major connector

Major Connector

Definition
The Major Connector: is the component of the partial denture that connects the parts of the prosthesis located on one side of the arch with those on the opposite side. It is that unit of the partial denture to which
all other parts are directly or indirectly attached.

The chief functions of a major connector include:

1. unification of the major parts of the prosthesis.
A major connector units all other components of a partial denture so that the partial denture acts as one unit.

2. distribution of the applied force throughout the arch to selected teeth and tissue ( stress distribution).
By unifying all elements of a partial denture the major connector can distribute functional loads to all abutment teeth, so that no one abutment is subjected to extreme loading. Unification of the direct retainers with the denture bases aids in distributing forces between both the teeth and the mucosa. This is particularly important in Class I and II partial dentures.

3. minimization of torque to the teeth ( cross-arch stability ).

A properly designed rigid major connector effectively distributes forces throughout the arch and acts to reduce the load to anyone area while
effectively controlling prosthesis movement.
A rigid major connector will limit movement possibilities by acting as a counteracting lever. This phenomenon is referred to as cross-arch
stability. Cross-arch stability becomes more important in situations associated with a high potential for greater prosthesis movement ( distal extensions).
By uniting one side of the arch to the other bracing elements on one side of the arch can aid in providing stability to the other. This can aid in dissipating twisting and torquing forces.


Location
Major connectors should be designed and located with the following
guidelines in mind:
1.Major connectors should be away from movable tissue.
2. Impingement of gingival tissue should be avoided.
3. Bony and soft tissue prominences should be avoided during placement and removal.
4. Relief should be provided beneath a major connector to prevent its settling into areas of possible interference, such as inoperable tori or elevated median palatal sutures.
5. Major connectors should be located and /or relieved to prevent impingement of tissue because the distal extension denture rotates in function.

Margins of major connectors adjacent to gingival tissue should be located

far enough from the tissue to avoid any possible impingement. The gingival tissue must have an unrestricted superficial blood supply to remain healthy .To accomplish this, it is recommended that the superior border of a lingual bar connector be located a minimum of 4 mm below the gingival margin ,In the maxillary arch it is also recommended that the borders of the palatal connector be placed a minimum of 6 mm away from the gingival margins.
Structurally the tissue covering the palate is well suited for placement of the connector because of the presence of firm submucosal connective tissue and an adequate, deep blood supply. However, when soft tissue covering the midline of the palate is less displaceable than the tissue
covering the residual ridge, varying amounts of relief under the connectors must be provided to avoid impingement of tissue.

Requirements of Major Connector

1. Rigidity Rigidity is necessary to ensure that the partial denture functions as one unit. If the denture flexes, stress distribution and cross arch stabilization can be compromised since different portions of the denture can move independent of the others.
therefore rigidity provides cross-arch stability through the principle of broad distribution of stress
A major connector can be made more rigid by:
a. using a more rigid alloy (Chrome-cobalt > gold alloys; cast > wrought metal)
b. using a 1/2 round or 1/2 pear shaped bars (more rigid than flat bars)
c. increasing the bulk as the length increases
d. corrugating linguo-plate or rugae areas.


2.Non-Interference with the Soft Tissues
Major connectors should be placed as far from the free gingival margin as possible and practical. It does not interfere with the tongue and not impinge on oral tissue when the restoration is placed, removed, or rotates in function . Of particular importance are the mandibular lingual frenum
and the maxillary movable soft palate.
In the maxillary arch, the borders of a major connector should be located at least 6 mm from the free gingival margins. In the mandibular arch,
the borders of a major connector should be positioned at least 4mm from the free gingival margins
3. Minimize Food Impaction
This can be minimized by locating the margins of the connectors at the prescribed distance from the free gingival margin and by taking care that the presence of minor connectors, clasp arms and major connectors does not create "traps" or large concavities where food can collect.
4. a major connector must promote patient comfort .
The margins of the major connector should have a smooth transition from connector to tissue so as to minimize the discomfort.
All line angles and edges should be smooth and rounded.
Borders should not be placed in locations where they might interfere with
speech.

Maxillary Major Connector

Six basic types of maxillary major connectors are considered:
1. Single palatal bar
2. Single palatal strap
3. Combination anterior and posterior palatal strap type connector
4. Palatal plate-type connector
5. U-shaped palatal connector
6. Combination Anterior-posterior palatal bar


Note: Bar: less than 8 mm in width
Strap more than 8 mm in width.

1. Single palatal bar

It is narrow half oval with its thickest point at the center, its width should be less than 8 mm.
Disadvantages of the palatal bar.
To provide the necessary rigidity, a palatal bar major connector must be
bulky. Consequently, patients find the palatal bar uncomfortable.
The palatal bar should only be used in tooth supported cases where no other connector can be used. It is usually objectionable due to its bulk. It should never be used in cases involving distal extensions or replacement of anterior teeth since it must be made too bulky for rigidity.
Indication:
Only in short span Kennedy class III
At present time the single palatal bar is used as an interim partial denture until a more definitive treatment can be done for the patient.

Contraindication:

it should not be placed anterior to the second premolar because its bulk produce noticeable discomfort and severe interference with the tongue.
it should never be used in a distal extension situation and when anterior teeth require replacement.

2.Single palatal strap

Indication:
Bilateral edentulous spaces of short span in a tooth -supported restoration.
it is preferable to the palatal bar for posterior tooth supported cases. However, other connectors should be chosen if there is a large torus or if many teeth are being replaced.


