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Impressions in removable

partial dentures

DR. HEMANT SHARMA

Impression : a negative likeness or copy

in reverse of the surface of an object; an

imprint of the teeth and adjacent

structures for use in dentistry

Diagnostic impressions

Permit analysis of contour of hard and soft tissues

Types of restorations on abutment teeth

Determination of need for surgical correction of exostosis, frena, tuberosities and undercuts

Serve as blueprint for placement of restorations, recontouring of teeth and rest seat preparation

Permit analysis of patients occlusion

Adequacy of interarch space

Presence of overerupted, malposed teeth

and tuberosity interference.

Material of choice for diagnostic

impression

Irreversible hydrocolloid (alginate)

Technique for Making

Diagnostic Impressions

1)Position of patient and Dentist

2)Impression Trays

a) selection

b) Checking trays for Correct size

c) Extending impression trays

3)Control of Gagging

4)Control of saliva

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Technique for Making

Diagnostic Impressions

Contd)Manipulation of the impression material

6)Making the Impressions

7)Removal of Impression from the mouth

8)Inspecting the Impression

9)Cleaning the impression

10)Disinfecting the impression

11)Poring the cast

Tray Selection for Diagnostic

Impressions

➢Tray of choice - Rim lock tray because it is rigid- it confines the impression material, helping toforce it into all the areas to be included in theimpression.

➢Perforated trays are rigid, but do not confine thematerial as well as the rim lock tray .

➢Disposable plastic trays - too flexible to ensurethe accuracy of impression and cast that isneeded for removable partial dentures

Extending an Impression Tray

➢ The modeling plastic is softened in a 60° C (140° water bath, kneaded, and adapted to the tray partially removed several times to prevent the locking of the tray into the undercuts.

➢ Frequently an impression tray that has a correct width is too short to cover the entire desired impression area. The impression tray can be lengthened by the use of modeling plastic .

➢ After the modeling plastic has been chilled, it is relieved to provide approximately 5 to 7 mm of clearance & then coated with alginate adhesive

Extending an Impression Tray

Extending an

Impression Tray

Working properties of Alginate

Easy to use and inexpensive

Available as bulk and preweighted quantity

Deteriorates rapidly at high temperature

and humidity

Is contaminated by gypsum

Accuracy not affected by changes in water

to powder ratio

Cont.

Ideal temp of water 22degreeC

Cooler water will provide more working

time

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Storage of impression

Measurable distortion if not poured within

12 minutes

Technique of making alginate

impressions

Position of patient and dentist

Dentist position-standing

Patient position-upright

Occlusal plane parallel to floor

Patients mouth is at same level as dentists

elbow

Stand behind the patient for maxillary

impression

Checking tray

Clearance of 5-7mm between tray and the

ridge

Tray should cover all anatomic landmarks

or can be modified

Gagging

Methods to prevent gagging

Seating patient in upright position

Correcting palatal area with modelling plastic

Not overfilling the tray with alginate

Seating the posterior part first

Patient to keep eyes open during procedure

Use of astringent mothwash and cold water

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Control of saliva

Use of gauze packs

Saliva ejection

15mg propantheline bromide 30min before

procedure

Mixing impression material

Hand spatulation

Mechanical spatulation

Mechanical spatulation under vacuum

Inspecting the impression

Alginate sticking to teeth

Alginate pulling away from tray

Voids

Layered impression

Granular impression

Inadquate extension

Contact between teeth and tray

Problems

Error. Using irreversible hydrocolloid that has beenfrozen, even when it is stored in its original,sealedcontainer.

Problem: Freezing may alter the setting time of thematerial drastically.

Solution: In the winter, when temperatures in some partsof the country are considerably below freezing,irreversible hydrocolloid should be tested before use.

. Error: Using irreversible hydrocolloid that has beenstored in defective packaging or in an unsealedcontainer after being opened for first use.

Problem: Moisture contamination due to water uptakefrom the atmosphere can accelerate or retard the settingtime and cause rapid deterioration of physical andchemical properties of the irreversible hydrocolloid.4

Solution: Test the irreversible hydrocolloid before using it

Solution: Use prepackaged irreversiblehydrocolloid to eliminate this error, even thoughit is more costly than a can of irreversiblehydrocolloid or bulk irreversible hydrocolloid. Ifbulk irreversible hydrocolloid is used, separateand weigh amounts for individual use; then sealeach portion in an airtight container such as aspecimen containers. In addition, use adedicated mixing bowl and spatula only formixing irreversible hydrocolloid. When in doubtabout the deterioration of the irreversiblehydrocolloid, test it before use

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Error: Using a mix of irreversible hydrocolloidthat is too thick.

Problem: A thick mix of irreversible hydrocolloidmay set before it is fully seated in the mouth.When this happens, the irreversible hydrocolloidwill set under pressure. When irreversiblehydrocolloid sets as pressure is applied, it isalways distorted.6

The irreversible hydrocolloid may not flow into theinterproximal spaces between the teeth or pick up theanatomy of the soft tissues. This error may also result inthe creation of drag marks in the impression and on thecast during seating of the impression. The marks will notfill in because the material is too stiff to flow after it isseated.

Solution: Follow the manufacturer's instructions forwater/powder proportions by weight rather than byvolume.

Error: Attempting to control the setting time ofirreversible hydrocolloid by altering thewater/powder ratio.5'6

Problem: If the mixture is thin one time and thickanother time, a standardized procedure cannotbe established for seating the impression tray.The resulting inconsistency can cause unreliableresults, in addition to other problems (see errors9 and 10).

Solution: Control the water temperature to vary the setting time of irreversible hydrocolloid mixes. Always use the manufacturer's recommended water-to-powder ratio. Use water heated to more than room temperature to make the irreversible hydrocolloid set faster; use water chilled to lower than room temperature to increase the working time.7 A 10°F increase or decrease in the water temperature will increase or decrease the working time by approximately 40 seconds.

Error: Failing to adequately mix the irreversiblehydrocolloid.

Problem: If irreversible hydrocolloid is not mixed long orthoroughly enough to completely saturate all of thepowder with water, pockets of dry or partially wetirreversible hydrocolloid can cause distortions.

Solution: Hand mix the irreversible hvdrocoll-oidthoroughly for 60 seconds. Alternately, vacuum mix theirreversible hydrocolloid for 15 seconds with at least 25inches of vacuum

Error: Allowing partially mixed irreversible hydrocolloidfrom around the top of the mixing bowl to beincorporated into the mix as the tray is loaded.

Problem: Dry irreversible hydrocolloid particles absorbwater when the impression is washed. The dry particlesexpand as they get wet and set. If a pocket of dry orpartially wet irreversible hydrocolloid is in contact with atooth or other critical area when the impression is made,dry material will expand after impression is removedfrom mouth and washed, resulting in inaccuracies.5'6

Solution: Make certain that partially mixed or dryirreversible hydrocolloid powder is not incorporated intothe mix for the impression.

