Precision Attachments

PRECISION

ATTACHMENTS

CONTENTS

Introduction

History

Definition and synonyms of attachments

Classification

Indications / Applications of precision attachments

Contraindication

Advantages

Disadvantages

Selection of the abutment teeth

Requirement of the abutment teeth

Selection of the retainer

Selection of the attachment

Intracoronal attachment

• Precision / Semiprecision attachments

• Mechanics of retention

Extracoronal attachment

• Rigid / Resilient attachment

• Extracoronal resilient attachment (ERA)

• O-ring attachment

Role of attachment as stress breaker : “Broken stress philosophy”

Bar attachments

Stud attachments

Magnets as attachment

Auxillary attachments

Conclusion

INTRODUCTION

• The desire to balance between functional stabilityand cosmetic appeal in partial dentures gave rise tothe development of Precision Attachments

• Precision Attachments have always beensurrounded by an aura of mystery.

• The use of Precision Attachments for partial denture retention is

• A practice builder for the better class of dentistry

• It helps to elevate the general standard of partial denture

prosthetics.

• The precision attachment is sometimes said to be aconnecting link between fixed and removable partial dentureas it incorporates features common to both types ofconstruction.

HISTORICAL BACKGROUND

Winder

“Winders design”

Screw joint retention

Parr (1886)

Extracoronal socket attachment

Stair

Telescopic abutment restoration

Ash (1912)

Split bar attachment system

Late 19th century :

Dr.Herman, ES Chayes

First attachment to be available in the general market

“T shaped”

Precision Attachment (1906)

“H shaped”

Chayes Attachment

(1912)

Precision – quality or state of being precise

Attachment – Mechanical device for the fixation, retention and

stabilization of dental prosthesis.

Pin slot

chayesCeka &

dallabona

• Precision Attachment (GPT-8) :

• A retainer consisting of a metal receptacle (matrix)and a closely fitting part (patrix); the matrix is usuallycontained within normal or expanded contours ofthe crown on the abutment tooth and the patrix isattached to a pontic or the removable partialdenture framework.

• An interlocking device, one component of which isfixed to an abutment or abutments, and the other isintegrated into a removable prosthesis to stabilizeand/or retain it.

Mechanical device – Direct retainer

• They are designed to replace occlusal rest, bracing arm, and

retaining arm of the conventional clasp retained partial denture.

• They function to retain, support and stabilize the removable

partial denture.

SYNONYMS OF ATTACHMENTS

Patrix Matrix

Flange Slot

Insert Crypt

Key Keyway

Fitting part Receptacle

Internal attachments

Frictional attachments

Parallel attachments

Slotted attachments

Key and Key way attachments.

Male attachments Female attachments

CLASSIFICATION OF ATTACHMENTS

Based on method of fabrication and the tolerance of fit

I. Precision attachment (prefabricated types)

II. Semiprecision attachment (custom made / laboratory made

types)

Prefabricated wax / plastic / nylon patterns

According to their relationship to the abutment teeth

Intracoronal (Internal attachment) Extracoronal (External attachment)

Based on stiffness of the resulting joint

Rigid attachments Resilient attachments (Non rigid)

Based on geometric configuration and design of the attachment.

Key and Keyway

Interlocks

Ball and socket

Bar and clip / sleeve

Hinge

Telescopic

Push button

Latch

Screw units

Classification used in literature :

M.C. Mensor (1973)

Classification according to shape, design and primary area of

utilization of attachment.

Coronal Radicular Accessory

Intracoronal

Extracoronal

Telescope studs (pressure

buttons)

Bar attachment

(Bar joints and Bar units)

Auxillary

Screw units

Bar connectors

Bolts

Stabilizers

Balances

Interlocks

Gerardo Beccera and others (1987)

Intradental attachments

- Frictional

- Magnetic

Extradental attachments

- Cantilever attachment

- Bar attachment

ADVANTAGES

Improved esthetics and elevated psychological acceptance

Mechanical advantage

- Direct the forces along the long axis of the teeth / more apically

- Force application closer to the fulcrum of the tooth

Reduces Non axial loading

Decreases Torquing forces

Rotational movement of the abutment

In Distal extension base cases – “Broken stress philosophy”

