Clasp designs / dentist technology

CLASPCLASP DESIGNSDESIGNS..
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

 A removable partial denture mustA removable partial denture must
havehave
 SupportSupport
 StabilizationStabilization
 RetentionRetention

RETENTIONRETENTION
FOR RPDFOR RPD
 Is derivedIs derived mechanicallymechanically byby
placing the retaining elements onplacing the retaining elements on
the abutment tooth.the abutment tooth.

Direct retainerDirect retainer
 Is that component of removableIs that component of removable
partial denture used to retain andpartial denture used to retain and
prevent dislodgement , consistingprevent dislodgement , consisting
of clasp assembly or precisionof clasp assembly or precision
attachment.attachment.
-GPT.-GPT.

 Two types of direct retainers :Two types of direct retainers :
1) Intra coronal retainer (Attachments).1) Intra coronal retainer (Attachments).
2) Extra coronal retainer (clasps).2) Extra coronal retainer (clasps).

Intra coronal retainerIntra coronal retainer

Extra coronal retainer.Extra coronal retainer.
 Two configurations areTwo configurations are
1) Manufactured retainers (Dalbo)1) Manufactured retainers (Dalbo)
2) Custom-made retainers:2) Custom-made retainers:
a) Occlusally approaching (Circumferential ora) Occlusally approaching (Circumferential or
Akers clasp)Akers clasp)
b) Gingivally approaching (Bar or Roachb) Gingivally approaching (Bar or Roach
clasp)clasp)

 Principle of extra coronal directPrinciple of extra coronal direct
retainer.retainer.
Resistance of the metal to theResistance of the metal to the
deformation.deformation.

ClaspClasp
 Is the component of the clasp assemblyIs the component of the clasp assembly
that engages a portion of the tooth surfacethat engages a portion of the tooth surface
and either enters an undercut for retentionand either enters an undercut for retention
or remains entirely above the height ofor remains entirely above the height of
contour to act as a reciprocating element.contour to act as a reciprocating element.
 Generally, it is used to stabilize and retainGenerally, it is used to stabilize and retain
a removable prosthesis.a removable prosthesis.
-GPT.-GPT.

Clasp assembly.Clasp assembly.
 The part of a removable partial dentureThe part of a removable partial denture
that acts as a direct retainer and orthat acts as a direct retainer and or
stabilizer for a prosthesis by partiallystabilizer for a prosthesis by partially
encompassing or contacting an abutmentencompassing or contacting an abutment
tooth.tooth.
-GPT.-GPT.

ComponentComponent
parts.parts.
FunctionFunction LocationLocation
RestRest SupportSupport Occlusal, Lingual, IncisalOcclusal, Lingual, Incisal
MinorMinor
connectorconnector
StabilizationStabilization Proximal surfaces extendingProximal surfaces extending
from the prepared marginalfrom the prepared marginal
ridge to the junction of theridge to the junction of the
middle and gingival third ofmiddle and gingival third of
abutment crown.abutment crown.
Clasp armsClasp arms StabilizationStabilization
ReciprocationReciprocation
RetentionRetention
Apical portion of middle third ofApical portion of middle third of
crown.crown.
Apical portion of middle third ofApical portion of middle third of
crowncrown
Gingival third of crown inGingival third of crown in

 The critical areas of an abutment that isThe critical areas of an abutment that is
responsible forresponsible for retention, stabilization,retention, stabilization,
reciprocation and guide planesreciprocation and guide planes can onlycan only
be identified with the use ofbe identified with the use of dentaldental
surveyors.surveyors.

 General considerations:General considerations:
A clasp should be located at the undercutA clasp should be located at the undercut
area in relation to the determined path ofarea in relation to the determined path of
insertion and removal of the prosthesis.insertion and removal of the prosthesis.

Prothero’s cone theory.Prothero’s cone theory.
According to him , the
tooth is considered as a pair
of cones sharing a common
base
A clasp arm or tip that
ends on a cervical cone
would resist movement in the
occlusal direction because to
release from the tooth it
would be forced to undergo
deformation.www.indiandentalacademy.com

 The line which the two converging conesThe line which the two converging cones
meet is called themeet is called the height of contourheight of contour, the, the
term first coined byterm first coined by Kennedy.Kennedy.
 DevanDevan referred to the surface of a toothreferred to the surface of a tooth
that is occlusal to the height of contour asthat is occlusal to the height of contour as
supra bulgesupra bulge, and the tooth surface that is, and the tooth surface that is
cervical to its height of contour ascervical to its height of contour as infrainfra
bulge.bulge.

