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Systemized Orthodontic Treatment Mechanics

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    www.al l is lam.net

    Problem

    Systemized or thodont ic

    t reatment mechanics

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    Systemized or thodont ic

    t reatment mechanics

    Richard P McLaugh l in

    S a n D i e g o , C a l i f o rn i a , U S A

    John C Benne t t

    L o n d o n , UK

    Hugo J Trevis i

    Pres iden te Pruden te , B raz i l

    - .

    M Mosby

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    MOSBY

    An imprint of Harcourt Publishers Limited

    Mosby In terna tional I-(d 2001

    M is a registered tradem ark ofI larcourt Pu blishers Limited

    The right of L)r Richard P McLaughlin, Dr John C Bennett and Dr

    1

    lugo

    I

    Trevisi to be identified as

    authors of this work has been asserted by them in accordance with the Copyright , Designs and Patents

    Act 1988

    All rights reserved. No pail of this publication may be reproduced, stored in a retrieval system, or

    transmitted in any form or by any means, electronic, mechanical , photocopying, recording or

    Otherwise, without ei ther the prior permission of the publishers (Permissions Manager, Harcourt

    Health Sciences, Robert Stevenson House, 1-3 Baxter's Place, Leith Walk, Edinburgh EH1 3AF), or a

    licence permitting restricted copying in the Llniled Kingdom issued by the Copyright Licensing Agency,

    90 Tottenha m Court Road, London W l I' OI.P.

    f irs t published 2001

    1SBN072343171X

    Brit ish Library Cataloguing in Publicat ion Data

    A catalog ue record for this boo k is available from the British Library

    Library of Congress Cataloging in Publicat ion Data

    A catalog record for this book is available from the Library of Congre ss

    The

    publisher's

    policy is lo use

    paper manufactured

    from sustainable forests

    Typeset by IMH(Cartrif), Loanhead, Scotland

    Printed in Spain

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    PREFACE AND ACKNOWLEDGEMENTS

    - .aaii'n 1 iinHiiiii ttmBamargemKsmamBBmuBammmmmBimmmmmmammmmmmmmmmmmmmmm

    Goal -d i rec ted o r t hd don t ic t rea tm en t is ex t remely imp or ta n t .

    If the goals of t rea tm ent goa ls are no t kept in min d from the

    d iagnos i s and t rea tmen t -p lann ing phase th rough lo the phase

    of re ten t ion , co n t in uou s e r ro rs can be ma de . T rea tmen t then

    becomes inefficient and resul ts are dis ap po int ing . How ever,

    if t reatmen t goals are kept constan t ly in min d, resul ts b ec om e

    m u c h m o re c o n s i s te n t , a n d wh e n m i n o r c o m p ro m i s e s m u s t

    occur , the reasons fo r these can be unders tood , and many o f

    them can be avoid ed in the future. The goals of t rea tm ent for

    the autho rs are l is ted belo w. They ho pe the read er wil l keep

    these in mind when reading the text , to provide greater

    insight into thei r inte nt. It is ho pe d tha t in th at way it will

    have more mean ing . The t rea tmen t goa l s a re :

    Cond yles in a seated posi t io n - in centric re lat ion

    Relaxed heal th y mu scu latu re

    A 'six keys' (Mass I occ lus ion

    Ideal func t iona l mo vem ent s - a mu tua l ly p ro tec ted

    occlusion

    Periodontal hea l th

    Best possible aesthet ics .

    Th is book was o r ig ina l ly p lanned as a second ed i t ion o f

    the fi rs t Bennett and McLaughlin text , ent i t led

    Orthodontic

    Treatment Mechanics and the Preadjusted Appliance,

    p u b l i s h e d

    in 1993 . However , there have been so many techno log ica l

    changes and improvements over the pas t 8 years tha t an

    en t i re ly nex t t ex t became necessary , supp lemen t ing the

    general message of the first.

    A second Bennet t and M cla ugh l in t ext , en t i t l ed

    Orthodontic

    K4anagemenl of the Dentition with the P readjusted Appliance, wa s

    published in 1997. T his dev oted a cha pter to each too th in

    the den t i t ion , emphas iz ing c l in ica l s i tua t ions re la t ing to each

    tooth. I t evolved into a far m or e extensive project tha n

    ini ti al ly in tended , and requ i red a subs tan t ia l ma nusc r ip t to

    cover the wide range of material .

    With this th ird textb ook, t he in te nt io n is to retur n to a

    concise format somewhat s imilar in scope to the fi rs t . I ts

    p r imary focus is on o r tho don t ic t rea tmen t m echan ics , in

    par t i cu lar in t ra -arch cons idera t ions , o r the maneuvers

    invo lved in a l ignment and main tenance o f the den t i t ion in

    each individual arch. These factors are deal t with in Chapter

    5 Anchorage con t ro l du r ing too th l eve l ing and a l ign ing ' ,

    Chapter 6 'Arch level ing and overbi te control ' , Chapter 9

    'Space c losu re and s l id ing m echan ics ' , and Ch ap te r 10

    'Finishing the case ' . In ter-arc h consid era t ion s, or the

    coord ina t ion o f the upper and lower a rches in th ree p lanes o f

    space within the facial complex, are also given a s l ight ly

    g rea te r emphas i s than p rev ious ly ; in par t i cu lar , Chap ter 7 and

    8 deal with Class II t reatment and Class III t reatment ,

    respec t ive ly . These a re ex tens ive sub jec t s , bu t an a t t empt has

    been made to p resen t a concise and up- to -da te perspec t ive on

    the genera l management o f these two ca tegor ies o f case .

    Th e tex t d i scusses bo t h ex t rac t ion and non-e x t rac t ion

    t rea tm en ts . Grea ter em pha s i s is p laced on ex t rac t ion

    t rea tmen t , because the mechan ics o f these cases a re more

    com plex . This is no t to infer tha t the au tho rs t reat mor e cases

    on an extract ion basis ; in general , every effort is made to t reat

    on a non-ex t rac t ion bas i s wherever poss ib le , and the au thors

    t rea t a much h igher percen tage o f cases in th i s manner .

    Af te r us ing the o r ig ina l 'S t ra igh t -Wire* App l iance ' (SWA)

    for near ly 20 years , i t became impor tan t to p rov ide

    m o d i f i c a t i o n s t o t h e a p p l i a n c e t o m o re c l o s e l y c o m p l e m e n t

    m o d e rn t r e a t m e n t m e c h a n i c s . C h a p t e r 2 o n a p p l i a n c e

    spec i f ica t ion dea l s wi th the ra t iona le beh ind the changes

    ma de in the app l ian ce sys tem. Em phas i s i s p laced on th e new

    variat ions, as well as on the versat i l i ty of the appliance

    (compar i sons a re res t r i c ted to the o r ig ina l SWA and do no t

    re fer to o ther o r thodon t ic app l iances ) .

    A b racke t p lace me n t char t , deve loped in 1995 , has been

    mos t va luab le in the im por tan t a rea o f b racke t p lace men t .

    The tex t d i scusses recen t deve lopments in b racke t -p lacemen t

    techn iques - renewed in te res t in ind i rec t bond ing , fo r

    ins tance , has occurred because o f improved mater ia l s , such as

    adhes ive sys tems and t ray mater ia l s . An overv iew o f th i s

    subject is provided.

    Archwire t echno logy has improved d ramat ica l ly over the

    pas t 8 years . Th e use o f hea t -ac t iva ted n icke l - t i t an ium wires

    ( I IANT) has beco me a vi ta l part o f the t rea tme n t sys tem, and ,

    c o n s e q u e n t l y , m o d i f i c a t i o n s t o t h e t r e a t m e n t m e c h a n i c s h a v e

    occurre d . In fo rm at ion o n HANT wires , a lon g wi th a

    d i scuss ion o f a rchwire sequencing , i s p resen ted in Chap ter 5

    'Anchorage con t ro l du r ing too th l eve l ing and a l ign ing ' .

    S ince i t s in t roduct ion in the 1970s , a t t empts have been

    made wi th the p read jus ted app l iance to se lec t and use a s ing le

    arch fo rm on m os t pa t ien t s . Even us ing the mos t f requen t ly

    observed arch fo rm in the o r tho do n t i c pop u la t ion , the

    au thors observed numerous cases tha t were e i ther too narrow

    or over-e xpand ed . Therefo re , Cha p ter 4 is ded ica te d to the

    subject of arch form, and presents efficient techniques for

    manag ing arch fo rm se lec t ion and archwire coord ina t ion .

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    Chap ler 11 is ded ica te d to re te n t ion p ro toc o l , wh ic h i s a

    new subject for th is text . I t g ives an overv iew of the pro toc ol ,

    as well as desc ribing the me th od s mo st frequently used by th e

    authors .

    Drs Bennett and McLaughlin have spent a great deal of

    t ime wi th Dr Hugo Trev is i o f Pres iden te Prud en te , Brazi l, w ho

    has used this system of t re atm en t for over 20 years . Dr Tre vis i

    has p rov ided a num be r o f im por tan t in s igh ts in to the

    techn ique , and therefo re a dec i s ion w as mad e to in t rodu ce

    him as a th ird author of the text , thus reinforcing i ts

    in te rna t iona l perspec t ive , and b r ing ing toge ther the bes t ideas

    from three continents .

    The success of a project of th is scope and complexity

    d e p e n d s o n t h e c o m m i t m e n t o f m a n y i n d i v i d u a l s . T he

    a u t h or s a c k n o wle d g e a n d a p p re c i a t e t h e d o c u m e n t a t i o n s k il ls

    and extra photography carried out by the assis tants in each of

    the autho rs ' pract ices . The w ork of Pat ty Knecht an d Laura

    I ' lanie in San Diego, and Cath West in London, was

    invaluable, as were the in terpret ing ski l ls of Michelle Trevis i

    Araujo in Brazil.

