Indirect retainers / implant dentistry course/ implant dentistry course

Indirect retainersIndirect retainers
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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CONTENTSCONTENTS
 IntroductionIntroduction
 DefinitionDefinition
 Auxiliary functions of indirect retainersAuxiliary functions of indirect retainers
 Factors determining effectiveness of indirectFactors determining effectiveness of indirect
retainersretainers
 Forms of indirect retainersForms of indirect retainers
 ConclusionConclusion
 BibliographyBibliography

IntroductionIntroduction
 A Removable partial denture that is supportedA Removable partial denture that is supported
by healthy natural teeth posses adequateby healthy natural teeth posses adequate
stability and retention to resist functionalstability and retention to resist functional
displacement, but a denture base that isdisplacement, but a denture base that is
supported at one end by a healthy naturalsupported at one end by a healthy natural
abutment and at the other by movable softabutment and at the other by movable soft
tissues will rotate toward or away from thetissues will rotate toward or away from the
residual ridge when subjected to occlusal forcesresidual ridge when subjected to occlusal forces
or the pull of sticky foods.or the pull of sticky foods.

 This rotational movement occurring within aThis rotational movement occurring within a
prosthesis supported by natural teeth and softprosthesis supported by natural teeth and soft
tissue was first described bytissue was first described by F.H.BALKWILLF.H.BALKWILL inin
1880.1880.
 In 1916,In 1916, J.H.PROTHEROJ.H.PROTHERO coined the termcoined the term
FULCRUM LINEFULCRUM LINE to identify the primary axis ofto identify the primary axis of
rotation.rotation.

 When occlusal loadWhen occlusal load
is applied to a distalis applied to a distal
extension removableextension removable
partial denture, thepartial denture, the
prosthesis rotatesprosthesis rotates
around a fulcrum linearound a fulcrum line
that passes through thethat passes through the
most posterior rests,most posterior rests,
one on each side of theone on each side of the
dental arch.dental arch.
 This displacement isThis displacement is
resisted by broad andresisted by broad and
accurate adaptation ofaccurate adaptation of
the denture base to thethe denture base to the
supporting tissues.supporting tissues.

 Forces acting to dislodge the prosthesis inForces acting to dislodge the prosthesis in
occlusal direction occurs by sticky foods whichocclusal direction occurs by sticky foods which
pull on the artificial teeth and move thepull on the artificial teeth and move the
extension base away from the underlying ridges.extension base away from the underlying ridges.
 Active tissues such as the tongue andActive tissues such as the tongue and
buccinator muscle also displace the denturebuccinator muscle also displace the denture
base during speech, mastication, or swallowing.base during speech, mastication, or swallowing.

 During these forces, theDuring these forces, the
associated fulcrum line passesassociated fulcrum line passes
through the tips of the retentivethrough the tips of the retentive
clasps and the anterior portionclasps and the anterior portion
of the prosthesis rotates in anof the prosthesis rotates in an
apical direction resulting inapical direction resulting in
unwanted prosthesisunwanted prosthesis
impingement into the softimpingement into the soft
tissues of the floor of the mouth.tissues of the floor of the mouth.
 This impingement of theThis impingement of the
prosthesis into the floor of theprosthesis into the floor of the
mouth is negated as the fulcrummouth is negated as the fulcrum
line is transferred to the anteriorline is transferred to the anterior
rest which acts as an indirectrest which acts as an indirect
retainerretainer

Indirect retainerIndirect retainer
““The component of a partial removableThe component of a partial removable
dental prosthesis that assists the direct retainersdental prosthesis that assists the direct retainers
in preventing displacement of the distalin preventing displacement of the distal
extension denture base by functioning throughextension denture base by functioning through
lever action on the opposite side of the fulcrumlever action on the opposite side of the fulcrum
line when the denture base moves away fromline when the denture base moves away from
the tissues in pure rotation around the fulcrumthe tissues in pure rotation around the fulcrum
line.line.

