The document discusses different types of extracoronal retainers used in removable partial dentures. It defines extracoronal retainers as components that reside entirely outside the normal contours of abutment crowns and derive retention from closely fitting parts. It then describes 10 common types of extracoronal retainers, including their components, advantages, disadvantages, and indications for use.

1. DR PRAKASH NIDWANI
MDS
Dept Of Prosthodontics
Navodaya Dental College

2. DEFINiTION
According to GPT – 9,
It is that component part of a removable partial
denture that is used to retain & prevent
dislodgement consisting of a clasp assembly or
precision attachment.

3. CLASSIFICATION (According to Stewart)

4. EXTRACORONAL retainers
• Introduced by Henry R. Boos and later modified by
F . Ewing Roach.
• These retainers consists of components that reside
entirely outside the normal clinical contours of
abutment crowns.
• They derive their retention from closely fitting
components.
• The amount of retention can be varied by depth of
undercut and the flexibility of clasp arm positioned in
the undercut.

5. Analysis of Tooth Contours for Retentive
Clasps
• Teeth that are engaged by RPD must be contoured to
support, stabilize and retain the prosthesis
• Critical areas of an abutment that provide retention and
reciprocation can be identified using –Dental Surveyor
• Relationship of vertical arm of surveyor to the cast
represent the path of placement of prosthesis
• Vertical arm contacts the tooth at the height of contour
which determines areas for retention and that for support

6. • Tooth above height of contour (survey line)is accessible to
prosthesis
• Tooth below the height of contour can be accessed by
flexible parts (retentive terminal)

7. IDEAL REQUIREMENTS OF CLASP DESIGN
1. Retention
2. Stabilization
3. Support
4. Reciprocation
5. Encirclement
6. Passivity

8. 1. RETENTION
• The retention is the property which enables the clasp to
resist dislodgement from the tooth in an occlusal
direction.
• A dislodging force may be
activated by speech, Muscle
action, mastication, deglutition ,
sticky foods and gravity.

9. Factors Producing Retention
Tooth
Prosthesis
Size Angle of cervical
convergence
Distance into angle of
cervical convergence
Cross-section
Diameter of clasp arm
Length of clasp arm
Material
flexibility

10. Size And Distance Into The Angle Of Cervical
Convergence
• When surveyor blade contacts a tooth on cast at height of
contour , triangle is formed
• Apex- at point of contact of surveyor blade and tooth
• Base- area of gingival tissues
• This apical angle : Angle of cervical convergence

11. - Supra bulge
-
- height of contour
infra bulge
angle of cervical
convergence
• Areas cervical to height of contour may be used for
placement of retentive clasp component
• Areas above it for non-retentive components
• Location &depth of undercut(angle of cervical
convergence) is relative to path of placement

12.  According to Stewart,
For a 0.010” undercut - Cast chrome alloy
0.015” undercut - gold alloy
0.020” undercut - wrought wire

13.  Flexibility Of Clasp
Directly proportional to cube of length
Inversely proportional to diameter

14. Length Of Clasp Arm
Longer flexibility
Length measured along centre
portion of arm until it joins clasp
body or denture base
Curved clasp increases the flexibility

15. Diameter Of Clasp Arm
Greater average diameter less flexibility
(all other factors being equal)
Average diameter is at a point midway between clasp origin
and its terminates if taper is uniform

16. Cross-section Of The Clasp Arm
- half –round one direction
- Round universally flexible
- Tooth –borne: half-round circumferential clasp
(flexes only during placement and removal)
- Distal –extension: round circumferential clasp
(flexes during placement and removal &
during functional movements)

17.  Taper
Uniform taper
A clasp should be half as thick at its tip as at the origin

18. Material Used
-Chrome alloys high modulus of elasticity
less flexible
- smaller cross-sectional
- less depth of undercut
- wrought wire internal grain structure
more flexibility
for equal retention deeper
undercut required

19. 2 .STABILITY
 Stabilization or bracing is the resistance which the clasp
contributes to displacement of the prosthesis in a
horizontal plane.
All clasp components except the retentive terminals
contribute to this property in varying degrees.
Greatest amount of stabilization is provided by cast
circumferential clasp

20. 3. SUPPORT
• It is the quality of clasp assembly that resists the
displacement of a prosthesis in an apical direction.
• Body and Shoulder which is placed above the height of
Contour also aids in support.

21. 4. ENCIRCLEMENT
 Clasp assembly must be designed to provide direct
contact over at least 180 degrees of the tooth
circumference.

22. 5. RECIPROCATION
• Reciprocation is the quality of a clasp assembly that
counteracts lateral displacement of an abutment when
the retentive clasp terminal passes over the height of
contour.
• It should be rigid and must contact the abutment tooth
at or occlusal to the height of contour
• During insertion of the prosthesis, the reciprocal element
should contact the abutments slightly before the retentive
arm contacts the abutment.