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Dr. HEMANT

SHARMA

Introduction

◼ Retention is that quality inherent in the

removable partial denture that resists the vertical

forces of dislodgement for e.g., the force of

gravity, the adhesiveness of foods, or the forces

associated with the opening of the jaws.

◼ A retainer is defined as any type of clasp,

attachment, device etc. used for the fixation,

stabilization or retention of a prosthesis.

◼ Direct retention is the retention obtained in a

removable partial denture by the use of

attachments or direct retainers (clasps) resist the

displacement or removal of the partial denture

from the abutment teeth in a direction opposite

to that of their insertion.

◼ Direct retainer is any unit of removable partial

denture that engages an abutment tooth in such

a manner as to resist displacement of the

prosthesis away from basal seat tissues by

1. Functional means by engaging a tooth

undercut lying cervically to the height of the

contour.

2. Wedge principle.

3. Mechanical means

DEFINITION

According to the Glossary of Prosthodontic Terms, a direct

retainer is that component of a removable partial denture

used to retain and prevent dislodgement, consisting of a

clasp assembly or precision attachment.

Factors affecting the retention in Removable

Partial Dentures:

I. Primary retention : This is mechanical in action.

II. Secondary Retention: Achieved by intimate relationship

of the denture base and the rigid major connector to

the underlying soft tissues.

a. Adhesion

b. Cohesion

c. Atmosphere pressure

d. Molding of tissues

e. Effect of gravity

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1. Clasps which engage undercuts.

2. Acting through the polished surfaces.

3. Coverage of mucosa by the denture.

Classification of direct retainers

◼ Direct Retainers are of two types:

◼ Extra Coronal

◼ Intra Coronal

Extra Coronal Direct Retainers:

Mechanical resistance to displacement.

There are of three types:

a. Manufactured attachment.

Eg. Dalbo, Spring loaded plungers.

b. Flexible clips/Rings.

c. Clasp type retainer.

The flexible area engages a prepared depression are

an undercut area cervical to the area of greatest

convexity of the tooth.

◼ Intra Coronal Retainer:

Regarded as an internal/precision attachment.

◼ Formulated by Dr.Herman.E.S. Chayes in 1906.

◼ Cast/Attached within the tooth structure

◼ Prefabricated

◼ Frictional resistance.

EXTRACORONAL DIRECT RETAINERS

◼ Occlusally approaching / Suprabulge / Ney Type I clasp / Circumferential

◼ Gingivally approaching / Infrabulge/ Bar/ Roach / Ney Type II Clasp

The basic parts of a clasp assembly :

◼ Rest : It is the part of the clasp that lies on the occlusal, lingual or incisal surface of a tooth and resist tissue ward movement of the clasp.

◼ Body of the clasp : It is the part of the clasp that connects the rest and shoulder of the clasp to the minor connector.

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◼ Shoulder : It is the part of

the clasp that connects the

body to the clasp terminals.

It must lie above the height

of contour and provide

some stabilization against

horizontal displacement of

the prosthesis.

◼ Reciprocal arm : A rigid

clasp arm placed above the

height of contour on the side

of the tooth, opposing the

retentive clasp arm.

◼ Retentive arm : It is the

part of the clasp comprising

the shoulder which is not

flexible and is located

above the height of the

contour.

◼ Retentive terminal : It is

the terminal end of the

retentive clasp arm. It is the

only component of the

removable partial denture

that lies on the tooth

surface cervical to the

height of the contour. It

possesses a certain degree

of flexibility and offers the

property of direct retention.

◼ Minor connector : It is

the part of the clasp that

joins the body of the clasp

to the remainder of the

framework and must be

rigid.

◼ Approach arm : It is a

component of the bar

clasp. It is a minor

connector that projects

from the framework, runs

along the mucosa and

turns to cross the gingival

margin of the abutment

tooth to approach the

undercut from a gingival

direction.

PRINCIPLES OF CLASP DESIGN

◼ Encirclement:

More than 1800 of greatest circumference of the

tooth must be included passing from diverging axial

surface to converging axial surface.

This may be in the form of continuous contact when

circumferential clasp arms are used.

Bar clasps are used, at least 3 areas of tooth contact

must be embracing more than ½ the tooth

circumference. These are occlusal rest area, the

retentive terminal area and reciprocal terminal area.

The surveyed cast clasp embraces about 270° of the

abutment tooth. Its parts are : Bracing arm (blue).

Retentive arm (red).

Shoulder and rest (yellow).

Minor connector (green).

◼ Support:

Property of the clasp that resist the displacement of

the clasp in gingival direction.

Primary support units of a clasp are occlusal, lingual

or incisal rest.

The occlusal rest must be designed so that cervical

movement of the clasp arm is prevented.

The rest should provide only vertical support.

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◼ Reciprocation:

◼ Each retentive terminal should be opposed by a

reciprocal arm or element capable of resisting

any orthodontic pressures exerted by the

retentive arm. Reciprocal and stabilizing

elements must be rigidly connected bilaterally.

◼ This arm is positioned on the opposite side of

the tooth from the retentive arm.

◼ In addition to reciprocating stress generated

against the tooth by the retentive clasp, it also

play an important role in stabilizing the denture

against horizontal movement.

◼ Some cases, additional rest is positioned on the

opposite side of the tooth and minor connector

will provide reciprocation.

◼ Reciprocal clasp must be rigid, it is not tapered as

the retentive clasp. Reciprocal arm should be

positioned on the surface of a tooth is reasonally

parallel to the denture’s path of insertion and

removal.

◼ If it is placed on the surface that is tapered

occlusally, a slight movement of denture will cause

the clasp to loose contact with the tooth and

reciprocation and retention is lost.

◼ It must be positioned above the height of contour at

the junction of the gingival and middle 3rd.

◼ To reciprocate the forms properly, it should contact

the tooth at the same time or before the retentive

arm does.

◼ Retention:

The path of escapement of each retentive clasp terminal should be other than

parallel to the path of removal of the prosthesis.

The amount of retention always should be the minimum necessary to resist

reasonable dislodging forces.

Only the terminal third of an

occlusally approaching

clasp (stippled section)

should engage the undercut.

A gingivally approaching claspcontacts the tooth surface only at

its tip.

The retentive clasp is divided into 3 parts; each with its

arm functional requirement. The terminal third is flexible

and engages the undercut.

The middle third has a limit degree of flexibility and

may engage a minimal amount of undercut.

Proximal third, or shoulder, is rigid, and must be

positioned above the height of contour.

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◼ Stability / Bracing:

All 3 clasp have reciprocal or bracing arm, which provides

equal amount of stability.

Stability is the resistance to horizontal displacement of a

prosthesis.

All clasp terminal except the retentive clasp terminals

contribute to this property in varying degree.