Component parts of a clasp.Component parts of a clasp.
 The component parts of a clasp assemblyThe component parts of a clasp assembly
may be rigid or flexible.may be rigid or flexible.
 The flexible components are designedThe flexible components are designed
below the height of contourbelow the height of contour

Component parts of a claspComponent parts of a clasp
 Retentive clasp armRetentive clasp arm
 Retentive terminalRetentive terminal
 Reciprocal armReciprocal arm
 Occlusal restOcclusal rest
 ShoulderShoulder
 BodyBody
 Minor connectorMinor connector

Retentive armRetentive arm
 A flexible segment of a removable partialA flexible segment of a removable partial
denture which engages a under cut on andenture which engages a under cut on an
abutment which is designed to retain theabutment which is designed to retain the
denture – GPTdenture – GPT
Retentive arm retentive clasp armRetentive arm retentive clasp arm
++
retentive terminalretentive terminal

Retentive armRetentive arm
 Retentive clasp arm - not flexibleRetentive clasp arm - not flexible
- located above thelocated above the
height of contourheight of contour
Retentive terminal - flexibleRetentive terminal - flexible
- located below thelocated below the

Reciprocal armReciprocal arm
A component of a clasp assemblyA component of a clasp assembly
specifically designed to providespecifically designed to provide
reciprocation by engaging a reciprocalreciprocation by engaging a reciprocal
guiding plane andguiding plane and
it counteracts the action of the clasp duringit counteracts the action of the clasp during
the removal and insertion of the partialthe removal and insertion of the partial
denture - GPTdenture - GPT

 Location - on the side of the toothLocation - on the side of the tooth
opposite to the retentive armopposite to the retentive arm
 - always placed in the supra- always placed in the supra
bulge areabulge area

 Function - resists the lateral forcesFunction - resists the lateral forces
exerted by the retentive armexerted by the retentive arm
when it passes through thewhen it passes through the
 - acts as an indirect retainer- acts as an indirect retainer
when placed on an abutmentwhen placed on an abutment
located anterior to thelocated anterior to the
fulcrum linefulcrum line

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

BodyBody
 Part of the clasp that connects the rests andPart of the clasp that connects the rests and
shoulders of the clasp of the minor connectors.shoulders of the clasp of the minor connectors.
 It is rigid and lies above the height of contourIt is rigid and lies above the height of contour
 It contacts the guide plane of the abutment duringIt contacts the guide plane of the abutment during
the insertion and removalthe insertion and removal
 Part of the body that contacts the guiding plane -Part of the body that contacts the guiding plane -
proximal plateproximal plate

restrest
 A rigid extension of a removableA rigid extension of a removable
partial denture which contacts apartial denture which contacts a
remaining tooth or teeth toremaining tooth or teeth to
dissipate vertical or horizontaldissipate vertical or horizontal
forcesforces
 part of the clasp assembly thatpart of the clasp assembly that
lies on the occlusal or lingual orlies on the occlusal or lingual or
incisal edge or surfaces of theincisal edge or surfaces of the
teethteeth
 Resist tissue ward movement ofResist tissue ward movement of
the clasp by acting like a verticalthe clasp by acting like a vertical
stopstop

Minor connectorMinor connector
 It joins the clasp with the remaining part ofIt joins the clasp with the remaining part of
the frameworkthe framework
 In gingivally approaching clasp –In gingivally approaching clasp –
Approach armApproach arm

BASIC PRINCIPLES OF CLASPBASIC PRINCIPLES OF CLASP
DESIGNDESIGN
 Any clasp assembly must satisfy the basicAny clasp assembly must satisfy the basic
principle of clasp design, isprinciple of clasp design, is
ENCIRCLEMENTENCIRCLEMENT
 which is that more than 180 degrees ofwhich is that more than 180 degrees of
the greatest circumference of the crown ofthe greatest circumference of the crown of
the tooththe tooth
 passing from diverging axial surfaces topassing from diverging axial surfaces to
converging axial surfacesconverging axial surfaces

 In the form of continuous contact whenIn the form of continuous contact when
circumferential clasp arms are used.circumferential clasp arms are used.
 When bar clasp arms are used, at leastWhen bar clasp arms are used, at least
three areas of tooth contact must bethree areas of tooth contact must be
embracing more than one half of toothembracing more than one half of tooth
circumferencecircumference
 These are the occlusal rest the retentiveThese are the occlusal rest the retentive
terminal area, and the reciprocal terminalterminal area, and the reciprocal terminal
area.area.

