INDIRECT RETAINER
It is that part of removable partial denture which assists the direct retainers in preventing displacement of distal extension denture bases by resisting lever action from the opposite side of the fulcrum line, when the denture moves away from tissue in pure rotation around the fulcrum line.

Fulcrum line
It is an imaginary axis passing through the most posterior abutments (through occlusal rests or any other rigid portion of a direct retainer assembly located occlusally or incisally to the height of contour of the primary abutments), around which the denture rotates slightly when subjected to various forces directed toward or away from residual ridge.

• In Class I arch: Fulcrum line passes through the most posterior abutments, provided some rigid component of framework is occlusal to abutment s heights of contour.

• In Class II arch: Fulcrum line is diagonal, passing through abutment on distal extension side and the most posterior abutment on opposite side.
If abutment tooth anterior to modification space lies far enough removed from fulcrum line, it may be used effectively for support of indirect retainer.

• In Class IV arch: Fulcrum line passes through two abutments adjacent to single edentulous space.

• In Class III arch with posterior tooth on right side, which has a poor prognosis and will eventually be lost, fulcrum line is considered the same as though posterior tooth were not present. Thus its future loss may not necessitate altering original design of the removable partial denture framework.

• In Class III arch with non-supporting anterior teeth, adjacent edentulous area is considered to be tissue-supported end, with diagonal fulcrum line passing through two principal abutments as in Class II arch.

FORMS OF INDIRECT RETAINERS
1- 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.
•

2- Canine Rests
They are used when:
A- The mesial marginal ridge of the first premolar is too close to the fulcrum line.
B- When the teeth are overlapped so that the fulcrum line is not accessible.
C- When only anterior teeth including canines is remain.


3- Canine Extensions From Occlusal Rests
Occasionally a finger extension from a premolar rest is placed on the prepared lingual slope of the adjacent canine tooth. Such an extension is used to effect indirect retention by increasing the distance of a resisting element from the fulcrum line.
4- Cingulum Bar and Linguoplate
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 in the form of auxiliary occlusal rests or canine rests.
In tooth-supported partial dentures, a cingulum bar or linguoplate is placed for other reasons but always with terminal rests.

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