Reduced stress to the abutment

Stress free rotational/vertical movements

Cross arch load transfer and prosthesis stabilization

Compared to conventional clasp retained partial denture

Less liable to fracture than clasp

Less bulky and more esthetics

Better retention and stability

Less food stagnation

DISADVANTAGES

Complexity of design, procedures for fabrication & clinical

treatment

Minimum occlusogingival abutment height (4-6mm)

To incorporate attachment without overcontouring

Enough length of parallel contact

Anatomy of the tooth – Limited faciolingual tooth width

(incisor and canine areas)

Expensive

Complexity of laboratory and clinical procedure

Attachment maintenance (repair or periodic replacement)

Wearing of attachment components

Require high technical expertise – Dentist and laboratory

technician

Requires aggressive tooth preparation

Cooperation and manual dexterity on the part of the patient

Difficult to insert and remove

Visually or manually challenged patient

Increase demand on oral hygiene performance

INDICATION / APPLICATIONS OF PRECISION

ATTACHMENTS

Removable Prosthodontics

As a retainer in a removable tooth supported partial denture

4 large well rounded abutments are available

For esthetic concern in the anterior part of the mouth

Stress Breakers – Free end saddles/Distal Extension Base cases (DEB)

– When cantilevered pontic is to be used as abutment

For movable joints in sectional dentures

Periodontal involvement of the tooth

Contraindicates rigid FPDs

Most efficient bilateral bracing and support are essential

Divergent abutment teeth with high survey lines – parallel path

of placement.

As a retainers in tooth supported over denture

Fixed Prosthodontics

As a connector in fixed partial denture construction

(long span bridges)

To overcome alignment problems where abutments have

differing path of withdrawal.

IMPLANT PROSTHODONTICS

Implant supported over denture

They are used for connection between the tooth and the implant

CONTRAINDICATIONS OF PRECISION ATTACHMENTS

Poor periodontal support.

Poor crown to root ratio

Poor oral hygiene habits

Abnormally high carious rate

Inadequate space / room to employ the

attachment

Compromised endodontic and restorative

conditions

SELECTION OF THE ABUTMENT TEETH

Factors :

Condition of abutment teeth

Number of the abutment teeth

Location of the abutment teeth

Periodontal condition – Crown root ratio

– Periodontal support

Pulpal status – Vitality of the pulp

– Size of the pulpchamber

Minimum attachment length

4mm

Inadequate attachment

length < 4mm

Maximum attachment

length 6-7 mm

Axial space requirement

Sufficient clinical crown length – for minimum of 4mm attachment length

Adequate space between the pulp and the normal contour of the tooth

Buccolingual space requirement

REQUIREMENTS FOR THE ABUTMENT TEETH

SELECTION OF THE TYPE OF RETAINER

Full crown retainers

Intracoronal attachments

More retentive / rigid

Ideal contours

Caries protection

Partial coverage retainers

Kennedys Cl III partial denture

Splinted abutment teeth

Most vulnerable

Inadequate retention

Marginal leakage Inlays / onlays / pin ledges

Not used for intracoronal attachments

Lack of retention

Marginal caries

Less life

Selection of the attachments

Intracoronal vs

Extracoronal

Resilient vs

Non resilient

75 mm in length

Red 3-4 mm

Yellow 5-6 mm

Black 7-8 mm

EM attachment gauge (Matsuo (1970)

EM attachment selector (Dr. MC Mensor (1973)

Quick reference

Communication between the dentist & laboratory technician

105 attachments

30 points of information

INTRACORONAL ATTACHMENTS

Intracoronal precision attachment

(Dr. Herman E.S Chayes)

Precision attachment

(prefabricated type)

Semiprecision attachments

(custom made)

Conventional attachment

T shaped attachments

Modern attachment

H shaped attachments

Contact plate

Adjustment slot

Tube Head

Rein forcing

plate

MECHANICS OF RETENTION

Frictional : Preiskel group I

Retention – Surface area contact

Function of the length – Controlled by height of clinical crown

– Intermaxillary space available

Function of cross sectional dimensions

Mechanical : Preiskel group II

Auxillary mechanical retentive features

Ex. Spring loaded plunger / clips

Passive Attachment :

