Minor connectors & rests in removable partial denture

This presentation consists of detailed explanation about what a minor connector is ,its function and principles . Classification of minor connectors and also about rest and rest seats.

1. Done by,
M.ALAGAMMAI
POST GRADUATE 1
st
yr

MINOR CONNECTORS &
RESTS

2. CONTENTS
•
•
•
•
•
•
•
Introduction
Functions of minor connectors
Principles of design
Types of minor connectors
Rests and rest seats
References
Conclusion

3. INTRODUCTION
Definition:
The connecting link between the major connector or base of a
removable partial denture and the other units of the prosthesis,
such as the clasp assembly, indirect retainers, occlusal rests, or
cingulum rests
- GPT 9

4. FUNCTION OF MINOR CONNECTORS
1.
2.
3.
4.
5.
Joins the components of RPD to major connector

Transfers functional stresses to abutment teeth
prosthesis  abutment

Transfers the effect of retainers, rests, stabilizing components
throughout the prosthesis abutment  prosthesis .Forces
applied in one portion of the denture resisted by components
placed elsewhere in the arch
Provides unification and rigidity to the prosthesis
Maintains path of insertion through contact with guiding plane

5. 6. Rigidity is an essential characteristic of all minor
connectors.
7. The broad distribution of forces prevents any one
tooth or any one portion of an edentulous ridge from
bearing a destructive amount of stress. In contrast,
bending or deformation of a minor connector may result
in stress concentration and damage to the supporting
teeth and soft tissues.

6. PRINCIPLES OF DESIGN
1.
2.
Must have sufficient bulk to be rigid

Minor connectors placed into embrasures between
two adjacent teeth should not be located on a convex
surface

7. PRINCIPLES OF DESIGN
3. It should be thickest towards the lingual surface that tapers
to the contact area







4. Bulk of connector should be ensured in such a way that there
is least interference to placement of teeth (concentrate bulk
towards lingual aspect of tooth)

8. PRINCIPLES OF
DESIGN
5. It should conform to the interdental embrasure passing vertically from the
major connector, covering little gingival area






6.Minor connector on either side of tooth embrasures should be tapered to
the teeth, to prevent hindrance of tongue movement, eliminates spaces that
could entrap food

9. PRINCIPLES OF
DESIGN
7. Junction of minor connector and major connector
should be a butt joint .

10. 8. Junction of the major and minor connector should
be
2 mm medial to the lingual surfaces of the artificial
teeth
PRINCIPLES OF DESIGN

11. TYPES OF MINOR CONNECTORS
Joins clasp assemblies to Major connector
Joins indirect retainers(auxillary rest) to Major
connector
Joins denture bases to Major connector
Serve as approach arm for bar type clasps
1
2
3
4

12. 1 2
3 4
Proximal plate minor
connector
Embrasure minor connector
Denture base minor connector
Serves as approach arm

13. PROXIMAL PLATE MINOR CONNECTORS
1.Minor connectors joining clasp
assemblies
to major connectors

14. MINOR CONNECTORS JOINING CLASP
ASSEMBLIES
TO MAJOR CONNECTORS




Minor connectors must have sufficient bulk to ensure rigidity
Must be positioned so they do not irritate the oral tissues.
Located on proximal surfaces of teeth adjacent to edentulous
areas.
These minor connectors should be broad buccolingually, but thin
mesiodistally. The resultant shape makes it easier to place a
prosthetic tooth in a natural position.

15. •
•
•
When Clasp assembly is positioned on a
tooth that is not adjacent to an
edentulous space a minor connector
should be positioned in the associated
lingual embrasure.
This results in a sufficient bulk of metal
without encroaching on the tongue
space.
A minor connector should never be
positioned on the convex lingual surface
of a tooth where its bulk will be evident.

16. EMBRASURE MINOR
CONNECTOR
2. Joins indirect retainers(auxillary rest) to Major
connector

17. MINOR CONNECTORS JOINING INDIRECT
RETAINERS
OR AUXILIARY RESTS TO MAJOR CONNECTORS

•
•
•
Minor connectors that support indirect
retainers or auxiliary rests are often used
in removable partial denture therapy.
These minor connectors should form
right angles with the corresponding major
connectors, but junctions should be
gently curved to prevent stress
concentration.
Minor connectors should be positioned in
lingual embrasures to disguise their bulk
and promote patient comfort.