    Text and i l lu s tra t ions were assemble d in Londo n , and

    product ion and pub l ica t ion were hand led by the Mosby team

    in Ed inburgh . On behal f o f the pub l i shers , Barbara S immons ,

    p ro jec t deve lopment manager , and her co l leagues con t r ibu ted

    unfai l ing energy' and ent hus ias m to th is project . The ir

    p ro fess iona l ism a nd respec t o f the au th ors ' so me t im es

    unconven t iona l work pa t te rns he lped make the pub l i sh ing

    process both efficient and enjoy able . Th e au th or s freely

    acknowledge the valuable help and advice given by Michael

    Park inson , com miss io n ing ed i to r . They a l so wish to m ake

    p a r t i c u l a r m e n t i o n o f t h e c o n t r i b u l i o n o f Gra h a m B i rn i e , wh o

    labor iou s ly checked and ed i ted the o r ig ina l t ex t, and o f lud i th

    W r i g h t , w h o wa s r e s p o n s i b l e fo r t h e d e s i g n . L o o k i n g a h e a d ,

    there a re p lans fo r a t l eas t 12 fo re ign co -ed i t ions , and the

    au t hor s a re g ra te fu l to I lona Turn iak fo r her work on d i i s

    i m p o r t a n t a s p e c t o f p u b l i c a t i o n .

    C h a p t e r s 7 a n d 8 i n c l u d e i n fo rm a t i o n o n t h e d i a g n o s t i c

    methods o f Dr Bi l l Arne t t , who gave cons iderab le t ime and

    a s s i s ta n c e , a n d m a d e i m p o r t a n t m a t e r i a l a v a i l a b l e for C h a p t e r

    8 . Th e au tho rs a re a l so g ra te fu l for Dr Fredr ik Bergs t ra nd ' s

    a d v i c e o n b o n d i n g , a n d for t h e p h o t o g ra p h . T h e a u t h o r s '

    work has benef i t ed over the course o f many years f rom the

    i n p u t o f i n t e rn a t i o n a l c o l l e a g u e s - a l t h o u g h s p a c e c o n s t r a i n t s

    make i t imposs ib le to acknowledge each ind iv idua l ly , the i r

    f r i e n d s h i p , e n t h u s i a s m a n d s u p p o r t d o e s n o t g o

    u n re c o g n i z e d .

    T h e fo l lo wi n g t e c h n i c a l p ro d u c t i o n i n fo rm a t i o n m a y b e o f

    in te res t . Th e o r ig ina l t ex t was gene ra ted in App le Work s 5 .0

    on a Ma cin tosh C4 com put er . L ine d raw ings were c rea ted in

    Apple Freehand 8 .0 , and tee th a re rep resen ted approx imate ly

    to sca le , wi th fo rm based on den ia l ana tomy tex t s . The co lo r

    p h o t o g r a p h s we re m a i n l y o r i g i n a l e d in Ko d a c h ro m e 6 4 . No

    d ig i ta l en ha nc em en t o f c l in ica l mater ia l too k p lace . Apa r t

    from the removal of red-eye on some of the facial

    ph o to gra ph s , il has been pu b l i sh ed d i rec t ly f rom the o r ig ina l

    Ko d a c h ro m e s l i d e s .

    F ina l ly , the au thors wou ld l ike to thank 3M Uni tek fo r i t s

    e f fo r t s in des ign ing the new app l iance , as wel l as fo r suppor t

    in the o ther a reas o f the t rea tmen t sys tem, such as b racke t -

    p l a c e m e n t g a u g e s a n d c h a r t s .

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    CONTENTS

    1. A br ie f h is tory an d overview of t rea tm en t m ech anic s 1

    2.

    Appliance specificat ion s - var ia t io ns an d versa t i li ty 25

    3. Bracket pos i t ion ing and case se t -up 55

    4.

    Arch form 71

    5.

    Anchorage con t rol du r in g too th leve l ing an d a l ign ing 93

    6. Arch level ing and overb i te con t rol 129

    7.

    An overview of Class II t rea tm ent 161

    8. An overview of Cla ss

    111

    t r e a t m e n t 2 1 7

    9. Space c losure and s l id in g me cha nics 249

    10.

    Finishing th e case 27 9

    11. A ppl iance removal and re ten t ion pro toco ls 30 5

    Index 319

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    CHAPTER 1

    A br ief h is to ry an d o v erv iew o f

    t reatment mechanics

    Introduction 3

    Fundamentals of treatment mechanics 3

    Bracket design

    Bracket positioning

    Archwire selection

    Force levels

    The work of And rews 4

    Wide range of brackets

    Center of the crown

    Various arch forms

    Heavy forces

    The work of Roth 6

    Roth brackets

    Center of the crown

    Wide arch form

    Articulators

    McLaughlin and Bennett 1975 to 1993 7

    Mainly standard brackets

    Center of the crown

    Ovoid arch form

    Light forces and sliding mechanics

    The work of McLaughlin, Bennett, and Trevisi

    between 1993 and 1997 8

    Re-designed bracket system - MBT

    Improved bracket posit ioning with gauges

    The work of McLaughlin, Bennett, and Trevisi

    between 1997 and 2001 12

    The decis ion to use three arch forms

    Updated l ight forces and s liding mechanics

    Overview of the MBT treatment ph ilos op hy 13

    Bracket selec tion 13

    Versatility of th e bracke t system 13

    Accuracy of bracket po siti on ing 13

    Light co nt in uo us forces 13

    The .022 versus the .018 slot 14

    Anchorage contro l early in treat m ent 15

    Gro up mov ement 16

    Th e use of three arch form s 16

    O ne s ize of rectangular s teel wire 17

    Archwire hoo ks 18

    M etho ds of archwire l igation 20

    Awareness of tooth s ize discrepancies 21

    Persistence in finishing 21

    Ca se SS 22

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    INTRODUCTION

    FUNDAMENTALS OF TREATMENT

    MECHANICS

    Andrews published his landmark article' in 1972, and

    subsequently designed an appliance based on his findings.

    However, soon after the introduction of the preadjusted

    appliance, it became clear that the bracket system required a

    whole new program of treatment mechanics and force levels

    lo fully realize its potential. In turn, the new treatment

    mechanics and force levels brought about a need for

    modifications to the bracket system. Ultimately, it has

    become the mechanics and force levels that have determined

    the appliance design, and not vice versa. This chapter reviews

    the evolution of orthodontic treatment mechanics since the

    early 1970s (the start of the modern era), and goes on to

    review the principles of the method currently used.

    Appliance design and treatment mechanics are closely

    inter-related. To some extent, bracket design can be scientific

    and based on research, so that bracket designs can be

    produced in a matter of months. However, development and

    refinement of ap propriate treatment mechanics take years,

    and have to be based on experience with numerous treated

    cases. Consequently, the information on treatment mechanics

    is often anecdo tal, and based on reco mm end ation s from

    experienced clinicia ns. F.ven well-structured investigatio ns

    into treatment efficiency tend to be inconclusive.

    3

    -

    3

    Orthodontic treatment mechanics are determined by four

    elements - bracket selection, bracket positioning, archwire

    selection, and force levels (Fig. 1.1). Ifabalanced

    com bina tion of these elements is used, efficient and

    systemized treatm ent can b e achieved. However, variation in

    one (for example archwire selection) can substantially

    influence the other elements and can undermine the

    effectiveness of the treatment approach.

    / Bracket

    / selection

    \ Bracket

    \ posi t ion ing

    Archwire \

    selection \

    Force /

    levels /

    F i g .

    1 .1 Or th odo n t i c t r ea tm en t mechan ics a re de te rm ined by

    fou r e lemen ts .

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    THE WORK OF ANDREWS

    Andrews is rightly regarded as the father of the preadjusied

    bracket system, and it is interesting to review his contribution

    in the light of experience over the last 25 years of clinical use.

    When the original Straight-Wire Appliance (SWA) beca me

    available in 1972, it was based on science, but included many

    of the traditional features of Siamese edgewise brackets.

    Andrews' paper was based on the measurement of 120 non-

    orthodontic normal cases. He then used the data as a basis to

    design a bracket system.

    Although the SWA was radically new, traditional heavy

    edgewise forces continued to be used. No special anchorage

    control measures, such as second order archwire bends, were

    employed. This may have been due to his clinical experience

    as an edgewise orthodontist and the force levels that were

    used. He also emphasized the 'wagon wheel effect' where tip

    was lost as torque was added. Hence, he chose to add

    additional tip to the anterior brackets. (Fig. 1.2).

    Bracket positioning was based on the center of the clinical

    crown. Because less wire bendin g was needed with the new

    appliance, there was also a trend to standardize arch form. As

    a result of Roth's influence, there was a general movement

    toward a broad or square arch form, although Andrews

    continued to use the basal bone of the mandible as an arch

    form reference. Various arch forms were used because no clear

    direction w as available.

    S W A t i p

    R e s e a r c h t i p

    2

    - 2 " 11 9

    C

    5 " 2 . 8 2 .7 '

    !

    8.4" 8.0 3.6

    SWA tip

    1.5" 1.3 2.5" 0.4" 0.5

    Research t ip

    F ig .

    1 .2 The o r i g i na l S t ra igh t -W i re App l i ance (SWA) was based on mea su remen t o f 120 non -o r th odo n t i c no rm a l cases, a l t ho ugh

    ext ra t ip was bu i l t in to the anter ior brackets .

