Classification of Attachments

8/9/2019 Classification of Attachments

1/6

FAYZ, ESLAMI, AND GRASER

8.

Pound E. Applying harmony in selecting and arranging teeth.

Refmnt requests to:

Dent Clin North Am 1962;6:241-58.

DR. FARHAD FAYZ

9.

Pyott JE. Centric relation and vertical dimension by cephalomet- UNIVERSITYOF ILLINOIS

ric roentgenograms. J PROSTHETDENT 1954;4:35-41. COLLEGEOF DENTISTRY

10.

McGrane HF. Five basic principles of the McGrane full denture

CHICAGO, L 60612

procedure. J Florida Dent Sot 1949;20:5-8.

11, Ellinger CW. Radiographic study of oral structures and their

relation to anterior tooth position. J PROSTHETDENT 1968;

19:36-45.

A classification of precision attachments

Gerard0 Becerra, Odontol. Dr.,* and Michael MacEntee, L.D.S., R.C.S. (I), F.R.C.D. (C)**

University of British Columb ia, Faculty of Dentistry, Vancouver, B.C., Canada

I

some situations, usually in the anterior segments of

the mouth, a fixed partial denture cannot fulfill the

cosmetic needs of a patient without imposing hygiene

problems. The removable partial denture is most useful

here because it can be placed over the residual alveolar

ridge in the shape necessary to produce a natural

appearance. This cosmetic advantage is offset to some

extent by conspicuous extracoronal clasps on anterior

teeth or by the lack of retention of the prosthesis when

the clasps are avoided. The balance between functional

stability and cosmetic appeal is a major challenge to

dentists, and a variety of solutions have been proposed in

the form of small interlocking devices, often called

precision attachments, designed to connect the pros-

thesis to the abutment teeth.

Attachments have been designed since the past century

and more than 100 types are available. This article

describes a system of classifying these devices to provide

an overview of the designs available and to identify the

common feature of each class.

INTRADENTAL ATTACHMENTS

This class includes the largest number of attachments.

As the name implies, they are contained in part within

the crown or root structure of a natural tooth. Intraden-

tal attachments may be subdivided into two groups to

reflect the type of retentive mechanism used to hold the

parts together. They are (1) frictional, with designs that

include tapered and parallel-walled boxes and tubes,

adjustable metal plates, springs, studs, or locks; and (2)

magnetic.

*Visiting Dentist, Department of Clinical Dental Sciences.

**Professor, Department of Clinical Dental Sciences.

322

A

a

b

b

I)

Fig. 1. Prefabricated patterns. A, Internal walls of

female part (a) are tapered to accommodate male part (b)

when assembled. B, Walls o f male (a) and female Cb)

parts are parallel.

Frictional

Tapered and parallel-walled boxes and tubes.

These attachments are designed to join sections of a fixed

partial denture. They can be made individually by a

dental technician who prepares a deep interproximal

occlusal rest or box within the wax pattern of a crown.

After the crown is cast, the male section of the attach-

ment is made by flowing wax into the box and this wax

pattern is joined to the wax pattern of the adjacent crown

or pontic. It is possible to buy plastic prefabricated

patterns (Attachments International Inc., San Mateo,

Calif.) that can be incorporated into the wax pattern of

the fixed partial denture or splint (Fig. 1).

There is no resistance to separation of these attach-

ments along their path of placement; consequently they

SEPTEMBER 1987 VOLUME 58 NUMBER 3


2/6

CLASSIFICATION OF PRECISION ATTACHMENTS

b

b

a

A

Fig. 2. A, Adjustable metal plates. McCollum attach-

ment in which width of slit in metal block (b) can be

adjusted to increase frictional contact against sides of

box (a). B, Springs. Schatzmann attachment has a male

part (a) that contains a spring-loaded (b) rod (c), retained

by a threaded ring (not shown), to engage a hollow

within female part (d) when assembled.