Matrix : Simple channels closes at one end to provide stop

Patrix : Solid slide

Channels of passive attachment may be round / elliptical slides

DEPENDING ON ARTICULAR RETENTION

Passive attachment Active attachment Locked precision attachment

Omega Beyeler

ACTIVE ATTACHMENT

Active friction grip attachment Active snap grip attachments

Locked precision attachment

Attachments bolted by means of a sliding bolt or latch

Pinned or screwed together

McCollum Crismani Crismani

Latch retained

Mc Collum attachment :

H shaped attachment

Single adjustment slot

Retention expanding the adjustment slot

Stern attachment

Stern Gold latch retained

Two adjustment slots

Crismani attachment :

Available as Rigid / Resilient

Rigid crismani attachment

Frictional grip

Mechanical Spring clip

Ney’s attachment :

Latch retained

Conventional

H shaped

Ney loc split

lingual

Bakers attachment

Schatzmann attachment

Frictional retention

Mechanical retention

(spring loaded plunger & coil spring)

Semiprecision attachments

Semiprecision rest – intracoronal rest seat and resilient lingual arm.

“Laboratory fabricated rigid metalic extension (patrix) of a fixed or

removable dental prosthesis that fits into a slot type key way (matrix)

in a cast restoration allowing some movement between the

component”. - GPT8

Gillete (1923) : The first semiprecision attachment

Rectangular deep rest with buccal and lingual wrought clasps arms

Ira D Zinner (1979)

Locking semiprecision

attachment Non locking semiprecision

attachment

Louis blatter fein (1969) : Four aspects of rest seat preparation

Occlusal form / outline form – controls amount of rotation

Circular Dove tail Rectangular Mortice

(Rigid – locking type) Resilient Some resiliency

(Non-locking type)

Proximal form / side walls – lateral force control

Parallel outline Tapering outline

The angle of the proximal wall with the gingival floor

Gingival floor form : serves the function of reciprocation

Flat Inclined Channeled

Added

reciprocation

Mortice occlusal

form Rectangular

occlusal form

Ney‟s MS Intracoronal attachment (circular rest)

Locking Semiprecision Attachments

Neurohr – Williams No. 1 (Mortice rest)

Advantages :

Versatility for clinical situations – employing various rest seat

outline forms.

Variation in tooth size and shapes are easily accommodated.

Better crown contour compared to prefabricated type

Disadvantages :

Long term wear is more – softness of alloy used.

No standardization of sizing : Lack of interchangiability of

male and female attachment.

Greater degree of laboratory skill and attention in detail.

EXTRACORONAL ATTACHMENTS

Introduced by Henry R. Boos (1900)

Modified by F Ewing Roach (1908)

Application

Kennedy‟s class I and class II

Boitel (1978)

Rigid attachments

Resilient attachments

Bar attachments

EXTRACORONAL ATTACHMENT

Rigid attachments Hinged attachments

(Stress breaking action) Resilient

attachments

ERA

O-ring

Advantages :

• No alteration of contour of the abutment crown

• Can be used in short abutment teeth

• Greater freedom in the design

• Ease of insertion and removal

Disadvantages (Wolf RE 1980) :

Lack of occlusal satability

Bulky

Rebasing problems

Improper control of force distribution

Encroachment on the gingival papilla – use of mini attachment

RIGID EXTRACORONAL ATTACHMENTS

Roach attachment (ball and tube attachment)

Oldest attachment

Patrix – round ball

Matrix - tube

Pin and tube attachment

The simplest

Patrix - pin

Matrix – tube

Conex attachment

(Smaller version)

Stabilex attachment

Two retention pins

Disadvantage is increased length

Matrix Patrix

Assembled

Two types pins

Frictional retention

Mechanical locking

RESILIENT EXTRA CORONAL ATTACHMENT

•Dalbo / Dallabona attachment

Assembled

a) Patrix

b) Matrix

Dalbo stress breaker

Rotational and Vertical movement

Matrix and patrix

Ceka attachment

Developed by karl cluytens (1951)

