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TitleContemporary Orthodontics 4th Edition
File Size92.1 MB
Total Pages762
Table of Contents
Section 1 : The Orthodontic Problem
	CH 1: Malocclusion and Dentofacial Deformity in Contemporary Society
Section 2 : The Development of Orthodontic Problems
	CH 2 : Concepts of Growth and Development
	CH 3 : Early Stages of Development
	CH 4 : Later Stages of Development
	CH 5 : The Etiology of Orthodontic Problems
Section 3 : Diagnosis & Treatment Planning
	CH 6 : Orthodontic Diagnosis:The Development of a Problem List
	CH 7 : Orthodontic Treatment Planning:From Problem List to Specific Plan
	CH 8 : Orthodontic Treatment Planning:Limitation,Controversies & Special Problems
Section 4 : Biomechanics,Mechanics & Contemporary Orthodontic Appliances
	CH 9 : The Biologic Basis of Orthodontic Therapy
	CH 10 : Mechanical Principles in Orthodontic Force Control
	CH 11 : Contemporary Orthodontic Appliances
Section 5 : Treatment in Preadolescent Children
	CH 12 : Treatment of Nonskeletal Problems in Preadolescent Children
	CH 13 : Treatment of Skeletal Problems in Children
Section 6 : Comprehensive Orthodontic Treatment in the Early Permanent Dentition
	CH 14 : The First Stage of Comprehensive Treatment:Aligment & Leveling
	CH 15 : The Second Stage of Comprehensive Treatment:Correction of Molar Relationship & Space Closure
	Ch 16 : The Third Stage of Comprehensive Treatment:Finishing
	CH 17 : Retention
Section 7 : Treatment in Adults
	CH 18 : Special Considerations
 in Treatment for Adults
	CH 19 : Combined Surgical & Orthodontic Treatment
Document Text Contents
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Page 381




Changing either the length of a beam or the way in which i t is attached dramatical ly affects i ts propert ies. Doubling
the length of a canti lever beam cuts i ts strength in half , but makes i t 8 t imes as springy and gives i t 4 t imes the range. More general ly,
strength varies inversely with length, whereas springiness varies as a cubic function of the length rat ios, and range as a second power

func t ion . Suppor t ing a beam on bo th ends makes i t much s t ronger bu t a lso much less spr ingy than suppor t ing i t on on ly one end.
Note that i f a beam is r igidly attached on both ends, i t is twice as strong but only one fourth as springy as a beam of the same mate-
r ial and length that can sl ide over the abutments. For this reason, the elast ic propert ies of an orthodontic arch wire are affected by
whether i t i s t ied t igh t ly o r he ld loose ly in a b racket .

but not as strong. Their useful sizes therefore are larger than
steel and quite close to the sizes for gold.

Effects of Length and Attachment
Changing the length of a beam, whatever its size or the mate-
rial from which it is made, also dramatically affects its prop-
erties (Figure 10-13). If the length of a cantilever beam is
doubled, its bending strength is cut in hall but its springi-
ness increases eight times and its range four times. More gen-
erally, when the length of a cantilever beam increases, its
strength decreases proportionately, while its springiness
increases as the cubic function ofthe ratio ofthe length and
its range increases as the square of the ratio of the length.
Length changes affect torsion quite differently from bending:
springiness and range in torsion increase proportionally
with length, while torsional strength is not affected by length.

Changing from a cantilever to a supported beam, though
it complicates the mathematics, does not affect the big
picture: as beam length increases, there are proportional
decreases in strength but exponential increases in springi-
ness and range.

The way in which a beam is attached also affects its prop-
erties. An arch wire can be tied tightly or loosely, and the
point of loading can be any point along the span. As Figure
10-12 shows, a supported beam like an arch wire is four
times as springy if it can slide over the abutments (in clini-
cal use, through a bracket into which it is loosely tied) rather
than if the beam is firmly attached (tied tightly). With mul-
tiple attachments, as with an arch wire tied to several teeth,
the gain in springiness from loose ties of an initial arch wire
is less dramatic but still significant.T

Controlling Orthodontic Force by Varying Materials
and Size-Shape
Obtaining enough orthodontic force is never a problem. The
difficulty is in obtaining light but sustained force. A spring

or arch wire strong enough to resist permanent deformation
may be too stiff, which creates two problems: the force is
likely to be too heavy initially and then decay rapidly when
the tooth begins to move. A wire with excellent springiness
and range may nevertheless fail to provide a sustained force
if it distorts from inadequate strength the first time the
patient has lunch. The best balance of strength, springiness,
and range must be sought among the almost innumerable
possible combinations of beam materials, diameters, and

The first consideration in spring design is adequate
strength: the wire that is selected must not deform perma-
nently in use. As a general rule, finger springs for removable
appliances are best constructed using steel wire. Great
advantage can be taken of the fact that finger springs behave
like cantilever beams: springiness increases as a cubic func-
tion of the increase in length of the beam, while strength
decreases only in direct proportion. Thus a relatively large
wire, selected for its strength, can be given the desired spring
qualities by increasing its length.