Eg: Cast circumferential clasp great amount of stability,

because its shoulder is rigid and it aids in stabilization.

The wrought wire clasp has flexible shoulder

Bar clasp does not have a shoulder so both provide less

stability.

◼ Passivity:

A clasp in place should be completely passive the

retentive function is activated only when dislodging

forces are applied to the partial denture.

◼ Bilateral Opposition:

Unless guide planes will positively control the path

of removal, retentive clasp should be bilateral

opposed. i.e., buccal retention on the other or

lingual on one side opposed by lingual on the other.

In class II situation, the 3rd abutment may have

either buccal or lingual retention.

In class III retention may be either bilaterally or

dimeterically opposed.

◼ Stress Breaking:

Clasp retainers on abutment teeth adjacent to distal

extension bases should be designed so that they will

avoid direct transmission of tipping and rotational

forces on abutments. In effect they must act as

stress breakers either by their design or by their

construction. This is accomplished by proper

location of the retentive terminal or by use of a

more flexible arm is relation to rotation of the

denture under varying direct forces.

◼ Location of components:

The reciprocal element of the clasp assembly should

be located at the junction of the gingival and middle

3rd of the crowns of an abutment teeth. The terminal

end of the retentive arm is placed in the gingival 3rd of

the crown.

Criteria for Clasp Selection

1. Surveyline location and degree of undercut.

2. Requirement of retention and stability depending on

whether upper or lower arch and configuration of

edentulous area or areas; axis of rotation and selection

of retainers.

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SURVEY LINE

◼ Blatterfein in 1951 put forth a simple

and comprehensive classification of

surveyline with suggestion on clasp

selection.

◼ He divided the buccal and lingual

tooth surface into two halves using a

vertical imaginary line through the

long axis of the tooth. These halves

were described as the nearzone and

farzone depending on its closeness to

the edentulous space.

◼ He described four kinds of surveyline:

1. Typical surveyline or medium

2. Atypical A or Diagonal

3. Atypical B or High

4. Atypical C or Low

Typical or medium:

Extends from the occlusogingival midpoint in the

near zone to the junction between the occlusal two

third and cervical one third in the far zone.

Clasps suggested for use where such a survey line

exists include the occlusally approaching and

gingivally approaching clasps.

◼ Atypical A or diagonal:

This runs diagonally across the tooth surface from

a high position in the nearzone to a low position in

the farzone.

- A reverse action or hairpin clasp is

recommended.

- Gingivally approaching clasp may also be used.

◼ Atypical B or High Surveyline:

This type of surveyline is parallel to the occlusal surface and lies

close to it.

A wrought occlusally approaching clasp arm may be used.

If accompanied by a low surveyline on the opposite side of the

tooth, a ring, back action or reverse back action have been

recommended.

◼ Atypical C or Low Surveyline:

The low surveyline is parallel to occlusal surface but has just above

the level of the gingival margin.

This type of surveyline contraindicate the placement of a retentive

clasp arm on the tooth surface concerned, as the arm would need to

be placed too close to the gingival margin for safe application.

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When all the usable surface of a tooth present the

surveylines of this type, retention may be obtained by

1. Placement of a crown on the tooth to artificially

develop undercuts.

2. Placement of a class IV gold inlay – a dimple is in

the inlay and a ball head on a gingivally approach

arm is positioned to engage the dimple.

3. An extended clasp may be used where the tooth

offers favourable conditions for retention.

4. Undercut may be developed by recontouring the

tooth.

◼ Ney: 3 basic surveyline with an appropriate clasp

form.

◼ Class I :

Surveyline runs diagonally across the tooth surface

from a low position on the side of the rest to a

high position on the other proximal side.

A cast occlusally approaching arm or its variants,

back action, reverse back action and ring clasps are

recommended called as Ney class I clasps.

◼ Class II:

Similar to Blatterfein atypical A or Diagonal

surveyline. Here gingivally approaching is

recommended and termed as Ney class II clasp.

◼ Class III:

It is the same as the Blatterfein Atypical B or High

surveyline. The wrought wire arm is used and termed

as the Ney class III clasp.

Selection of clasp based on requirement of

retention & stability

◼ A large number of edentulous area, bilaterally placed would

mean more number of clasps and guide planes, thus the

entire prosthesis has greater retention and stability.

◼ Cast circumferential clasp properly designed shows greater

retentive and bracing properties than a bar clasp used in a

similar situation.

◼ Ideal amount of retention is that which will retain the

removable partial denture against reasonable dislodging

forces without placing the undue strain on the abutment

teeth. Thus minimum retention and maximum stability is the

ideal.

◼ Support:

Selection based on nature of support

whether tooth / tissue or tooth and tissue

borne and length of the edentulous span.

In case of long span – class I situation

preservation of abutment teeth is important,

where a RPI, RPL clasp is used to prevent

torque on the abutment.

◼ Root size and form of the tooth:

Clinical conditions of supporting structures is

alveolar bone and periodontal ligament should be

considered abutment teeth with short, conical roots,

bone loss, and periodontal ligament, mild

periodontal problem may not be able to withstand

lateral forces that would be within physiologic limits

of a healthy sound tooth. Such tooth must be

preserved.

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◼ Oral hygiene and caries:

1. Maintaining oral hygiene is pre requisite to

treatment with cast partial denture.

2. High caries index. Contraindicate the use of clasp

with an unprotected tooth surface as with a ring

clasp.

3. Bar clasp has minimum tooth structure contact

and less interference with natural cleansing action.

Patient education is essential to maintenance of

oral hygiene, proper use of prostheses, its

placement and removal.

◼ Esthetics:

Gingivally approaching claps are generally

preferred for esthetics reason but may be more

unestheics than occlusally approaching clasp if the

patient has a high lip line and exposes the excessive

gingiva.

◼ Presence of excessive tissue undercut:

Gingivally approaching clasp is contraindicate in

the presence of excessive tissue undercut.

Factors affecting retention of a clasp

Size of the angle of cervical convergence

◼ When the surveyor blade contacts a tooth on the

cast at its greatest convexity, a triangle is formed, the

apex of which is at the point of contact of the

surveyor blade with the tooth, and the base is the

area of the cast representing the gingival tissues. The

apical angle is called the angle of cervicalconvergence.

◼ To be retentive a tooth must have an angle ofconvergence cervical to the height of contour.

◼ Guiding planes determine the path of placement andremoval of a partial denture. Therefore without the use ofguide planes, clasp retention will either be determined orpractically non existent.

◼ The guide plane moves down the proximal surface which is

prepared on the distal aspect of the tooth. When thedenture

is fully seated, the plane contacts the lower parts of that

surface.

DEGREE OF UNDERCUT

◼ Relative uniformity of retention will depend on the

location of the retentive part of the clasp arm, which is not

in relation to the height of contour, but in relation to the

angle of cervical convergence.