I 1

a

A 8

Fig. 3. Studs. A, Ceka attachment in which metallic

male stud (a) is attached to a cast post and core. Female

part (b) is conta.ined within denture base. B, Zest-Anchor

attachment has a metallic tube (a) inserted into root

canal and a plastic stud and spacer (b) attached to

denture base. Spacer is removed to permit movement of

assembled attachment.

are not used to retain a removable partial denture unless

an additional device is available for direct retention. The

tapered varieties are the simplest of the interdental

attachments and, like a deep occlusal rest, they provide

vertical support and lateral stabilization. In effect, they

are simple pin and tube or rectangular block and box

assemblies. Because they should be contained within the

natural contours of the teeth, it is necessary to prepare

the teeth to accommodate them. In some teeth the extra

tooth reduction can jeopardize the health of the pulp.

Adjustable metal plates.

These attachments are

similar to the rectangular block and box variety, but are

a

b

Fig. 4. T-Block attachment consists of a male (a) and

female (b) box that can be locked together with a screw

Cc).

A

B

C

Fig. 5. Cobalt-samarium magnet. Metal keeper can be

cemented into root canal (A), retained with pins (B), or

incorporated within a cast post and core (C) to attract

closed-field magnet (D) that is placed in denture base.

made so that friction between the parts can be increased.

A narrow slit is provided in the metal block or male part

of the attachment (Fig. 2, A). This slit can be widened

with a scalpel blade to enlarge the block and enhance the

friction against the sides of the box. This provides a

simple but effective form of direct retention; examples

are McCollum, Crismani, or Stern attachments (APM

Sterngold, Stamford, Conn.), and Chayes or Ney attach-

ments (J. M. Ney Co., Bloomfield, Conn.). The length

of the slit within the block influences the resiliency of the

retaining mechanism so that at least 2.5 mm of tooth

height is required to accommodate them. There is a limit

to the movement and durability of the metal and

eventually these attachments succumb to fatigue. When

this occurs the male portion attached to the denture must

be replaced.

Springs.

Some manufacturers consider it more effi-

cient to include a small spring within the metal block to

control the friction between the male and female parts

(Fig. 2, B). The spring activates a plunger rod that

protrudes from the block to engage a depression in the

wall of the box and it can be replaced when it deterio-

rates; an example is the Schatzmann attachment (APM

THE JOURNAL OF PROSTHETIC DENTISTRY

323


3/6

a

A B

Fig, 6. Rigid attachments. A, Spang Conex consists of a male part that has a housing (a)

to contain a threaded (b) and conical pin (c). Female part consists of a retentive tube

Cd). B,

Scott attachment uses a custom-made telescopic crown (a) containing internal parallel

pins that fit into a metal block

(b)

soldered to abutment teeth. Metal block has a recess (c)

for an axial rotation joint that may be incorporated into design if rotational movement is

desired. This extra device will allow axial and slight rotational movement to attach-

ment.

Sterngold). Approximately 4 to 5 mm of vertical height

is required between the occlusal surface and the gin-

gival crest to accommodate these more complex attach-

ments.

Studs. Another form of direct retention for a remov-

able partial denture or overdenture is obtained by using

a stud that clips into a flexible ring (Fig. 3, A). A

metallic stud can be soldered to a post and core and

cemented into an abutment tooth, while the ring is

contained within a cavity in the denture base; examples

are the Ceka attachment (Ceka N.V., Antwerp, Bel-

gium) and the Gerber or Rotherman attachments

(Cendres and Metaux S.A., Bienne, Switzerland). The

ring may be adjusted to grip the stud or the head of the

stud may have two intersecting slits to increase its

circumference. The stud or the ring are replaced when

they are no longer resilient. The height of the stud

should not interfere with the arrangement of the artifi-

cial teeth on the denture and when vertical space is

small, the Rotherman attachment, with a height of 1.6

mm, is particularly useful.

A stud attachment is available that can be assembled

directly in the mouth without using a cast post and core

(Fig. 3, B). It consists of a metallic funnel-shaped tube

that is cemented into the root canal of a tooth and a

polyethylene stud that is attached to the denture base

(Zest-Anchor, San Diego, Calif.). The head of the stud

squeezes past a constriction in the neck of the funnel to

retain the denture on the tooth and it can be replaced

easily when necessary.

