Direct retainer/ course in dentistry/ cosmetic dentistry training

Direct Retainers
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com
www.indiandentalacademy.comwww.indiandentalacademy.com

ContentsContents
 IntroductionIntroduction
 Classification of direct retainers.Classification of direct retainers.
 Requirements of claspRequirements of clasp
 Principles of clasp designPrinciples of clasp design
 Comparison of Circumferential andComparison of Circumferential and
Bar claspsBar clasps
 Other clasp systemOther clasp system
 Recent advancesRecent advances
 ConclusionConclusion
 BibliographyBibliography

IntroductionIntroduction
 In case of removable partial denture,In case of removable partial denture,
mechanical retention is achieved bymechanical retention is achieved by
means of direct retainermeans of direct retainer by frictionalby frictional
means, by engaging a depression in themeans, by engaging a depression in the
abutment tooth or by engaging a toothabutment tooth or by engaging a tooth
undercut lying cervically to its height ofundercut lying cervically to its height of
contour.contour.

 Primary RetentionPrimary Retention: for the removable partial: for the removable partial
denture is accomplished mechanically by placingdenture is accomplished mechanically by placing
retaining elements on the abutment teeth.retaining elements on the abutment teeth.
 Secondary RetentionSecondary Retention: is provided by the intimate: is provided by the intimate
relationship of minor connector contact with therelationship of minor connector contact with the
guiding planes, denture bases, and majorguiding planes, denture bases, and major
connectors (maxillary) with underlying tissues.connectors (maxillary) with underlying tissues.

DefinitionsDefinitions
““That component of a partial removableThat component of a partial removable
dental prosthesis used to retain anddental prosthesis used to retain and
prevent dislodgment, consisting of a claspprevent dislodgment, consisting of a clasp
assembly or precision attachment”assembly or precision attachment”
-GPT.-GPT.

Classification of Direct RetainersClassification of Direct Retainers
It is broadly classified intoIt is broadly classified into
1 Intracoronal direct retainers1 Intracoronal direct retainers
a.Precision attachmentsa.Precision attachments
b.Semiprecision attachmentsb.Semiprecision attachments
2 Extracoronal direct retainers2 Extracoronal direct retainers
a.Retentive clasp assembliesa.Retentive clasp assemblies
 SuprabulgeSuprabulge
 infrabulgeinfrabulge
b.Attachmentsb.Attachments

INTRA-CORONAL RETAINERS / INTERNALINTRA-CORONAL RETAINERS / INTERNAL
ATTACHMENTS / PRECISIONATTACHMENTS / PRECISION
ATTACHMENTS:ATTACHMENTS:
- This principle was first formulated by- This principle was first formulated by
Dr.Herman E.S. ChayesDr.Herman E.S. Chayes in1906.in1906.
 It is an interlocking device, residesIt is an interlocking device, resides
within the normal contours of anwithin the normal contours of an
abutment & functions to retain &abutment & functions to retain &
stabilize a RPD.stabilize a RPD.
 2 parts- matrix and patrix.2 parts- matrix and patrix.

 Based on method of fabrication andBased on method of fabrication and
tolerance of fit between the components;tolerance of fit between the components;
1.precision attachments.1.precision attachments.
fabricated in metal using high-fabricated in metal using high-
precision manufacturing techniques.theyprecision manufacturing techniques.they
usually exhibit long, parallel walls andusually exhibit long, parallel walls and
exceptional surface adaptation.exceptional surface adaptation.

2.semi-precision attachments.2.semi-precision attachments.
this displays a less intimate fit betweenthis displays a less intimate fit between
matrix and patrix.matrix and patrix.
they are usually originate as wax orthey are usually originate as wax or
plastic patterns, which are subsequentlyplastic patterns, which are subsequently
cast in metal.cast in metal.
they often display gently taperingthey often display gently tapering
walls.walls.

AdvantagesAdvantages
1.1. Elimination of visible rest and supportElimination of visible rest and support
componentcomponent
2.2. Better vertical supportBetter vertical support
3.3. Horizontal stabilizationHorizontal stabilization

DisadvantagesDisadvantages
1.1. Require prepared abutments and castingsRequire prepared abutments and castings
2.2. They eventually wear with progressive loss ofThey eventually wear with progressive loss of
frictional resistance to denture removal.frictional resistance to denture removal.
3.3. Difficult to repair and replaceDifficult to repair and replace
4.4. Complicated clinical and laboratory proceduresComplicated clinical and laboratory procedures
5.5. Difficult to place completely within theDifficult to place completely within the
circumference of toothcircumference of tooth
6.6. ExpensiveExpensive

LimitationsLimitations
1.1. Size of the pulp depends on ageSize of the pulp depends on age
2.2. Short or abraded teethShort or abraded teeth
3.3. Not to be used in extensive tissue supportedNot to be used in extensive tissue supported
distal extension cases unless some form ofdistal extension cases unless some form of
stress breaker is used.stress breaker is used.

EXTRA-CORONAL DIRECT RETAINERS /EXTRA-CORONAL DIRECT RETAINERS /
CLASPS:CLASPS:
 It consists of components that reside entirelyIt consists of components that reside entirely
outside the normal clinical contours of theoutside the normal clinical contours of the
abutment.abutment.
 They serve to retain & stabilize RPD.They serve to retain & stabilize RPD.
 They are divided into 2 distinct categoriesThey are divided into 2 distinct categories
 Extra coronal attachmentsExtra coronal attachments
 Retentive clasp assemblyRetentive clasp assembly

EXTRA CORONAL ATTACHMENTSEXTRA CORONAL ATTACHMENTS
 It was first introduced byIt was first introduced by Henry.r.BoosHenry.r.Boos in thein the
early 1900’s, modified byearly 1900’s, modified by F. Ewing RoachF. Ewing Roach
 It derives retention from the close fittingIt derives retention from the close fitting
components such as matrices & patricescomponents such as matrices & patrices
 It permits vertical movement of the prosthesisIt permits vertical movement of the prosthesis
during occlusal loading.during occlusal loading.

