Removable appliances yesterday and today

Removable appliances yesterday and today C. P. Adams, Belfast,

Northern

M.D.S.,

F.D.S., F.F.D.R.C.S.I.,

D.Orth.

Ireland

R

emovable appliances are not often a topic of discussion today, although they are widely used in orthodontic treatment. To some extent, this may be due to a tendency to regard orthodontics as a discipline in a particular appliance method, so that in courses of training greater time and attention are given to the more comprehensive, multiband technique. However, only through the realization that the solution of orthodontic problems must come through an understanding of their nabure and t,hat the most appropriate technical method must be used in any given situation can real progress in meeting the orthodontic needs of a community be made. Removable

appliances-What

are

they?

Moyers7 left the impression that, in America, the term ~cn~,ovccbIcnpplinu~cs means functional appliances of the Andresrn or n~onobloc type. In the Scandinavian countries, removable appliances are considered to be of two kind-( 1) appliances which are clasped to the teeth and are ret’erred to as fixed plates and (2) removabke appliamm, which arc those that lit loosely in the mouth and product their effect by moclifying the pattern of act.ivity of the omfacial musculature and hence the pressures produced on the teeth by these activities. In practice there is a third small group of appliances which fall in between these two in that, while they are clasped 60 the teeth and arc, by definition, fixed plates, they produce their effect t,hrough the use of muscular pressures and are also functional appliances. Strictly speaking, the term remoz*ubZe appliaacc can be applied to all these types of appliance, although the appliances which harness muscular activities are more generally referred to as funct,ional appliances, activators, functional regulators, or by the names of their originators (Antlrcsen appliance, FrGnkel appliance, Robin monobloc). There is a clear distinction between clasping for partial prosthetic purposes and clasping for orthodontics. In partial prosthetics the existing natural denti748

Removable

appliances

749

tion is, in the great majority of cases, fully developed and erupted, and often the supporting tissues may have retreated beyond the anatomic necks, exposing deep and extensive undercut areas. In these circumstances undercut areas which are needed for clasping purposes arc not difficult to find. Dentitions on which it is desired to place orthodontic appliances are much younger, often with deciduous teeth present, and in those permanent teeth which are erupted more often than not the anatomic necks are not exposed. Thus, there were, at first, continual problems of clasping removable orthodontic appliances securely. This restricted the scope and effectiveness of removable orthodontic appliances and led many to discard them and turn to fixed-appliance methods as being more certain in their action. Problems

of

removable

appliance

design

In 1926 McKeagS published a study of the mechanics of appliance design in which he showed that the laws which regulate the stresses and bending of flexible metal beams of any size apply equally within the relatively minute dimensions of orthodontic springs. These laws are embodied in a formula which describes the relationship between the length of a spring, its thickness, the presswe which is required to deflect it, and the amount of deflection produced. The formula

states that

r) CCJ$

where P is pressure exerted upon the spring,

1

is the length of the spring, t is its thickness (for a wire of round section), and D is the deflection produced. Practical experience tells us that, for a given amount of pressure, a longer and thinner spring will be deflected more than a shorter, thicker spring, but the formula defining this relationship emphasizes the large differences introduced by small changes in length and thickness. This is a guide for making changes in these two factors which make it possible to produce the appropriate amount and direction of pressure on any required tooth with a removable appliance in the most efficient and direct manner possible. There is no doubt that the materials formerly available imposed restrictions on the design and construction of removable appliances. Precious-metal wires could not be made thin enough to develop the ranges of action that are considered desirable today. Hard soldering softened the materials and removed their elastic properties, and the nonstainless steel materials needed to be tinned for protection against the oral fluids and presented problems in making joints secure enough to stand up to conditions in the mouth. The availability of stainless steel soon led to further studies of the design and construction of appliances. The most fundamental of these, by Friel and McKeag,3 were concerned with the use of fixed appliances because the constmction of bands in the chrome alloys had raised some problems. The only real difference between labiolingual appliances and clasped removable appliances is the mode of retention of the appliances on the dental arches. In one case cemented bands are used, and in the other the appliances are held with clasps. It was the problem of efficient clasping that retarded the progress of development of removable appliances for many years; today, when simple positive

750

Am.

