b- Retainers of RPDs

Preclinical course of Removable Partial Denture:
1- Introduction and Definitions
2- Forces acting on RPD.
3- Biomechanical considerations
4- Denture bases
5- Rests
6- Major and Minor connectors
7- Retainers
8- Indirect retainers
9- Stress equalizing Designs

3. Dr. Amal Fathy Kaddah
Dr. Mohamed Farouk
Dr. AmroAbdullah
Faculty of Oral and Dental Medicine
Cairo University
RETENTION OF REMOVABLE
PARTIAL DENTURES

5. Is the resistance of
the partial denture
to vertical
displacement away
from the tissues

6. 1-Adhesion
2-Cohesion
3-Interfacial s.t.
4-At. pressure
6-Gravity
Mechanical
Retention
PhysiologicalPhysical
-The physiologic
molding of the
tissues around the
polished surfaces
-neuromuscular
control
•Direct retainers
•Indirect R.
•Frictional fit
•Parts of the
denture
engaging tooth
and tissue
undercuts.

7. •Frictional fit
Mechanical means of
Retention
Indirect R.
Direct
retainers
Parts of the denture
engaging tooth and
tissue undercuts.
•Clasps
•Attachments

11. The most universally
employed of all clasps
designs
It is a double-armsclasp;
relatively rigid.
Engages an undercut of
0.01inch (1/4 mm)on the
buccal (or lingual) surface of
molars or premolars far from
the edentulous area
2-Aker’s Clasp (Circlet Clasp)

12. Retentive arm
Bracing arm
Occlusal
rest
Minor connector
0.01 of an inch
Aker’s clasp (circlet)
Engages the undercut from occlusal direction

13. Indications
Unilateral and bilateral
tooth borne
Best suited for strong
abutments teeth
Advantages
Provides support, retention, and the best
bracing.
Does not distorteasily.
Easily constructed.
Simple to repair.

14. Disadvantages
More tooth surface is covered.
Changes the morphology of the abutment
crown.
Due to its half round cross-section, the Aker
clasp can be adjusted to the tooth surface in
an inward or outward (Bucco -lingual) and not
upward or downward (occluso-gingival)
direction.
Cannot be used in free-end saddle cases due
to its rigidity, except with a stress equalizing
design or reversed.

15. 2-The Reversed Aker Clasp
•Occlusal rest located away from
the edentulous area.
•Retentive arm that engages an
undercut near the edentulous
area.
•A rigid reciprocal arm.
Indication:
In distal extension cases when the bar clasp is
contraindicated (when?).

16. 2-The Reversed Aker Clasp
Advantage:
Clasp disengagement . Reduce
torque transmitted to the
abutment tooth.
Disadvantage:
May produce some wedging
force. This can usually be
countered by occlusal rests on
the approximating surfaces of
both teeth.

17. 3-DOUBLE AKER
(Embrasure, Butterfly, Compound clasp )
•Two Acker clasps arising
from a common body and
from the same minor
connector, Minor C. located
in the embrasure between
the two clasped teeth.
•Used on the dentulous side
of unilateral edentulous
(class II,III) cases having
no modifications, class IV.

18. •Provide bilateral
stabilization, and
bracing, in addition
to retention.
It also splints the
two teeth
3-DOUBLE AKER
(Embrasure, Butterfly, Compound clasp )

19. 4-Circumferential `C` Clasp
Retentive arm turned back (curved ) to engage an undercut near
the edentulous area (below the point of origin (distobuccal un.)
Disadvantages:
Greater coverage of tooth surface, increase the functional
load on abut.
Food trapping at the loop of the arm, and
Inferior esthetics.

20. 5-Multiple Clasp
Consists of two opposing Aker ’s
clasps,
Two Lingual rigid reciprocal arms are
connected together at the terminal
ends to augment their rigidity.
When Splinting of periodontally affected teeth is needed.
When RPD replaces an entire side of the dental arch.
Available retentive areas are only adjacent to each other.
Disadvantage:
Utilizing two embrasures rather than a common one.
Indications:

21. 6-Extended arm clasp
Indication:
Utilizing Adjacent tooth has a reasonable undercut
Advantages:
•The clasp has splinting action.
•Distributes the lateral load
over the two teeth.
Used when the undercut on the
tooth near the edentulous area is
poor, while that on the adjacent
tooth is suitable.

