Download 3D Retraction Force Vector Indicator for Anterior en masse

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10.5005/jp-journals-10021-1069
CLINICAL INNOVATION
3D Retraction Force Vector Indicator for Anterior en masse Retraction with Miniscrew Anchorage
3D Retraction Force Vector Indicator for
Anterior en masse Retraction with Miniscrew
Anchorage
Pavankumar Janardan Vibhute
ABSTRACT
Miniscrews are used for providing anchorage in orthodontics and have become an integral part in the orthodontic treatment of severely
protrusive patients for maximum retraction of anterior teeth after premolar extractions. Often the miniscrews are placed according to the
availability of safe zone, interradicular clearance and type of mucosa. Sometime loosening and failure of miniscrew and reinsertion with
change in site lead to asymmetry in positioning. This uneven positioning of miniscrew imposes unbalanced biomechanics in the same jaw.
Force vectors of space closing auxiliary spring differs on both side and causes disturbance in occlusion or asymmetry in arch form. This
article shows how ‘3D force vector indicator’ can be used to overcome the problems arise due to asymmetric retraction forces with miniscrew
anchorage. This technique measures and specifies the correct location of implant head, i.e. 3D position of the posterior point of attachment
for retraction auxiliary and its direction of vector with respect to the fixed appliance and the underlying dentition.
Keywords: Biomechanics, 3D force vector indicator, En masse retraction, Miniscrew anchorage, Retraction force.
How to cite this article: Vibhute PJ. 3D Retraction Force Vector Indicator for Anterior en masse Retraction with Miniscrew Anchorage.
J Ind Orthod Soc 2012;46(2):103-108.
INTRODUCTION
Miniscrews are used as anchorage in orthodontics and have
become an integral part in the orthodontic treatment of severely
protrusive patients for maximum retraction of anterior teeth after
premolar extractions.1-5 During insertion of miniscrew, emphasis
is given on the host factors (safe zone), 6-14 miniscrew
dimensions,15-18 sterilization and biomechanical demand of
directing the retraction force vector toward center of resistance
of posterior teeth.19
In conventional sliding retraction (without miniscrew),
importance to the arch form is indispensable and retraction forces
are balanced posteriorly by the posterior teeth. But, with sliding
mechanics which is most commonly followed with miniscrew
retraction, forces are not balanced posteriorly by the posterior
teeth but by the miniscrew.20,21 It causes certain idiopathic effects
on the arch form. These biomechanical side effects occur in all
the three-dimensions.21 Archwire suffers the external forces
which tend to alter the arch form of the base wire. These effects
are directly related to the magnitude and vectors of force. If
miniscrews are not placed in the symmetrical and balanced position
bilaterally in both arches, retraction force vector causes a
disturbance in the original arch form coordination. Ignorance of
uniformity/symmetry in positioning the miniscrew head in proper
positions does create the asymmetry in the retraction forces and
biomechanics in all three planes (Figs 1A to C). No method is
available to evaluate the patient for the consideration of balanced
biomechanics, so that correct positioning of miniscrew head
delivers the optimum biomechanics and treatment success with
miniscrew anchorage.22
Fig. 1A: Asymmetry of retraction forces and biomechanics visualized
by measuring the angle between the force vector and base archwire in
sagittal plane
Associate Professor
Department of Orthodontics, Sharad Pawar Dental College, Datta
Meghe Institute of Medical Sciences, Nagpur, Maharashtra, India
Corresponding Author: Pavankumar Janardan Vibhute, Associate
Professor, Department of Orthodontics, Sharad Pawar Dental College
Datta Meghe Institute of Medical Sciences, Nagpur, Maharashtra
India, e-mail: [email protected]
Received on: 11/7/11
Accepted after Revision: 11/9/11
Fig. 1B: Symmetry of retraction forces and biomechanics evaluated
in transverse plane
The Journal of Indian Orthodontic Society, April-June 2012;46(2):103-108
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Pavankumar Janardan Vibhute
be slightly crimped, so that they have ‘semitight-fit’ when base
archwire and brass wire used is inserted through them.
