Minor Connectors and Rests in Removable Partial Dentures

MINOR CONNECTORS
RESTS & REST SEATS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

MINOR CONNECTORSMINOR CONNECTORS
CONTENTS:
• Definition
• Functions of minor connectors
• Basic principles of design of a minor
connector
• Types of minor connectors
• Tissue stops and finish lines

Definition:
Minor connectors can be defined as the connecting link
between the major connector or base of a removable partial
denture to other units of a prosthesis such as clasp
assembly,indirect retainers,rests etc G.P.T-8.

FUNCTIONS OF A MINOR CONNECTOR
1.To transfer functional stress to the abutment
teeth.
Prosthesis- to- abutment function
2.To transfer the effect of retainers, rests and
stabilizing components to the rest of the
denture.
Abutment - to - prosthesis function

Basic principles of design of a minor connector
1. Should be rigid
2. Should have triangular cross section with
thickest portion near the lingual line angle and
the thinnest portion near the buccal line angle of
the tooth.
3. Should be broader buccolingually and thinner
mesiodistally.
4. Should form a right angle with the major
connector so that the gingival crossing is abrupt
and cover as little gingival tissue as possible.
5. Sharp angles should be avoided and spaces
should not exist for trapping of food debris.
6.Should never be placed on the convex lingual
surfaces of the tooth where its bulk will be
evident.

Types of minor connectors
1. Join clasp assembly to the major connector.
2. Join indirect retainers and auxilary rests to
major connector.
3. Join denture base to the major connector
4. Serve as an approach arm for a vertical
projection or bar type of clasp

1.Minor connectors joining clasp assembly to
major connector
- Rigid

• Minor connectors contacting the guide plane surfaces
are as broad as 2/3 the distance between the tips of
adjacent buccal and lingual cusps of the abutment
tooth.
• They should extend gingivally contacting an area of
the abutment tooth from the marginal ridge to 2/3 the
length of the enamel crown.
• If no clasp arm is formed as when a bar clasp
originates elsewhere, the connector should be tapered
to a knife edge the full length of the buccal surface.

• When an artificial tooth is to be placed the thickest
portion should be at the lingual line angle of the
abutment tooth.This way bulk is ensured with least
interference to the placement of the artificial tooth.
• If the clasp assembly is not being placed on a tooth
adjacent to the edentulous space, the minor
connector must be positioned in the embrasure
between two teeth.

2. Minor connectors that join indirect
retainers or auxiliary rests to major
connector
- Should form a right angle with the major connector
- Should lie in embrasure between teeth to disguise its
bulk as much as possible.

3.Minor connectors that join the denture base
to the major connector
• It should be rigid enough to support and resist
breakage of the denture base.
• In maxillary distal extension cases it should extend up
to the maxillary tuberosity.
• In mandibular distal extension case the minor
connector should cover 2/3 the length of edentulous
ridge.
3 types:
1. Lattice work construction
2. Mesh construction
3. Bead,wire or nail head minor connector

1.Open latticework construction
•Consists of longitudinal and transverse struts that form a
ladder like network www.indiandentalacademy.com

• In the mandibular arch, one longitudinal strut should be
positioned buccal to the crest of the ridge and one should be
positioned lingual to the crest of the ridge.
• In the maxillary arch, one longitudinal strut should be
positioned buccal to the crest of the ridge and the border of
the maxillary major connector will act as the second
longitudinal strut.
• Transverse struts should be placed such that they do not
interfere with tooth placement. relief should be given
between struts and the ridge for acrylic to flow. This is done
with the help of tissue stops.
• Relief provides space between minor connector and tissues
of the residual ridge.the space permits an acrylic resin to
encircle longitudinal and transverse struts.

Advantages
• Provides the strongest attachment of the
acrylic resin denture base to the removable
partial denture.
• Easiest to reline if necessary because of ridge
resorption.

2.Mesh construction
Rigid metal screen with channels that pass through the
connector which are intended to permit acrylic resin
penetration,which allows resin encirclement of the minor
connector and mechanical retention of denture base.www.indiandentalacademy.com

• Main drawback is that it is more difficult to
pack acrylic resin dough because more
pressure is needed against the resin to force it
through the small holes.
• It also does not provide as strong an
attachment for the acrylic denture base as
compared to the lattice framework

3.Bead ,wire or nail head retention
minor connector
- Used with a metal denture base which is cast to fit
directly against the edentulous ridge. Hence no relief
is provided beneath this minor connectors.