Other principles to be considered inOther principles to be considered in
the design of a clasp are asthe design of a clasp are as
follows:follows:
 1. The occlusal rest must be designed so that1. The occlusal rest must be designed so that
movement of the clasp arms cervically ismovement of the clasp arms cervically is
prevented.prevented.
 2. Each retentive terminal should be opposed by2. Each retentive terminal should be opposed by
a reciprocal arm or element capable of resistinga reciprocal arm or element capable of resisting
any orthodontic pressures exerted by theany orthodontic pressures exerted by the
retentive arm.retentive arm.
 Reciprocal and stabilizing elements must beReciprocal and stabilizing elements must be
rigidly connected bilaterallyrigidly connected bilaterally

 3. Retentive clasps should be bilaterally3. Retentive clasps should be bilaterally
opposed,opposed,
 that is, buccal retention on one side of the archthat is, buccal retention on one side of the arch
should be opposed by buccal retention on theshould be opposed by buccal retention on the
other, or lingual on one side opposed by lingualother, or lingual on one side opposed by lingual
on the other.on the other.
 In Class II situations the third abutment mayIn Class II situations the third abutment may
have either buccal or lingual retention.have either buccal or lingual retention.
 In Class III situations, retention may be eitherIn Class III situations, retention may be either
bilaterally or diametrically opposedbilaterally or diametrically opposed

. A, Retentive clasps should be bilaterally opposed.
B, In Class II situations the retention on the third abutment may be on the buccal or the
lingual
. C, In Class III situations retention may be either (a) bilateral or (b) diametrically
opposed.

 4. The path of escapement of each retentive4. The path of escapement of each retentive
clasp terminal should never coincide with theclasp terminal should never coincide with the
path of removalpath of removal
 5. Amount of retention should be the minimum,5. Amount of retention should be the minimum,
necessary to resist reasonable dislodgingnecessary to resist reasonable dislodging
forces.forces.
 6. Clasp retainers on abutment teeth adjacent to6. Clasp retainers on abutment teeth adjacent to
distal extension bases should be designed sodistal extension bases should be designed so
that, it should never exert tipping forces on thethat, it should never exert tipping forces on the
abutment teeth.abutment teeth.

 7. Reciprocal elements of the clasp7. Reciprocal 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.crowns of abutment teeth.
 The terminal end of the retentive arm isThe terminal end of the retentive arm is
optimally placed in the gingival third of theoptimally placed in the gingival third of the
crowncrown

Functional requirements of a clasp.Functional requirements of a clasp.
 RetentionRetention
 StabilityStability
 SupportSupport
 ReciprocationReciprocation
 EncirclementEncirclement
 Passivity.Passivity.

Retention.Retention.
 The function of retentive clasp arm is toThe function of retentive clasp arm is to
provide retention.provide retention.
 The retentive clasp is divided into threeThe retentive clasp is divided into three
parts.parts.
 The terminal third – engages the undercutThe terminal third – engages the undercut
area.area.
Middle third - engages a minimalMiddle third - engages a minimal
amount of undercut.amount of undercut.

 The proximal third - is positioned aboveThe proximal third - is positioned above
or shoulder the height of contour.or shoulder the height of contour.

Three dimensions of a retentiveThree dimensions of a retentive
undercut.undercut.

The following factors determine theThe following factors determine the
amount retention a clasp is capable ofamount retention a clasp is capable of
generating.generating.
 1) Size of angle of cervical convergence.1) Size of angle of cervical convergence.
 2) How far into the angle of cervical2) How far into the angle of cervical
convergence the clasp terminal is placed.convergence the clasp terminal is placed.
 3) Flexibility of the clasp arm, which is the3) Flexibility of the clasp arm, which is the
product of -product of -
a) Its length which is directly proportionala) Its length which is directly proportional
to the flexibility.to the flexibility.

 b) Its diameter is inversely proportionalb) Its diameter is inversely proportional
to the flexibility of the clasp arm.to the flexibility of the clasp arm.
 c) Its cross-sectional form or shape, thatc) Its cross-sectional form or shape, that
is, whether it is round, half-round, or some otheris, whether it is round, half-round, or some other
form.form.
round clasp - flex in all spatial planes.round clasp - flex in all spatial planes.
half-round clasp-flex only in a single plane.half-round clasp-flex only in a single plane.

d) The material of which the clasp is made,d) The material of which the clasp is made,
that is whether it is made of a gold alloy,that is whether it is made of a gold alloy,
or chrome alloy.or chrome alloy.
Chrome alloy have a higher modulus ofChrome alloy have a higher modulus of
elasticity and is less flexible.elasticity and is less flexible.

A smaller cross sectional form of the clasp
and less depth of the retentive undercut
is engaged when chrome alloy is used and
vice versa while using gold alloy.

Cast vs. wrought alloy.Cast vs. wrought alloy.