RETENTIVE CLASP ASSEMBLYRETENTIVE CLASP ASSEMBLY
 It’s the most common method for Extra coronalIt’s the most common method for Extra coronal
direct retention.direct retention.
 It was first appeared in the dental literature withIt was first appeared in the dental literature with
Dr W.G.A. Bonwill’s description.Dr W.G.A. Bonwill’s description.
 It operates on the principle of resistance ofIt operates on the principle of resistance of
metal to deformation.metal to deformation.

 In 1916 – Prothero’sIn 1916 – Prothero’s ConeCone
TheoryTheory was introduced which iswas introduced which is
the basis of clasp retention. Shapethe basis of clasp retention. Shape
of the crowns of PM and molarof the crowns of PM and molar
teeth can be considered as twoteeth can be considered as two
cones sharing a common base.thecones sharing a common base.the
line formed at the junction of theseline formed at the junction of these
cones represents thecones represents the greatestgreatest
diameterdiameter of the tooth.of the tooth.

 Kennedy called it asKennedy called it as Height of contourHeight of contour
 Cummer asCummer as GuidelineGuideline
 De Van asDe Van as Supra & infra bulge regionsSupra & infra bulge regions
 Height of contour changes depending onHeight of contour changes depending on
position of teeth. Retentive undercut exists onlyposition of teeth. Retentive undercut exists only
in relation to given path of placement or removal.in relation to given path of placement or removal.

TYPES OF CLASPSTYPES OF CLASPS
1) Circumferential/ Supra bulge/ Akers clasp:1) Circumferential/ Supra bulge/ Akers clasp:
 Has two clasp arms that encircle theHas two clasp arms that encircle the
abutment tooth. Clasp approachesabutment tooth. Clasp approaches
undercut from above the height of contourundercut from above the height of contour
2) Bar Clasp/ Infra bulge clasp:2) Bar Clasp/ Infra bulge clasp:
 Has an approach arm ending up in twoHas an approach arm ending up in two
clasp arms one placed above and theclasp arms one placed above and the
other placed below the height of contour.other placed below the height of contour.
Clasp approaches undercut from belowClasp approaches undercut from below
the height of contour.the height of contour.

Component parts of a claspComponent parts of a clasp
 RestRest
 BodyBody
 ShoulderShoulder
 Retentive clasp armRetentive clasp arm
 Reciprocal armReciprocal arm
 Minor connectorMinor connector
 Approach armApproach arm

Rest:Rest:
 Part of the clasp assemblyPart of the clasp assembly
that lies on the occlusal orthat lies on the occlusal or
lingual or incisal edge orlingual or incisal edge or
surfaces of the teethsurfaces of the teeth
 Resist’s the tissue wardResist’s the tissue ward
movement of the clasp.movement of the clasp.
 Transmit functional forcesTransmit functional forces
along the long axis of thealong the long axis of the
tooth.tooth.

Body:Body:
 Part of the clasp that connectsPart of the clasp that connects
the rests and shoulders of thethe rests and shoulders of the
clasp to the minor connectors.clasp to the minor connectors.
 It is rigid and lies above theIt is rigid and lies above the
height of contourheight of contour
 It contacts the guide plane ofIt contacts the guide plane of
the abutment during thethe abutment during the
insertion and removalinsertion and removal

ShoulderShoulder
 Part of the clasp thatPart of the clasp that
connects the body to theconnects the body to the
clasp terminalclasp terminal
 Lies above the height ofLies above the height of
contourcontour
 Provides stabilizationProvides stabilization
against horizontalagainst horizontal
displacementdisplacement

Retentive ClaspRetentive Clasp
““A flexible segment of a removable partial denture thatA flexible segment of a removable partial denture that
engages an undercut on an abutment which isengages an undercut on an abutment which is
designed to retain the denture”designed to retain the denture” – GPT– GPT
 Terminal 3rd / retentive terminal/ TerminusTerminal 3rd / retentive terminal/ Terminus
 Middle 3rdMiddle 3rd
 Proximal 3rdProximal 3rd

Components of clasp armComponents of clasp arm

Terminal 3rd / retentive terminal/Terminal 3rd / retentive terminal/
TerminusTerminus
 It is flexible and should point towardsIt is flexible and should point towards
occlusal surfaceocclusal surface
 Only component to lie cervical to height ofOnly component to lie cervical to height of
contour to provide direct retention.contour to provide direct retention.

Middle 3rdMiddle 3rd
 Provides limited flexibilityProvides limited flexibility
Placed above the height of contourPlaced above the height of contour
Proximal 3rdProximal 3rd
 RigidRigid
 Placed above the height of contourPlaced above the height of contour

Reciprocal Arm:Reciprocal Arm:
 It is rigid and placed above the height of contour.It is rigid and placed above the height of contour.
 It is not tapered like retentive claspIt is not tapered like retentive clasp
 It is designed to contact the tooth before theIt is designed to contact the tooth before the
retainer clasp does and to remainretainer clasp does and to remain
in contact while the retentivein contact while the retentive
terminal passes the height ofterminal passes the height of
contour.contour.
 Reciprocal element may be cast clasp, a lingualReciprocal element may be cast clasp, a lingual
plate or a combination of mesial and distal minorplate or a combination of mesial and distal minor
connectors.connectors.

Purpose:-Purpose:-
 Resist tipping force generatedResist tipping force generated
by the retentive terminal as itby the retentive terminal as it
passes over the height ofpasses over the height of
contour when partial denture iscontour when partial denture is
inserted or removed.inserted or removed.
 Helps in stabilization andHelps in stabilization and
reciprocation against retentivereciprocation against retentive
armarm
 May act as indirect retainer ifMay act as indirect retainer if
placed on the opposite side ofplaced on the opposite side of
fulcrumfulcrum www.indiandentalacademy.comwww.indiandentalacademy.com

Minor Connector:Minor Connector:
 Part of the clasp that joins thePart of the clasp that joins the
body to the remainder of thebody to the remainder of the
frameworkframework
 it may serve as ait may serve as a
- guiding plate- guiding plate
- reciprocal element- reciprocal element
- approach arm for an- approach arm for an
infrabulge clasp.infrabulge clasp.