Adams

6. Orthodontics June 1969

clasping of teeth is now possible, removable appliances are fully as effective as labiolingual types and have taken over many of the funct.ions of such fixed appliances. Evolution

of

clasp

design

The first consideration in the design of any clasp is a study of tooth crown form when it can be seen that on the buccal and lingual surfaces there are slopes outward from the occlusal or incisal region toward the anatomic neck (Fig. 1, A). In the molar and premolar teeth these outward slopes quite suddenly turn inward toward the tooth axis just before the anatomic neck is reached, giving slightly undercut areas which may be used by a clasp encircling the tooth to procure a grasp. It is these undercuts which are used by the plain free-end clasp and by the plain crib clasp to effect a grip on the t,ooth, the tooth being gripped buecolingually between the clasp wire and the base plat,t? (Fig. 3). If the teeth are viewed from the buccal or labial aspect (Fig. 1, B), it can be seen that nearly all the mesial and distal surfaces, from the contact points t,o t,hc anatomic neck, slope inward toward the long axis of the tooth. This is true not only of the molars but also of the premolars, canines, and incisors. The undercut areas in the mesial and distal aspects of the teeth arc not only better defined than those on the buccal and lingual aspects, but they extend r~~uc11 farther coronally and are accessible at a much earlier stage of crrtptiorl than the buccal undercuts.

A

B

Fig.

1.

A,

maximum seen surface

Molar, crown

from

the

or incisal

premolar, diameter buccal edge.

or

canine, is near, labial

view.

and or

incisor

virtually The

teeth at,

maximum

the

seen

from

anatomic crown

diameter

the neck. is

mesial

aspect.

B, The

same

near

the

The teeth

occlusal

Rcmovuhlc

appliam?s

751

It was appreciation of the possibilities inherent in the use of the mesial and distal undercut areas that led, in due course, to the development of the modern, effective type of orthodontic arrowhead clasp. Jackson4 describes the construction of a crib clasp which has a square form and is designed not only to grasp the tooth buccally but, by running forward and backward and turning sharply at a right angle, to grasp the tooth anteroposteriorly (Fig. 2). The illustration of this cla%p, shown on an extracted tooth, implies that the clasp can be fitted and made effective clinically. This is not necessarily so, for the surfaces that it is required to fit anteroposteriorly are not easy to reach with this particular construction; also, it is difficult to make the wire fit buccally and anteriorly and posteriorly as well, even if an accurate impression of these areas can be obtained. It is impossible to obtain a good fit if the anteroposterior surfaces arc hidden by gingival tissue. It is better to use either the mesial and distal undercuts or the buccal undercut, but it is unwise to try to use them both, as in this event neither is properly effective. A different, and in some ways better, approach to the problem was adopted by Crozat,* who gained contact with the mesial and distal undercut areas by fixing an additional short length of wire to the loop of a plain crib clasp and causing the ends of this additional wire to run round the gingival margin and make contact with the tooth anteroposteriorly (Fig. 3). A feature that has appeared from time to time in clasp forms of the crib

Fig.

2

Fig,

2.

The

wire

and

Fig.

Adaptation of

the

of clasp

distal

undercut

Philadelphia,

1904,

Fig. plate left mesial

3.

On using

the the

is a Crozat and

distal

the

crib

clasp

is carried areas.

well (From

buccal clasp

is a plain and which

undercuts.

extracted and

tooth

as

distally,

shown

by

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Orthodontia

and

to

Orthopedia

V.

H.

reach

Jackson.

the of

mesial

the

Face,

Company.

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Jackson:

J. B. Lippinicott

right

to

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an

clasp

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undercut

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crown gingival and

against margin. distally

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base

On

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into

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d nt. ,T. Orthodontics June 1969

Fig.

4.

The

belo SW the

Schwarz point

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of

contact

clasp. between

The two

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for

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SFraces ‘died

in a clasp.

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5.

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Removable permission.]

