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Classification of clamps, indications for use

June 1, 2024

Classificatioof clamps, indications for use.

Biomechanics nclasp dentures.

Direct retainers are flexible nparts of the casting that are designed to engage undercuts on the abutment nteeth to resist removal of the prosthesis and to help prevent ndislodgement. There are two basic types of direct retainers – infrabulge nand suprabulge rertainers. This program describes how each of these types of nretainers are employed in the RPI and RPA systems.

Direct and nIndirect Retainers

I. Retention

Retention is the ability of a nremovable partial denture to resist dislodging forces during function.

Retention depends upon several nfactors:

a. adhesion, cohesion, ninterfacial surface tension and atmospheric pressure

b. gravity

c. frictional retentio(guiding planes, bracing elements)

e. indirect retention

f. direction of dislodging nforce relative to the path of placement.

g. mechanical retention

Mechanical nRetention

Mechanical retention is obtained nby placing portions of the partial denture into tooth or soft tissue undercuts. nMaximizing the other retentive factors can minimize the need for mechanical nretention.

Most mechanical retention is nderived from the use of direct retainers (clasp assemblies) utilizing tooth nundercuts. There are two classes of mechanical retainers: intracoronal and nextracoronal.

Intracoronal nretainers (precision attachments) are nmechanical devices set into the casting of a full crown. These are generally nreserved for removable partial denture therapy that requires exceptional effort nin producing ideal esthetics. There are many contraindications and ndisadvantages to precision attachments.

Extracoronal nretainers engage an external surface of nan abutment in a natural undercut or in a prepared depression. There are two nmain classes of clasps: 1) those that approach the undercut from above the nheight of contour (suprabulge retainers) and 2) those that approach the nundercut from below (infrabulge retainers).

II. Extra-Coronal nDirect Retainers

Definition – A ndirect retainer is a unit of a removable partial denture that engages aabutment tooth in such a manner as to resist displacement of the prosthesis naway from basal seat tissues. It is usually composed of a retentive arm, a nreciprocal (bracing) element or arm, a rest and a minor connector.

Retention is derived by placing na clasp arm into an undercut area so that it is forced to deform upon vertical ndislodgment. Resistance of the clasp to deformation generates retention.

Resistance is proportionate to nthe flexibility of the clasp arm. Non-flexible portions of clasp arms must be nplaced occlusal to the height of contour (suprabulge area).

Requirements of nDirect Retainers

All clasp assemblies should nmeet the following requirements:

1. Support – resistance nto gingival displacement (occlusal rests)

2. Reciprocity – nresistance to orthodontic movement of teeth using reciprocal arms or

elements placed against guiding nplanes. During placement and removal of the partial

denture the retentive arm nflexes over the height of contour and generates energy. At this point the rigid nreciprocal arm should contact the guiding plane and prevent orthodontic nmovement from taking place.

3. Stability – nresistance to lateral movement (reciprocal arms, minor connectors)

4. Retention – retentive narms located in undercuts on the abutments

5. Encirclement of greater nthan 180° of the tooth – prevents the prosthesis from moving away from the ntooth

6. Passivity – at rest, na direct retainer should not exert force against a tooth

Wherever possible direct nretainers should be selected to fit the existing teeth. This is preferable to npreparing teeth to fit a particular clasp design. It may be possible to select na different clasp design to meet the retentive requirements for a partial ndenture. Nonetheless, judicious tooth preparation should not be avoided at all ncosts, since it can immeasurably improve prosthesis biomechanics.

Factors affecting nthe magnitude of retention

1. Size of the angle of nconvergence.

2. How far into the angle of nconvergence the clasp terminal is placed.

When the angle of convergence nbetween two abutments differs uniformity of retention can be obtained by nplacing the clasp arms into the same degree of undercut. A guiding principle of npartial denture design is that retention should be uniform in magnitude and nbilaterally opposed amongst abutments.