Requirements of the claspRequirements of the clasp
1.1. RetentionRetention
2.2. SupportSupport
3.3. StabilityStability
4.4. ReciprocationReciprocation
5.5. EncirclementEncirclement
6.6. PassivityPassivity

RetentionRetention
““It is the quality of the claspIt is the quality of the clasp
assembly that resists forcesassembly that resists forces
acting to dislodgeacting to dislodge
components away from thecomponents away from the
supporting tissues”.supporting tissues”.
 Provided by the retentiveProvided by the retentive
clasp.clasp.

Factors affecting retentionFactors affecting retention
 1.1. prosthesis factorsprosthesis factors [planned by[planned by
dentist and executed by the technician]dentist and executed by the technician]
>> clasp flexibility - clasp lengthclasp flexibility - clasp length
- clasp diameter- clasp diameter
- c/s form- c/s form
- clasp curvature- clasp curvature
- clasp material- clasp material
- longitudinal taper.- longitudinal taper.

 2.2. Tooth factorsTooth factors [planned and executed[planned and executed
by dentist]by dentist]
a. Angle of cervical convergence/deptha. Angle of cervical convergence/depth
of undercut.of undercut.
b. how far the clasp terminal is placedb. how far the clasp terminal is placed
in undercutin undercut

Flexibility dependsFlexibility depends
on:on:
>Length of clasp arm>Length of clasp arm
Flexibility of the clasp armFlexibility of the clasp arm
is directly proportional to theis directly proportional to the
cube of its length.cube of its length.
By increasing the flexibilityBy increasing the flexibility
horizontal stresses impartedhorizontal stresses imparted
to an abutment is reduced.to an abutment is reduced.

 Diameter of clasp armDiameter of clasp arm
The average diameterThe average diameter
of the clasp arm will beof the clasp arm will be
at a point midwayat a point midway
between its origin and itsbetween its origin and its
terminal end.terminal end.
Flexibility is inverselyFlexibility is inversely
proportional to the cubeproportional to the cube
of the clasp diameter.of the clasp diameter.

Cross-sectional form ofCross-sectional form of
the claspthe clasp
 Round -increasesRound -increases
flexibility and ability toflexibility and ability to
flex in all planes.flex in all planes.
 Half round - decreasesHalf round - decreases
flexibility and flexesflexibility and flexes
only in single planeonly in single plane

 Curvature of the clasp armCurvature of the clasp arm
curvature of clasp in more thancurvature of clasp in more than
one spatial plane reduces the claspone spatial plane reduces the clasp
flexibility.flexibility.
This is due to multiple bends of theThis is due to multiple bends of the
clasp produce permanent deformationclasp produce permanent deformation
of the microstructure and lead toof the microstructure and lead to
increased rigidity.increased rigidity.

MaterialMaterial
Alloys with higher elastic modulus exihibitAlloys with higher elastic modulus exihibit
greater stiffness, alloy with lower elastic modulusgreater stiffness, alloy with lower elastic modulus
exhibit greater flexibility.exhibit greater flexibility.
co-cr and Ni-cr has got increased elasticco-cr and Ni-cr has got increased elastic
modulus than gold and wrought alloy.modulus than gold and wrought alloy.
 Materials used and the undercut to beMaterials used and the undercut to be
engagedengaged
Cast chrome - 0.010”Cast chrome - 0.010”
Cast goldCast gold - 0.015”- 0.015”
Wrought alloy - 0.020”Wrought alloy - 0.020”

 Longitudinal taperLongitudinal taper
uniform tapered clasp is twice flexible than auniform tapered clasp is twice flexible than a
non-uniform clasp arm. The taper should benon-uniform clasp arm. The taper should be
consistent for width and thickness . The crossconsistent for width and thickness . The cross
sectional dimension at the shoulder of the claspsectional dimension at the shoulder of the clasp
should be twice the cross sectional dimensionsshould be twice the cross sectional dimensions
at the clasp terminus . If the taper is notat the clasp terminus . If the taper is not
uniform , point of flexure and point of weaknessuniform , point of flexure and point of weakness
exist.exist.

2, The depth of the retentive terminal2, The depth of the retentive terminal
extending into the undercut.extending into the undercut.
 Its described in 2 distinct dimensionsIts described in 2 distinct dimensions
 A medio-lateral or horizontal dimension.A medio-lateral or horizontal dimension.
 A occluso-apical or vertical dimension.A occluso-apical or vertical dimension.

The position of the terminus is
determined by the dental surveyor, by
using the undercut gauge to visualize the
amount of undercut.
Angle formed between the analyzing rod
& the tooth surface apical to the height of
contour is angle of gingival convergence
If the angle of gingival convergence is
great, either the tooth is recontoured or
specific clasp is given.

Location of Retentive Terminal:Location of Retentive Terminal:
 Usually mesial or distal line angle preferablyUsually mesial or distal line angle preferably
the facial surface.the facial surface.
 Maxillary premolar rarely shows lingualMaxillary premolar rarely shows lingual
inclination. So buccal retentive area.inclination. So buccal retentive area.
 Molar teeth exhibit undercut on either or bothMolar teeth exhibit undercut on either or both
of facial or lingual surfaces so retention mayof facial or lingual surfaces so retention may
be used on buccal or lingual.be used on buccal or lingual.