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    Difficulties were encountered with treatment mechanics in

    the early years, clue to the heavy forces and possibly d ue to

    the increased tip in the anterior brackets. Consequently,

    deepening of the anterior bite, with creation of a lateral open

    bite, was seen in many cases, and this became known as the

    'roller coaster' effect (Figs 1.3-1.6).

    Fig .

    1.3 In the ear ly years of the p read justed ap pl ianc e, heavy

    forces were used, and these wer e associated wi t h de epe ning of

    the anter ior b i te and creat ion of a la tera l open b i te which

    became known as the ' ro l ler coaster ' e f fect .

    i

    Fig. 1.4

    F i g . 1.5

    F i g .

    1.6

    Figs. 1.4 to 1.6 The t r ea t me nt sequence above shows t he ' r o l l e r coas t e r' e f f ec t deve lop i ng i n an ear l y t r ea t me nt w i t h t he o r i g i na l

    SWA. The un wa nte d dee pe nin g of the o verb i te was due to excess force a nd the use of e last ic ret ra ct io n m echanics.

    These early clinical experiences led Andrews to introduce a

    series of modifications, and after using the original 'standard'

    Straight-Wire Appliance for a period of time, he

    recommended a wide range of brackets. For example, he

    determined that for extraction cases, canine brackets with

    anti-tip, anti-rotation and power arms were needed (Fig. 1.7).

    He also recommended the use of three different sets of incisor

    brackets, with varying deg rees of torq ue for different clinical

    situations.

    \

    Wide range

    of brackets

    Brackets

    pos i t ioned a t

    the center of the

    clin ical crown

    \

    Various \

    a rch forms \

    \

    eavy force /

    levels j

    /

    F i g .

    1 .7 Or t ho don t i c t r ea t m en t mechan ics in t he ear l y years o f

    t he SWA.

    w w w . a l l i s l am. ne t

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    THE WORK OF ROTH

    Following his ear ly experiences with the or ig ina l SWA, Roth

    in t roduc e d me a s u re s to ove rc ome da y - to -da y s ho r t c omings

    which he had found in c l in ica l use . Whereas Andrews , wi th

    the f i rs t genera t ion of preadjus ted brackets , was

    recommending a la rge range of bracket spec if ica t ions , Roth

    was anxious to avoid the in vento ry diff icul ties of a m ul t ip le

    b rac ket s ys te m. He the refo re re c o mm e nd e d a s ing le a pp l i a nc e

    sys tem, cons is t ing primari ly of minimum extrac t ion ser ies

    brackets , which he fe l t would a l low him to manage both

    extrac t ion and non-extrac t ion cases .

    This has been described as the second genera t ion of

    p re a d jus t e d b ra c ke t s , a nd R o th ' s r e c omme nda t ions we re

    widely accepted by c l in ic ians , some of whom had experienced

    s imilar d i ff icul t ies in t rea tment mechanics and were confused

    by the wide varie ty of ava i lable brackets . The appl iance

    prescript ions developed by Andrews and Roth were based on

    the overa ll t rea tm ent me chan ics used in the ir prac t ices .

    The R o th t r e a tme n t a pp roa c h e mpha s iz e d the us e o f

    ar t icula tors for d iagnos t ic records , for ear ly spl in t

    cons truc t ion, and for the cons truc t ion of gnathologica l

    pos i t ioners a t the end of t rea tment (Fig . 1 .8) . This approach

    was used to a id in es tabl ishing correc t condyle pos i t ion. He

    used the center of the c l in ica l c rown for bracket pos i t ioning,

    as advo caiec ib y Andrews . As s ta ted abov e , h is a rch form was

    wider than Andrews ' in order to avoid damage to canine l ips

    du r ing t r e a tme n t a nd to a s s i s t i n ob ta in ing good p ro t rus ive

    function.

    Bracket posit ioning at

    the cent re of the

    cl inical crown

    Emphasis o n

    ar t icu la tors

    F i g . 1 . 8 R o t h s e l e c t e d a r a n g e o f b r a c k e t s t o c r e a t e a s i n g l e

    a p p l i a n c e s y s t e m .

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    THE WORK OF MCLAUGHLIN AND

    BENNETT BETWEEN 1975 AND 1993

    Although they evalua ted many bracket varia t ions , inc luding

    (he Andrews ' ' t rans la t io n ' se r ies , in the period 1975 to 199 3

    McLaughl in and Bennet t preferred lo work mainly with the

    s tandard SWA bracket sys tem. Ins tead of in i t ia l ly m odif ying

    the bas ic bracket des ign, for more than 15 years they

    developed and ref ined t rea tment mechanics based on s l id ing

    mechanics and cont inuous l ight forces , mainly us ing s tandard

    SWA brackets . These m echa nics we re pu bl is hed in i t ia l ly as a

    series of papers in the early 1990s '

    1,51

    ' an d t hen as a bo ok in

    1 9 9 3 '

    ( pi g i 9 )

    a n t

    |

    n a v e s e e n

    wide s p re a d a c c e p ta nc e .

    T h e i r t r e a t m e n t m e c h a n i c s r e c o m m e n d a t i o n s i n c l u d e d

    a c c ura te b ra c ke i pos i t ion ing , a nd l a c e ba c ks a nd be ndba c ks fo r

    early anchorage control , wi th l ight a rchwire forces (Fig . 1.10).

    S l i d i n g m e c h a n i c s w e r e r e c o m m e n d e d o n . 0 1 9 / . 0 2 5 s t e e l

    rec tangu lar wires , wi th l ight .014 f in ishing w ires .

    They used the middle of the c l in ica l c rown for bracket

    pos i t ion ing du r ing th i s de ve lopme n t pe r iod . A me d ium-s iz e d

    s tandard ovoid arch form was used for the majori ty of cases ,

    and the s ize re f lec ted the fac t tha t many of the ir pa t ients were

    c h i ld re n w i th ma loc dus ions , un l ike Andre ws ' s a mple o f 120

    norma l s , wh ic h we re non-e x t ra c t ion a du l t s w i th l a rge a rc he s .

    / Standard

    / SWA bracke t

    / select ion

    Brackets

    \ posit ion ed at

    V the center of the

    \ c l inical cro wn

    Ovoid \

    archwire \

    select ion \

    Light force I

    levels and sl iding /

    mechanics /

    ^

    F i g .

    1.9 Orthodontic Treatment M echanics and the Preadjusted

    Appliance was publ ished in 1993.

    F i g .

    1 .1 0 O r t h o d o n t i c t r e a t m e n t m e c ha n ic s e v a l u a t e d b y

    M c Lau gh l i n and Benn e t t f r om 1975 to 1993 .

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    THE WORK OF MCLAUGHLIN. BENNETT,

    AND TREVISI BETWEEN 1993 AND 1997

    Having es tabl ished an overa l l approach and a success ful

    sys tem of t rea tment mechanics us ing the preadjus ted bracket

    sys tem in i ts s tandard form, M cLaughl in a nd B ennet t the n

    worked with Trevis i to re -des ign the ent i re bracket sys tem to

    c omple me n t the i r p rove n t re a tme n t ph i lo s ophy a nd to

    overcome the perce ived inadequacies of the or ig ina l SWA.

    They re-examined Andrew s ' or ig ina l f indin gs , and too k in to

    account addi t ional research input from Japanese sources

    8, 1

    '

    when des ignin g the MBT bracket sys tem .

    This th i rd-genera t ion bracket sys tem re ta ined a l l tha t was

    bes t in the or ig ina l des ign, but a t the same t ime in t roduced a

    ra nge o f improve me n t s a nd s pe c i f i c a tion c ha nge s to ov e rc om e

    the c l inica l shor tcom ings . I ts des ign was based on a ba l anc e

    of bas ic sc ience and many years of c l in ica l experience . MBT'"

    is a version of th e prea dju sted brac ket system specifically for

    use with light, co nt in uo us forces , lacebacks an d b end bac ks ,

    and i t was des igned to work idea l ly with s l id ing mechanics .

    Th e o r ig ina l s yst e m o f do t s a nd d a s he s wa s s upe rs e de d by

    la se r nu m be r ing o f s t a nd a rd s i z e me ta l b ra c ke t s , a nd the

    re c ta ngu la r s ha pe wa s re p la c e d by the rhomboida l fo rm. Th i s

    re duc e d the bu lk o f e a c h b ra c ke t a nd c oo rd in a te d pe rs pe c t ive

    l ine s th rough on ly two p la ne s , t he re by a s s i s t ing a c c u ra c y o f

    b ra c ke t p l a c e me n t . The b ra c ke t s ys t e m wa s ma de a va i l a b le in

    s t a nda rd me ta l (F ig .

    1.11),

    mid-s i z e d , a nd c l e a r fo rms

    (Fig.

    1.12).

    It had suff ic ient versa t i l i ty to dea l wi th mos t

    c l in ica l s i tua t ions , and to l imit inventory leve ls .

    As p re v ious ly s t a t e d (p . 4 ) , t he a n te r io r l i p s pe c i f i c a t ions

    for the or ig in a l SWA wer e a ll grea ter tha n th e research

    f ind ings . Add i t iona l t i p ba d be e n bu i l t i n , ove r a nd a bove the

    s c ien t i fi c me a ns . For e xa m ple , t he im por t a n t u ppe r c a n ine

    carri ed 11 in th e first-generation (SWA) an d the n 13 in th e

    s e c o n d - g e n e r a t i o n ( R o t h )

    1

    " s ys t e m, c om pa re d w i th the

    research f inding of 8 .

