Preadjusted edgewise techniques /certified fixed orthodontic courses by Indian dental academy

Preadjusted Edgewise Techniques

INDIAN DENTAL ACADEMY
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Contents
♦
♦

♦

Development and evolution of the preadjusted
appliance.
Design considerations
- SWA by Andrews
- Roth prescription
- Alexander Discipline
- MBT bracket system
- Level anchorage system
Treatment mechanics

►
►
►
►
►

Misconceptions and Myths about the SWA.
Pitfalls of the straight wire system
Future developments
Conclusions
References.


Development of the Preadjusted appliance.
► Angle (1927) suggested angulating the bracket to free

the archwire from second order bends.
► Holdaway (1952) overangulated the brackets adjacent
to the extraction site for second order correction.
► Jarabak (1957) incorporated slot inclination in the
brackets and recommended bracket angulation.
► Stifter (1958) introduced bracket with three
dimensional control. Brackets had male and female
parts.The female part was attached to the tooth.The
male part was altered

according to the various combinations of inclination,
angulation and crown prominence.
► Lawrence Andrews was credited with the scientific
development of the concept and mechanotherapy of the
preadjusted appliance.(1971)
► The preadjusted, preangulated appliance was based on
the concept that in an ideal gnathological set up for a
given patient, the bracket bases would accurately fit
each tooth at a predetermined point, and the bracket
slots would passively accept a straight wire.

► This original straight wire appliance was a Hybrid Twin

Edgewise appliance with built in tip, torque and in –out
values, to achieve the six keys of normal occlusion.
► Later many straight wire techniques were introduced
which were modifications of Andrew`s concept of
Straight wire technique.


Andrew`s Straight Wire Appliance
► Andrew introduced the Straight Wire Appliance in

1972, based on the measurements of 120 non
orthodontic normal cases. He used the data as a basis to
design the bracket system.
► These were the first generation preadjusted brackets

which were developed to overcome inadequacies in the
standard edgewise brackets.


► When brackets were sited on a full complement of

optimally positioned teeth the final archwire requires
76 primary wire bends if it is to be placed passively into
the slots of the standard edgewise brackets.


► Bracket design- the fully programmed

appliances
incorporate all the features that were sited by Andrew`s
in order to enable the use of straight unbent wires.
► The original SWA brackets were designed to treat only
non extraction cases with an ANB differential of less
than 5 degrees.
► Extraction series brackets were developed with two
additional features, countermesiodistal tip and
counterrotation to allow translation of teeth as much as

TIP

5 9 11 2 2 5 5
2 2

TORQUE

7 3 -7

5

2 2 2 2
-7

-7 -9

-9

-1 -1 -11 -17 -22 -30 -35


much as possible and to offset any relapse tendency by
overcorrection.
► Translation series brackets were further classified as
- minimum (>2mm)
- medium (2- 4mm)
- maximum (>4mm)
► Andrew`s later introduced different series and sets of
brackets for different combinations of extractions, ANB
differentials and different anchorage needs.

► He also recommended the use of three different sets of

incisor brackets with varying degrees of torque.
► Increased inclination for Class III and decreased
inclination for Class II in maxilla and reverse in the
mandible.


► Bracket placement - Accuracy in bracket placement is

essential so that the built in features of the bracket
system can be fully and efficiently expressed.
► Andrew`s chose the centre of the clinical crown as a
horizontal reference point for consistent I and III order
expression.
► The FACC is the vertical reference plane, which refers
to the centre of the middle developmental lobe.


► Andrew`s concept of treatment involved correction of

malocclusion totally by translation of teeth without
being tipped.
► He believed that some amounts of relapse is normal
after appliance removal and it is not possible to
precisely position the teeth into occlusion before
appliance removal due to bracket interference.
► In the original SWA heavy forces were continued to be
used, no special anchorage control measures were

► employed. Andrew`s also emphasized on the ‘wagon

wheel effect’ where tip was lost as torque was added.
► Hence additional tip was added to the anterior brackets.
► Difficulties were also encountered in the treatment
mechanics due to use of heavy forces and also due to
increased tip in the anterior brackets.
► This consequently led to the “roller coaster effect”.


