Rest, rest seat , direct retainer & indirect retainer

Rest and Rest Seat, Direct retainer,
Indirect retainer
Dr.Laju.s
Reader , Dept of prosthodontics
Malabar dental college & research centre
Edappal

Rest and rest seat
 Definitions
 Introduction
 Classification
 Forces on RPD
 Primary rests
 Occlusal rest and rest seat
 Lingual / Cingulam rest
 Incisal rest
 Internal rest

Definition of rest
 A projection or attachment usually
on the side of an object (GPT 8)
 The component of a removable
partial denture that serve primarily
to transfer forces occuring against
the prosthesis down the long axis of
the abutment teeth (Stewart)
 Any component of the removable
partial denture that is placed on an
abutment tooth , ideally in a
prepared rest seat , so that it limits
movement of the denture in a
gingival direction and transmit
functional forces to the tooth(
McCracken)

Definition of Rest seat
 The prepared recess in a
tooth or restoration created
to receive the occlusal ,
incisal, cingulum or lingual
rest (GPT 8 )
 Rest seat is the prepared
surface of a tooth or fixed
restoration into which a rest
fits (Stewart)
 The prepared surface of an
abutment to receive the rest
is called the rest seat
(McCracken)

Introduction
 In 1899 Bonwill
recommended use of rest in
RPD
 Rest preserve the remaining
oral structures by
 - Controlling the position of
the prosthesis in respect to
the teeth
 - Position of the prosthesis in
respect to the periodontium
and mucosa

 Controlling the amount and
the direction of movement of
abutment teeth
 The rest can thus be
considered as the control
factor in the triad of
prosthesis- tooth -
periodontium

Classification of rest
 A) Primary rest : That is a component part of a direct retainer unit
 B) Secondary / Auxillary rest : Additional rest used for indirect
retention or extra support
 According to location a) Anterior b) Posterior
 According to surface : occlusal , incisal, cingulam, onlay,
interproximal,internal

Functions of rests
 To transmit forces apically down the
long axis of the tooth
 Acts as a vertical stop
 Maintain the retentive clasp in its
proper position

Rest can be designed so that it
can act as a reciprocal clasp
arm
Rest may also help establish a
more acceptable occlusal plane.
Helps to transmit lateral or
horizontal forces applied to the
partial denture during function
to the supporting teeth
Prevents food impaction
between minor connector and
tooth

Forces on removable partial denture
 Vertical or occlusal forces during chewing, swallowing
 Lateral forces : developed when the lower jaw moves side to
side with teeth in contact
 Anteroposterior forces : Forward and backword movement of
the lower jaw with teeth in contact

The forces acting on the partial denture are a result of a composite of
forces arising from three principal fulcrums
 Fulcrum line is a theoretical line
passing through the point around
which a lever functions and at right
angle to its path of movement .
 With respect to removable partial
denture , it is an imaginary line
connecting occlusal rests around
which a removable partial denture
tends to rotate under masticatory
forces

 One fulcrum line is on horizontal
plane that extends through two
principal abutments , one on
each side of dental arch .
 This fulcrum controls the
rotational movement of the
denture in the sagittal plane
 The resulting force on the
abutment tooth is usually mesial
apical or distal apical

 A second fulcrum line is on the
sagittal plane and extends
through the occlusal rest on the
terminal abutment and along
crest of the residual ridge on
one side of the arch
 This fulcrum controls the
rotational movement of the
denture in the vertical plane
(rocking , or side to side
movement over the crest of the
ridge)

 The main direction of the
resulting force is more nearly
horizontal and not well resisted
by the tissues

 Third fulcrum line is located in
the vicinity of the midline just
lingual to the anterior teeth .
 This fulcrum line is vertical and
it controls the rotational
movement of the denture in the
horizontal plane or the flat
circular movement of the
denture

Primary rests
 These prevent the vertical movement of the prosthesis towards the
tissue or help transmit lateral or horizontal forces down the long axis of
the tooth
 The action of transmitting lateral forces may be increased by
deepening the rest seat but only for a tooth supported prosthesis

 3 forms of primary rests
 1) Occlusal rest - It is seated on the occlusal surface of the posterior
teeth
 2) Lingual or Cingulam rest – Seated on the lingual surface of the
tooth
 3) Incisal rest - Seated on the incisal edge of a tooth

Occlusal rest
 It is a rigid extension of a
removable partial dental
prosthesis that contact the
occlusal surface of a tooth or a
restoration , the occlusal
surface of which may have been
prepared to receive it

Site selection
 A suitable clasp design for a
given clasping situation may
often depend on the availability
of interocclusal space and on a
proper site on the tooth for the
rest recess.

 In case of bicuspids and molars,
the occlusal rest is placed in the
fossa of the abutment tooth
adjacent to the edentulous
space though not compulsarily.
 Placing the rest as far
posteriorly in the mouth as
possible in the distal extension
base type of denture is
advantageous due to the
leverage control

Form of occlusal rest and rest seat
 The outline form of the occlusal
rest seat should be a rounded
triangular shape with the apex
towards the center of the
occlusal surface
 The base of the triangular
shape (at the marginal ridge)
should be at least 2.5mm for
both molars and premolars

 The marginal ridge of the
abutment tooth at the site of
the rest seat must be lowered
to permit a sufficient bulk of
metal for strength and rigidity
of the rest and the minor
connector. Approx 1.5mm
marginal reduction is necessary

 The floor of the occlusal rest
seat should be concave or
spoon shaped and slightly
inclined apically from marginal
ridge and also there will not be
any sharp edges or line angles
in the preparation

The angle formed by the occlusal
rest and the vertical minor
connector from which it
originates should be less than
90 degree

 For distal extension partial
denture , the rest seat should
be shallow and saucer shaped
so that the rest can move
slightly like a ball and socket
joint allowing the horizontal
forces to be dissipated

Occlusal rest seat preperation
 It is essential that rest seat
preparation should be done for each
rest before final impression for
master cast are made
 If this is not done , the forces
transmitted from the prosthesis to
the abutment teeth will occur
against inclined planes , resulting a
pushing action against the teeth and
a sliding effect on the prosthesis
 The rest seat must always be
prepared after guiding planes have
been established on abutment teeth