Locks. It is possible to obtain a device with parts that

lock rigidly together, for example, the T-Block attach-

ment (Attachments International, Inc.). Sections of a

fixed prosthesis are assembled by the dentist directly on

the supporting teeth and held in place by the attachment

screw (Fig. 4). If necessary, the sections can be easily

removed by the dentist. However, the vertical height

required for this attachment is at least 6 mm.

Magnets Although magnets have been used in various

forms to help retain complete dentures, they were not

effective until a small but strong closed-field cobalt-

samarium (CO Sm) magnet (Commonwealth Steel

Company Ltd., Alexandria, N.S.W., Australia) was

developed that would fit onto the surface of a tooth.2*3A

metal keeper is attached to the tooth surface, usually into

the root canal, and the magnet is contained within the

resin of the denture base (Fig. 5). The alloy in the

magnet produces a magnetic force that is both constant

and extraordinarily strong. It is claimed that the magnets

cause no tissue damage and the constant force implies

that they never need to be adjusted. Nevertheless, the

magnets are brittle and will corrode in the mouth unless

protected in a stainless steel shield. Clinical experience is

lacking, but magnets show considerable potential for

long-term retention of both intraoral and extraoral

prostheses.

EXTRADENTAL ATTACHMENTS

This class of attachment devices may be subdivided

into two groups: cantilever and bar attachment. The

cantilever designs may be rigid or mobile, and the mobile

designs include rotational and resilient types.

324

SEPTEMBER 1987 VOLUME 58 NUMBER 3


4/6


a-

Fig. 7. Rotational joint. Thompson dowel-rest system is

a custom-made attachment in which a retentive dimple

(a) and box (b) are placed in a cast crown on abutment

tooth. Removable partial denture has a flexible cast arm

(c) that engages, dimple on lingual surface of crown, and

a metallic block (d) that seats in the box.

Cantilever

The

limitations placed on the size of intradental

attachments and a desire to provide movement between

the abutment crown and the denture base prompted the

development of joints that project from the surface of a

cast crown and are cantilevered over the ridges.

Rigid. The design of this group emphasizes the need

for a rigid connection between the parts, and movement

can occur only along the path of insertion. Therefore, the

prosthesis becomes a rigid extension of the cantilever;

examples are the Stabilex or Conex attachments

(Cendres and Metaux) and the Scott Attachments (Pre-

cision Attachments Ltd., Vancouver, B.C., Canada).

Essentially they are pin and tube joints that use a slit in

the pin, or multiple pin tubes and slots, to enhance the

retentive frictian between the parts (Fig. 6). With

natural teeth on either side of the edentulous spaces and

strong periodontal support, these attachments offer

excellent stabili-ty and retention to a removable partial

denture supported entirely by natural teeth.

Mobile. The cantilever inherent in the rigid a ttach-

ment can produce destructive force on the periodontium

of the abutment teeth. Consequently, a variety of attach-

ments have been developed to allow rotation and resil-

ience within the joints in the hope of minimizing the

torque on the teeth. They range from relatively simple

hinges to complex devices that attempt to combine the

rigidity of the intradental attachments with some rota-

tion around a movable horizontal axis.

b

a

Fig.

8. Rotational joint. Dalbo hinge joint has a ball (a)

at end of a parallel-sided metal block soldered to an

abutment cast crown. This serves as a retentive rest seat

for socket (b) that fits over and engages circumference of

ball. Socket is connected to prosthesis and can rotate

around ball and away from metal block.

b

B

Fig. 9. Resilient joints. A, Movement within Dalbo ball

(a) and socket (b) hinge joint has been expanded by

using a spring (c) within socket. B, A more complex

design is used in Crismani resilient joint with metal

block (a) resting on a spring (not shown) attached to

base of box (b). Block consists of two parts tha t allow

rotation around a fixed axis. Combined axial movement

on spring and rotational movement of block produce a

resilient joint.

