Direct retainer. (Part I & II)PRESENTED BY:

DR. TUSHAR BHAGAT

Content

Direct retainer role in prosthesis movement control

1)Intra-coronal direct retainers

2)Extra-coronal direct retainers

i) Basic requirements of clasps

ii) Factors that determine the amount of retention provided by a particular clasp arm

iii) Classification of extra-coronal direct retainers

iv) Suprabulge Direct Retainers

i) Types of suprabulge direct retainers

ii) Indications

2

Direct retainer (DR) role in prosthesis

movement control

In FPD retention gain by preparation geometry,

luting agent;

In RPD retention is gain by direct retainer, denture

base;

3

Ref: McCraken’s Removable partial prosthodontics. P.no.79

Introduction

A removable partial denture (RPD) include

components that prevents displacement of

prosthesis from patients mouth during function.

And that component engaging abutment

tooth & resists dislodging forces is

direct retainer (DR).

4

Definition of DR

Is that component, used to retained & prevent

dislodgement, consisting of clasp assembly or

precession attachment. GPT-8

5

Classification of DR 6

Ref: 1) Stewart’s. Page.no.52. 2) McCraken. P.no.80

Direct retainer

Intracoronal Extracoronal

Precision

attachment

Retentive

clasp

Semiprecision

attachment

Attachment

Suprabulge

Infrabulge

Intracoronal direct retainer

This principle was first formulated by

Dr.Herman E.S. Chayes in1906.

7

Matrix

Patrix

Intracoronal direct retainer 8

Precision

attachment

Semiprecision

attachment

Intracoronal

direct retainer

Precision AttachmentIntracoronal direct retainer

Patrix & Matrix type of attachment.

It resides within the normal contours

of an abutment & functions to retain &

stabilize a RPD.

9

Matrix

Patrix

Precision Attachment Intracoronal direct

retainer

Matrix is metal receptacle contained within

the normal clinical contour of fixed

restoration.

Patrix is a type of attachment to the

corresponding RPD.

10

Matrix

Patrix

Semiprecision AttachmentIntracoronal direct retainer

Less intimate fit between matrix & patrix component.

11

Advantages of Intracoronal direct retainer

12

1. Elimination of visibility

2. Better vertical support

3. Horizontal stabilization

4. Better stimulation of underlying tissues

because of intermittent vertical massage

Disadvantages of Intracoronal direct retainer

13

1. Require prepared abutments and castings

2. They eventually wear with progressive loss of frictional resistance to denture removal.

3. Difficult to repair and replace

4. Complicated clinical and laboratory procedures

5. Difficult to place completely within the circumference of tooth

6. Expensive

Limitations of Intracoronal direct retainer

14

1. Size of the pulp

2. Short or abraded teeth

3. Not to be used in extensive tissue

supported distal extension cases unless

some form of stress breaker is used.

Extra coronal direct retainer

15

Extracoronal direct retainer 16

It consists of components that reside

entirely outside the normal clinical

contours of the abutment.

They serve to retain & stabilize RPD.

Extracoronal DR subcategories as 17

1. Extracoronal attachments

• Introduced by Henry R. Boos, in early 1900

• Derives retention from matrices & patrices.

• Provides vertical movement of RPD

2. Retentive clasp assemblies

• Common method for retention of RPD.

• Metal clasp arm with limited amount of flexibility.

Prothero’s Cone theory 18

In 1916 – Prothero’s Advanced

Cone Theory was introduced by

M. M. DeVan, which is the basis

of clasp retention.

According to theory, the tooth is

considered as a pair of cones

sharing a common base.

Prothero’s Cone theory 19

Prothero’s Cone Theory

introduced the term;

SUPRABULGE

INFRABULGE

INFRABULGE

Or

Undercut

SUPRABULGE

SUPRABULGE

INFRABULGE

Height

of contour

Categories of retentive clasps 20

Circumferential or Suprabuldge direct

retainers.

Vertical projection, bar type, or Infrabuldge

direct retainers.

Direct Retainers. - II

Circumferential or Akers Clasp or

Suprabuldge direct retainers.

22

Structure of clasp assembly 23

A properly designed clasp

assembly has following parts;

A rest (R)

A retentive arm (RA)

A reciprocal element (RE)

One or more minor connector (M)

(R)

minor

connector

(RA)

(RE)

Structure of clasp assembly 24

1. A rest (R): provides vertical support.

2. A retentive arm (RA): only portion of

to reach in undercut area. Retentive

arm are of two types

Suprabuldge Arm &

Infrabuldge Arm

(R)

Suprabuldge Arm

Infrabuldge Arm

(RA)

Structure of clasp assembly 25

3. A reciprocal element (RE): that

braces an abutment during

prosthesis insertion & removal.

4. One or more minor connector

(M): connecting the parts of

direct retainer to major

connector.

(R)

minor connector

Bracing arm

Retentive arm

RE

RA(M):

M

M

Requirement of clasp assembly 26

1) Retention

2) Support

3) Stability

4) Reciprocation

5) Encirclement

6) Passivity

(R)

Requirement of clasp assembly;

1) Retention27

Provide retention for the prosthesis.

Retention depends on:

a. Flexibility of clasp arm.

b. Depth that retentive terminal extends into the undercut.

c. Amount of clasp arm that extends below height of

contour.

Requirement of clasp assembly;

1) Retention28

a. Flexibility of clasp arm:

i. Length of clasp arm

ii. Diameter of clasp arm.

iii. Taper of clasp arm.

iv. Cross-sectional form of the clasp arm.

v. Material from which clasp is made.