Occlusal rest seat preparation in Enamel
 Occlusal rest seat in enamel should
be prepared with a round diamond
stone approximating the size of a
no. 4 round carbide bur
 First a channel of the correct depth
and at the desired outline of the
preparation is created by using the
small round diamond stone to lower
the marginal ridge at either the
buccal or lingual extent of the rest
seat, to continue inward towards
the center of the tooth and to
return to the marginal ridge

 With the same diamond stone
remove the island of enamel so
that sufficient tooth structure is
removed to produce the
thickness of metal required for
strength of the rest
 There should not be any
undercut in the path of insertion

 Deepest portion of the rest seat
should be towards the center
of the tooth
 The preparation should
gradually rise towards the
marginal ridge
 Properly prepared rest seat is
round and smooth. So rest in its
rest seat can act as a ball and
socket joint

 An occlusal rest must be at least
1mm thick at its thinnest point if
chrome alloy is used for the
frame work, 1.5mm if gold is to
be used.
 The mesiodistal extension of the
rest seat should not be less
than 3mm
 Buccolingual extent should be
half the distance between the
buccal and lingual cusp tips

Occlusal rest seat preparation in new gold restorations
 Occlusal rest seats in cast gold
restorations should always be
placed in the wax patterns.
 The preparation for the rest
seat must be carved in the wax
after the establishment of
guiding planes
 Ensure that enough
interocclusal space will be
present to accommodate
thickness of crown casting plus
thickness of rest.

 No 4 round steel bur or wax
instruments like small
excavators can be used for rest
preparation in wax pattern
 After the preparation has been
cast , the rest preparation must
be polished with a small round
finishing bur

Occlusal rest seat preparation in existing gold restorations
 Preparation is same as for
sound enamel .
 Any proximal preparation is
done first
 The possibility of perforation of
the restoration is always
present
 The rest may be widened to
compensate for shallowness but
the floor of the rest seat should
be inclined apically from the
marginal ridge. If not possible
secondary occlusal rest is
considered

Occlusal rest seat preparation in Amalgam restoration
 An occlusal rest seat
preparation in amalgam
restoration is less desirable
since the amalgam alloy tends
to flow when placed under
constant pressure
 No 4 round carbide bur is used
for rest seat preparation in
amalgam restoration
 Preparation is polished by
reversing the revolution of no 4
round bur

Rest seat preparation for embrasure clasp
 This preparation extends over
the occlusal embrasure of two
approximating posterior teeth ,
from mesial fossa of one tooth
to the distal fossa of other tooth
 A small round diamond stone is
used to establish the outline
form for a normal occlusal rest
in each of the approximating
fossa.

 The contact point between the
teeth should not be broken
 No 4 diamond stone is used to
carry the buccal and lingual
extensions of the occlusal rests
over the buccal and lingual
embrasures
 An alternative method is the use
of cylindrical diamond stone
held horizontally from the
buccal surface of the teeth
pointing towards the lingual
surface

 The stone is held against the
distal incline of buccal cusp of
one teeth and the mesial incline
of the buccal cusp of the other
tooth
 Preparation over the buccal and
lingual embrasure should be 1.5
– 2mm wide and 1- 1.5 mm
deep

Rest seat in rotated teeth
 When it is necessary to clasp a tooth rotated out of its normal position ,
the preferred treatment is to cover the crown with a restoration that
realigns the surface of the tooth in a more conventional relationship to
other teeth in the arch
 If not , axial surfaces are altered sufficiently to render it more suitable
for clasping and to place the occlusal rest on the mesial or distal or on
the buccal or lingual side of the alveolar ridge as a result of rotation .

Rest recess in abraded teeth
 Preparation of rest recess in enamel that has been worn thin is
questionable , therefore covering the teeth with cast restoration
incorporating the rest seat is preferable

Extended occlusal rest
 In Kennady class11 modification
1 , and Kennady class111
situations in which the most
posterior abutment is a mesially
tipped molar , an extended
occlusal rest should be designed
and prepared to minimize
further tipping of the abutment
and to ensure that the forces
are directed down the long axis
of the abutment

 This rest should extend more
than one half the mesiodistal
width of the tooth and one third
the buccolingual width of the
tooth and allow for a minimum
of 1mm thickness of the metal
and the preparation should be
rounded with no undercut or
sharp angles

Lingual or Cingulam rest
 Lingual rest is a metallic
extension of a removable partial
denture frame work that fits
into a prepared depression with
in an abutment tooth’s lingual
surface
 Used primarily on maxillary
canine

 The thickness of the enamel on
the lingual surface of
mandibular canine does not
permit a lingual rest to be
placed
 Lingual rest on incisor teeth are
rarely used
 In some instances where canine
is missing multiple incisor teeth
are used for lingual rests to
distribute the stresses over a
number of teeth

 A lingual rest is preferred to an
incisal rest . Because it is nearer
the center of rotation of the
supporting tooth, so it does not
tend to tip the tooth.
 Minor connector required for an
incisal rest magnifies the forces
being transferred to the
abutment tooth
 Since lingual rest is confined to
lingual surface , it is more
acceptable esthetically

Form of Lingual rests
 Out line form of lingual rest is
half moon shaped. Sharp angles
must be avoided and slope of
outer lip of rest seat must be
labiogingival , forming an angle
of less than 90 degree to long
axis of tooth

Lingual rest seat preparation in Enamel
 Indication
 Tooth should be sound
 Good oral hygiene
 Low caries index
 Prominent cingulum with
gradual slope to the lingual
surface rather than a steep
vertical slope

 To prepare the lingual rest in
enamel ¼ inch diamond disk
should be used.
 The disk must be held so that it
parallels or is inclined slightly
labial to the path of insertion
 The cut with the disk should
start low on one marginal ridge,
pass over the cingulum, and
then pass gingivally to contact
the opposite marginal ridge.
This will provide the desirable
half moon shape

 A flat end large diamond
cylinder is the next best choice
for lingual rest seat preparation
 It must be held at the proper
angle , inclined slightly
gingivally from the horizontal ,
so that the cutting is done by
the flat end and side of the
cylinder

 The preparation must be
polished with the carborundum
imprignated rubber wheels and
points to polish the enamel
surfaces and to round angles
and corners

Lingual rest seat preparation in cast restoration
 If a cast restoration is to be
placed on the abutment tooth,
rest seat should be carved in
the wax pattern using a wax
excavator. So that a definite
rest preparation can be
developed that will direct the
forces of occlusion through the
long axis of the abutment tooth

