Centre of Resistance Simulator is an Innovative Customized Orthodontic Appliance for Retraction of Protruded dentition especially proclined upper front Teeth. Biomechanics of Extraction Space Closure with Sliding Mechanics has been elaborated mathematically using Equilibrium Force Diagram. Comparatively Simple and Statically determinate Force system using the Centre of Resistance Simulator (CRS) has been described. Vertical Anchorage Control has been challenging task in patients having Long Faces and high Mandibular Plane Angle (Vertical Growers). This concept of Simulating Centre of Resistance facilitates vertical Anchorage control during Extraction Space Closure without Temporary Anchorage Devices (Microimplants or Bone Screws). Judicious use of TADs is definitely required for En Masse Distalization cases and absolute Anchorage demanding extraction cases e.g. extreme long faces where maximum extraction space is to be utilized for Retraction of Anterior Teeth Segment. Bodily Retraction of Upper Anterior Teeth without bite deepening and without Molars extrusion ( i.e.opening of Mandibular Plane Angle) is also possible with the concept. This appliance may also be used in patients having lingual braces and clear aligners for improving outcome. This Orthodontic Force System provides Frictionless and Loopless Retraction Mechanics for Extraction Space Closure. Designing of the appliance on Cephalometric Tracing and then accordingly locating estimated Centre of Resistance on Models has been mentioned stepwise in the video. Techno Savvy young Orthodontists can design and fabricate CRS by CAD-CAM using 3D designing softwares and DMLS 3D Printing. Biomechanical explanation of each minute sense has been described in this video. Please watch and listen carefully from start to finish in one go. I humbly request to all Orthodontists especially those affiliated with Institutes to explore the concept. I will be more than happy to be involved in such work. Please feel free to contact me on vishvadental@gmail.com for detailed insight.

1. CENTRE OF RESISTANCE SIMULATOR
FOR FRICTIONLESS & LOOPLESS
RETRACTION MECHANICS
DR. VISHNU JAGDISHBHAI PATEL
M.D.S.
CRS
1
Protruding dentition is one of the most common problems in Orthodontics. Distalization
without extraction and extraction followed by space closure are two ways to retract
protruding dentition.
Centre of resistance simulator is an innovative customized appliance for Retraction
Mechanics.

2. For bodily retraction, a line of action should ideally pass
through centres of resistance of the segments to be moved.
If it is not feasible practically.
then at least
the line of action must pass at the level of the Centres of
Resistance in all 3 planes of space.
2
The concept is based on this principal of biomechanics.

3. ----10mm---
<---8mm---
--9mm---
3
Let’s analyse sliding mechanics of space closure with continuous wire. The line of action
is about 8, 9 AND 10mm occlusal from CR of Posterior teeth, entire system and CR of
anterior teeth respectively.

4. 4
This force diagram is prepared to achieve pure bodily movement of the anterior teeth.
Force values are for understanding purpose only.
Applied force is about 200gm. Consider Sliding resistance about 100 gm, and therefore
Force to overcome sliding resistance is 100 gm. In response to this 100 gm force, a
clockwise moment of 900 gmmm is generated on entire system or dentition.
Now coming to the actual space closure component: 100 gm retraction force on anterior
teeth is balanced by 100 gm protraction force on posterior teeth. Because of 2mm
shorter moment arm length of posterior teeth, 200gmmm of counterclockwise moment
is felt by the entire system.
So a net effect of 700 gmmm clockwise moment is felt by the entire system leading to
bite deepening, which is undesirable in most of clinical situations except open bite cases
requiring incisor extrusion. A reverse curve of spee can be placed in archwire to oppose
this bite deepening moment on the system, but adverse effect is extrusion of posterior
dentition which is undesirable for many reasons.
This extrusion is fortunately opposed by muscle forces in horizontal growers and in
normal growers up to some extent, but in long faces having poor muscle tone, this
extrusion is always undesirable. Trans-palatal arch in patients with wide palate and
normal tongue posture can be very helpful in such vertical growers. But in patients with
narrow palate and lower tongue posture, TADS are required to prevent this extrusive
component of the force system. This is how we achieve bodily retraction of the anterior
teeth without bite deepening and without opening of the mandibular plane angle.

