Angle of wire entry in orthodontic treatment

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Angle of wire entry in orthodontic treatment

  1. 1. Angle of Wire Entry Implications in orthodontic treatmment
  2. 2. A textbook reference
  3. 3. The farther the point of force application is from the center of resistance the greater the moment (rotational tendency) that is produced.
  4. 4. Couple • Two forces that are equal, parallel, and non-collinear • Translational effects cancel each other out and pure rotational forces remain
  5. 5. Couple •The moments are in the same direction and are additive
  6. 6. Rotation caused by a couple • Center of resistance and center of rotation are the same
  7. 7. Commonly seen couple • Wire contacts 2 of the 4 corners of the slot • A couple can produce a….
  8. 8. Moment of a couple
  9. 9. “Moment of a Couple” • Rotation resulting from the moment of the couple is responsible for many tooth movements • This rotation can affect one tooth or a group of teeth
  10. 10. Tom, age 13
  11. 11. Or Blake, age 13
  12. 12. Angle of Entry
  13. 13. Angle of entry can be affected by: • Tip in the bracket (angle of bracket slot) • Tipped teeth due to malocclusion • Bend in the wire • Combination of all three
  14. 14. Appliance Prescription-Tip
  15. 15. Concepts to remember • Greatest angle of entry produces greatest moment of couple • The canine bracket, especially on the upper, has the most tip built in. Therefore, greatest angle of entry is most often at the canine bracket. • Large variations in canine position are often present pretreatment. This can also result in large angle of entry changes
  16. 16. Assume a fully bracketed maxillary arch What effect does a straight wire have on the incisors in each of these illustrations? Remember Dr Prittinen’s angle of entry concept R R L L
  17. 17. R R L L The incisors intrude. The incisors extrude.
  18. 18. Assume a fully bracketed maxillary arch What effect does a straight wire have on the incisors in each of these illustrations? Remember Dr Prittinen’s angle of entry concept R R L L
  19. 19. R L The incisors will cant running downhill right to left. R L The incisors will cant running downhill left to right.
  20. 20. Normally positioned canine
  21. 21. Distally tipped canine
  22. 22. What happens? • Combining the distal tipping of the tooth with the tip built into the bracket produces a VERY LARGE angle of wire entry.
  23. 23. Implications • Extrusive force on the anteriors (expressed due to small root surface area) • Intrusive force on posteriors (not expressed due to large root surface area, and because posterior intrusion is tough to do)
  24. 24. Net effect • Bite deepens and becomes very difficult to open • Intrusive and extrusive forces produced as a result of the moment of the couple results in tendencies for some teeth to flare and some to roll in lingually
  25. 25. Intrusive/Extrusive force results • Vertical forces – Extrusive forces create the potential for LINGUAL crown tipping – Intrusive forces create the potential for BUCCAL (or LABIAL) crown tipping
  26. 26. Axial inclination of canines. Look at this example
  27. 27. Archwire at rest
  28. 28. Engaging wire produces these forces
  29. 29. Moment of couple on canine (greatest angle of wire entry) • Creates extrusive force on the incisors • Intrusive force on the molars • Distally inclined cuspid crowns present a big mechanical problem
  30. 30. Distally inclined canine crowns
  31. 31. Distally inclined canine crowns
  32. 32. Another solution • When angle of entry will be a problem, start the case by not bracketing the 4 anterior teeth – 6543-----3456 are bracketed • The angle of entry can’t affect anterior teeth if they are not engaged • Align the canines (this will take 3-4 months) then after canine angulation is more ideal, bracket and engage the anteriors.
  33. 33. What do you expect to happen here?
  34. 34. Does angle of entry make bite easier or more difficult to open?
  35. 35. How can this be controlled? • Brackets could be positioned to negate these effects if desired. • Horizontal, as well as vertical position of slot could be altered.
  36. 36. Effect of vertical forces • Remember the moment • Extrusive forces result in lingual crown movement • Intrusive forces result in facial (or buccal) crown movement
  37. 37. Another example Q#1. Does the greatest angle of entry encourage an intrusive or extrusive force on the upper anteriors? Q#2 Would you expect flaring or de-torquing of those upper anteriors?
  38. 38. Another example Q#1. Does the greatest angle of entry encourage an intrusive or extrusive force on the upper anteriors? (Intrusive) Q#2 Would you expect flaring or de-torquing of those upper anteriors? (Flaring due to moment of the intrusive force)
  39. 39. 3 months later • Is what happened to the upper anteriors predictable?
  40. 40. Yes!