Incisal rest and Rest seat
 Incisal rest is a rigid extension
of an RPD that contacts at the
incisal edge.
 Requirements of ideal Incisal
rest
 It should provide the seat by
extending over the incisal edge
onto labial surface of tooth.
 Restore anterior anatomy as
required
 Stabilize mobile teeth

Indications are
 Sound abutment , non interference with opposing occlusion
 Cast restoration not indicated
 Used as auxillary rest or indirect retainer
 On mandibular canine applicable mostly to restore anterior guidance

Advantages
 Provide definite support, may be incorporated into lingual plate
 Little loss of tooth structure

Disadvantages
Display of metal
Irritating to tongue

Forms of incisal rest
 According to Kelly incisal rest can be prepared in the form of a V
shaped notch at the incisal angle or edge approx 1.5 -2mm from
proximo incisal angle of tooth
 Deepest part is towards center of tooth mesiodistally
 Notch is rounded extends on to facial surface to provide a positive rest
 Enamel on lingual surface prepared as a shallow depression to
accommodate the minor connector and avoid annoying the tongue

 Minor connector has greater length , So it should be rigid
 An incisal rest should be approximately 2.5mm wide and
1.5mm deep for adequate strength without having to exceed
natural contour of incisal edge

Incisal rest seat preparation
 Incisal rest seats should be
used only on enamel surfaces.
 The incisal rest seat is placed
near one of the incisal angles of
canine
 If the incisal rest is used in
conjunction with a
circumferential clasp the rest
should be placed at the distal
incisal angle .

 If it is used in conjunction with
a bar clasp that uses a distal
buccal undercut , the
preparation should be made at
the mesial incisal angle
 In this position the mesial
incisal rest will reciprocate the
action of bar clasp

 The incisal rest seat preparation
is begun with a small safe side
diamond disk or a knife edge
stone held parallel to the path
of insertion
 The first cut is made vertically
1.5 to 2mm deep in the form of
a slice or notch and approx 2to
3 mm inside the proximal angle
of the tooth

 A small flame shaped diamond
point is used to complete the
preparation
 The notch created by the disk
must be rounded
 The enamel wall created by the
disk towards the center of the
tooth must be rounded with
flame shaped diamond point.
 The groove must be carried
slightly over on to the labial
surface

 This projection on to the labial
surface provide a locking device
to prevent the tooth from being
tipped or moved facially
 This groove should be
continued partway down the
lingual surface as an indentation
 This will help to accommodate
the minor connector
 After the preparation , the
enamel surface should be
polished with carborundum
containing rubber wheel

Full incisal rest
 In the absence of other suitable
placements for incisal rest and rest
seat , full incisal rest may be
considered for the following reasons
 To restore defective or abraded
tooth anatomy
 Provide stabilization
 Restore or provide anterior guidance
 In cases where tooth morphology
does not permit other designs

Milled rest or semiprecision rest or internal rest
 It consists of a narrow slot or key
way built into a metal casting that
has been constructed for an
abutment tooth , and into which is
fitted a male attachment that has
been made as an integral part of
the removable partial denture
framework

 The depth and taper of the rest
seats are important
considerations for retention
together with bracing action
 The rest seat depth should not
be less than 3mm and
convergence of the lateral walls
should not exceed 5 degree
 Increasing the angle of
convergence of the walls
facilitate insertion and removal
of the prosthesis, but decreases
the bracing and retentive action
of the unit

 Advantages
 1. Elimination of a visible clasp
arm buccally
 2 .Permits the location of the
rest seat in a more favorable
position in relation to the
tipping axis (horizontal) of the
abutment
 3. Retention is provided by the
lingual clasp arm either clasp or
wrought wire lying in a natural
or prepared infrabulge area on
the abutment tooth

 Disadvantages
 Bracing action may be less
 It can not be relied upon by itself to produce adequate retention

Rest seat designs for inclined posterior abutments : A
comparitive study
Byron P Sansome, Robert J Flinton JPD1987 58 (1)
 Designs investigated were 1 . Mesial rest only 2. Distal 3. Mesial and
Distal 4 Lingual groove rest 5. Long channel occlusal rest
 Results
 1. Rest seat placement of the abutment tooth primarily affects stress
concentration of that tooth. There is no direct relationship between rest
seat design on one abutment and resultant stress on another
 2. Inclined abutment demonstrate greater resultant bending of
interradicular bone than vertical abutment, and the greater the
inclination, the greater the bending (as the result of tipping force)

 3. Mesial rests on inclined molar
abutments demonstrate maximum
tipping forces
 4. Channel rests on inclined molar
abutments demonstrate the least
amount of tipping force

Bibiliography
 Mc Cracken ‘s Removable Partial Prosthodontics, 11th Ed, 2005
 Stewart , Clinical removable partial Prosthodontics
 Lammie & Osborne, Partial Denture 4th Ed
 Miller Removable Partial Prosthodontics
 Boucher Removable Partial Denture

Contents - Direct retainers
 Introduction
 Direct retainers
 Requirements of clasp design
 Strategic clasp positioning
 Basic clasp designs
 R.P.I Concept
 R.P.A Clasp Design
 Rotational path design
 Other clasp designs

Introduction
 An essential key to success in practice of removable partial
denture prosthodontics is thorough knowledge about each
structure details of prosthesis
 Removable partial denture must have support derived from
abutment teeth through use of rest and from residual ridge
through well fitting base.
 It must be stabilized against horizontal movement through use
of rigid connectors, indirect retainers , and other stabilizing
components

 In addition , removable partial denture should have sufficient
retention to resist reasonable dislodging forces.
 Retention is that quality inherent in a prosthesis that resist force
of gravity , the adhesiveness of food and forces associated with
opening of jaw.
 Retention of removable partial denture is accomplished
mechanically by placing retaining elements on abutment teeth
(primary retention) and also by the intimate relationship of
denture base and minor connectors with underlying tissue
(secondary retention)

 Secondary retention is similar to the retention of complete
denture and proportionate to the
 - Accuracy of impression registration
 - Accuracy of fit of denture base
 - Total area of contact involved

Direct retainer
 According to MC Cracken , direct retainer is any unit of
removable partial dental prosthesis that engages on abutment
tooth in such a manner as to resist displacement of prosthesis
away from basal tissue
 According to Stewart and Rudd, it is the component that
engages on abutment tooth and in so doing resists dislodging
forces applied to a removable partial denture
 According to GPT -8 , Direct retainer is that component of a
removable partial denture used to retain and prevent
dislodgement , consisting of a clasp assembly or precision
attachment.