““It is the property of the clasp thatIt is the property of the clasp that
resist displacement of theresist displacement of the
prosthesis in the gingivalprosthesis in the gingival
direction”.direction”.
 It is provided by occlusal,It is provided by occlusal,
lingual and incisal restslingual and incisal rests
 It should transmit forcesIt should transmit forces
parallel to the long axis of theparallel to the long axis of the
abutment.abutment.
Support

““It is the resistance toIt is the resistance to
horizontal displacement ofhorizontal displacement of
the prosthesis”.the prosthesis”.
 It is provided by allIt is provided by all
components except retentivecomponents except retentive
terminalterminal
 Cast Circumferential claspCast Circumferential clasp
provides the greatestprovides the greatest
stability.stability.
Stability

““It is the quality of the clasp assembly thatIt is the quality of the clasp assembly that
counteracts lateral displacement of ancounteracts lateral displacement of an
abutment when the retentive claspabutment when the retentive clasp
terminal passes over the height ofterminal passes over the height of
contour”contour”
 It must be rigidIt must be rigid
 It should be placed above the height of contour.It should be placed above the height of contour.
Preferably at the junction of the middle & gingivalPreferably at the junction of the middle & gingival
33rdrd
..
 If the height of contour lies in the occlusal 3If the height of contour lies in the occlusal 3rdrd
ofof
the tooth either the tooth has to be reshaped or athe tooth either the tooth has to be reshaped or a
lingual plate is more effective.lingual plate is more effective.
Reciprocation:

Encirclement:Encirclement:
““It is the characteristic of theIt is the characteristic of the
clasp assembly that preventsclasp assembly that prevents
movement of the abutmentmovement of the abutment
away from the associatedaway from the associated
clasp assembly”.clasp assembly”.
 Clasp must encircle 180Clasp must encircle 18000
or half ofor half of
the circumference of the tooththe circumference of the tooth
 It may be continuousIt may be continuous
(circumferential) or broken (bar(circumferential) or broken (bar
clasp). If broken it must contact atclasp). If broken it must contact at
least 3 different areas of tooth.least 3 different areas of tooth.

Passivity:Passivity:
A clasp in place should be completelyA clasp in place should be completely
passive.passive.
 The retentive function is activatedThe retentive function is activated
only when dislodging force areonly when dislodging force are
applied to the partial denture.applied to the partial denture.
 A clasp must be completely seatedA clasp must be completely seated
on a tooth to be completelyon a tooth to be completely
passive.passive.

BASIC PRINCIPLES OF CLASPBASIC PRINCIPLES OF CLASP
DESIGNDESIGN
 principle of encirclementprinciple of encirclement
 The occlusal rest must be designed to preventThe occlusal rest must be designed to prevent
the movement of the clasp arms toward thethe movement of the clasp arms toward the
cervical.cervical.
 Each retentive terminal should be opposed by aEach retentive terminal should be opposed by a
reciprocal component capable of resisting anyreciprocal component capable of resisting any
transient pressures exerted by the retentive armtransient pressures exerted by the retentive arm
during placement and removal.during placement and removal.
 Clasp retainers on abutment teeth adjacent toClasp retainers on abutment teeth adjacent to
distal extension bases should be designed sodistal extension bases should be designed so
that they will avoid direct transmission of tippingthat they will avoid direct transmission of tipping
and rotational forces to the abutment.and rotational forces to the abutment.www.indiandentalacademy.comwww.indiandentalacademy.com

 Unless guiding planes will positively control theUnless guiding planes will positively control the
path of removal and stabilize abutments againstpath of removal and stabilize abutments against
rotational movements, retentive clasps shouldrotational movements, retentive clasps should
be bilaterally opposed.be bilaterally opposed.
 The path of escapement for each retentive claspThe path of escapement for each retentive clasp
terminal must be other than parallel to the pathterminal must be other than parallel to the path
of removal for the prosthesis to require claspof removal for the prosthesis to require clasp
engagement with the resistance to deformationengagement with the resistance to deformation
that is retention.that is retention.
 The amount of retention should always be theThe amount of retention should always be the
minimum necessary to resist reasonableminimum necessary to resist reasonable
dislodging forces.dislodging forces.

 Reciprocal elements of the claspReciprocal elements of the clasp
assembly should be located at the junctionassembly should be located at the junction
of the gingival and middle thirds of theof the gingival and middle thirds of the
crowns of abutment teeth. The terminalcrowns of abutment teeth. The terminal
end of the retentive arm is optimallyend of the retentive arm is optimally
placed in the gingival third of the crown.placed in the gingival third of the crown.
These locations permit better resistance toThese locations permit better resistance to
horizontal and torquing forces because ofhorizontal and torquing forces because of
a reduction in the effort arm .a reduction in the effort arm .

CIRCUMFERENTIAL CLASP/CIRCUMFERENTIAL CLASP/
SUPRABULGE CLASP/ AKERSSUPRABULGE CLASP/ AKERS
CLASPCLASP
 It was first introduced byIt was first introduced by Dr N. B. NesbittDr N. B. Nesbitt inin
1916.1916.
 DESIGN RULESDESIGN RULES

1. Clasp should originate from the portion of the frame work
that lies above the height of contour. Only the
terminus should engage the undercut.
2. Terminus should be directed occlusally .
3. It should terminate at mesial/distal line angle never at mid
facial /mid lingual.
4. Retentive arm should be as far apical on the abutment.
5. For a distal extension base, clasp shouldn’t engage
mesiofacial surface of the posterior edentulous space &
distofacial surface of the anterior edentulous space.

Advantages:-Advantages:-
 Most logical clasp of choice for toothMost logical clasp of choice for tooth
supported partial denture because of itssupported partial denture because of its
excellent support, bracing and retentiveexcellent support, bracing and retentive
qualities.qualities.
 Easy to design, construct and repairEasy to design, construct and repair
 Fewer problems of food entrapmentFewer problems of food entrapment
compared to bar claspcompared to bar clasp

Disadvantages:-Disadvantages:-
 Covers more tooth surface so decalcification /Covers more tooth surface so decalcification /
cariescaries
 Damage to gingival tissue because of lack ofDamage to gingival tissue because of lack of
physiological stimulation of the tissue.physiological stimulation of the tissue.
 Not possible to adjust with pliers because of itsNot possible to adjust with pliers because of its
half-round configuration.half-round configuration.
 Alters the normal bucco-lingual contour ofAlters the normal bucco-lingual contour of
tooth.tooth.
 Can increase the width of food table ifCan increase the width of food table if
positioned high on the tooth.positioned high on the tooth.

