Direct retainer/ courses in dentistry

1111INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com
www.indiandentalacademy.comwww.indiandentalacademy.com

DIRECT RETAINERS
 Introduction
The removable partial denture must have
sufficient retention to resist reasonable dislodging
forces.
 Primary Retention: for the removable partial denture
is accomplished mechanically by placing retaining
elements on the abutment teeth.
 Secondary Retention: is provided by the intimate
relationship of minor connector contact with the guiding
planes, denture bases, and major connectors
(maxillary) with underlying tissues.

 Definition: A direct retainer is any unit of removable
dental prosthesis that engages an abutment tooth in
such a manner as to resist displacement of the
prosthesis away from basal seat tissues.
 The two basic types of direct retainers:
Intracoronal retainer
Direct Retainers (precision attachment)
Extracoronal Retainer
(clasp)

 Intracoronal Retainers: which is cast or attached
totally within the restored natural contours of an
abutment tooth. This type of retainer is composed of
a prefabricated machined key and keyway, with
opposing vertical parallel walls that serve to limit
movement and resist removal of the partial denture
through frictional resistance.
 Extracoronal Retainers: which uses mechanical
resistance to displacement by components placed on
or attached to the external surfaces of an abutment
tooth
 Extracoronal D.R. Circumferential clasp

 Components of clasp Assembly
1. Rest – Provides support for prosthesis
2. Body – Connects rest and clasp arms to
minor connector
3. Reciprocal arm – must be rigid above the
height of contour
4. Retentive arm – Provides direct retention
below the height of the contour
5. Shoulder
6. Approach arm
7. Terminal

a. The occlusal
rest
b. The body
c. The shoulders
d. The terminals
e. The clasp arms
f. The strut
g. the approach
arm
h. the terminal

 Clasps can be classified on the basis of
construction
1. Cast clasp
2. Wrought wire clasp
3. Combination clasp
 Clasps classified on a basis of design
1. Circumferential clasp (Akers –
suprabulge)
2. Bar clasp (vertical projection – Roach
infrabulge)

Circumferential clasp: It approaches the
undercut from occlusal direction – “pull” type of
retention

Bar clasp: Retentive terminal approaches the
undercut from gingival direction – below the
surveyline – “push” type of retention.

a.a. Circumferential
clasp
b. Bar clasp

ATTRIBUTES OF PROPERLY
DESIGNED CLASP
 The clasp should possess the attributes
of
 Retention
 Stabilization
 Support
 Encirclement
 Reciprocity
 Passivity

RETENTION
 Retention is the property which enables the clasp to
resist dislodgement from the tooth in an occlusal
direction. A dislodging force may be activated by
speech, muscle action, mastication, deglutition,
sticky foods, or gravity.

Retentive arm of the clasp

 The length of the clasp arm. The greater the length,
the greater the resiliency.
 The diameter of the retentive arm. The smaller the
diameter, greater the resiliency.
 The cross sectional form. A round clasp arm is more
resilient than one that is half round or oval in shape.
 The taper. Proper taper can increase flexibility as
much as fourfold. The retentive arm of the clasp
should taper evenly and uniformly from its origin at
the body of the clasp to its terminal extremity.

 The kind of alloy. The chromium Cobalt alloys have a
higher modulus of elasticity, hence are not as
resilient as gold alloys of the same diameter.
 The type of alloy. An alloy is wrought form is more
resilient than the same alloy of identical diameter in
cast form, because of its internal structure.
 Heat treatment of the alloy. Proper heat treatment,
gold in particular, will increase the resilience
substantially, whereas improper heat treatment may
render it brittle and with no resilience whatever.

Cast Clasp Wrought clasp
Flex in
horizontal
plane
Flex in
all
planes

Flexibility of a clasp arm increases
as length of clasp increases
Uniform taper in both
thickness and width
necessary
Clasp terminal should be
half as thick as origin

STABILIZATION
 Stabilization, or bracing is the resistance which
the clasp contributes to displacement of the
prosthesis in horizontal plane . All of the clasp
components, with the exception of the retentive
terminal, contribute this property in varying
degrees.

SUPPORT
 Support is the property of the clasp which
enables it to resist displacement in a gingival
direction. The occlusal rest is the prime support
unit of the clasp, although the body and the
shoulder of the clasp, positioned as they are
above the greatest diameter of the tooth, also
contribute a substantial amount of support.

ENCIRCLEMENT
 The clasp should be so designed that it encircles at
least 180 degrees of the crown of the tooth, to
preclude movement of the tooth out of the clasp arms
as strmsses are applied.

Each clasp assembly
must encircles
more than 1800
A clasp that fails to
produce encirclement
will act as orthodontic
appliance

RECIPROCITY
• Reciprocation may defined as “ the means by
which one part of the appliance is made to
counter the effect created by another part”.
• Reciprocation is needed most when the
retentive terminal flexes over the bulge of the
crown during insertion and removal of the
prosthesis.