5. 5
Though We are achieving very much predictable results with sliding mechanics,
CRS is having non-extrusive biomechanics and simple force diagram in comparison to
sliding mechanics provided it is precisely planned and executed.

6. • PRIOR ATTEMPTS
• POWER ARMS
• QUESTIONABLE RIGIDITY
• EFFECTIVENESS IN BUCCAL VESTIBULE ???
• LIMITATIONS OF HEIGHT IN BUCCAL VESTIBULE
6
Prior attempts have been tried to simulate centre of resistance with C retractor by
Korean Researchers.
Bending of power arm in response to applied force not only fails to achieve bodily
retraction, but also makes system statically indeterminate and taxes anchorage a bit
more if bending does not occur at anchorage segment.
Whereas, Such design allows 100% force transmission to the anterior segment which in
turn makes the force system statically determinate.

7. 7
Considering right and left side posterior segment rigidly splinted as one multirooted
tooth and anterior segment as the other multirooted tooth, these are their respective
centres of resistance. In this proposed concept, THERE IS NO CONTINUOUS WIRE
BETWEEN ANTERIOR AND POSTERIOR SEGMENTS. Retraction force is applied three
dimensionally at the levels of their respective Centres of Resistance. As there is no
rotational tendency, no moments are generated and hence no countermoments are
required to balance thus reducing number of force elements and related hurdles.

8. 8
The line of action is not necessarily at the level of centres of resistance, it can be apical
or occlusal to these points if anterio-posterior tipping of occlusal plane along with space
closure is desired.
If line of action is apical from CR of posterior segment, there will be intrusion and distal
tipping of posterior segment along with space closure.

9. 9
If line of action is like this, there will be extrusion and mesial tipping of posterior
segment intrusion and torquing of incisors along with space closure.
In such clinical situations at least 016 continuous ss wire with slot obliteration is
mandatory to maintain bracket slot line up at canines and premolars during space
closure.
Additional 35-40 gm force is required to overcome minimum friction value.
Such cases do require constant supervision for any unwanted movement.

10. SAGGITAL CORONAL TRANSVERSE
10
Let’s understand the line of action in 3 planes of space when using CRS.
Centre of resistance in anterior segment lies in alveolus between two central incisors.

11. 11
SAGGITAL PLANE
In sagital plane, the line of action is at the level of the Centres of Resistance of the
anterior and the posterior segments. So teeth move not only maintaining their
inclination but their vertical relationship to the occlusal plane as well

12. 12
CORONAL PLANE
In coronal plane, again the lines of action are at the level of Centres of Resistance of the
segments to be moved, so teeth move without canting the occlusion plane.

13. 13
TRANSVERSE PLANE
In Transverse plane, the lines of action are equidistant to their respective centres of
resistance. So the resultant force is passing at the level of the Centres of the Resistance
of the anterior and posterior segments. Anteriorly if single point of force application is
available in midline then also responsive moments on either side cancels each other.

14. Bonding Pads
Vertical
connectors
Force engaging part
APPLIANCE DESCRIPTION
14
The appliance has two bonding pads, two vertical connectors and a force engaging part .
Back side of bonding pads may have optional rough mesh for improved adhesion to
bonging material.
It is fabricated by casting procedure in chrome-cobalt for adequate rigidity in thinnest
possible cross-section. Force engaging part can be compact like this or even smaller for
individual case.

15. Thickness 0.1 mm
Thickness 0.8 mm
Thickness 1.2 mm
Thickness 0.7 mm
Width 2.0 mm
15
These measurements are determined to offer optimum rigidity in minimum possible
cross section and simplifying debonding procedure.

16. Posterior CRS
16
Ideally posterior appliance should also be casted for adequate rigidity. But if it is
supported or reinforced by one midline microimplant or two bilateral palatal micro-
implants, such modified trans-palatal arch can be used for space closure.

