Wire Selection for Optimal Biomechanic

Efficiency in the MBT Versatile+ Appliance System

by Dr. Dietmar Segner
Dr. Dietmar Segner
earned his specialty
in orthodontics
from Hamburg
University, Germany,
and also received
his PhD from that institution. He worked as
professor of orthodontics at the university

It is the wire that drives or guides the teeth, no matter how advanced the brackets may be,
or whether they are self-ligating or not. The sensible selection of the archwires during the
different treatment phases has therefore a major influence on the treatment efficiency.
This article will show the principle and give the clinician a guide to select the right wire
at the right time. It should be pointed out that due to the variety of malocclusions and
the variability of individual tissue reaction, it is not possible to give fixed time frames for
changing to the next archwire. Rather, it is an important clinical decision if the tasks of a
certain treatment stage are resolved and the treatment can progress to the next stage and
next archwire.

clinic and now works in his private practice

in Hamburg specializing in the treatment of
adults using aesthetic appliances. For two
decades he has lectured all over the world
on adult orthodontic treatment, and results
of his research into biomechanical and
ortho materials.

What is the Archwires Task?

The tasks of archwires during an orthodontic treatment can be split into two, which I
will call Mode 1 and Mode 2 (Figure 1-2). In the first mode, the wire is in its active state.
Activation of the wire is carried out by ligating the archwire to the irregularly positioned
teeth. Energy is stored by pushing the elastic wires into the bracket slots. After this
activation, the archwire uses this energy to move the teeth. Such an operating mode is
typical for the aligning and leveling stages. It would also be relevant in all situations where
the orthodontist inserts loops or other active elements into the archwire through bends, as
for example retraction loops. As these applications are not used on a regular basis in the
MBT Versatile+ Appliance System, they will be excluded from the further deliberations.
In the other application of an archwire (Mode 2), the archwire is used as a guiding track for
the mesial or distal movement of teeth along the arch. Here the archwire is initially passive
and its stiffness and elasticity only comes into play when the teeth start to show side
effects such as tipping or rotations. Then the wire creates corrective forces and moments
and assures that the teeth do not deviate from the intended track and angulations. The
activation is achieved by elastomeric chains, super-elastic springs, inter-maxillary elastics
or similar. These auxiliaries store the energy for the tooth movement. This application
mode is typical for the working and retraction phases. In this mode the wire should have a
significant stiffness in order to keep the undesired rotations or tipping to a minimum.

1
Figure 1: Wire in an active state.

2
Figure 2: Wire in a passive state.

Dimension
During the alignment phase there is no need for a tight fit of the archwire in the bracket
slot, as the differences between the archwire dimension and the slot dimension are up to
0.15 mm, while the positioning precision during the first alignment stage needs to be only
about 0.5 mm. For a number of reasons, it is even desirable to have undersized wires in the
alignment stage. The play between archwire and bracket slot reduces friction and potential
binding with severely irregularly positioned teeth. Also the force-deflection curves of thin
super-elastic wires are usually better because they show the correct force level immediately

at the beginning of the deactivation while thicker super-elastic

archwires can show rather high forces during the first days after
the ligation. It is also important to note that the slot dimension does
not play a major role in selecting the first aligning wire. The same
dimension is suitable for the 18 and 22 slot system.
During the leveling stage and also later in treatment the wire
dimension becomes important. For de-rotation in self-ligating
brackets and for effective torque effect, the wire dimension needs
to be adjusted to the slot size. To get the standard designed torque
effect the vertical dimension of the (rectangular) archwire needs
to be 16 in the 18 slot and 19 in the 22 slot. Another requirement
is that the horizontal slot dimension needs to be 25 in both the
18 and 22 slot systems for good rotational control. It is therefore
clear that in the MBT Versatile+ Appliance System, the standard
working wire as well as the finishing wires should be 1625 in the
18 system and 1925 in the 22 system.
It should be kept in mind that an increase in wire dimension results
in a stronger expression of the torque built into the prescription of
the MBT system, resulting in additional torque angulation. Using a
1725 wire instead of a 1625 in the 18 system or a 2025 instead
of a 1925 in the 22 system increases the torque value by about 3.
Of course the same is true for undersized archwires: using a 1425
wire instead of a 1625 wire in the 18 system decreases the torque
angle by 6, using a 1725 instead of 1925 in the 22 slot system
will decrease the torque effect by 7.