◼ Retentive clasp arms must be located so that they lie in the

same approximate degree of undercut on each abutment

tooth, despite the variation in the distance below the

height of contour.

◼ The measurement of the degree of undercut by mechanical

means is achieved by the help of an undercut gauge

attached to a dental surveyor.

The retentive force is dictated by tooth shape and by clasp design.

Though clasps 1 and 2 are in an undercut of 0.25mm, 1 offers

more retention than 2.

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Flexibility of clasp arms

Length of the clasp arm : The longer

the clasp arm, the more flexible it is,

all other factors being equal. The

length of a clasp arm is measured from

the point at which a uniform taper

begins.

A Co-Cr clasp arm engaging

the same degree of undercut will have

different flexibility and resistance to

distortion on the molar and the

premolar because of the difference in

length.

Circumferential Bar type

Length

(inches)

Flexibility

(inches)

Length

(inches)

Flexibility

(inches)

0-0.3 0.004 0-0.7 0.004

0.3-0.6 0.008 0.7-0.9 0.008

0.6-0.8 0.012 0.9-1.0 0.012

Diameter of clasp arm

◼ The diameter of a clasp arm is inversely

proportional to its flexibility, all other factors

being equal.

◼ The average diameter to be considered is at a

point midway between its origin and its terminal

end.

◼ The thickness of the clasp arm in the

buccolingual direction is to be considered rather

than the width in the occluso-gingival direction.

Cross-sectional form

◼ Round cross-sectional form enables the clasp to be

flexible in all directions whereas the half-round form

limits the flexibility to only one direction.

◼ Cast clasps are half round in form and they flex away

from the tooth, but edgewise flexing is limited.

◼ If the cross-sectional area of clasp is doubled,

the stiffness will be increased 4 times and the

flexibility reduced 4 times.

Material used for clasp arm :

▪ Type IV gold alloys and cobalt-chrome alloys

which have different modulus of elasticity.

▪ The modulus of elasticity of cobalt-chrome

alloys is greater than that of cast golds, which

have a higher modulus than wrought gold

wires.

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▪ The retentive terminal has to be flexible and therefore have

low modulus of elasticity. The reciprocal elements have to

be stiff and unyielding and have high modulus of elasticity.

▪ Therefore a clasp of the same cross-section is stiffer in

cobalt-chrome than in cast gold. This can be overcome by

using longer clasps of thinner section, and by doing

contour modification so as to reduce the degree of undercut.

Structure of the alloy

◼ The alloy may be cast or wrought in nature. Wrought

wires have greater flexibility than a cast structure due to

its grain structure being fibrous.

◼ The tensile strength of a wrought structure is at least

29% greater than that of the cast alloy from which it was

made.

◼ Wrought forms can be used in smaller diameters to

enhance the flexibility and they offer minimum friction

and can have a stress breaking effect.

Support

◼ Support is the property of the clasp which

enables it to resist displacement in a gingival

direction.

◼ Primary support is obtained by the occlusal or

incisal rest.

◼ Secondary support is obtained by the rigid

components i.e. body and shoulder of the clasp

which are placed above the greatest diameter of

the tooth.

Stabilization or Bracing:

◼ It is the resistance which the clasp contributes to

displacement of the prosthesis in a horizontal plane.

◼ All of the clasp components, with the exception of the

retentive terminal, contribute this property in varying

degrees.

◼ Bracing elements, united by rigid major connector, are

capable of distributing horizontal forces throughout the

partially edentulous arch.

◼ The components of the cast circumferential clasp offer

better stabilization than either the bar clasp or the

wrought wire clasp, because of greater amount of rigidity

of the clasp material.

Reciprocation

◼ Reciprocation may be defined as “the means

by which one part of the appliance is made to

counter the effect created by another part”.

◼ For effective reciprocation clasps should be

planned and designed so that the two arms of

the clasps are in balanced.

RECIPROCATION

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Indirect Retention

◼ The reciprocal arm may behave as an indirect

retainer when it rests occlusal to the height of

contour on the abutment tooth, lying anterior

to the fulcrum line.

◼ Lifting of a distal extension base away from

the tissues is resisted by a rigid arm, which is

not displaced cervically

TYPES OF CLASP RETAINERS

◼ Circumferential clasps/ Occlusally approaching

• Circumferential clasp

• Embrasure clasp.

• Ring clasp.

• Back action clasp.

• Reverse action / hair pin clasp.

• Multiple clasps.

• Half-and-half clasp.

• Combination clasp.

• Onlay clasp.

Bar/Roach clasps / Gingivally

approaching clasps.

◼ T-clasp

◼ Modified T-clasp

◼ Y-clasp

◼ I-clasp

◼ RPI concept.

Other clasp designs

▪ RPA clasp.

▪ VRHR clasp.

▪ Clasps utilizing proximal undercuts

-Mesiodistal clasp

-Devan clasp.

▪ Movable arm clasp.

▪ Cingulum clasp

CIRCUMFERENTIAL CLASP

◼ Although a thorough knowledge of the principles of clasp

design lead to the logical application of those principles. It is

better to understand some of the more common clasp

design individually.

◼ The clasp is usually the most logical drip to use with all

tooth borne partial denture. Beam of its retentive and

stabilizing ability.

◼ Basic forces of the clasp is a buccal and lingual arm

originating from a common body.Circumferential clasp on a molar

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Advantages:

1) The clasp fulfills the requirement of support,

stability reciprocation, encirclement & passivity

better than any other type of clasp.

2) It is easy to construct.

3) It is simple to repair.

Disadvantages:

1. It tends to increase the circumference of the crown.

2. In is not acceptable in the anterior region.

3. It covers more tooth surface then the bar clasp and prone to

caries.

4. Retentive undercuts on some teeth are difficult to reach with

retentive terminal of the clasp

EMBRASSURE CLASP

◼ Bonwill clasp

◼ Rib clasp

◼ Double a

◼ Back to back clasp

◼ This clasp is essentially two single circlet clasps

joined at the body.

Embrasure clasp on a maxillary premolar and

molar

▪ Kennedy class II, III, IV cases where no

edentulous space on opposite side of the arch

sufficient space must be provided between the

abutment teeth in their occlusal third to make

room for the body of embrasure clasp.

▪ Contact area should not be eliminated

completely.

◼ Abutment tooth should be protected with crowns or inlays

if necessary. This depends upon the age of the patient caries

index and oral hygiene.

◼ This clasp should be used with double occlusal rest.

◼ Proximal shoulder be established. To avoid interproximal

wedging by the prosthesis.

◼ This clasp should have two retentive clasp arms and two

reciprocal arms either bilaterally or diagonally opposed.

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◼ An auxillary rest or a bar clasp arm can be

substituted for a circumferential reciprocal arm as

long as definite reciprocation and stabilization is

achieved.