    F ig . 1 .11 S tan dard meta l

    cont ro l .

    MB T b racke ts g ive op t ima l too th F i g . 1 .12 Th is case has C lar i ty brackets on the u ppe r a n te r io r

    tee th and m id -s ized me ta l b racke ts on the low e r an te r io r tee th .

    T he th re e d i f fe ren t b racke t op t ions o f s tanda rd me ta l , m i d

    s ized meta l and c lear fo rms may be used in combinat ion fo r the

    same pa t ien t .

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    Additional anterior tip was a disadvantage for three

    reasons:

    1. It created a significant drain on antero-posterior (A/P)

    anchorage.

    2. It increased the tendency to bite dee pening during the

    alignment stage.

    3. It brought the upper canine root apex too close to the first

    premolar root in some cases.

    As lighter forces were being used in all stages of tre atm ent,

    this additional 'anti-tip', or second-order com pensa tion, w as

    not needed. Therefore, when designing the MBT" bracket

    system, it was decided to base the anterior tip on the original

    research values. These assisi treatment mech anics becau se they

    reduce the anchorage control needs, reduce the tendency to

    bite deepening in the early stages of treatment, and put less

    demand on patient cooperation. When the original research

    values for tip are used for incisors and canines, a total of 10

    less distal root lip in the upper anterior segment and 12 less

    distal root lip in the lower anterior segment is needed,

    com pared with the original SWA (Pig.1.13).As the M BT"

    measurements are based on Andrews' original research

    figures, there is no compromise in ideal static occlusion. And

    if the condy les are in centric relation, there is no com prom ise

    in ideal functional occlusion as described by Roth.

    SWAtip Recommended tip

    Fig. 1 .13 The rec om m ende d t i p m e as urem ents f o r t he M BT brac k e t s y stem a re bas ed on A ndrew s ' o r i g ina l r es earc h f i gu res , and

    these features g ive less d is ta l root t ip in the up pe r and lo we r an ter io r se gments .

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    The preadjusted appliance system is a development of the

    edgewise bracket, which is relatively inefficient in delivering

    torque. When designing the MBT bracket system, it was

    therefore necessary to build extra torque into the important

    incisor and molar regions in order to meet clinical goals in

    these areas with a minimum of wire bending (Figs 1.14 &

    1.15).

    This design feature helps to overcom e the fund ame ntal

    shortcoming of the original edgewise bracket.

    Brackets with three options for canine torque were needed

    to deal with different patient arch forms and other clinical

    variables. Andrews' research finding of-7 torque in the

    upper canines, and a reduced torque figure o f- 6 (from

    -11) in the lower canines, is satisfactory for the canines in

    many cases.Ilowever,atypical ortho don tic caseload is a

    different sample from the 120 non-extraction adults. Hence

    there is a need for three canine torque options.

    It was decided that upper canine brackets would be

    available with -7, 0 and +7 torque values in the new

    MBT" system, because versatility was needed. The 0" and +7

    C

    options are preferred for cases with narrow maxillary bone

    , Central

    F ig . 1.14

    -1

    -1

    Original SWA

    Recommended torque

    F ig . 1.15

    Original SWA

    -14

    c

    Recommended torqu e

    10

    F igs . 1 .14 and 1 .15 Extra to r que was bu i l t in to the MBT bracket sys tem in the i mp or tan t inc isor and mola r reg ions com par ed

    w i th the o r ig ina l S WA .

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    form and/or prominent canine roots (Fig.1.16).Lower canine

    torque is -6, but 0 or even +6 is available for some cases

    (Fig.

    1.17),

    if needed.

    In the period from 1993 to 1997, McLaughlin and Bennett

    also revised their recom me ndations on bracket positioning, to

    improve vertical accuracy. In the early years, they had used the

    middle of the clinical crown for bracket positioning, but they

    subsequently" developed a better system. This accepted the

    principles advocated by Andrews, but also used gauges to

    ensure greater vertical accuracy (p. 62 ). Their w ork on the

    revised bracket designs and the new bracket positioning

    technique was incorporated into a second bo ok,

    1 2

    published

    in 1997 (Fig.1.18).

    F i g .

    1 .16

    -7 torque

    0" torque

    F i g .

    1.17

    -* torque 0" torque

    +7 lorque

    + 6 t o r que

    CD

    7 3

    O

    -

    n

    >

    n

    tyi

    Figs. 1.16

    and

    1.17

    V e rsa t i l it y w as needed fo r can ine to rqu e , and the re fo re th ree op t ions w e re m ade ava i lab le fo r uppe r and low e r

    canines.

    Orthodontic

    Management of

    tfee Dentition with

    the ['readjusted

    Appliance

    ORTHODONTIC

    MANAGEMENT OF

    THE DENTITION Wlffl

    1HE PREADJUSTED

    APPLIANCE

    .Win C Iknm-li Ri.-ta UMaug Wii

    KA

    M*J

    / New range

    / of MBT "*

    / brackets

    \ Brackets posit io ned

    \ w i t h the he lp

    \ of gauges

    V^_

    Ovoid

    archwire \

    select ion \

    L ight force

    levels and sl iding /

    mechanics /

    ^ y

    Fig.

    1.18 Orthodontic Manag ement of the Dentition with the

    Preadjusted Appliance was pub lishe d in 1997 an d is sche duled

    to be republished in January, 2002.

    F i g . 1 .19

    Or th odon t i c t rea tme n t mechan ics deve loped by

    McLaugh l in , Bennet t , and Trev is i up to 1997.

    11

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    THE WORK OF MCLAUGHLIN, BENNETT,

    AND TREVISI BETWEEN 1997 AND 2001

    In orde r to c omple te a mode rn s ys t e miz e d me thod o f

    t rea tment mechanics , i t became necessary to address the

    subjects of archwire selection and force levels .

    Al though an ovoid arch form had proved useful in (he

    early years , because of prev ious an d cu rrent a rch form

    research, i t was rec om me nd ed (Fig . 1 .20) tha t th ree bas ic

    shapes of a rch form - tapered, squa re , an d ovoid - w ou ld be

    re qu ire d (p . 74 ) . W h e n s upe r im pos e d , t he y va ry ma in ly in

    inter-canine and in ter-premolar width , g iving a range of

    a pprox ima te ly 6 mm . In t e r -m ola r w id th s o f the th re e s ha pe s

    a re qu i t e s imi l ar , bu t t he m o la r a re a s o f w i re s c a n be w id e ne d

    or narrowed as needed, by easy wire bending.

    R e c omme nda t ions we re pub l i s he d c onc e rn ing a rc h fo rm a nd

    archwire se lec t ion.

    IS

    This th i rd boo k brings a l l (he four t rea tm ent me cha nics

    essentials togeth er. I( covers brack et desig n, b rack et

    placement , and archwire se lec t ion, and i t re -defines force

    le ve l s ( fo r e xa mple lo inc o rpora te re c omme nda t ions fo r the

    use of hea t-ac tiva ted nickel- t i tan ium (H A NI ) wires ) , re -s ta t ing

    the overal l t rea tment phi loso phy . I t describes a w el l - tes ted

    and effec t ive sys tem of t rea tment mechanics for the

    preadjus ted appl iance sys tem.

    F i g .

    1 .20

    Or th odo n t i c t rea tme n t mechan ics deve loped by

    McLa ugh l in , B enn e t t , and T revis i up to 2001 .

    12

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    OVERVIEW OF THE MB T TREATMENT

    PHILOSOPHY

    The fo llowing e l e me n t s m a ke up the M BT t re a tme n t

    phi losophy, and in the remainder of th is chapter each wil l be

    reviewed in turn:

    Bracket selec tion

    Versatility of the bracket sy stem

    Accuracy of bracket p os i t i oni ng

    Light co nt inu ou s forces

    The .022 versus the .018 s lo t

    Anchorage control ear ly in t rea tm ent

    Group move m e n t

    The use of three arch form s

    On e size of recta ngu lar steel wire

    Archwire ho ok s

    Methods of a rchwire l iga l ion

    Awareness of too th s ize discrepa ncies

    Persistence in finishing

    Bracket selection

    At the heart of the tech niq ue is a h igh qual i ty , versa t i le

    bracket sys tem. A range of s tanda rd me ta l , m id-s ized , a nd

    clear brackets is available. The exact bracket specifications are

    impor ta n t , a nd a t t e mpts to u s e ' s ome th ing s imi l a r ' c a n

    adverse ly affec t the ba lance of the t rea tment mechanics , and

    may not produce the des i red t rea tm ent resul t .

    The o r thodon t i s t ' s t ime i s t he mo s t va lua b le c omm odi ty in

    the or thod ont ic c l in ic . Th ere is a need for the or tho do nt i s t to

    have comple te confiden ce in a re l iable bracket sys tem, whic h

    gives cons is tent perform ance , and can be used to save

    chairside time in the finishing stages of treatment.

    Versati l i ty of the bracket system

    The sys tem's ful l nam e is MBT Versa t i le+ a nd as the na m e

    implies, it is des igned to be versa t i le , in orde r to dea l wi th

    most t rea tment cha l lenges . Th is versa t i li ty (p p 39 -5 1 ) is

    useful in both co ntrol l in g invento ry cos ts and avo idin g

    needless wire b end ing.