• Retention of the acrylic resin is obtained by
projection of metal on its surface These
projections may be in the form of beads,wires or
nail heads.
Advantages:
• Most hygienic
• Thermal stimulation

Disadvantages:
-Difficulty to adjust the metal base.
-Cannot be adequately relined in case of
ridge resorption.
-Weakest attachment.

Tissue stops
-Used on all distal extension partial dentures using
latticework or mesh retention.www.indiandentalacademy.com

FINISH LINES
• The term finish line in a partial denture denotes the junction
between the acrylic denture base and major connector or
any polished metal surface.
• To provide sufficient bulk of acrylic resin to produce a
smooth and even joint with the metal framework, provision
must be made to provide space for a butt joint so that the
acrylic resin can be finished evenly with the major
connector.
2 types
- Internal finish line
- External finish linewww.indiandentalacademy.com

• Resin-metal interfaces must be created on both internal and
external surfaces of associated major connectors.
• In case of metal base minor connectors, acrylic resin is
processed only on the external surface. Therefore resin-
metal interfaces should be created only on external surfaces.
• These resin-metal interfaces are referred to as finish lines
and if they are located on the outer surface of the major
connector, they are called external finish lines and if they
are positioned on the inner or tissue surfaces they are
termed as internal finish lines

• Internal finish line
• External finish line

Internal finish lines :
• They are formed as a result of relief wax placed on the
edentulous ridge prior to duplication. The relief wax creates
an elevated area on the resultant refractory cast. The
margins of the relief wax establish internal finish lines in
the completed metal frame work. Margins should be sharp
and well defined.
External finish lines:
• This also must be sharp and should be slightly
undercut to help lock the acrylic resin to the major
connector.the internal angle formed at the junction of major
and minor connector should be less than 90 degrees.
• An external finish line is formed by the placement and
carving of the wax during framework fabrication.the
contours of external finish line should be consistent with the
contours of major connector.www.indiandentalacademy.com

4. Minor connectors that serve as an
approach arm for vertical projection or bar
type of clasp
The only minor connectors that are not required to be
rigid.these components supports direct retainers and therefore
must exhibit some degree of flexibility.a minor connector of
this type approaches the tooth from an apical direction rather
than from an occlusal direction

RESTS AND REST SEATSRESTS AND REST SEATS

RESTS & REST SEATS
CONTENTS :
• INTRODUCTION
• HISTORICAL REVIEW
• TYPES / CLASSIFICATION
• FUNCTIONS
• REQUIREMENTS
• BASIC CONSIDERATIONS
• OCCLUSAL RESTS AND REST SEATS
– INTERNAL OCCLUSAL RESTS
– LONG/CONTINUOUS RESTS
– INTERPROXIMAL OCCLUSAL RESTS
– EXTENDED OCCLUSAL RESTS
• LINGUAL REST AND REST SEATS
• INCISAL REST AND REST SEATS
• SUMMARY AND CONCLUSION
• REFERENCES

The forces acting on the occlusal surface of a partial denture must
ultimately be absorbed by the alveolar bone, through underlying soft
tissues and teeth supporting the partial denture.
controlling factor in the triad of prosthesis-tooth- periodontium.
Since Bonwill (1899) first introduced and recommended the use of
rests in RPD, the use of rests have been inviolate and has gone
unchallenged.
INTRODUCTION

DEFINITION
According to glossary of Prosthodontic terms:
1. Rest - is a projection or attachment, usually on the
side of an object .
2. Rest seat - is the prepared recess in a tooth or
restoration created to receive the occlusal, incisal,
cingulum or lingual rest.

According to Ernest L. Miller:
• Rest - is a projection of the clasp which lies in a
prepared recess of the abutment tooth and acts
to support and stabilize the removable partial
denture.
• Rest seat - The prepared recess in a tooth
created to receive the occlusal, incisal or lingual
rest.

According to McCracken’s -
• Rest - Any unit of a partial denture that rests on
a tooth surface to provide vertical support.
• Rest seat - The prepared surface of an abutment
to receive the rest

HISTORICAL REVIEW
• Russell states that rest is a rigid extension of a
partial denture that contacts the remaining tooth
structure to dissipate functional forces.
• According to Grant A.A. and Johnson W. a rest
is an extension from partial denture which is
positioned on the surface of a standing tooth
capable of providing resistance to displacement of
the denture in tissueward direction.