17. • Preparation of bonding surface of CRS
o Sand-blasting
o etching with 10% Hydrofloric Acid of the bonding surface for 1 minute
followed by rinsing and drying
o Apply silane coupling agent on the HF etched surface
o Wait for 2 minutes
o Apply bonding material on the bonding surface of CRS
• Prepare tooth surface for bonding .
• Prophylaxis cleaning of the teeth surface
• Acid etching 37% Phosphoric acid for 30 seconds followed by rinsing and
drying
• Apply compatible bonding agent cure, it with Light for 10 seconds
• Fix the CRS on prepared tooth surface
• Remove excess bonding material from the edges
• Apply light for 20 seconds from all the edges on lingual side and from labial
side as well
BONDING 17
These are clinical steps for appliance fixation. Hydrofloric acid etching and silane
coupling agent are used for improving bonding strength in absence of the rough mesh.

18. 18
METHOD
•DIAGNOSIS
•APPLIANCE FIXING
•TEETH ALIGNMENT
•BITE OPENING
•SPACE CLOSURE / DISTALIZATION
•FINISHING
•APPLIANCE REMOVAL
•RETENTION
These are standard steps to correct protruding dentition.

19. METHOD
15-20 degree progressive buccal
root torque in posterior segments
Bilateral posterior Segments stabilized
with trans-palatal arch anchored with
one palatal micro-implant
19
All steps except space closure and distalization are according to standard Orthodontic
Protocol. In Space closure, Centre of Resistance Simulator and modified Transpalatal
arch are designed and fabricated from fresh study models and Lateral Cephalogram.
After appliance fixation and segmental stabilization, Space closing force measured with
dontrix gauge is applied at predetermined line of action between the anterior segment
and the posterior segment. The force modules is periodically changed untill entire
spaces are closed. For Total arch distalization, entire dental arch is first stabilized on full
sized stainless steel arch wire. Distalizing force is applied from two microimplants
anchored in accordance with required line of action.

20. Designing CRS
20
For Designing the appliance
On Cephalogram,
1. Draw occlusal plane connecting incisal edge and cusp tips of posterior teeth. and mark centres
of resistance of anterior and posterior segment.
2. Draw a line of action between these two points. Mark a point 5mm posterior to the palatal
bony contour on the line of action to compensate for soft tissue thickness and hygienic
clearance.
3. Drop down perpendicular lines from the points on occlusal plane and measure vertical
distances.
4. Measure horizontal distance between labio-incisal edge and these points on the occlusal
plane.
Now on model,
1. cover palatal area by 1mm thick wax sheet.
2. Transfer anterior and posterior points in midline as per their horizontal distances.
3. Transfer the posterior horizontal distance on either side until it marks on wax with the
vertical distance between occlusal plane and centre of resistance of the posterior segment.
4. Measure distance between line of occlusion and these points at occlusal level.
5. Transfer this distance in the anterior region and mark a perpendicular point which locates
right and left points of force application. This may not necessarily at the level of Centre of
Resistance of anterior segment, but in midline will definitely get a point at the level of CR of
anterior segment and even more apical.
6. Plan Lines of action required for particular case. Make provision for additional points in
transverse and vertical plane if required.

21. Line of Action
Perpendicular Vertical measurement is from Occlusal plane
Horizontal measurement is from Incisor labial surface to
perpendicular points on occlusal plane
21
IA’ is used to locate coronal plane for marking point of force application in midline.
IB’ is used to locate coronal plane for marking points of force application of the posterior
segment

22. Marking points with vertical measurement
Endo Gauze
Endo file with stopper
22
Then BB’ and AA’ measurements are used to locate particular point on the respective
coronal planes.
So far all appliances I have used are designed and fabricated by manual casting
procedure. More precise and faster designing and fabrication may be possible with CAD-
CAM using DMLS 3D. For that, dicom files from CBCT and models are required.