    Accuracy of bracket posi t ioning

    This is a cor ner s ton e of the t rea tm ent a pp roa ch. Every effort

    sho uld be m ad e to ens ure accuracy, an d i t i s par t of the

    t e c hn ique to re p os i t ion b ra c ke t s if ne c e s s a ry a s t r e a tme n t

    p rog re s s e s. Ga uge s a nd ind iv idua l b ra c ke t -po s i t ion ing c ha r t s

    are recommended. In teres t ingly , the search for accuracy has

    l e d to a n ups u rge o f r e ne we d in t e re s t i n ind i re c t bond ing

    (p . 69) .

    Light continuous forces

    The t e c hn ique re qu i re s the us e o f l i gh t c on t inuous fo rc e s . The

    au tho rs be l ieve th is is the mo s t e ffec tive way to mov e tee th ,

    be ing c omfor t a b le fo r the pa t i e n t a nd min im iz in g the th re a t

    to anchorage . Light forces a re espec ia l ly important a t the s ta r t

    o f t r e a tm e n t , wh e n the b ra c ke t t i p pu t s de m a n d u po n a n le ro -

    pos te r io r (A /P) a nc ho ra ge , a nd wh e n it i s im por t a n t t o

    mi n im iz e pa t i e n t d i s c omfor t .

    I t i s not poss ible to exac t ly quant i fy the te rm ' l ight forces ' .

    Trad i t ional ly , forces in the range be low 200 gm were referred

    to as light forces, and forces in the range ab ove 6 00 gm w ere

    referred to as heavy forces! Esse ntially ther e is a need for the

    ort ho do nt i s t to use th in , f lexible wires ear ly on, wi th m inim al

    de f l e c t ion , a nd to a vo id too f re que n t a rc hwi re c ha nge s . A l s o ,

    the c l in ic ian needs to recognize the s igns of excess force , such

    a s t i s sue b l a nc h ing , pa t i e n t d i s c omfor t , a nd u nwa n te d too th

    movements (for example rol le r coas ter e ffec t) , and take s teps

    to avoid these .

    Later in t rea tment , during s l id ing mechanics , l ight

    cont inuous forces a re appl ied us ing ac t ive t iebacks and r ig id

    .019 / .025 s t e e l work ing w i re s (p . 254) . In the f in i s h ing s t a ge s ,

    l ight wires such as .014 s tee l or .016 1IANT are used for

    de ta i l i ng o f too th pos i t ions a nd s e t t l i ng .

    Alth oug h ' l ight forces ' can not b e define d or quan t i f ied , i t i s

    hoped tha t careful s tudy of th is text and the various case

    reports wi l l g ive c lear c l in ica l guide l ines on th is subjec t to the

    reader .

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    33

    m

    The .022 versus the .018 slot

    >

    TO

    O

    n

    >

    F ig .

    1 .23 Can ine lacebacks are an im por tan t fea tu re o f the MB T

    I M

    t re a tm en t ph i los ophy an d are used to assist in con tro l o f can ine

    crowns dur ing leve l ing and a l ign ing .

    F ig .

    1 .24 Bendbacks he lp to preven t mes ia l mo vem ent o f the ante r io r tee th and ensure com for ta b le p os i t io n ing o f the arch w ire

    ends in the molar regions.

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    n

    Group m ov em en t The use o f t h re e a rch fo r m s

    >

    CD

    73

    o

    Where poss ible , tee th a re managed in groups ( l - ' ig . 1.25). In

    pre pa ra t ion fo r g roup move me n t in p re mola r e x t ra c t ion c a s e s ,

    for example , lacebacks are used to control canines and re t rac t

    them suff ic iently to a l low a l ig nm en t of the inc isors . In the

    lower a rch, canin es a re re t rac ted with lacebacks unt i l ante r ior

    crowding is resolved. After th is , the lower anter ior segment is

    ma na ge d en masse, as a group of s ix or e ight tee th . In the

    upper a rch, canines a re not normal ly re t rac ted away from

    la tera l inc isors . How ever , i t i s im po rta nt to m ain ta in a Class I

    canine re la t ionship . Therefore , a laceback should be

    c on t inue d in the uppe r a rc h to ma in ta in the C la s s I c a n ine

    re l a t ions h ip , e ve n i f i t me a ns mov ing the c a n ine a wa y f rom

    the lateral incisor (Case JN, p. 1 23 ). It is als o necess ary t o

    mo ve the cani ne away from th e la te ra l inc isor in s i tu a t io ns

    where a la te ra l inc isor is smal l , and wil l require future bui ld

    up , and in some cases with a midl ine shif t .

    Un t i l t he mid -1 990 s the ovo id a rc h fo rm (p . 76 ) wa s

    preferred for mos t of the authors ' cases . They regarded i t as a

    re l i a b le fo rm fo r a h igh pe rc e n ta ge o f p re a d jus t e d a pp l i a nc e

    cases.

    During the la te 1990s , the authors found i t benefic ia l to

    us e a t a pe re d a rc h fo rm fo r ma ny c a s e s , a nd s ome t ime s a

    s qua re a rc h fo rm. Th e t a pe re d form h a s the na r rowe s t i n t e r -

    c a n ine w id t h a nd i s obv ious ly ind ic a te d fo r pa t i e n t s w i th

    na r row , t a pe re d a rc h fo rms . The s qua re a rch fo rm i s i nd ic a te d

    in cases with broad arch forms and for cases tha t require

    buc c a l up r igh t ing o f the lowe r pos te r io r s e gme n t s a nd

    e x p a n s i o n o f t h e u p p e r a r c h . C u r r e n t l y , t h e r e c o m m e n d e d

    tec hn iqu e is to c rea te an indiv idual i zed form for a ll pa t ien ts ,

    ba s e d on the ovo id , t a pe re d , o r s qua re fo rms (pp 78 -79) .

    F ig . 1 .25 Wh ere poss ib le, g ro up mo vem ent is carr ied ou t , and the uppe r and lower ant er io r segm ents are ma nag ed as a gr ou p o f

    s ix o r e igh t tee t h . In s i tua t ion A , the space has been c losed by mes ia l move me nt o f molars and prem olars - a min i m um anc hora ge

    treatm ent . In s i tu a t ion B , the inc isors and can ines have been re t rac te d in t o the ava i lab le space - a max imu m anch orag e s i tu a t io n as

    might occur in a Class II I case or a bimaxil lary protrusion case.

    16

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    One size of rectangular steel wire

    Only one size of steel rectangular wire is used in normal

    treatment, and this is .019/.025. Larger, full thickness steel

    wires have been evaluated, but although they provide greater

    control, they are less effective for sliding mechanics.

    Occasionally .021/.025 wires in steel or HANT may be

    considered in the later stages of treatment, to obtain full

    expression of the bracket system. The technique is a 'full arch'

    approach, and closing loops (p. 252 ) or sectional wires are

    seldom used.

    Theoretically, there is approximately 10 of'slop' between

    the .019/.025 wire and the .022 slot (Fig.1.26). However, in

    clinical use the wire performs better than expected, and this is

    presumed to be due to residual tip which remains unconecied

    at the time of placement of the rectangular wire, and persists

    intermittently during treatment as teeth are moved

    (Figs 1.26-1.30).

    F i g . 1 .26

    CO

    33

    O

    _

    -

    n

    on

    - . . ' .

    Fig. 1.27

    F i g .

    1.28

    F i g .

    1.29

    F i g .

    1.30

    Figs 1.26 t o 1.30 The .019/ .025 stee l rec tan gula r w i re pe r forms be t ter th an expe c ted. This is presum ed to be due to res idual t ip a t

    the t ime of p lacement of the re c tangu lar w i re , so th at th e torq uin g ef fe c t is prod uced at po ints X and Y.

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    O

    -v

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    i / i

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    ro

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    ( 1

    DESIGN FEATURES OF A MODERN

    BRACKET SYSTEM

    Range o f b racke t s

    The baseline of expectation concerning orthodontic brackets

    has risen consider ably since th e original SWA was released in

    the 1970s. The modern orthodontist expects to have three

    main bracket systems available to meet the needs of a typical

    caseload:

    Standard size metal brackets - where control is the main

    requirem ent (Fig. 2.1).

    Mid-size metal brackets - th ese give less control, bu t are

    useful for cases with average to small teeth, where there is

    poor oral hygiene, or where control needs are modest

    (Fig. 2.2) . "

    Esthetic brackets - the se will be neede d for older patien ts,

    where a m etal appearance is not accep table (Fig. 2.3).

    These are general developments in orthodontic bracket

    technology. They are not specific to the preadjusted system,

    but they are changes which were incorporated into the new

    concept.

    The original i .d. system of dots and dashes has been

    superseded by laser numbering of standard size metal

    brackets (Figs 2.1 , 2.4 & 2.5). This feature can not be carried

    through into mid-size brackets, owing to their smaller size,

    and it is technically not possible with clear brackets. So for

    these groups of brackets, a more conve ntional i .d. system of

    colored dots continues to be used.

    F i g .

    2 .1 S tanda rd s ize meta l b rackets .

    F i g .

    2 .2 Mid-s ize meta l b rackets .

    28

    F i g .

    2 .3 Esthet ic C lar i ty brackets .

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    Rhomboidal shape

    The original rectangular shape of the standard metal SWA

    (Fig. 2.4) has been supe rseded by the rhom bo ida l form

    (Fig. 2.5).

    This reduces the bulk of each bracket and allows reference

    lines in both the horizontal and the vertical planes, thereby

    assisting accuracy of bracket place me nt.

    >

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    1/1

    F ig .

    2 .4 The or ig in a l s tandard m eta l SWA brackets we re

    rectangular in shape, and the i.d. system was based on dots in

    the upper arch and dashes in the lower arch.

    F i g .

