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Page 1

REMOVABLE
ORTHODONTIC
APPLIANCES

K. G. ISAACSON • J. D. MUIR
R. T. REED

Page 2

Removable Orthodontic
Appliances

K. G. Isaacson F.D.S., M.Orth R.C.S. Eng.

Consultant Orthodontist, North Hampshire Hospital, Basingstoke, UK

J. D. Muir B.D.S., F.D.S., M.Orth R.C.S. Eng.

Consultant Orthodontist, North Staffordshire Hospital, Stoke-on-Trent, UK

and

R. T. Reed B.D.S., F.D.S.R.C.P.S. Glas. M.Orth R.C.S. Eng.

Consultant Orthodontist, North Hampshire Hospital, Basingstoke, UK

OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI

Page 66

58 Removable Orthodontic Appliances

Figure 7.13 A stainless steel connecting bar
(2 mm X 1 mm half round) can be used to
reduce the amount of lingual acrylic.

Retention

Lower appliances have poorer retention than
upper appliances. This is partly because of
absence of palatal support but also because the
shape of many of the lower teeth can be less
favourable for clasping. The buccal aspect of
the lower first molar presents a sloping surface
and little undercut is obtainable. The conven-
tional Adams' clasp is more difficult to fit and
adjust satisfactorily than in the upper arch.
Therefore an additional clasp may be necessary
further forwards, perhaps on a first premolar or
canine.

Design of springs

Lingual springs

The size and shape of the lower baseplate is
such that it is difficult to incorporate springs on
the lingual side of an appliance for mesio-distal
movement of teeth. A limited amount of buccal
movement may be obtained with a lingual
spring particularly in the lower incisor region.

Buccal springs

The sulcus surrounding the lower arch is shal-
low and the design of a buccal spring has to take
this into consideration. Springs such as that
shown (Figure 7.14) are well tolerated and

Figure 7.14 A buccal spring (0.7 mm) to retracts3|.

useful in the retraction of canines. The spring
should be activated by curving the end of the
spring inward and cutting off a short piece of
wire (Figure 7.15). It is better not to adjust at
the loop because this moves the active end of
the spring occlusally so that secondary adjust-
ment is required. The spring should be flexed
lingually to ensure that it engages on the canine

Figure 7.15 The buccal canine spring is activated by
curving the end inwards and shortening the wire.

Page 67

and will, because this tooth is commonly
outstanding, assist in moving it into line.

Examples of design: retraction of
lower canines

Distal movement of lower canines is required
where there is anterior crowding. Space is
usually provided by extraction of first premo-
lars. Provided that the extractions are carried
out in the developing dentition, preferably
before the canines have reached the occlusal
level, they will usually drop back into the line of
the arch, allowing spontaneous alignment of
the incisors. Occasionally, this may not occur,
particularly when the occlusion prevents the
canine from improving and active retraction
with a removable appliance will be necessary.

An appliance to retract lower canines
(Figure 7.14)

Active component
A buccal spring in 0.7 mm wire.

Retention
Clasps on 6l6. Some operators also use a labial
bow but this adds little to retention and may
interfere with spontaneous alignment of the
incisors during canine retraction.

Baseplate
The baseplate must be thin enough for comfort
but thick enough for strength. A lower remov-
able appliance is always weak and the patient

Class I malocclusions 59

must handle it with care. A lingual bar rather
than acrylic in the incisor region may be
stronger and more comfortable for the patient.
The appliance will have to be trimmed lingual
to the canines and so the baseplate should be
made thicker in these areas (Figure 7.16).

Anchorage
This is provided by the clasped teeth and by the
teeth and alveolar process that are contacted by
the appliance. It is very difficult to supplement
anchorage in the lower arch when removable
appliances are used. This makes it all the more
important that light forces are used to retract
the canines.

Points to note
If there is occlusal interference with the retrac-
tion of the canines, an upper appliance with an
anterior bite plane is the most convenient way
of clearing the occlusion. If upper arch treat-
ment is not required, thin molar capping may
be included in the lower appliance and may add
to its stability and comfort.

Distal movement of lower molars

Where early loss of deciduous teeth has
allowed a first permanent molar to drift
forwards, encroaching on space for the second
premolar, it may be necessary to move the first
molar distally. This should be done only in an
otherwise uncrowded arch. The tooth move-
ment should be completed, if at all possible,
before the lower second permanent molar has

Figure 7 .16 The acrylic lingual to lower right
canine is too thin. Note how the acrylic is
correctly made thicker on the left.