3. Flexibility of the clasp arm. This nis influenced by the following factors:

i. Length

c. increased length increases nflexibility (increasing clasp curvature increases length

d. length is measured from the npoint where the taper begins

e. length may be increased by nusing curving rather than straight retentive arms

ii. Diameter

” diameter is inversely nproportional to flexibility

” in a uniform taper the naverage diameter lies midway

” if the taper is not nuniform a point of flexure will exist at the narrowed

” area, weakening the nclasp arm (possible fracture area)

” the point of flexure ndetermines flexibility regardless of average diameter

A narrowing of the clasp arm ncreates a point of flexure which weakens, and affects the flexibility of the nclasp, since flexure begins at this point

iii. Cross-sectional form

a. round forms are usually more nflexible (wrought or cast)

b. l/2 round shape is limited nto flexure in only two directions (cast)

iv. Clasp material

a) with cast alloys flexibility nis inversely proportional to bulk

b) gold clasps are not as nflexible or adjustable as wrought wire

c) wrought wire clasps have ngreater tensile strength than cast clasps and hence

can be used in smaller ndiameters to provide greater flexibility without fatigue

or fracture.

Direct Retainers nFor Tooth-Borne RPD’s

Clasps for tooth-borne partial ndentures (Class III, IV) have one function – to prevent

dislodgment of the prosthesis nwithout damage to the abutment teeth. Since there is little or no rotatiocaused by tissueward movement of the edentulous area (as happens in distal nextension cases) stress releasing properties are usually not required. These nclasps can also be used in modification spaces for tooth and tissue supported nremovable partial dentures (Class I, II).

1. nCircumferential (Circle or Akers) clasp

a. the most simple and nversatile clasp (clasp of choice in tooth-borne cases)

b. clasp assembly has one retentive narm opposed by a reciprocal arm originating from the rest

c. the retentive arm begins nabove the height of contour, and curves and tapers to its terminal tip, in the ngingival 1/3 of the tooth, well away from the gingiva

d. the bracing arm is in the nmiddle 1/3 of the tooth, and is broader occluso-gingivally, does not taper and nis either entirely above the height of contour or completely on a

prepared guiding plane – it nshould never be designed into an undercut, as it is a rigid element.

Advantages:

a. Excellent bracing qualities

b. Easy to design and construct

c. Less potential for food naccumulation below the clasp compared to bar clasps

Disadvantages:

a. More tooth coverage than bar nclasps

b. More metal is displayed thawith bar or combination clasps

c. Adjustments are difficult or nimpossible due to the half round nature of the clasp

A direct retainer should be ndesigned with its elements in the proper positions and in the correct nproportions. If the height of contour is incorrect for placement of the arms of nthe direct retainer, the heights of contour and NOT the direct retainer should nbe altered (i.e. perform abutment modifications – don’t distort the design of nthe direct retainer)

2. Ring clasp

a. Encircles nearly the entire nabutment tooth

b. Usually used with mesially nand lingually tilted mandibular molars (with a m-l

undercut) or mesially and nbuccally tilted maxillary molars (with a m-b undercut)

c. The undercut is on the same nside as the rest seat (i.e. adjacent to edentulous span)

d. Should always be used with a nsupporting strut on the non-retentive side with an

auxiliary occlusal rest on the nopposite side. Omission of the supporting strut will allow the clasp arm to nopen and close with minimum or no reciprocation.

e. Use a cast circumferential nclasp with lingual retention and buccal bracing, in preference to a ring clasp nwhenever possible, unless a severe tilt of the tooth will not permit

Advantages:

a. Excellent bracing (with nsupporting strut)

b. Allows use of an available nundercut adjacent to edentulous area

Disadvantages:

a. Covers a large area of tooth nsurface, therefore requiring meticulous hygiene

b. Very difficult to adjust due nto the extreme rigidity of the reciprocal arms

c. The lower bracing arm should nbe at least 1 mm from the free gingival margin and

relieved to prevent impingement nof the gingival tissues.

Contraindications: excessive tissue undercuts prevent the use of a nsupporting strut.

3. Embrasure n(Double Akers) Clasp

! Used in a quadrant where no nedentulous area exists, or where a distal approach clasp cannot be used on the nmost posterior tooth (i.e. No usable retentive undercut).

! Two rests, two retentive arms, nand two bracing arms

! Double rests with definite nshoulders to prevent weakening of clasp arms, separation of teeth and food nimpaction

! Buccal and lingual proximal nareas must be opened (i.e. Blend with axial contours, reduce height of ncontours, round occluso-axial line angles)

! Use minimum retention – prone nto distortion

! Use with discretion – use nanother clasp if possible

Advantages:

a. Allows placement of direct nretainer where none could otherwise be placed (especially contralateral to the nedentulous span on a Class II case)

Disadvantages:

a. Extensive interproximal nreduction is usually required

b. Covers large area of tooth nsurface – hygiene considerations

4. “C” nclasp (Hair-pin or Reverse action)

a. The retentive area n(undercut) is adjacent the occlusal rest.

b. The upper arm is a minor a nconnector giving rise to tapered lower arm.