• Kratochvil stated that rest must be positive and
should not allow the prosthesis to slide off the
tooth. They must provide a positive connection
between prosthesis and tooth.
• McGregor and Stewart et al stated that rests
maintain clasps in their correct position, prevent
food impaction and prevent the denture from
sinking into or causing overdisplacement of the
soft tissues.

CLASSIFICATION/TYPES
• According to McCracken, on the basis of tooth
surface prepared to receive them:
• Occlusal
• Incisal
• Lingual/cingulum

According to Stewart,on the basis of function they
serve :
• Primary rests
• Secondary or auxiliary rests
According to Kratochvil, on the basis of their location
in the arch, rests can be :
• Anterior rests
• Posterior rests

FUNCTIONS OF THE RESTS
• The primary purpose of the rest is to provide
vertical support for the partial denture and thus
resist the movement in a cervical direction .
-maintains components in
their planned positions
- Provide reciprocation
and stabilization.

• It transmits vertical load as well as the horizontal
forces to the tooth.

Directs and distributes occlusal loads to the abutment
teeth and directs forces in the long axis of the teeth

• Provide rigid prosthetic support.
• Maintains established occlusal relationships by
preventing settling of the denture.
• Prevent supra eruption.
• Restore occlusion.

• Deflection of food by bridging the gap between
two teeth

• Prevents impingement of soft tissues.
• Protects the denture/abutment tooth junction.

• Restore anterior guidance- anterior rests.
• Restores anterior anatomy as required.
• Provides positive seat by extending over the
incisal edge.

• Splints mobile
teeth.

BASIC CONSIDERATIONS FOR RESTS
AND REST SEATS
• Rests should be placed in
properly engineered recesses,
in the surfaces of the teeth.
• The recess should be
prepared within the confines
of the greatest tooth mass-
more PDL fibers.
• Vertical stress will be resisted
by all of the fibers.

• Floor of rest seat
1. Floor of the recess should be
less than 90° to the long axis
of the tooth- to direct stresses
axially.
2. Apical to the marginal ridge.

• Rest should not be
placed on inclined
tooth surfaces-

• Anterior rests should
be as close to the
center of the tooth as
possible.
• Positioned in line
with the residual
ridge.

Rounded in all aspects (no
sharp line angles).
Minimal preparation in
dentin.

• Center should be
deeper than the
surrounding rest
surface.

Anterior positioning of the
rest and the rotation axis to
favor biomechanics:
1. Forward and downward
movement,
disengagement of Direct
retainer.
2. More vertical direction of
forces.
3. More advantageous
vertical support from
denture base area.

• Placed as close to the
gingiva and bone as
possible to reduce
leverage.

Placement of rest on tooth
surface away from
edentulous area-
• Tipping force in opposite
direction
• Maintain contact with
adjacent teeth results
• Multiple tooth support
• Favorable direction of
force

Basic requirements of rests and rest seats
• Provides rigid support.
• Extends to center of the tooth in tooth supported
situations.
• Rounded, with no sharp angles (for ease of cleaning,
making impressions, prevent tooth fracture).

• No undercuts in the path of insertion.
• Minimum of 1 mm thick.
• Restores the occlusal plane.
• Provides reciprocation.
• Contoured so that when increased force is applied
to the prosthesis the rest will engage more securely
to prevent separation.

OCCLUSAL REST AND REST SEAT
Outline form
• Rounded triangle with the base resting on the
marginal ridge and apex toward the center of the
occlusal surface.
• Should follow outline of mesial or distal fossa.
• Dimensions- ½ the buccolingual width from
cusp tip to cusp tip and 1/3 to ½ the mesiodistal
width. Is as long as it is wide, should be at least
2.5 mm for both molars and premolars.www.indiandentalacademy.com

Reduction of the marginal ridge of
approximately 1.5 mm is usually
necessary.
Junction of occlusal rest to the abutment
should be shallow ball and socket joint
in distal extension cases.
The floor of the occlusal rest seat should
be apical to the marginal ridge and the
occlusal surface.
- Can be concave, or spoon shaped- for
distal extension.
- Can be box shaped- for tooth
supported. www.indiandentalacademy.com

• Rest seats not prepared opposing functional cusps.
• In tooth borne cases rest must be extended to the center
of the tooth.
• Minimum metal thickness is 0.5mm at thinnest point
and 1-1.5mm at marginal ridge.
• proximo-occlusal line angle of the preparation should
not be sharp.