Support.Support.
 Is the property of a clasp that resistsIs the property of a clasp that resists
displacement of the clasp in a gingivaldisplacement of the clasp in a gingival
direction.direction.
 The support units of a clasp are occlusal,The support units of a clasp are occlusal,
lingual, or incisal rests.lingual, or incisal rests.

Stability.Stability.
 All clasp components except the retentiveAll clasp components except the retentive
clasp terminals contribute to this propertyclasp terminals contribute to this property
in varying degrees.in varying degrees.
 Cast circumferential –offers greatestCast circumferential –offers greatest
clasp amount of stability.clasp amount of stability.

Reciprocation.Reciprocation.
 Each retentive clasp terminal must beEach retentive clasp terminal must be
opposed by a reciprocal clasp arm oropposed by a reciprocal clasp arm or
another element of the partial dentureanother element of the partial denture
capable of resisting horizontal forcescapable of resisting horizontal forces
exerted on the tooth by the retentive arm.exerted on the tooth by the retentive arm.

 The reciprocal arm of the clasp isThe reciprocal arm of the clasp is
positioned on the opposite side of thepositioned on the opposite side of the
tooth from the retentive arm.tooth from the retentive arm.
 It also stabilizes the denture againstIt also stabilizes the denture against
horizontal movement.horizontal movement.
 It should be placed preferably at theIt should be placed preferably at the
junction of the gingival and middle thirds ofjunction of the gingival and middle thirds of
the abutment tooth (always positionedthe abutment tooth (always positioned
above the height of contour.)above the height of contour.)

 It should contact the abutmentIt should contact the abutment
tooth along with or before thetooth along with or before the
retentive arm during insertion orretentive arm during insertion or
removal.removal.
 Other parts which offerOther parts which offer
reciprocation are:reciprocation are:
 Lingual plate major connector.Lingual plate major connector.
 An additional occlusal restAn additional occlusal rest
placed on the opposite side of theplaced on the opposite side of the
tooth along with the minortooth along with the minor
connector.connector.

Encirclement.Encirclement.
 It is the property ofIt is the property of
the clasp assembly tothe clasp assembly to
encompass moreencompass more
than 180 degree ofthan 180 degree of
the abutment tooththe abutment tooth
either by continuouseither by continuous
or broken contact toor broken contact to
prevent dislodgementprevent dislodgement
during function.during function.

 It can be either a continuous contact as inIt can be either a continuous contact as in
circumferential clasp or a broken contactcircumferential clasp or a broken contact
as in bar clasp with at least 3 differentas in bar clasp with at least 3 different
areas of contact.areas of contact.
 The three points of contact are:The three points of contact are:
 retentive terminalretentive terminal
 occlusal contactocclusal contact
 reciprocal armreciprocal arm

Passivity.Passivity.
 A clasp in place should be completelyA clasp in place should be completely
passive.passive.
 The retentive function is activated onlyThe retentive function is activated only
when dislodging force are applied towhen dislodging force are applied to
the partial denture.the partial denture.
 A clasp must be completely seated onA clasp must be completely seated on
a tooth to be completely passive.a tooth to be completely passive.
 If a clasp designed to reach a retentiveIf a clasp designed to reach a retentive
undercut of 0.010 inch cannot reachundercut of 0.010 inch cannot reach
that depth, it will exert a constant forcethat depth, it will exert a constant force
on tooth. Over time this can produceon tooth. Over time this can produce
pain or tooth movementpain or tooth movement

 The types of clasps are:.The types of clasps are:.
 Circumferential or Aker ' s clasps.Circumferential or Aker ' s clasps.
 Vertical projection or Bar or RoachVertical projection or Bar or Roach
clasps .clasps .

Cast circumferential claspCast circumferential clasp
 A clasp that encircles a tooth by moreA clasp that encircles a tooth by more
than 180 degrees, including oppositethan 180 degrees, including opposite
angles, and which usually has totalangles, and which usually has total
contact with the tooth (throughout thecontact with the tooth (throughout the
extent of the clasp), with at least oneextent of the clasp), with at least one
terminal being in the infra bulge (gingivalterminal being in the infra bulge (gingival
convergence) area"convergence) area"
- GPT- GPT

Vertical projection claspVertical projection clasp // BarBar
claspclasp // Roach clasp:Roach clasp:
 A clasp having arms which are bar typeA clasp having arms which are bar type
extensions from major connectors or fromextensions from major connectors or from
within the denture base;within the denture base;
 the arms pass adjacent to the soft tissuesthe arms pass adjacent to the soft tissues
and approach the point or area of contactand approach the point or area of contact
on the tooth in a gingivo- occlusalon the tooth in a gingivo- occlusal
direction"direction" - GPT.- GPT.