In practice, this lengthening often means doubling the
wire back on itself or winding a helix into it to gain length
while keeping the spring within a confined intraoral area
(Figure l0-14). The same technique can be used with arch
wires, of course; the effective length of a beam is measured
along the wire from one support to the other, and this does
not have to be in a straight line (Figure 10-15). Bending
loops in arch wires can be a time-consuming chairside pro-
cedure, which is the major disadvantage.

Another way to obtain a better combination of springi-
ness and strength is to combine two or more strands of a
small, and therefore springy, wire. Two l0mil steel wires in
tandem, for instance, could withstand twice the load as a
single strand before permanently deforming, but if each
strand could bend without being restrained by the other,
springiness would not be affected. The genesis of the "twin

SrcrroN IV BrourcHexrcs, MECHANTcs, AND Coutr lrponeRy ORTHoDoNTIC AppLIANCES

1 A1lz

l l q


Page 382

CHlptrn ro MEcHrurcar PnrNcrprEs rN OntHoooNrIc Forcr Cournor

A removab le app l iance incorpora t ing a can-
t i lever spr ings fo r in i t ia l t ipp ing o f a max i l la ry can ine toward a
premolar extract ion site. Note that a hel ix has been bent into the
base ofthe canti lever spring, effect ively increasing i ts length to
obtain more desirable mechanical propert ies.

wire" appliance system (see Chapter 12) was just this obser-
vation, that a pair of l0mil steel wires offered excellent
springiness and range for aligning teeth, and that two wires
gave adequate strength although one did not. Later, three or
more strands of smaller steel wires, twisted into a cable, came
into common use (see Figure 10-15). The properties of the
multistrand wire depend both on the characteristics of the
individual wire strands and on how tightly they have been
woven together. Multistrand wires offer an impressive com-
bination of strength and spring qualities, but now have been
displaced for most applications by NiTi wires.

The exceptional springiness of A-NiTi makes it a partic-
ularly attractive alternative to steel wires in the initial phases
of treatment when the teeth are severely malaligned. A con-
tinuous NiTi arch wire of either type will have better prop-
erties than multistrand steel wires and properties similar to
a steel arch wire with loops. TMA, as an intermediate
between NiTi and steel, is less useful than either in the first
stage of full-appliance treatment. Its excellent overall prop-
erties, however, make it quite useful in the later stages of

into the arch wire, as shown in the lower arch here, to increase the length of the beam segments between adjacent teeth; or using mult i-

stranded or small diameter steel wires, as shown in the upper arch. B, The exceptional range and f lat force-deflect ion curve of modern

supere las t ic A-N iT i w i re make i t poss ib le to use a s ing le s t rand o f r4 o r r6mi l w i re fo r in i t ia l a l ignment . Us ing these w i res is more e f f i -

cient than using mult i-strand steel wires because of the greater range of A-NiTi, and takes less cl inical t ime than bending loops, so A-

NiTi has almost total ly replaced both the steel alternatives. C, A round steel wire can be used advantageously to change the axial

incl ination of incisors i f this is needed at the init ial stage of treatment (as i t may be in Class l l division z patients), by bending loops

that contact the gingival area of the teeth when the wire is t ied in place. l f the end of the wire is free to sl ide forward, the result is facial

t ipping of the incisors; i f i t is bent over so that the teeth cannot t ip facial ly, the result is torque.

