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Retainers in RPD/ Labial orthodontics
1. Retainers in RPD
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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2. Retention can be defined as that
quality inherent in a prosthesis that
resists the vertical forces of
dislodgement.
Or
It is the resistance to removal from
vertical forces which tend to dislodge
prosthesis away from its foundation.
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3. Retention for removable partial denture is
achieved primarily by
Mechanical means (Direct & indirect
retainers)
Harnessing the patient’s muscular control
acting through polished surfaces of denture
Using inherent physical forces which arise
from coverage of mucosa by the denture
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4. Movement of partial denture
Distal extension partial
denture can move
along three axis.
Rotation about an axis
through the most
posterior abutments,
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5. Movement of partial denture
Rotation about a
longitudinal axis
as the distal
extension base
moves in a
rotary direction
about the
residual ridge.
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6. Movement of partial denture
Rotation about
an imaginary
vertical axis
near the centre
of the dental
arch.
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9. Intracoronal retainers
Advantage
Batter esthetics
Better vertical support trough a rest seat
located more favorably in relation to
horizontal axis of the abutment tooth
Horizontal stabilization is similar to that of an
internal rest
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10. Intracoronal retainers
Disadvantages
Require prepared abutments and castings
Require somewhat complicated clinical and
laboratory procedures
They eventually wear with resulting loss in retention
Difficult to repair and replace
Effective in proportion to their length and are
therefore least effective on short teeth
Difficult to place completely within the circumference
of an abutment tooth
More expensive
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13. Amount of retention
Size of angle of cervical convergence
How far clasp arm is place in cervical
convergence
Flexibility of clasp arm
It’s length
It’s relative diameter
It’s cross-sectional form
Material of clasp arm
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15. Angle of cervical convergence
Area cervical to height of contour
Amount of convergence – relative to
path of placement and removal
A definitive path of placement is
possible- guiding planes.
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16. How far clasp arm is place in
cervical convergence
Relative uniformity of retention
Location of clasp arm in relation to angle of
cervical convergence, not in relation to
height of contour.
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17. Flexibility of clasp arm
Length α Flexibility
Diameter 1/ α Flexibility
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18. Flexibility of clasp arm
Cross sectional form
Half round form →Unidirectional
Round form →universal
Material of clasp: Wrought wire > cast
gold > chrome alloys
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19. Stabilizing- reciprocal cast clasp
arm
It should be rigid
It should taper in one dimension only
It’s average diameter must be greater then
retentive arm
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20. REQUIREMENTS OF
CLASP DESIGN
Retention
Stability
Support
Reciprocation
Encirclement
Passivity
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21. Basic principles of clasp
design
More than 180° of the greatest
circumference of the crown of the
tooth must be included
Continuous contact
Three widely separated area
Occusal rest must be designed
Each retentive terminal must
oppose a reciprocal component.
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22. Basic principles of clasp
design
Positive guiding planes
Retentive clasps should be bilaterally
opposed
Path of escapement of each
retentive clasp must be other then
parallel to path of removal of the
prosthesis.
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23. Basic principles of clasp
design
Amount of retention should always be minimum
necessary
Clasp retainer should not transmit off-vertical forces
to the abutment tooth.
Reciprocal element →at the junction of gingival and
middle thirds
Terminal end or retentive arm →Gingival third
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24. Type of clasps
Circumferential clasp
Ring clasp
Embrasure clasp
Multiple clasp
Half- and –half clasp
Reverse action clasp
Bar clasp or RPI clasp
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25. Circumferential clasp
This clasp consists of occlusal rest & a
buccal and lingual arm originating from
a common body
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26. Circumferential clasp
Most logical clasp for tooth supported partial
dentures because of excellent support,
bracing and retentive qualities
Can be used in a wide variety of situations
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27. Circumferential clasp
Disadvantages
More tooth coverage
It’s occlusal approach may increase the width of
occlusal surface of the tooth
More metal may be displayed than bar clasp
It’s half round form prevents to increase or decrease
retention
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28. Ring clasp
Encircles nearly all of a tooth from it’s point of origin
Indications: Tipped molars were a proximal undercut
cannot be approached by any other means
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30. Multiple clasp
Simply two opposing circumferential
clasps joined at the terminal end of the
two reciprocal arms
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31. Half- and –half clasp
It consists of a circumferential
retentive arm arising from one
direction and reciprocal arm
arising from another
The second arm must arise from
a second minor connector and is
with or without occlusal rest
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32. Reverse-action clasp
When retentive undercut is adjacent to occusal rest
Bar clasp cannot be used because of soft tissue
undercut
Ring clasp cannot be used due to lingual undercut
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33. Bar clasp
The bar clasps approach the
undercut or retentive area on
the tooth from a gingival
direction
Flexibility of bar clasp → taper
and length of approach arm
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34. Bar clasp
DISADVANTAGES
Greater tendency to trap food debris
Does not contribute as much to
bracing and stabilization as most
circumferential clasps do
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40. Combination clasp
It is a circumferential clasp, but bar
clasp may be used
wrought wire retentive clasp arm and a
cast reciprocal clasp arm
If high heat chrome alloy is used, the
wrought wire must be soldered to the
completed framework
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42. How to select a clasp design
It’s flexibility
Stabilization for horizontal & rotational
forces
Sufficient rigidity
Applicable to malposed or rotated tooth
Presence or absence of tissue undercut
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43. How to select a clasp design
Clasp terminal is adjustable or not
Area to be covered by clasp
Effect on width of occlusal table
Can it be replaced.
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44. Indirect Retainers
Restrict the movement of denture base away from
basal seat, as it tend to rotate around one of the
fulcurum line .
Rigid unit of partial denture framework, that are
located on definite rest seats on the opposite side of
fulcurum line from the distal extension base .
Theses component should be placed as far as
possible from fulcurum line for best possible
leverage.
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46. Fulcurum line
This is an imaginary line passing through teeth and component
part of partial denture, around which denture rotates slightly
when subjected to various forces directed towards or away from
the residual ridges.
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47. Indirect retainer - types
Auxiliary occlusal rest
Canine extension from occlusal rest
Canine rest
Linguoplate with rest on terminal ends
Modification areas.
Rugae support
The proximal plate
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48. Factor influencing effectiveness
of indirect retainer
Stable principal occlusal rests
Distance from the fulcrum line
Rigidity of the connectors supporting
the indirect retainer
Effectiveness of the supporting tooth
surface.
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49. CONCLUSION
We can select any of the clasp
designs but that should be
based on sound biological &
mechanical principles of clasp
designs
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50. THANK YOU
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