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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
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