Page 761


Tooth movement-cont'd
forces, moments, and couples in,

with frontal versus undermining

resorption, 339f
growth modification and, 355
headgear and, 489, 528, 529
mandibular midline shift requiring,

mechanical principles for, 331
orthodontic, PDL reorganization and,

prolonged forces and, 333f, 333t, 337 t
reciprocal, 344-345, 344f
relationship of force to,344
segmented arch systems and,392
springs or screws in removable

appliances and,524
subdivision of, for anchorage control,

3 8 1 . 3 8 l f
Tooth size; see also Teeth

discrepancies in, 6l0f
defined, 199
malocclusion and, 138
space analysis and, 199
treatment during finishing.

present and past, l5f
proportional analysis of, 199, lc)9t,201
of unerupted permanent teeth, estimates

for, 197 -I99

edgewise system and, 376-377
of incisors during finishin g, 605 -607,

of incisors during minimum retraction,

600, 600f
moment-to-force ratios fot 37 5
placement in bracket, 421,423f
symmetric, lingual arch and, 391

Torque bends
in straight-wire appliances, 410-4ll
in utility arch wire, 385, 386f

Torquing arches, 603f, 605, 606f
Torquing springs

anterior, 40lt
stabilization of functional appliances,

523, s23f

geometry of wire, shear stress and,

ratios, as stiffness of wires, 366, 366t
Torticollis. 134. l35f
Toxoplasma, dentofacial development and,

1 3 1 1
Transforming growth factors, 39
Translation (bodily movement), optimum

forces for, 339 -340, 340f, 340t
Translocation, during jaw rotation, l18
Transpalatal arch

for molar rotation in Class II treatment,

overbite finishing and, 607
for space maintenance, 47 7 f

Transpalatal lingual arch, 389, 391, 391f,

Transpositions, treatment of, 457, 460f

Transverse plane of space; see also

evaluation of skeletal and dental

relationships in, 225 -226, 225f

Transverse problems; see also Surgically-

assisted palatal expansion
ma'<illary deficiency

treatment in mixed dentition,
498-s02, 499-501f

treatment planning, 284-287

Trauma; see also Fractures

during birth, Class II malocclusion and,


displacement ofteeth, 140-141, 14If, 160

orthodontic triage and, 244, 246f

treatment in mixed dentition,
457 -458, 46t-462, 462f, 463f

intrusive, orthodontic tooth movement

mandibular ankylosis and, 56, 56f

orthodontic treatment as prevention for,


orthodontic treatment for, l8

to teeth, root resorption and, 318

Treacher Collins syndrome, 73t, 7 4, 7 5f,

l3tr, r32,239
Treatment; see Orthodontic treatment

Treatment planning; see Orthodontic
treatment planning

Treatment Priority Index (TPI), Grainger's,
l 8

Triage, orthodontic
dental developm ent, 240, 242-243, 242f

facial profile analysis in, 239-240, 240f

nonskeletal problems in preadolescent

children, 433
other occlusal discrepancies, 243-245,

space problems, 243, 244f

syndromes and developmental

abnormalities, 238 -239, 239f

Tricyclic antidepressants, 343
Trifocal ellipse, as dental arch form,

427 -428

Triple-flex ar ch wir e, 362t
Trust, basic, development of , 63-64, 63f

Tubes; see nlso Brackets; Headgear tubes

in Herbst appliance, 398f

offset, first order bends and,420,42lf
stamped versus cast stainless steel, 418

Turbo arch wire,362t
Tweed, Charles,268, 278, 408
Tweed technique for maximum incisor

retraction, 599
22 slot bracket

for adjunctive treatment in adults, 637,

for extraction space closure

maximum anchorage, 599-600
moderate anchorage, 597 -598, 597 f

for finishing
incisor torquin g, 606-607, 607 t

individual tooth adjustments, 603
root paralleling, 604

for leveling by extrusion, 569,572
presurgicai orthodontic treatment and,


22 slot bracket-cont'd
sequence of arch wires in continuous

arch edgewise technique and, 604b

Twin-block appliances

bonded, indications for use, 51 l-512

clinical management of, 525-526

for mandibular deficiency, 5I5, 517,

for mixed dentition treatment of short

face problems, 535
properties of, 398-399, 398f
speech interference with, 400

malocclusion in, dental and facial

variations among, 144
mirror-image asymmetries in dentition

thumbsucking effects on, 149f

Twin-wire appliances, 37 0-37 l, 37 lf
Twist steel; see also Multistrand steel wire

in continuous arch edgewise technique,

Two point contact in root position control,
373-376, 373f,37 4f, 375f, 376f

2x 4 apphance
for anterior crossbite, 443
as bypass arch for leveling, 573,573f
to change incisor positions, 389
for maxillary midline diastema, 465
for mixed dentition treatment, 434-435,

