Friction mechanics /certified fixed orthodontic courses by Indian dental academy


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Friction mechanics /certified fixed orthodontic courses by Indian dental academy

  2. 2. INDIAN DENTAL ACADEMY Leader in continuing dental education
  3. 3. FRICTION  It is a function of relative roughness of two surfaces in contact.  Force that resists movement of one surface past another and acts in direction opposite the direction of movement.
  4. 4. CLASSIFICATION OF RETRACTION MECHANICS A] Based on wire configuration Continuous arch mechanics Segmented arch mechanics B] Based on friction Friction mechanics Frictionless mechanics
  5. 5. C] Based on type of tooth movement Tipping followed by uprighting Translation Based on mode of retraction Cuspid retraction En masse retraction Based on Anchorage Type A – Maximum Anchorage Type B – Moderate Anchorage Type C – Minimum Anchorage
  6. 6. INTRODUCTION Two schools of thought of Retraction Mechanics 1.Seperate canine and incisor retraction 2.En masse retraction
  7. 7. Seperate canine and incisor retraction
  8. 8. En masse Retraction
  9. 9. Sliding Mechanics Separate Canine Retraction Frictionless Mechanics En masse Space closure
  10. 10. BIOMECHANICS OF SLIDING MECHANICS  Friction plays an important role in sliding space closure, hence the term ‘Friction mechanics’.
  11. 11.  E-link is the force component of the retraction assembly and moment is produced by the Archwire-bracket assembly
  12. 12.  One moment rotates the tooth mesial out and other causes the distal tipping of the crown.
  13. 13. The distal tipping contributes to the retraction by causing binding of the arch wire, which in turn produces moment that results in distal root movement. WALKING MOVEMENT OF THE CANINE
  15. 15.  As the tooth uprights, the moment decreases until the wire no longer binds.  The crown then slides along the archwire again distal crown tipping again causes binding.  This process is repeated until the tooth is retracted or the elastic force is dissipated.
  16. 16. MOMENT TO FORCE RATIO DURING RETRACTION  The moment to force ratio is at its lowest during the first few days after placement of E- chain because the magnitude of force is at highest level.  As the teeth are retracted the moment to force ratio improves because the elastic force dissipates and the archwire bracket interaction due to crown tipping produces a moment.
  17. 17.  To optimize the use of sliding mechanics, sufficient time must be allowed for the distal rot movement to occur.  A common mistake is to change the elastic chain too often, thus maintaining the high force levels and moment to force ratio that produces distal tipping only.
  18. 18. ADVANTAGES OF FRICTION MECHANICS 1. Complicated wire configuration is not required 2. Initial wire consuming. 3. Enhances patient comfort. placement is less time
  19. 19. DISADVANTAGES OF FRICTION MECHANICS  Higher force levels.  Tendency to over activate elastic and spring forces.
  20. 20. STEPS BEFORE RETRACTION 1. 2. 3. 4. 5. Selection of the best bracket system Proper bracket placement Proper alignment of the teeth Anchorage control Retraction control
  21. 21. CANINE RETRACTION  Major cuspid retraction consists of controlled tipping or translation of the canine when more than 3mm of arch length per side is required.  Minor cuspid retraction consists of uncontrolled tipping of the canine when 1-2 mm of arch length per side is required.
  22. 22.  It can be carried out with the help of lacebacks.
  23. 23. Minor cuspid retraction with lacebacks
  24. 24.  As the canine is retracted the anterior crowing unravels. The lateral incisors tend to move distally due to the pull of transeptal fibres.
  25. 25. CANINE RETRACTION WITH ‘J’ HOOK HEADGEAR  It involves extraoral anchorage so effective in maximum anchorage cases  Involves use of headgear with a J hook applying the force on the canine such that they slide along the archwire.
  26. 26. EN MASSE SPACE CLOSURE WITH SLIDING MECHANICS  In 1990s, a method of controlled space closure was described using sliding mechanics.  The MBT technique recommends following
  27. 27. ARCHWIRES  Rectangular .019/.025 steel wires with the . 022” slot.  This wire size has good overbite control while allowing free sliding through the buccal segment
  29. 29. Clinical example of Roller Costar Effect
  30. 30. SOLDERED HOOKS  0.7 brass hooks are preferred.  Soft SS 0.6 soldered hooks can be a useful alternative.  The most common hook positions are 3638mm in Upper and 26mm in the Lower.
  32. 32. ACTIVE TIEBACKS USING ELASTOMERIC MODULES  Placement is not difficult.  Active tiebacks using elastomeric modules are preferred for space closure.
  33. 33. Active tiebacks Passive tiebacks
  35. 35. ACTIVE TIEBACKS   1. 2. 3. 4. ADVANTAGES Convenient means of force application DISADVANTAGES Variation of efficiency of force delivery High initial force levels Degradation of force levels over a period of time Tendency to absorb moisture and accumulate food debris and bacteria
  36. 36. NiTi COIL SPRINGS  1. 2.  ADVANTAGES Efficient and relatively quick to close extraction space owing to their continuous force No frequent activation required DISADVANTAGES Expensive
  37. 37. FORCE LEVELS  Active tiebacks are stretched their original size during activation.  Without pre-stretching the force levels range in between 200-300 gms.  If large spaces are to be closed NiTi coil spring are used instead of Elastomeric module.
  38. 38. INHIBITORS OF SLIDING MECHANICS  Inadequate leveling  When torque is being manifested in the posterior segment  The ligature wire around the molar tube can block the distal end of the wire
  39. 39. INHIBITORS OF SLIDING MECHANICS  Any damage or compressed bracket binds with the archwire and prevents sliding.  Soft tissue resistance due to its overgrowth in extraction spaces.
  40. 40. PHYSICAL FACTORS 1. ARCH WIRE  Material  Cross sectional shape and size  Surface texture  Stiffness 2. LIGATION OF ARCHWIRE TO BRACKET  Ligature wires  Elastomerics  Method of ligation
  41. 41. PHYSICAL FACTORS 3. BRACKET  Material  Manufacturing process (cast or sintered SS)  Slot width & depth  Design of the bracket – Single / Double width  1st order ( in-out), 2nd order (angulations), 3 rd order (inclinations) specifications.
  42. 42. PHYSICAL FACTORS 4. ORTHODONTIC APPLIANCE  Inter-bracket distance  Force levels  Level of bracket slot between adjacent teeth
  43. 43. BIOLOGICAL FACTORS    Saliva Plaque Corrosion
  44. 44. Leader in continuing dental education