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0.018 Vs 0.022
When there are two orthodontists in a room there will be at
least a minimum of three opinions. There are two slots 0.018” VS
0.022” each of their own pros and cons. This seminar will examine
in a un-biased manner the advantages and disadvantages of each of
these slots in various stages of PAE.
An Edgewise Bracket Design
Edward H. Angle – Edgewise arch mechanism.
Angle’s concept of the “line of occlusion”.
Metal bracket, rectangular slot-0.022 x 0.028”.
Rectangular wire of 0.022” x 0.028”.
Wire was inserted into the bracket in the narrowest or edgewise
position–hence the name EDGEWISE.
EDGEWISE BRACKET DESIGN
Single Width Bracket
1
TWIN BRACKET
Junior Twin Standard Twin
Intermediate Twin Extra Wide
Posterior/ Wide Width Curved Base Twin
Primary arch wire bend intended for the most direct
movement of teeth. Secondary arch wire bends – any bend for tooth
guidance that are nor primary bends.
2
- Secondary bends are needed to compensate for slot-siting
irregularities caused by bracket design and unreliable bracket-siting
techniques, wire bending and wire forming side effects and
judgement errors in bendings.
Tertiary wire bends – one placed for any reason other than
guidance. Examples are omega loops for stops, loops for increasing
wire flexibility and loops for elastics. Previously the orthodontist,
relied on modification in the arch wire in the form of first, 2 n d , 3 r d
order bends to detail the teeth.
PRIMARY BENDS OF THE ARCH WIRE- EDGEWISE
The first order bends
The second order bends
The third order bends
THE ADVENT OF SWA
The straight wire appliance was based on ANDREW’S six
keys to normal occlusion(1972)
Philosophy – an ideal bracket system.
– an ideal force system .
Advantages
Reduction in wire bending.
3
Use of sliding mechanics.
Precision and finishing.
Flexibility of biomechanics.
Multiple bracket design.
Siamese
Single
Mini series
Midi series
Vertical slot
Self ligating
Disadvantages
Friction
Anchorage demands
Deceptive simplicity traps the unwary.
VARIOUS PRESCRIPTIONS AVAILABLE:
Roth
MBT
Alexander
EDGE- WISE PEA
Primary Bends In–Built Priscription
First Order Bends In–Out/ Prominence
4
Pre-adjusted appliances build corrections directly into the
brackets.
- Labio-lingual position previously placed into the arch wire
bends are now programmed with the in – out depth of the bracket
slots (or) within the bracket bases
EDGE- WISE PEA
Primary Bends In – Built Prescription
Tip/ Angulation
5
Preangualted slots in the brackets provide for precision
mesiodistal angulation.
EDGE- WISE
Primary Bends
Third Order Bends
PEA
In–Built Priscription
Torque/ Inclination
Labio-lingual inclination (or) torque previously managed with
auxiliary torquing appliances and arch wire adjustments are now
provided with accuracy by pre-torqued bracket slot and bases.
THE BIFURCATION OF SWA BASED ON SLOT DIMENSIONS
0.018” and 0.022”
SLOT SIZE: SLOT HEIGHT & SLOT DEPTH
HEIGHT:
The SWA is available with slot heights of 0.022” & 0.018”.
6
SLOT DEPTH:
0.022” x 0.028”
0.018” x 0.025”
Rectangular wires in torque applications must be seated with
their outer working edges fully engaged in the slot.
Slots should be deep enough to ensure full engagement.
WIDTH
Proffit
0.018” - Narrow brackets.
Rectangular wires,-when they fill the slot in
later stages are more effective in large inter-bracket span.
Sliding teeth along arch-wire is relatively
unimportant.
0.022” – Wider brackets.
Larger slot provides clearance needed for
sliding
Single width Double width
7
Mini Uni - Twin
AUTHORS SUPPORTING THE USE OF 0.022”SLOT
ROTH
Available both in 0.018” & 0.022 slot brackets
His preference is 0.022” slot, based on the
type of mechanics he uses. 0.018 is too restrictive in wire
size selection
He prefers 0.022”in terms of wire selection
stabilizing arches as anchor units, for orthognathic
surgery& for torque control, mainly in the buccal
segments.
M.B.T.
8
The larger slot allows more freedom of movement for the
starting wires, keeping the forces light.