18. DENTURE BASE MINOR CONNECTOR
3. Joins denture bases to Major connector

19. MINOR CONNECTORS JOINING DENTURE BASES
TO
MAJOR CONNECTORS
•Minor connectors that join a denture base to a major connector
may be described as follows:
1. Open construction
2. Mesh construction
3. Bead, wire, or nailhead components on a metal base

20. Must be strong enough to anchor a denture base to the
removable partial denture framework.
Must be rigid enough to resist fracture and displacement.
Must provide minimal interference with the arrangement of artificial
teeth.

21. 



In the maxillary arch, a distal extension base must
extend the entire length of the ridge and should cover
the tuberosity.
Should be extended as far posteriorly as is practical.
In many instances, the minor connector may extend
beyond the most prominent portion of the tuberosity.
In other cases, the minor connector must be
terminated anterior to this area.

22. In the mandibular arch, a distal extension base must
cover the retromolar pad. Therefore, the minor
connector should extend two-thirds the length of the
edentulous ridge. This provides adequate support and
retention for the associated resin base.

23. OPEN CONSTRUCTION/OPEN
LATTICE TYPE
•
•
•
•
Open construction consists of longitudinal and transverse struts
that form a ladder-like network .
Placement of the longitudinal and transverse struts is a critical
factor in prosthetic tooth arrangement.
In the mandibular arch, one longitudinal strut should be positioned
buccal to the crest of the ridge and the other lingual to the ridge
crest. In the maxillary arch, one longitudinal strut should be
positioned buccal to the ridge crest.
The border of the major connector generally will act as the second
longitudinal strut.

24. 



Positioning of a longitudinal strut along the crest of the ridge must be
avoided. This not only interferes with the placement of artificial teeth,
but also predisposes the denture base to fracture.

Transverse struts also must be positioned to facilitate the placement
of artificial teeth.

When vertical space is minimal, improperly placed struts may create
difficulties in tooth placement.

Ideally, transverse struts should be designed to pass between the
necks of the artificial teeth. This aids in tooth arrangement and often
results in improved esthetics.

25. Relief provides space between the completed minor connector and
the tissues of the residual ridge.The space permits an acrylic resin
to encircle the longitudinal and transverse struts, thereby providing
retention for the denture base.

Open construction can be used whenever multiple teeth are to be
replaced. Studies have shown that this form of minor connector
provides the strongest attachment of acrylic resin to the removable
partial denture framework. It also facilitates relining and rebasing of
removable partial dentures.

26. MESH
CONSTRUCTION
•
•
A mesh minor connector may be compared to a rigid metallic
screen. Channels that pass through the connector are intended
to permit acrylic resin penetration.
This allows resin encirclement of the minor connector and
mechanical retention of the denture base.

27. 


Relief and border extension for a mesh minor connector should
be identical to those described for open construction.

The main drawback of a mesh minor connector is the difficulty it
presents during the packing of acrylic resin. Increased pressure is
needed to force resin through the small holes in the minor
connector.

Insufficient packing pressure may result in inadequate resin
penetration and a weak attachment to the framework. Studies
have shown that the smaller the openings in this minor connector,
the weaker the attachment.

28. 

Mesh construction also may interfere with the arrangement of
prosthetic teeth. Mesh must cover the entire ridge crest and
cannot be limited to those areas between the necks of artificial
teeth.

Mesh construction may be used whenever multiple teeth are to
be replaced. Nevertheless, open construction is preferred.

29. THE IMPORTANCE OF CAST STOPS

•
•
•
As previously noted, relief is provided beneath minor connectors
of open construction and mesh construction.
This relief provides space between the minor connector and the
underlying master cast (or residual ridge). This space permits
resin to encircle the minor connector and provides a mechanism
for attachment of the denture base to the framework.
While this method works quite well for tooth-supported
removable partial dentures, it must be modified for distal
extension applications.
THE IMPORTANCE OF CAST STOPS

30. In a distal extension prosthesis, the use of relief produces a minor
connector that is supported at only one end. As a result, the minor
connector may bend when a load is applied. Since considerable force is
applied during the packing and processing of acrylic resin, the
probability of bending is increased during these procedures.

To prevent bending, a small area at the free end of the minor connector
should contact the master cast. This portion of the minor connector is
termed a cast stop.

31. A cast stop is created by removing a small square of relief wax (2 × 2
mm) where the posterior strut of the minor connector crosses the
center of the ridge. This depression is incorporated into the refractory
cast. During the waxing process, this depression is filled with wax.

Upon casting the framework and returning it to the master cast, the
cast stop should contact the surface of the master cast . Because the
minor connector is supported at both ends, bending of the framework
can be minimized or eliminated.