Contra indication:

1. Short and bulboss crown.

2. Not preferred in teeth with more undercuts.

Disadvantages:

◼ Needs adequate cleaness in occlusal surface.

◼ Breakage of inadequate preparation and clearance

◼ Wedging action.

RING CLASP

◼ Indication:

1. In tilted molar :

2. Single standing tooth

Unsupported mandibular molar tend to drift and tip in a

mesiolingual direction.

Maxillary molar tip is a mesio buccal direction. So qvileble

retentive undercut will be located on the mesiolingual line

angles of a mandibular molar and the mesiobuccal line angle

of maxillary molar.

◼ This ring clasp permits engagement of this undercut by

encircling almost the entire tooth from its point of origin.

◼ Mandibular molar, clasp encircles the tooth beginning on

the mesiobuccal surface and terminating in an infra bulge

area on the mesiolingual surface.

◼ Because of the length of the clasp, it must be designed with

additional support, usually in the form of an auxillary bracing

arm.

In mandible, bracing arm usually extends from the acrylic

resin retention metal, run across the mucosa and turns

upward to engage the buccal arm of the ring clasp near the

center of the buccal surface.

◼ This can provide reciprocation and some amount of

stability for the denture.

◼ The entire clasp except the retentive terminal shall be

placed above the height of the contour.

◼ An additional occlusal rest can be placed may provide

additional support and prevent mesial migration of tooth.

◼ Contra indication:

1. In mandibular molar, where the attachment of

buccinator muscle is so close to the tooth, that

the auxillary bracing arm encroaches on it.

2. When the bracing arm must cross the soft

tissue undercut.

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14

◼ Advantages:

1. Excellent bracing

2. Decreased leverage

3. Less stress to abutment teeth.

◼ Disadvantages:

1. Needs long crown and enough occlusal clearance.

2. Difficult to repair.

REVERSE ACTION CLASP OR HAIR PIN

◼ This clasp is essentially a simple circlet clasp in which the

retentive arm after crossing the facial surface of the tooth

from its point of origin. Loops back in a hairpin turn to

engage a proximal undercut below its point of origin.

◼ The upper part of the retentive arm must be considered to

be minor connector and should be rigid.

◼ The lower part of the clasp arm should be tapered. It is the

only flexible part of the clasp arm.

◼ The crown of the abutment tooth must have

sufficient occlusogingival height to accommodate

this double width of the clasp arm.

◼ The upper and lower arms of the retentive clasp

must also be shaped in such a way that food debris

will not be retained between them.

◼ And there must be enough space between the arms

so that the metal may be adequately finished and

polished.

◼ Indication:

1. Distal extension partial denture.

2. Mesially inclined posterior.

3. Undercut addition to the edentulous area.

4. If proximal undercut must be used on a posterior

abutment and when the tissue undercut or high tissue

attachment prevent the use of bar clasp arm, the reverse

action clasp may be preferable.

5. If lingual undercut in present which prevent the

placement of a supporting strut without tongue

interference hairpin clasp is indicated.

◼ Contra Indication:

1. Tight occlusal contact, increase posterior overbite short

crown,

2. Clasp cover considerable tooth surface and may trap

debris.

◼ Advantages:

◼ Easier to construct

◼ Adjust

◼ Disadvantages:

◼ Food trapment

◼ Esthetics

◼ Caries

◼ Multiple clasp is two opposing simple circlet clasp joined

at the terminal end of the two reciprocal arms.

MULTIPLE CLASP

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15

MULTIPLE CLASP

Indication:

1. When additional retention is needed.

2. Tooth borne partial denture

3. Multiple clasping required, when the partial

denture replaces an entire half of the dental arch.

4. When the principal abutment tooth it periodontal

support can be used in the form of splinting

tooth.

◼ Advantages:

1. Less metal display

2. Less tooth coverage

3. Leaves room for the mesial portion of the denture base

to a larger extent than it would be otherwise.

4. It braces the abutment on the mesial even if the tooth is

tipped distally.

5. Marginal gingiva can be left uncovered of the abutment

teeth for better partial denture health.

◼ Advantages:

1. It provides additional support for the weakened

premolar.

2. Use of adjacent retentive arm on approximately teeth.

Half-and-half clasp

◼ This clasp consists of a circumferential retention arm

arising from one direction and a reciprocal arm arising

from another minor connector.

◼ This design provides retention , a principle that

should be applied only to a unilateral denture design.

◼ The buccal arm provides for bracing only.

◼ The lingual arm utilizes an undercut adjacent to the

edentulous space for retention.

◼ Indication:

• Lingually inclined premolars where lingual undercut are

close to the edentulous space.

◼ Contra indication:

• Buccal inclined premolars –

If it is used for distal extension RPD a distal rest

should be placed. Mesial rest also can be used in

conjunction with the distal rest.

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16

BACK ACTION CLASP

◼ It is a modification of the ring clasp.

◼ It has a rest which is connected to a rigid minor connector.

Indication:

For unilateral and bilateral distal extension partial denture.

Combination clasp

• This type of clasp consists of a wrought wire retentive clasp

arm and a cast reciprocal clasp arm.

• The retentive arm is usually occlusally approaching, but it may

also be used from a gingivally approaching direction.

Uses:

◼ It is used on abutment tooth adjacent to a distal

extension base where only a mesiogingival undercut

exists on the abutment or where a large tissue

undercut contraindicates a bar type retainer.

◼ The tapered wrought wire retentive arm offers

greater flexibility than does the cast clasp arm and

therefore better dissipates functional stresses.

Advantages

◼ Flexibility on account of fibrous grain structure of the

wrought wire retentive arm.

◼ Adjustability : It can be adjusted later to increase or decrease

the retention without danger of breakage.

◼ Esthetic appearance since it is used in smaller diameters of

round cross-section.

▪ A minimum of tooth surface is covered because of its line

contact with the tooth, rather than a surface contact of a

cast clasp arm.

▪ Fatigue failures in service are less likely to occur with the

tapered wrought wire retentive arm.

Disadvantages

◼ It involves extra steps in fabrication, particularly

when high fusing chromium alloys are used.

◼ It may be distorted by careless handling on the part

of the patient.

◼ Since it is bent by hand, it may be less accurately

adapted and therefore provide less stabilization

above the height of contour.

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17

EXTENDED CLASP ARM

◼ It is similar to the circumferential arm but it covers two

teeth. It remains above the surveyline of the 1st tooth;

crosses the undercut of the adjacent tooth. It is rarely

used direct retainer.

Indications:

• Tooth supported RPD.

• Tooth next to edentulous space has no buccal and lingual

undercut.

• The occlusion in the embrasure area will not allow passage

of the clasp arm to an undercut on the second tooth from

the edentulous space.

• The second tooth from edentulous space has a buccal

undercut available.

◼ Contra Indication:

1. Distal extension dentures because the retentive

lies forward of the axis rotation. Functional

forces will cause rotation around the rest and

upward movement of clasp tip.