22. 7-Half & Half clasp
It is used withisolated premolars and
molars for bounded .partial denture.
•Retentive armarising from one
side of the tooth
•A reciprocal armarising from the
other direction on the opposite
side of the tooth.
•Two minor connectors
•An auxiliary restmay sometimes
be used..

23. 8-R.P.A
A mesial occlusal rest .
A proximal plate
An Akerretentive arm
arising from the superior
portion of the proximal
plate.
Indication:
•In distal extension RPDs presented
with shallow vestibule or severe tissue
undercut

24. 1.Mesio-occlusal surface of
the tooth, permitting the
other components to release
from the tooth and drop into
undercuts when occlusal
loads are placed on the
denture base.
Advantages:
2.This in turn prevents tipping of the abutment.
3.Absence of a lingual rigid reciprocal arm minimizes
rotational forces falling on the abutment.

25. a-Properly designed RPA clasp showing movement from
occlusal forces. Proximal plate, 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, and moves gingivally and mesially.
Retentive end of clasp arm moves mesially and slightly gingivally.
b-Improperly designed RPA clasp located above survey line.
8-R.P.A
a- b-

26. 9-Ring Clasp
Provides unilateral bracing. Used for single tilted molars
More flexible than Aker because it is one arm clasp.

27. It is a single-arm
clasp, indicated on
tilted, isolated
molars.
Originates by a rest mesiallylocated on the
marginal ridge. And the single arm encircles
nearly all the tooth surface resembling a
ring.
Exhibiting a mesiobuccal undercutin case of
upper molars and a mesiolingual undercut
on lingually tilted lower molars.
Engages a 0.02 or 0.03 of an inch undercut.
An auxiliary distal restis preferably added to
prevent further mesial tilting of the tooth
A reinforcing supporting strut arm located on
the non-retentive side is usually considered
to limit the flexibility of the clasp.
9-Ring Clasp

28. Disadvantages of ring clasp:
1.Excessive tooth coveragethat may
result in enamel decalcification and
caries.
2.Easily distortedbecause of length
and difficult to adjust.
3.Reinforcing arm may cause
marginal irritation and inflammation
and may act as a food trap.
9-Ring Clasp

29. 10-Back action clasp
Single arm clasp
Minor connector starts mesio-
lingually
It engages mesio-buccal
undercut.
O.R. is located distally.
Some times an additional rest
could be employed on the
mesial side to improve
support
Used in free end saddle.

30. Engage a mesiobuccal
undercut of 0.01 of an inch.
Disadvantages
•Excessive tooth coverage.
•Easily distorted
•Excessive display of metal,
•The occlusal rest is supported by the clasp arm and not by a rigid
minor connector, hence the rest cannot function adequately.
•Poor bracing and reciprocation.
•Food trap

31. ??
??

32. 11-Reverse Back action clasp
Minor C.
originating
Mesio-
buccally
Retentive arm
engage
Mesio-lingual
undercut
•The minor connectors originates mesiobuccal line angle from the
saddle and ends to engage a mesiolingual undercut of 0.01 or 0.02
of an inch
•The clasp is Frequently used on lingually tipped bicuspids.
•It also provides single bracing only.
•It has an additional esthetic disadvantage.

33. Reverse Back action
clasp
Back action clasp

34. 12-Mesio-Distal clasp
•Used only in anterior teeth
•Depends on frictional resistance for retention

37. •A retentive clasp arm
•A rigid reciprocal clasp
arm
•An occlusal rest and a
minor connectorThe tip
of the retentive armmay
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

38. T clasp
Modified T clasp
Different forms of gingivally approaching clasps
I claspU clasp

39. 2-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
A mesial occlusal rest.
A proximal plate
I Bar retentive arm

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

41. Contraindications for the use of
gingivally approaching clasps
•Shallow vestibule.
•High floor of the mouth
•Severe tissue or tooth undercut to avoid food or
tissue trap.
Contraindications
Indications:
•In distal extension cases, as it
provides a stress releasing
action.
•When tissue undercuts are
not severe

42. When tissue undercuts
begin 3 mm away from
the gingival margin, an
RPI clasp is used no
matter how deep the
facial surface tissue
under cut.
When tissue undercuts
begin less than 3mm from
the gingival margin and are
more than 1 mm in depth an
RPA may be used.

