minor connectors -...

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DR. LUMA NASSRAT

ASSISSTANT LECTURER, DEPARTMENT OF PROSTHODONTICSCOLLEGE OF DENTISTRY

TIKRIT UNIVERSITY

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RPD LEC.8 | PROSTHODONTICS | 24-12-2018

Minor Connectors3RD GRADE

LEC. 8

Minor Connectors

Definition:

• Any rigid component that links between the major connector or base of RPD

and other components of the prosthesis.

• Or: The portion of a PD framework that supports the clasp and the occlusal

rest.

Rigidity is an important characteristic of all minor connectors as it aids in force

distribution. So, any bending or deformation will lead to concentration of forces.

Function:

1. Primary function is to join units of the prosthesis and denture base to the

major connector.

2. Transfer functional stresses to abutment teeth.

3. Transfer the effect of the retainers, rests & stabilizing components to the

prosthesis.

4. Distribute stresses on the edentulous ridge to the ridge & remaining teeth.

Types of minor connectors:

There are four categories of minor connectors. They may be

described as follows:

1. Minor connectors that join clasp assemblies to major Connectors.

2. Minor connectors that join indirect retainers or auxiliary rests to major

connectors.

3. Minor connectors that join denture bases to major connectors.

4. Minor connectors that serve as approach arms for vertical projection/bar-type

clasps.

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1. Minor Connector joining Clasp Assemblies to Major Connector:

They must be rigid, because they support the active components of the

removable partial denture, the retentive clasps. They also support the rests,

which prevent vertical movement of a prosthesis toward the underlying tissues.

As a result, minor connectors must have sufficient bulk to ensure rigidity, yet

they must be positioned so they do not irritate the oral tissues.

Most minor connectors that support clasp assemblies are 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.

In many instances, a clasp assembly must be positioned on a tooth that

is not adjacent to an edentulous space. When this occurs, 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. Hence, the

minor connector may be rigid yet unobtrusive.

A minor connector should never be positioned on the convex lingual

surface of a tooth where its bulk will be evident.

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2. Minor Connector joining Indirect Retainers or Auxiliary Rests to

Major Connectors:

They should form right angles with the corresponding major

connectors, but junctions should be gently curved to prevent

stress concentration. As previously noted, minor connectors

should be positioned in lingual embrasures to disguise their bulk

and promote patient comfort.

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3. Minor Connector joining Denture Base to Major Connectors:

Described as follows:

1. Open construction.

2. Mesh construction.

3. Bead, wire, or nailhead components on a metal base.

These minor connectors must be strong enough to anchor a denture base to

the removable partial denture framework. They must be rigid enough to resist

fracture and displacement. In addition, these components must provide

minimal interference with the arrangement of artificial teeth.

In the maxillary arch, a distal extension base must extend the entire length

of the ridge and should cover the tuberosity. Consequently, the minor

connector 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.

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.

1.Open Construction

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. 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 there is adequate room for the placement of teeth, the number

of cross struts is not critical. 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.

During the framework fabrication process, those areas of a master cast that are

to feature open retention must be relieved using an appropriate thickness of wax.



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.

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2.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. Relief and border extension for a mesh minor

connector should be identical to those described for open construction.

The main disadvantage 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


Screen*: الشبكة المعدنیة في الشبابیك التي تستعمل لمنع دخول الحشرات.


penetration and a weak attachment to the framework. Studies have shown that the

smaller the openings in this minor connector, the weaker the attachment.

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. As a result, the ridge lap areas of artificial teeth may

require significant reduction to facilitate proper arrangement. When restorative space

is minimal, this reduction may be significant and may result in compromised

esthetics.

Mesh construction may be used whenever multiple teeth are to be

replaced. Nevertheless, open construction is preferred.

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➢ Tissue Stoppers (Cast Stops):

When providing relief under the RPD framework, there is a difference between

tooth-supported RPD and distal extension RPD, as in the latter the minor

connector is supported from one end so it may bend under load and acrylic

packing and processing. To prevent this a small area the free end of the minor

connector should contact the master cast. This area that resembles a small

square metal projection is termed as tissue stopper or cast stops. Formed

by removing a (2×2 mm.) of relief wax.



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3.Beads and nail heads:

They 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.

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. Nailheads may be produced in a

similar manner. Projections also may be added by casting or soldering irregular wire

forms to a metal base.

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, nailhead, and wire construction should be limited to short-

span, tooth-supported applications in patients with well-healed ridges.

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Attachment of minor connectors to major connectors: 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.



Currently, acrylic resin is used to construct the overwhelming majority of

denture bases. Because acrylic resin gains its strength with increasing bulk, it should

not be finished to a thin edge. If this is attempted, the material may chip or fracture.

This can create unhygienic and potentially irritating conditions.

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. 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.

✓ Internal finishing line: Formed as a result of relief wax placed on edentulous

ridges of a master cast prior to duplication, wax will form an elevated area on

the refractory cast, the margins create internal finishing lines in the metal

frame. They should be sharp and well defined.

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external finishing line internal finishing line External finishing line



! (tissue-side of the denture metallic framework)

External finishing line:

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.

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. The external finish line

should be well defined along its entire length.

The contour of the external finish line should be consistent with the contours of

the major connector. Transition from the external finish line to a denture base should

be smooth and flowing.

When viewed from an occlusal perspective, the external finish line should follow

an arc established by the lingual surfaces of the remaining teeth. This permits the

development of contours that are not irritating to the patient.

4. Minor Connectors that Serve as approach arm for vertical projection /

bar –type clasp:

Approach arms for vertical projection/bar-type clasps are the only minor

connectors that are not required to be rigid. These components support direct

retainers (clasps) 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. 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.

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REFERENCES: Stewart's Clinical Removable Partial Prosthodontics. CH.2



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