indirect retainers for Removable Partial Dentures for dental undergraduate students

1. Indirect Retainers
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2. Contents
 Introduction
 Principle of levers
 Rotation of denture bases around various axes
 Definition
 Principle of Indirect Retainers
 Types of Fulcrum Lines
 Factors Influencing Indirect Retainers
 Auxillary Functions
 Forms of Indirect Retainers
 Summary
 References
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3. Introduction
William E. Avant said “Indirect retention is required on
all extension base partial dentures retained by
clasps. It is required also when tooth at one end of
the denture base is clasped for retention but the
tooth at the other end is not suitable for retention.
Extension base partial dentures are needed more
often than any other type of removable partial
denture. If these statements are true, then we need
to consider indirect retainers carefully.”
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4. Principle of Levers
FF
EERR
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5. Mechanical Advantage= Effort Arm
Resistance Arm
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6. Rotation Around a TransverseRotation Around a Transverse
AxisAxis
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7. Rotation Around A
Longitudinal axis
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8. Rotation Around A vertical
Axis
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9. “The component of a removable partial denture
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
pure rotation around the fulcrum line.”-GPT
Definition
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10. An indirect retainer does not control the movement of
the denture base in the tissueward direction
Amount of movement =amount of compressible
mucosa
Fulcrum line runs between the most posterior rests.
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11. Movement away from ridge
 Sticky foods
 Functions of tissues at the borders
 Gravity (maxillary denture)
Fulcrum line runs through retentive tip of direct retainer
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12. Principle of Indirect Retainer
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13. Types of Fulcrum Lines
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14. www.asiandentalacademy.org

15. Factors Influencing Effectiveness
of Indirect Retainers
• Principal
Occlusal rests
• Fulcrum line
1. Length of extension
base
2. Location of fulcrum
line
3. Position of indirect
retainer
• Rigidity of
Connectors
• Supporting tooth
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16. Auxiliary Functions
 Reduce leverage
 Stabilization
 Support
 Prevent lingual movement
 Need to reline
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17. Form of Indirect Retainer
Auxillary Occlusal Rest
 Consists of a minor connecter and a
rest placed in a rest seat
 Class I arch –bilateral rests on
mesial marginal ridge of 1st
premolar
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18. Preparation of Rest Seats
Occlusal rest seat:
 Rounded triangle
 Base at the marginal ridge
and apex at the centre of
the tooth
 One-half the intercuspal
distance and one-third/one-
half the mesiodistal width
 Base must be less than 900
to long axis of tooth.
 Depth 0.5 at the thinnest
portion and 1.5mm at the
marginal ridge.
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19. Canine Extensions from
Occlusal Rests
To effect indirect
retention by
increasing the
distance from
fulcrum line
Should always be
used with terminal
rests.
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20. Canine Rests
 Used when premolar is
too close to fulcrum line
 Teeth are overlapped
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21. Lingual Rest
 Prepared mostly on
maxillary canines.
 Multiple incisors
 Closer to centre of
rotation, more esthetic,
less prone to breakage.
 Rest seat is V-shaped
and half moon shaped
in configuration.
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22. Cingulum Bar (Continous Bar)
and Lingual Plate
They rest on
unprepared lingual
inclines. Aid the
terminal rests in
indirect retention.
Stress distribution
Reduces the cross
sectional area of
major connector
Splints of weak anterior
teeth
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23. May cause
orthodontic movement
of teeth
Irritating to tongue
Cannot be used in
deep overbite cases
Retroclined anteriors
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24. Cummer arms
Metal arm extending from
saddle or connectors to
end on unprepared
palatal or lingual
surface of an anterior
tooth(upper canines)
May cause tooth
movement
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25. Rugae area
Coverage of rugae area –advocated by some
clinicians as the rugae area is thought to be firm and
will also help in providing support.
Not as effective as positive tooth support.
Usually as palatal arms, palatal bearing connectors
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26. Summary
 Indirect retainers do not play a role in vertical
movement towards tissues
 They only facilitate the direct retainers in retention
 They act by moving the fulcrum line anterior to the
force
 Principle forms of indirect retainers used are the
occlusal rests
Therefore, proper design and placement of the
component parts of a removable partial denture will
not prevent but at least minimise the displacing
forces. Which will go a long way in assuring the
success of the prosthesis.
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27. References
 A.A.Grant and W.Johnson,Removable denture Prosthodontics,
ed 2.1992,Churchill livingstone Inc.
 Ernest L.Miller and Joseph E.Grasso,Removable Partial
Prosthodontics, ed 2. 1979,Williams and Willkins.
 Glen P. Mcgivney, Alan B. Carr.Mccraken’s Removable Partial
Prosthodontics, ed10. St. Louis ;2000 ,The C.V. Mosby Co.
 Stewart ,Rudd and Keubker, Clinical Removable Partial
Prosthodontics,ed 2.1997,Ishiyaku EuroAmerica Inc. U.S.A
 William E. Avant.Indirect retention In partial denture Design.J
Prosthet Dent.16:1103-1110
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28. Thank you
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