Advantages:

a. Allows use of undercut nadjacent to edentulous space

Disadvantages:

a. Almost impossible to adjust

b. Non-esthetic

c. Difficult to fabricate so nthe upper portion of the retentive arm clears the opposing

occlusion

d. Covers extensive tooth nsurface and acts as a food trap

e. Insufficient flexibility oshort crowns due to insufficient clasp arm length

Cast suprabulge clasps should nbe used in most tooth borne cases. Exceptions to this rule include:

1. Esthetic concerns. nSince wrought-wire clasps can be placed into greater undercuts

(0.02″) than cast clasps n(0.01″) they can be placed lower on teeth, allowing better

esthetics in some cases. nInfrabulge clasps are also less visible.

2. Where a posterior nabutment is mobile or of questionable prognosis, the treatment plan could ncall for the use of the stress-breaking qualities of a wrought clasp on the nanterior abutment. This would allow the prosthesis to be converted into a ndistal extension type if the weak posterior abutment should be lost.

3. Where abutments are nmobile, the tooth borne segment is extensive, the use of the

stress-breaking clasps should nbe considered.

Disadvantages of ncast suprabulge clasps:

1. Create a n”pump-handle” action on the abutment teeth in distal extension cases nif the guiding plane on the distal surface is too long, with insufficient nrelief.

2. Some clasps can be nineffective on teeth tilted buccally or lingually

3. Some varieties cover more ntooth surface than is desirable

4. Poor esthetics in the nanterior region

There have been many nmodifications to cast suprabulge clasps. Some are too complex and impractical nfor common use.

Direct Retainers nFor Tooth and Tissue Borne RPD’s

Tooth and tissue borne nsituations (Class I & II) require special attention in direct retainer nselection, due to stresses created by rotational movements of the prostheses. nWhen the denture bases are placed under function, rotation occurs about the nrest seats of the most posterior abutments. Excessive occlusal forces on the ndistal-extension portion of the denture could cause a torquing action on the nabutment teeth unless direct retainers are designed with stress-breaking ncapabilities. Stress releasing clasp assemblies include:

1. the bar clasp with mesial nrest (e.g. RPI)

2. the RPA clasp

3. the combination clasp

1. Bar Clasps

a. The bar clasp is a cast clasp nthat arises from the partial denture framework and approaches the retentive nundercut from gingival direction (as opposed to a circumferential clasp that napproaches the undercut from the occlusal direction).

b. Retentive clasps are nidentified by shape of retentive terminal, i.e. T, Y, L, I, U, and S.

c. The shape is unimportant as nlong as the direct retainer is mechanically and functionally stable, covers nminimal tooth structure with minimum display (the I bar most often meets these nrequirements)

d. T-and Y-shaped terminal ends nare the most misused clasps. The full area coverage of the T and Y terminal nends is rarely necessary for adequate retention.

e. L-shaped clasp is same as aI clasp with a longer horizontal component. The U-shaped clasp is same as aL-shaped clasp with a terminal like a double I-clasp.

f. The S-shaped terminal end is nused to avoid a mesial soft tissue undercut.

g. Soft tissue relief is nprovided under the approach arm with 28 or 30 gauge wax, to prevent tissue nimpingement

Contraindications:

a) deep cervical undercuts – nfood trap or impingements result

b) severe soft tissue or bony nundercuts – food trap or impingements result

c) insufficient vestibular ndepth for approach arm (requires 4 mm – 3 mm from free

gingival margin, 1 mm for nthickness of the approach arm)

d) pronounced frenal nattachments in area – impingement

The R-P-I Clasp

1. The components of this clasp nassembly are:

“R” – rest (always mesial)

“P” – proximal plate

“I” – I-bar n(retentive arm)

2. The rest is located on the nmesio-occlusal surface of a premolar or mesiolingual surface of a

canine. The minor connector is nlocated in the mesio-lingual embrasure but is not in

contact with the adjacent tooth n(prevents wedging).

3. The proximal plate n(essentially a wide minor connector) is located on a guide plane on the distal nsurface of the tooth. The superior edge of the proximal plate is located at the nbottom of the guide plane (at approximately the junction of the occlusal and nmiddle third of the guide plane). The proximal plate extends lingually so that nthe distance between the minor connector and the proximal plate is less thathe mesio-distal width of the tooth. The plate is approximately l mm. thick and njoins the framework at a right angle.