32. BEAD, NAILHEAD, OR WIRE
CONSTRUCTION
•
•
Bead, nailhead, or wire components are
often used in conjunction with metal
denture bases. The metal bases are cast
to fit directly against the underlying soft
tissues.
Hence, no relief is provided beneath these
minor connectors. Resin is attached to the
free surface of such bases, and retention
is gained by encompassment of surface
projections.

33. Projections may be created by placing resin beads on the
appropriate segments of the wax pattern, investing the completed
pattern, eliminating the pattern materials via heat application, and
casting the framework.

Nail heads may be produced in a similar manner. Projections also
may be added by casting or soldering irregular wire forms to a metal
base.

34. 

The primary advantage of a metal base is related to
improved hygiene and enhanced thermal stimulation.

Disadvantages include difficulty in adjusting and relining cast
metal
bases.

Furthermore, the attachment of resin is relatively weak. Bead,
nail head, and wire construction should be limited to short-span,
tooth-supported applications in patients with well-healed ridges.

35. 



A minor connector that supports an acrylic resin denture base
must be joined to the major connector with sufficient bulk to
avoid fracture.

In addition, each acrylic resin denture base must join the major
connector in a smooth, even fashion. Any irregularity or “step”
between the two surfaces will irritate the tongue or the soft
tissues of the ridge.

Consequently, the interfacial geometry and material properties
must be considered.
Attachment of minor connectors to major
connectors

36. 


To prevent the acrylic resin from becoming too thin, the
design of the resin-metal interface must be considered.

Ideally, a butt joint should be provided so the acrylic
resin can blend evenly with the major connector.

37. 

Because acrylic resin is processed completely around open minor
connectors and mesh minor connectors, resin-metal interfaces must be
created on both the internal and external surfaces of the associated
major connectors.
For metal base minor connectors, acrylic resin is processed only on the
external surface. Therefore, resin metal joints should be created only at
the external surfaces.

These interfaces are
referred to as finish lines.
If they are located on the
outer surfaces of major
connectors, they are
called external finish
lines. If they are
positioned on the inner or
tissue surfaces, they are
termed internal finish
lines.
These interfaces are
referred to as finish lines.
If they are located on the
outer surfaces of major
connectors, they are
called external finish
lines. If they are
positioned on the inner or
tissue surfaces, they are
termed internal finish
lines.

38. Internal finish lines. Internal finish lines are
formed as a result of relief wax placed on the
edentulous ridges of a master cast prior to
duplication .
The relief wax creates an elevated area on the
resultant refractory cast. This elevation is
necessary to create space for acrylic resin
beneath open and mesh connectors.
The margins of the relief wax establish internal
finish lines in the completed metal framework.
The margins of the relief wax should be sharp
and well defined.

39. External finish lines

External finish lines 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 the major and minor
connectors should be less than 90 degrees .

40. An external finish line is formed by the placement and carving of
wax during framework fabrication. It should originate at the
lingual extent of the rest seat and continue down the lingual
aspect of the minor connector.

Transition from the external finish line to a denture base should
be smooth and flowing.

41. MINOR CONNECTORS SERVING AS APPROACH
ARMS
FOR VERTICAL PROJECTION/BAR-TYPE CLASPS
4. Serve as approach arm for bar type clasps
Approach arms for vertical projection/bar-type clasps are the only
minor connectors that are not required to be rigid. These
components support direct retainer (clasps) and therefore must
exhibit some degree of flexibility.

42. A minor connector of this type approaches the tooth
from an apical direction rather than from an occlusal direction.

The approach arm should display a smooth, even taper from its
origin to its terminus. It must not cross a soft tissue undercut,
and for this reason its use is contraindicated in some instances.

43. RESTS AND REST
SEATS
•
•
The components of a removable partial denture that transfer
forces down the long axes of the abutment teeth are called rests.
( Stewart 4
th
ed )
The prepared surfaces of the teeth into which rests fit are called
rest seats. ( Stewart 4
th
ed )

44. •
•
RESTS: A rigid extension of a removable partial denture that
contacts the occlusal, incisal, cingulum or lingual surface of tooth
or restoration, the surface of which is commonly prepared to
receive it.(GPT – 9)

REST SEAT: The prepared recess in a tooth or restoration
developed to receive the occlusal, incisal, cingulum or lingual rest.
( GPT – 9)

45. Rest seat for
Posterior
teeth
Occlusal rest
seat
Embrasure
rest seat
Rest seat for
Anterior teeth
Cingulum rest
seat
Incisal rest
seat
REST SEAT


Occlusal rest seat as a part of
new cast metal restoration
Occlusal rest seat on
amalgam restoration

46. The relationship between a rest and a rest seat must be such
that forces transmitted from the prosthesis to an abutment are
directed apically down the long axis of the tooth.