◼ Advantages:

1. It has splinting and stabilization action.

2. Distribution of lateral loads over two teeth.

◼ Disadvantages:

1. Tooth structure covered.

2. Easily distorts.

3. Breakage of the arm.

4. If made in gold limited o 2 premolar

in Cr. Ch – longer arm can be used.

- 2 molars can be clasped.

MESIODISTAL CLASP

◼ Used to clasp canine and central only if little undercut on

buccal surface.

Disadvantage:

◼ Metal displaces alloy made of gold.

If diastema between the lateral incisor and canine, then

the space provides a accommodation for the mesial part

of the clasp otherwise space reaction with safe side disc,

contact point with L.I. is returned when clasp an

position. It is similar to inlay.

ONLAY CLASP

1. Extends from an occlusal onlay into an undercut

located mesio distally.

2. This clasp is an extended occlusal rest with buccal and

lingual clasp arms.

3. This clasp may originate from any point on the onlay

that will not create any occlusal interference.

4. If the onlay is prepared with chrome cobalt alloy, and

is opposed by natural teeth, the occlusal surface should

be constructed of acrylic resin or gold, if you use

chrome alloy, because of its extreme hardness will

cause rapid wear of enamel

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18

Indications:

1. When the occlusal surface of the abutment tooth is the

occlusal plane mesially tilted rotated tooth molar.

2. Only in caries resistant mouth unless it is covered by

gold crown.

◼ Advantages:

1. Mesially tilted molars to be used to provide retention.

2. 3rd molar occlusion may be improved.

◼ Disadvantages:

1. Difficult to fir clasp to tooth.

2. Increased contact area, accurate impression and the

resultant cast is difficult to achieve.

DEVAN CLASP

◼ Uses proximal undercut and has a small head that bears

on tooth entirely below survey line.

◼ Clasp arises and lies closely against at the periphery of

the denture base.

◼ Denture base is under extended to provide room for

the approaching arm.

◼ It is reciprocated with lingual and palatal strut.

◼ It gives little bracing effect.

Devan clasp

◼ Advantages:

1. Esthetically acceptable, became of interproximal

location, or it is hidden behind the buccal concavity.

2. The distribution of stress during insertion and

removal is minimal.

3. Increased retention without tipping action on the

abutment.

4. Less chance of accidental deformation because it

doesn’t project very far away from the denture base.

GINGIVALLY APPROACHING CLASPS

◼ Infra Bulge

◼ Push Clasp

◼ Roach Clasp

◼ This bar clasp approaches the retentive undercut in a

gingival direction resulting in a push type of retention.

This push type of retention is more effective than pull

type retention characteristic of circumferential clasp.-

tripping action.

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19

◼ This clasp is termed by F.E.

Roach in 1930 and hence

the name Roach clasp.

◼ The bar clasp is classified by

shape of the retentive

terminal T, modified T, I, Y

forms, all of which originate

from the denture base frame

work and approaches the

undercut from gingival

direction.

◼ Advantages:

1. Minimal tooth contact and minimal distortion of

normal tooth contours, leading to improved tissue

stimulation and oral hygiene and caries and

periodontal problems.

2. Improved esthetics if the approach portion of the arm

is not visible as it crosses the gingiva.

3. Increased retention became of tripping action.

4. Decreased torquing forces applied to terminal

abutments in extension RPDs.

5. Large undercut can be engaged.

◼ Disadvantages:

1. Cannot be used in the presence of soft tissue undercuts

shallow vestibule. And high frenum attachments.

2. Bracing action provided by bar clasp is considerable less

than that provided by cast circumferential clasps.

3. The bar clasp will not totally disengage in certain distal

extension cases.

4. Appearance may be adversely affected if he smile line high

enough to expose the approach arm as it crosses the

gingiva

5. Food trapment.

6. Difficult to fabricate and adjust.

◼ Indication:

1. Class I and Class II distal extension partial dentures to

engage the distobuccal undercut on abutment, It can be

employed on canines and sometimes even on molars.

2. Where the anterior retention is needed: It is often used

on distobuccal surface of maxillary canines and

mandibular premolar as the retentive arm can be hidden

from the vision.Esthetically this clasp is superior to

circumferential clasp it is inferior in providing stability

because of greater flexibility of the retentive arm.

◼ Guidelines for use:

1. The approach arm of the bar clasp must not impinge on

the soft tissue. It is not desirable to provide an area of

relief under the arm.s But the tissue side of the approach

arm should be smoothed and polished.

2. Minor connector that attaches the occlusal rest to the

frame work should be strong and rigid. To provide some

bracing.

3. The approach arm must always be tapered uniformily

from its attachment at the framework to the clasp

terminal.

4. The approach arm positioned over a soft tissue

undercut will collect food and irritates lips or cheeks.

5. The approach arm should cross the gingival margin

at a 90 degree angle.

6. The bar retentive clasp is used only when the

retentive undercut is adjacent to the edentulous

from which the approach arm originate.

The approach arm must extend on the abutment

tooth to the height of contour.

The retentive terminal leaves the approach at that

point and extends into the undercut area.

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20

◼ The other terminal which is away from edentulous area

is positioned above the height of contour.

◼ The retentive terminal tip must point towards the

occlusal surface never towards the gingiva.

◼ The bar clasp should be placed as low as on the tooth

as possible while engaging the height of contour to

reduce the leverage induced stress to the abutment

tooth.

TYPES OF BAR CLASP

◼ T Clasp

◼ Modified T Clasp

◼ Y clasp

◼ I clasp

T-Clasp:

• Used in combination with cast circumferential reciprocal arm.

• The retentive terminal and its opposing encircling finger

projects laterally from the approach arm to form T.

• The retentive terminal must cross under the height of contour

to engage the retentive undercut, while the other finger of the

T stays on the suprabulge of the tooth.

• The approach arm should taper gradually and uniformly

from its origin to the retentive terminal.

• The approach arm contacts the tooth only at the height

of contour.

◼ Indication:

- Most frequently used is distal extension ridge where the

usable undercuts is on the distobuccal surface of the

terminal abutment tooth.

- It can also be used for tooth supported partial denture

when the retentive undercut is located on the abutment

tooth adjacent to the edentulous space.

◼ Contra Indication:

- Should not be used on a terminal abutment adjacent to a

distal extension base if the usable undercut is located on

the side of the tooth away from the edentulous space.

- The T clasp can never be used if the approach arm is in

the soft tissue undercut.

- This clasp cannot be used when the height contour is a

large space will be created between the approach arm of

the clasp and the tooth, which would result in irritation of

the lips or cheeks and in trapping food debris.

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21

MODIFIED T-CLASP

◼ It is a T clasp with the non retentive (mesial) finger of

the cross bar of the T terminal is omitted.

◼ Indication:

- Used on canines or premolar for esthetic reasons.