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clasp teeth to

makes are

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753

type is the attempt to improve the clasping of teeth on the lingual side, that is, by gaining access to the lingual undercut area by means of a fine spur which lies in the lingual gingival sulcus (Visick, 1926) or by using the anterior and posterior undercut areas from the lingual aspect by adding small spurs soldered to the tags of clasps of the crib type. 2, ‘3 G Devices of this kind did certainly improve the effectiveness of crib clasps, but they also tended to be time consuming to make, delicate, troublesome to adjust, and likely to cause discomfort, and they required the use of precious metals. They a,re rarely heard of today. The next real advance in clasp design was the introduction of the arrowhead t.ppe of clasp, usually attributed to Schwarz” and introduced in England by Tischlcr. As can be seen in Fig. 4, the clasp demands the use of a considerable a.mount of space in the oral vestibule. Special instruments are entailed in its construct,ion, and fabrication and adjustment are fairly complex operations. The arrowhead clasp, however, made use of the best principle of clasp design-the use of the mesial and distal undercuts-but there appeared to be room for improvement in the working out, of this principle in pracbice. The modified arrowhead clasp, introduced by Adams in 1949 and today widely referred to as the Adams clasp, makes use of the mesial and distal undercuts of a single tooth only and can in practice be applied to a,ny tooth, deciduous or permanent. This clasp develops the maximum retentive potential of whatever tooth it is placed upon in the simplest and most unobtrusive way. Fabrication is easy, provided the recommended bending procedures are followed and pliers of a basic universal pattern are used. Since the clasp was given its definitive form in 1953,l no changes in the basic principle and design have been found necessary (Fig. 5). Over the years there have been suggestions for improvements in the design, variations in the way the clasp is applied, and changes in wire thickness. It is usually to be found t,hat such suggestions arise from difficulties in using the clasp which are caused by a misapprehension as to how the clasp works, inefficient fabrication methods (which may be caused by the use of the wrong pliers or of pliers that are not well made), or attempts to treat malocclusions with removable appliances when a different t,reatment technique should be used. Design

of

springs

In practice, springs used on removable appliances must be of a size which can be accommodated in t,he mouth, and an important requirement is that they should have such a range of action that their activity will last for 4 weeks at least; this is in order to keep visits for adjustments to a manageable frequency. In general, there are three basic sprin, e designs which can be used in most situations : 1. The simple finger spring of 0.5 mm. (0.020 inch) thickness, which has a single coil near the point of attachment. This spring is exceedingly versatile, but it always requires a guard or guide to ensure that it remains securely applied to the tooth to be moved (Fig. 7). 2. The fine apron type of spring of 0.3 mm. (0.012 inch) wire, which is attached to and coiled around a heavy supporting arch wire. This spring

754

Adams has a long activity range of up to 8 mm. for a pressure of 20 Gm. (Fig. 8). 3. A stiffer self-supporting spring of 0.7 mm. (0.028 inch) wire. This spring has a coil when the sprin g arms arc short; when used as a long spring, a coil is not usually necessary. The spring combines within it.self support and activity. The range of action may be as short as 1.5 mm. for a pressure of 20 Gm. (Fig. 14).

Effect

of

spring

pressure

at

tooth

surfaces

Both the material of springs and the enamel toot,h surface are intensely hard and polished and, therefore, frictionless so that pressure between such surfaces can only be at right angles to the surfaces. If applied obliquely or at a sloping surface, the pressure becomes resolved into two components-one at right

B

Fig.

6.

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surface. and

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Rcmocable

appliamxx

755

angles to the surface (in the present context, tending to produce movement of the tooth in the direction of the resolved component) and a second component parallel to the inclined surface, tending to produce sliding between the two surfaces being pressed together. Vhen a metallic spring is applied to a tooth with curved surfaces, pressure is, in fact, exerted only at a single point and the direction of pressure on the tooth is at right angles to a tangent drawn at that point. The application of these facts can be illustrated by considering the proclination of an upper incisor by a pressure on the sloping lingual surface and the distal movement of a premolar by means of a finger spring acting from the lingual or palatal side. In the first instance the pressure exerted tends not only to procline the incisor but to depress it in its socket, and in the second instance a slight maladjustment of the spring could cause the premolar to move in a buccal direction (Fig. 6). Use