In this manner, stress can be absorbed by the fibers of the
periodontal ligament without damaging the ligament or the
supporting bone.

47. 


In the case of a tooth-supported removable partial denture, all
the stresses are transferred to the abutment teeth. In a tooth-
tissue–supported removable partial denture, only a portion of
the stresses are transferred to the teeth, while the edentulous
ridge must absorb the remainder of the load.

In addition to transferring forces, each rest should serve as a
vertical stop for the prosthesis.

Firm, positive contact between a rest and rest seat minimizes
vertical displacement of the prosthesis and prevents injury to
the soft tissues.

48. A rest also must maintain the retentive clasp in
its proper position. If the clasp is not supported, it
will lose its ability to retain the prosthesis in its
intended position.

49. A rest that is part of a retentive clasp assembly is referred to
as a primary rest.










A rest that is responsible for additional support or indirect
retention is called an auxiliary rest or secondary rest.

50. 

Primary rests prevent vertical movement of a
prosthesis toward the tissues and also help transmit
applied forces to the supporting teeth.
Rest seats should be shallow and saucer shaped and
should function as ball-and-socket joints. This
geometry permits dissipation of potentially harmful
lateral forces.

51. Auxiliary or secondary rests are used as indirect
retainers in extension base removable partial dentures
(Class I, Class II, and long-span Class IV applications).
These rests are placed anterior or posterior to the axis
of rotation to prevent the extension bases from lifting
away from the underlying ridges.

52. 1. Occlusal rests —so named because they are
seated on
the occlusal surfaces of posterior teeth

2. Lingual or cingulum rests —those seated on the
lingual surfaces of anterior teeth, usually maxillary
canines

3. Incisal rests —those seated on the incisal edges
of
anterior teeth

53. OCCLUSAL RESTS AND REST SEATS
•The outline form of an occlusal rest seat should be
roughly triangular, with the base of the triangle located
at the marginal ridge and the rounded apex directed
toward the center of the tooth.

54. 

Sharp angles, walls, and ledges must be avoided. Any portion
of the rest seat that restricts movement of the rest may
transmit undesirable horizontal forces to the tooth.

The shape of the rest seat should follow the outline of the
mesial or distal fossa for the chosen abutment. The rest seat
should occupy one-third to one-half the mesiodistal diameter
of the tooth and approximately one half the buccolingual width
of the tooth measured from cusp tip to cusp tip.

55. 

The floor of the occlusal rest seat must be inclined slightly
toward the center of the tooth.

The enclosed angle formed by a line dropped down the
proximal surface of the tooth parallel to the long axis of the
tooth and the floor of the rest seat must be less than 90
degrees so that the transmitted occlusal forces can be
directed along the vertical axis of the tooth.

56. An angle greater than 90 degrees will not yield the
desired axial loading and will produce an inclined
plane effect. This inclined plane effect can produce
slippage of the prosthesis away from the abutment
teeth. In addition, it can cause orthodontic
movement of abutment teeth, with concurrent pain
and bone loss.

57. When viewed in cross section, the deepest part of an occlusal rest
seat should be located near the center of the mesial or distal fossa.
From its depth, the floor of the rest seat should rise gently toward
the marginal ridge.







The most common mistake in occlusal rest seat preparation is
insufficient reduction of the marginal ridge. This leads to
construction of a rest that is extremely thin and subject to fracture.
An occlusal rest must be at least 0.5 mm thick at its thinnest point
and should be between 1.0 and 1.5 mm thick where it crosses the
marginal ridge.

58. OCCLUSAL RESTS ON AMALGAM
RESTORATIONS
•
•
Placing occlusal rests on large amalgam restorations is
hazardous at best. The primary reason for attempting this is
economics, since an amalgam restoration costs less than a
complete coverage restoration (ie, crown).
The unfavorable flow characteristics and poor tensile
characteristics of amalgam increase the probability of
restoration failure. In addition, replacement of a defective
restoration under an existing removable partial denture is
difficult, and the result is usually less than optimal. Retreatment
may require restoration of the abutment as well as fabrication of
a new removable partial denture. This is both costly and
inefficient and should be avoided.