Stiffness and Force Levels

In the active Mode 1 of archwires, the force acting on the teeth
depends mainly on the archwire used. Super-elastic archwires
have a major advantage in that the force is almost constant no
matter how irregularly the teeth are positioned or how short the
inter-bracket distance is, in clear contrast to the twisted wires,
braided wires or non super-elastic Nickel-Titanium wires. In the
graph (Figure 3) we compare a 16 super-elastic nickel-titanium
wire (Nitinol HA) and a 16 non super-elastic Nickel-Titanium wire
(Nitinol Classic). We easily see that the super-elastic wire develops
significantly less force. The difference is shown by the combination
of the red and yellow areas in the graph.
But even if we try to reduce the force of the non super-elastic
archwires by selecting a thinner wire (14 Nitinol Classic) we see
that for all deflections above 1.2 mm, the thicker but super-elastic
wire develops lower forces that are also constant over much of the
deflection range. Below 1.2 mm deflection, the force of the non
super-elastic wire, decreases so much that it becomes less than the
super-elastic wire, and eventually it would not move the teeth any
more, and an archwire change needs to be conducted. On the other
hand, the super-elastic archwire continues to exert constant forces

3
Figure 3: Force associated with 3 archwires.

4
Figure 4: Force characteristics of Nitinol HA (HANT) in dimension 14 round.

until the deflection falls below 0.35 mm, so with one single archwire
we achieve almost perfect leveling if we just leave the wire in and
give it a chance to express itself fully, which might take anywhere
from 5 weeks to 5 months.
In order to optimize the biological response, and avoid the risk of
force that is too high, the initial archwire should be super-elastic
and its force level should be significantly below 100 g of force. The
optimal wire therefore is the 14 Nitinol Heat Activated both for the
18 system and the 22 system (Figure 4).
After the alignment phase, the slots will be quite well aligned.
If a second archwire is necessary for the leveling stage, the
deflection of that archwire due to misaligned bracket slots will
be below 0.5 mm. Since none of the super-elastic archwires
has a plateau of constant force below 0.5 mm, the aspect of
superelasticity becomes unimportant for the second and all
following wires of the treatment. Now it becomes crucial that the
wire has the correct dimension to get full expression of the bracket
prescription as described above.

During the working stage the wires operate in the passive Mode 2.
They should have sufficient stiffness to counteract any undesired
movements or rotations. Since the leveling phase achieved perfect
alignment of the bracket slots, insertion of such a stiff archwire
should not present a problem. Only wires of Beta III Titanium or
stainless steel provide sufficient stiffness. Especially in extraction
cases, steel is to be given preference.
5

Making Bends
Although the philosophy of the MBT appliance system is to
avoid bending as much as possible, by achieving perfect bracket
positioning through indirect bonding and if required early
repositioning of brackets in the leveling phase, it sometimes might be
necessary to implement bends, especially during the finishing phase.
When a corrective bend is applied, it is usually to achieve a change
from the previous situation. This means that in this moment the
archwire is changing into Mode 1 again, the active mode. In
addition to the property of accepting precise bends, the archwire
material should also deliver the stored energy with physiologic
forces. Especially in the 22 system even small corrective bends in a
stainless steel wire exert significant amounts of force. To decrease
the force level and associated pain for the patient, it is of benefit
to use the lower modulus of elasticity of the Beta III Titanium
material. The same corrective bend in the same dimension archwire
will exert only 50% of the force in comparison to a stainless steel
wire. Therefore, the Beta III Titanium material is the recommended
material for finishing wires.

Self-Ligating Brackets
In principle, treatment with self-ligating brackets in the MBT system
can proceed with the same wires as with conventionally ligated
brackets. The only difference of significance is the rotational control
in the leveling phase. All self-ligating brackets have a fixed slot
depth of 0.0275" (0.027" for the lower anteriors) defined by the
clips or slides. In order to be able to effect de-rotation or control
undesired rotation, the archwire needs to fill this slot depth with a
play of not more than 0.0025". Therefore a single round wire will
not give perfect rotational control without adding a ligature on the
tooth in question.
Two options are available to the orthodontist: the first is to finish the
leveling with an archwire that has a 25 for the horizontal dimension.
For the 18 slot dimension, archwires of the dimension 1425 and
1625 were introduced, while in the 22 system 1725, 1825,
and 1925 wires have been available for a long time. The second
option is to fill the slot in the buccolingual direction using two round
archwires, which is called the Tandem Archwire Technique. For the
18 slot system this would be two 14 Nitinol HA archwires, while in
the 22 slot system it could either be also two 14 dimension wires
or a 14 and a 16 Nitinol HA wire used in tandem. The latter variant
might activate the clip a bit, leading to some pressure of the clip on
the wire(s) (Figure 5).

Figure 5: Tandem Archwire Technique examples.

In many cases, the initial alignment wire from the upper jaw can
be transferred to the lower jaw and added to the alignment wire
already present there. Often it would also be possible to transfer a
lower alignment wire to the upper jaw and let this second wire run
only up to the first molar.