  41. 41. Melanie, Age 28
  42. 42. Initial arch wires after 2 mo (l) and 3 mo (r)
  43. 43. To summarize… • The extrusive force imparted to the incisors because of the moment (rotational tendency) of the couple (angle of entry on the canine bracket) results in lingual crown movement.
  44. 44. If distally positioned canine crowns result in bite deepening… What happens with mesially inclined canine crowns?
  45. 45. Mesially inclined canine crowns
  46. 46. Mesially inclined canine crowns
  47. 47. Would this case make you nervous?
  48. 48. • Open bite tendency with mesially tipped canine crowns • This bite may open excessively
  49. 49. Management • Encourage mesial root movement of cuspid with mesio-gingival slot angulation • Discourage bite opening by gingival bracket placement in anteriors (Question: Did I do this?)
  50. 50. Would this case make you nervous?
  51. 51. • Open bite tendency with mesially tipped canine crowns • Again, the bite could open excessively without modifications to bracket positioning
  52. 52. Summary • Positioning the slot to attain proper root angulation may increase the already large angle of entry • If the greatest angle of entry is working against you, change the inciso-gingival and/or mesio-distal position to offset the angle of entry effect, or consider modifications to initial bracketing protocol
  53. 53. Summary, continued • Use bite opening or bite closing techniques after root alignment or • If you expect angle of entry side effects to be severe, do not bracket anteriors until after canines are uprighted, or use spring system as previously described
  54. 54. Bracketing Concept • In the 1960’s, the best orthodontics was done by the best wire benders. Today, the best orthodontics is done by the best bracket positioners. • Vertical control by bracket positioning….
  55. 55. Anteriors; inciso-gingival placement • Deep bite patients – Position brackets 1 to 2 mm incisal to the center of the tooth • Open bite patients – Position brackets 1 to 2 mm gingival to the center of the tooth
  56. 56. Deep bite Normal bite Open bite
  57. 57. Premolars- inciso-gingival placement • Deep bite cases – Position brackets 1 to 2 mm gingival to the center of the tooth • Open bite cases – Position brackets 1 to 2 mm occlusal to the center of the tooth
  58. 58. Deep bite Open bite
  59. 59. Concept • Step 1-Identify greatest angle of entry • Step 2-Vertically position brackets to compensate for this, if necessary
  60. 60. Rule • If I want the root to move to the distal, angle the slot disto-gingivally. • If I want the root to move toward the mesial, angle the slot mesio-gingivally.
  61. 61. Hands-on demo • Step 1- Outline 2nd bicuspid and “move” it (this represents pre-treatment position) • We now want root to move to distal, and crown to mesial.
  62. 62. Another example
  63. 63. Bone Anatomy • Thick cortical plate around canines make them the slowest moving teeth • Angle of entry is most critical here • Tip: palpate canine eminence to determine difficulty of movement
  64. 64. Bracket position modifications to this case?
  65. 65. Management • Encourage mesial root movement of cuspid with mesio-gingival slot angulation • Discourage bite opening by gingival bracket placement in anteriors
  66. 66. Mallory, age 12
  67. 67. Questions • What will happen during initial leveling and aligning? • What 2 things could you do to prevent this?
  68. 68. If angle of entry issues are not recognized, excessive bite opening will occur. To prevent this from happening, do not bracket the canines at the initial appointment. Also, compensate for bite opening by placing the anterior brackets gingivally.
  69. 69. Month 2
  70. 70. Evaluation • Ben has a tougher initial level and align • But angle of entry makes bite opening more difficult in Cory
  71. 71. After 6 months of treatment
  72. 72. Angle of entry Case examples
  73. 73. Indiscriminate leveling and aligning will cause occlusal plane canting. To prevent this, do not place brackets on the upper incisors until after the canines are uprighted.
  74. 74. Chris, Age 14
  75. 75. Nicole, Age 15
  76. 76. Chris Nicole
  77. 77. Chris • Excessive mesial inclination of canines could lead to excessive bite opening.
  78. 78. 1st month of treatment-Chris
  79. 79. 2nd month of treatment- Chris
  80. 80. Questions • Is this the expected treatment response? • Could anything have been done to prevent this? Explain.
  81. 81. Questions • Is this the expected treatment response? • Could anything have been done to prevent this? Explain. • This is the expected response. Bracket positioning and bracketing scheme should have been altered to compensate for angle of entry issues.
  82. 82. Nicole- Month 1
  83. 83. Nicole-Month 2
  84. 84. Nicole: initial aligning complete
  85. 85. Chris: initial aligning complete
  86. 86. Chris Nicole

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