Andrew`s philosophy


Roth`s appliance
► The Roth prescription was introduced in 1976.

Following his early experiences with the SWA, he
introduced measures to overcome day to day
shortcomings which he had found in clinical use.
► Roth recommended a single appliance system,
consisting primarily of minimum extraction series
brackets, which he felt would allow him to manage both
extraction and non extraction cases.
► This was then called the second generation of
preadjusted brackets.

Roth prescription
► Bracket design- the bracket design was similar to

Andrew`s with few modifications.
- torque was increased for maxillary incisors and molars,
unchanged for premolars, and decreased for the canine.
- torque for the mandibular teeth were unchanged.
- tip was increased for the upper and lower canines and
was decreased for the incisors and premolars.
- counterrotation features were incorporated in the
brackets in order to prevent rotation during retraction.

TIP

TORQUE

5

9

13

0

0

0

0

2

2

7

-1

-1

-1

-1

12

8

-2

-7

1

-1

-11

-17 -22 -30 -30


-7

-14 -14

► Bracket placement – Andrew`s recommended placing

wires with compensating or reverse curves during the
finishing phase of treatment. Variations in the bracket
placement was recommended in the Roth set up to
permit placement of flat, unbent full size arch wires.
► The key in determining bracket height is the canines
and premolars.( 2nd premolar in an extraction case)
► The brackets should be placed at the maximum
convexity of the crown of posterior teeth.

► The canine bracket is placed 1mm more incisally than

the lateral incisors which are at the same level as the
centrals.
► Generally, the bracket position will appear to be more
incisal than the FA point of Andrew`s and this allows
for vertical overcorrection of tooth positions.


► Arch Form- The arch wires are relatively flat around

the upper and lower incisors, curve more tightly around
the cuspids and bicuspids and then curve gently towards
the distal .
► The most prominent point in the front curvature of the
arch is the first premolar and the most prominent and
widest pint in either arch is at the mesiobuccal cusp of
the first molar.


► Roth`s arch form was wider than Andrew`s in order to

avoid damage to the canine tips during treatment and to
assist in obtaining good protrusive function.


Roth Philosophy
► Since its introduction in 1975, the Roth bracket

prescription has basically remain unchanged with only
modifications in the configuration of brackets and
hooks.
► The most recent information from several companies is
that the Roth treatment accounts for almost 70pc of
bracket sales worldwide and this indicates its
effectiveness.


► Reason for the Roth treatment coming into being-----

Andrew`s idea was a total concept –of which the
appliance was one part- ‘the guidance system’. His
objective was to move teeth in straight line vectors from
their malpositions to their final positions by translation
or bodily movement. However the ideal force system to
accomplish this has not been developed.
- Hence to accomplish this with the force systems
currently available, different bracket values must be

used depending on how far a tooth or group of teeth
must be moved.
► Andrew thus attempted to translate teeth throughout
treatment without tipping the teeth ( use of sliding
mechanics). In the Roth approach tipping of teeth is
allowed but the attempt is to keep it to a minimum.


► Anchorage Loss- whenever mesially angulated brackets

are placed on posterior teeth the teeth tend to tip
mesially and migrate forward. The original Andrew`s
treatment was devised for treatment of cases less than a
5degree ANB difference and nonextraction. However
the mesial inclination of buccal teeth creates an
anchorage loss problem in extraction cases.
► In Roth treatment the uprighting of upper premolars and
overrotation of upper molars would help maintain
anchorage as would the distal rotation of lower molars.

► Overcorrection- the general overcorrection built into

the Roth treatment has to do with the concept of where
the teeth should be at the end of appliance therapy.
► As some degree of settling of the teeth after full fixed
appliance therapy takes place, it seems obvious that
treatment to an ideal occlusion with appliances in place
should not be done as the teeth most likely would move
out of those positions after the appliances are removed.
► Hence overcorrection was employed in the treatment.

Roth`s treatment philosophy
► Precise individualized orthodontic and orthopedic

goals.
► Treatment mechanics tailored to individual situation
and individual facial type.
► The appliance should provide correct tooth position
prior to appliance removal that would allow teeth to
settle in normal occlusion.
► Altered bracket placement to allow for overcorrection
► Space closure by tipping –translation to allow for
greater efficiency and shorter treatment duration.