Later in treatment, the steel rectangular working wires of
0.019/0.025 have been found to perform well
With the 0.018 slot the main working wire is normally
0.016/0.022 or 0.017/0.025.These wires shows greater
deflection & binding during space closure with sliding
mechanics.
AUTHORS SUPPORTING THE USE OF 0.018” SLOTS
WICK ALEXANDER
• His concept was that 0.022” slot with heavy rectangular
wires was cumbersome for patients.
• He used 0.018” slot with 0.017” wires lighter forces
would result in less patient discomfort .
RICKETTS
• He used the edgewise bracket slot (0.018 x 0.030) to keep
the bracket and wire sizes smaller.
• The deep slot (0.030) permits two light arches to be
employed at once (Base archwire for stabilization & the
auxillary arch or section for rotation or movement).
PLAY (OR) SLOP
• The clearance between the arch wire and bracket.
• Four types of play.
(Straight wire the next generation –AJO 1998)
Torquing play
Play in the tipping plane
Vertical play
9
Rotational play
Torquing play – depends on size of rectangular wire relative to the
size of the slot. Most prescriptions have excessive lingual root torque
in the maxillary anterior brackets that may deliver adequate lingual
root torque for retraction movements using less than full-sized arch
wires. Brackets with these excessive torques are incapable of
delivering labial root torque during protraction movements, without
extensive reverse torquing bends in the arch wire.
Play in tipping plane generally depends upon size of the arch-
wire, size of slot and overall width of the slot. Tipping play is less
than torquing play. But if torquing play is minimized by increasing
the arch wire size relative to slot size, then tipping play will be
minimized, regardless of the width of the bracket.
Vertical play
Play in the vertical plane will result in incomplete bracket to
bracket leveling.
Rotational play
Tendency of the tooth to rotate on its own axis. Rotational play
increases narrow bracket, decreases wide brackets. Play can
never be eliminated but can be minimized, in the tipping, torquing
and vertical planes, by “filling” the slot as much as possible.
Rotational play is minimized by using brackets with adequate
rotational lower arm length and ligating with sufficient force to keep
the arch wire seated in the bottom of the slot.
For every .001” difference between arch wire & slot - 4°play.
0.018” slot with 0.018 Wire 0.022” slot with 0.018 Wire
10
IN – BUILT TORQUE Vs EXPRESSEDTORQUE
The area of torque application is small.depends on the twist
effect of a relatively small wire compared with the bulk of the
tooth.
.019/.025 steel wires have a slop about 12° in a 0.022 slot.
As a result of the relative inefficiency of pre-adjusted brackets
in delivering torque, it was necessary to built in extra torque
into the incisor, molar& lower premolar brackets
EFFECTIVE TORQUE
11
ASPECTS INCORPORATED TO GET THE FULL EXPRESSION
OF TORQUE
• FILL THE SLOT
• INCORPORATE TORQUE INTO THE WIRE
THE THREE STAGES OF TREATMENT
• ALIGNMENT & LEVELING
• RETRACTION & SPACE CLOSURE
• FINISHING
ALIGNING &LEVELING
0.018” SLOT
Proffit prefers round wires for this stage .Says that rectangular
arch wires, particularly those with a tight fit with in the bracket slot,
so that the position of root apex could be affected, normally should
be avoided.
12
The principle is that it is better to tip crowns to position during
initial alignment, rather than displacing the root apices, because
rectangular arch wire will create unnecessary and undesirable root
movement during alignment.
0.014 NITI
0.016 NITI
0.016 HANT
16x22 HANT
0.022” SLOT
• 0.015 MULTISTRAND
• 0.0175 MULTISTRAND
• 0.014 SS
• 0.016 SS
• 0.018 SS
• 0.020 SS
• 0.016 HANT
• 19 x 25 HANT
RETRACTION
Individual canine retraction- friction ,frictionless
Enmasse & Anterior retraction –friction, frictionless.
INDIVIDUAL CANINE RETRACTION
• Round wires are preferred than rectangular wires
• Decrease in the contact surface area – less friction
13
FRICTION
0.018” Slot
• 0.016 Round SS
• 16 X 22 SS
0.022” Slot
• 0.018 Round SS
• 16 x 22 SS
• 17 x 25 SS
• Tip- edge bracket.
FRICTION-LESS
PG SPRING – 16 X 22 SS wire - 0.018” /0.022” slots.
