SIUST, College of Dentistry Removable Prosthodontics, Lec.10

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Indirect Retainers

When an individual wearing a partial denture chews a piece of sticky food,

there is a tendency for the partial denture to be displaced vertically, i.e. away

from the supporting tissue.

  If there is no sufficient retention on the abutment teeth, the denture is

dislodged.

When the partial denture has a free-end extension and the retention on the

abutment teeth is adequate, there is a tendency for a free-end extension to

rotate away from the tissue.

  Indirect retention keeps the free-end extension in place in these

situations.

The Fulcrum line is the line about which a free-end extension partial

denture tends to rotate and is determined by joining the most distal occlusal

rests in a straight line.

Mandibular distal extension

removable partial denture shows

distal extension base being lifted

from the ridge, the clasp assembly

being activated & engaged, with

the indirect retainer providing

stabilization against dislodgement.

SIUST, College of Dentistry Removable Prosthodontics, Lec.10

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The ideal location of the indirect retainer is determined by bisecting the

fulcrum line and placing the indirect retainer as far as possible from the

fulcrum line opposite the free-end extension. However, the logical location

of the indirect retainer is often a little different from the ideal location.

  E.g. the ideal position of the indirect retainer perpendicular to the

fulcrum line would be in vicinity of the central incisors, which are too

weak & 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 axis of rotation.

Indirect retainers, therefore, can be defined as that unit of the partial

denture which rests upon suitable surfaces of the teeth which are located as

far as possible from the free-end of the base, so that the movement of the

base away from the surface of the supporting tissue is resisted.

In other words, the indirect retainer is the component of a partial denture

prosthesis that assists the direct retainers in preventing displacement of the

distal extension denture base by functioning through lever action on the

opposite side of the fulcrum line when the denture base moves away from

the tissues in pure rotation around the fulcrum line.

Mandibular Class II design

shows best location for

indirect retainer on mesial-

occlusal of first premolar #28.

SIUST, College of Dentistry Removable Prosthodontics, Lec.10

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Characteristic of an Indirect Retainer:

  It should rest perpendicular to the long axis of the tooth.

  If it does not seat perpendicular to the long axis, it may tend to

displace the tooth against which it rests.

  When a lingual plate act as an indirect retainer, an occlusal rest should

be placed on the mesio-occlusal surface of first premolar.

The occlusal rest of clasp on the anterior abutment on the tooth-bound

edentulous space acts as indirect retainer.

Indirect retainer may not be necessary if a broad major connector is used on

a maxillary partial denture.

By; Noor Al-Deen M. Al-Khanati