 It is most versatile andIt is most versatile and
widely used clasp.widely used clasp.
 Approaches undercut,Approaches undercut,
which is remote fromwhich is remote from
edentulous space.edentulous space.
 It is the clasp of choiceIt is the clasp of choice
in tooth-supportedin tooth-supported
partial denture.partial denture.
Simple Circlet Clasp:

Reverse Circlet Clasp:Reverse Circlet Clasp:
 Indicated whenIndicated when
undercut is locatedundercut is located
adjacent to edentulousadjacent to edentulous
space and bar clasp isspace and bar clasp is
contraindicated.contraindicated.
It requires sufficientIt requires sufficient
occlusal clearance,occlusal clearance,
failure to do so resultsfailure to do so results
in a thin clasp that arein a thin clasp that are
susceptible to fracture.susceptible to fracture.

 It involves 2 simple circletIt involves 2 simple circlet
clasps joined at their terminalclasps joined at their terminal
end of their reciprocalend of their reciprocal
elements.elements.
 Used for multiple clasping inUsed for multiple clasping in
instances in which the partialinstances in which the partial
denture replaces an entiredenture replaces an entire
half of dental arch.half of dental arch.
 Form of splinting forForm of splinting for
weakened abutment teeth .weakened abutment teeth .
Multiple Circlet Clasp:

 Two simple circlet claspsTwo simple circlet clasps
joined at their bodies.joined at their bodies.
 Used on the side of the archUsed on the side of the arch
where there is no edentulouswhere there is no edentulous
space, used only when spacespace, used only when space
is gained from opposingis gained from opposing
occlusion.occlusion.
Embrasure Clasp/ Modified crib clasp:

 Requires removal of increased tooth structureRequires removal of increased tooth structure
and occlusal rest preparationand occlusal rest preparation
 Breakage is more commonBreakage is more common
 Requires abutment protection in most of theRequires abutment protection in most of the
cases by using inlays or crown sincecases by using inlays or crown since
vulnerable areas of tooth are involved.vulnerable areas of tooth are involved.

 Engages the undercut afterEngages the undercut after
encircling almost the entire toothencircling almost the entire tooth
from its point of origin. Indicatedfrom its point of origin. Indicated
in cases of tipped molars, usuallyin cases of tipped molars, usually
mandibular teeth tilted mesio-mandibular teeth tilted mesio-
lingually .lingually .
 It requires additional supportIt requires additional support
with an auxiliary bracing arm andwith an auxiliary bracing arm and
distal occlusal rest.distal occlusal rest.
Ring Clasp

DisadvantageDisadvantage
 It alters the contour of tooth and interferesIt alters the contour of tooth and interferes
with the normal stimulation of surroundingwith the normal stimulation of surrounding
mucosa.mucosa.
 It is susceptible to distortion.It is susceptible to distortion.
Contraindications:-Contraindications:-
1) Limited vestibular depth.1) Limited vestibular depth.
2) When bracing arm must cross soft tissue2) When bracing arm must cross soft tissue
undercut.undercut. www.indiandentalacademy.comwww.indiandentalacademy.com

 A simple circlet clasp in whichA simple circlet clasp in which
the retentive arm loops back tothe retentive arm loops back to
engage an undercut apical to theengage an undercut apical to the
point of origin.point of origin.
 Upper part of retainer arm is rigidUpper part of retainer arm is rigid
and lower is tapered and flexible.and lower is tapered and flexible.
 Indicated when retainer claspIndicated when retainer clasp
must engage an undercutmust engage an undercut
adjacent to the occlusal rest oradjacent to the occlusal rest or
edentulous space.edentulous space.
C, Fish Hook, Hairpin, Reverse Action:

 It should have a sufficient vertical height.It should have a sufficient vertical height.
 Adequate space is required between theAdequate space is required between the
occlusal & apical aspect of the retentive armocclusal & apical aspect of the retentive arm
to provide finishing of metal & to avoidto provide finishing of metal & to avoid
entrapment of food debris.entrapment of food debris.
 Esthetically unacceptable if used on premolarEsthetically unacceptable if used on premolar
& canine.& canine.
 There should be no interference with theThere should be no interference with the
opposing arch in maximum intercuspation.opposing arch in maximum intercuspation.

 It consists of a rest that covers theIt consists of a rest that covers the
entire occlusal surface & serves asentire occlusal surface & serves as
the origin for the buccal & lingualthe origin for the buccal & lingual
arms.arms.
 It is indicated when occlusal surfaceIt is indicated when occlusal surface
of abutment tooth is below theof abutment tooth is below the
occlusal plane, as a result of tooth,occlusal plane, as a result of tooth,
rotated or tipped. Onlay is used torotated or tipped. Onlay is used to
restore normal occlusal plane.restore normal occlusal plane.
 Should be used only in cariesShould be used only in caries
resistant mouth unless tooth isresistant mouth unless tooth is
covered by acrylic or gold crown.covered by acrylic or gold crown.
Onlay Clasp:

 Consists a circumferential retentiveConsists a circumferential retentive
arm arising from one direction & aarm arising from one direction & a
reciprocal arm arising from thereciprocal arm arising from the
other.other.
 The design was originally intendedThe design was originally intended
to provide dual retention, a principleto provide dual retention, a principle
that should be applied only tothat should be applied only to
unilateral partial denture design.unilateral partial denture design.
Half and Half Clasp:

 Introduced by Dr O. C Applegate inIntroduced by Dr O. C Applegate in
1965.1965.
 Consists of an occlusal rest, a castConsists of an occlusal rest, a cast
reciprocal clasp arm, and a wroughtreciprocal clasp arm, and a wrought
wire retentive arm.wire retentive arm.
 Indicated in distal extention casesIndicated in distal extention cases
with undercut on mesio-buccalwith undercut on mesio-buccal
surface..surface..
Combination Clasp:

Advantages:-Advantages:-
 FlexibilityFlexibility
 Better esthetic because it can be placed inBetter esthetic because it can be placed in
gingival 3rdgingival 3rd
 It can be adjusted in all planesIt can be adjusted in all planes
 Because of minimum contact it can beBecause of minimum contact it can be
used in caries prone mouthsused in caries prone mouths

 Extra steps for fabricationExtra steps for fabrication
 No bracing or stabilization qualities becauseNo bracing or stabilization qualities because
of increased flexibilityof increased flexibility
 Prone to breakage or damage when theProne to breakage or damage when the
patient mishandles it.patient mishandles it.