- When we use this type of a clasp the encirclement of

the abutment tooth is sacrificed.

Y-CLASP

◼ It is basically a T-clasp, its configuration occurs when the

height of contour on the facial surface of the abutment

tooth is high on mesial and distal line angles but low on

the center of the facial surface.

I-CLASP

◼ Used on distobuccal surface of maxillary canine for

esthetic reason.

◼ Disadvantage:

- The contact of the retentive clasp with the abutment tooth

is the tip of the clasp an area of 2-3 mm. Encirclement

horizontal stabilization may be compromised.

RPI System (Rest, Proximal plate, I-bar)

Kratochvil in 1963 developed the early clasp assembly which

consisted of three separate units connected to each other

only through the framework. They were the mesial occlusal

rest, a distal guide plane and an I-bar retainer. He preferred a

full length guide plane that is subsequently relieved in the

mouth to prevent torque or binding.

◼ His purposes were:

◼ Elimination of the V-shaped food trap distal to

the tooth.

◼ A highly polished metal contact with the marginal

gingiva, rather than resin .

◼ Intimate metal-to-tooth contact to minimize

food impaction

◼ This design had certain basic disadvantages:

◼ Physiologic relief was required to prevent

impingement of gingival tissues during function.

◼ Since the proximal plate covers a greater surface

area of the tooth, the functional forces are

directed in the horizontal direction, thus the tooth

is located more than the edentulous ridge.

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22

◼ Krol in 1973 made certain modifications in the design of

the proximal plate and named it the RPI bar clasp

design.

◼ He had a 2-3mm of contact of the tooth with the guide

plane, the section below this point being relieved and he

felt that the V shaped space that is left underneath was

not as detrimental as the possible restriction of rotation.

◼ This design however, leaves a region occlusal to the

proximal plate where contact between the abutment and

denture must be made by the replacement tooth.

BASIC PRINCIPLES OF RPI CONCEPT

◼ The mesiobuccal rest with the minor connector is placed

into the mesiolingual embrasure, but not contacting the

adjacent tooth.

◼ A distal guiding plane, extending from the marginal ridge

to the junction of the middle and gingival thirds of the

abutment tooth, is prepared to receive a proximal plate.

▪ The buccolingual width of the guiding plane is

determined by

the proximal contour of the tooth.

▪ The proximal plate in conjunction with the mesial

occlusal

rest and minor connector provides the stabilizing and

reciprocal aspects of the clasp assembly.

◼ The I-bar contributes to the retentive aspect and

should be located in the gingival third of the buccal

or labial surface of the abutment in 0.01 inch

undercut.

◼ The whole arm of the I-bar should be tapered to its

terminus, with no more than 2mm of its tip

contacting the abutment.

◼ The approach arm must be located at least 4mm from

the gingival margin and even more if possible.

OTHER CLASP DESIGNS

RPA clasps

◼ The rest-proximal plate-Aker’s clasp was

developed and described by Eliason in 1983. It

consists of a mesial occlusal rest, proximal plate

and a circumferential clasp arm, which arises

from the superior portion of the proximal plate

and extends around the tooth to engage the

mesial undercut.

VRHR Clasp

◼ The vertical reciprocal horizontal retentive arm concept

was developed by Grasso in 1980 and is characterized by:

◼ A distal occlusal rest supported by a minor connector.

◼ A lingual vertical reciprocal component originating

from the major connector.

◼ A horizontal retentive arm attached to either the

major connector or the retention latticework for the

denture base.

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23

Cingulum clasp

◼ Miller in 1972 designed a clasp to satisfy both the

mechanical and esthetic requirements without the

shortcomings of the internal attachment.

◼ The cingulum clasp has 2 lingual clasp arms. The use

of this clasp requires that the lingual surface of the

abutment tooth be covered with a gold casting.

◼ A guiding plane is incorporated into the distal surface

of the crown and the clasp is designed as an integral

part of the rigid metal framework.

Advantages◼ Esthetic

◼ A tooth of short clinical crown can be used.

◼ The young pulp is not imperiled by close proximity to metal which shows thermal conduction.

◼ Less expensive.

Disadvantages▪ The clasp arms are vulnerable to breakage.

Use▪ The cingulum clasp can be used as a retainer on cuspid

teeth when other extracoronal retainers are esthetically unacceptable

Occlusally and gingivally approaching clasps:

Relative merits and demerits

Retention : The bar clasp approaches the undercut

from below the height of contour and to resist

dislodgement, the clasp pushes towards the occlusal

surface of the abutment tooth. The circumferential

clasp engages the retentive undercut from above the

height of contour and pulls towards the occlusal

surface from the undercut to resist dislodgement.

◼ Bracing : The circumferential clasp is rigid in the

upper two-thirds of the retentive arm and offers

some bracing or stabilization against lateral stresses.

On the other hand, the bar clasp is flexible

throughout its length and does not contribute to

stability.

◼ Stress breaking effect : The gingivally approaching

clasp allows a certain degree of functional movement

of the distal extension base which helps to dissipate

the stresses and lessen the load on the abutment.

Occlusally approaching clasps have the potential to

torque abutment teeth in distal extension based partial

denture situations.

◼ Contact with tooth structure : The gingivally

approaching clasp contacts minimum tooth structure

and has a minimum interference with natural tooth

contour permitting maximum natural cleansing action,

whereas the occlusally approaching clasps covers more

of tooth structure. This occlusal approach may increase

the width of the occlusal table.

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24

◼ Damage to oral tissues : The area of food

lodgement is at the neck of the tooth, with the cementum

in this area being more likely to be affected by caries than

enamel. Trauma to the gingiva can also occur with bar

claps unless sufficiently relieved. Mishandling of the

clasps by the patients during removal of the prosthesis

can result in deformation of the clasp and damage to soft

tissues.

◼ Esthetics : Gingivally approaching clasps are more

esthetic than occlusally approaching clasps except in

instances where large amounts of gingiva is visible

on smiling.

Relative merits & demerits of

cast and wrought wire clasps

◼ Flexibility : The wrought wire clasp has a high degree of

flexibility which helps to better dissipate functional stress

and give a stress breaking effect.

◼ Adjustability : The wrought clasp is adjustable to the

required retention.

◼ Toughness and resiliency : The fabricating process

imparts to the wrought wire a fibrous structure which

accounts for its toughness and resiliency.

◼ Stabilization : The cast clasp on account of

rigid crystalline structure offers better stability.

◼ Cost : Cast clasp requires less cost as soldering

is not required

◼ Fit : The adaptation of a cast clasp to the

abutment tooth is accurate and not subject to

variation by the clinician’s adjustment as with

wrought wire clasps.

◼ Strength and durability : A solder joint near

the origin of a wrought wire clasp reduces its

flexibility and increases the likelihood of

breakage.