Types of direct retainer
 Direct retainer
 Intracoronal Extracoronal
 A.Precision attachment
 B.Semi precision attachment a.Retentive clasp assemblies
 1.Suprabulge clasp
 2.Infrabulge clasp
 b.Attachments

 Based on construction direct retainers can be classified in to
 1. Cast clasp
 2.Wrought clasp
 3.Combination clasp
 Based on design
 1.Circumferential clasp
 2.Bar clasp


Retention clasp assembly
 Retention clasp assembly represents most common method of
extracoronal direct retention .
 First appeared in dental literature with W.G.A.Bonwill
description in 1899
 Proper use of dental surveyor is only reliable method of
effectively analyzing teeth for their contribution to the retention
of partial denture

Parts of a clasp assembly
 Rest
 Reciprocal arm
 Retentive arm
 Minor connector

 The component of clasp that
provides vertical support for
the prosthesis is called rest
and portion of the abutment
tooth prepared to receive
rest is called rest seat.
 Properly prepared rest seat
and rest serve to resist
displacement of prosthesis
towards supporting tissue
and transmit functional
forces parallel to the long
axis of the abutment.

 Retentive arm is the only
portion of the RPD that contacts
the surface of the abutment
apical to the height of contour.
Depending on their approach to
the undercut region of the
abutment they are termed-
suprabulge clasp arm and
Infrabulge clasp arm

 The portion of the clasp arm
arising from the minor
connector is known as shoulder
.
 From the shoulder the clasp
arm follows a curved path on
the surface of the abutment and
the clasp arm passes over the
height of contour and its tip
contacts undercut and this
portion of the clasp is terminus.

 Infrabulge clasp arm consists of
approach arm and terminus.
 Approach arm is a minor
connector that originates from
frame work travels horizontally
along the surface of the mucosa
and then turns vertically to
cross the free gingival margin at
90 degree.
 The terminus arises from the
vertical portion of the approach
arm and engages undercut area
of the abutment.

 Reciprocal arm is that part of
clasp assembly which provide
reciprocation to the prosthesis.
The reciprocal element may be
a cast clasp,lingual plate or a
combination of mesial and distal
minor connectors.
 Reciprocal elements must
contact the abutment tooth
occlusal to the height of
contour.

Mechanism of action of reciprocal arm
 As the retentive arm passes
over the height of contour
the arm displaces a slight
amount of flexure. This
flexure places lateral stress
in the abutment and
significant damage to the
supporting periodontium.
 To prevent these effects , a
rigid reciprocal element
should be used.

 Minor connectors join the
other units of prosthesis
such as clasp, rest, indirect
retainers , and denture
bases to the major
connector.
 It must be rigid enough to
distribute the stresses to
other components.

Basic principles of clasp design
 Surround more than 180 degree or three areas of tooth contact
 Occlusal rest - prevent the cervical movement of the clasp arms
 Each retentive tip should be opposed by the reciprocal arm
 Retention should be as minimum as possible, should only resist
the minor dislodging forces
 Retainers on the abutment should not transmit tipping or
rotational forces on the abutment tooth

 The retentive tip should be placed more gingival than the
reciprocal element
 Closer the retentive area to the edentulous area greater the
retention

Criteria for selecting clasp design
 Flexibility
 Rigidity
 Stability
 Esthetic
 Adjustibility
 Repairability
 Maintains the original morphology
 Malposed and rotated abutment tooth
 Undercut

Requirements of clasp design
 Retention - resist forces in occlusal direction
 Stability - against horizontal forces
 Support - against vertical forces
 Encirclement – surround more than 180 degree
 Reciprocity – equal and opposite forces by clasp arm
 Passivity - at rest when seated

Retention
 In 1916 Prothero advanced a
cone theory as basis for
clasp retention.
 He described the shape of
crowns of premolars and
molars as that of two cones
sharing a common base

 The clasp tip that ends on
cervical cone would resist
movement in occlusal
direction because to release
from the tooth it would be
forced to undergo
deformation.

 The metal used for clasp
construction is resilient and
will deform when the
stresses acting on it exceed
the proportional limit.
 It is essential to have a
definite path of insertion and
removal for a RPD

Height of contour
 The term used by Kennedy
to indicate the line at which
two converging cones meet.
Or it is a line at which
occlusally sloping surface
meet cervically sloping
surface
 It represents the greatest
bulge or diameter of crown
when viewed from specific
angle

 Devan in 1955 described the
surface of a tooth that is
occlusal to the height of
contour as suprabulge and
the surface inclining
cervically as infrabulge

Retention of the clasp assembly is determined by
 Magnitude of angle of cervical convergence below the point of
convexity
 Depth of which clasp terminal is placed in the angle
 Flexibility of clasp arm

Angle of cervical convergence
 When the surveyor blade
contacts a tooth on the cast
at its greatest convexity , a
triangle is formed .The apex
of the triangle is at the point
of contact of the surveyor
blade with the tooth and the
base is the area of the cast
representing the gingival
tissue. The apical angle is
called the angle of cervical
convergence

 According to Robert L
Schnerdor (1987) – greater
the angle of cervical
convergence the greater
potential for clasp retention
 Necessitates the placement
of clasp terminus nearer the
height of contour

Retentive undercut has three dimentions
 1. Distance between the tip of
the clasp and height of contour
 2. Mesiodistal length of the
clasp
 3. Buccolingual depth of the
clasp

 Buccolingual dimention is more
critical because when the clasp
tip enters or leave the
infrabulge area of the tooth it
has to flex an amount equql to
the depth of this undercut
 Undercut can be measured by
undercut gauge and is
expressed in thousandths of an
inch

 Clasp made up of cast
chrome metal are placed in
undercut of 0.010inch
 Cast clasp of gold- 0.015
inch
 Clasp of wrought metal-
0.020 inch
 0.030 inch undercut rarely
used in conventional partial
denture

Flexibility of the clasp arm
 Length of the clasp
 Diameter of the clasp
 Cross sectional form
 Material from which clasp is made