    2 .5 Brackets o f a rho mb oid a l shape have reduced bu lk an d

    the re i s coo rd ina t ion o f pe rspec t ive l ines th r ou gh on ly tw o

    planes, which assists in accuracy of bracket placement.

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    >

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    o

    en

    Torque in base - th e com pu te r -a ided

    des ign (CAD) fac tor

    Torqu e-in-base was an im por tant is sue with the f irst - and

    second-genera t ion preadjus ted brackets , because leve l s lo t

    l ine-up was not poss ible wi th brackets des igned with torque-

    in-face . Tech nolog y w as not av a i lable to se t bracket s lo ts in

    the correct position relative to the facial surfaces of the crowns

    wi thou t to rque - in -ba s e . M ode rn b ra c ke t s ys t e ms , i nc lud ing

    the M BT s ys te m, ha ve be e n de ve lope d us ing c om pu te r -

    a ide d de s ign a nd c ompu te r -a ide d ma c h in ing - t he C AD-C AM

    system. This a l low s m ore f lexibi l ity of des ign , not o nly to

    place the s lo ts in the correc t pos i t ion in the brackets , but a lso

    to enhance bracket s t rength and fea tures such as depth of t ie

    wing and lah io-l ingual profi le . The co mp ute r is f irst able to

    locate the precise location for the bracket slot, relative to

    in -o u t d i s t a nc e a nd to rque pos i t io n fo r e a c h too th . On c e th i s

    pos i t ion is es tabl ished , i t can then bui ld up t he ' in-f i ll ' a reas

    to opt imize a l l requirements of the brackets (Figs 2 .6-2 .8) .

    The brackets may be finished with all torque-in-base (full

    s i ze a nd c l e a r ) o r w i th a c om bin a t io n o f to rque - in -b a s e a nd

    torque-in-face (mid-s ize) wi th absolute ly no difference in s lo t

    pos i t ion. Since the advent of CAD-CAM bracket des ign, i t i s

    not necessary to d iscuss th is h is tor ica l i s sue any longer!

    F ig 2 .6 B rack e ts w i t h t o rqu e i n base w e re des igned s o t ha t t h e

    LA po in t , t he bas e po in t , and the s lo t po in t w ere on the s am e

    hor izonta l p lane. To accompl ish th is an acute (90) angle at the g ing iva l aspec t o f the bracket base.

    F ig 2.7 The CAD sys tem analyzes the id eal s lo t locat ion a nd

    then des igns the in- f i l l o f the bracket as necessary .

    F ig 2 .8 The ou tc o m e o f t he C AD p roc ess is t h a t t he res u l t i ng

    bracke t can have to rq ue in base, to rq ue in face, or a

    c o m b i n a t i o n o f t h e t w o .

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    IN-OUT SPECIFICATION

    Expression of in-out

    The in-out feature of preadjusted brackets is 100% fully

    expressed, because the archwire lies snugly in the slot. The

    jabio-lingual movement is rapid, and normally occurs in one

    visit. The original SWA in -o ut specification was therefore

    used as a basis when designing the MBT

    IM

    system.

    Upper second premolars

    Andrews' 120 research normals all had teeth with full-size

    crowns in the labio-lingual dimension, but in clinical practice

    upper second premolars have small crowns in approximately

    20%

    of cases. An alternative bracket, which is 0.5mm thicker

    than normal, is useful for such teeth (Figs 2.9-2.11), This

    feature is helpful in obtaining good alignment of marginal

    ridges in cases with small u pper second premo lars and is

    discussed on page 52. For cases with upper first and second

    premo lars of the same size, the upper first premolar bracket is

    used for both teeth. Only a small inventory of upper second

    premolar brackets is required, and this should be monitored

    by one staff mem ber.

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    Fig.

    2.9 This case has small up pe r second pre mo lars.

    F i g . 2 . 1 0

    A p rem o la r b rac k e t w h ic h is 0 .5m m th i c k e r t h an

    norm a l i s us e fu l f o r s m a l l upper s ec ond p rem o la r s .

    Normal

    bracket

    0.5mmthicker

    bracket

    Fig.

    2.11 App rox im ate ly 2 0% of cases have uppe r second prem olars w i t h smal l c l in ica l c rown s , an d a bracke t wh ich is 0 .5mm th icke r

    is he lp fu l in ob ta in ing go od a l i g nm e n t o f m a rg ina l r i dges w i t h ou t w i r e be nd in g fo r t hes e c as es .

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    NJ

    TIP SPECIFICATION

    Express ion o f t ip

    >

    n

    m

    t / i

    T3

    m

    n

    %

    O

    -z.

    50 Qc

    0

    F i g . 2 .12

    R e c o m m e n d e d t i p .

    The tip feature of preadjusted brackets is almost fully

    expressed. A .019/.025 wire in an upp er ca nine bracket with

    8" of built-in tip will express most of that tip. More than 7

    of the 8 will be fully expressed (Fig. 2.13). With light

    continuous force mechanics, tip can be well controlled, and

    tip specifications are fully and rapidly expressed in clinical

    use. The research figures for tip were closely adhered to when

    the MBT bracket system was designed, although small

    changes were made to the tip specification for molar and

    upper premolar at tachm ents.

    For all molars, a 0 tip bracket is recom me nded . If placed

    parallel to the buccal cusps of the molars, a 0 lip bracket will

    deliver 5 of tip for the uppers and 2 of tip for the lowers

    (Fig. 2.14). This issue has been discussed at length elsewhere,

    and the reader is referred to other lexts for more detailed

    information.'

    1

    For the upper premolars, the authors prefer brackets with

    0 of tip, com pare d with 2 in the original SWA. This places

    the crowns of these teeth in a slightly more upright position,

    more in the direction of Class I. It also reduces anchorage

    needs in som e cases. The 2 may seem insignificant, b ut th e

    total of 8 from the four upper premolars does become

    significant in anchorage terms. For the lower pre molars, the

    2 of mesial crown tip in the original SWA brackets works

    well, keeping the crowns inclined forwards in a Class I

    direction, and continues to be used and recommended.

    Less

    than 1

    (

    i

    N

    .

    ...\ \ \\

    .019/.025

    \\:A H ]

    Less

    than 1

    F i g .

    2 . 1 3 The t i p f e a tu r e o f p read jus ted b rac k e ts is a lm os t f u l l y

    expressed,

    an d the re is less tha n 1 of ' s lo p ' whe n a .019 / .025

    rec ta ngu lar w i re is p laced .

    F i g . 2 . 1 4 U p p e r a n d l o w e r m o l a r a t t a c h m e n t s h a v e 0 " t i p .

    W he n p laced para l le l to th e buccal cusps of th e molars , th is

    del ivers 5 of t ip in the u ppers and 2 of t ip in the lowers .

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    TORQUE SPECIFICATION

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    >

    T3

    o

    >

    n

    m

    T3

    m

    n

    n

    >

    o

    +7 0 -7

    -14

    -7

    Molars

    Premolars Canines

    - 1 7

    r

    Central

    incisors

    +60- 6

    -12"

    F ig .

    2.15 R ec om m en ded to rque s pec i f i ca t i ons

    Expression of torque

    As

    discussed above, in-out and tip features are efficiently

    expressed by the preadjusted appliance system. In contrast,

    torque is not efficiently expressed, owing to two mechanical

    reasons:

    The area of torque application is small, and dep end s on

    the twist effect of a relatively sm all wire, com pare d with

    the bulk of the tooth (Fig. 2.16).

    In order to slide teeth, it is normal practice to use

    .019/.025 steel wires in a .022 slot, because a full-thickness

    wire prevents sliding. These wires have 'slop ' of about 10,

    depending on the tolerances in bracket and wire

    manufacturing, and the amount of wire edge 'rounding' or

    'radiusing' (Fig. 2.17).

    F ig . 2 .16

    Torq ue is no t e f f ic ient ly expressed by the prea djus te d

    appl iance sys tem, par t ly due to the smal l area of torque

    appl icat ion.

    F i g . 2 .1 7

    A rec tan gula r .019/ .025 s tee l w i re in .022 s lo t w i l l

    have app rox im ate ly 10" of ' s lop ' . The exac t am ou nt dep ends on

    the p rec i s ion o f m anu fac tu re o f t he w i re and b rac k e t s lo t and

    t h e a m o u n t o f w i r e e d g e ' r o u n d i n g ' o r ' r a d i u s i n g '.

    33

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    As a result of the relative inefficiency of preadj listed

    bending. Arch form factors, together with canine prominence

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    >

    "O

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    n

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    -u

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    Q

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    o

    z

    brackets in delivering torc|ue, it was necessary to build extra

    torque into the incisor, molar, and lower premolar brackets,

    in order to meet clinical goals with a minimum of wire

    Incisor torque

    It is helpful clinically to have torque control (Figs 2.18-2.21)

    which moves upper incisor roots palatally and lower incisor

    roots labially. This treatment requirement is necessary for

    many types of malocclusion:

    Class II cases, where Class II elastics can cau se torq ue to be

    'lost' on the upper incisors, and where lower incisors tend

    to procline during leveling and in response to Class II

    elastics.

    Class I cases, whe re correct incisor torque helps to achieve

    good anterior tooth fit.

    and other issues, made it necessary to have brackets with

    three options for canine torque, as discussed on pages 44

    to 48.

    F i g .

    2 . 1 8

    Uppe r cent ra l inc isor bracke t .

    Class III cases, where correct torque can help to

    compensate for mild Class III dental bases.

    F i g . 2 . 1 9 Upp er la tera l inc isor brac ket .

    F i g .

    2 . 2 0

    Lower inc isor bracket .