4. The I-bar clasp is located non the buccal surface of the premolar and on the mesio-buccal surface of the ncanine. The I-bar originates at the gridwork and approaches the tooth from the ngingival direction. The bend in the I-bar should be located at least 3 mm. from nthe gingival margin. This distance will prevent food entrapment and provide the nlength for the necessary flexibility in the clasp arm. The clasp is usually ncast and is placed just below the height of contour line.

5. On premolars, the nproximal plate should extend lingually so that the distance between the nproximal plate and the mesio-occlusal rest is less than the mesio-distal width nof the tooth. The proximal plate in conjunction with the mesial rest (and nminor connector) acts as the reciprocating element of the clasp and nprevents the lingual migration of the tooth when the clasp arm moves nover the height of contour.

6. On cuspids, the minor nconnector cannot be used for reciprocation since it does not contact the tooth nuntil after the retentive element has passed across the height of contour and nthe partial denture is seated. This is because the mesio-lingual rest is nlocated fairly low on the cingulum of the tooth. Therefore, the I-bar is nlocated in the mesio-buccal undercut and is reciprocated directly by the nproximal plate.

7. The guiding plane is a nparallel surface prepared on the occlusal one third of the distal surface of nthe tooth. The guiding plane extends lingually enough so that, along with the nmesial rest, it can prevent lingual migration of the tooth. It is approximately n2 to 3 mm in height.

Contraindications nto the R.P.I. Clasp

1. Insufficient depth of the nvestibule. (The inferior border of the I-bar must be located at least 4 mm. nfrom the gingival margin.)

2. No labial or buccal undercut non the abutment

3. Severe soft tissue undercut

4. Disto-buccal undercut (less nthan 180° encirclement)

2. RPA Clasp

This clasp assembly is similar nto the RPI design except a wrought wire circumferential clasp (Akers) is used ninstead of the I-bar. This clasp arises from the proximal plate and terminates nin the mesiobuccal undercut. It is used when there is insufficient vestibule ndepth or when a severe tissue undercut exists.

3. CombinatioClasp

The combination clasp is nsimilar to the cast circumferential clasp with the exception that the retentive narm is fabricated from a round wrought wire (platinum-gold-palladium alloy or nchromecobalt alloy).

a. a cast reciprocal arm.

b. the wrought wire is flexible n(round form)

c. more adjustable than cast or n1/2 round forms

d. better esthetics (due to its nround form and smaller

diameter – 18 gauge)

e. can used with a mesial or nbuccal undercut

f. can be placed in 0.02″ nundercut due to its flexibility

(allows lower placement for nbetter esthetics)

g. can be used in tooth borne ncases as described earlier

h. for best results, the wire nshould be soldered remotely to the framework so it is not

overheated, which would cause nrecrystallization of the metal and loss of flexibility. If wrought wire clasps nare cast into the framework, a low heat chromium alloy should be used to avoid nrecrystallization as well

The Distal Rest nConcept

The proponents of the mesial nrest concept (i.e. RPI, RPA designs) believe that the use of the clasp assembly nwith a disto-occlusal rest (in a distal extension case) could lead to distal ntilting and possible loss of the abutment tooth. However, if correctly designed nand executed, the distal rest concept is as viable a treatment alternative as nthe mesial rest concept.

The premise of the mesial rest nconcept is that during vertical loading the distal extension base causes the nI-bar to move mesio-gingivally away from the tooth and the proximal plate to nmove further into the undercut of the tooth.

The I-bar and the proximal nplate disengage the abutment tooth and thereby reduce torquing of the tooth. nThis is an accurate deduction. Therefore the RPI design be used wherever npossible.

However, an I-bar cannot be nused routinely due to the fact that a tissue undercut frequently exists in the nregion of the abutment.

A distal rest concept has ndrawbacks if designed incorrectly. If the guiding plane on the distal surface nof the abutment covers the entire length of the tooth, loading of the denture nbase will cause the minor connector contacting the guiding plane to act as a n”wrench” and torque the tooth.

However, if a short guiding nplane is prepared with a relief area between the converging surface of the ntooth and the minor connector, the distal tilting of the abutment can be nprevented or minimized. During distal loading, the minor connector could move ninto the relief area and the rest would be permitted to escape from the rest nseat. This would change the fulcrum point from point A to point B, driving the nabutment tooth mesially against adjacent tooth.