43. 3-RLS Clasp
Mesio-occlusalRest,
A distolingual L-bar direct retainer
that is located on the abutment tooth
adjacent to the residual ridge and
DistobuccaStabilizer
Advantages:
•The mesial rest reduces the anterior component of movement
of the denture and reduces torque on the abutment tooth.
•A retentive clasp tip placed on the most distal part of the tooth
will undergo a downward vertical movement and disengage as
the distal extension base moves tissue-ward in function
It consists of

44. The design of clasp for a distal
extension RPDthat helps
preserve both the abutment
teeth and the tissuesof the
edentulous ridge is described.
The clasp assembly takes
advantage of surveyed lingual
undercutsto provide support,
retention, and stability.
Hiding Denture Clasp
3-RLS Clasp

45. 4-Devan clasp
be used if additional flexibility is required
•More esthetic due to interproximal position
•No distortion due to it`s proximity to denture border
•Food debris may be entrapped between the arm and
the denture base.
•Two occlusal rests on
abutment are used.
•The bar arm arises from the
border of the denture base.
Wrought wire clasp arm
could

46. 5-Combination clasp
Gingivally app. Retentive arm (buccally) &
Occlusally app.Bracing arm (lingually)
!!!!!!!!!!!!

47. •Buccal wrought wireretentive arm
soldered to the base
•Lingual castedbracing arm
Wrought wireretentive arm and castedbracing arm
5-Combination clasp

49. Clasps with splinting action
Double Aker clasp
Extended arm clasp
Multiple Aker clasp

50. Clasps with stress breaking action
Gingivally approachingclaspsexcept Devan
clasp
Occlusally approaching clasps
–Reverse Aker clasp
–Back action clasp
–Reverse back action clasp
–R.P.A.
–R L S
–Ring (bounded sad., isolated molar)
Combination clasps (wrought wire + casted)

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

52. 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 occlusallyor gingivally approaching clasps

53. 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

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

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

56. Tripping actionis 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.

57. Occlusally Gingivally
Retention due totripping
action
Bracing
2 Arms above
survey line provide
bracing
Esthetics less visible due to
gingival position
Tolerance Gingivally app.clasparm relievedfrom
gingiva creating space accumulating food
and causing discomfort
Caries
More tooth coverage
increasing the risk
for caries
Gingival health
Trauma may occur
due to distortion or
inadequate relief

58. Special
Considerations for
Clasp design in Free
End Saddle Cases

59. 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.

60. 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).

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

62. A cantilever design allows
excessive vertical movement
toward the residual ridge also.

63. Reverse Aker Clasp
F
Class ? Lever

64. 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

65. a-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
a-

66. 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

67. 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

68. Combination Akers and modified
“T” bar clasp with distal rest and
distal undercut

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

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

71. Mesially or Mid buccal ???????????

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

73. 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.

74. Positioning the occlusal rest on the abutment teeth
Changing the location of the occlusal rest from
the distal fossa to the mesial fossa
Changes the character, direction and often
the magnitude of the forces
that are transmitted to the
abutment tooth.

75. Advantages of Placement of occlusal rests
away from the saddle.
1. Buttressing effect

76. Changing the direction of torque on the abutment
from the distal to the mesial side of the tooth, the
force tends to move the tooth towards the adjacent
tooth mesially. Thus the adjacent tooth absorbs
some of the forces of occlusion. (Buttressing effect )

77. Reverse Aker Clasp
F
2-Changing the stresses acting on the saddle
and Transfer the design from Lever I to
favorable Lever II decrease Torque on
the abutment tooth.

78. 3. Disengagement of the clasp during
tissue ward forces (elimination of
the torque)
a. Proximal plate should contact approximately
1 mm of the gingival portion of the guiding plane
in distal extension cases
RPI
RPI Clasp

79. b. Clasp Disengagement
Reverse Aker
The circumferential clasp arm and proximal
plate move in mesiogingival direction
disengaging from the tooth
RPA

81. 4. Increase the length of the arc of
rotation, so the forces transmitted to
the ridge are more vertical. A vertical
force is better tolerated by ridge than
the horizontal oblique force
Increase the length of lever arm

83. 5. The area of support is increased
(decrease force /unit area)

84. 6. Placing the occlusal rest away from the
distal extension base beside achieving
mechanical advantages it helps in favorable
distribution of occlusal load between abutment
tooth and the ridge