Characteristics and Location
(1) Anterior border follows the valleys between rugae as nearly as possible at right angles to median suture line.
(2) Posterior border at right angle to median suture line.
(3) Strap should be 8 mm wide or approximately as wide as the combined width of a maxillary premolar and first molar.
(4) Confined within an area bounded by the four principal rests.

Advantages :

1.because the strap is located in three planes ( vault of the palate , the lateral slopes of the palate and the anterior slope of the palate) , it offers great resistance to bending and twisting forces.
2. because the palatal strap is strong , it can be kept thin, thus increasing patient comfort.
3. retention of partial denture through the forces of adhesion and cohesion is increased by the intimate contact between the metal and soft tissue.
4. the increased tissue coverage helps distribute applied stresses over a larger area.

Disadvantages:

the patient may complain of excessive palatal coverage.
adverse soft tissue reaction in the form of papillary hyperplasia this is due to:
denture wearing 24 hours daily
poor oral hygiene
inadequate patient instructions.

3. Anterior - posterior palatal strap-type major connector

The anterior-posterior palatal strap provides maximum rigidity and minimum bulk. The strength of this connector lies in the fact that the anterior and posterior sections are joined together by longitudinal
connectors on either side. Each component braces the other against possible torque and flexure. It can be used in most maxillary partial denture designs and is especially useful in cases with a torus palatinus.


Indications for Use ( 1) Class I and II arches in which excellent abutment and residual ridge support exists, and direct retention can be made adequate without the need for indirect retention.
(2) Long edentulous spans in Class II, modification 1 arches.
(3) Class IV arches in which anterior teeth must be replaced with a removable partial denture.
(4) Inoperable palatal tori that do not extend posteriorly to the junction of the hard and soft palates.

Characteristics and location

(1) Parallelogram shaped and open in center portion .
(2) Relatively broad (8 to 10 mm) anterior and posterior palatal straps.
(3) lateral palatal straps (7 to 9 mm) narrow and parallel to curve of arch; minimum of 6 mm from gingival crevices of remaining teeth.
(4) Anterior palatal strap: anterior border not placed farther anteriorly than anterior rests and never closer than 6 mm to lingual gingival crevices; follows the valleys of the rugae at right angles to the median
palatal suture. Posterior border, if in rugae area, follows valleys of rugae at right angles to the median palatal suture.
(5) Posterior palatal connector: posterior border located at junction of hard and soft palates and at right angles to median palatal suture
and extended to hamular notch area(s) on distal extension sides.

Advantages:

1.It is rigid because the structural encirclement produced by the anterior and posterior straps contributes to the rigidity of the connector.
2.It provide good support to the partial denture.

4. COMPLETE PALATAL COVERAGE MAJOR CONNECTOR

Characteristics and Location
1) Contacts all or almost all of the teeth remaining in the arch.
2) Posterior border: terminates at the junction of the hard and soft palates; extended to hamular notch area (s) on distal extension side(s); at a right angle to median suture line.
Indications for Complete Palatal Coverage Major Connector:

(1) In most situations in which only some or all anterior teeth remain.
(2) Class II arch with a large posterior modification space and
some missing anterior teeth.
(3) Class I arch with one to four premolars and some or all anterior
teeth remaining, and abutment support is poor and cannot otherwise be enhanced; residual ridges have undergone extreme vertical resorption; direct retention is difficult to obtain.
(4) In the absence of a torus.


5. U-SHAPED PALATAL MAJOR CONNECTOR
"Horse-Shoe" Palatal Connector
This connector should be used only in those situations in which inoperable tori extend to the posterior limit of the hard palate.
The U-shaped palatal major connector is the least favorable design of all palatal major connectors ,because it lacks the rigidity of other types of connectors. From a biomechanical standpoint the palatal horseshoe is a
poor connector and should never be used unless absolutely necessary.
Where it must be used, indirect retainers must support any portion of the connector extending anteriorly from the principal occlusal rests.
Anterior border areas of this type of connector must be kept at least 6 mm away from adjacent teeth. If for any reason the anterior border must contact the remaining teeth, the connector must again be supported by rests placed in properly prepared rest seats. it should never be supported even temporarily by inclined lingual surfaces of anterior teeth.

6. Combination Anterior-posterior palatal bar

Structurally, this combination of major connector exhibits many of the same disadvantages as the single palatal bar
To be sufficiently rigid and to provide the needed support and stability, these connectors could be too bulky and could interfere with tongue function.

Beading of the Maxillary Cast

Beading is a term used to denote the scribing of a shallow groove on the maxillary master cast outlining the palatal major connector exclusive of
rugae areas .
The purposes of beading are as follows:-
1. To transfer the major connector design to the investment cast
2. To provide a visible finishing line for the casting
3. To ensure intimate tissue contact of the major connector with selected palatal tissue
Beading is readily accomplished by using an appropriate instrument, such as a cleoid carver. Care must be exercised to create a groove not in excess of 0.5 mm in width or depth.


Review of indications for maxillary major connectors
If the periodontal support of the remaining teeth is weak, a complete palatal coverage is indicated.

For long-span distal extension bases where rigidity is critical, an anteroposterior palatal strap or complete palatal coverage is indicated.

If a torus is present and is not to be removed, an anteroposterior palatal strap may be used.

4.U-shaped palatal connector the least desirable - can be used if a large inoperable palatal torus that extend posteriorly is present.



Single palatal strap major connector Combination anterior and posterior palatal strap type connector


U-SHAPED PALATAL MAJOR CONNECTOR
PALATAL PLATE MAJOR CONNECTOR


 SHAPE \* MERGEFORMAT 


major connector should be located
at least 6 mm away from gingival margins COMPLETE PALATAL COVERAGE










PAGE 

PAGE 7