BAR CLASP/ VERTICAL PROJECTIONBAR CLASP/ VERTICAL PROJECTION
CLASP / ROACH CLASP/ INFRABULGECLASP / ROACH CLASP/ INFRABULGE
CLASPCLASP
 Introduced in early 1900,Introduced in early 1900,
but received attention inbut received attention in
1930 by DR F. Ewing1930 by DR F. Ewing
Roach.Roach.
 It approaches the undercutIt approaches the undercut
on the tooth from gingivalon the tooth from gingival
direction resulting in Pushdirection resulting in Push
type of retention.type of retention.

Rules for use:-Rules for use:-
 The Approach arm must not impinge on the softThe Approach arm must not impinge on the soft
tissue, no relief should be given under the approachtissue, no relief should be given under the approach
arm, tissue surface of the approach arm should bearm, tissue surface of the approach arm should be
smooth & well polishedsmooth & well polished
 The Approach arm should cross perpendicular to freeThe Approach arm should cross perpendicular to free
gingival margin.gingival margin.
 The Approach arm should never be designed under theThe Approach arm should never be designed under the
soft tissue undercut.soft tissue undercut.
 The approach arm should be uniformly tapered from itsThe approach arm should be uniformly tapered from its
point of origin to the terminus.point of origin to the terminus.
 The terminus should be positioned as apical asThe terminus should be positioned as apical as
possible.possible.
 The minor connector that connects the Rest should beThe minor connector that connects the Rest should be
rigid & stabilize the prosthesis.rigid & stabilize the prosthesis.

Indications:-Indications:-
 Retentive undercut adjacent to edentulousRetentive undercut adjacent to edentulous
area.area.
 When small degree of (0.01”) undercut existsWhen small degree of (0.01”) undercut exists
in cervical 3rdin cervical 3rd
 If buccal sulcus is more than 4mm in depthIf buccal sulcus is more than 4mm in depth
 Tooth supported cases in the anterior regionTooth supported cases in the anterior region
of the mouth.of the mouth.

Contraindications:Contraindications:
 Shallow vestibuleShallow vestibule
 Severe tooth and/or tissueSevere tooth and/or tissue
undercutundercut
 Excessive buccal or lingualExcessive buccal or lingual
tilt of abutment teethtilt of abutment teeth

Advantages:Advantages:
 Better retention because increase length ofBetter retention because increase length of
retentive arm and trip action.retentive arm and trip action.
 Better esthetics because of gingivalBetter esthetics because of gingival
approachapproach

 Greater tendency to collect and hold food debrisGreater tendency to collect and hold food debris
 Reduced bracing and stabilization.Reduced bracing and stabilization.

T-ClaspT-Clasp
 It derives its name from theIt derives its name from the
shape created where theshape created where the
retentive clasp arm joins theretentive clasp arm joins the
vertical aspect of the approachvertical aspect of the approach
arm.arm.
 It is indicated in kennedy classIt is indicated in kennedy class
1 of 2 partially edentulous1 of 2 partially edentulous
situations when an undercut issituations when an undercut is
located adjacent to thelocated adjacent to the
edentulous area.edentulous area.

ContraindicationsContraindications
 If soft tissue undercuts exists.If soft tissue undercuts exists.
 When the height of contour is located on theWhen the height of contour is located on the
occlusal 3occlusal 3rdrd
..

Modified-T / L Clasp:Modified-T / L Clasp:
 It’s a T clasp that lacksIt’s a T clasp that lacks
non-retentive horizontalnon-retentive horizontal
projection.projection.
 It is used on canines orIt is used on canines or
premolar for estheticpremolar for esthetic
reason.reason.

Y-ClaspY-Clasp
 A ‘Y’ clasp is formedA ‘Y’ clasp is formed
when the approach armwhen the approach arm
terminates in the cervical 3terminates in the cervical 3rdrd
of the abutment, while theof the abutment, while the
mesial & distal projectionsmesial & distal projections
are positioned near theare positioned near the
occlusal/ incisal 3occlusal/ incisal 3rdrd
..

I-BarI-Bar
 Only contact of retentive clasp withOnly contact of retentive clasp with
abutment tooth is the tip of the clasp,abutment tooth is the tip of the clasp,
which is circular or oval.which is circular or oval.
 It rarely used on disto-buccal surfaceIt rarely used on disto-buccal surface
of maxillary canine for estheticof maxillary canine for esthetic
reason.reason.
 Advantage includes better esthetics,Advantage includes better esthetics,
minimum interference with naturalminimum interference with natural
tooth contours.tooth contours.
 Disadvantage being problems withDisadvantage being problems with
stabilization.stabilization. www.indiandentalacademy.comwww.indiandentalacademy.com

RPI – ConceptRPI – Concept
 It was introduced byIt was introduced by KRATOCHVIL in 1963.KRATOCHVIL in 1963.
 Modified byModified by krolkrol in 1973. It consists of Mesial Rest,in 1973. It consists of Mesial Rest,
Proximal plate and I- Bar.Proximal plate and I- Bar.
 Mesial rest extends only in the triangular fossa, even in aMesial rest extends only in the triangular fossa, even in a
molar preparation, circular concave depression onmolar preparation, circular concave depression on
mesial marginal ridge of the canine.mesial marginal ridge of the canine.
 The proximal plate contacts only 1mm of guide planeThe proximal plate contacts only 1mm of guide plane
which is only 2-3mm high occlusogingivally.which is only 2-3mm high occlusogingivally.
 I bar terminus is a pod shaped to allow more toothI bar terminus is a pod shaped to allow more tooth
contact.contact.