Indirect retentionIndirect retention
““ The effect achieved by one or moreThe effect achieved by one or more
indirect retainers of a partial removable dentalindirect retainers of a partial removable dental
prosthesis that reduces the tendency for aprosthesis that reduces the tendency for a
denture base to move in an occlusal direction ordenture base to move in an occlusal direction or
rotate about the fulcrum line”rotate about the fulcrum line”
The concept of indirect retention wasThe concept of indirect retention was
originally described byoriginally described by Dr.W.D.CUMMERDr.W.D.CUMMER

Action of indirect retainersAction of indirect retainers

 Auxiliary functions of indirect retainersAuxiliary functions of indirect retainers
 When in positive contact with rest seat, an indirectWhen in positive contact with rest seat, an indirect
retainer contributes to the overall support andretainer contributes to the overall support and
stability of the prosthesis.stability of the prosthesis.
 For long span lingual bar, it can provide additionalFor long span lingual bar, it can provide additional
support and rigidity to the major connector.support and rigidity to the major connector.
 It tends to reduce anteroposterior-tilting leveragesIt tends to reduce anteroposterior-tilting leverages
on the principal abutments, particularly whenon the principal abutments, particularly when
isolated tooth is being used as an abutment.isolated tooth is being used as an abutment.

 Contact of its minor connector with axial toothContact of its minor connector with axial tooth
surfaces aids in stabilization and also acts assurfaces aids in stabilization and also acts as
auxiliary guiding plane when the tooth surface isauxiliary guiding plane when the tooth surface is
made parallel to the path of placement.made parallel to the path of placement.
 Anterior teeth supporting indirect retainers areAnterior teeth supporting indirect retainers are
stabilized against lingual movement.stabilized against lingual movement.
 It provides the first visual indications for the need toIt provides the first visual indications for the need to
reline an extension base partial denture by thereline an extension base partial denture by the
dislodgement of indirect retainers from theirdislodgement of indirect retainers from their
prepared rest seats when the denture base isprepared rest seats when the denture base is
depressed and rotation occurs around the fulcrum.depressed and rotation occurs around the fulcrum.

 Fulcrum lines inFulcrum lines in
various types ofvarious types of
partial edentulouspartial edentulous
arches and location ofarches and location of
indirect retainers.indirect retainers.

Factors influencing effectiveness ofFactors influencing effectiveness of
the indirect retainers.the indirect retainers.
1. The principal occlusal rests on the primary1. The principal occlusal rests on the primary
abutment teeth must be reasonably held in theirabutment teeth must be reasonably held in their
seats, rotation about an axis should occur, whichseats, rotation about an axis should occur, which
activates the indirect retainers. If totalactivates the indirect retainers. If total
displacement of the rests occurs, there would bedisplacement of the rests occurs, there would be
no rotation about the fulcrum, and the indirectno rotation about the fulcrum, and the indirect
retainers would not be activated.retainers would not be activated.

2. Distance from the fulcrum line. The following2. Distance from the fulcrum line. The following
three areas must be considered:three areas must be considered:
a. length of the distal extension basea. length of the distal extension base
b. location of the fulcrum line & indirect retainer.b. location of the fulcrum line & indirect retainer.
c. how far beyond the fulcrum line the indirectc. how far beyond the fulcrum line the indirect
retainer is placed.retainer is placed.
3. All connectors supporting the indirect retainer3. All connectors supporting the indirect retainer
must be rigid .must be rigid .
4. The indirect retainer must be placed on a4. The indirect retainer must be placed on a
definite rest on which slippage or toothdefinite rest on which slippage or tooth
movement will not occur. Tooth inclines andmovement will not occur. Tooth inclines and
weak teeth should never be used.weak teeth should never be used.

 Forms of indirect retianersForms of indirect retianers
 Auxiliary occlusal rests.Auxiliary occlusal rests.
 Cingulum rests.Cingulum rests.
 Incisal rests.Incisal rests.

Occlusal restOcclusal rest
Occlusal rest isOcclusal rest is
most preferredmost preferred
because of itsbecause of its
location and verticallocation and vertical
orientation, permitsorientation, permits
forces to be directedforces to be directed
within the long axis ofwithin the long axis of
the abutment.the abutment. www.indiandentalacademy.comwww.indiandentalacademy.com

Cingulum restCingulum rest
 A cingulum rest isA cingulum rest is
commonly limited tocommonly limited to
maxillary caninesmaxillary canines
because of its normalbecause of its normal
morphology whichmorphology which
lends itself tolends itself to
appropriate rest seatappropriate rest seat
preparation withpreparation with
minimal recontouring.minimal recontouring.