Variations in Roth Treatment
► Several variations in Roth treatment are available for

special circumstances.
- Super torque - upper anterior canine to canine model.
Cases when two upper premolars only are extracted and
a size discrepancy is created.( because half of a molar is
smaller than an upper premolar).The additional torque
and tip makes the upper anteriors occupy more space.
These are used in conjunction with the zero rotation
upper molars as the mesial molar rotation created
causes the molars to occupy more space in the arch.

► In this way the tooth size discrepancy is compensated

for and proper overjet and overbite can be established
and the upper extraction sites remain closed.
► The Super torque device also is used in Class II div 2

cases and any case that requires 6mm or more of upper
anterior retraction.


► The Zero Tip canine brackets-

These are used for segmental surgical cases to ensure
space between the canines and premolars for the
osteotomy cut. After healing from surgery has occurred
the standard Roth canine brackets are placed to achieve
final finishing.
► These variations are the only ones needed to treat
almost any case that might arise.


MBT system
► Mc Laughlin and Bennet worked for more than 15yrs

and developed and refined the treatment mechanics
based on sliding mechanics, mainly using the standard
SWA brackets.( 1975-1993)
► Their treatment mechanics included adequate bracket
positioning, lacebacks and bendbacks for early
anchorage control and light archwire forces.
► In the period between 1993-1997 they worked with
Trevisi to redesign the entire bracket system to

overcome the perceived inadequacies of the SWA. They
re- examined Andrew`s original findings and took into
account additional research input from Japanese sources
when designing the MBT bracket system.
► In the period between 1997- 2001 they developed a
completely modern systemized method of treatment
mechanics.
► These were then called the third generation of pre
adjusted brackets.

MBT Prescription
► Bracket design- The tip was reduced in the upper and

lower anterior teeth due to the following reasons.
- to prevent anchorage loss
- to prevent bite deepening during the aligning stage.
- to prevent over proximity of the canine root apex and
the premolar root.
- Torque was increased for the maxillary anteriors with a
range of torque values available for the canine bracket.

TIP

0

TORQUE

4
0

8
0

8
3

0
2

0
2

0

0

17 10

7

-1

-6

-6

-12 -17 -20

-6


-1

0

-10

-10
-10

► Brackets with three options for canine torque were

needed for different patient arch forms and other
clinical variables. The 0 and 7 degree options are
preferred for cases with narrow maxillary bone form,
prominent canine roots.
► Lower canine torque is -6, 0 degrees but even 6 degree
is available for some cases.


► Bracket placement- The MBT bracket placement

approach is similar to the Andrew`s approach .He
recommended a bracket placement chart devised on the
measurement of the clinical crown height of the
errupted teeth. Different bracket positioning charts are
available for premolar extraction cases and molar
extraction cases. The variations in extraction cases are
to achieve good marginal ridge contact adjacent to the
extraction site. Bracket positioning gauges also used
for vertical accuracy.

► Arch form- a medium sized standard ovoid arch form

was used for majority of the cases, and the size reflected
the fact that many of their patients were children with
malocclusions , unlike Andrew`s sample of 120 normals
,which were non extraction adults with large arches.
► The recommended technique is to create an
individualized form for all the patients based on ovoid,
tapered or square arch forms.


Versatility of the MBT Versatile bracket systemSeven areas of versatility are present in the third
generation brackets which are
- Options for palatally displaced upper laterals.-10 degrees
- 3 torque options for upper canines.-7,0,7
- 3 torque options for lower canines.-6,0,6
- Interchangeable lower incisor and interchangeable
upper
premolar brackets.

-

Use of upper 2nd molar tubes on the 1st molars in non
headgear cases
Use of lower 2nd molar tubes for the upper 1st and 2nd
molars of the opposite side when finishing cases to a
class II molar relationship.


► Treatment mechanics – in the early stages of treatment

the main threat to anchorage comes from the influence
of the anterior bracket tip.
► Lacebacks are used to assist control of canine crowns in
premolar extraction cases.
► Bendbacks are used at the start of treatment to prevent
mesial movement of anterior teeth.
► Lacebacks and Bendbacks are the primary methods of
supporting anchorage in the early phase of treatement.