Continuous claspContinuous clasp
 A metal bar usually resting on the lingualA metal bar usually resting on the lingual
surface of teeth to aid in their stabilizationsurface of teeth to aid in their stabilization
and to act as an indirect retainer"and to act as an indirect retainer"
 - GPT.- GPT.

Cast Circumferential ClaspCast Circumferential Clasp
 TheyThey are popularly known as Aker’sare popularly known as Aker’s
clasps.clasps.
 These clasps embrace more than half ofThese clasps embrace more than half of
the abutment tooth.the abutment tooth.
 This architecture helps the clasp to holdThis architecture helps the clasp to hold
the abutment firmly enough to prevent thethe abutment firmly enough to prevent the
rotation of the denture.rotation of the denture.
 They approach the undercut from anThey approach the undercut from an
occlusal direction.occlusal direction.

 Advantages:Advantages:
 Easiest clasp to make and repair.Easiest clasp to make and repair.
 Less food retentionLess food retention
 Best when applied in a tooth supportedBest when applied in a tooth supported
partial denture.partial denture.
 Derives excellent support, bracing andDerives excellent support, bracing and
retentionretention

 Disadvantages :Disadvantages :
 It covers a large tooth surface area.It covers a large tooth surface area.
 It also alters the Bucco lingual width of the crownIt also alters the Bucco lingual width of the crown
 This affects the normal food flow pattern leadingThis affects the normal food flow pattern leading
to food accumulation.to food accumulation.
 This causes decalcification of the toothThis causes decalcification of the tooth
structure.structure.
 Damage to soft tissue will occur due to lack ofDamage to soft tissue will occur due to lack of
physiological stimulation.physiological stimulation.
 Difficult to adjust with pliers because of it'sDifficult to adjust with pliers because of it's half-half-
round configuration.round configuration.

 If these clasps are placed high (more occlusally)If these clasps are placed high (more occlusally)
on the tooth, the width of the food tableon the tooth, the width of the food table
increases leading to generation of greaterincreases leading to generation of greater
occlusal forces.occlusal forces.
 All cast circumferential claspsAll cast circumferential clasps should nevershould never bebe
used to engage the mesio buccal undercut of anused to engage the mesio buccal undercut of an
abutment adjacent to the distal edentulousabutment adjacent to the distal edentulous
space (Fig. 18.167). Hence they cannot be usedspace (Fig. 18.167). Hence they cannot be used
for cases with an undercut away from thefor cases with an undercut away from the
edentulous space.edentulous space.

Types of Cast CircumferentialTypes of Cast Circumferential
ClaspsClasps
 11. Simple circlet clasp.. Simple circlet clasp.
 Most versatile and widely used.Most versatile and widely used.
 Best for tooth supported partial denture.Best for tooth supported partial denture.
 It approaches the undercut from theIt approaches the undercut from the
edentulous space.edentulous space.
 It engages the undercut, located awayIt engages the undercut, located away
from the edentulous space.from the edentulous space.

 Clasp can be adjusted only in oneClasp can be adjusted only in one
 They cannot be used for distal extensionThey cannot be used for distal extension
cases as they engage a mesio buccalcases as they engage a mesio buccal
undercut.undercut.

 2. Reverse circlet clasp or reverse2. Reverse circlet clasp or reverse
approach clasp:approach clasp:
 This clasp is used when the retentiveThis clasp is used when the retentive
undercut on the abutment tooth is locatedundercut on the abutment tooth is located
adjacent to the edentulous space.adjacent to the edentulous space.
 Used in distal extension denture base toUsed in distal extension denture base to
control the stresses acting on the terminalcontrol the stresses acting on the terminal
abutment teeth.abutment teeth.

 Disadvantages.Disadvantages.
 If sufficient occlusal clearance is notIf sufficient occlusal clearance is not
present, the thickness of the clasp has to bepresent, the thickness of the clasp has to be
reduced. This will affect the strength of thereduced. This will affect the strength of the
clasp.clasp.
 An occlusal rest away from the edentulousAn occlusal rest away from the edentulous
space does not protect the marginal gingivaspace does not protect the marginal gingiva
adjacent to the abutment tooth.adjacent to the abutment tooth.
 Poor esthetics as the clasp runs from thePoor esthetics as the clasp runs from the
mesial to the distal end of the facial surfacemesial to the distal end of the facial surface
 Wedging may occur between the abutmentWedging may occur between the abutment
and its adjacent tooth if the occlusal rest isand its adjacent tooth if the occlusal rest is
not well prepared.not well prepared.www.indiandentalacademy.com

 3.Multiple circlet3.Multiple circlet
clasp.clasp.
 It is a combination ofIt is a combination of
two simple circlettwo simple circlet
clasps joined at theclasps joined at the
terminal end of theterminal end of the
reciprocal arms.reciprocal arms.