Preparation of occlusal rest.
Armamentarium
for rest
preparation:
Preparation in
enamel:

Method of obtaining positive support
Rest seat preparations in sound enamel.
• Preparation of occlusal rest seats always must follow
proximal preparation, never precede it.
• Occlusal rest seats in sound enamel may be prepared with
diamond points of approximately the size of nos. 6 and 8
round burs or with carbide burs.
Occlusal rest seat prep. in existing restoration.
• It is same as in enamel. Proximal preparation first and then
rest seat should be placed.
• Rest seat preparation in amalgam should be avoided
because of creep.
• Though some compromise is permissible, the basic
principles of rest seat preparation should not be violated.
When perforation occurs it may be filled with gold foil.

Occlusal rest seats in new restoration.
• - They should be placed in the wax pattern.
• - The location of the occlusal rest should be shown when the
tooth is prepared for a crown or an inlay so that sufficient
clearance may be provided in the preparation for the rest.
•
Occlusal rest seats in crown/inlays/onlays.
• - Most ideal way of getting positive support.
• - Indicated in - rotated/inclined tooth.
• - mandibular bicuspid with rudimentary cusp.
• - abraded tooth.
• - These are generally made larger and deeper than the enamel.
• - Those made in abutment crowns supporting tooth borne
dentures maybe slightly deeper than those in abutments
supporting a distal extension base.

Types of occlusal rests.
Internal Occlusal rests
• A totally tooth supported partial denture
may use internal occlusal rests for tooth
occlusal support and horizontal
stabilization.
• An internal occlusal rest is not an internal
attachment .
• Occlusal support is derived from the floor
of the rest seat and from an additional
occlusal bevel if provided.

• Horizontal stabilization is from the near-vertical walls
of this type of rest seat.
• Should be parallel to the path of placement slightly
tapered occlusally and dovetailed to prevent
dislodgement proximally.
AdvantageAdvantage:
• Facilitates the elimination of visible clasp arm
buccally
• Permits the location of the rest seat in a more
favorable position in relation to the “tipping” axis of
the abutment. Retention provided by lingual clasp
arm lying in a natural or prepared infrabulge area on
the abutment tooth.

Long Or Continuous Rests
Splinting periodontally weakened
teeth
• The long or continuous rest can serve as an
effective stabilizing or unifying device. The rest
can be designed to extend entirely across the
occlusal surface of two or more teeth and, in
some instances, across the entire arch.
• When occlusal force is delivered in one area, all
the remaining teeth act in unison to provide
support. With planning, this type of rest can
restore the occlusal plane, provide support, and
splint the arch.

Control position of unopposed teeth
Many times a situation exists in which a
tooth has lost its antagonist in the
opposing arch but does not need a
replacement for masticating functions.
Extending the rest in the partial denture
planning and design not only gains
support from that tooth but also holds it
in position, preventing elongation and
eliminating the necessity of a second
prosthesis in the opposing arch.www.indiandentalacademy.com

Inter Proximal Occlusal Rests ( embrasure rest)
The design of a direct retainer assembly
may require that interproximal occlusal
rests be used.
Interproximal occlusal rest seats are
prepared as individual adjoining occlusal
rest seats.
Preparations must be extended farther
lingually.
The lingual interproximal area requires
only minor preparation.www.indiandentalacademy.com

Adjacent rests rather than a single rest
are used to
- Avoid inter proximal wedging by
the framework.
- Also to shunt the food away from
contact points.
Care must be exercised to avoid
eliminating contact point of abutment
teeth.
Sufficient tooth structure must be
removed to allow for adequate bulk of
the component to be so shaped thatwww.indiandentalacademy.com

EXTENDED OCCLUSAL REST
Indicated - in Kennedy class II, modification 1 and Kennedy class III
situations when the most posterior abutment is a mesially tipped molar
1. Minimize further tipping of the abutment forces are directed down the
long axis of the abutment.
2. This rest should extend more than one-half the mesiodistal width of the
tooth, be approximately one-third the buccolingual width of the tooth.
3. If abutment is severely tilted the extended occlusal rest may be in the
form of an onlay.