Reciprocal arm of the clasp is rigid.

PASSIVITY
 When the clasp is in place on the tooth, it should be
passive. Passivity is an important requirement of a
properly designed clasp. A clasp so designed will
permit a slight degree of movement of the base
without transmitting any appreciable amount of the
stress to the abutment tooth.

A clasp must be completely seated to be passive

SIMPLE CIRCLET CLASP
 This is the most widely used clasp
 It is the clasp of choice on tooth supported
removal partial dentures
 This clasp approaches the undercut on the
abutment tooth from the edentulous areas and
engages the undercut from the edentulous
space.

Advantages:
• The clasp fulfills the requirement of support,
stability reciprocation, encirclement & passivity
better than any other type of clasp.
• It is easy to construct.
• It is simple to repair.

Disadvantages:
• It tends to increase the circumference of the crown.
• In anterior part of the mouth is not acceptable.
• It covers more tooth surface then the bar clasp and
prone to caries.
• Retentive undercuts on some teeth are difficult to
reach with retentive terminal of the claspwww.indiandentalacademy.comwww.indiandentalacademy.com

REVERSE CIRCLET CLASP
Reverse circlet clasp is used when the retentive
undercut is located on the surface of the
abutment tooth adjacent to the edentulous
space.
In distal extension edentulous ridge partial
denture the reverse approach clasp helps to
control the stresses transmitted to the terminal
abutment tooth on the edentulous side.

REVERSE CIRCLET CLASP

MULTIPLE CIRCLET CLASP
It is opposing simple circlet
clasps joined at the
terminal end of the 2
reciprocal arms.
It is indicated in
periodontally weakened
teeth.
This is the form of splinting
weakened teeth by a
removable partial denture.www.indiandentalacademy.comwww.indiandentalacademy.com

EMBRASURE CLASP
(MODIFIED Crib Clasp)
The embrassure clasp is 2 simple circlet clasps
joined at the body.
It is most frequently used on the side of the
arch where there is no edentulous space.
Occlusal rest preparations must be made on
both teeth and tooth structure must be removed
from the buccal inclines of both teeth to provide
space for adequate thickness of metal.

EMBRASURE CLASP

RING CLASP
Indicated on tipped molars.
Ring clasp engages the undercut by encircling
the entire tooth from its point of origin.
On mandibular molar the clasp encircles the
tooth beginning on the mesio-buccal surface
and eliminating in an infrabulge area on the
mesio-lingual surface.
On a maxillary molar the direct of the clasp is
reversed.

RING CLASP

The entire clasp must be placed above the left
of the contours except retentive tip.
It must be designed with additional support in
the form of an auxillary bracing arm.
An additional occlusal rest on the opposite side
of the tooth from the clasp origin provide
additional support and proved further movement
of the mesially inclined tooth.

C clasp Fishhook, or Hairpin Clasp
The C clasp is a simple circlet clasp in which the retentive
arm crosses the facial surface of the tooth from its point of
origin, loops back in hairpin turn to engage a proximal
undercut below its point of origin.
The upper part of retentive arm must be rigid, the lower
apart of the retentive arm should be tapered. It is the only
flexible part of the clasp arm.
The crown of the abutment tooth must have sufficient
occlusogingival height to accommodate this double width
of the clasp arm.
The upper and lower arms of the retentive clasp must be
designed such that food debris will not be retained.www.indiandentalacademy.comwww.indiandentalacademy.com

C Clasp, Hairpin Clasp, Fishhook

Indications:
 When the retentive clasp must engage an
undercut adjacent to the occlusal rest or
edentulous space and a soft tissue undercut
precludes the use of of a bar clasp
 The C Clasp is indicated when the reverse
circlet clasp cannot be used because of lack of
occlusal space.

Disadvantages:
 The clasp covers a considerable amount of
tooth structure, which may trap food debris.
 It is not good choice for a young patient or one
who is prone to caries, and it is often
unacceptable esthetically, particularly on
premolar teeth.

ONLAY CLASP
 The onlay clasp is an extended occlusal rest with
buccal and lingual clasp arms.
 The clasp may originate from any point on the onlay
that will not create occlusal interferences.
 This clasp is generally indicated when the occlusal
surface of the abutment tooth is below the occlusal
plane, usually as a result of the tooth being tipped or
rotated.
 The onlay is used to restore the normal occlusalwww.indiandentalacademy.comwww.indiandentalacademy.com

Onlay clasp

COMBINATION CLASP
The combination clasp consists of a Wrought wire
retentive clasp arm and a cast reciprocal clasp arm.
The cast reciprocal arm is normally a circumferential
clasp. But a bar clasp may be used.
The Wrought wire retentive arm is a circumferential
clasp arm.
It is used when maximum flexibility is required.
Esthetics advantage because Wrought structure in
smaller diameter than the cast clasp.www.indiandentalacademy.comwww.indiandentalacademy.com

COMBINATION CLASP

Advantages:
 Flexibility.
 Adjustability.
 Appearance of the Wrought wire retentive arm.
 Minimum of tooth surface covered.