 Flexibility is directly proportional to the length of the clasp
 Flexibility is inversely proportional to the diameter of clasp
 A round clasp has greater flexibility than a half round clasp with
same diameter
 Chrome alloys have higher modulus of elasticity (218 Gpa) than
gold alloys (99.3Gpa) and therefore less flexible

 Wrought alloys – internal longitudinal structure – greater ability
to flex
 A recent study on comparison of titanium clasp and Co-Cr clasp
by Jay .T and Bridgeman et al (1997) revealed that titanium
and titanium alloy clasp is more useful for situations involving
deeper undercut because of higher flexibility
 Titanium and titanium alloys have long term retentive resiliency
and risk of fracture in case of titanium is comparatively less to
Co-Cr clasp

Support
 It is the property of a clasp to
resist the displacement in a
gingival direction
 Rest is the prime support unit of
the clasp

Stability
 It is the property of a clasp to resist the horizontal displacement
of prosthesis.
 All the clasp components except the retentive clasp terminal
contributes to this property
 Cast circumferential clasp has a rigid shoulder and provide
more stabilization than wrought wire clasp

Reciprocation
 Reciprocal arm provides reciprocation by resisting the horizontal
forces exerted on tooth by retentive arm
 Reciprocal arm should be at the level of retentive arm otherwise
when the denture is withdrawn the bracing arm looses contact
with tooth and retentive arm can cause displacement

Encirclement
Each clasp should be designed
to encircle more than 180 of
the abutment tooth
Encirclement may be in the
form of continuous contact
(circumferential clasp) or
broken contact (bar clasp)

Passivity
 When clasp is in place on tooth , it should be passive
 The retentive action is activated only when dislodging forces are
applied on partial denture
 Incomplete seating of the clasp can cause pain or tenderness on
the abutment tooth

Factors in clasp selection
 Tooth to be clasped- Whether molar , bicuspid , or cuspid
 Tooth surface – lingual , labial , buccal
 The area on the tooth where the most favorable retentive undercut is
to be found
 The esthetic requirement
 If two retentive clasp are to be used on the same side of arch it is
possible to have one clasp on such side engage a buccal undercut and
other clasp on such side engage a lingual undercut

 Effect of friction coefficient – According to a recent study by Yuji
Sato et al (1997) on” Effect of friction coefficient in Akers clasp
retention” suggested that retentive force increased linearly by
increased friction coefficient between abutment material and
clasp material. Therefore clasp design should be changed
depending on abutment material.

Strategic clasp positioning
 Leverage can be controlled by means of clasp if there are
sufficient abutment teeth and if they are strategically distributed
in the dental arch
 Even when number and location of potential abutment is less
than ideal, harmful effects of leverage can be reduced by
strategic placement of clasp

Quadrilateral configuration
 When four abutment teeth
are available for clasping ,
partial denture can be
confined with in these four
clasp and this quadrilateral
pattern of clasping reduces
the leverage

Tripoid configuration
 When distal abutment on
one side of the arch is
missing , the lever arm is
created by distal extension
bone . In this circumstances
leverage can be controlled to
some degree by creating
triangular pattern of clasp
placement

Bilateral configuration
 In bilateral distal extension
situations, the single retentive clasp
on each side of the arch should be
located near the center of the
dental arch or denture bearing area
 The terminal abutment tooth on
each side of the arch must be
clasped
 In bilateral configuration the clasp
exert little neutralizing effect on the
leverage induced stresses generated
by the denture base and these
stresses must be controlled by other
means

Types of direct retainer
 Circumferential clasp - Where the retentive arm approaches
the retentive undercut area from above the survey line
 Bar clasp - Where the retentive arm approaches the undercut
area from below the survey line
 Combination clasp - which is a modification of circumferential
clasp

Cast circumferential clasp (Aker’s clasp,Simple
circlet clasp)
 It is the most logical clasp
choice for tooth supported
partial denture because of its
excellent support , bracing,
and retentive qualities
 Easiest to repair
 It cause fever problems of
food retention

Disadvantages
 More tooth surface is
covered than bar clasp. So
increased chance of dental
caries
 This clasp changes the
morphology of the abutment
crown
 Normal buccolingual contour
of the tooth is altered

 This alteration may interfere
with the normal food flow
pattern. This could leads to
the damage of the gingival
tissue because of a lack of
physiologic stimulation of the
tissue

 If these clasps are
positioned high on the
tooth, they can increase the
width of the food table
which in turn causes greater
occlusal force to be exerted
on the tooth
 Can be adjusted only in one
plane , inwards and
outwards ie, perpendicular to
the tooth surface

Reverse circlet clasp
 It is used when retentive
undercut is located on the
surface of the abutment
tooth adjacent to the
edentulous space
 Usually bar clasps are used
for such type of undercut ,
but in cases of presence of
soft tissue undercut reverse
circlet clasp is the clasp of
choice

 Disadvantage
 Sufficient occlusal clearance is
needed
 Poor esthetics with excessive display
of metal
 An occlusal rest on the surface of
the tooth away from the edentulous
space does not protect the marginal
gingiva adjacent to the abutment
tooth. This marginal gingiva may be
traumatized if food packs between
the denture base and tooth. So it is
advisable to place an additional
occlusal rest next to the edentulous
space

Multiple circlet clasp
 Multiple circlet clasp is two
opposing simple circlet
clasps joined together at
terminals of reciprocal arms
 It is used to share retention
among several teeth
 This may be considered a
form of splinting weakened
teeth by a removable partial
denture

Disadvantages
 More tooth surface is
covered . So increased
chance of dental caries
 This clasp changes the
morphology of the
abutment crown
 Normal buccolingual
contour of the tooth is
altered

Embrasure clasp or Modified crib clasp
 It is two simple circlet clasps
joined at the body
 It is indicated most
frequently on the side of the
arch where there is no
edentulous space
 The greatest problem with
this clasp is providing
sufficient space for adequate
thickness of metal

Ring clasp
 Ring clasp can be used on
tipped molars
 It permits the engagement
of undercut by encircling the
tooth from its point of origin
 Because of its greater length
clasp must be designed with
additional support , in the
form of auxiliary bracing
form

Contraindication
 When there is a soft tissue
undercut on buccal side
adjacent to the mandibular
molar
 When there is close
attachment of buccinator to
crown of abutment toooth

Disadvantage
 Coverage of excessive
amount of tooth structure
 Esthetically unacceptable

