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Indirect retainers

Dr.shanai mohammed

partial denture movement can exist in three planes horizontal, frontal, and sagittal.

Tooth-supported partial dentures effectively use teeth to control movement away from the tissues.
Tooth-tissue–supported partial dentures do not have this capability because one end of the prosthesis is free to move away from the tissue. This may occur because of the effects of gravity in the maxillary arch or adhesive foods in either arch.
thus, there is an axis or line about which the denture will rotate when the bases move a way from the residual ridge and this is associated with tooth-tissue support partial dentures.
A fulcrum line is a theoretical line around which a removable dental prosthesis tends to rotate when subjected to forces



This movement away from the residual ridge around the fulcrum line can be prevented by the action of an indirect retainer
Indirect retainer is the component of removable partial denture that assists the direct retainer(s) in preventing displacement of the distal extension denture base by functioning through lever action on the opposite side of fulcrum line when the denture base moves away from the tissues in pure rotation around the fulcrum line. Therefore, the main function of indirect retainer is to prevent movement of a distal extension base away from the tissues.
An indirect retainer consists of one or more rests and the supporting minor connectors and should be placed as far from the distal extension base as possible.
The most effective location of an indirect retainer is in the area of incisor tooth, but this tooth may not be strong enough may have steep inclines that cannot support a rest thus, the nearest canine or the mesio-occlusal surface of the first premolar may be the best location for the indirect retention and on both sides of the arch closer to fulcrum line are used to compensate for the compromise in distance

The following factors influence the effectiveness of an indirect retainer:

1. The principal occlusal rests on the primary abutment teeth must be reasonably held in their seats by the retentive arms of the direct retainers.
2. Distance from the fulcrum line. The following three areas must be considered:
a. Length of the distal extension base
b. Location of the fulcrum line
c. How far beyond the fulcrum line the indirect retainer is placed
3. Rigidity of the connectors supporting the indirect retainer.
4. Effectiveness of the supporting tooth surface. Tooth inclines and weak teeth should never be used to support indirect retainers.


In addition to the main function there are auxiliary functions which the indirect retainers may serve to achieve and these are ae following
1. It tends to reduce anteroposterior tilting forces on the principal abutments
2. Contact of its minor connector with axial tooth surfaces aids in stabilization against horizontal movement of the denture
3. Anterior teeth supporting 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. For example, a lingual bar may be supported against settling into the tissues by the indirect retainer acting as an auxiliary rest.
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 dislodgment of indirect retainers from their prepared rest seats when the denture base is depressed and rotation occurs around the fulcrum.

Forms of Indirect Retainers

• Auxiliary Occlusal Rest
The most commonly used indirect retainer is an auxiliary occlusal rest located on an occlusal surface and as far away from the distal extension base as possible.
In a Class I arch, this location is usually on the mesial marginal ridge of the first premolar on each side of the arch. The ideal position for the indirect retainer perpendicular to the fulcrum line would be in the area of the central incisors, which are too weak and have lingual surfaces that are too perpendicular to support a rest. Bilateral rests on the first premolars are quite effective, even though they are located closer to the axis of rotation.

auxiliary occlusal rests on the first premolars to prevent settling of the anterior portion of the major connector and to provide stabilization against horizontal rotation.

Indirect retainers for Class II partial dentures are usually placed on the marginal ridge of the first premolar tooth on the opposite side of the arch from the distal extension base
Mandibular Class II design showing a favorable
location for the indirect retainer on the mesio-occlusal of the first premolar . This location is at 90 degrees to the fulcrum line

2. Canine Rests

a rest, lingual or incisal, on the adjacent canine tooth may be used when the mesial marginal ridge of first premolar is too close to the fulcrum line or when the teeth are overlapped
3. Canine extensions from occlusal rests
A finger extension from a premolar rest is placed on the prepared lingual slope of the adjacent canine tooth when the first premolar must serve as primary abutment


4. Cingulum bars (continuous bars)
In Class I and Class II partial dentures, a cingulum bar or linguoplate may extend the effectiveness of the indirect retainer. Technically, cingulum bars (continuous bars) and linguoplates are not indirect retainers because they rest on unprepared lingual inclines of anterior teeth. The indirect retainers are actually the terminal rests at either end that occur in the form of auxiliary occlusal rests or canine rests.
even when there is no need for indirect retention, continuous bar (cingulum bar) or linguopalate major connector should never be used without terminal rests because of the resultant forces on inclined planes of the anterior teeth

4. modification areas

the occlusal rest on a secondary abutment in a Class II partial denture may serve as an indirect retainer. This use will depend on how far from the fulcrum line the secondary abutment is located.
A secondary abutment is an abutment adjacent to a bounded edentulous span other than the free end extension. If the modification space were not present, as in an unmodified Class II arch, auxiliary occlusal rests and stabilizing components would be essential to the design of the denture. However, the presence of a modification space conveniently provides an abutment tooth for support, stabilization, and retention.
If the occlusal rest on the secondary abutment lies far enough from the fulcrum line, it may serve adequately as an indirect retainer. Its dual function then is tooth support for one end of the modification area and support for an indirect retainer.
If the secondary occlusal rest is too close to the fulcrum line to be effective than an auxiliary rest farther from the fulcrum line should be placed, both for indirect retention and for support for an otherwise unsupported major connector.

6. Rugae support

the rugae area of the maxillary arch as a means of indirect retention because the rugae area is firm and usually well situated to provide indirect retention for a Class I removable partial denture. Although it is true, rugae coverage is undesirable and should be avoided if possible
The use of rugae support for indirect retention is usually part of a palatal horseshoe design. Because posterior retention is usually inadequate in this situation, the requirements for indirect retention are probably greater than avoiding rugae coverage.