LINGUAL RESTS(Cingulum rests)
Anterior teeth may be used to support an
indirect retainer or auxiliary rest.
Canine is preferred over an incisor as an
indirect retainer or an auxiliary rest. Normal
morphology requires minimal tooth
preparation.
When a canine is not present, multiple rests that
are spread over several incisor teeth are
preferable to the use of a single incisor.
Lingual rest should be kept near the center of
rotation. www.indiandentalacademy.com

Preferable to an incisal rest
- It is placed nearer the horizontal axis of rotation (tipping
axis) of the abutment , less tendency to tip the tooth.
- More esthetically acceptable.
A lingual rest may sometimes be placed in an enamel seat at
the cingulum or just incisally to the cingulum.
Lingual rest seat preparations in enamel are rarely
satisfactory on mandibular anterior teeth because of a lack of
thickness of enamel in which to prepare a seat of adequate
form to be truly supportive.

Outline form
A slightly rounded V(half moon shaped) is
prepared on the lingual surface at the junction
of the gingival and the middle -one third of the
tooth. The apex of the V is directed incisally.
The floor of the rest seat should be toward the
cingulum rather than the axial wall. Care must
be taken not to create an enamel undercut,
which interferes with placement of the denture.
preparation is broadest at lingual aspect..
Dimensions – mesiodistal width = 2.5-3mm,
labiolingual width = 2mm,
incisoapical depth = 1.5mm

Preparation
Preparation may be started by using an
inverted cone-shaped diamond stone and
progressing to smaller, tapered stones with
round ends to complete the preparation.
All line angles must be eliminated, and the
rest seat must be prepared within the
enamel and must be highly polished.
A predetermined path of placement for the
denture must be kept in mind in preparing
the rest seat.

Method of obtaining support
In a cast restoration
Plan and execute a rest seat in the wax
pattern
Contour of the framework restores the
lingual form of the tooth.
Cast Co-Cr rest seats attached to lingual
surface of anterior teeth
Composite may be added to lingual surface

Inlay with pins
Crowns / onlays

INCISAL RESTS AND REST SEATS
Less desirable - more unfavorable leverage than lingual rest - orthodontic
movement of the tooth
Incisal rests are placed on prepared rest seats at the incisal angles of anterior
teeth
Used predominantly as auxiliary rests or as indirect retainers.
May be used on a canine abutment in either arch, but more commonly on the
mandibular canine.
Provides definite support , relatively little loss of tooth structure and little
display of metal.

Outline form
 Small ‘V’- shaped rounded notch is prepared at
the incisal angle of a canine or on the incisal
edge of an incisor, with the deepest portion of
the preparation apical to the incisal edge.
Dimensions - 2.5 mm wide and 1.5 mm deep.
The notch is beveled both labially and lingually,
and the lingual enamel is shaped to
accommodate the rigid minor connector
connecting the rest to the framework.
The floor of rest seat is extended slightly onto
the labial aspect of tooth.www.indiandentalacademy.com

 Incisal rest is placed either at mesioincisal or distoincisal
angle.
 It can be incorporated into a lingual plate – for additional
stabilization.
 Multiple incisal rests can be placed for additional support.

Summary and conclusion
• Rests and rest seats deserve special consideration in removable
partial denture construction. Proper understanding of the
functions, biomechanical design and placement of the rests is
necessary in partial denture treatment.
• Rests play a crucial role in maintaining health of supporting
structures.
• The topography of any rest should be such that it restores the
topography of the tooth existing before the rest seat is prepared.www.indiandentalacademy.com

References
• A.A. Grant, W. Johnson: Removable denture prosthodontics. 2nd edition.
• Albert Seidin. Occlusal rests and rest seats. J Prosthet Dent. 1958; 8:431-
440
• Bert T Cecooni. Effect of rest design on transmission of forces to abutment
teeth. J Prosthet Dent. 1974; 32:141-151
• Davenport, Basker and Heath :A color atlas of removable partial dentures,
1st
edition, 1980.
• Ernest L. Miller, Joseph E. Grasso : Removable denture prosthodontics. 2nd

Frank J. Kratochvil. Influence of occlusal rest position and clasp design on
movement of abutment teeth. J Prosthet Dent. 1961; 13:114-121
Kratochvil Partial removable prosthodontics. Ist edition, 1988, W.B.Saunders.
Mc Cracken’s Removable partial denture prosthodontics. 11th edition, 2004.
Stewart, Rudd and Kuebker: Clinical Removable denture prosthodontics. 2nd
edition, 2001.

- Clinical removable partial prosthodontics, 2nd
edition
Kenneth L Stewart
- Removable partial prosthodontics,2nd
edition ,
Ernest L Miller
- McCrackens Removable partial prosthodontics, 8th
edition
Glen p McGivney
- Colour Atlas of Removable Partial dentures,
John C Davenport

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Minor Connectors and Rests in Removable Partial Dentures

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