of

removable

appliances

Treatment with removable appliances will not provide the best answer to every orthodontic problem. Some small degrees of irregularity are impossible to treat with removable appliances, and some severe malocclusions respond well. Removable appliances can be designed easily to produce tooth movements labio- and buccolingually and mesiodistally. Expansion of the dental arches and the correction of dental arch relationship anteroposteriorlp require the movement of numbers of teeth labio- or buccolingually and mesiodistally. With removable appliances, it. is possihlc also to rotate certain tcrth or to more their roots to product uprighting. Lnhio- Ned huccohlgl~al tooth ~~1o~~e~)1P)lt. ~!pprr incisors may be proclincd

Fig. 7. An upper appliance with a single cantilever spring of 0.5 mm. (0.020 inch) wire with a guard or guide to ensure correct application to the tooth. There are bite planes to prop the bite temporarily so that the upper left central incisor can move across the bite. (From Friel and McKeag: The Design and Construction of Removable Orthodontic Appliances, Third edition, John Wright & Sons, Ltd., Bristol, by kind permission.)

756

Aw?. J. Gthodontics June 1969

Adams

singly, or two, three, or four at a time, using a single cantilever spring far a single tooth and a double cantilever spring for two or more teeth. The spring is made of 0.5 mm. (0.020 inch) stainless steel wire, and a guard is placed over it to ensure that it does not slip from its point of application to the tooth. In those circumstances in which a guard wire cannot be used efficiently, the base plate may be carried over the sprin g to provide some degree of guiding and protection (Fig. 7).

Fig. 8.

An

(0.040inch) coils

wire,

wound

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and

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edition,

Fig. used

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to and

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of apron

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are

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of

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Upper incisors can be retroclined a strong and rigid high labial arch of activity and, if made individually control of tooth movement (Fig. 8). The proclination of lower incisors a lingual arch to which are attached

Fig.

10.

cisors

Retroclination

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struction Bristol,

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of by

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ances,

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of

and

lower

incisors.

in a lingual Orthodontic

by means of apron type springs fixed to wire. Such springs have a generous range for each tooth, afford a high degree of may be effected by using a base plate with apron springs. This method is particularly

Elastics

direction.

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appliances

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across and

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of

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spring

of

0.5

Construction Ltd.,

Bristol,

of by

mm.

(0.020

Removable kind

permission.)

inch)

wire

Orthodontic

is used. Appli-

effective in that the springs used have a lon g range of action (Fig. 9). Ilower incisors can be retroclined in the same way as upper* incisors with a heavy arch wire and apron springs, but space in the lower labial sulcus is restricted and better t,o use a simpler appliance with elastics strotchrd Emn sicle it is asnally to side across the labial surfaces of the lowc~r incisors (Fig. 10). I~ahiolingual niovfxient 0 f the canine, pimlolar, and molar teeth is effected without difficulty b?- nicans of springs of 0.5 nim. (0.020 inch j and 0.7 mm. (0.028 inch) thickness, the finer springs havin g guards and the heavier springs being self-supporting (Figs. 11 and 12 j . Mesiodistal movement. The mesiodistal movement of teeth is brought, about, by making use of space that already exists in a mesiodistal direction or 1)~ using a space created by the extraction of teeth.

Fig.

12.

Lingual

thickness

is used.

Fig. 13.

Distal

wire

with

after

fitting

movement

movement

a guard of

of

the

and

of guide.

appliance.

a premolar.