 It is used for sharing the retention withIt is used for sharing the retention with
additional teeth on the same teeth on theadditional teeth on the same teeth on the
same side of the arch when the principlesame side of the arch when the principle
abutment tooth has poor periodontalabutment tooth has poor periodontal
support.support.
 It is a mode of splinting weakened teeth.It is a mode of splinting weakened teeth.
 It’s disadvantages are similar to that ofIt’s disadvantages are similar to that of
simple and reverse circlet clasps.simple and reverse circlet clasps.

 4. Embrasure clasp or4. Embrasure clasp or
modified crib clasp.modified crib clasp.
 It is a combination ofIt is a combination of
two simple circlet claspstwo simple circlet clasps
joined at the body.joined at the body.
 It is used on the sideIt is used on the side
of the arch where thereof the arch where there
is no edentulous space.is no edentulous space.

 The clasp must cross the marginal ridges of twoThe clasp must cross the marginal ridges of two
teeth, emerge to cross the facial surfaces ofteeth, emerge to cross the facial surfaces of
both teeth, and engage undercuts on theboth teeth, and engage undercuts on the
opposing line angles of these teeth.opposing line angles of these teeth.
 Occlusal rest seat preparation must be made onOcclusal rest seat preparation must be made on
both teethboth teeth
 Tooth structure must be removed from theTooth structure must be removed from the
buccal inclines of both teeth to provide space forbuccal inclines of both teeth to provide space for
adequate thickness of the metal.adequate thickness of the metal.

 Indications: It is used in kennedy’s class 2Indications: It is used in kennedy’s class 2
and class 3 cases without anyand class 3 cases without any
modifications.modifications.
 Occasionally, a very small edentulousOccasionally, a very small edentulous
space can be closed by a modifiedspace can be closed by a modified
embrasure clasp called a pontic claspembrasure clasp called a pontic clasp

 5. Ring clasp5. Ring clasp
 Indicated in tipped molarsIndicated in tipped molars
 In Distal edentulous conditions withIn Distal edentulous conditions with
distolingual undercut - the retentive armdistolingual undercut - the retentive arm
is extended all around the tooth from theis extended all around the tooth from the
disto buccal end to terminate in thedisto buccal end to terminate in the
distolingual undercut across the mesialdistolingual undercut across the mesial
side of the toothside of the tooth

 As clasp is long – additional support isAs clasp is long – additional support is
provided by auxiliary bracing armprovided by auxiliary bracing arm

 DisadvantagesDisadvantages
 Alteration in food flow patternAlteration in food flow pattern
 Increased tooth surface coverageIncreased tooth surface coverage
 Difficult to adjust or repairDifficult to adjust or repair
 Contra indicationsContra indications
 Not considered in mandibular molar whereNot considered in mandibular molar where
attachment of the buccinator is close toattachment of the buccinator is close to
tooth that the auxiliary arm encroaches ontooth that the auxiliary arm encroaches on
itit

 6. fishhook or hairpin or reverse action6. fishhook or hairpin or reverse action
claspclasp
 Type of simple circlet clasp.Type of simple circlet clasp.
 retentive armretentive arm – crosses the facial– crosses the facial
surface of the tooth from its point of origin,surface of the tooth from its point of origin,
loops back in a hairpin turn to engage aloops back in a hairpin turn to engage a
proximal undercut below its point of originproximal undercut below its point of origin

 Upper arm - rigidUpper arm - rigid
 Lower arm - flexibleLower arm - flexible
 Sufficient space should be presentSufficient space should be present
between the two arms – to avoid foodbetween the two arms – to avoid food
accumulation & for properaccumulation & for proper
finishing and polishingfinishing and polishing

 IndicationIndication
 Crown with sufficient occluso gingivalCrown with sufficient occluso gingival
heightheight
 The undercut is adjacent to edentulousThe undercut is adjacent to edentulous
areaarea
 Presence of a soft tissue undercutPresence of a soft tissue undercut
 Reverse circlet can’t be used – lack ofReverse circlet can’t be used – lack of
occlusal spaceocclusal space

 Poor estheticsPoor esthetics
 Tends to trap and accumulate food debrisTends to trap and accumulate food debris

 Onlay clasp ;Onlay clasp ;
 Extension of a metal crown or onlay withExtension of a metal crown or onlay with
buccal and lingual clasp arms.buccal and lingual clasp arms.
 Used in occlusal surfaces of submergedUsed in occlusal surfaces of submerged
abutment teeth – thus restoring theabutment teeth – thus restoring the
occlusal plane with an onlay.occlusal plane with an onlay.