Page 131

124 Index

Retraction,
canines, 50, 70
first molars, 52
premolars, 51
forces for on canines, 16
incisors, 71

Reverse loop buccal retractor, 23
Reverse loop labial bow, 26, 27
Roberts' retractor, 24

activation of, 99
Rotations, 5, 8

derotation of upper central incisor, 56
pericision after, 14
relapse after, 14

Screws, 27
developments in designs, 113

Self-straightening wires, 26
Single cantilever spring, 19
Skeletal patterns, 77,78
Soft tissues, 64
Soldered auxiliary spring, 23
Southend clasp, 33
Space closure in class I malocclusions, 49
Space maintainers in class I malocclusions,

47
Space opening in class I malocclusions, 48
Spontaneous movements,

eruption guidance, 2
mesial migration, 3
timing of, 4

Springs,
activation, 16
adjustment, 20
apron, 24
Bauschinger effect, 15
buccal, 58
buccal canine, 17
coffin, 21
construction, 19
design of, 58
guard wires for, 19
insertion and comfort of, 18
light wires, activation of, 99
Ungual, 58
mechanics of, 16
palatal, 19
recommended wire diameters, 119
stability of, 17
T spring, 20
unsupported, 18
Z spring, 20

Stability of springs, 17
Stability ratio, of buccal canine springs, 17
Stainless steel wire, properties of, 15
Study models, 86
Supported buccal canine spring, 18
Supported buccal retractor, 22
Supra-alveolar connective tissue, 12

T springs, 18, 20
activation of, 100

Tipping, 4, 8
bucco-lingual, 5
forces used in, 13
mesio-distal, 5
movement in plane of long axis, 9

Tissue changes during tooth movement, 11
Tongue,

effect on tooth position, 2
thrust, 64

Tooth movements, 8, 9
biochemical aspects of, 12
capillary blood pressure, 11
direction of and active components, 18
forces used in, 13
measurement of, 94
satisfactory progress with, 95
unwanted, 95

Traumatic tooth loss, 108
Twin screw appliance, 73

U loop labial bow retainer, 103
U loops, 25
Undercuts,

appliance fit, 93
in children, 30
lower removable appliances for, 57
problems in adults with, 31

Unilateral crowding, 109
Unsupported buccal canine spring, 18
Upper arch contraction, 56
Upper arch expansion, 55
Uprighting, 2

Vacuum-formed retainers, 103

Wind instruments, 117
Wire bending pliers, 87
Wire diameters, 119
Wire fractures and repairs, 116

Z springs, 20
activation of, 100

Page 132

REMOVABLE ORTHODONTIC
APPLIANCES

K. G. Isaacson F.D.S, M.Orth. R.C.S.(Eng.)
Consultant Orthodontist, North Hampshire Hospital Trust. Basingstoke, UK

J. D. M u i r B.D.S., F.D.S., M.Orth. R.C.S. (Eng.)
Consultant Orthodontist, North Staffordshire Hospital NHS Trust, Stoke-on-Trent, UK

R. T. Reed B.D.S., F.D.S. R.C.P.S. Glas. M.Orth. R.C.S. (Eng.)
Consultant Orthodontist, North Hampshire Hospital Trust. Basingstoke, UK

• definitive guide to the design and use of removable appliances providing essential practical
information for all dental undergraduates, practitioners and postgraduate trainees

• clear line diagrams show appliance design and components, useful for the practitioner
and technician

• accompanying CD-ROM contains clinical records of cases treated with removable appliances

Despite a great increase in the use of fixed appliances, the majority of courses of orthodontic treatment are
still carried out using removable appliances. This practical guide contains essential information on the design
and construction of removable appliances, in addition to guidance on diagnosis and treatment through the use
of clinical case studies. Written by three leading authorities in the field. Removable Orthodontic Appliances
contains relevant, up-to-date information making it an invaluable purchase for all dental undergraduates,
practitioners involved in orthodontic treatment and dental technicians.

An accompanying CD-ROM illustrates clinical cases in full colour, showing the results of effective
treatment when using removable appliances, whilst also highlighting areas of potential limitation.

CONTENTS: Preface • Introduction • Biomechanics of tooth movement • Active components • Appliance
retention • The baseplate • Anchorage • Class I - Class II - Class III malocclusions • Chairside;
management • Retainers • Problem cases • Appendices • CD-ROM: Clinical case records of patients
treated with removable appliances

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