2 x 6 appliance

to change incisor positions,390f
for mixed dentition treatment, 434-435,

for transverse movement of posterior

teeth, 389
Two-couple systems, 385

to change incisor positions, 389
continuous, 393
lingual arches as, 389, 391, 391f, 392f
segmented, 391-393
symmetric and asymmetric bends in,

386-389, 387-389f, 3881
for transverse movement of posterior

teeth, 389
Tylenol, 348


Ugly duckling stage of development, 100,

Undermining resorption
activation of orthodontic appliances

force magnitude and, 334, 337 t, 338-339,

Unerupted permanent teeth

size assessment , 197 -199, 198- 199t, 198b,

tooth movement in mixed dentition and,

Unilateral crossbite
lingual arch with buccal root torque for,

maxillary arch narrowing and,,175
treatment of, 438-439, 44Lf

Unilateral fixed appliances, 245

Page 762

Universit6 catholique de Louvain (UCL),
68 I -683

University of North Carolina orthodontic
clinic, 27 8 -27 9, 27 9f , 68 | - 683

for anchorage control, 381
of impacted second molars, 566,565f
optimum forces for, 3401
of posterior teeth in adjunctive

treatment, 639 - 644, 639 -644f
segmented arch mechanics for, 600

Uprighting springs, 37 4f, 603f
in finishing, root paralleling, 604, 605f
sectional, single molar uprighting in

adjunctive treatment, 641

genetic causes of malocclusion and,142
tooth decay, malocclusion, periodontal

disease and, 15
U.S. Public Health Service

dental radiography guidelines, 193t
Division of Public Health, 6

Utility arches
to change incisor positions, 389, 389f
with complex bends, 389
leveling by intrusion, 573,574
as two-couple system, 385, 386f

Valium, dentofacial development and, 13lt
Variability in growth and development,

Variability in outcomes and presentation,

data analysis and, 27 l-272, 272f,

Vascular system, in periodontal ligament

closing loop as, 594
lingual arch and, 391
properties of, 386-389, 3871 3881

Velocity curves, of growth, 32f, 33f,36, 37f,
109. l09f

Vertebral pathology, cephalometric
radiology and, 201, 204f

Vertical face
development of, jaw rotation and,

l l 7 - I 18 , 1 18 f
mandibular plane angle and, 185
palatal expansion in late mixed dentition

and, 499-500
proportion assessment during clinical

evaluation, 177, 179, l80l 182b, 183
Vertical plane of space

classification of,224b
evaluation of skeletal and dental

relationships in, 226 -227, 228f
Vertical problems; see also Long face

pattern; Overbite; Short face pattern
components for functional appliances,

and growth after implants, 671,673,673f
maxillary deficiency treatment and,

502-s05, 502-5081 508
Video digital recording, of facial views, 195
Visualized treatment objectives (VTOs),

Vital staining, 36-37, 38f
Vitamin D

excess, dentofacial development and,
l 3 l t

response to orthodontic force and,343
Voice control, 61

W-arch appliance

for arch expansion in primary dentition,

for posterior crossbite in mixed
dentition, 438-439, 439f

unequal, to correct unilateral maxillary
constriction, 441f

Wax bite, 193, 514-516, 5171


Wear, on teeth, bruxism and, 122
Weight; see ako Low birth weight

growth charts, 30f,3lf
Whites; see also Carcasians of European

anterior open bite and, 160
facial pro6.le in, 181, l83f
incisor crowding/malalignment in, 7,

Index of Tieatment Need for, 18, 2lf
lip and incisor prominence in, 183
lip prominence in, 182-183
overbite prevalence in, I I
percent estimated to need orthodontics,

1965-170 versus 1989-1994 in U.S.,

thumbsucking and/or tongue-thrust
swallowing in, 155f

Wire sizes, 555:. see also Arch wires
in U.S. and Europe,36l

Wire-bending robots, for forming, 428-429,
428f, 673, 67 4, 67sf, 676f

Wits cephalometric analysis, 206, 2I2
Wolff's law of bone, 276-277,277f
Working bite, Class II malocclusion

treatment, 514-516, 5L7f
Wraparound retainers, 623 -624

Wrist radiograph, developmental age
assessment and, 103, l03f

X-rays, dentofacial development and, l3lt


Yaw; of esthetic line of dentition,22O, 221f,

Yield strength, of elastic materials, 360,


Zygomatic anchors,681
Zy gomatic car tllage, 42 - 43


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