Rotational. Hinges allow the prosthesis to rotate

around a horizontal axis and transmit some of the

occlusal forces to the residual alveolar ridge; examples

are the Gerber hinge (Cendres and Metaux) and the


325


5/6

BECERRA AND MAcENTEE

Fig. 10. Bar attachments. A, Ackerman bar is circular (a) with short matrices or riders (b)

that attach to denture base. B. Dolder bar (a) has an ovoid superior surface around which

matrix (b) can clip.

Gaerny hinge (APM Sterngold). They can be used to

attach a unilateral prosthesis to an abutment tooth, but

because of the precise fit of the parts it is difficult to align

two of them across the arch in a bilateral removable

partial denture.

A method of anchoring a bilateral distal-extension

removable partial denture to crown restorations on

abutment teeth has been described by Thompson4 and

Becker et a1.5 t consists of a rest that ro tates within an

intracoronal box and an extracoronal clasp arm that

engages a dimple undercut on the lingual surface of the

crown. This arrangement will retain the removable

partial denture on the abutment teeth while allowing

horizontal rotation (Fig. 7).

The Dalbo a ttachment (APM Sterngold) is a good

example of a ball and socket joint in which the ball is

cantilevered off the abutment tooth and the socket is

attached to the prosthesis. The wall of the metal socket

has several small slits to provide a resilient entrance to

the socket and offers some direct retention to the

attachment when the socket engages the ball over its

height of contour (Fig. 8).

Resilient. The action of the Dalbo ball and socket oint

has been expanded with the addition of a spring within

the body of the socket to allow a small amount of vertical

settling of the removable partial denture beside the

abutment teeth (Fig. 9, A). Without this spring, the

prosthesis will rotate around the horizontal axis through

the ball and socket, and the distal-extension base will not

be evenly supported by the edentulous ridge. It has been

suggested that this uneven pressure is undesirable and

possibly destructive to the alveolar bone.

A slightly different and more elaborate design is

available from the Crismani attachment (Cendres and

Metaux). It consists of a metal block in two parts that

rotates around a fixed axis and rests on a spring that is

contained within a box on the distal surface of a cast

326

crown (Fig. 9 , B). The springs provide axial movement

and the split block allows rotation.

Bar attachments

Bars connected to cast metal crowns or copings can be

used to support and retain dentures. Custom-made bars

can be cast with a flat upper surface to support the

prosthesis and parallel sides that help to stabilize it.

They can be obtained in standard forms consisting of a

bar with an overlapping matrix. The Ackerman bar

(Cendres and Metaux) may be bent to conform to the

contour of the edentulous ridge, and several short

matrices rest on the bar to attach the denture base (Fig.

10, A). An oval cross-section has been used in the Dolder

bar (Cendres and Metaux) to offer direct retention to a

resilient matrix (Fig. 10, B) but it must be placed in a

straight line between the abutment teeth.

SUMMARY

This overview of attachments is intended to provide an

explanation of the design characteristics of 13 different

groups. The clinical situation for which an attachment is

intended will place specific demands that can be met

more closely if the forces acting on the prosthesis are

considered. No universal or ideal design is available, so if

attachments are used, they should be selected from the

group with the most suitable characteristics for the task

required.

The stress-breaking effect of attachments is vague.

They offer a potential for rotational and resilient move-

ment between the prosthesis and the abutment teeth, but

the amount of stress that must be broken to protect the

periodontium of the teeth may exceed the capabilities of

any particular attachment used. Nevertheless, attach-

ments can provide an effective answer to prosthesis

stability and retention in a way that is cosmetically

pleasing.

SEPTEMBER 1987

VOLUME 58 NUMBER 3


6/6


REFERENCES

1. Boitel HR. Precision attachments: an overview. In: Tylman SD,

Malone WFP, eds. Tylmans theory and practice of fixed

prosthodontics. 7th ed. St Louis: The CV Mosby Co, 1978, chap

22.

2. Gillings BRD. Magnetic retention for the overdenture. In:

Brewer AA, Morrow RM, eds. Overdentures. 2nd ed. St Louis:

The CV Mosby Co, 1982, chap 25.