Connecter can be adjusted by sliding (in mesiodistal direction)
or rotating (in buccopalatal direction) on the base archwire.
Length of the brass wire can also be adjusted, so that it
coordinates and denotes the exact location of the miniscrew
head by posterior pointers and anterior hook by anterior pointers.
Fig. 1C: Asymmetry in the retraction forces and
biomechanics in vertical plane
This article illustrates how the ‘3D force vector indicator’
can be used to overcome the problems arise due to asymmetric
retraction forces with miniscrew anchorage. This technique
measures and specifies the correct location of implant head, i.e.
3D position of the posterior point of attachment for retraction
auxiliary and its direction of vector with respect to the fixed
appliance and the underlying dentition.
Fig. 2B: Four ‘connectors’ formed by welding the bases of two round
buccal tubes with keeping lumen perpendicular to each other
Fabrication
Weld the bases of two weldable round buccal tubes (length
5 mm) facing toward each other with their lumen oriented
perpendicular to each other (Fig. 2A), this is known as the
‘connector’ (Fig. 2B). Insert the base archwire (0.018 round
stainless steel) through the lumen of one of round tube of the
four connectors. Another round tube of each connector will lie
perpendicular to the base archwire. One pair of connector are
adjusted to the molar section of base archwire and the other
pair in the canine region bilaterally (Fig. 2C). A piece of brass
wire (Fig. 2D) is passed through the lumen of the round tube
which is perpendicular to the base archwire and known as
‘pointers’ (Fig. 2E). Round buccal tubes of 0.032" lumen should
Fig. 2C: One pair of connector adjusted at molar section of
base archwire and other pair at canine region bilaterally
Fig. 2A: Two round buccal tubes (5 mm length) before and after
welding with each other
Fig. 2D: Pieces of brass wire are used to pass through the lumen of
round tube which is perpendicular to base archwire to form ‘pointers’
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3D Retraction Force Vector Indicator for Anterior en masse Retraction with Miniscrew Anchorage
Fig. 2E: Base archwire (green arrow), posterior connector (blue arrow),
anterior connector (red arrow), brass wire used as pointer (yellow arrow)
A 5 mm length of round tube can easily be adjusted to any
inter-bracket span.
Components
1. Base archwire consists of pair of posterior and second pair
of anterior pointers (Fig. 2E).
2. Posterior pointer shows the location of miniscrew head,
where retraction ‘space closing spring’ is to be attached
(Fig. 2E).
3. Anterior pointer shows the location of anterior hook between
lateral incisor and canine (Fig. 2E).
4. Arch form template graph is used in selecting the shape of
base archwire and evaluates discrepancies in the force vector
(location of pointers) in three planes.
5. Goniometer** (one plane, uniaxial 14" transparent, plastic
180° or 360°).
Technique
1. Technique is performed usually before start of en masse
retraction in each arch, where alignment and leveling is
completed; miniscrews* are inserted and ready to load with
retraction force auxiliary (Figs 3A to C).
2. Base archwire on which the two pairs of anterior and
posterior pointers are rolled is adjusted in form, so that it
matches to the patient’s selected arch form (Fig. 4).
3. Insert the base archwire into the molar tube and all slots of
brackets, with adjusting the anterior pointers to simulate
the position of anterior hooks between canine and lateral
incisor and posterior pointers to denote the position of
miniscrew head, i.e. posterior point of retraction auxiliary
attachment (Figs 5A to C). Anterior connector positioned
at interbracket span between lateral incisor and canine while
posterior connector between 2nd premolar and 1st molar.
4. Gently take out the base archwire without disturbing the
positions of the pointers and ready to evaluate it against
the graph from all three planes. Retraction force vector is
simply the straight distance between anterior and posterior
Figs 3A to C: Alignment and leveling completed in both arches where
miniscrew is inserted between 2nd premolar and 1st molar roots
depending upon the availability of safe zone
pointers in each quadrant. This force vector is measured in
sagittal, transverse and vertical planes, keeping base
archwire against the graph.
A. Sagittal plane/lateral view (Figs 6A to C): With the help of
goniometer,
• Angle between retraction force vector and base archwire
is measured bilaterally. Discrepancy between two sides
shows the tendency to the asymmetric biomechanics.
