This document discusses indirect retainers in removable partial dentures. It defines an indirect retainer as a component that assists direct retainers in preventing displacement of the distal extension denture base through lever action. When a dislodging force acts, the fulcrum line moves from the occlusal rests to the retentive tip of the direct retainer. An indirect retainer placed farther from the fulcrum line is more effective because it increases the mechanical advantage of leverage. The effectiveness of an indirect retainer depends on factors like its distance from the fulcrum line and ability of its supporting tooth to transmit forces along the tooth's long axis without movement. Common forms of indirect retainers include auxiliary occlusal rests

1. INDIRECT RETAINERS
in
RPD
Dr Meenu Merry C Paul
Professor-Prosthodontics
Malabar Dental College&Research Centre

2. Movements of tooth–borne PD
& how its prevented
Movement of base toward the edentulous
ridge….. prevented by rests on abutment teeth
& by any rigid portion of the framework
located occlusal to the height of contour
Movement of base away from ridge…. Is
prevented by direct retainer,situated at each
end of each edentulous space

3. Movements of distal extension base
Rotational movement occurs around fulcrum line,either towards/away from the
ridge.
Movement toward ridge is limited by
supporting ridge(depends on amount of bone
resorption, compressible mucosa)
An indirect retainer does not control this
movement

4. Vertical movement away from ridge….may
be due to sticky foods, tissues adjacent to
border of denture base (tongue,buccinator)
& Gravity(maxillary PD)
Indirect retainer
will counteract the
movements produced
by these forces

5. Fulcrum Line
An imaginary line,connecting occlusal rests,around which an
RPD tends to rotate under masticatory forces.
The determinants for the fulcrum line are usually the cross arch
occlusal rests located adjacent to the tissue borne components
……(GPT)

6. In bilateral distal extension PD,occlusal rests on terminal abutment teeth act as
fulcra,& an imaginary line drawn b/w the occlusal rests will be the fulcrum line

7. Indirect Retainer
The component of a partial removable dental 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
….(GPT)

8. When dislodging forces are acting,
Fulcrum line moves from posterior
occlusal rests to retentive tip of
Direct Retainer
Indirect retainer uses mechanical
advantage of leverage by moving
the fulcrum line farther away from
the force

9. When an occlusally directed displacing force act on saddle, the retentive clasp tips engage
the undercuts on abutment teeth & provide only mechanical resistance to the movement.
The saddle thus pivots about the clasp tips
PRINCIPLE OF INDIRECT RETAINER

10. If IR is placed on an anterior tooth,this rest (IR) becomes the fulcrum of movement of
the saddle in an occlusal direction causing the clasp to move up the tooth,engage the
undercut & thus resist the tendency for denture to pivot.
F = Fulcrum…IR, a component which obtains support
R = Resistance…retention generated by clasp
E = Effort....Displacing force, eg: bolus of sticky food

11. Components of indirect retainer
Proximal plates adjacent to edentulous
areas also provide indirect retention
1 / more rests
 Supporting minor connectors

12. LOCATION OF INDIRECT RETAINER
A perpendicular line projected anteriorly
from fulcrum line indicate the most
effective location of IR (incisor/ canine
rest/ mesio occlusal rest on 1st premolar)

13. FUNCTIONS OF INDIRECT RETAINER
Main Function
Assist the direct retainer to prevent movement of distal extention
base away from the tissue
Auxiliary Functions
1. Tends to reduce anteroposterior tilting leverages on the principal
abutments
2. Anterior teeth supporting IR are stabilized against lingual
movement

14. 3. Contact of its minor connector with axial tooth surfaces aids in stabilization
against horizontal movement of denture…. support&stability of denture

15. 4. It may act as an auxiliary rest to support a portion of major connector
facilitating stress distribution
5. It provides first visual indications for the need to reline distal
extention PD
6. IR also acts as 3rd point of contacting tooth structure to ensure accurate
repositioning of framework on teeth during relining/rebasing

16. Factors influencing the effectiveness of indirect retainer
1. IR must be placed in rest seats that transmit applied forces through long axis of tooth.
The principal occlusal rests on primary abutment teeth must be held in their seats by
the retentive arms
of Direct Retainer

17. 2. Distance from Fulcrum line
 Lengthof distal extention base
 Location of fulcrumline
 Distance b/w fulcrumline & indirect retainer
Greater the distance b/w fulcrum line & IR , more effective will be the indirect
retainer

18. IR should be placed as far as possible from distal extention base
Longer the line projected at right angles from fulcrum line, more effective location of IR

19. 3. Effectiveness of the supporting tooth surface
IR must be placed on a definite rest seat on which slippage/tooth movement will not occur.
Tooth inclines & weak teeth should never be used to support IR
4. IR must be rigid… If arms of IR were to flex, forces will multiply instead of
dissipating
5. Direct retainer must prevent the denture base & rests from being lifted
from tissues and abutment tooth,for IR to function. If not,the action is
displacement & not rotation…. And IR doesn’t resist displacement

20. FORMS OF INDIRECT RETAINER
Auxiliary Occlusal rest
Incisal and Cingulum rests
Canine extention from occlusal rests
Cingulum Bars(continuous bars) &Linguoplates
Modification areas
Rugae support

21. ….most often used, located on occlusal surface & far away from distal extention base….
Occlusal rest seat is prepared on occlusal surface so that forces transmitted to it are
apically directed along long axis of tooth
Auxiliary occlusal rest
(bilateral rests on mesial marginal ridge of 1st
premolar)

22. Incisal &Cingulum rests(on incisor/canine)
Lingual/cingulum rests are preferred over incisal rest,because of its mechanical
advantage
Incisal rest represents a long lever arm (a) that concentrates
stresses transmitted to PD on incisal edge of abutment teeth.
This multiplies forces than in case of lingual rest (b)

23. Incisal rests are used if there is no other source of IR(usually on mandibular canine)
Length of approach arm of incisal rest & concentration of stresses on incisal edge of
crown can produce detrimental tipping forces to the tooth….; give crown on that tooth…
make lingual rest on crown
Incisor teeth are not good
candidates for supporting IR.
Canine rests are preferred

24. Canine extentions from occlusal rests
Finger extensions from a premolar
rest prepared on lingual slope of
canine
• This is used to effect indirect retention by increasing
the distance of resisting element from fulcrum line
• Used when 1st premolar is primary abutment

25. Cingulum bars(continuous bars)& Linguoplates
 Technically not indirect retainers…..
 In Class I & II PD, these may extend the
effectiveness of IR if it is used with a
terminal rest at each end

26. References
McCracken’s Removable Partial Prosthodontics