3. Gillings BRID. Magnetic retention of complete and partial

overdentures. Part I. J PROSTHETDENT 1981;45:484-91.

4. Thompson M. Solution for specific problems in replacing

missing teeth with partial dentures. Ill Dent J 1957;26:251-3.

5. Becker CM, Campbell H, Williams DL. The Thompson dowel-

rest system modified for chrome-cobalt removable partial denture

frameworks. J PROSTHETDENT 1978;39:384-91.

Refmnt requests o:

DR. MICHAEL MACENTEE

UNIVERSITYOF BRITISH COLUMBIA

FACULTYOF DENTISTRY

VANCOUVER,B.C. V6T 127

CANADA

Effect on the fit of removable partial denture

frameworks when master casts are treated with

cyanoacrylate resin

Mickey J. Calverley, D.D.S.,* and James R. Moergeli, Jr., D.D.S., M.A.**

U.S. Army Dental Activity,

Walter Reed Army Medical Center, Washington, D.C.

S

veral studies have been published on the effective-

ness of cyanoacrylate resin as a hardener of artificial

stone dies for the fabrication of cast restorations.-3 The

purpose of this study was to determine whether coating a

removable partial denture master cast with cyanoacry-

late resin perm:its more complete seating of a fabricated

framework in the patients mouth.

MATERIAL AND METHODS

A metal model of a partially edentulous jaw was used

to simulate the patient (Fig. 1). Final impressions were

made by using a stock tray (Rimlock, L. D. Caulk Co.,

Milford, Del.) and irreversible hydrocolloid (Jeltrate,

L. D. Caulk Co.). The powder/water ratio was careful-

ly controlled according to the manufacturers recommen-

dation. It was mixed by using an Alginator II mechani-

cal spatula (CADCO Products, Los Angeles, Calif.) and

Commercial products and equipment are identified in this report to

specify the experimental procedure. Such identification does not

imply recommenfdation or endorsement or that the materials or

equipment are necessarily the best available for the purpose.

Furthermore, the opinions expressed herein are the private views of

the authors and a:-e not to be construed as official or as reflecting the

views of the Department of the Army or the Department of

Defense.

*Lieutenant Colonel, Dental Corps; Chief, Prosthodontic Service, Ft.

Eustis, Va.; formerly Senior Resident, Removable Prosthodontics.

**Colonel, Dental Corps; Chief, Removable Prosthodontic Service,

Maxillofacial Prosthetic Service, and Director, Prosthodontic Resi-

dency Program.


allowed to set for 5 minutes on the metal model. A stand

was constructed to ensure exact placement of the tray for

each impression, maintaining the recommended I- to

/-inch clearance for the impression material4 (Fig. 2).

The impression was removed vertically with a snap.

All of the impressions were poured immediately with

an improved dental stone. One hundred grams of powder

was mechanically mixed with 24 ml of water for 15

seconds under a vacuum of 28 in of mercury. A

noninverted, single-pour technique was used. The casts

were separated 1 hour after the start of mixing. The

casts were surveyed, and the design was drawn on each

cast. Half of the master casts were randomly selected and

the abutment teeth were coated with a single coat of

cyanoacrylate resin (Duro Super Glue, Loctite Corp.,

Cleveland, Ohio). A drop was spread on each abutment

tooth, and the excess was blown off with light air

pressure, leaving a thickness of less than 2 pm as

reported by Fukui et a1.2 They were then sent to the

dental laboratory for framework fabrication. The

instructions were to place no clasps in retentive zones

and to relieve all soft tissue parts (Fig. 3). Thus, the

removable partial denture framework would contact the

metal model only on the abutment teeth.

Each returned framework was inspected to determine

that (1) it accurately fit the master cast on which it was

fabricated, (2) the master cast had not been grossly

damaged, and (3) the intaglio surface of the removable

partial denture framework had no obvious defects.

Although the dentist would normally adjust small defects

327

Documents

Classification of Attachments