Direct retainer. (Suprabuldge type)...Content Direct retainer role in prosthesis movement control...
Transcript of Direct retainer. (Suprabuldge type)...Content Direct retainer role in prosthesis movement control...
Direct retainer. (Part I & II)PRESENTED BY:
DR. TUSHAR BHAGAT
Content
Direct retainer role in prosthesis movement control
1)Intra-coronal direct retainers
2)Extra-coronal direct retainers
i) Basic requirements of clasps
ii) Factors that determine the amount of retention provided by a particular clasp arm
iii) Classification of extra-coronal direct retainers
iv) Suprabulge Direct Retainers
i) Types of suprabulge direct retainers
ii) Indications
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Direct retainer (DR) role in prosthesis
movement control
In FPD retention gain by preparation geometry,
luting agent;
In RPD retention is gain by direct retainer, denture
base;
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Ref: McCraken’s Removable partial prosthodontics. P.no.79
Introduction
A removable partial denture (RPD) include
components that prevents displacement of
prosthesis from patients mouth during function.
And that component engaging abutment
tooth & resists dislodging forces is
direct retainer (DR).
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Definition of DR
Is that component, used to retained & prevent
dislodgement, consisting of clasp assembly or
precession attachment. GPT-8
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Classification of DR 6
Ref: 1) Stewart’s. Page.no.52. 2) McCraken. P.no.80
Direct retainer
Intracoronal Extracoronal
Precision
attachment
Retentive
clasp
Semiprecision
attachment
Attachment
Suprabulge
Infrabulge
Intracoronal direct retainer
This principle was first formulated by
Dr.Herman E.S. Chayes in1906.
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Matrix
Patrix
Intracoronal direct retainer 8
Precision
attachment
Semiprecision
attachment
Intracoronal
direct retainer
Precision AttachmentIntracoronal direct retainer
Patrix & Matrix type of attachment.
It resides within the normal contours
of an abutment & functions to retain &
stabilize a RPD.
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Matrix
Patrix
Precision Attachment Intracoronal direct
retainer
Matrix is metal receptacle contained within
the normal clinical contour of fixed
restoration.
Patrix is a type of attachment to the
corresponding RPD.
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Matrix
Patrix
Semiprecision AttachmentIntracoronal direct retainer
Less intimate fit between matrix & patrix component.
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Advantages of Intracoronal direct retainer
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1. Elimination of visibility
2. Better vertical support
3. Horizontal stabilization
4. Better stimulation of underlying tissues
because of intermittent vertical massage
Disadvantages of Intracoronal direct retainer
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1. Require prepared abutments and castings
2. They eventually wear with progressive loss of frictional resistance to denture removal.
3. Difficult to repair and replace
4. Complicated clinical and laboratory procedures
5. Difficult to place completely within the circumference of tooth
6. Expensive
Limitations of Intracoronal direct retainer
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1. Size of the pulp
2. Short or abraded teeth
3. Not to be used in extensive tissue
supported distal extension cases unless
some form of stress breaker is used.
Extra coronal direct retainer
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Extracoronal direct retainer 16
It consists of components that reside
entirely outside the normal clinical
contours of the abutment.
They serve to retain & stabilize RPD.
Extracoronal DR subcategories as 17
1. Extracoronal attachments
• Introduced by Henry R. Boos, in early 1900
• Derives retention from matrices & patrices.
• Provides vertical movement of RPD
2. Retentive clasp assemblies
• Common method for retention of RPD.
• Metal clasp arm with limited amount of flexibility.
Prothero’s Cone theory 18
In 1916 – Prothero’s Advanced
Cone Theory was introduced by
M. M. DeVan, which is the basis
of clasp retention.
According to theory, the tooth is
considered as a pair of cones
sharing a common base.
Prothero’s Cone theory 19
Prothero’s Cone Theory
introduced the term;
SUPRABULGE
INFRABULGE
INFRABULGE
Or
Undercut
SUPRABULGE
SUPRABULGE
INFRABULGE
Height
of contour
Categories of retentive clasps 20
Circumferential or Suprabuldge direct
retainers.
Vertical projection, bar type, or Infrabuldge
direct retainers.
Direct Retainers. - II
Circumferential or Akers Clasp or
Suprabuldge direct retainers.
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Structure of clasp assembly 23
A properly designed clasp
assembly has following parts;
A rest (R)
A retentive arm (RA)
A reciprocal element (RE)
One or more minor connector (M)
(R)
minor
connector
(RA)
(RE)
Structure of clasp assembly 24
1. A rest (R): provides vertical support.
2. A retentive arm (RA): only portion of
to reach in undercut area. Retentive
arm are of two types
Suprabuldge Arm &
Infrabuldge Arm
(R)
Suprabuldge Arm
Infrabuldge Arm
(RA)
Structure of clasp assembly 25
3. A reciprocal element (RE): that
braces an abutment during
prosthesis insertion & removal.
4. One or more minor connector
(M): connecting the parts of
direct retainer to major
connector.
(R)
minor connector
Bracing arm
Retentive arm
RE
RA(M):
M
M
Requirement of clasp assembly 26
1) Retention
2) Support
3) Stability
4) Reciprocation
5) Encirclement
6) Passivity
(R)
Requirement of clasp assembly;
1) Retention27
Provide retention for the prosthesis.
Retention depends on:
a. Flexibility of clasp arm.
b. Depth that retentive terminal extends into the undercut.
c. Amount of clasp arm that extends below height of
contour.