a premolar The

tooth

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using behind and

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Removable

appliances

759

Such movements can be carried out in the majority of cases by means of finger springs acting from the lingual side. In the upper arch this arrangement works very well (Fig. 13). In the lower arch the same method can be used, although there are restrictions on the design and fitting of such springs into the space between the tongue and the alveolar process. In cases in which the upper canine tooth is outstanding and overlies the lateral incisor, it is difficult, from the lingual aspect, to reach t,he correct spot upon the canine tooth to exert pressure upon it. Under these circumstances it is better to use a heavier, selfThis arrangement is very efficient supporting spring placed in the buccal sulc~xs. and is well tolerated by patients. It is important not to overactivate such springs, for when this is done the springs do not remain in position but easily slip off and come to rest on an incorrect spot on the tooth surface (Fig. 14). Correction of arch relationships. The correction of occlusal malrelations as a whole by such means as intermaxillary and extraoral tract,ion can be done with removable traction of simple design (Fig. 15). The basic traction appliances consist of lower and upper plates, each clasped with four clasps, the lower carryin, 0 also a bow fitted accurately to the labial surfaces of the incisors and canines and the upper appliance bearing a screw or heavy lingual expansion arch. The expansion device in the upper appliance is to permit expansion of the appliance to follow the expansion of the dent,al arch as distal movement of the buccal segments takes place; it may also be used for active expansion if this is deemed necessary. Hooks for the attachment of elastics are formed in the construction of the clasps, and tubes for the attachment of a sliding labial arch or for extraoral attachments are quite easily placed in the clasps of t,he upper appliance by soldering. Xrith appliances of this kind, corrections in occlusal relationship in such conditions as Class II, Divisions 1 and 2 can be effected.

Fig. of flat

14. a

and

McKeag: John

Distal

movement

self-supporting applied The Wright

of spring

at

or

the of

above

upper

canine

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(0.028

the

anterior

Design

and

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end of

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Friel

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edition,

Am.

J. Orthoclmtics June 1969

The caution which it is usually necessary to exercise in applying intermaxillary traction to a postnormal occlusal condition with any appliance technique must also be exercised when removable traction plates are used. The lower appliance is designed to stabilize the low-cr dental arch as far as possible by distributing the active load over every tooth and, by means of a labial bow, to prevent forward inclinin g of the lower incisors ant1 crowding toget,hcr of these teeth. If there should be any doubt as to the stability of the lower labial segment, however, it is better to rely on the rise of extraoral traction alone, used at night, with the patient wearing the intraoral part. of the traction a.ppliance during the daytime as well (Figs. 16 and 17). nzm~ement. These movements arc not usually thought Rotation awl root

B

Fig. molar

15.

The

lower

Note

B, One

incisors. that

A,

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kind

will

take

an

Friel

and

McKeag:

Third

edition,

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traction

labial of

bow upper

extraoral The Wright

plate fitted traction attachment

Design & Sons,

and Ltd.,

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near

to as

four

appliance, which Construction Bristol,

teeth

possible

to

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be

added

of

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having

incisal

with

four for

edge clasps;

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hooks of

on the

the lower

also

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Appliances,

of as lying within the province of the removable appliance and, indeed, the teeth which can be rotated are relatively few in number, being the upper incisors and the upper premolar and molar teeth. The method used is to bring a mechanical couple of two equal and opposite pressures to bear on the extreme corners of the incisor tooth whereby the tooth is made to rotate (Fig. 18). The rotation of a tooth in this way is exceedingly effective, the forces produce a gentle turning moment, and the tooth remains comfortable throughout the movement. Adjustments need be made only at monthly intervals. Overrotation can be brought about, and after a period of retention the rotated tooth will settle to the final position required (Fig. 19).

Fig.

16.

the

upper

by

means

A case of

treatment

unilateral

The

the

incisors of

upper

occlusion

with

spacing

on

lower

lip.

rested

intermaxillary

occlusion

leaving

postnormal

upper

unilateral

the

duced,

of

arch.

traction

the

buccal

incisor

teeth

the with

segments inside

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the

lip.

the

lower

and Before

by

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well

carried

At

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A,

as

was

appliances.

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in Treatment

the

had

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end been

of re-

B, final

treatment;

result.

Fig.

17.

Severe

premolars

B, the were

and final

extracted.

Class use

stable

of

II,

Division

extraoral

result.