Special Treatment Objectives

If there are special tasks during the leveling stage, the use of
additional archwires may increase treatment efficiency. Typical
examples would be the leveling of a pronounced Curve of Spee.
Here round stainless steel archwires of the dimension 18 in the
18 slot system, or of the dimensions 18 or 20 in the 22 slot system,
might enhance the efficiency. A number of orthodontists like to
use a Nitinol SE reversed curve archwire of the dimension 1622
(18 slot) or 1925 (22 slot) for the same task. For transverse arch
form adaptations, stainless steel wires would also be beneficial.
If the special application of torque is required, the use of non
super-elastic nickel-titanium should be preferred over the superelastic nickel-titanium variant. With super-elastic rectangular wires,
the torsional moments are in the range of 200 to 500 gmm, which
is on the low side of effective torque application. With non superelastic wire materials, the torsional moment depends on the amount
of activation and can be adjusted to up to about 1500 gmm. For the
18 slot system, a 1625 Nitinol Classic, and for the 22 slot system,
a 1925 Nitinol Classic left in the mouth a sufficient amount of
time will effect the specific torque requirements efficiently. Up to
2.5 per month can be achieved.

Wire Selection
To make the selection of wires for an optimal biomechanic
efficiency easier, a table has been assembled that lists the
recommended wires for the different treatment stages in the
MBT appliance system (Table 1). The table has columns for the
18 system as well as the 22 system. Also, the special requirements
of self-ligating brackets in the MBT system are addressed in the
table. In the rightmost column, suggestions for special treatment
tasks are given. These wires are only needed in certain cases
to make the treatment easier and more efficient for the patient.
Listing a strict, non-negotiable order of archwires or recommended
time intervals for the archwires to reside in the mouth has been
purposely avoided. Such inflexible cookbook-style recommendations
violate clinical experience as well as common sense and would be
contrary to the philosophy of the MBT system.

MBT Versatile+ Appliance System

Treatment Phases and Wire Requirements
Treatment Stage
Aligning Stage

14 HANT

Tasks:

Requirements for Wire:

Activating cellular
reaction

Low forces, especially with large

irregularities

Initial slot alignment

Force limitation desirable (force

limitation by superelastic plateau)

Initial de-rotation

Recommended Wire Products and Variations

MBT System Brackets 18 Slot
MBT System Brackets 22 Slot
Variations:

14 HANT

Variations:

14 NCL with push coil

and not all teeth ligated

then for
self-ligating only:

14 NCL with push coil and

not all teeth ligated

14+16 HANT
Tandem

Avoid binding
Torque effect initially usually
not desirable

Leveling Stage

Self-Ligating:

Variations:

Tasks:

Requirements for Wire:

F inal de-rotation/
re-establishing correct
contact points

Not too high forces

1425 HANT
or
14+14 HANT
Tandem

If torque matters
1625 NCL

Establishing torque
Correcting angulations
Leveling Curve of Spee

Elasticity to correct angulations/tip

Good rotational control
Dimension needs to fill slot height
for torque effect
Stiffness to level Curve of Spee

Non-Self-Ligating:
16 Australian
then
1625 Beta III
Titanium

Working Stage
Tasks:

Requirements for Wire:

C
 losing of extraction
spaces

Enough stiffness to avoid vertical

and horizontal bowing

Closing of other spaces

Dimension needs to fill slot height

for torque effect

R
 etracting anterior teeth
with torque control

Self-Ligating +
Non-Self-Ligating:
1925 HANT

For additional
vertical leveling:
18 SS
1622 NSE
reversed curve

Variations:
If torque matters
1925 NCL instead of
1925 HANT
For additional
vertical leveling:
18 SS
20 SS
1925 NSE
reversed curve
1925 Beta III Titanium

Variations:

1925 SS

Variations:

If no space closure
required:
1625 Beta III
Titanium

(with crimp hooks)

Optional: 2125 hybrid

1625 Beta III

Titanium

Variations:

1925 Beta III

Titanium

Variations:

1622 Braided

Alternative would be
using a positioner

1925 Braided

Alternative would be
using a positioner

1625 SS
or
1725 SS Hybrid
(with crimp hooks)

If no space closure
required:
1925 Beta III Titanium

Good rotational control

Low friction

Finishing Stage
Tasks:

Requirements for Wire:

Correct midlines

Corrective bends possible without

too high forces

Root alignment
Overbite/overjet
Functional occlusion

If already in place:
1725 SS hybrid
1625 SS

If already in place:
1925 SS

Good rotational control

Dimension needs to fill slot height
for torque effect
Enough stiffness to hold or
fine-tune arch form and overbite

Settling Stage
Tasks:

Requirements for Wire:

Maximizing
intercuspidation

Allows minor tooth movement by

occlusion and elastic traction

Table 1: Recommended wires by treatment phase, MBT Versatile+ Appliance System. Note: Wire selection should be made on a case-by-case basis.
NCL: Nitinol Classic; NSE: Nitinol Super-Elastic; HANT: Nitinol HA; SS: Stainless Steel.

Reprinted from Orthodontic Perspectives Vol. XVIII No. 1.

2011, 3M. All rights reserved.