 There are three basic approaches for theThere are three basic approaches for the
application of the RPI system;application of the RPI system;
- the location of the rest, the design of the- the location of the rest, the design of the
minor connector as it relates to the guide planeminor connector as it relates to the guide plane
and the location of the retentive arm are theand the location of the retentive arm are the
factors that influence how this clasp systemfactors that influence how this clasp system
functions.functions.
Vatiations in these factors provide the basisVatiations in these factors provide the basis
for the differences among these approaches.for the differences among these approaches.
The location of the rest and the retentive armThe location of the rest and the retentive arm
are similar in all three approches , differencesare similar in all three approches , differences
is only in proximal plate to the guiding plane,is only in proximal plate to the guiding plane,

1. The guide plane and the corresponding1. The guide plane and the corresponding
proximal plate minor connector extendingproximal plate minor connector extending
the entire length of proximal tooth surface,the entire length of proximal tooth surface,
with physiological tissue relief to eliminatewith physiological tissue relief to eliminate
impingement of free gingival margin.impingement of free gingival margin.
2. The guide plane and the proximal plate2. The guide plane and the proximal plate
minor connector extend from the marginalminor connector extend from the marginal
ridge to the junction of the middle andridge to the junction of the middle and
gingival 3gingival 3rdrd
of the proximal tooth surface.of the proximal tooth surface.
3. The proximal plate minor connector contacts3. The proximal plate minor connector contacts
approximately 1mm of the gingival portionapproximately 1mm of the gingival portion
of the guiding plane.of the guiding plane.

Modifications of RPI System:Modifications of RPI System:
R P AR P A
 Similar to RPI but instead of ISimilar to RPI but instead of I
bar, Akers or circumferentialbar, Akers or circumferential
clasp retentive arm is fabricated.clasp retentive arm is fabricated.

AdvantagesAdvantages
 Easier to grasp for removal of prosthesis .Easier to grasp for removal of prosthesis .
 It can be used in case of large tissueIt can be used in case of large tissue
undercuts, high frenum etc.undercuts, high frenum etc.
 Indicated when bar clasp isIndicated when bar clasp is
contraindicated and desirable undercutscontraindicated and desirable undercuts
is located in gingival 3rd of tooth awayis located in gingival 3rd of tooth away
from distal extention area.from distal extention area.www.indiandentalacademy.comwww.indiandentalacademy.com

R L SR L S – System by Aviv L. et al.– System by Aviv L. et al.
It consist of;It consist of;
 Mesio-occlusal restMesio-occlusal rest
 Disto-lingual L-bar It is the direct retainer,Disto-lingual L-bar It is the direct retainer,
located adjacent to edentulous ridge.located adjacent to edentulous ridge.
 Disto-buccal – stabilizer, It disengages from theDisto-buccal – stabilizer, It disengages from the
tooth as denture base moves tissue wards.tooth as denture base moves tissue wards.

VRHR CLASP CONCEPTVRHR CLASP CONCEPT
 Vertical reciprocal arm-horizontal retentive armVertical reciprocal arm-horizontal retentive arm
 Developed by GASSODeveloped by GASSO
 Characterized by;Characterized by;
1. a distal occlusal rest supported by a minor1. a distal occlusal rest supported by a minor
connector.connector.
2. a lingual vertical reciprocal arm originating from2. a lingual vertical reciprocal arm originating from
the major connector.the major connector.
3. a horizontal retentive arm fixed either to the major3. a horizontal retentive arm fixed either to the major
connector or to the retentive lattice work that is usedconnector or to the retentive lattice work that is used
to support the artificial teeth.to support the artificial teeth.

 VRHR clasps are usually used onVRHR clasps are usually used on
mandibular molars and premolars thatmandibular molars and premolars that
have height of contour in the occlusal thirdhave height of contour in the occlusal third
of the crown.of the crown.
 Reciprocal arm contacts the lingual heightReciprocal arm contacts the lingual height
of contourof contour

 ADVANTAGES;ADVANTAGES;
It makes minimal tooth contact , at theIt makes minimal tooth contact , at the
same time provides continuous contactsame time provides continuous contact
during insertion and removal of theduring insertion and removal of the
prosthesis.prosthesis.
there is no need to develop lingual ledgesthere is no need to develop lingual ledges
or broad parallel contralateral tooth surfaceor broad parallel contralateral tooth surface
to co-ordinate initial and continuous contactto co-ordinate initial and continuous contact
with the retentive and reciprocatingwith the retentive and reciprocating
components to their respective surfaces.components to their respective surfaces.

Comparison of Circumferential andComparison of Circumferential and
BarBar clasp;(Dr.Eugene R.Stone 1936)clasp;(Dr.Eugene R.Stone 1936)
CircumferentiCircumferenti
al claspal clasp
Bar claspBar clasp
RetentionRetention Pull typePull type Push typePush type
BracingBracing GreaterGreater AverageAverage
CariesCaries
susceptibilitysusceptibility
MoreMore LessLess
GingivalGingival
healthhealth
BetterBetter PoorPoor
AestheticsAesthetics PoorPoor ExcellentExcellent
ToleranceTolerance WellWell PoorPoor
CompactnessCompactness MoreMore LessLesswww.indiandentalacademy.comwww.indiandentalacademy.com

Other Clasp Systems:Other Clasp Systems:

Clasps with Splinting Action:Clasps with Splinting Action:
1) Extended arm clasp: made1) Extended arm clasp: made
of Cr-Co alloy It can beof Cr-Co alloy It can be
used for splinting maxillaryused for splinting maxillary
teethteeth

Clasps utilizing proximalClasps utilizing proximal
undercuts:undercuts:
Saddle lock hidden claspSaddle lock hidden clasp
partial dentures.partial dentures.
 It uses only proximal walls ofIt uses only proximal walls of
abutment teeth for retentionabutment teeth for retention
and uses infrabulge claspand uses infrabulge clasp
which approaches thewhich approaches the
retention area from gingivalretention area from gingival
aspect.aspect.