Disadvantages:
 It involves extra steps in fabrication.
 It may be distorted by patient.
 It may be less accurately adapted.

Bar or Vertical Project Clasp
Bar clasps approach the undercut from a gingival
direction.
It is more effective than the “pull” retention
characteristic of circumferential clasps.
Patient in contouring less difficulty inserting and
more difficulty in removing removable partial
denture with bar clasp than with circumferential
clasp.
Flexibility of the bar clasp can be controlled by the
taper and length of the approach arm.
Because of the gingival approach of the bar clasp
it is usually esthetics than a circumferential clasp.

DISADVANTAGES
Greater binding to collect and hold food debris
Because of the increased flexibility of the
retentive arm it does not contribute to
stabilization.

T - BAR CLASP
T Bar clasp is frequently used on distal
extension ridge where the usual undercut
.

I-bar clasp
 Used on distobuccal surface of maxillary
canines for esthetic reasons.
 Retentive tip is in contact with abutment teeth.
 I bar is a component of a partial denture
referred to as RPI concept.

Y- BAR CLASP
 Y-Bar is basically a T-clasp its configuration
occurs where the it is contour on the facial
surface of the abutment tooth is high on the
medial and distal angles.

REVIEW OF LITERATUREREVIEW OF LITERATURE
I. David n. Firtell, in his review article stated thatI. David n. Firtell, in his review article stated that
Applegate listed 4 factors which determines theApplegate listed 4 factors which determines the
amount retentionamount retention
Angle of infrabulge convergenceAngle of infrabulge convergence
1.1. Distance below height of contourDistance below height of contour
2.2. Accuracy of adaptation to the contacting surfaceAccuracy of adaptation to the contacting surface
3.3. Flexibility of the clasp arm.Flexibility of the clasp arm.
Stone showed experimentally that a properly adaptedStone showed experimentally that a properly adapted
infrabulge clasp could deliverinfrabulge clasp could deliver
143 % more retention than a suprabulge clasp143 % more retention than a suprabulge clasp
According to Mc Cracken the clasp with a roundAccording to Mc Cracken the clasp with a round
wought wire retentive arm to be the best.wought wire retentive arm to be the best.
JPD :VOL 20 NO-1 1968JPD :VOL 20 NO-1 1968

II. Bert T.Cecconi in his review article “THEII. Bert T.Cecconi in his review article “THE
EFFECT OF PARTIAL DENTURE CLASPEFFECT OF PARTIAL DENTURE CLASP
DESIGN ON ABUTMENT TOOTH MOVEMENTDESIGN ON ABUTMENT TOOTH MOVEMENT
“ stated that Clayton measured clasp forces“ stated that Clayton measured clasp forces
exerted on the abutment teeth, he concludedexerted on the abutment teeth, he concluded
that wrought wire clasps exerted more force onthat wrought wire clasps exerted more force on
abutment teeth than the cast bar clasps of sameabutment teeth than the cast bar clasps of same
length.length.
JPD VOL 25,NO 1 1971JPD VOL 25,NO 1 1971

GENE A. ZACHGENE A. ZACH stated that in constructing a distalstated that in constructing a distal
extension RPD, a system of design using mesial restsextension RPD, a system of design using mesial rests
has certain advantages over a system of design usinghas certain advantages over a system of design using
distal rests.distal rests.
JPD 1975 VOL 33 NO 1JPD 1975 VOL 33 NO 1
Advantages:Advantages:
1.1. axis of rotationaxis of rotation
2.2. trauma to tissue distal to abutment teeth.trauma to tissue distal to abutment teeth.
3.3. indirect retention with mesial and distal restsindirect retention with mesial and distal rests
4.4. mesial rests in conjugation with guiding planesmesial rests in conjugation with guiding planes
5.5. assistance to distal displacementassistance to distal displacement

Axis of rotation:Axis of rotation:
A mesial rest results in an axis of rotationA mesial rest results in an axis of rotation
that is more anterior with the dental archthat is more anterior with the dental arch
than is the axis of rotation resulting form athan is the axis of rotation resulting form a
distal rest. This position of the axis ofdistal rest. This position of the axis of
rotation causes the reduction of therotation causes the reduction of the
torquing force applied to the abutmenttorquing force applied to the abutment
tooth during mastication.tooth during mastication.