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    Because of these frequent clinical requirements, there is

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    generally a need for greater palatal root torque of the upper

    incisors and for more labial root torque of the lower incisors.

    For these reasons, the authors rec omm end +17 of torque for

    the upper central incisors, +10 of torque for the upper lateral

    incisors, and -6 of torque for the lower incisors (Fig. 2.21).

    La te ra

    inc isors

    C e n t r a l

    inc isors

    L a t e r a

    inc isors

    r i / -1

    O r i g i n a l S W A

    - 6 * \ - / - 6 "

    R e c o m m e n d e d

    >

    n

    m

    v-i

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    m

    n

    n

    >

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    O

    Fig.

    2 .21 The au tho rs r ec om m en d + 17 o f t o rq ue fo r t h e upper c en t ra l inc i so r , + 10 o f t o rq ue fo r t he up per l a te ra l i nc is o rs , an d -6

    of torque for the low er inc isors to ass is t in mo vem en t of up pe r inc isor roots pa lata l ly and low er inc isor roots lab ia l ly .

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    Andrews' 120 non-orthodontic normals were non-extraction

    adults. However, a typical orlhodontic caseload is a different

    sample. The finding o f- 7 torque for the uppe r canines has

    proved to be satisfactory for m ost cases, but the o riginal SWA

    value of

    -11

    torque for the lower canines has not been

    satisfactory, as it tends to leave the lower canine roots in a

    prom inen t po sition in most cases. Versatility is needed for

    canine torque values. A range of -7 , 0 an d +7 torque,is

    therefore available for the upper canine s (Pigs 2.22 & 2.23)

    an d - 6 , 0 , an d + 6 for lower canines (Figs 2.24 & 2.25), as

    described on pages 44 and 45.

    F ig . 2 .22 The upper c an ine b rac k e t has -7 t o r qu e . W hen

    inver ted i t has +7 torque.

    F i g . 2 .23 The upper c an ine b rac k e t w i t h ho ok has 0 t o r qu e .

    F ig . 2 .24 The l ow er c an ine b rac k e t has -6 t o rq ue . Wh en

    inver ted i t has +6 torque.

    F i g . 2 .25 The l ow er c an ine b rac k e t w i t h h ook has 0 t o r qu e .

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    Upper premolar and molar torque

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    The upper premolar torque value of -7 has proven to be

    satisfactory in clinical use, and the authors continue to work

    with it.

    For upper molars, on the other hand, the -9 of the

    original SWA has proven to be inadequate, and they prefer

    -14 , as this gives better control of the palatal cusps (Fig.

    2.26). The -1 4 specification for the uppe r m olars helps to

    reduce interferences during function, by preventing the palatal

    cusps from hanging dow n. It is imp ortant to have a

    sufficiently wide maxilla to allow this torque change. If not,

    cortical plate interference prevents achievement of correct

    torque.

    >

    n

    m

    t o

    -o

    m

    n

    n

    >

    H

    o

    F i g . 2 . 2 7 Upper second mola r tub e.

    -14'

    o

    Original SWA

    Recommended

    Fig.

    2 .26

    U pper mo la r a t tachmen ts w i th -14 o f to rq ue g ive

    better control of the palatal cusps.

    F i g .

    2 . 2 8

    Upper fi rs t mo la r tub e.

    F i g .

    2 . 2 9

    Upper f i rs t and second prem olar b racket .

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    Lower premolar and molar torque

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    >

    r-

    >

    n

    m

    1/1

    "0

    m

    n

    n

    >

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    O

    z

    1/1

    Many orthodontic cases have narrow maxillary arches, with

    the lower arches showing a com pensa ting narrowing. These

    cases normally require buccal crown torque (uprighting) of

    the lower molars and prem olars. Also, the original SWA first

    molar torque (-30) and second molar torque (-35)

    specifications allowed 'rolling-in' of lower molars. Therefore

    the authors have made the important decision to change

    lower premolar torque by 5, first molar torque by 10, and

    second molar torque by 25 (Fig. 2.30).

    F i g .

    2 .3 0

    The authors have reco mm end ed substant ia l changes

    in to rque fea tures fo r the a t tachments in the lower bucca l

    segments , comp ared w i t h the or ig i na l SW A. Th is reduces the

    ' ro l l ing- in '

    of lo wer molars as we ll as assist ing in th e

    deve lopmen t o f the mand ibu la r

    arch.

    Original SWA Recommended

    38

    F i g . 2 .3 1 Lower f i rs t p rem olar b rack et . F i g . 2 . 3 2 Lower second prem olar b rac ket .

    * * " . &

    F i g . 2 .3 3

    Lower f i rs t mo la r conver t ib le bucca l tu be .

    F i g . 2 .3 4

    Lower second mola r tub e.

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    THE VERSATILITYOF THE BRACKET

    SYSTEM

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    The firsl

    and

    s e c ond ge ne ra t ion

    (p. 6) of

    bra c ke t s

    and

    buccal

    tubes

    had a

    s ing le op t io n

    for

    each spec if ic tooth , wi th

    a

    re c omme nda t ion

    for

    p r o p e r

    tip,

    t o r q u e

    and

    i n - o u t

    c ompe ns a t ion . The re

    was

    l i t t le room

    for

    v ersa t i l i ty .

    The

    MBT Versa t i le+ bracket s ys tem

    has

    overa l l de s ign

    improve me n t s c ompa re d w i th p re v ious a pp l i a nc e s . The s e

    inc lude chang esin tip and t o r q u e , aswell as des ign fea tures

    which in t roduce

    a new

    charac ter is t ic

    for the

    pre a d jus t e d

    system

    -

    tha t

    of

    versatility.

    As de s c r ibe d b e low, the innov a t ion inc o rpora te s s e ve n

    different bracket

    and

    buc c a l t ube pos s ib i l i t i e s , de pe nd ing

    on

    t h e n e e d s

    of the

    case . This c rea tes

    a

    pla tform

    for the

    archwires

    a n d

    the

    bracket sys tem

    to

    p r o d u c e

    the

    necessary

    i n d i v i d u a l i z a t i o n

    an d

    ove rc o r re c t ion

    for

    certa in types

    of

    case.

    The be ne f i t

    can

    a p p l y

    to

    ind iv idua l t e e th

    or to

    g r o u p s

    of

    t e e th ,

    in

    s ome ins t a nc e s . Th i s r e duc e s

    the

    ne e d

    for

    first-,

    s e c o n d -

    an d

    th i rd -o rde r be nds l a t e r

    in

    t re a tme n t ,

    and

    improves eff ic iency.

    Aspects of versatility

    Seven main areas

    of

    v ersa t i l i ty

    are

    l is ted be low,

    an d

    they will

    be

    reviewed

    in

    turn:

    1 . Opt ions for pala ta l ly d isplaced up per la te ral inc isors (- 10 ) .

    2 .

    Thre e to rque op t ionsfor the u p p e r c a n i n e s (- 7 , 0 , and +7).

    3 . Thre e to rque op t ions

    for

    lowe r c a n ine s

    (- 6 , 0 , and +6 ).

    4 . Interchangeable lower inc isor brackets

    - the

    s a m e

    tip and

    to rque .

    5. In te rc ha nge a b le uppe r p re mola r b ra c ke t s

    - the

    s a m e

    tip and

    to rque .

    6.

    Use of

    upp e r s e c ond m ola r tube s

    on

    fi rs t molars

    in

    non-1

    IC

    cases.

    7.

    Use of

    lowe r s e c ond mola r tube s

    for the

    upper f i rs t

    and

    s e c o n d m o l a r s

    of the

    oppos i t e s ide ,

    when finishing cases

    to a

    Class

    II

    mola r r e l a t ions h ip .

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    Palataliy displaced upper lateral incisors

    The orthodontist is often called upon to correct upper lateral

    A convenient way to m anage these cases involves the

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    incisors which are palataliy displaced. Cases with upper

    anterior crowding on Class

    1

    or Class III dental bases are

    liable to have upper lateral incisors which are in crossbile,

    and it can be difficult to achieve stable root correction. There

    is a risk of moving the crown labially, while leaving the root

    palataliy placed. In this situation, there will be a need for

    additional wire bending, and treatment time will be extended.

    following procedures:

    Du ring the alignm ent stage, il is necessary to create enoug h

    space for the palataliy displaced tooth. This is achieved

    using coil spring. The brackets on the adjacent teeth are

    lied with wire ligatures, to prevent rotations (figs 2.35 &

    2.36).

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    Ifone or both upper lateral incisors are missing, a decision

    may be made to close the spaces, and bring the canines

    mesially into contact w ith the c entral incisors. In this

    situation, it is helpful to invert the -7 upper canine bracket

    180.This changes the torque to+7, but the tip stays the

    same at 8" . The left side bracket is placed on the left canine

    and the right side bracket is placed on the right ca nine. It is

    not correct to place the left canine bracket on th e right canine

    or vice versa.

    The inverted canine bracket is well adapted to the tooth

    surface, and the in-out dimension will be correct. At the

    rectangular wire stage, this helps to torque the canine root

    into a palatal position with a m inimum of wire bend ing

    (Fig.2.47).

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    For the lower incisor brackets, 0" tip was used to reflect the

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    F i g . 2 . 55 Uppe r second molar a t tac hm ents may be used on upp er f i rs t mo lars in cases wh ere he adge ar is no t r equ i re d .

    F i g . 2 . 56 Th is non-e x trac t ion case d id not requ i re head gear

    suppo r t , and an uppe r second mo la r tube w as bonded on to the

    upper f i rs t mo lar .