23. 5mm right
3mm Coronal
Right CR
3 Mm Apical
5mm Left
3mm Coronal
Left CR
3 Mm Apical
3mm coronal CR 3mm apical
Midine
23
These are possible points of force application shown in one of primitive version of the
appliance design.
1-3 points of force application are enough for particular case.

24. •Extraction Cases
•Non-extraction cases
Requiring more than 3mm
retraction of anterior teeth.
INDICATIONS
24
This appliance is indicated for both….. This is to balance cost-benefit ratio.

25. 25
25
25
This is 15 year old boy with chief complain of protruding teeth. He is having average
growth pattern with convex profile and obtuse naso-labial angle. Intraoral findings are
Class II malocclusion, increased overjet, proclined lower incisors.
Upper arch enmass bodily distalization with torque correction of incisors were principal
treatment goals.

26. PRE RX MID RX
After distalization
26
After reaching on working ss wire, CRS was designed, fabricated and fixed. Distalizing
force was applied from two palatal micro-implants. For first 6 months, there was hardly
any distalization, but after adding progressive buccal root torque in posterior segments,
faster distalization was achieved. Occlusal view showing noticeable change after
distalization.

27. PRE
RX
POST
RX
27
Improvement in appearance and smile, profile changed from convex to straight.

28. PRE RX POST TREATMENT
28
Class II Malocclusion corrected to Normal Class I Occlusion.

29. Pre distalization Post Treatment
MP to SN 34
MP to FMA 18
MP to SN 32
MP to FMA 16
29
mandibular plane angle reduced by 2 degree.

30. 30
Superimposition showing distalization of maxillary dentition, Along with intrusion of the
dentition - 3mm in incisor region and 1-2 mm in posterior region. I did not applied direct
intrusive force on molars. It happened as a result of line of action being above the
centre of resistance of the dentition. So Class II correction is a combined result of both
distalization and intrusion of upper dentition followed by counterclockwise rotation of
the mandible.

31. • 1mm intrusion,
• 2mm distalization
• 1 mm forward and
downward growth of
the maxilla
Distalization of entire
dentition
•Without TPA
•Without loosing Torque
•With correction of MPA
•With incisor Intrusion
31
CBCT measurements showing 1mm intrusion and 2mm distalization at distal cusps and
distobucal root apices of upper second molars
This is inspite of a mm forward and downward growth of the maxilla

32. PRE RX POST TREATMENT 3years post retention
32
3 years post retention showing stable class I occlusion and blending of palatal vault in
accordance to roots of anterior teeth.
Contact slip in lower left incisor region did happen due to overexpanded inter-canine
width.

33. Why precise planning required when designing appliance?
Reasons:
1. Right side line of action is occlusal to CR (Randomly planned)
2. too rigid splinting at archwire in anterior segment
Especially for space closure.
Iatrogenic Problems encountered here are distal tipping of segment, lateral open bite
and disturbed slot line up on right side. Along with distorted arch form and constricted
anterior segment.
Reasons are ……..which did not allow expansion during retraction.
I again had to go back with the conventional mechanics to finish this case.
So precise planning is very very important especially when there is no continuous
archwire.
Good points here are anchorage control without continuous ss wire between the
segments and faster rate of movement.

34. 34
An adult patient with cc of proclined teeth, average growth pattern full set of 32 teeth
reported to correct protruding dentition.

35. 35
Mild crowding in lower arch, lack of overbite and little space required to retract upper
and lower incisors were in favour of all second premolars extraction followed by fixed
appliance. Space closure with Group C anchorage class was determined

36. 29-11-19 27-12-2019 20-02-2020 PRE LOCKDOWN
20-06-2020 POST LOCKDOWN 01-8-08-2020 09-11-2020
36
After reaching on working ss wire, CRS appliance fixed with segmental stabilization.
Because of rotated right second premolar, extraction space is large on that side, so force
application was aimed to balance it on either side. Only very mild force is applied on left
side than on the right. Here 8 teeth are being retracted against 4 molars. TADs were not
used to assess anchorage control without continuous wire. I could dare this because of
Group C anchorage situation. This is progress during space closure.
Patient is coming from 100kms distant place. She could come only for few times after
lockdown for regular follow up, and this is current status. Minor Slot-line up disturbance
on left side is because of unequal force. I could have applied mild force in this direction
during this visit to avoid this.

