Copy of biomech /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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Copy of biomech /certified fixed orthodontic courses by Indian dental academy

  1. 1. Basic Biomechanics of Tooth Movement INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. Introduction Scalars and vectors Orthodontic force:   Resultants and Components Types of tooth movements Centers of rotation and resistance Equivalent systems www.indiandentalacademy.com
  3. 3. Moment of a force Moment of a couple Moment to force ratio Conclusion www.indiandentalacademy.com
  4. 4. Mechanics An area of study within physical science that is concerned with the state of rest or motions of bodies subjected to forces. Understanding of mechanics is based on particle mechanics formulated by Sir Isaac Newton www.indiandentalacademy.com
  5. 5. Newtonian Mechanics Static – body at rest and under action of forces Dynamic – moving bodies   Kinematics – study of motion itself Kinetics – relationship between the force systems and characteristics of body motion are explored www.indiandentalacademy.com
  6. 6. Newton's Laws 1st law: particle subjected to balanced system of forces will remain at rest, if originally at rest, or move with constant speed in a straight line, if originally in motion. 2nd law: particle subjected to unbalanced system of forces will accelerate in the direction of the net force 3rd law: every action has an equal and opposite reaction. www.indiandentalacademy.com
  7. 7. Reduce empiricism or trail and error Relates concepts of stress distribution in the PDL to that of bone remodeling Increase efficiency and efficacy of the appliance. www.indiandentalacademy.com
  8. 8. On a sub clinical level:    Control the centre of rotation of the tooth To maintain a desirable stress level in the pdl To maintain a relatively constant stress level On a clinical level:    The M:F ratio The load deflection rate The maximal forces or moment of any component of an appliance www.indiandentalacademy.com
  9. 9. Scalars and Vectors Scalars---- completely described by their magnitude alone. Eg. Mass, distance , temperature. Vectors---- described by magnitude and direction. Eg. Force www.indiandentalacademy.com
  10. 10. Force Is defined as an act on a body that changes or tends to change the state of rest or motion of the body. As per Newton's laws two bodies are always associated with a force i.e. one that exerts the force and the other that receives the force www.indiandentalacademy.com
  11. 11. Smith and Burstone (1984) www.indiandentalacademy.com
  12. 12. Resultants form a single point www.indiandentalacademy.com
  13. 13. Resultant form two point of application www.indiandentalacademy.com
  14. 14. R2 = a2 + b2 – 2ab www.indiandentalacademy.com
  15. 15. p q Tan theta = p/q R2 = p2 + q2 for mutually perpendicular forces R2 = p2 + q2 – 2pq (cos theta) for not perpendicular to Each other. www.indiandentalacademy.com
  16. 16. Forces in general can be    Active and reactive (Newton) Concentrated or distributed External or internal www.indiandentalacademy.com
  17. 17. Static equilibrium This states that for every appliance, not necessarily every tooth, the sum of moments and sum of forces be equal to zero, i.e. the net force should be zero, regardless of the type of appliance that is being used. www.indiandentalacademy.com
  18. 18. Intrusive force on the incisors is balanced by an extrusive force on the molars www.indiandentalacademy.com
  19. 19. www.indiandentalacademy.com
  20. 20. Types of tooth movement Pure translation Pure rotation Combination of both www.indiandentalacademy.com
  21. 21. When a tooth in the mouth move during orthodontic therapy there is no pure translation or pure rotation there is always a combination of the two. (Hurd and Nikolai) www.indiandentalacademy.com
  22. 22. terminology Centre of Mass: is that point where all the mass of a body is concentrated when the body is in space. Centre of Gravity: is the same point but when gravity is acting on the body. Centre of Resistance: is that point, through which if a force is applied will move a object bodily, or produce a pure translation. www.indiandentalacademy.com
  23. 23. Centre of resistance in tooth Depends on the root length and Depends on the height of the alveolar bone. In a tooth of paraboloid shape the centre of resistance lies at h/3 where h is the length of the root. www.indiandentalacademy.com
  24. 24. C res. Of a Single rooted tooth---on the long axis between 1/3rd and ½ of the root apical to alveolar crest. Multirooted tooth--- between the roots, 1 to 2 mm apical to the furcation. www.indiandentalacademy.com
  25. 25. www.indiandentalacademy.com
  26. 26. Effect of forces Translation: If the line of action of an applied force passes through the center of resistance of a tooth, the tooth will respond with pure bodily movement (translation) in the direction of the line of action of the applied force. www.indiandentalacademy.com
  27. 27. www.indiandentalacademy.com
  28. 28. A moment of a force is the rotational tendency of the force The moment of a force is equal to the magnitude of the force multiplied by the perpendicular distance from its line of action to the center of resistance. m = f x d (gmm) www.indiandentalacademy.com