Hairpin clasp ( Fish hook or c clasp or Reverse loop )
 This clasp is designed to
permit engaging the
proximal undercut from an
occlusal approach
 When a proximal undercut
must be used on posterior
abutment and when tissue
undercut or high tissue
attachment prevent the use
of bar clasp , this clasp may
be used successfully

 Properly designed reverse
action clasp should make a
hairpin to engage an
undercut below the point of
origin
 The upper arm of this clasp
is considered as a minor
connector giving rise to
tapered lower arm

Disadvantage
 This clasp covers
considerable tooth surface
and may trap the food debris
 Its occlusal origin may
increase functional load on
tooth and flexibility is limited
 Display of more metal

Onlay clasp
 Onlay clasp is an extended
occlusal rest with buccal and
lingual clasp arms
 It is indicated where occlusal
surface of one or more teeth
is below occlusal plane

Disadvantage
 Onlay clasp covers a large
amount of tooth structure
and may lead to the break
down of enamel surface
 Opposing enamel occlusal
surface may also be
subjected to rapid wear

Combination clasp
 It consists of a wrought
round wire retentive clasp
arm and a cast reciprocal
clasp arm
 It is most often indicated on
an abutment tooth adjacent
to the distal extension space
When the usable undercut is
on the mesiobuccal surface

 The greater flexibility of the
wrought wire acts as a stress
equalizer
 Because of the greater
flexibility of the combination
clasp , it is placed on deeper
undercut area.
 It can be placed in the
gingival third of the clinical
crown of the abutment tooth

 So it is esthetically
acceptable
 It can be used in caries –
prone individuals
 Round wrought wire clasp
makes only a line contact
with tooth surface

Disadvantage
 It requires extra steps in
laboratory fabrication
 More prone to breakage or
damage
 It can be easily distorted by
the careless handling of the
patient .Because of the
increased flexibility of the
retentive arm it does not
posses stabilizing qualities of
most circumferential clasp

Bar clasp or Vertical projection clasp or roach clasp
 Approaches the retentive
undercut from gingival
direction, giving a push type
retention
 Push type retention is more
effective than pull type
retention characteristic of
circumferential clasp

Advantage
 More retention
 Flexibility of the bar clasp
can be controlled by the
taper and length of the
approach arm
 Since it is gingivally
approaching , esthetics is
good

Disadvantages
 Greater tendency to collect
and hold food debris
 Increased flexibility of the
retentive arm does not
provide much stabilization
 Additional stabilizing units
should be employed in the
design of partial denture

Rules for use
 The bar retentive clasp is
used only when the retentive
undercut is adjacent to the
edentulous area from which
the approach arm originates
 Approach arm must not
impinge on soft tissue
 It is desirable to provide an
area of relief under the arm

 Minor connector that
attaches occlusal rest to the
framework should be strong
and rigid to provide some
bracing
 The approach arm must be
tapered uniformly from its
attachment at the frame
work to the clasp terminal

 The approach arm must never
be designed to bridge a soft
tissue undercut
 The approach arm should cross
the gingival margin at a 90
angle
 Retentive terminal of bar clasp
should point towards occlusal
surface
 The clasp should be placed as
low on tooth as possible

Types of bar clasp
 Depending on retentive
terminal, bar clasp may be
classified as T, modified T,
I, Y

T clasp
 It is used most frequently on
a distal extension ridge
where the usual undercut is
on the distobuccal surface of
the abutment tooth
 T clasp is used in
combination with a cast
circumferential reciprocal
arm

 The fingers of the T clasp
should point toward the
occlusal surface of the
abutment tooth
 The one finger should
engage the retentive
undercut and the other stays
on the supra bulge of the
tooth

 T clasp can never be used if
the approach arm must
bridge a soft tissue undercut
 It should not be used on a
terminal abutment adjacent
to a distal extension base if
the undercut is located on
the side of the tooth away
from the edentulous space

Modified T clasp
 It is a T clasp with non
retentive finger of the
crossbar of the T terminal
omitted
 Clasp is indicated for
premolars and canines for
esthetic reason
 Care must be taken to
ensure 180 degree
encirclement of abutment

Y clasp
 It is basically a T clasp
 It is indicated when the
height of contour on the
facial surface on the
abutment tooth is high on
the mesial and distal line
angles but low on the center
of the facial surface

I clasp
 I clasp is usually used on the
distobuccal undercut of the
abutment tooth for esthetic
reason
 Since only a 2-3mm contact
of the retentive clasp on the
abutment tooth,
encirclement and horizontal
stabilization may be a
problem with I clasp

I bar
 The I bar is a component
part of the partial denture
design philosophy referred to
as the RPI Concept
 It differs from I clasp in
position on abutment tooth
that retentive undercut is
selected
 I bar retention is normally
near center of facial surface
of tooth

The RPI clasp concept
 The modification of I bar
clasp was advocated by
Krotochvil in 1965
 Krol in 1973 introduced the
RPI clasp concept
 It consist of buccal I bar
retentive arm engaging a
0.10 inch undercut

 A proximal plate contacting a
proximal guiding plane
adjacent to edentulous area
 Mesial occlusal rest and
minor connector positioned
on the opposite side of the
tooth from the proximal
plate

Advantages
 Proximal plate and I bar
move away from the tooth
during function to reduce
torque
 Mesial minor connector and
proximal plate provide
reciprocation and eliminate
need for a lingual arm
 I bar is more esthetic

 Minimal contact alters
contour less , advantageous
on caries prone individuals
 Mesial rest eliminate class 1
lever

Contraindication
 Shallow vestibule
 Lingually tilted tooth
 Labially or buccally flared
tooth
 Soft tissue undercut
 High floor of the mouth in
which lingual plate is used

Three basic philosophies on application of RPI system
 The location of the rest , design of minor connector(proximal
plate) as it relates to guiding plane and location of the retentive
arm are factors that influence how this clasp system function
 Variation in these factors provide the basis for the difference
among philosophies

 Second philosophy suggest that guiding plane and
corresponding proximal plate minor connector extends from
marginal ridge to the junction of middle and gingival third of
proximal surface
 Both philosophies recommend that retaining clasp arm be
located in the gingival third of buccal and labial surface of
abutment
 Functional stresses in second philosophy distribute to both tooth
and edentulous ridge

 One philosophy recommends that guiding plane and
corresponding proximal plate minor connector extend the entire
length of proximal tooth surface with minimum tissue relief to
eliminate impingement of free gingival margin. In this case
teeth are loaded more with functional stress than edentulous
ridge