37. 29-11-19 27-12-2019 20-02-2020 PRE LOCKDOWN
20-06-2020 (POST LOCKDOWN) 01-08-2020 09-11-2020
37
Initially I applied lower than required retraction force, hence space closure in upper arch
is little slower than the lower arch.
Passive ligature tie was placed between the anterior and posterior segments to control
the segments. Reasonable second order slot line up and anchorage control has been
maintained throughout retraction.

38. •
21/11/19
20/2/20
20/6/20
PRE Rx
21/11/19
2
APPOINT
MENTS
20/2/20
NO
APPOINT
MENTS
20/6/20
38
Rate of space closure seems to be faster between last two appointments, even though
force modules was not changed because of lockdown.
If proper amount of force is applied between the segments at regular interval, space
closure could have been even faster.

39. 39
After removal of CRS, 016 continuous ss wire is in place for settling of the occlusion.

40. PRE TREATMENT PRESENT STAGE
40
Improvement in profile and smile is evident here.

41. PRE RX POST RETRACTION
41
Radiographic comparison after retraction showing strain free lip seal.

42. 42
Superimposition showing bodily retraction of upper anterior teeth maintaining vertical
occlusal relationship at both anterior and posterior segments. In spite of stronger
anchorage in lower arch, bodily movement of upper anterior teeth as opposed to
controlled tipping of lower arch seems to have a positive indication for antro-posterior
control as well.

43. CLINICAL RECOMMENDATIONS
• Segmental stabilization on working ss wire
• 100gms force on either side
i.e. 200gms force total
• Consolidate posterior segments like a rigid splint.
• Consolidate anterior segment on working wire.
• Anchorage reinforcement : for absolute control
FOR RETRACTION OF 6 ANTERIOR TEETH
43
May be needed for

44. FOR ENMASSE DISTALIZATION
• A piece of 21 X 25 SS wire Is Joined Between Cingulum Of
Canines to force engaging part of the Appliance on either side
with flowable composite.
• IF FORCE IS AT CR level then 150-180 gm force on either side, i.e.
300-360 gm force total can be applied.
• IF Distalizing FORCE IS ABOVE CR level, then initial force should
not exceed 50-60 gm on either side till root apices of incisors are
well within centre of spongy bone.
• After intrusion and proper inclination of incisors is achieved, then
150-180 gm force on either side, i.e. 300-360 gm force total can be
applied
• Progressive Buccal Root Torque in posterior teeth is required for
• Anatomic reasons
• Distalizing Force Transduction till second molars.
CLINICAL RECOMMENDATIONS44
…..at CR level for bodily distalization of entire maxillary dentition.
Why Buccal root torque for distalization?
Palatal root is in close vicinity of dense palatal cortex in molar region, especially in
second molars areas. Maxilla widens apically on buccal side, whereas it is limited by
greater palatine groove and foramen on the palatal side, so if roots apices are positioned
on buccal side, less biomechanical activity is required for effective distalization.

45. 150 gms 240 gms
45
We can apply other active force modules like elastic chains, Niti Closed Coil Springs in
different modes. Upto 240 gm consistant force can be applied With a short distance of
10 mm between the points of force application.

46. CASES TO START WITH
• ENMASS DISTALIZATION
• Extraction cases When line of action is at the level of CR
• where the line of action is below level of Centres of resistance of
any of anterior or posterior segment. Especially extraction cases
• Force application only after
• reaching/stabilizing on working SS wire
• Bite opening
NOT TO START WITH
46
I have already burnt my fingers by jumping on force application before time.