  29. 29. (Note that there will be only a single net moment or net force on a tooth) www.indiandentalacademy.com
  30. 30. Couple :  Is a system consisting of two forces that are equal in magnitude, with parallel but non collinear lines of action and opposite senses. M = 50x10 = 500gmm Net moment = 1000gmm or M = f x (distance between the two forces) M = 50 x 20 M = 1000gmm www.indiandentalacademy.com
  31. 31. M =( f1d1) + ( f2d2) M =( -50x10 ) + ( 50 x 30) M = 1000gmm www.indiandentalacademy.com
  32. 32. www.indiandentalacademy.com
  33. 33. Center of rotation a centre of rotation can be defined as that point about which a body appears to have rotated as shown by the initial and final positions of the tooth www.indiandentalacademy.com
  34. 34. www.indiandentalacademy.com
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  36. 36. www.indiandentalacademy.com
  37. 37. Centre of rotation can also be defined as that point that has the least magnitude of moment (m = 0) or Can also be defined as the point that has moved the least during tooth movement www.indiandentalacademy.com
  38. 38. Changing centre of rotations in A ( Nilkolai and Hurd) The centre of rotation for a combined translation and rotatory movement (Hocevar) www.indiandentalacademy.com
  39. 39. Forces within cross hatched areas will produce rotation as well as translation whereas the blank areas will produce simple tipping www.indiandentalacademy.com
  40. 40. Forces in the shaded areas will produce translation And rotation at a rate that is continuously accelerating www.indiandentalacademy.com
  41. 41. Changing the positions of the centers of rotation can bring about changes in the type of tooth movement but not the extent of tooth movement www.indiandentalacademy.com
  42. 42. Equivalent systems www.indiandentalacademy.com
  43. 43. Criteria for systems to be equivalent :    (1) the sums of forces in the x direction are identical, (2) the sums of forces in the y direction are identical, (3) the sums of moments about any point are identical. Smith and Burstone(1984) www.indiandentalacademy.com
  44. 44. www.indiandentalacademy.com
  45. 45. 150gm 1200gmm What would the force system at the bracket in B be so that It would be equivalent to the system in A www.indiandentalacademy.com
  46. 46. www.indiandentalacademy.com
  47. 47. www.indiandentalacademy.com
  48. 48. Moment to Force ratio The type of tooth movement would be determined by the ratio of the moment of the couple and the force applied at the bracket. www.indiandentalacademy.com
  49. 49. What is the net moment here considering all forces to be 5 and distances to be 2 The type of movement occuring would depend on the location Of the center of rotation which is determined by the moment to force ratio (not their magnitudes) www.indiandentalacademy.com
  50. 50. 10/1 Burstone and Pryputniewicz A = uncontrolled tipping B = controlled tipping C = bodily movement D = bodily movement E = root movement F = pure rotation 7/1 0 20/1 12 or 13/1 www.indiandentalacademy.com
  51. 51. www.indiandentalacademy.com
  52. 52. F3dc > F1d F1d = F3dc F1d>f3dc F3dc >> F1d www.indiandentalacademy.com
  53. 53. www.indiandentalacademy.com
  54. 54. Statically determinate systems (one couple system)  This means that the magnitudes and the direction of the forces and moments exerted by the wire can be determined clinically once the appliance is inserted into the bracket www.indiandentalacademy.com
  55. 55. One couple system-examples Cantilever springs used to bring severely displaced teeth into the arch Auxiliary intrusion or extrusion arches Begg intrusion arch www.indiandentalacademy.com
  56. 56. www.indiandentalacademy.com
  57. 57. Statically indeterminate systems (two couple systems)   The ,magnitude of the force systems produced cannot be determined clinically but the direction can be. The force systems produced depend both on the wire geometry and the bracket angulations www.indiandentalacademy.com
  58. 58. www.indiandentalacademy.com
  59. 59. www.indiandentalacademy.com
  60. 60. Conclusion The laws of physics are fundamental, and though their application in the different hands may vary the knowledge of the fundamentals is a necessary prerequisite to achieve the desired tooth movement in the most effective and efficient manner. www.indiandentalacademy.com
  61. 61. www.indiandentalacademy.com
  62. 62. references Graber and Swain :Orhtodontics: Current principles and practice Smith and Burstone: mechanics of tooth movement, AJO 1984; 85: 295 – 300. Hocevar: understanding, planning and managing tooth movement, AJO 1981; 457 -477 Mulligan: Common sense mechanics JCO – 13; 676 – 683 1979. Hurd and Nikolai: centers for rotation of combined vertical and transverse tooth movements, AJO 1976; 70 : 551 www.indiandentalacademy.com
  63. 63. Nikolai : bioengineering analysis of orthodontic mechanics Burstone and Koening, Forces in an ideal arch. AJO; 1974: 65, 2670 – 289. Demange C: Equilibirium situations in bend force systems. AJO – DO; 1990: 98, 333 – 339 Marcotte MR: AJO: 1969, 511 – 523, 1976. www.indiandentalacademy.com
  64. 64. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com

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