 3rd philosophy favours a proximal plate minor connector that
contacts approx 1mm of gingival portion of guiding plane and
retentive clasp arm located in a 0.01 inch undercut in gingival
third of tooth at greatest prominence or to mesial away from
edentulous arch
 In case of 3rd philosophy more functional force is distributed to
residual ridge than on abutment tooth

RPA clasp system (Rest, Proximal plate, Aker’s retentive
arm)
 Akers clasp arises from the proximal plate adjacent to
edentulous base area
 The shoulder of the clasp arm should be constructed so that
only its occlusal border contacts the tooth at height of contour
 The retentive component of the direct retainer engages a
retentive undercut located on the facial surface of the abutment
tooth at height of contour at junction of middle and gingival
third of tooth

 According to Kratochvil and Krol this type of clasp is best suited
for distal extension RPDs where the undercut is located away
from edentulous area

Rotational path removable partial denture design
 The main advantage of this design is minimal use of clasp . This
enhances esthetics and reduce tendency towards plaque
accumulation
 With conventional path of insertion all the rest are seated more
or less simultaneously. With rotational path of insertion one
segment of removable partial denture is seated first , then
remainder of the prosthesis is rotated in to position

 This concept uses a rigid portion of frame work as retentive
component
 Either a minor connector or proximal plate provides retention
through its intimate contact with proximal tooth surface below
ht of contour or survey line indicated at 0 degree tilt
 These rigid retentive component must gain access to infrabulge
portion of tooth by rotating on to place
 A specially designed rest in conjunction with retentive
component satisfy basic requirement of clasp design

Swing lock attachment system (Simmons 1963)
 I bars can be used with swing
lock attachment system
 It consists of labial bar which is
attached to the RPD by hinge at
one end and latch at other end
 Reciprocation is achieved
through a lingual plate
contacting all clasped teeth
 The teeth are directly retained
by I bar on labial surface

Advantages
 Abutment tooth with poor
periodontal support
 Key abutment is missing
 Tooth that requires splinting
 Tooth contours unfavourable

Contra indication
 Shallow vestibule
 Extended frenum
 High lip line
 Improper hygiene

Spring Clasp
 Proposed by D M Belles in 1997
 It is an esthetic alternative for anterior retention that maintains
excellent esthetic called as Spring clasp or Twin flex clasp
 Here a wrought wire of 19 guage is soldered in to channel in major
connector that is previously casted

Hinge clasp assembly
 This clasp assembly was first proposed by Oddo in 1996 and later
described by Campbell and Weener
 It has a rigid clasp arm that is hinged at a point of attachment of
denture base and held in place where it contact with tooth by clasp or
spring lock


Advantages
 Retention with hinge clasp is considerably better
 Can be used in severe soft tissue undercut
 Minimal display of metal
 Complete passivity during insertion and removal

VRHR Clasp concept
 This concept was developed by Dr . Grasso
 Vertical reciprocal arm contacts the lingual height of contour at
greatest mesiodistal prominence.
 Horizontal retentive arm is completely below height of contour with
only terminal third of clasp contacting abutment tooth.
 The remaining two third is positioned slightly out of contact

Intracoronal retainers
 Internal attachment or intracoronal
retainer was developed by Dr.
Herman.E.S.Chayes in 1906
 It consists of two parts, one which
is a receptacle(keyway) that is built
in to a crown or inlay constructed
on abutment tooth. And the second
part is an insert (key) that is
attached to removable partial
denture

 The insert is machined to fit
precisely in to the
receptacle.The retention does
not result from friction between
insert and receptacle but from
torsional resistance by binding
or wedging
 Eg: Ney attachment, Stern
Goldsmith,Bakers

 Some intracoronal attachments include locking mechanisms and
frictional or spring retention . Eg : Schatzmann Snap
 Advantages of Intracoronal attachments :
 Elimination of visible retentive and support component
 Better vertical support and horizontal stabilization

 Disadvantages:
 They require prepared abutment and castings
 Complicated clinical and lab procedures
 Eventual wearing away of assembly
 Difficult to repair and replace
 More expensive
 Length of clinical crown may prevent its use

Extracoronal direct retainers
 It can be classified into
1.Retentive clasp assembly
2. Attachments
 Extracoronal attachments
 Any prefabricated attachment
for support and retention of a
removable dental prosthesis.
The male and female
components are positioned
outside the normal contour of
the abutment tooth
 Eg: ASC 52, Dalbo,Ceka And Era

 Advantages
 It has an ability to provide more resilience as a stress director
 Insertion of these attachment is easier than intracoronal
attachment
 Esthetically acceptable
 They are indicated for anterior prosthesis for younger patients
who have large dental pulps.

 Disadvantages :
 It is bulky outside the tooth crown so that more space is
required with in the removable partial denture
 Many of them have springs and parts that can break or wear
and require adjustments or replacement

J P D 1983 ,49, 25
RPA clasp design for Distal extension removable partial
denture - Eliason
 Purpose : To define the features of RPA clasp design
 Discussion : The mesial rest and proximal plate are designed
identically to those of the RPI clasp. The difference is in the
retentive arm. Aker’s clasp or circumferential clasp arm is used
 If a conventional Aker’s clasp is used , with the retentive arm
coming off the proximal plate above the survey line and
crossing the survey line in the middle of the tooth to engage the
undercut,the releasing capability will be lost

 With RPA clasp system the circumferential clasp is placed so
that the rigid portion of the clasp arm will contact the tooth only
along its superior border at the level of survey line
 Conclusion
 The circumferential type retentive arm is easier to grasp for
removal of the prosthesis
 Simple in design
 Avoid problems associated with large tissue undercut , excess
tissue surrounding the abutment teeth and high frenum
attachments

RLS – Lingually retained clasp assembly for distal extention
removable partial denture Aviv et al
quint Int 1993 21, 221
 Purpose : To describe a clasp assembly for distal extension
partial denture that takes advantage of surveyed lingual
undercut
 RLS : 1. Mesio occlusal rest
 2. A distolingual L bar direct retainer , located on the
abutment tooth adjacent to the residual ridge
 3. A disto buccal stabilizer

 Summery : The tip of the direct retainer is placed distal to the
mesial occlusal rest to maintain the class 11 lever effect,
minimizing damage to the abutment tooth. A distobuccal
reciprocating stabilizer disengages from the tooth as the
denture base moves tissueward