59. OCCLUSAL RESTS ON CAST RESTORATIONS

•When a cast restoration is planned for an abutment tooth, the
wax pattern should display ideal contours. An appropriate rest
seat should be carved into the wax pattern. Upon completion of
the casting process, restoration contours should be refined in
preparation for delivery.

60. LINGUAL OR CINGULUM RESTS AND REST
SEATS
•
•
Lingual or cingulum rests are used primarily on
maxillary canines. The normal morphology of a
maxillary canine permits preparation of a
satisfactory rest seat with minimal tooth
reduction.
The thickness of enamel on the lingual surface of
a mandibular canine rarely allows a lingual rest to
be used. Lingual rests on incisors are also rare.
The main indication for their use is missing
canines. In this instance, multiple incisors should
receive lingual rests to distribute the stresses
over a number of teeth because a single incisor
seldom offers adequate support.

61. 


However, a lingual rest is preferred to an incisal rest. A lingual
rest is located closer to the rotational center of the supporting
tooth and does not tend to tip the tooth. The longer lever arm
associated with an incisal rest magnifies the rotational
movement of the prosthesis and may result in significant
tooth movement.
Since a lingual rest is confined to the lingual surface of an
anterior tooth, it permits improved esthetics. Because of the
configuration of the lingual rest, it is also less subject to
breakage and distortion.

62. 

The form of a lingual rest seat should be V shaped when viewed in
cross section. The preparation should display a relatively upright
lingual wall that originates at the level of the cingulum and
extends incisally.

The remaining wall should originate at the crest of the cingulum
and incline labiogingivally toward the center of the tooth. This wall
must provide a definite seat for the rest and must prevent the
migration of the abutment away from the framework.

63. 1. The cingulum is prominent enough to permit
appropriate tooth recontouring.
2. The patient practices good oral hygiene.
3. The caries index is low.
When viewed from the lingual aspect, the outline form of a lingual
rest seat should be crescent shaped. This geometry provides some
freedom of movement in a mesiodistal direction. Hence, the rest
and rest seat may function as a ball-and-socket assembly.

Sharp line angles and corners must be avoided because they
complicate the fit of the cast framework and may serve as stress
concentrators.

Placement of lingual rest seats in enamel surfaces is a sound
practice provided the following circumstances exist:

64. LINGUAL REST SEATS ON CAST
RESTORATIONS

•When a crown is to be placed on an anterior tooth and
a rest seat is required, the rest seat should be placed
in the wax pattern. The cingulum of the restoration
should be accentuated to allow development of a rest
seat that will direct occlusal forces along the long axis
of the tooth.

65. INCISAL RESTS AND REST SEATS

•
•
Incisal rests and rest seats are less desirable than lingual rests and
rest seats for anterior teeth. Nevertheless, they may be used
successfully if abutments are sound and cast restorations are not
indicated. If a cast restoration is planned for an anterior abutment,
an incisal rest is never indicated. A lingual rest should be
incorporated into the restoration instead.
Incisal rests are most frequently used on mandibular canines, but
may be used on maxillary canines.

66. Incisal rests should be positioned near
the incisal angle of abutment teeth.
An incisal rest seat should appear as a small, V-shaped notch
located approximately 1.5 to 2.0 mm from the proximal-incisal angle
of the tooth.

The deepest part of the preparation should be toward the center of
the tooth mesiodistally. The notch should be rounded and should
extend slightly onto the facial surface to provide a positive seat for
the rest.

The enamel on the lingual surface should be prepared as a shallow
depression to accommodate the minor connector and avoid
annoying the tongue.

67. CONCLUSION
•

Selection of a minor connector and its design
consideration plays an important part in the
long term success of a cast partial denture

68. REFERENCES
•
•
•
•
•
•
Stewart 4
th
ed
McCracken 12 th ed
Minor connectors: Al-Anbar University, Dental Faculty, Prosthodontics Unit Dr.
Salah Kh. Al-Rawi (BDS, MSc, PhD)

Minor connector designs for anterior acrylic resin bases: A preliminary study
James A. Dunny, D.M.D.,* and Gordon E. King, D.D.S.** Naval Dental Clinic, Pearl
Harbor, Hawaii

Host response to two different designs of minor connector
J. RUNOV, H. KROONE*, K. STOLTZE, T. MAEDAt,
E. EL GHAMRAWYJ and ^. BRILL Institute of Dental Prosthetics, Royal Dental
College Copenhagen, Denmark