Mechanics of tooth movement /certified fixed orthodontic courses by Indian dental academy


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Mechanics of tooth movement /certified fixed orthodontic courses by Indian dental academy

  1. 1. Mechanics of tooth movement INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. Scalers &vectors • Force (F=MA)_force is that which changes or tends to change the state of rest of a body or of uniform motion along a st line Force acts in three dimensions of space
  3. 3. Resultants of orthodontic force Forces with common point of application
  4. 4. Forces with different points of application Law of transmissibility of forces =external effect of force on a rigid body may be considered to have a point of application anywhere along its line of action
  5. 5. Resolving a force in to components
  6. 6. Force & movement • Center of gravity ~A point on which a free body can be perfectly balanced (C of mass) • Center of resistance~A point through which the line of action of force passes, producing translation
  7. 7. Determinants of center of resistance • Size &shape of the crown & rootroots • periodontal attachment • level &density of alveolar bone • multirooted 1~2mm apical tofurcation • 50% of root Proffit & Nikolai • 50~33% Smith & Burstone • 25~33% Nanda
  8. 8. Types of tooth movement • Translation-pure bodily movement • Pure rotation-It indicates movement of points of the tooth along the arc of a circle with cent of resist as cent of circle • Combination
  9. 9. Translation • If the line of action of an applied force passes through the center of resistance of a tooth it responds by translation in the direction of line of action
  10. 10. Moment of a force • Moment (potential for rotation) = magnitude of force * perpendicular distance from line of action to point of resistance
  11. 11. Direction of moment (positive &negative ) Combined translation & rotation
  12. 12. Rotations / Couples Couple consists of two forces of equal magnitude , with parallel but noncolinear lines of action & opposite senses Moment of couple = magnitude of forces * dist between them
  13. 13. AntiCl wise~10*50=500 gm mm Cl wise ~30*50 =1500gm mm Net ~1500-500 =1000 gm mm Force *dist ~50*20 =1000gm mm Couple is a “free vector”
  14. 14. Recap • Force ~ physical entity applied to an . . object • Moment ~turning tendency of force (pt of . reference ) • Couple ~inherent moment not relative to . any point
  15. 15. Center of rotation • Center of rotation # a point about which a body appears to have rotated
  16. 16. Center of rotation &tooth movement
  17. 17. • Hurd & Nikoli ~Point which moves the least on the line of long axis of tooth • Hocevar ~geometric point about which no moment has occurred
  18. 18. Force system &center of rotation • Only net force translation (infinity ) • net moment only rotation (cent of resist ) • moment &force ( ? )
  19. 19. Equivalent force systems • Sums of forces in x direction are identical • Sum of forces in y direction are identical • sum of moment about any point are identical
  20. 20. Moment about any point
  21. 21. Clinical situation of canine distalization
  22. 22. Center of rotation Clockwise apical Counter clock wise incisal
  23. 23. All put together
  24. 24. M/F ratio &tooth movement 10mm Units millimeter
  25. 25. summary • Orthodontic forces are vectors • They can be combined or divided • They produce translation ,rotation ,combination • couple • center of resistance • center of rotation • M/F ratio key to controlled tooth movement • Understanding of mechanics controls one of the variable
  26. 26. Thank you For more details please visit