Trauma to tissue distal to abutmentTrauma to tissue distal to abutment
teeth:teeth:
The use of a mesial rest in the distalThe use of a mesial rest in the distal
extension RPD design results in the lessextension RPD design results in the less
trauma to the soft tissue immediately distaltrauma to the soft tissue immediately distal
to the abutment tooth than results from useto the abutment tooth than results from use
of a distal rest.of a distal rest.

Trauma to tissue distal to abutment teeth:Trauma to tissue distal to abutment teeth:
The use of a mesial rest in the distalThe use of a mesial rest in the distal
extension RPD design results in the lessextension RPD design results in the less
trauma to the soft tissue immediately distal totrauma to the soft tissue immediately distal to
the abutment tooth than results from use of athe abutment tooth than results from use of a
distal rest.distal rest.

Mesial rest in conjugation with guidingMesial rest in conjugation with guiding
planes:planes:
A mesial rest used in conjugation with theA mesial rest used in conjugation with the
guiding plane creates a favourable fulcrumguiding plane creates a favourable fulcrum
point on the abutment tooth that does distalpoint on the abutment tooth that does distal
rest.rest.

Resistance to distal displacement:Resistance to distal displacement:
A system of clasp design using a mesial restA system of clasp design using a mesial rest
with retention located distally on the abutmentwith retention located distally on the abutment
tooth offers more resistance to distaltooth offers more resistance to distal
displacement of a distal extension RPD thandisplacement of a distal extension RPD than
does a system of a clasp design using a distaldoes a system of a clasp design using a distal
rest with retention located mesially on therest with retention located mesially on the
abutment tooth.abutment tooth.

Joseph E. Grasso, in his study, described a new
removable partial denture clasp assembly. A new claps
assembly is presented which incorporates a desirable
feature of both the bar and the circumferential clasp.
With this clasp assembly, the horizontal retentive arm
and the vertical reciprocal arm are designed to make
simultaneous contact with their respective tooth surface
during placement and removal of the prosthesis.
JPD 1980 VOL 43 NO 6

Advantages:
•it improves esthetics
•the survey line doesnot have to be followed in
positioning the nonflexible two ends of the retentive arm
•no special instrumentation is required to make the
lingual surfaces parallel to the path of insertion.
•tooth contact is kept to a minimum
•there is no need to prepare broad parallel tooth surface
to provide reciprocal contacts
•only small contact areas on the lingual surfaces of the
abutment teeth are required for parallelism with the path
of insertion.

David N. FirtellDavid N. Firtell, studied the effect of clasp, studied the effect of clasp
design upon the retention of the removabledesign upon the retention of the removable
partial dentures. He constructed a model topartial dentures. He constructed a model to
represent an ideal removable partial denturerepresent an ideal removable partial denture
situation with standardized undercut, ninesituation with standardized undercut, nine
chrome cobalt alloy test frameworks, eachchrome cobalt alloy test frameworks, each
representing a different clasp design, wererepresenting a different clasp design, were
fabricated according to manufacturersfabricated according to manufacturers
directions. The amount of force required todirections. The amount of force required to
dislodge each framework from the model wasdislodge each framework from the model was
recorded.recorded.

The framework showed the followingThe framework showed the following
decreasing order of resistance to verticaldecreasing order of resistance to vertical
displacement from a 0.02” undercut.displacement from a 0.02” undercut.
1.1. U-shaped infra-bulge claspU-shaped infra-bulge clasp
2.2. Ring claspRing clasp
3.3. Akkers claspAkkers clasp
4.4. Akkers clasp with wrought gold wire retentiveAkkers clasp with wrought gold wire retentive
armarm
5.5. ““I” infra-bulge claspI” infra-bulge clasp
6.6. ““I” infra-bulge clasp with a wrought gold wireI” infra-bulge clasp with a wrought gold wire
retentive armretentive arm
Back action claspBack action claspwww.indiandentalacademy.comwww.indiandentalacademy.com

Disadvantages:Disadvantages:
1.1. food entrapmentfood entrapment
2.2. inability of the horizontal retentive arm toinability of the horizontal retentive arm to
provide bracingprovide bracing

SUMMARYSUMMARY

ReferencesReferences
Mc CrackensMc Crackens
Atlas on RPD by :Atlas on RPD by :
StuartStuart
JPD 1968 VOL 20, NO- 1JPD 1968 VOL 20, NO- 1
JPD 1968 VOL 20, NO-1JPD 1968 VOL 20, NO-1
JPD 1971 VOL 25, NO -1JPD 1971 VOL 25, NO -1

Thank you
For more details please visit
www.indiandentalacademy.com

Direct retainer/ courses in dentistry

Recomendados

Recomendados

Más contenido relacionado

La actualidad más candente

La actualidad más candente (20)

Similar a Direct retainer/ courses in dentistry

Similar a Direct retainer/ courses in dentistry (20)

Más de Indian dental academy

Más de Indian dental academy (20)

Último

Último (20)

Direct retainer/ courses in dentistry

Notas del editor