Indirect retainer
 The component of a partial
removable denture prosthesis
that assist the direct retainer 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
tissue in pure rotation around
fulcrum line (GPT 8)

Factors that influence the effectiveness of indirect retention
 The principal occlusal rest on
the primary abutment teeth
must be reasonably held in their
seats by the retentive arms of
the direct retainer . If they are
held in their seats , rotation
about an axis will occur which
activate the indirect retainer .
If the total displacement occurs
, there would be no rotation
about the fulcrum and the
indirect retainers would not be
activated

 Distance from the fulcrum line. The following three areas must
be considered
 1. Length of the distal extension base
 2. Location of the fulcrum line
 3. How far beyond the fulcrum line the indirect retainer is
placed

 Rigidity of the connectors supporting the indirect retainer. All
connectors must be rigid if the indirect retainer is to function as
intended
 Effectiveness of the supporting tooth surface. The indirect
retainer must be placed on a definite rest seat on which
slippage or tooth movement will not occur. Tooth inclines and
weak teeth should never be used to support indirect retainer

Auxiliary functions of indirect retainer
 In addition to effectively activating the direct retainer to prevent
movement of distal extension base away from the tissue, an
indirect retainer may serve the following auxillary functions
 1. It tends to reduce the anteroposterior tilting leverages on the
principal abutments
 2. Contact of its minor connector with axial tooth surface aids in
stabilization against horizontal movement of the denture

 3. Anterior teeth supporting the indirect retainers are stabilized against
lingual movement
 4. It may act as an auxiliary rest to support a portion of the major
connector facilitating stress distribution
 5. It may provide the first visual indications for the need to reline an
extension base partial denture. Deficiencies in basal seat support are
manifested by the dislodgement of indirect retainers from their
prepared rest seats when the denture base is depressed and rotation
occurs around the fulcrum

Fulcrum lines and indirect retention
 Fulcrum line is an imaginary line connecting occlusal rest around which
a partial removable dental prosthesis tends to rotate under masticatory
forces
 Determinants for the fulcrum line are usually the cross arch occlusal
rests located adjacent to the tissue borne components

 The primary fulcrum line on distal
extension partial denture is an
imaginary line passing through the
most distal rest seat on each side of
the arch. If the denture base
extends mesially, the primary
fulcrum line passes through the
most mesial rest seat on each side
of the arch

Secondary fulcrum line
 A secondary fulcrum line is the line
established when a partial denture
includes indirect retention
 When a second fulcrum line is
produced by indirect retention , the
prosthesis rotate around the
primary fulcrum line if the denture
base is forced tissueward, and
around the secondary fulcrum line if
the denture base is lifted off the
tissue

Forms of Indirect retainers
 Auxiliary occlusal rest
 An occlusal rest can be
prepared on an occlusal surface
so that forces transmitted to it
can be directed apically through
the long axis of the tooth.
 Occlusal rest seat can be
prepared in enamel, as part of a
new cast metal restoration, on
the surface of an existing cast
metal restoration

 Rest should never be placed on
a tooth that has not been
adequately prepared
 The outline form of an occlusal
rest seat should be triangular,
with the base of the triangle
located at the marginal ridge
and the rounded apex directed
towards the center of the tooth

 The rest seat should occupy one
third to one half the mesiodistal
diameter of the tooth and
approx one half the
buccolingual width of the tooth
measured from cusp tip to cusp
tip

Canine rest
 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 may be used on the
adjacent canine tooth.
 Such a rest may be made more
effective by placing the minor
connector in the embrasure
anterior to the canine, either
curving back onto a prepared
lingual rest seat or extending to
a mesio incisal rest

Canine extension from occlusal rest
 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 molar
must serve as primary
abutment.
 The distance anterior to the
fulcrum line is only the distance
between the mesio occlusal rest
and the anterior terminal of the
finger extension

Continuous bar retainers and linguoplates
 In class1 and class11 partial
dentures , a cingulam bar or
linguoplate may extend the
effectiveness of the indirect
retainer if it is used with a
terminal rest at each end.
 In tooth supported partial
denture , a cingulam bar or
linguoplate is placed for other
reasons but always with
terminal rest

 In class1 and class11 partial dentures a continuous bar retainer or the
superior border of the linguoplate should never be placed above the
middle third of the tooth so that the orthodontic movement is
prevented during the rotation of a distal extension denture.

Modification areas
 Occasionally the occlusal rest on a
secondary abutment in a class11
partial denture may serve as an
indirect retainer . This will depend
on how far from the fulcrum line the
secondary abutment is located.
 The primary abutments in class 11
modification 1 partial denture are
the abutment adjacent to the distal
extension base and the most distal
abutment on the tooth supported
side. The fulcrum line is a diagonal
axis between the two terminal
abutments

 The anterior abutment on the tooth
supported side is a secondary
abutment serving to support and
retain one end of the tooth
supported segment as well as
adding horizontal stabilization to the
denture.
 The presence of a modification
space conveniently provides an
abutment tooth for support ,
stabilization and retention

Rugae support
 Coverage of the rugae area of the
maxillary arch can be considered as
a means of indirect retention since
the rugae area is firm and usually
well situated to provide indirect
retention for a class 1 denture

Edentulous situations
 Class 1
 Indirect retainer must always be
used and is positioned as far
anteriorly as possible

Class 11
 Its use is not as critical as in
class 1
 If no modification space exists –
an abutment tooth suitable for
clasping should be selected as
far anterior on the tooth
supported side as possible
 This rest and the clasp
assembly may serve as the
indirect retainer if it is located
far enough anterior to the
fulcrum line

 Two indirect retainers should
generally be used in a class 1
design, where as one placed on
the side opposite the distal
extension base may be
adequate in a class 11 design

 If modification space exists-
most anterior abutment on
the tooth supported side ,
with its rest and clasp
assembly, may be located far
enough anterior to the
fulcrum line to serve as the
indirect retainer

Class 111
 Auxillary rest may be needed to
provide additional vertical
support for a lingual plate major
connector , lingual bar major
connector or an extensive
palatal major connector

Class 1V
 The indirect retainer must be
located as far posterior as
possible

Rest, rest seat , direct retainer & indirect retainer

Rest, rest seat , direct retainer & indirect retainer

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