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Indirect Retainers for RPDs

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Title: Indirect Retainers for RPDs


1
Indirect retainers
Dr. Shujah a khan Mds resident, Department of
prosthodontics, Dikiohs, duhs
2
Indirect Retainer
  • The component of a partial removable dental
    prosthesis that assists the direct retainer(s) in
    preventing displacement of the distal extension
    denture base by functioning through lever action
    on the opposite side of the fulcrum line when the
    denture base moves away from the tissues in a
    pure rotation around the fulcrum line.
  • Glossary of Prosthodontic Terms

3
Fulcrum Line
  • An imaginary line around which a denture tends to
    rotate.

4
  • Indirect retainer components should be placed as
    far as possible from distal extension base, which
    provides the best leverage advantage against
    dislodgement

5
Types of Fulcrum Lines
  • Class I
  • Fulcrum line passes through most posterior
    abutments

6
  • Class II
  • Diagonal fulcrum line, passing through the
    abutment on the distal extension side and the
    most posterior abutment on the opposite side.

7
  • Class III
  • Fulcrum line passes through two principal
    abutments

8
  • Class IV
  • Fulcrum line passes through two abutments
    adjacent to the single edentulous space

9
Indirect Retainer Principle
10
  • What does an Indirect Retainer Comprises of??
  • One of more RESTS and the supporting Minor
    Connectors.
  • Proximal plates adjacent to edentulous areas also
    provide indirect retention

11
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12
Principles for Using Indirect Retainers
  • More than one fulcrum line maybe present
  • IRs must be placed as far as possible from the
    distal extension base for better leverage
    advantage
  • Most effective location is Incisor region but due
    to their poor strength canines or premolars are
    used
  • Whenever possible, two IRs, closer to the fulcrum
    line are taken to compensate for the compromise
    in distance

13
Factors Influencing Effectiveness of Indirect
Retainers
  • Principal occlusal rests on the primary abutment
    teeth must be reasonably held in their seats by
    the retentive arms of direct retainers
  • Distance from fulcrum line
  • Length of distal extension base
  • Location of fulcrum line
  • How far beyond the fulcrum line the indirect
    retainer is placed

14
  • 3. Rigidity of connectors supporting the
    indirect retainer
  • 4. Effectiveness of the supporting tooth
    surface.
  • Must be placed on a definitive rest seat to
    prevent slippage or tooth movement
  • Tooth inclines and weak tooth never to be used

15
Auxiliary Functions of Indirect Retainers
  • Reduces antero-posterior tilting leverages on
    principal abutments
  • Contact of its minor connector with axial tooth
    surfaces aids in stabilization against horizontal
    movement of the denture
  • Anterior teeth supporting indirect retainers are
    stabilised against lingual movement
  • Act as auxiliary rest to support a portion of
    major connector
  • E.g lingual bar supported against settling into
    tissues

16
  • It may provide the first visual indications for
    the need to reline an extension base partial
    denture.

17
Forms of Indirect Retainers
  • Auxillary Occlusal Rests
  • Canine Rests
  • Canine extensions from Occlusal Rests
  • Modification Areas
  • Rugae Support

18
Auxillary Occlusal Rest
  • Most commonly used
  • Class I arch ? Mesial Marginal Ridge of First
    Premolar on either side
  • Class II arch ? Mesial Marginal Ridge of First
    Premolar on opposite side

19
Canine Rests
  • When the mesial marginal ridge of the first
    premolar is too close to the fulcrum line, or
    when the teeth are overlapped so that the fulcrum
    line is not accessible, a rest on the adjacent
    canine tooth may be used

20
Canine Extensions from Occlusal Rests
  • Occasionally, a finger extension from a
    premolar rest is placed on the prepared
    lingual slope of the adjacent canine tooth.
  • Such an extension is used to effect
    indirect retention by increasing the distance
    of a resisting element from the fulcrum line.
  • This method is particularly applicable when a
    first premolar must serve as a primary abutment

21
Cingulum Bars / Linguoplates
  • In Class I and Class II partial dentures, a
    cingulum bar or linguoplate may extend the
    effectiveness of the indirect retainer if it is
    used with a terminal rest at each end.

22
Modification Areas
  • Depending on the fulcrum line in modification
    areas, the secondary abutments are used for
    placing indirect retainers

23
Rugae Support
  • The use of rugae support for indirect
    retention is usually part of a palatal
    horseshoe design. Because posterior retention
    is usually inadequate in this situation, the
    requirements for indirect retention are
    probably greater than can be satisfied by this
    type of tissue support alone

24
  • Thank You!
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