► Anchorage control for lower molars

- use of lingual arches
- class III elastics and headgear.
► Anchorage control for upper molars
- use of cervical, combination or occipital pull
headgears.
- use of transpalatal bars.


► The tip built into the anterior brackets caused the

crowns of the anterior teeth to incline forward and
deepen the bite. Also there was a tendency for lateral
open bite.( roller coaster effect). This effect is seldom
seen in today`s cases owing to the reduced tip in the
MBT brackets.
► Also the use of light archwire forces will put less
demand on anchorage and will also be comfortable to
the patient.

MBT Philosophy


Alexander`s Vari - Simplex Discipline
►

1.
2.
3.

Vari simplex discipline was introduced by Alexander
in 1978.This technique grew out of Tweed`s
technique and today maintains its fundamental
principles.
Anchorage preparation (uprighting mandibular
molars)
Positioning of mandibular incisors over the basal
bone
Orthopedic alteration with head gear.

Concept of the Vari Simplex Discipline.
► This system revolves around five factors related to

brackets.
bracket selection, bracket height, bracket angulation,
bracket torque and bracket in –out.
► Bracket selectionTwin brackets- maxillary anteriors.
Lang brackets- maxillary and mandibular cuspids
Lewis brackets- maxillary and mandibular bicuspids
and mandibular incisors.

► Bracket height- the bicuspid bracket

height is the key because of its
Variable clinical crown height.
The normal height is 4.5mm,
the other bracket heights are
calculated in relation to it.


► Bracket angulation-


► Bracket torque-


► Bracket in-out-


► Alexander principle however is much more than a

bracket system or arch form. The technique involves
specific treatment mechanics.
► The maxillary arch is treated first with the use of multi
stranded, spiral round wires.
The patient is given an extraoral appliance called the
retractor. When the final archwires are placed in the
maxillary arch then the treatment of the mandibular
arch is started. The reasons for this delay in treatment

include
- To avoid interference of the mandibular brackets with
the maxillary teeth
- As the maxillary arch improves the mandibular curve of
spee improves naturally
- It allows more time for the mandibular 2nd molars to
errupt.
- Allows physiological drifting of crowded lower
anteriors. (driftodontics)

-

During canine retraction there is no interference and or
attrition on the cusp tips from the mandibular canine
brackets.
This system is best designed for .017x .025 inch arch
wire in .018 inch bracket slot.


Level Anchorage System
► The Level anchorage system is a complete orthodontic

treatment system designed to treat efficiently to a pre
determined goal and to reach that goal on a routine
basis.( Terrel Root 1981)
► Tweed advocated anchorage preparation by placing tip
back bends in the lower arch wire.
► Root incorporated the concepts of preadjusted tip in the
edgewise appliance in order to reduce


the wire bending needed during anchorage preparation.
► This was followed by Holdaway preangulating the
edgewise appliance in the mandibular buccal segments
depending on the severity of the malocclusion.
► The Level Anchorage System is described as a straight
wire appliance utilizing the anchorage preparation as
described by Holdaway


► Pre adjustments of the level anchorage appliance –

There are two choices of distal crown tip for the
mandibular buccal teeth.
► Regular and Major- the choice depends on the severity

of the malocclusion and is determined by the use of the
analysis chart.


TIP

4 7 6 0 0 0 15

(regular)

2 2 6 4 4 6 10

TORQUE

15 7 0 -7 -7 10 10
0 0 0 11 17 22 25


TIP

4 7 6 0 0 0 15

(major)

2 2 6 4 6 10 15

TORQUE

15 7 0 -7 -7 10 10
0 0 0 11 17 22 25


► The Level Anchorage system has made the practice of

orthodontics much more satisfying.
► Treatment plan is formulated by using the analysis
chart.
► Arch wire bending is reduced due to the preadjusted
appliance. Efficiency is improved because routine
check ups for each step allows the progress to be
monitored.
► Parents also prefer this system for they can understand

the importance of treatment steps to achieve an ideal
goal. They like the positive approach that the
orthodontist takes when the treatment steps and time
sequence have been predetermined.


