Beyond the EU: DORA and NIS 2 Directive's Global Impact
Direct & indirect retainers in rpd
1. Direct and indirect
retainers
Vinay Pavan Kumar .K
2nd year P G student
Dept of Prosthodontics
AECS Maaruti College of Dental Sciences
2. Direct
retainers
Indirect
retainers
Definition
Classification
Principles of
design
Extracoronal
retainers
Types
Definition
Factors
affecting
types of indirect
Requirements retainers
3. Direct retainer: It is that component of a
removable partial denture that is used to retain
and prevent dislodgment, consisting of a clasp
assembly or a precision attachment (GPT 8)
7. Clasps mainly divided 2 types
Occlusally approaching which approach the undercut
from the occlusal area and gingivally approaching which
enter the undercut crossing the gingival margin.
8.
9. Clasp Assembly
The part of a removable dental prosthesis that acts as a
direct retainer and/or stabilizer for a prosthesis by
partially encompassing or contacting an abutment tooth.
Components of the clasp assembly include the clasp,
the reciprocal element, the cingulum, incisal or occlusal
rest, and the minor connector.
10. Parts of clasp assembly
Circumferential
Clasp
(Retentive Arm)
Reciprocating
(Bracing) Arm
Distal
Occlusal
Rest Seat Proximal
Plate
11. Principles of Clasp Design
1. Encirclement- more than 180 degrees in greatest
circumference if the tooth engaged by the clasp assembly
2. Occlusal rest - to prevent the movement of the clasp arms
cervically.
3. Each retentive terminal should be opposed by a reciprocal
component
12. 4. Clasp retainers on abutment teeth adjacent to distal
extension bases should be designed to avoid direct
transmission of forces to the abutment
5.The amount of retention should always be the minimum
necessary to resist reasonable dislodging forces.
6. Reciprocal elements – junction of gingival and middle
third
Terminal retentive arm – gingival third
14. Retention
Is obtained by the incorporation of a flexible element of
the clasp into the undercut.
Sufficient undercut to be engaged to obtain desired
retention.
Force from the clasp arm on flexing must be within the
tolerance of the PDL and must be less to prevent
deformation of the clasp arm itself.
15. Factors affecting retention
◦ Tooth factors: Size of the angle of cervical
convergence
◦ How far the clasp terminal is placed into the angle of
cervical convergence
16. Clasp arm flexibility
Material used: cast chrome (0.010”)
cast gold (0.015”)
wrought alloy (0.020”)
17. Length of the clasp
•The longer the clasp arm the more flexible.
• Flexibility is directly proportional to the cube of its length.
•By increasing the length, the horizontal stresses imparted
to the abutment during placing and removal is reduced
18. Cross section: round > half round
Modulus of elasticity: more the modulus - less flexibility
Diameter of clasp: flexure inversely proportional to the
diameter.
Alloy: wrought > cast
19. Support
Support is the quality of the clasp assembly to resist
displacement of the prosthesis in the apical direction.
a rest must contact the surface of the abutment tooth at
a properly prepared surface- rest seat
20. A properly prepared rest will prevent the
tissueward movement of the prosthesis.
maintains the position of the clasp assembly in
relation to the abutment.
Transmits forces along the long axis of the
abutments
22. Reciprocation
Counteracts lateral displacement of an abutment when
retentive clasp terminus passes over the height of
contour
23. Encirclement
Prevent movement of abutment away from associated
clasp assembly
More than 180 degrees
24. Passivity
Prevent the transmission of the adverse forces
to the associated abutment
Be passive until a dislodging force is applied
25. Classification of extra-coronal retainers
Supra bulge clasps (occlusally approaching,
circumferential clasps)
Infrabulge clasps (gingivally approaching,
projection or bar clasps)
Combination clasps
26. Circumferential clasps
The cast circumferential clasp design was introduced by
Dr N B Nesbitt in 1916.
Simple, easy to construct- excellent support, bracing,
retentive properties.