Advantages:Advantages:
 EstheticsEsthetics
 Increased retention because of trip actionIncreased retention because of trip action
 Can be used when buccal or lingual surveyCan be used when buccal or lingual survey
line unfavourableline unfavourable
 Compact design prevents dislodgementCompact design prevents dislodgement

RECENT ADVANCES:RECENT ADVANCES:

The various methods used to mask the metallicThe various methods used to mask the metallic
direct retainer are as follows.direct retainer are as follows.
Macromechanical retention:Macromechanical retention: RetentiveRetentive
beads and meshwork have been used tobeads and meshwork have been used to
retain facing of either acrylic or compositeretain facing of either acrylic or composite
resin.resin.
Esthetic clasp

• Bulk that is created by adding the veneer will• Bulk that is created by adding the veneer will
enlarge the total size of the clasp thus defeatingenlarge the total size of the clasp thus defeating
the purpose of disguising the clasp,the purpose of disguising the clasp,
• Bonding is unreliable,• Bonding is unreliable,
• GAP formation and microleakage when used in• GAP formation and microleakage when used in
combination with composites.combination with composites.

 Micromechanical retention:Micromechanical retention: It involves airIt involves air
borne particle abrasion. This helps to improveborne particle abrasion. This helps to improve
retention between the alloy and the resin.retention between the alloy and the resin.

This newThis new silica coatingsilica coating techniquetechnique involvesinvolves
coating the metal with silica intermediatecoating the metal with silica intermediate
layer (SiOlayer (SiOxx-C) that bonds to metal and also-C) that bonds to metal and also
supplies the -OH group for silane bonding.supplies the -OH group for silane bonding.
• Bond strengths obtained after the use of• Bond strengths obtained after the use of
micromechanical systems are insufficientmicromechanical systems are insufficient
especially after thermal conditioning.especially after thermal conditioning.

Tooth coloured occlusal
approaching polymethylene
clasps are alternative to metal
clasps

The Twin-Flex clasp/springThe Twin-Flex clasp/spring
claspclasp
 This consists of a wire claspThis consists of a wire clasp
soldered into a channel that is cast insoldered into a channel that is cast in
the major connector.the major connector.
 This clasp is flexible, it does notThis clasp is flexible, it does not
generate as much as torque whengenerate as much as torque when
the distal extension is depressed.the distal extension is depressed.
 The ability to adjust this clasp and itsThe ability to adjust this clasp and its
conventional path of insertionconventional path of insertion
provides an excellent design optionprovides an excellent design option
for retention to an adjacentfor retention to an adjacent
edentulous segmentedentulous segment

Disadvantages Disadvantages
• There is extra thickness of major connector• There is extra thickness of major connector
over the wire clasp,over the wire clasp,
• an extra laboratory step incurs extra cost,• an extra laboratory step incurs extra cost,
• Difficulty in repairing the clasp if breakage• Difficulty in repairing the clasp if breakage
occursoccurs

Conclusion:Conclusion:
 How to clasp a tooth depends on survey line,How to clasp a tooth depends on survey line,
root size and form and clinical condition ofroot size and form and clinical condition of
supporting structures.supporting structures.
 The choice of the clasp design should beThe choice of the clasp design should be
based on biologic as well as mechanicalbased on biologic as well as mechanical
principles.principles.
 The dentist responsible for the treatmentThe dentist responsible for the treatment
rendered must be able to justify the clasprendered must be able to justify the clasp
design used for each abutment tooth indesign used for each abutment tooth in
keeping with these principles.keeping with these principles.

BibliographyBibliography
 Mc Cracken’s –Removable partial prosthodontics.Mc Cracken’s –Removable partial prosthodontics.
 Stewart’s – Clinical Removable partialStewart’s – Clinical Removable partial
prosthodontics- third editionprosthodontics- third edition
 Osborne & Lammie’s – Removable prosthodonticsOsborne & Lammie’s – Removable prosthodontics
 The Twin-flex Clasp: An esthetic alternative. JThe Twin-flex Clasp: An esthetic alternative. J
Prosthet Dent 1997;77:450-2. Prosthet Dent 1997;77:450-2.
 The use of chairside silica for different dentalThe use of chairside silica for different dental
application: A clinical report. J Prosthet Dentapplication: A clinical report. J Prosthet Dent
2002;87:467-72. 2002;87:467-72. www.indiandentalacademy.comwww.indiandentalacademy.com

 Eliason, C. RPA Clasp Design for DistalEliason, C. RPA Clasp Design for Distal
Extension Removable Partial Dentures. JExtension Removable Partial Dentures. J
Prosthet Dent 49:25,1983Prosthet Dent 49:25,1983
 Aviv, I. et al. RLS-The Lingually RetainedAviv, I. et al. RLS-The Lingually Retained
Clasp Assembly for Distal ExtensionClasp Assembly for Distal Extension
Removable Partial Dentures. Quint Int.Removable Partial Dentures. Quint Int.
21:221-223,1990.21:221-223,1990.
 Cherkas L. and Jaslow E. Saddle lock hiddenCherkas L. and Jaslow E. Saddle lock hidden
clasp partial dentures. Comp Contin Educclasp partial dentures. Comp Contin Educ
Dent 12:746-752, 1991.Dent 12:746-752, 1991.
 Direct retainers: Esthetic solutions in theDirect retainers: Esthetic solutions in the
smile zone : JIPS 2005: 5: 1 4-9smile zone : JIPS 2005: 5: 1 4-9www.indiandentalacademy.comwww.indiandentalacademy.com

 J. C. Davenport Clasp designJ. C. Davenport Clasp design , BDJ 190, no., BDJ 190, no.
2, january 27 20012, january 27 2001

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