Advantages of the Straight Wire Appliance
►
►

►
►

Ease of arch wire construction due to the elimination
of bends in the arch wires.
No need of interbracket span. An interbracket span of
great magnitude is unnecessary to reduce the force
levels as there are no bends in the wire.
Ease of arch wire placement
Less round tripping of teeth as the teeth move in more
direct vector lines from their maloccluded to their
final positions.

►
►
►
►

►

Better control of tooth positions.
Better and more consistent results with shorter
treatment time.
Patient comfort
Complete space closure can be achieved with one set
of wires since there are no bends in the wire to
interfere with the brackets themselves during space
closure.
Ease of ligation

► Bracket identification
► More accurate bracket placement


Misconceptions and Myths about the SWA
► It is usually misinterpreted that the 2 degree tip in the

lower SWA brackets will end up with the crown being 2
degrees mesially inclined. The SWA will not produce
this effect if properly used. The key here is in proper
bracket placement.
► Using the lower molar as an example, its long axis is
the dominant groove on the buccal surface which is at
an angle of 2 degrees with the line perpendicular to the
occlusal plane. So when SWA brackets are properly

located, the 2 degree tip in the bracket offsets the 2
degree distal tip of the crown`s long axis. So the molar,
at the end of treatment will be as upright as with a zero
angulation edgewise bracket that uses the occlusal plane
as a reference point.
► Another misconception is that the SWA is wedded to a
specific technique. The 1976 AAO meeting
presentations related the SWA to direct bonding, Tweed
mechanics, utility arches, sectional arch mechanics and

activator treatment for gross correction followed by
SWA treatment for finished mechanics. It was
demonstrated that SWA does not require specific
technique .
► Another misconception is that no wire bending at all is
ever necessary with the SWA. The SWA reduced the
need for many primary archwire bends with their
accompanying side effects. It has not however
eliminated the need for reverse or accentuated curves,
which produce forces that influence the curve of spee.

► Another misconception is that the SWA in order to work

properly, must be sited on the crown with more
precision than an orthodontist can routinely achieve.
► The SWA carries its own placement guidelines the
vertical tie wings, the welding tabs for the molar tubes.
It is just a matter of placing the straight guidelines
parallel to the long axis of the clinical crown. And if
equal amounts of error are introduced in a test against
edgewise, the SWA will prove to be more forgiving.

► Torque in base- another straight wire myth.

It is possible to incorporate torque either into the
bracket base or machine it on the bracket face, but to
fulfill strict straight wire design criteria only the former
method is acceptable.
Torque in face brackets do not fulfill the criteria of the
SWA as they could lead to 2 problems.


► In built errors in final vertical tooth positioning and

interference with sliding mechanics.
► But studies by Ferguson ( 1990) evaluating the two
bracket systems concluded that the torque in face
systems are capable of producing comparable results.
► It seems that the method of torque incorporation is
unlikely to be of practical significance and that its
importance has been greatly been exaggerated.


Pitfalls of the Straight Wire Appliance
► Frequently the anticipated results are not achieved by

using the preadjusted appliances and straight wires.
► There are at least 5 reasons of not achieveing ideal tooth
positions.
► First is the inaccurate bracket placement. Misplaced
brackets in the mesiodistal plane results in rotational
irregularities and those in the occlusogingival plane
alters the torque. A 3mm occlusal displacement of the
mandibular premolar bracket can result in 15 degree
alteration of torque.

► Second is the variation in tooth structure such as

irregular facial surfaces, crown root angulations,
unusual crown shapes . These require variations in their
tip, torque and height parameters to achieve optimum
results.
► Third is that the -Variations in vertical and
anteroposterior jaw relations require variations in the
position of maxillary and mandibular incisors. It is clear
from class II and III frameworks that the concept of
‘one appliance fits all’ defies the normal biologic

variation.
► The fourth reason is the tendency for relapse during
retention. The overcorrections which are done for tissue
rebound or relapse tendencies should not be limited
only to rotational movements but also include
overcorrections for tip, torque and height.
► Fifth is that the edgewise appliances have 3 significant

mechanical deficiencies.


-

Force applied to the teeth through brackets located
away from the centre of resistance.
Play between the archwire and the arch wire slot.
Force diminution.