Incisal restIncisal rest
 An incisal rest used as indirect retainer onlyAn incisal rest used as indirect retainer only
when all other rests are contraindicated.when all other rests are contraindicated.
 It is given in maxillary and mandibular incisorsIt is given in maxillary and mandibular incisors
and mandibular canines.and mandibular canines.
 Incisal rests are esthetically objectional andIncisal rests are esthetically objectional and
exhibit long approach arms that may transferexhibit long approach arms that may transfer
harmful tipping forces to abutmentsharmful tipping forces to abutments

 Most effective indirectMost effective indirect
retention is achievedretention is achieved
by preparing theby preparing the
incisor to receiveincisor to receive
either full coverageeither full coverage
restoration or a castrestoration or a cast
metal rest seat that ismetal rest seat that is
bonded to the lingualbonded to the lingual
surface of the tooth.surface of the tooth.

 Canine extensionsCanine extensions
from occlusal rests.from occlusal rests.
A finger like extensions from aA finger like extensions from a
premolar rest is placed on a lingualpremolar rest is placed on a lingual
slope of the adjacent canine tooth.slope of the adjacent canine tooth.
It is particularly applicable when aIt is particularly applicable when a
first premolar serves as a primaryfirst premolar serves as a primary
abutment.abutment.
No preparation is required onNo preparation is required on
cuspid. Such a design exploits thecuspid. Such a design exploits the
excellent indirect retention that theexcellent indirect retention that the
cuspid is capable of supplying andcuspid is capable of supplying and
combines it with the equallycombines it with the equally
excellent vertical support offered byexcellent vertical support offered by
the bicuspid.the bicuspid.

 Cingulum barsCingulum bars
( continuous bars )( continuous bars )
and linguoplatesand linguoplates ..
Technically these are notTechnically these are not
indirect retainers, becauseindirect retainers, because
they rest on unpreparedthey rest on unprepared
lingual inclines of anteriorlingual inclines of anterior
teeth, but proves to beteeth, but proves to be
effective if it is used with aeffective if it is used with a
terminal rest at each end.terminal rest at each end.

 Rugae supportRugae support

ConclusionConclusion
The distal extension partial denture tends to rotate aroundThe distal extension partial denture tends to rotate around
the fulcrum lines, this movement away from the tissues can bethe fulcrum lines, this movement away from the tissues can be
resisted by the activation of the direct retainer, stabilizingresisted by the activation of the direct retainer, stabilizing
components of clasp assembly. Ultimately it is a indirectcomponents of clasp assembly. Ultimately it is a indirect
retainer, a part of the rigid component of the partial dentureretainer, a part of the rigid component of the partial denture
frame work that are located on the definitive rests on theframe work that are located on the definitive rests on the
opposite side of the fulcrum line away from the distal extensionopposite side of the fulcrum line away from the distal extension
base which is responsible to resist the movements away frombase which is responsible to resist the movements away from
the tissue .the tissue .
 Hence the choice of the indirect retainer should be based onHence the choice of the indirect retainer should be based on
biologic as well as mechanical principles.biologic as well as mechanical principles.
 The dentist responsible for the treatment rendered must beThe dentist responsible for the treatment rendered must be
able to justify the indirect retention used for each abutmentable to justify the indirect retention used for each abutment
tooth in keeping with these principles.tooth in keeping with these principles.www.indiandentalacademy.comwww.indiandentalacademy.com

 BibliographyBibliography
 Mc Cracken’s –Removable partialMc Cracken’s –Removable partial
prosthodontics.prosthodontics.
 Stewart’s – Clinical Removable partialStewart’s – Clinical Removable partial
prosthodontics- third editionprosthodontics- third edition
 Ernest L. Miller – Removable partialErnest L. Miller – Removable partial
prosthodontics.prosthodontics.
 Osborne & Lammie’s – RemovableOsborne & Lammie’s – Removable
prosthodonticsprosthodontics

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