23. 6. PASSIVITY
• Passivity is the quality of clasp assembly that prevents the
transmission of adverse forces to the associated abutment
when the prosthesis is completely seated.
• When the clasp is in placed on the tooth, it should be
passive.
• It should not exert pressure on the tooth until it is
activated by the movement of the prosthesis in function

24. Component Parts Of Clasp
Body
Shoulder
Rest
Retentive arm
Retentive
terminal
Reciprocal arm

25. 25

26. 1. REST
• A rigid extension of removable partial denture which
contacts a remaining tooth or teeth to dissipate vertical or
horizontal forces.
- GPT
It lies on the occlusal ,lingual or incisal edge .
It resists tissue ward movement of the clasp by acting
like a vertical stop. ( gives support).

27. 2. BODY
Part of the clasp that connects the rest and shoulders of
the clasp to the minor connectors.
It must be rigid and must be above the height of
contours.

28. 3. SHOULDER
It is that art of the clasp that connects the body to the
clasp terminal.
It must be above the height of contour and should
provide stabilization against horizontal movement of the
prosthesis.

29. 4. RECIPROCAL ARM
A component of the clasp assembly
specifically designed to provide reciprocation by
engaging a reciprocal guiding plane.
- GPT
It is placed above the height of contour on the side of the
tooth opposing the retentive clasp arm

30. FUNCTION -
1. Stability &reciprocation against retentive arm.
2. Stability against horizontal movement.
3. Indirect retention.

31. 5. RETENTIVE ARM
A flexible segment of a removable partial denture that
engages an undercut on an abutment and that is designed
to retain the prosthesis.
- GPT
It comprises of the retentive clasp arm and retentive
terminal

32. - Retentive arm , not flexible and is located above the
height of contour
- Retentive terminal is flexible and lies below the
height of contour.

33. Location Of Retentive Clasp Terminal
• Retentive clasp should be positioned on the facial surface
of the abutment
• Facial placement permits increased length of the retentive
arm and yields improved clasp flexibility
• In contrast, lingual placement of the retentive arm results
in decreased clasp length and an accompanying decrease
in flexibility

34. • Lingual retentive elements can be used with molar
abutments.
• If retentive clasp on one side of the arch is positioned on
the facial surface of an abutment , at least one retentive
clasp on the contra lateral side of the arch should be
located on the facial surface of an abutment.

35. 35
 Types
› I. Circumferential clasp
 Approaches undercut : Occlusal direction
› II. Bar clasp / Vertical projection clasp
 Approaches undercut : Cervical direction

36. 36

Height of Contour
Retentive arm Reciprocal arm

37. 37
 Advantages
• Most logical clasp design
• Excellent support, bracing & retention
• Easiest to repair
• Less food retention

38. 38
 Disadvantages
• More tooth surface coverage
• Changes morphology of crown
• Interference in normal food flow pattern
• Poor adjustability
• Poor esthetics

39. 39
 Rules Of Use
Retentive terminal
• Points towards the occlusal surface
• Terminates at the mesial/ distal line angle

40. 40
 1. Simple Circlet Clasp
• Easy to construct
• Indicated in tooth
supported RPD
• Increases crown
circumference
• Poor adjustability

41. 41
 2. Reverse circlet clasp
• Used in distal
extension cases.
• Retentive undercut
adjacent to the
edentulous space.
• Poor esthetics.
• Wedging effect in the
absence of rests

42. 42
3. Multiple Circlet Clasp
• Two opposing ‘C’ clasps joined at terminal
end of two reciprocal arms.
• It provides additional retention &
stabilization.
• Indicated in RPD’s fabricated to replace
entire half of dental arch

43. 43
 4. Embrasure Clasp / Modified Crib Clasp
• Two Circlet clasps joined at their body
• Used at the side of arch with intact dentition

44. 44
5. Ring Clasp
• Encircles tooth from its point of origin.
• It is indicated when tipped molars are present.
• Additional support : Auxiliary bracing arm /
rest.

45. 45
6. Back action clasp
• This is modified Ring Clasp.
• Used on protected abutments.

46. 46
7. Hairpin / Fishhook / Reverse Action Clasp
• It engages proximal undercut from occlusal
direction.
• This is indicated when RPI clasp cannot be
used.
• Poor esthetics.

47. 47
8. Half and Half Clasp
• In this clasp, retentive & reciprocal arm arises
from opposing direction from two minor
connectors.
• Used in unilateral RPD design.

48. 48
9. Combination Clasp
• It is fabricated using wrought round wire for
retentive arm and cast circumferential for
reciprocal arm.
• This allows functional movements in distal
extension RPD.

49. 49
Advantages
• Flexibility & Adjustability
• Stress equalizer
• Utilizes deep undercut
• Esthetically Superior

50. 50
Disadvantages
• Additional laboratory steps
• Fatigue fracture
• Distortion if carelessly handled
• Poor bracing

51. 51
Indication
• To engage mesiobuccal undercut adjacent to
distal extension bases
• When a RPI clasp is contraindicated

52. 52
10. Onlay Clasp
• Extended occlusal rests with arms.
• Abutments are below the occlusal plane.
• Can cause increased wear of opposing natural
teeth .

53. THANK
YOU