Future Developments
► In the 1984`s ‘Attract’ brackets were introduced which

were single width brackets having rounded contours
and micro molar tubes. The base of the slot was of the
width of a twin bracket . They also had short ball hooks
in the Roth prescription.
► The latest version of the SWA is a perfectly clear
bracket grown from 100pc pure liquid alumina
(sapphire) into a single crystal, which gives a unique
crystal clear appearance. All SWA values of tip, torque

are grown integrally into the crystal. State of the art
diamond machinery is used to fabricate these brackets.
► Over the years due to technological advances the
appliance has become smaller, more comfortable and
more esthetic.
► A variety of bracket configurations are now available in
a variety of prescriptions.


Use of CAD- CAM in bracket designing
► Torque in base was an important issue with the 1st and

2nd generation SWA brackets because level slot line up
was not possible with the brackets designed with torque
in face.
► Modern MBT systems use the CAD- CAM system for
more flexibility of design, to enhance bracket strength
and features such as tie wings and labiolingual profile.


Conclusion
► Is the Straight wire appliance, then the ultimate

appliance concept? Is it the appliance to end all
appliances? Definitely not. Perhaps at this time it is
what Angle would call the ‘latest and best’ but further
improvements in this and the other systems are
expected.
► Development of brackets of sufficient strength which
will better withstand the forces applied by ligatures and
wires. With increased resiliency the bracket rather than
the wire will have initial deformation and recovery.

► Development of plastic wires rather than metal wires

and light force applications of great range.
► Decrease in the friction by means of special bracket slot
coatings.
► Development of brackets which can be adjusted once
they have been attached to the teeth.


References
1 Andrews LF. Six keys to normal occlusion. AJO
1972;62;296-309.
2 Andrews LF. Straight wire appliance, origin,
controversy and commentary .JCO 1976,10;99-114.
3 Roth. 5 years clinical evaluation of Andrew`s
SWA.JCO,1976;836-850.
4 Roth. Straight wire appliance 17 years later. JCO
1987, 21;632-642.


5 Mauric Bergman- Straight wire myths. BJO 1988 ;
115;57
6 Ferguson. Torque in base –Another straight wire
myth.BJO;1990;15;57
7 Mc Laughlin, Bennet. Transition from Standard
Edgewise to Preadjusted appliance.JCO1989;23;142153.
8 Meyer, Nelson. Preadjusted edgewise appliancestheory and practice. AJO 1978;73.5.485-498

9 Creekmore. Straight wire- the next generation. AJO
1993;104;8-20.
10 Yogesh Midha, Valiathan A. Straight wire technique.
KDJ;18.1;1049.
11 Randhawa G, Valiathan A. Anchorage loss with
Straight wire appliance. JIDA ,1993,64(10);313
12 Sameer S, Valiathan A- Comparative analysis of
Andrew`s SWA, Roth`s Technique and Vari simplex
discipline. KDJ ;19;4;115.

13 Joseph J, Randhawa S, Valiathan A. Class I
bimaxillary protrusion treated with straight wire
Andrew`s appliance.JPFA 1994;8;55
14 McLaughlin, Bennet JC. Finishing and detailing with
the preadjusted appliance system.JCO1991;21;4;251264.
15 Mc Laughlin, Bennet. Controlled space closure with
the preadjusted appliance.JCO 199024;251-260.
16 Mc Laughlin, Bennet, Trevisi- Systemized
orthodontic treatment mechanics. Mosby 2001.

17
18
19
20

AlexanderRG. The Vari Simplex Design.
JCO1983;17;6;380-392.
Lawrence Andrews- Straight wire, the concept and
appliance. San Diego, L.A.Wells 1989.
WB Magness. The Straight wire concept. AJO
1978;73;5;541-550.
Terrell Root. The level anchorage system for
correction of orthodontic malocclusions. AJO
1981,80;4;395-410.

21 Hocevar R A. Why edgewise? A compendium of
means to gentle resilient fixed appliances. AJO
1981,80;3;237-255.
22 Orthodontics – Current principles and techniques. third
edition. Graber, Vanarsdall.
23 Contemporary orthodontics. third edition, Proffit.


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