However, if the retentive arm nis place into a mesiobuccal undercut, torquing might still occur, since the nretentive tip would tend to rotate in an occlusal direction, thereby engaging nthe tooth.

To minimize the activating neffect of the retentive arm, a wrought wire arm should be used (greater nflexibility, less ability to torque). In addition and where possible, the nretentive undercut should be place in the mid-buccal of the tooth, with the nmesial clasp tip placed above the height of contour. Thus occlusal movement of nthe clasp tip will disengage rather than engage the tooth.

Similarly, lingual bracing arms nshould not be carried too far into embrasures in distal extension cases, since ntissueward movement could also result in torquing forces being placed on the nabutments.

If the distal rest retainers nare correctly designed, they can be just as effective and safe as the mesial nrest retainer.

Direct Retainer nSelection

Selection is based on:

1. Position of tooth undercuts, nrestorations, occlusion, classification of edentulous arch, tooth type

2. Nature of the bony and soft ntissue support. Is there an unfavourable:

a) bony undercut

b) frenal attachment

c) vestibular depth

3. Esthetics

Direct Retainer nChoices

– Kennedy Cl III & IV (Tooth nBorne)

–

– – Clasp of choice: cast ncircumferential

– if can’t use cast ncircumferential next to edentulous space, use double embrasure

clasp

– if abutment is severely ntilted use (depending on location of undercut):

! Cast circumferential clasp nwith lingual retention

! Ring clasp with nsupport strut

! Rotational path removable npartial denture

– Kennedy Cl I & II (Tooth n& Tissue Borne)

– For posterior abutments, or nany tooth needing stress release:

– Clasp of choice: RPI n(mesial rest, distal proximal plate and I-bar)

– If can’t use an I-bar ivestibule, because of

! frenum

! shallow vestibule

! deep soft tissue undercut

then use an RPA retainer n(mesial rest, distal proximal plate and wrought wire clasp)

– If can’t use a mesial rest nbecause of:

– rotation

– heavy centric contact omesial

– – large amalgam restoratioon mesial

– then use Combination Clasp n(distal rest, buccal ww retention, lingual bracing)

– for abutments adjacent nmodification spaces (use tooth borne retainers)

– # of direct retainers –, nminimum of 2 posterior abutments for Cl. I & II, all abutments for Cl III, nIV to maximum of 4 normally

– if eliminate a direct nretainer for esthetics, plan more retention with other features (soft tissue ncoverage, longer guiding planes, etc)

Clasp design

Direct retainers may come in various designs:

Cast circumferential clasp (suprabulge)

Akers’

Half and half

Back-action

Ring clasp

Wrought wire clasp

Roach clasp (infrabulge)

I-bar

T-bar

Y-bar

7-bar

Both cast circumferential and wrought wire nclasps are suprabulge clasps, in that they engage an undercut on the tooth by noriginating coronal to the height of contour, while Roach clasps are infrabulge nclasps and engage undercuts by approaching from the gingival.

In addition there are a couple of specific ntheories which include the clasp design:

RPI: mesial rest, distolingual guide plate, nI-bar

Described by Kratochvil in 1963 and modified by nKroll in 1973

An illustration of the RPI design function

RPA: mesial rest, distolingual guide plate, nAkers’ clasp-style retentive arm

RPC: mesial rest, distolingual guide plate, nother type of cast circumferential clasp

So named in response to the RPI Philosophy nintroduced by Kratochvil and Kroll

Direct nRetainers

Direct nretainers

1. Intracoronal nretainers

2. Extracoronal nretainers

–Structure nof clasp assembly

–Requirements nof clasp assembly

–Cast ncircumferential clasp

–Infrabulge nclasp

Indirect retainers

Retainers: any type nof device used for the stabilization or retention of a prosthesis.

Direct retainer: that component of a partial removable ndental prosthesis used to retain and prevent dislodgment, consisting of a clasp nassembly or precision attachment.