*1.5 mm diameter, 11.6 mm long, bracket head type (Aarhus Mini-Implant ScanOrto. Hans Edvard Teglers Vej 2, 29 20 Charlottenlund, Denmark,
www.aarhus-mini-implant.com)
**Goniometer (Blundell Harling Ltd, 9 Albany Road, Granby Industrial Estate, Weymouth, Dorset, DT4, 9TH, Phone: +44(0)1305206000,
www.blundellharling.com)
The Journal of Indian Orthodontic Society, April-June 2012;46(2):103-108
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Pavankumar Janardan Vibhute
Fig. 4: Base archwire is adjusted in form so that it matches to the
patient's selected arch form
Figs 5A to C: Maxillary '3D retraction force vector indicator' in place.
Posterior pointer records the 3D location of miniscrew head (posterior
point of attachment of retraction auxiliary), anterior pointer record the
3D location of anterior hooks (anterior point of attachment of retraction
auxiliary). After confirmation of all pointers it is gently taken out without
disturbing the positions of pointers
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Figs 6A to E: Evaluation of symmetry in biomechanics: (A to C) Angle
formed by the retraction force vector with base archwire or occlusal
plane (shown by curved yellow arrow) and linear distance between two
points of attachments (red line) of space closing auxiliary spring
measured in sagittal plane with the help of goniometer. (D) Direction of
retraction force vector measured in transverse plane and compared to
contralateral side. (E) Distance of miniscrew head from base archwire
measured in vertical plane
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3D Retraction Force Vector Indicator for Anterior en masse Retraction with Miniscrew Anchorage
•
Distance between anterior and posterior pointers should
be similar on bilateral sides of same arch; otherwise
uneven stretch of auxiliary spring will create unequal
forces.
B. Transverse plane/occlusal view (Fig. 6D): In case, if
miniscrew and molars are not connected with a rigid wire,
the retraction forces from miniscrews attempt to alter the
arch form of base wire depending upon its vector direction.
• Too close placement of posterior pointer (miniscrew
head) near base archwire shows the retraction force
passing very closely to base archwire without changing
the arch form
• Buccal placement of posterior pointer away from
posterior base archwire: Retraction forces tend to create
expansive effect in base archwire
• Lingual placement of posterior pointer inside posterior
base archwire: Retraction forces tend to create
constrictive effect in base archwire.
C. Vertical plane/front view (Fig. 6E):
• Unequal distances of miniscrew head from occlusal
plane tend to change the angle of retraction force vector
and asymmetric intrusion in anterior segment, causing
canting of the occlusal plane.
DISCUSSION
Often the miniscrews are placed according to the availability of
safe zone, interradicular clearance and type of mucosa.22
Sometime loosening and failure of miniscrew and reinsertion
with change in site lead to asymmetry in positioning. This
uneven positioning of miniscrew imposes unbalanced
biomechanics in same jaw. Force vector of space closing
auxiliary spring differs on both side and causes disturbance in
occlusion or asymmetry in arch form.
Additionally, molar or posterior segment intrusion, and
change in intermolar width have been observed as drawback of
sliding (friction) method with miniscrew anchorage.21 These
effects further get exaggerated with incorporation of reverse
curve of Spee or compensatory curvature in lower or upper jaw
respectively. Again the direction of retraction force is decisive
in disturbing arch form. With this clinical aid, direction of
retraction force is more efficiently evaluated in all three planes.
This helps in planning the biomechanics according to the
situation.
ADVANTAGES
‘3D force vector indicator’ provides better results with the
following advantages:
• Helps in appropriate designing of biomechanics.
• For correcting the asymmetries, required adjustments can
be done easily.
• It can also serve as guide for miniscrew placement which
exactly shows the location of miniscrew head bilaterally in
a single step.
•
•
•
If same ‘3D force vector indicator’ is used before and after
space closure, treatment changes occurred in the threedimensions can be easily evaluated.
Easy to fabricate chair-side and sterilize.
It can be used for multiple patients by just adjusting the
position of connectors and length, deflection of pointers.
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