◼ Apart from these, cast clasps can be formed to

act as a bracing element, can easily include an

occlusal rest and be cast as an integral part of

gold alloy or a cobalt-chrome denture base.

INTRACORONAL RETAINERS

◼ The intracoronal retainer is usually regarded as an internal

attachment or precision attachment.

◼ The Glossary of Prosthodontic Terms defines precision

attachment as:

“A retainer consisting of a metal receptacle

(matrix) and a closely fitting part (patrix); the matrix is

usually contained within the normal or expanded

contours of the crown on the abutment tooth and the

patrix is attached to a pontic or the removable partial

denture framework.”

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25

As a direct retainer it must provide :

▪ Support

▪ Retention

▪ Reciprocation

▪ Stabilization

▪ Fixation

The precision attachment is the only type of intracoronal

attachment that provides for all three functions of a

removable partial denture system.

▪ Lateral force transmission or bracing from the parallel

proximal walls of the rest against the rest seat.

▪ Occlusal force transmission or support from the flat

gingival floor of the result on the rest seat.

▪ Primary retention from the frictional fit between the rest

and rest seat.

Advantages of intra coronal retainers:

1. Esthetically acceptable, because not much of metal display

like extracoronal retainers.

2. It is preferred in many of the situation because of its

vertical support through a rest seat located more

favourable to the horizontal axis of the abutment tooth.

3. Horizontal stabilization to some extent. Similar

to internal rest, but extracoronal stabilization is

needed.

4. Stimulation to the underlying tissues greater

when internal attachment are used because of

the intermittent vertical massage.

Disadvantages of intra coronal retainers:

1. They require preparation of abutment tooth and

casting.

2. Difficult clinical and laboratory procedure.

3. They eventually wear, result in loss of frictional

resistance to denture removal.

4. Difficult to repair and replace.

5. They are effective in longer teeth and least

effective in shorter teeth.

6. Difficult to place completely in the abutment

teeth.

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26

Limitations of intra coronal retainers:

1. Large pulp size which is usually related to the age of

patient.

2. Length of the clinical crown, not used in short or abraded

teeth.

3. Expensive

4. Distal extension denture bases.

Classification

Classification by Good Kind and Baker in 1976 :

1)Intra coronal

a. resilient

b. non resilient

2) Extra coronal

a. resilient

b. non resilient

Gerardo Becerra et al in 1987 classified precision attachments

as :

1) Intra coronal attachments

a. Frictional

- tapered and parallel walled boxes and tubes

- adjustable metal plates

- springs

- studs

- locks

b. Magnets

2) Extra coronal attachments

a. Cantilever attachments

- rigid attachments

- movable attachments

b. Bar attachments

Tapered And Parallel Walled Boxes And Tubes

◼ Designed to be used in FPD.

◼ Plastic pre fabricated patterns.

◼ Provides vertical support and lateral stabilization.

◼ Simple pin and tube or rectangular block and boxes.

E.g. : Mc Collum attachments.

McCOLLUM ATTACHMENTS

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27

Adjustable Metal Plates

◼ Similar to block and box variety .

◼ Provided with a narrow slit in the metal block or male portion of

the attachment to increase the friction.

◼ Provides a simple and effective form of direct retention.

◼ Atleast 2.5 mm of tooth height is required.

◼ E.g.: Crismani attachment.

Mc Collum attachment.

Stern attachment

Chayes or Rley attachment.

CHEYES

ATTACHMENT

CRISMANI

ATTACHMENT

Springs

◼ Incorporated in the male part to control the friction.

◼ Spring activates a plunger rod which protrudes from

male part to engage a depression in the female part.

◼ Approximately 4 – 5 mm of vertical height is required.

◼ E.g.: Schatzmann attachment.

SCHATZMANN ATTACHMENT

Studs

◼ A metallic stud can be soldered to post and core and

cemented into an abutment.

◼ Direct retention can be obtained by using a stud which

clips into an flexible ring.

◼ Sufficient clearance is required to arrange the artificial

teeth.

◼ E.g.: Ceka attachment

Rotherman attachment

Ceka attachment

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28

Locks

◼ These lock rigidly into the attachments .

◼ The vertical height required for this attachment is

atleast 6 mm.

◼ Retained with pins or incorporated in post and core .

◼ E.g.: T - block attachment

T-ATTACHMENT

Magnets

◼ Small metal keeper is attached to the tooth surface,

usually into the root canal and magnet is incorporated

into the resin.

◼ Alloy in the magnet produces a magnetic force that is

strong .

◼ Magnets are brittle and corrode unless protected in a

stainless steel shelf.

Cantilever attachments

◼ Rigid attachments

They are pin and tube joints that use a slit in the pin or

multiple pin tubes and slots to enhance retentive

friction between the parts with the natural teeth on the

either side of the edentulous space.

These attachments offer excellent stability and

retention in tooth supported partial dentures.

e.g.: Scott attachment

Thompson dowel rest system.

◼ Movable attachments.

◼ These allow the prosthesis to rotate around a horizontal

axis and transmit occlusal forces to the residual alveolar

ridge .

◼ E.g.: Dolbo attachments

Bar attachments

◼ These can be connected to

the cast metal crowns or

copings .

◼ Custom made bars can be

cast with a flat upper surface

to support the prosthesis

and parallel sides that help to

stabilize it.

E.g.: Dolder bar.

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29

Precision attachment selection

◼ Kennedy’s class III partially edentulous arch.

• Rigid internal attachments are recommended .

• Provides good retention, support and brazing because of

its rigid interlocking components.

• If the posterior abutment prognosis is questionable then a

resilient type of attachments are recommended with

anterior abutment.

Kennedy’s class I and class II partially

edentulous arches

◼ The most difficult type of treatment plan.

◼ Some practitioners advocate non rigid and

resilient attachments and some advocate resilient

attachment in distal extension to minimize

rotation and torquing of the abutment tooth,

when the components of an attachment are

rigidly connected.

◼ Another philosophy , known as the stable base

precison attachment RPD concept or floating

denture base concept recommends

incorporation of rigid internal attachments and a

cast metal base made from mucostatic

impression of the residual ridge. The male

portion of the attachment is connected to the

denture base , allowing the complete seating

within the abutment.

◼ The hinged or directionally oriented attachment such as

the Dolbo attachments are recommended to provide

additional bearing or resistance to lateral movement

when the residual ridge is severely resorbed.

◼ The Ceka attachments can be used successfully where

the ridges are not parallel to one another .

Kennedy’s class IV partially edentulous arch

◼ The ideal RPD design for such situation involves the

use of a tissue bar placed close to the edentulous ridge

and connected as a fixed unit to the abutment teeth on

either side of the space using crowns.

SUMMARY & CONCLUSIONS

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30

BIBLIOGRAPHY

◼ Applegate O.C. : Text book of Removable Partial

Prosthodontics, St. Louis, CV Mosby Co.

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