 If onlay clasp is made of chrome alloy –If onlay clasp is made of chrome alloy –
the opposing tooth should be protectedthe opposing tooth should be protected
with a gold crown to avoid attrition ofwith a gold crown to avoid attrition of
enamel.enamel.
 Used in caries resistant mouth.Used in caries resistant mouth.

 8. combination clasp8. combination clasp
 A cast circumferential clasp can’t be usedA cast circumferential clasp can’t be used
– when an undercut is adjacent to the– when an undercut is adjacent to the
edentulous space since it produceedentulous space since it produce
destructive rotatory forces on the distaldestructive rotatory forces on the distal
abutmentabutment
 A flexible wrought wire retentive arm isA flexible wrought wire retentive arm is
used to replace the rigid cast alloyused to replace the rigid cast alloy
retentive arm.retentive arm.

 It has greater flexibility it can be placed inIt has greater flexibility it can be placed in
a deeper undercut – without any hazard toa deeper undercut – without any hazard to
the abutment tooththe abutment tooth
 It is used in maxillary canines andIt is used in maxillary canines and
premolars due to its superior esthetics.premolars due to its superior esthetics.

 AdvantagesAdvantages
 The round configuration of the wroughtThe round configuration of the wrought
wire – has a thin line contact whichwire – has a thin line contact which
collects less debris and is easy tocollects less debris and is easy to
maintain.maintain.
 flex in all planesflex in all planes

 Tedious lab proceduresTedious lab procedures
 Easily breaks or distortsEasily breaks or distorts
 Poor stabilityPoor stability

Half and half claspHalf and half clasp
 It has a retentive arm arising from one directionIt has a retentive arm arising from one direction
and a reciprocal arm arising from anotherand a reciprocal arm arising from another
 Two minor connectors are needed for thisTwo minor connectors are needed for this
design. The first minor connector attaches thedesign. The first minor connector attaches the
occlusal rest and the retentive arm to the majorocclusal rest and the retentive arm to the major
connector. The second minor connectorconnector. The second minor connector
connects the reciprocal arm which is similar toconnects the reciprocal arm which is similar to
the bar clasp with or without an auxiliary rest.the bar clasp with or without an auxiliary rest.

 This design produces large toothThis design produces large tooth
coverage which can be reduced bycoverage which can be reduced by
converting the reciprocal arm into a shortconverting the reciprocal arm into a short
bar with an auxiliary occlusal rest.bar with an auxiliary occlusal rest.
 This design is intended to provide dualThis design is intended to provide dual
retention.retention.

 Back-action claspBack-action clasp
 It is a modification of the ring claspIt is a modification of the ring clasp
 Here the minor connector is connected to theHere the minor connector is connected to the
end of the clasp arm and the occlusal rest is leftend of the clasp arm and the occlusal rest is left
unsupported.unsupported.
 Lack of support to the occlusal rest reduces itsLack of support to the occlusal rest reduces its
function.function.
 It has both biological and mechanical unsoundIt has both biological and mechanical unsound
principles.principles.

 Grasso’s clasp or VRHR claspGrasso’s clasp or VRHR clasp
 Developed by Grasso,Developed by Grasso,
 This clasp consists of :This clasp consists of :
 A vertical reciprocal arm,A vertical reciprocal arm,
 an occlusal rest andan occlusal rest and
 a horizontal retentive arm arisinga horizontal retentive arm arising
separately from the major connector.separately from the major connector.

Grasso’s clasp or VRHR claspGrasso’s clasp or VRHR clasp
 Advantages :Advantages :
 Minimizes tooth contact without compromise in efficacy.Minimizes tooth contact without compromise in efficacy.
 Does not require the preparation of guide planes.Does not require the preparation of guide planes.
 Suitable for posterior teeth with high survey lines.Suitable for posterior teeth with high survey lines.
 The placement of the retentive arm is more aesthetic.The placement of the retentive arm is more aesthetic.

Grasso’s clasp or VRHR claspGrasso’s clasp or VRHR clasp
 Difficult to maintain as the block out zoneDifficult to maintain as the block out zone
between the base of the reciprocal armbetween the base of the reciprocal arm
and the tooth tends to collect food debris.and the tooth tends to collect food debris.

Rest-proximal plateRest-proximal plate –– AkersAkers
retentive arm (RPA) claspretentive arm (RPA) clasp
 The RPA clasp is a modified circumferentialThe RPA clasp is a modified circumferential
claspclasp
 The circumferential arm arises from the proximalThe circumferential arm arises from the proximal
plate adjacent to the edentulous base area.plate adjacent to the edentulous base area.
 The retentive component of this directThe retentive component of this direct
retainerretainer - engages a retentive undercut located- engages a retentive undercut located
on the facial surface of the abutment tooth awayon the facial surface of the abutment tooth away
from the edentulous area.from the edentulous area.