Classification of ndirect retainers

Intracoronal

Extracoronal

Clasps

•According to nconstruction

–Cast

–Wrought wire

–Combination

•According to ndesign

–Circumferential

–Bar type

Intracoronal direct retainers

•Introduced by Herman E.S. nChayes in 1906

•Consists of two components

– Matrix (slot)

– Patrix (flange)

Intracoronal direct retainers

Advantages

•Elimination of visible nretention and support system

•Better vertical support

•Better stimulation of nunderlying soft tissues

Disadvantages

•Require prepared abutment and ncastings

•Complicated clinical and lab nprocedures

•Eventually wear

•Difficult to repair and nreplace

•Least effective on short tooth

Retentive nclasp assemblies

Mechanics nof retainer can be understood with two concepts path of insertion

and nremoval, and height of contour

•Prothero’s n“cone theory”

•Share ncommon base referred to as greatest diameter of tooth

•Edward nKennedy termed as “height of contour”

M.M. DeVan terms

•Suprabulge direct retainers

•Infrabulge direct nretainer

Structure nof a clasp assembly

Requirements of a clasp assembly

Retention

Support

Stability

Reciprocation

Encirclement

Passivity

Retention

The nflexibility of the retentive clasp arm may be influenced by

•Length

•cross-sectional nform

•cross-sectional ndiameter

•longitudinal ntaper

•clasp ncurvature, and

•metallurgical ncharacteristics of the alloy

Retentio

Clasp nflexibility increases as clasp length increases

The nmathematical formula for deflection of a uniform cantilever beam. This formula nmay be expressed as:

D= nEwt3

n4PL3

where nD deflection, P = applied force, L = length, E = modulus of elasticity, w =beam nwidth, and t = beam thickness.

Retention

Cross-sectional ndiameter

Longitudinal ntaper

Cross-sectional nform

Metallurgical ncharacteristics of the alloy

•Locatioof each retentive clasp terminus relative to the height of contour

may nbe described in two distinct dimensions: (1) a mediolateral or horizontal dimensioand (2) an occlusal or vertical dimension.

Support

•Support is the quality of a clasp assembly that nresists displacement of a prosthesis in an apical direction.

•Other elements that contact the abutment occlusal to nthe height of contour (e.g., a

reciprocal element or shoulder of retentive clasp) nalso may contribute to the support function.

Stability

•Stability is the quality of a clasp assembly that nresists displacement of prosthesis in a horizontal direction. All framework ncomponents that are rigid and contact vertically oriented hard and soft tissues nmay contribute to the stability of prosthesis.

Reciprocation

•Reciprocatiois the quality of a clasp assembly that counteracts lateral displacement of aabutment when the retentive clasp terminus passes over the height of contour.

Encirclement

Location of retentive clasp terminus

Cast ncircumferential clasp

•Introduced nby Nesbitt in 1916

•Simple nand easy to fabricate

•Tooth nsupported RPD

•Advantages n

•Disadvantages

Desigrules for cast circumferential clasp

•A ncast circumferential clasp should originate from a portion of the framework nthat lies above the height of contour.

•retentive nterminus should be directed occlusally

•should nterminate at the mesial line angle or distal line angle of the abutment

•The nretentive arm should be positioned as farapically on the abutment as is npractical.

Reverse circlet clasp

Multiple circlet clasp

Embrasure clasp

Ring clasp

C-clasp

Onlay clasp

Wrought-wire circumferential clasp

•It nused as early as 1847, the wrought wire circumferential clasp

•I1965, Dr 0. C. Applegate introduced a modified wrought wire clasp assembly nknown as the ‘combination clasp”.

•consists nof an occlusal rest a cast metal reciprocal arm, and a wrought wire retentive narm. The wrought wire component is circular in cross section.

•Kennedy nClass I or Class II posterior edentulous area when the usable undercut is nlocated at the mesiofacial line angle of the most posterior abutment.

•Increased nflexibility hence can be used in the greater undercut area.

•Minimal ntooth surface contact

Infrabulge clasp

•clasp napproaches the undercut region of an abutment from an apical direction. nTherefore an infrabulge clasp exhibits a “push type” of retention that is more neffective than the “pull” retention associated with a suprabulge clasp.

•Flexibility nof the infrabulge clasp is controlled by the taper and length of the approach narm.

•more nesthetic than a suprabulge clasp

Design rules for infrabulge clasp

• The approach arm of an infrabulge clasp must not nimpinge on the soft tissues adjacent to the abutment

• The approach arm should cross perpendicular to the nfree gingival margin

• The approach arm should never be designed to bridge nan area of soft tissue undercut

• uniform tapering

• The clasp terminus should be more apically npositioned on the abutment

Types of infrabulge calsp

These clasps are described by their geometric shapes. nThere are four main types of infrabulge clasp.

•T-clasp,

• the modified T-clasp,