Vertical Force Consideration in
Differential Space Closure
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www...
Introduction
• Many class II patients are treated by extraction
to reduce overjet and obtain normal molar
relationship.
• ...
Differential Space Closure
• The ratio of the applied moment or torque to the
force at the bracket determines the center o...
• As the moment-to-force ratio increases,
the center of rotation moves apically. It
disappears into infinity when the forc...
www.indiandentalacademy.com
• The differential between the anterior
torque and the greater posterior moment
produces an intrusive force on the anterio...
Composite T-loop springs
• Composite T-loop springs made of .018” X .025”
and .017” X .025” TMA wire.
• Angulations is bui...
• If the vertical force is anterior to the center of
resistance of the anterior segment, the intrusive
force times the per...
Patient study
• Pretreatment head films from 25 class II
patients treated by first bicuspid
extractions, with retraction a...
• The center of resistance for the six-tooth
unit was then located halfway between
the mid point of the four incisors’ cen...
www.indiandentalacademy.com
Results
• The pretreatment estimate of the center of
resistance was, on average, close to the cuspid
bracket, but varied c...
Clinical considerations
• If the anterior teeth are markedly flared,
the vertical force may be anterior to the
center of r...
www.indiandentalacademy.com
• On the other hand, the vertical force
posterior to the center of resistance at the
beginning of treatment, particularly ...
• If they left in place too long, they can
cause intrusion of the anterior segment,
undue tipping of the anterior teeth, a...
www.indiandentalacademy.com
• There are a number of possible solutions to the
problem of the vertical force posterior to the
center of resistance.
• W...
www.indiandentalacademy.com
• The appropriate sequence might be for
en masse retraction:
1) Approximately 3mm of en masse tipping
around the apices of...
Conclusion
• The vertical forces that result from
differential moments between the anterior
and posterior segments can inf...
www.indiandentalacademy.com
Thank you
For more details please visit
www.indiandentalacademy.com
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Vertical force consideration in differential space closure /certified fixed orthodontic courses by Indian dental academy

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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call
0091-9248678078

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Vertical force consideration in differential space closure /certified fixed orthodontic courses by Indian dental academy

  1. 1. Vertical Force Consideration in Differential Space Closure INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. Introduction • Many class II patients are treated by extraction to reduce overjet and obtain normal molar relationship. • The composite T- loop spring has been advocated for space closure when anterior retraction is needed without loss of anchorage. • This article will discus how individual monitoring of the force system delivered form the composite T- loop can be used to minimize “round tripping” and avoid side effects. www.indiandentalacademy.com
  3. 3. Differential Space Closure • The ratio of the applied moment or torque to the force at the bracket determines the center of rotation. • A simple force at the bracket will produce uncontrolled tipping, in which the center of rotation is slightly apical to the center of resistance. • If moment is added to the force, the line of action of the resultant force is translated apically, and the displacement in milimeters is equivalent to the moment-to-force ratio. www.indiandentalacademy.com
  4. 4. • As the moment-to-force ratio increases, the center of rotation moves apically. It disappears into infinity when the force system produces pure translation. • Higher the moment-to-force ratios will produce root movement. • The laws of equilibrium for a retraction spring dictate that since there is a differential, vertical forces are produced. www.indiandentalacademy.com
  5. 5. www.indiandentalacademy.com
  6. 6. • The differential between the anterior torque and the greater posterior moment produces an intrusive force on the anterior which is useful in patients with deep overbites who require intrusion. • In open bite case require entirely different concept in anchorage space closure – perhaps the use of equal and opposite M/F ratios ( without vertical force) and headgear to the posterior segments. www.indiandentalacademy.com
  7. 7. Composite T-loop springs • Composite T-loop springs made of .018” X .025” and .017” X .025” TMA wire. • Angulations is built into the spring either in the form of posterior tipback bends or anterior “V” bends to control the centers of rotation of the anterior and posterior teeth. • If resulting vertical force acts through the center of resistance of the anterior segment it will not have any effect on the total torque or moment applied to the anterior segment. www.indiandentalacademy.com
  8. 8. • If the vertical force is anterior to the center of resistance of the anterior segment, the intrusive force times the perpendicular distance to the center of resistance increases the moment, thus tending to move the root lingually. • If the vertical force distal to the center of resistance, moment is created that reduces the amount of lingual root torque acting on the teeth. • The T-loop retraction spring is usually attached to a vertical tube on the cuspid bracket. www.indiandentalacademy.com
  9. 9. Patient study • Pretreatment head films from 25 class II patients treated by first bicuspid extractions, with retraction and intrusion of the incisors, were selected for this study. • A laser holography study has found that the center of resistance of an upper central incisors lies 30-40 % of distance from the marginal bone level. www.indiandentalacademy.com
  10. 10. • The center of resistance for the six-tooth unit was then located halfway between the mid point of the four incisors’ centers of resistance and the canines’ center of resistance. • In en masse retraction, the point of force application is usually the canine bracket. Therefore, the anteroposterior variation in position of the center of resistance was analyzed in relation to the canine bracket, with the occlusal plane as the horizontal axis. www.indiandentalacademy.com
  11. 11. www.indiandentalacademy.com
  12. 12. Results • The pretreatment estimate of the center of resistance was, on average, close to the cuspid bracket, but varied considerably from patient to patient, depending on the individual’s root length and inclination. (average .72mm). • After the simulated 3mm retraction, the point of force application change with an average of 1.9mm posterior to CR. Hence the cuspid bracket moved an average of 2.6mm distally relative to CR. www.indiandentalacademy.com
  13. 13. Clinical considerations • If the anterior teeth are markedly flared, the vertical force may be anterior to the center of resistance, and too much moment will be produced in the anterior segment. Clinically, one might observe little space closure and large amount of intrusion. The solution is to reduce the anterior( alpha) moment by reducing the angulation in the anterior part of spring. www.indiandentalacademy.com
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  15. 15. • On the other hand, the vertical force posterior to the center of resistance at the beginning of treatment, particularly if the anterior segment is inclined lingually. This problem becomes more pronounced after partial space is closure; as space is closed. • After 3mm closure, a full 6mm reactivation with about 60g of intrusion will reduces the moment on the anterior segment about 10%- a relatively small effect. www.indiandentalacademy.com
  16. 16. • If they left in place too long, they can cause intrusion of the anterior segment, undue tipping of the anterior teeth, and radical tipback with steepening of the occlusal plane of the posterior teeth. • During en masse tipping of the anterior segment, the center of resistance moves anterior to the vertical force. www.indiandentalacademy.com
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  18. 18. • There are a number of possible solutions to the problem of the vertical force posterior to the center of resistance. • We currently prefer to reduced the differential between the anterior and posterior moment would be to use a symmetrical T-loop with equal and opposite couples. • Still another possibility is to use the normal retraction spring, but the point moved anteriorly to the center of resistance. This can be done by soldering a vertical tube to an anterior stainless steel. www.indiandentalacademy.com
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  20. 20. • The appropriate sequence might be for en masse retraction: 1) Approximately 3mm of en masse tipping around the apices of the incisors. 2) En masse root movement, with the center of rotation around the incisor bracket. 3) Continued en masse tipping around the roots of the incisors, until space completed. www.indiandentalacademy.com
  21. 21. Conclusion • The vertical forces that result from differential moments between the anterior and posterior segments can influence the amount of tipping of the anterior teeth during space closure, and these vertical forces vary from case to case. www.indiandentalacademy.com
  22. 22. www.indiandentalacademy.com Thank you For more details please visit www.indiandentalacademy.com

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