Two types - Ceka NV attachment

- Ceka revax

Matrix metal ring retainer Patrix Attachment pin

(split metal post)

Functional aspect : Mark E, Waltz 1973

A) Support

B) Bracing

C) Retention

Attachment pin / split post

• Insertion and removal

• Reduces frictional wear

Ceka Revax

ROLE OF ATTACHMENTS AS STRESS BREAKER

Rigid system Non-rigid system

Stress breaker

Broken stress philosophy

Mensor stress can only be selected, altered or blocked

“Stress director”

Shohet (1969) Kratochvil (1981)

Low intensity forces on abutment teeth in contrast to rigid

attachments.

Rationale of stress breaker movement should be strictly only

to displaceable tissue

Disadvantages of stress director :

More complex, increased wear and breakage

Increased bone resorption and trauma

Occlusal contacts difficult to maintain

Spring like device tendency to fatigue

ASC-52

attachment

Extracoronal resilient attachment

Patrix and Matrix

STRESS BREAKER DESIGNS

Neys distal extension

stress breaker

Crismani resilient

attachment

“Hinge stress breaker”

Anchorvis attachment

Stern stress breaker

Extracoronal resilient attachment (ERA) :

(ERA)

Colour coded retention caps

Most flexible White > Orange > Blue > Gray Most rigid

Two types of ERA

Standard

Reduce vertical (ERA – RV) – male part is 0.5mm shorter

Matrix Patrix

Use of ERA in

DEB cases

Use in over denture

Yen Chen Ku et al (2000) : ERA provides esthetics, vertical

resiliency, easy replacement of worn dentures

Vertical resiliency of 0.4mm

Universal joint hinge action

O-SO ring / O-ring attachment

Patrix - post with the groove

or undercut.

Matrix – O-ring synthetic

polymer gaskets + encapsulator

O-ring are made up of

Silicone

Nitrile

Fluorocarbon

Ethylene propylene

Advantages of O-ring

Ease in changing the attachment

Wide range of movement

Low cost

Different degrees of retention

Elimination of the time / cost of the superstructure

STUD ATTACHMENTS (ANCHORS)

“Anchor the roots”

Simplest of all the attachment

Partrix – dowel / post retained restoration

Matrix – denture base of the prosthesis

Classified as :

Rigid stud unit

Resilient stud unit

Extraradicular units

Intraradicular units

Extraradicular Intraradicular

Space requirement of these attachment

is intermediate between dome shaped

coping and thimble shaped coping.

These should be placed parallel to the

long axis of the tooth.

DALBO STUD ATTACHMENT

Rigid unit

Ball and socket unit

(Vertical and

rotational movement)

Nylon ring – protects the lamella

Retention – altering the positions

of free ends of the lamella

ROTHERMAN ECCENTRIC ATTACHMENT

Button shaped attachment

Patrix – eccentric cylinder

with undercut or groove

Matrix – Clip or clasp arm

Activation : Bending the

clasp arm towards center

Resilient unit

Rigid units

ZEST ANCHOR ATTACHMENT

Patrix

Polyethylene – Nylon stud

Matrix

Funnel shaped tube

Instrumentation kit

Advantages :

Reduce vertical

space requirement

Loads are transferred

more apically.

GERBER ATTACHMENT

Resilient gerber Rigid gerber

Largest of the stud unit

Resilient – spring controlled

vertical plane

Patrix – threaded post

Matrix – retention spring and ring

Disadvantages :

Complex attachment system

Requires more space

Permits little rotation

CEKA ATTACHMENT

Ceka revax

Extra radicular Intra radicular

Patrix – metal ring

Matrix – attachment pin

(split metal post)

SPACER RING

Vertical movement of the

prosthesis

SCHUBIGER ATTACHMENT

Patrix : threaded post / screw

Matrix : recessed collar, cap nut / lock nut

Cut section

BAR ATTACHMENTS

Gilmore clip system (1913) - metal bar with retaining sleeve / clip.

