(buccally) &
Occlusally app.
Bracing arm
(lingually)

43. •Buccal wrought wire retentive arm soldered to
the base
•Lingual casted bracing arm
Another type of combination clasp

44. Clasps with splinting actionClasps with splinting action
Double Aker claspDouble Aker clasp
Extended arm claspExtended arm clasp
Multiple Aker claspMultiple Aker clasp

45. Clasps with stress breaking actionClasps with stress breaking action
All gingivally approaching clasps except
Devan clasp
Occlusally approaching clasps
Reverse Aker clasp
Back action clasp
Reverse back action clasp
R.P.A.
Combination clasps

46. Types of Survey Line
Near the saddle
Away from the saddle

47. A-MEDUIM SURVEY LINE
Midway between
Occlusal
surface&
Gingival margin
in the
Near zone
Nearer to
gingival margin
In the far zone
We can use occlusally or gingivally approaching clasps

48. B-DIAGONAL SURVEY LINE
Near occlusal
surface
In the near zone Near gingival
margin
In the far zone
Or Or Or
Back action&
Reverse back
C clasp
Ging.app. With T bar
Ging.app. With L bar

49. C-HIGH SURVEY LINE
Near to the occlusal surface
Wrought wire occlusally app.
Back action or reverse back action
commonly in inclined teeth
Bracing
Arm

50. D- LOW SURVEY LINE
Near the gingival margin
Extended arm clasp
• Devan clasp engaging
proximal undercut
• Crowning of the tooth

51. Tripping action is attributed to clasp arms
that engage the undercut directly from a gingival
direction.
Not all bar clasp arms have tripping action,
since the retentive terminal may actually engage
the undercut from an occlusal direction as is true
with the "T" bar or modified "T" bar.

52. OcclusallyOcclusally GingivallyGingivally
Retention due todue to tripping actiontripping action
Bracing 2 Arms above2 Arms above
survey line providesurvey line provide
bracingbracing
Esthetics less visible due toless visible due to
gingival positiongingival position
Tolerance Gingivally app.clasp arm relievedGingivally app.clasp arm relieved fromfrom
gingiva creating space accumulating food andgingiva creating space accumulating food and
causing discomfortcausing discomfort
Caries More tooth coverageMore tooth coverage
increasing the risk forincreasing the risk for
cariescaries
Gingival health Trauma may occurTrauma may occur
due to distortion ordue to distortion or
inadequate reliefinadequate relief

53. SpecialSpecial
ConsiderationsConsiderations
for Clasp designfor Clasp design
in Free Endin Free End
Saddle CasesSaddle Cases

54. MOVEMENT OF CLASP WITH DISTAL O.R.
Circlet clasp during function: Loading force (F)
causes clasp to rotate at (R). Where minor connector
breaks contact with tooth. Retentive clasp arm tip
moves occlusally during function and directs a distal
torquing force to the tooth.

55. In function, rotational forces take place
around distal occlusal rest. Cast
circumferential clasp places an extremely
destructive distal tipping or torquing force
on abutment tooth (arrows).

56. when force is directed against unsupported end of
beam cantilever can act as first class lever Torque
on the abutment tooth
F

57. A cantileverA cantilever
designdesign
allowsallows
excessiveexcessive
verticalvertical
movementmovement
toward thetoward the
residualresidual
ridgeridge

58. Reverse Aker Clasp
F
Class ? Lever

59. Improperly designed RPA clasp located above
survey line. Under occlusal force A, rigid
portion of retentive arm cannot move
gingivally. This moves center of rotation
distally. Mesial rest lifts out of its rest seats.
Retentive portion of clasp arm engages mesial
undercut, torquing tooth distally

60. Properly designed RPA clasp showing movement
from occlusal forces. Proximal plate, C. drops
gingivally and slightly mesially as rotation occurs
around mesial rest with approximate center of
rotation, B. Rigid portion of retentive arm contacts
tooth only along survey line, A. and moves gingivally
and mesially. Retentive end of clasp arm moves
mesially and slightly gingivally

61. Laboratory blockout of refractory cast for RPA
clasp. Rigid portion of retentive clasp arm is
waxed for casting over blocked-out distofacial
surface, E, only anterior border will be in
contact with tooth. Cast under retentive end of
clasp arm is not blocked out

62. Placement of the I bar
at the greatest
prominence (2) or to
the mesial (3) permits
the I bar under
function to move
freely away from the
tooth. The I bar placed
on the distal (1)
cannot move freely
away from the tooth
thereby producing a
torquing action

63. Combination Ackers and
modified “T” bar clasp with distal
rest and distal undercut

64. P.P minor connector should contact
approximately 1 mm of the gingival portion of
the g. p. in distal extension cases

65. Changing the position of the guiding plates changes
the center of rotation (.
) indicates center of rotation

67. MOVEMENT OF CLASP WITH MESIAL O.R.
The cicumferential clasp arm and proximal plate move in
mesiogingival direction disengaging from the tooth

68. WROUGHT WIRE CLASP DURING FUNCTION
Wrought wire (WW combination) clasp during function.
Loading force (F) causes clasp to rotate, where minor
connector breaks contact with tooth. WW clasp arm tip
moves occlusally and directs a distal torquing force to the
tooth. Flexibility of WW arm limits torquing.

69. Placing the occlusal rest away
from the distal extension base has
the following advantage
1- By changing the direction of torque on the abutment
from the distal to the mesial side of the tooth, the
resistance to torque action will be applied from the
neighboring teeth

70. Reverse Aker Clasp
F
Class ? Lever

71. Depression of the base does not exert a distal
stress (the pump handle effect) on the
abutment but rather a mesial one
2- Clasp disengagement from the tooth
1- Class II Lever

72. 4 - lever arm, represented by distance
from rest to denture base, is increased.
This increase in length makes rotational
action caused by up-and down movement
of denture base in function more vertical.
A vertical force in better tolerated by ridge
than is a horizontal oblique force

73. 5- As rest is moved anteriorly more
of residual ridge will resist rotation

74. THANK YOUTHANK YOU