Requirement of clasp assembly;
1) Retention28
a. Flexibility of clasp arm:
i. Length of clasp arm
ii. Diameter of clasp arm.
iii. Taper of clasp arm.
iv. Cross-sectional form of the clasp arm.
v. Material from which clasp is made.
Requirement of clasp assembly;
1) Retention29
a. Flexibility of clasp arm:
i. Length of clasp arm
By increasing flexibility- horizontal stresses can be reduced.
But clasp’s ability to provide retention should not be lost.
(More length, more flexibility).
Requirement of clasp assembly;
1) Retention30
a. Flexibility of clasp arm:
i. Length of clasp arm
ii. Diameter of clasp arm.
Flexibility is inversely proportional to the diameter
of clasp arm.
Requirement of clasp assembly;
1) Retention31
a. Flexibility of clasp arm:
i. Length of clasp arm
ii. Diameter of clasp arm.
iii. Taper of clasp arm.
A uniform taper in both thickness & width is essential.
A clasp should be half as thick at the tip as at the origin.
Requirement of clasp assembly;
1) Retention32
a. Flexibility of clasp arm:
i. Length of clasp arm
ii. Diameter of clasp arm.
iii. Taper of clasp arm.
iv. Cross-sectional form of the clasp arm.
Universally flexible form- round form.
Flexibility is limited to only one direction in case of half round form.
So cast retentive clasp arms are more acceptable in tooth-
supported partial dentures- flex only during placement & removable.
Requirement of clasp assembly;
1) Retention33
a. Flexibility of clasp arm:
i. Length of clasp arm
ii. Diameter of clasp arm.
iii. Taper of clasp arm.
iv. Cross-sectional form of the clasp arm.
v. Material from which clasp is made.
Chrome alloys have higher modulus of elasticity- less flexible.
Smaller cross-sectional form & less depth of retentive
undercut must be used.
Requirement of clasp assembly;
1) Retention34
1) Retention depends on:
a. Flexibility of clasp arm.
b. Depth that retentive terminal extends into the undercut.
c. Amount of clasp arm that extends below height of
contour.
Requirement of clasp assembly 35
1) Retention
2) Support:
Support is property of clasp that resists
displacement of clasp in gingival
direction.
Prime support units are rests.
(R)
Requirement of clasp assembly 36
1) Retention
2) Support
3) Stability:
It is resistance to horizontal displacement of prosthesis.
All clasp components except the retentive terminals
contribute to this property in varying degrees.
Cast circumferential clasp offers greatest stability- rigid
shoulder.
Support, stability & retention 37
Requirement of clasp assembly 38
1) Retention
2) Support
3) Stability
4) Reciprocation:
Each retentive clasp terminal must be opposed by
reciprocation.
Reciprocal arm reciprocates stresses generated against
the tooth by retentive clasp terminal.
Continue..
Requirement of clasp assembly 39
1) Retention
2) Support
3) Stability
4) Reciprocation:
It also stabilizes the denture against horizontal
movement.
Additional occlusal rest.
Reciprocal arm must be rigid.
(R)
Requirement of clasp assembly 40
1) Retention
2) Support
3) Stability
4) Reciprocation
5) Encirclement:
Each clasp must be designed to
encircle more than 180 degrees of
abutment tooth
(R)
Continue..
Requirement of clasp assembly 41
1) Retention
2) Support
3) Stability
4) Reciprocation
5) Encirclement:
If broken encirclement is planned- clasp
assembly must contact at least 3 different
tooth areas that embrace more than more
than half the tooth’s circumference.
(R)
Requirement of clasp assembly 42
Requirement of clasp assembly 43
1) Retention
2) Support
3) Stability
4) Reciprocation
5) Encirclement
6) Passivity:
A clasp in place should be completely
passive.
Retention function is activated only when
dislodging forces are applied.
(R)
Requirement of clasp assembly 44
1) Retention
2) Support
3) Stability
4) Reciprocation
5) Encirclement
6) Passivity
Suprabuldge clasps 45
1) Simple circlet clasp
2) Reverse circlet clasp
3) Multiple circlet clasp
4) Embrasure clasp
5) Ring clasp
Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..
1. Simple circlet clasp 46
Versatile & widely used clasp design.
Choice for tooth supported PD.
Originates from proximal surface of the
abutment adjacent to edentulous area.
Fulfils design requirements.
Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..
2. Reverse circlet clasp 47
Often used when undercut is located at the
distofacial side (preferably give infrabuldge
retainers, but as hard & soft tissue undercut does
not allow)
Class I & II help to control stresses
transmitted to abutment during function.
Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..
3. Multiple circlet clasp 48
It involves two simple circlet clasp joined at
the terminal aspect of their reciprocal
elements.
Given when primary abutment tooth is
compromised and stress originated from
prosthesis retention can be favorably
distributed to multiple teeth.
Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..
4. Embrasure clasp 49
Are essentially two simple circlet joined
at their bodies.
Design is most frequently used on side
of the arch where there is no
edentulous space
Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..
5. Ring clasp 50
Mostly indicated in tipped mandibular
molar.
Because of the length of the arm
additional support must be available to
ensure its rigidity.
By auxiliary bracing arm
Additional rest on disto occlusal surface
Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..
Summary 51
Direct retainer
Extracoronal Intracoronal
Precision
attachment
Semiprecision
attachment
Extracoronal
Attachment Retentive
clasp assembly
Suprabuldge
retainers
Infrabuldge
Retainers
Simple circlet
Reverse circlet
Multiple circlet
Embrasure Ring clasp
THANK YOU
Reference: McCraken & Stewart’s