BURSTONE T-Loop–0.017 x 0.025 TMA wire –0.018”/0.022”.
MARCOTTE SPRING – 0.016 SS wire – 0.018” /0.022”slots.
ENMASSE & ANTERIOR RETRACTION
0.018” Slot
• 16 x 22 SS
• 17 X 23 SS
0.022” Slot
• 18 x 25 SS
• 19 x 25 SS
FINISHING
0.018” Slot
• 17 x 25 NiTi
14
• 17 x 25 SS
• 17 x 25 beta Ti
• 17 X 25 Ti Niobium
0.022” Slot
• 21 x 25 NiTi
• 21 x 25 beta Ti
• 21 x 25 M- NiTi
• 21 X 25 Ti Niobium
SURGICAL ORTHODONTICS
Normally it is said that 0.022 slot is preferred for surgical
cases, but
William proffit & Raymond P. White
• 0.018”slot or 0.022” slot can be used
• Rigidity of a 17 x 25 SS wire in a 0.018”is adequate for
stabilization
• One exception where 0.022” is advantageous –when segmented
arch mechanics are needed,-particularly in patients with severe
periodontal breakdown.
• In a 0.022”slot – 21 x 25 TMA / SS
0.018” SLOT
Martin .B. Epstein (AO. Vol.72. 2002)
Advantage
The capacity to fill the slot allows for a greater use of the
prescription built into the bracket.
15
Disadvantage
Fewer choices of arch wire dimensions.
0.022” SLOT
Martin .B. Epstein (AO. Vol.72. 2002)
Advantages
Using undersized archwires, one can facilitate free sliding of
the archwire through the slot.
Hence less frictional resistance or binding at the bracket wings.
Larger wires are also useful
Large wires provide increased stiffness & facilitate to keep the
teeth upright during space closure & retraction mechanics.
Robert P. Kusy & John Whitley (EJO 1999)
Smaller brackets requires that the clinician be as much as 25%
more precise in the initial stage or else binding will occur.
This outcome suggests that inexperienced clinicians will find
the 0.022” slot more suitable for sliding mechanics.
To accomplish that “best case” scenario, most easily within the
strength & stiffness requirements of the appliance, the bracket
width & wire size should be small, & the bracket slot should be
large.
Disadvantages
Martin .B. Epstein (AO. Vol.72. 2002)
Disadvantage may be encountered when filling the slot.
16
Full sized rectangular wires becomes markedly reduced in
springiness and range,-thereby severly limiting the ability to
place effective torque & finishing bends.
VIEWS OF AUTHORS
Raymond E. Siatkowski. (JCO / Sep. 1999 )
Bracket slot & arch-wire dimensions have caused unpredictable
failures of formerly reliable mechanics,-especially those that
depend on protracting posterior teeth.
This has resulted in lingual tipping of incisors & in general loss
of incisor axial inclination control.
Robert P. Kusy (AJO. Apr. 2002)
In reality manufactures do not provide discrete slot sizes, but
rather a spectrum of slot sizes – 0.0178 to 0.0237.
Angle’s generation necessitated 0.022”, where he used gold
wire.
The SS wires, which displaced gold, permitted the slot to shrink
to 0.018”.
All might have turned okay if technology had not made a hair
pin bend and come full circle to offer a titanium – molybedneum arch
wire alloy with a stiffness close to that of gold.
As a result of which the world according to its preference split
into two
United States-0.022” slot and Europe –0.018”slot.
17
Resolution of the “slot – size” issue would simplify biomaterials &
biomechanic’s instruction for graduate residents too.
Lets not once again follow that well worn path as was done for
gold and S.S rather let’s walk the less trodden path that leads to
higher grounds.
Change never comes easy, but this modification is worth every
bit and effort.So let’s pick up one slot size, whatever it is & make it
metric.
CONCLUSION
Sheldon Peck. (AO – 71. 2001)
Experience with earlier manufacturing advances in other fields
shows that the company first to offer a progressive new standard,
becomes the “king of the road”, miles ahead of the latecomers trying
to jump on the bandwagon. With reference to these views of the
different authors, I believe that it would have reached the ears of
manufacturers too, who might have this “spark” of universal metric
system in the pipe line.
Understanding biomechanics is the matter; it is not the slot
dimension which in debate.
18