Requirement of clasp assembly;

1) Retention29

a. Flexibility of clasp arm:

i. Length of clasp arm

By increasing flexibility- horizontal stresses can be reduced.

But clasp’s ability to provide retention should not be lost.

(More length, more flexibility).

Requirement of clasp assembly;

1) Retention30

a. Flexibility of clasp arm:

i. Length of clasp arm

ii. Diameter of clasp arm.

Flexibility is inversely proportional to the diameter

of clasp arm.

Requirement of clasp assembly;

1) Retention31

a. Flexibility of clasp arm:

i. Length of clasp arm

ii. Diameter of clasp arm.

iii. Taper of clasp arm.

A uniform taper in both thickness & width is essential.

A clasp should be half as thick at the tip as at the origin.

Requirement of clasp assembly;

1) Retention32

a. Flexibility of clasp arm:

i. Length of clasp arm

ii. Diameter of clasp arm.

iii. Taper of clasp arm.

iv. Cross-sectional form of the clasp arm.

Universally flexible form- round form.

Flexibility is limited to only one direction in case of half round form.

So cast retentive clasp arms are more acceptable in tooth-

supported partial dentures- flex only during placement & removable.

Requirement of clasp assembly;

1) Retention33

a. Flexibility of clasp arm:

i. Length of clasp arm

ii. Diameter of clasp arm.

iii. Taper of clasp arm.

iv. Cross-sectional form of the clasp arm.

v. Material from which clasp is made.

Chrome alloys have higher modulus of elasticity- less flexible.

Smaller cross-sectional form & less depth of retentive

undercut must be used.

Requirement of clasp assembly;

1) Retention34

1) Retention depends on:

a. Flexibility of clasp arm.

b. Depth that retentive terminal extends into the undercut.

c. Amount of clasp arm that extends below height of

contour.

Requirement of clasp assembly 35

1) Retention

2) Support:

Support is property of clasp that resists

displacement of clasp in gingival

direction.

Prime support units are rests.

(R)

Requirement of clasp assembly 36

1) Retention

2) Support

3) Stability:

It is resistance to horizontal displacement of prosthesis.

All clasp components except the retentive terminals

contribute to this property in varying degrees.

Cast circumferential clasp offers greatest stability- rigid

shoulder.

Support, stability & retention 37

Requirement of clasp assembly 38

1) Retention

2) Support

3) Stability

4) Reciprocation:

Each retentive clasp terminal must be opposed by

reciprocation.

Reciprocal arm reciprocates stresses generated against

the tooth by retentive clasp terminal.

Continue..

Requirement of clasp assembly 39

1) Retention

2) Support

3) Stability

4) Reciprocation:

It also stabilizes the denture against horizontal

movement.

Additional occlusal rest.

Reciprocal arm must be rigid.

(R)

Requirement of clasp assembly 40

1) Retention

2) Support

3) Stability

4) Reciprocation

5) Encirclement:

Each clasp must be designed to

encircle more than 180 degrees of

abutment tooth

(R)

Continue..

Requirement of clasp assembly 41

1) Retention

2) Support

3) Stability

4) Reciprocation

5) Encirclement:

If broken encirclement is planned- clasp

assembly must contact at least 3 different

tooth areas that embrace more than more

than half the tooth’s circumference.

(R)

Requirement of clasp assembly 42

Requirement of clasp assembly 43

1) Retention

2) Support

3) Stability

4) Reciprocation

5) Encirclement

6) Passivity:

A clasp in place should be completely

passive.

Retention function is activated only when

dislodging forces are applied.

(R)

Requirement of clasp assembly 44

1) Retention

2) Support

3) Stability

4) Reciprocation

5) Encirclement

6) Passivity

Suprabuldge clasps 45

1) Simple circlet clasp

2) Reverse circlet clasp

3) Multiple circlet clasp

4) Embrasure clasp

5) Ring clasp

Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..

1. Simple circlet clasp 46

Versatile & widely used clasp design.

Choice for tooth supported PD.

Originates from proximal surface of the

abutment adjacent to edentulous area.

Fulfils design requirements.

Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..

2. Reverse circlet clasp 47

Often used when undercut is located at the

distofacial side (preferably give infrabuldge

retainers, but as hard & soft tissue undercut does

not allow)

Class I & II help to control stresses

transmitted to abutment during function.

Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..

3. Multiple circlet clasp 48

It involves two simple circlet clasp joined at

the terminal aspect of their reciprocal

elements.

Given when primary abutment tooth is

compromised and stress originated from

prosthesis retention can be favorably

distributed to multiple teeth.

Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..

4. Embrasure clasp 49

Are essentially two simple circlet joined

at their bodies.

Design is most frequently used on side

of the arch where there is no

edentulous space

Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..

5. Ring clasp 50

Mostly indicated in tipped mandibular

molar.

Because of the length of the arm

additional support must be available to

ensure its rigidity.

By auxiliary bracing arm

Additional rest on disto occlusal surface

Ref: Stewart’s Removable partial prosthodonics. Page.no.71-74..

Summary 51

Direct retainer

Extracoronal Intracoronal

Precision

attachment

Semiprecision

attachment

Extracoronal

Attachment Retentive

clasp assembly

Suprabuldge

retainers

Infrabuldge

Retainers

Simple circlet

Reverse circlet

Multiple circlet

Embrasure Ring clasp

THANK YOU

Reference: McCraken & Stewart’s