 The shoulder of the clasp arm - contacts theThe shoulder of the clasp arm - contacts the
tooth at the height of contour at the junction oftooth at the height of contour at the junction of
the middle and gingival thirds of the tooth.the middle and gingival thirds of the tooth.
 This direct retainer satisfies all the requirementsThis direct retainer satisfies all the requirements
for use in distal-extension RPD situations.for use in distal-extension RPD situations.
 Allows for mesially oriented support, which isAllows for mesially oriented support, which is
preferable in distal-extension RPDs.preferable in distal-extension RPDs.

 Excellent bracing is derived from theExcellent bracing is derived from the
contact of the minor connector supportingcontact of the minor connector supporting
the rest, the proximal plate contacting thethe rest, the proximal plate contacting the
tooth surface adjacent to the edentuloustooth surface adjacent to the edentulous
base area, and the shoulder part of thebase area, and the shoulder part of the
clasp arm.clasp arm.
 Acceptable retention is derived fromAcceptable retention is derived from
retentive areas located on surfaces of theretentive areas located on surfaces of the
tooth away from the edentulous area.tooth away from the edentulous area.

 Requirements for adequate encirclement andRequirements for adequate encirclement and
passivity can easily be accommodated by thispassivity can easily be accommodated by this
direct retainer.direct retainer.
 This type of clasp appears best suited for distal-This type of clasp appears best suited for distal-
extension RPDs - where the undercut is locatedextension RPDs - where the undercut is located
away from the edentulous area andaway from the edentulous area and
 for situations in which it has been determinedfor situations in which it has been determined
that the tooth need not be modified tothat the tooth need not be modified to
accommodate a different type of clasp.accommodate a different type of clasp.

Mesiodistal clasp.Mesiodistal clasp.
 This direct retainer might be consideredThis direct retainer might be considered
for a tooth-borne RPD when maxillaryfor a tooth-borne RPD when maxillary
incisors remain as the anterior abutmentincisors remain as the anterior abutment
teeth.teeth.
 Although the design exhibits goodAlthough the design exhibits good
supporting and bracing qualities,supporting and bracing qualities,
 it may be excessively traumatic to theit may be excessively traumatic to the
supporting abutment teeth when used onsupporting abutment teeth when used on
distal-extension RPDs.distal-extension RPDs.

 Retention for this direct retainer is gainedRetention for this direct retainer is gained
through parallelism and frictional resistance ofthrough parallelism and frictional resistance of
the clasp assembly against the natural teeth.the clasp assembly against the natural teeth.
 The teeth must be prepared so that theirThe teeth must be prepared so that their
proximal surfaces are parallel or have a slightproximal surfaces are parallel or have a slight
convergence to one another.convergence to one another.
 This direct retainer, like the other circumferentialThis direct retainer, like the other circumferential
designs, poses the same problems of coveringdesigns, poses the same problems of covering
excessive tooth structure and impairingexcessive tooth structure and impairing
esthetics.esthetics.

Bar or vertical projection or roachBar or vertical projection or roach
clasp.clasp.
 Approaches the undercut or retentive areaApproaches the undercut or retentive area
on the tooth from a gingival direction,on the tooth from a gingival direction,
resulting in a push type of retention.resulting in a push type of retention.
 Flexibility of the bar type of clasp can beFlexibility of the bar type of clasp can be
controlled by the taper and length of thecontrolled by the taper and length of the
approach arm.approach arm.
 More esthetic than the circumferentialMore esthetic than the circumferential
clasp.clasp.

 Disadvantages.Disadvantages.
 1. Greater tendency to collect and hold1. Greater tendency to collect and hold
food debris.food debris.
 2. Due to its increased flexibility of the2. Due to its increased flexibility of the
retentive arm, it does not contribute asretentive arm, it does not contribute as
much to bracing and stabilization as mostmuch to bracing and stabilization as most
circumferential clasps do.circumferential clasps do.

 Rules to use.Rules to use.
 The approach arm must always beThe approach arm must always be
tapered uniformly from its point oftapered uniformly from its point of
attachment at the frame work to the caspattachment at the frame work to the casp
terminal.terminal.

Thank you
For more details please visit

Clasp designs / dentist technology

Recomendados

Recomendados

Mais conteúdo relacionado

Mais procurados

Mais procurados (20)

Destaque

Destaque (20)

Semelhante a Clasp designs / dentist technology

Semelhante a Clasp designs / dentist technology (20)

Mais de Indian dental academy

Mais de Indian dental academy (20)

Último

Último (20)

Clasp designs / dentist technology