The

1

malocclusion

traction upper

with third

treated removable

molars

have

erupted;

of

A,

appliance. the

upper

Before lower

second treatment;

third

molars

.1 >)I. J. Orthodontics June 1969

The rotation of upper first molars which have rotated forward followiug early loss of deciduous teeth cau be brought about by a firm pressure upon the mesial contact point. The tooth rotates distally about the palatal root. It usual13 is not possible to perform this morerncut if the secoud molar has erupted, so rotation of the first molar should be done before the second molar corms up. The tipping of tooth apices is possible in the upper incisor region when, for instance, an incisor has been lost as a result of caries or trauma and it is necessary to align the adjoining teeth without. tilting, preparatory t,o jacket crowning. In bringing about such rnovcments, equal and opposite pressures must be applied to the crown of the tooth that is to be niovcd, one point of pressure application being at the giugival margin ou out side and mar the iucisal edge 011 the other. While such a method is suitable where tooth aligumcnt is goocl, if there is any

Fig.

18.

finger

Rotation

spring

produces

in

rotation

Removable

permission.)

Fig.

19.

Rotation

A,

Before

overrotation taneously

upper

of

the

was to

correct

A,

incisors.

lingual

Orthodontic

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of the

side. tooth.

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Removable

applia?aces

763

rotation or other irregularity to be corrected, a fixed appliance may be more appropriate (Figs. 20 and 21). Some functional appliances (for instance, the Andresen appliance) act rather by redirecting the forces of the masticatory muscles, altering the way in which the dental arches can be brought together and giving the whole mandible a new functional position while the a.ppliance is being worn. The Frankel appliance acts by redirecting the pressures exerted by the tissues and musculature of the cheeks, lips, and tongue. Removable

appliances

of

tomorrow

As for the future, we must ask in the context of this article: Will removable appliances be used more or less? Will removable appliances make more and better treatment possible?

Fig. 20. Root movement of kinds which may be used use finger springs placed The Design and Construction Wright & Sons, Ltd., Bristol,

Fig. 21. treatment;

Correction B, after

of the treatment.

the upper incisors. The springs shown are only one of various to produce this movement. It is often possible and better to on the palatal aspect of the teeth. [From Friel and McKeag: of Removable Orthodontic Appliances, Third edition, John by kind permission.]

axial

inclination

of

the

left

upper

central

incisor.

A,

Before

764

Adam

The answer to these questions will lie not in the appliances themselves but in the way in which they are used. In communities where dental and orthodontic treatments are the right of every person as measures toward health and wellbeing, treatments must be carried out with the greatest possible eficiency. Treatment by removable appliances is the most appropriate for many clinical problems and will undoubtedly come to play an increasing part in orthodontics in the future. REFERENCES

1. Adams, C. I’.: The modified 1 A. AddIns, C. F’. : The modified 333,

2. Crozat,

arrowhead arrowhead

clx~p, Tr. Rrit. Aoc. clasl~-Some further

Study Orthodont., cou~iclerations,

1’. 50, 1949. I). Sword 73:

195::.

(i.

ORTHOI)ONTIA

J%.: Possibilitit% 6:

1

and

use

of

rcmoml)le

lal)iolingual

spriug

appliancses,

TKT.

.J.

IgqJ1 .

3. E’riel, E. S., and ‘McKeag, H. 1’. A.: The design an11 construction of fixed orthodontic appliance% in stainless steel, D. Record 59: 359-399, 1939; Tr. European Orthodont. Sot. pp. 22, 53-84, 1938. 4. Jackson, V. 11.: Orthodontia and orthopaedia of the face, Philadelphia, 1904, .I. B. Lippineott Company. 5. Markham, L. M.: A new idea for retention of dental appliances, D. Record 49: 506, 1929. 6. Markham, L. M.: A new attachment for orthodontic appliances, Tr. Brit. Rot. Study Orthodont., p. 35, 1928; D. Record 48: 623, 1928. 7. Moyers, R. E.: An American view of removable appliances, Tr. Brit. Sot. Orthodont., 1964. 8. Mck’cag, H. T. A.: Physicsal laws and the design of orthodontic appliances, Tr. Brit. SOC. Study Orthodont., p. 69, 192X. 9. Schwarz, A. hf. : Lehrgang drr Gehissngclung, Band IJ, Vienna, 1956, Grl)an & Schwarzenburg. Tr. lirit. Sac. Study Orthodont., p. 33, 10. Visicdk, IT.: The retention of orthodontic plates, 1927.