Bar can be attached to the :

Coping or crowns over the vital teeth

Post coping on endodontically treated teeth

Screwed down into the coping (implant system)

Types of bar attachments :

Customised bar

Dolder bar

Ackermann’s bar

CM rider bar

Hader bar

Andrews bar

Two groups of bar attachments :

1) Bar units - rigid

2) Bar joints – permits rotation

Round / circular Oval / egg shaped „U‟ shaped / parallel sided bars

Multiple sleeve bar jointsSingle sleeve bar joints

Depending on cross section

BAR JOINTS

DOLDER BAR

Egg shaped bar in cross section

Open sided sleeve

Two sizes 3.5mm x 1.6mm,

3.0mm x 2.2mm

Spacer – degree of movement

MOVEMENTS SEEN IN DOLDER BAR

Sagittal rotation Rest position Vertical translation

Implant supported over denture

ACKERMANN BAR

Available in different cross

section

Circular cross section – can

be bent in all planes

CM BAR

Made up of precious /

semiprecious alloy

Retention tags in long axis

of the bar

HADERBAR

Helmut Hader in 1960

Available as a prefabricated plastic pattern

Notable feature

Resin / plastic sleeve

No spacer- more

support

English, Donnel & Staubli (1992)

Hader EDS system

System with 3mm height (8.3mm).

Clips with metal encapsulator

Advantage

Prefabricated plastic pattern – no need for soldering.

Precise fit, simplicity, versatility

Advantages of bar attachments :

Rigidly splint the teeth

Provides good retention, stability and support

Provides cross arch stabilization

Positioned close to the alveolar bone (exhibit less leverage)

Disadvantages :

Bulk of bar

Plaque accumulation

Wearing

Soldering procedure

Manual dexterity

MAGNETS AS ATTACHMENT

Since 1950 To retain maxillofacial prosthesis

Alu, Ni, Iron,Cobalt alloy (alnico)

Limited use – larger size

1960 “use of rare earth element” – High field strength

– Can be used in smaller size.

Somarium cobalt (Sm-Co) (Joseph Becker Hoffer 1967)

Neodymium iron boron (Nd-Fe-B) – 20% stronger

Somarium iron nitride – High magnetization

Used for retention of mandibular overdentures (tooth and implant

supported over dentures)

Gilling’s magnetic attachment

(cobalt somarium alloy magnets)

“Split pole paired magnets”

Closed field magnetic system

Magnetic retainer with magnets

Magnetic keeper

Jackson magnetic attachment

(cobalt somarium alloy magnets)

Cemented in keeper Screwed in keeper

Encapsulated magnetic retainer

and magnetic keeper

Assembled attachment

SANDWICH DESIGN

Attractive breaking force 4.9 N (500 gm)

Advantages of magnetic attachment :

Smaller size and strong attractive force

Produce constant force – constant retention

Easy to incorporate into the prosthesis

Automatic reseating

Boon for elderly patients (Parkinsonism, arthritic patient)

Less lateral force to the abutment tooth

Disadvantages :

Loss of retention due to corrosion or heat instability

Requires encapsulation within inert alloys

Cant be repaired

High cost

Short track records

Limited force transmission - Magnets can slide on their keepers.

AUXILLARY ATTACHMENTS

Screw and tube attachment

Key and keyway / interlocks

Presso Matic or Isoclip

Bar connectors

Attachments for sectional dentures / bolts

Screw and tube attachment

Indications :

To overcome alignment problems

Connecting one restoration of fixed partial denture to another

Allowing the removal of long span fixed partial denture for

repair and examination of abutment.

ATTACHMENT USED FOR SECTIONAL DENTURES

Two part dentures : One part - chrome cobalt base

Second part - removable acrylic flange with teeth

Advantage of superior esthetics and improved retention

Method of union :

Physical interference : Bolt retained prosthesis

Frictional resistance : Split post retained prosthesis

SECTIONAL DESIGNS

Individual sections / separate sections : uses mesial and distal

surface of the abutment teeth as guiding planes.

Bolt retain two parts prosthesis

Hinged sections : Buccal and lingual path of insertion

CONCLUSION