    F i g . 2 . 57 The upp er second mo lar tu be may be used on up per

    f i rs t mola rs fo r cases wh ere headg ear is no t nee ded .

    50

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    Use of low er second mo lar tube s for the

    upper f irst and second molars of the

    opposite s ide, w h e n f inis hin g cases in a

    can be achieved by using lower second molar tubes for the

    upper molars, and changing sides, left going to right, and

    right to left (Figs 2.58-2.60). Also the tube is placed at a

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    Class II molar relationship

    It is often difficult to achieve good finishing and detailing in

    cases which are treated to a Class II molar relatio nsh ip, after

    extraction of two premolars in the upper arch only.

    It helps if upper m olar tube s can b e used which will deliver

    zero rotation (compared with the normal 10 rotation) and

    zero tip (compared with the normal 5" tip). This versatility

    different tip position, with more enamel from the mesial cusp

    visible than from the distal cusp. This introduces the

    necessary tip adjustment.

    In some of these cases, it is correct to use no rmal upp er

    molar tubes to achieve most of the treatment objectives, and

    then to switch to lower second molar tubes for finishing. The

    lower second molar tube s may be used from the outset in

    cases where a lot of treatment mechanics will not be needed.

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    should be managed by the orthodontist, to ensure accuracy of

    appliance placement.

    The need for accuracy

    Accuracy of bracket posit ion ing is essential, so tha t th e b uilt-

    in features of the bracket system can be fully and efficiently

    expressed. This helps treatment mechanics and improves the

    consistency of the results.

    cooperation later in the treatment.

    1

    Proper post-set-up advice should be given, as discussed in

    Chapters (p. 112) .

    The use of light-cured systems for bonding brackets and

    cem entin g band s is helpful. These reduce time pressure on the

    orthod ontist when setting up cases. The bond ing materials

    should be carefully used exactly to the manufacturer's

    recommendations, with correct light, to ensure good bond

    strength and reduce the risk of bond failure.

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    FULL OR PARTIAL SET-UP?

    Enamel reduction cases

    For many pa t ients , i t i s correc t to p lace a l l the brackets and

    It i s normal ly necessary to carry out enamel reshaping in cases

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    bands a t the s ta r t of t rea tment so tha t any discomfort i s

    l imited to one episode , and a l l the tee th s ta r t to be correc ted

    from the outse t . However , in some s i tua t ions , l i s ted be low, i t

    may be benefic ia l to cons ider part ia l ly se t t ing up the case ,

    leaving individual tee th , and in some ins tances groups of

    t e e th , w i thou t a t t a c hme n t s .

    Blocked-out teeth

    If individual tee th a re vert ica lly or horizo nta l ly d isplac ed from

    the primary arch form (Fig . 3 .1) , i t i s of ten good technique to

    delay bracket ing the displaced tooth unt i l the other tee th a re

    wel l a l igned, and space has been made avai lable .

    Deep-bite cases

    The me th ods o f s t a r ting de e p -b i t e c a s es a re s how n on

    pages 134 and 135. In some cases , when i t has been dec ided

    not to use a b i te p la te or occ lusa l bui ld-up, upper a rch

    trea tment should be s ta r ted f i rs t . La ter , a f te r the overbi te has

    started to correct, i t will be possible to place the lower incisor

    brackets wi t hou t d iscomfort to the pa t ien t or risk of da m age

    to the enamel or the newly placed brackets .

    wi th i r i angu lar-sh aped inc isors (Fig . 3 .2 ) . It may be he lpful to

    delay bracket ing the inc isors , espec ia l ly in the lower a rch. I f

    lower inc isors a re bracketed a t the s ta r t of t rea tment , they wil l

    i ne v i t a b ly p roc l ine a l i t t l e du r ing too th a l ignme n t , e s pe c ia l ly

    in a non-e x t ra c t ion c a se . Sub s e que n t e na m e l re duc t ion ,

    fol lowed b y re t ro c l ina t io n is a form of ro un d t r ipp ing. This

    undes irable e ffec t can be avoided by not bracket ing lower

    inc isors a t the outse t .

    F ig . 3 .1 Th is ver t ica l ly and hor izonta l ly d isp laced upper r ig h t

    can ine was not b racketed a t the s tar t o f t rea tment . I t was

    necessary to c reate space before a t tempt ing to br ing i t in to the

    line of the arch.

    F i g . 3 .2 Tr iang u lar-sh aped inc isors norm al ly requ i re reshap in g

    to avo id unesthet ic b lack t r iang les . I t can be he lp fu l to de lay

    p lacem ent o f b rackets in the lo wer inc isor reg ion to re duce

    unw an t ed p roc l ina t ion ea r l y in t rea tme n t . T rea tme n t mechan ics

    can be easier i f low er incisors of a tr i an gu lar shape are

    re -shaped be fo re b racke t p lacemen t .

    Sliding jig cases and mixed dentition cases

    Uppe r b i c us p ids a nd s ome t ime s uppe r c a n ine s a re no rma l ly

    not bracketed when s ta r t ing cases where a s l id ing j ig (Case

    TC, p . 195) wi l l be used to control or d is ta l ize upper molars .

    In ma ny mixe d de n t i t i on t r e a tme n t s , on ly the pe rma ne n t

    tee th are inc luded in the se t -up. Primary tee th may be

    inc lude d in s ome c a s e s , e i the r to improve the s t re ng th a nd

    s ta b i l i t y o f the a pp l i a nc e , o r t o in f lue nc e the pos i t ion o f the

    primary tee th .

    58

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    THEORY OF BRACKET POS ITIONING -

    AVOIDING ERRORS

    Ever\' effort shou ld be m ad e lo achiev e accur ate bra cket

    with the SWA, with bracket wings para l le l to the long axis of

    u t

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    pos i t ioning. Idea l pos i t ioning can resul t in cases which show

    good occlusion with lit t le effort, an d will ma ke th e finishing

    stages of the treatment easier. This helps efficiency in a busy

    orthodo nt ic prac t ice .

    With the or ig ina l edgewise appl iance , bracket p lacement

    was normal ly carr ied out us ing gauges and s tandard

    mil l imeter measurements from the inc isa l or occ lusa l edge of

    each tooth, irrespective of tooth size. With this system,

    patients with large incisors had brackets placed more incisally

    than patients with small teeth, relative to the size of the teeth.

    The brackets were pos i t io ned a t d iffe rent c urva ture o n the

    tee th , and th is in turn led to varia t ions in the amount of

    torque and in-out produced by the brackets . However ,

    because archwire bending was needed in any case , th is sys tem

    was acceptable wi th the edgewise appl iance .

    Andre ws in t roduc e d the c onc e p t o f t he 'midd le o f the

    clinical crown ', as a mor e reliable theo retical p os iti on for use

    the c l in i c a l c row n .

    2

    T h i s o v e r c a m e t h e s h o r t c o m i n g s o f t h e

    o r ig ina l e dge wis e me thod c onc e rn ing va r i a t ions in the

    a m ou n t o f to rq ue a nd i n - ou t p roduc e d by the b ra c ke ts .

    How ever, as describ ed be low , it prove d diff icult to ob ta in

    a c c u ra t e ve r t i c a l pos i t ion ing us ing on ly the midd le o f the

    c l in ica l c rown. Many vert ica l e rrors occurred, and the authors

    now a dvoc a te the us e o f ga uge s , bu t w i th ind iv idua l i z e d

    bra c ke t -p os i t ion ing c ha r t s (p . 63 ) . The s e a dhe re to Andre ws '

    p r inc ip le o f the midd le o f the c l in i c a l c rown bu t e ns u re

    grea ter vert ica l accuracy, wi th less need for re -bracket ing.

    W hen d irec t bo nd in g brackets , i t i s he lpful lo avoid

    viewing tee th from the s ide , or f rom above or be low. To

    prope r ly v i e w the t e e th du r ing bond ing p roc e dure s i t w i l l be

    necessary for the pa t ien t to turn th e hea d, and the

    o r th odo n t i s t t o c ha n ge s e a t ing pos i t ion f rom t im e to t ime

    (Fig. 3.3).

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    View No

    F ig .

    3 .3 When p lac ing bracke ts , i t is im po r tan t to v iew th e tee th f r om th e co r rec t pe rspec t ive .

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    Horizontal accuracy during bracket

    posi t ioning

    Incisors and molars have relatively f iat facial and buccal

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    surfaces, and small errors do not significantly affect the

    posi t ion of these teeth (Fig. 3.4) . Canines and premolars have

    more rounded facial sur faces , and therefore accuracy is

    impor tan t because e r r or s in hor izonta l b r acke t pos i t ion ing

    cause r o ta t ions . V iew ing can ines , p r e mola r s , mola r s , and

    rotated incisors occlusal ly or incisal ly with a mouth mir ror

    (Fig. 3.6) help s bracket po si t io nin g rela t ive to the v er t ical

    long axis of the crown. Lower canine brackets should be

    placed on the ver t ical midline, or s l ight ly mesial to i t , to

    ensure good contact with the la teral incisors (Fig. 3.7) .

    F i g .

    3 .4 Errors in ho r izo nta l b racke t pos i t ion ing cause

    ro ta t ions .

    F i g . 3 .5 Hor izo nta l and ver t ica l accuracy can be checked f ro m

    the buccal aspect.

    F i g . 3 .6 Hor iz onta l accuracy in the can ine, p rern o lar , an d mo lar

    reg ions shou ld be checked w i th a mo u th m i r ro r .

    F ig . 3 .7 In th is case, the low er can ine brackets we re bo nde d

    s l igh t ly d is ta l to the ver t ica l mid l ine . The resu l t ing contac ts

    b