Close adaptation to tooth therefore minimises food
entrapment
Disadvantage- covers large amount of tooth surface
27. Circlet clasp.
Reverse circlet
Multiple circlet clasp
Embrasure clasp.
Reverse action or hair pin clasp
Ring clasp.
Back action and reverse back action clasp
28. Simple Circlet clasp
Tooth support RPD
Undercut remote from
edentulous area
Half round
Disadvantages
- Increase tooth coverage
- compromised esthetics
29. Variations of circlet clasp
Back action clasp
Reverse back action
Ring clasp
C clasp or hair-pin clasp
30. Reverse circlet clasp
Undercut located adjacent to edentulous area
Kennedy class I ,II
Disadvantages
- Lack of rest adjacent to
edentulous area
- Poor esthetics
31. Multiple circlet design
2 simple circlet clasp joined at the terminal aspect of
their reciprocal elements
Principle abutment is periodontal compromised and the
forces are distributed between multiple abutment teeth
32. Embrasure clasp
2 simple circlet joined at bodies
Used on side of the arch where there is no edentulous
space
Can be used only when adequate tooth preparation is
possible
33. C-clasp design
Fish hook” or “Hairpin” clasp
Simple circlet clasp with loop back retentive arm
Sufficient crown height
Disadvantages
- Insufficient flexibility
- Tooth coverage
- Esthetics compromised
34. Combination clasp
Cast metal reciprocal arm and wrought wire retentive
arm
abutment adjacent to Kennedy class I and II area
Advantage
• kinder to the tooth
can engage greater undercut
Disadvantage
• more prone to breakage than cast
• minimal stabilizing
36. Approach arm
• It is a minor connector that connect the retentive tip to
the denture base.
• It crosses the gingival margin at right angle and it is the
only flexible minor connector.
• Flexibility of the clasp is controlled by the taper and
length of the approach arm
• More esthetic
37. Retentive terminal
• It should end on the surface of the tooth below the
undercut.
38. T-clasp
Kennedy class I and II
Undercut locate adjacent edentulous area
Contraindication
- Severe soft tissue undercut
- Height of contour locate near
occlusal surface
39. Modified T-clasp
No retentive horizontal projection
Kennedy class I and II
Undercut locate near adjacent edentulous area
Canine and premolar
Advantage - esthetics
40. Y-clasp
Equivalent to T-clasp
Approach arm terminates in the cervical third
Mesial and distal projection terminate near occlusal
surface
41. I bar
Kennedy class I and II
RPI
- Mesial rest
- Proximal plate
- I bar
43. • Acetal resin clasps are esthetic and are available in
sixteen different shades.
• To evaluate the effect of cast Co-Cr and acetal resin
clasp on the surface of tooth.
• The retentive force of cast Co-Cr clasp showed a
decrease from 12.4 N to 8.1 N.
• The retentive force of acetal resin clasp, reduced
from 5.2 N to 4.03 N at the completion of experiment.
• Acetal resin clasps do not abrade the surface of tooth
and maintain retention
A comparative study on Co-Cr and Acetal resin clasps; Pal .H etal
TPDI • January 2014, Vol. 5, No. 1 pg 9- 13
44. Implants as direct retainers
• Eliminates a visible clasp
• placement of an implant within a modification space to
the advantage of retentive needs requires
consideration of anterior, mid, or distal placement
• retainers utilizing teeth have always been restricted to
tooth locations at either end of a span
45. Indirect retainer
Resists rotational displacement of an extension base
from the supporting tissue
Kennedy class I, II and IV
46.
47. Factors determining indirect
retainer
Occlusal rests must be held in rest seats by direct
retainer
Distance from fulcrum line
Placed on definite rest seat to prevent slippage
Rigidity
48. Auxiliary functions
Reduce A-P tilting of abutments
Stabilization – auxiliary guide planes
Anterior teeth stabilized
Auxiliary rest – stress distribution
Visual indication for reline
49. Forms of indirect retainer
Auxiliary occlusal rest
Canine extension from occlusal rest
Continuous bar retainer & lingual plate
Rugae Support