47. STATICALLY DETERMINATE
• 100% force for effective tooth movement.
• Rigidity of the appliance facilitates 100% force transmission to
segments to be moved.
• Forces and moments
involved in equilibrium can be measured and calculated
mathematically.
Anchorage savvy
In vertical Plane
• as line of action is at centre of resistance level, extrusion is avoided.
• Extrusion because of Sliding Resistance is out of Question
As there is no continuous wire, so no sliding on wire.
Anterio-Posterior plane
It may have some advantage OVER sliding and loop mechanics
47

48. Re-RX
Case
Pre Rx
Present
stage
48
This slide is just for planning line of action.
This is a re-treatment case requiring
intrusion of upper teeth and
torque regaining of incisors.
A mid-palatal TAD has been placed to have line of action apical to centre of resistance of
the incisor and entire dental arch.

49. •
•Space Closure
•CRS +Lingual Splints
•One anterior and
•Two posterior combined with
modified Trans-palatal Arch
PROSPECTS CLEAR ALIGNERS
49
Biggest limitation of clear aligners is their role in space closure, more specifically for
bodily retraction.
After alignment and levelling with clear aligners; stabilize one anterior and two posterior
segments with rigid palatal splints followed by suggested space closing mechanics. Fix
Centre of Resistance Simulator on anterior segment and combine two posterior
segments with modified trans-palatal arch to make one posterior segment. Apply
retraction force between the anterior and the posterior segments at desired level
according to clinical requirement. After space closure, couple of aligners may be
required for finishing. Thus CRS and lingual splints can take care of this limitation of Clear
Aligners.

50. LINGUAL
ORTHODONTICS
SPACE CLOSURE DISTALIZATION
This biomechanics can also be used for retraction in Lingual Orthodontics as well. Main
advantage here is Torque control of Incisors.

51. FIRST APPLIANCE
51
THIS IS HOW I STARTED clinically AFTER TYPODONT WORK. YOU CAN SEE IMPROVING
COMPACTNESS OF THE APPLIANCE.
If we are 100 % sure about exact location of centre of resistance and line of action, then
it can be even smaller in dimension.

52. ADVANTAGES
1. Simple: neither tedious wire bending nor complex mechanics
required as explained earlier.
2. Invisible, as it is not visible while mouth opening.
3. Faster as there is no sliding, thus resistance like friction and binding is
out of question
4. Anchorage savvy: Non-extrusive Mechanics.
5. Statically determinate and
6. Versatile biomechanics for
Controlled Extraction space closure in all 3 planes of space for various
anchorage demands.
Distalization: bodily distal movement of the dentition
- teeth segment (anterior teeth i.e. central incisors, lateral incisors
and canines ) unilateral or bilateral segments of dental arch or
enmasse dental arch
52
It is simple, because neither tedious wire bending nor complex biomechanics required
as explained earlier.
It is also invisible and faster.
It is anchorage savvy in vertical plane, staticlly determinate and versatile biomechnics for
controlled extraction space closure and all types of distalization either with labial or
lingual appliance.

53. DISADVANTAGES
• Requires Thorough and precise biomechanical planning for
• Locating CR
• Determining Line of action
• Requires additional laboratory procedure and clinical skill
• Limited clinical evidence available so far
• Debonding is time consuming
•Reducing cervico-incisal size of bonding pads
•Reducing thickness of bonding pads
53
Bonding Pads
I humbly request you all to explore this concept for benefiting patients and all of us.
Cumbersome debonding is being simplified by reducing cervico-incisal size of bonding
pads and by reducing thickness of bonding pads to 0.1mm.

54. CONCLUSION
• Too early to conclude especially for any new appliance
• without wide spread exploration
• Without large scale clinical study.
• This force system does have potential for further refinements and
advantages so as to be used more frequently.
Let’s join together to convert this hypothesis to real existence in our
day to day practice.
“we can”
54

55. Thank you
vishvadental@gmail.com
55
Please feel free to contact me on vishvadental@gmail.com for further insights and
evolution.