Straight wire – history, evolution and concepts /certified fixed orthodontic courses by Indian dental academy


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Straight wire – history, evolution and concepts /certified fixed orthodontic courses by Indian dental academy

  2. 2. Contents • • • • • • • • • • • • • Introduction Eras in orthodontics Early development of brackets and archwires Edgewise appliance- advantages & disadvantages Straight Wire Concept First order bend Second order bend Third order bend Keys of occlusion Deficiencies of conventional edgewise appliance Andrews fully programmed appliance Critical look at SWA Conclusion
  3. 3. Science divides itself most broadly into two categories: 1. Pure or theoretical science 2. Applied or technological science  In orthodontics, evolution of bracket design occurred precisely as a result of experience and practical intuition.
  4. 4.  With the introduction of Edgewise appliance by EH Angle in 1928, the orthodontic scenario was dominated by same appliance.  The course of appliance development after Angles Era can be divided into 1. Tweed era 2. Post Tweed era 3. Pre-adjusted era
  5. 5. Angle’s Era    E-arch which is the first appliance described by Angle in early 1900, was capable of tipping tooth crowns into proper alignment. Thereafter, developed the pin and tube appliance in 1910, by which the tooth roots could be brought into proper axial relationships. The next step in the evolutionary process was the development of the ribbon arch appliance in 1915.
  7. 7.  Chief advantage of the ribbon arch appliance was the fact that rotations were easily accomplished.  It is also offered of buccolingual and incisogingival movements. Gingivo-incisal and gingivo occlusal movements are also possible.
  8. 8.  In edgewise appliance the original buccal tube was a piece of 0.22X 0.028” gold or nickel silver tubing soldered to the molar band.
  9. 9.  The Edge wise appliance was introduced to the dental profession in 1925.  The Edgewise arch mechanism was designed to allow the orthodontist to place the teeth in to Angle’s concept of “Line of occlusion”.  The original bracket was designed with slot 0.022 by 0.028 inch.
  10. 10. Tweed Era   1. 2. 3. 4. Re introduced extraction of premolars Set four objectives of treatment: The best balance and harmony of facial lines, Stability of denture after treatment, Healthy oral tissues, Efficient chewing mechanisms.
  11. 11.  Introduced cephalometric diagnostic triangle  Classified growth trends  Introduced concept of anchorage preparation  Championed the benefits of the preorthodontic guidance program
  12. 12.  After demise of Tweed, his philosophy in a modified way was propagated by Merrifield.  Robert Strang  Cecil Steiner
  13. 13. Post Tweed Era    This era was dominated by Robert Ricketts, Joseph Jarabak and Charles Burstone. Evolution of Begg’s technique Bio-progressive therapy of Ricketts aims at unlocking the mandible. Used twin 0.018” brackets and 16* 16 elgiloy wires.
  14. 14.  Light wire Edgewise appliance developed by Jarabak. Developed .018 slot bracket with vertical slot.  Burstone introduced the concept of variable modulus orthodontics and development of TMA wires.  Others in this era- Holdaway, Schudy, Thurow, Stoner and Linquist.
  15. 15. Pre-adjusted Era   The idea of building treatment into the bracket, thus delegating some of the functions of the archwire to the brackets, reducing wire bending, was not new. Angle himself had proposed angulating the brackets, which was pursued later by Holdway and Jarabak for eliminating the second order bends.
  16. 16.  Similarly torquing the bracket slots for reducing or eliminating the third order bends was attempted by Ivan Lee and Jarabak.  Lawrence Andrews deserves kudos for integrating all the three (in-out, tip and torque) adjustments in the bracket design.
  17. 17. Early development of brackets and arch wire    Angle called Edge wise appliance- “the latest and best”. Steiner also thinking in same vein. Holdaway in 1952- placed brackets on bands so that they are centered on the strip of band material at right angles to the band, and in turn placed on teeth parallel to long axis.
  18. 18. Reason for artistic positioning bends are necessary at any time due to the malposition acquired when brackets are positioned parallel with the long axis of the tooth.  Jarabak and Fizzell – modified edgewise technique which incorporated second & third order mechanics in 1960. Called it “building treatment into the appliance”.  Lee – Series of pre torqued brackets to be used on upper and lower incisors. 
  19. 19.  Andrews - Total incorporation of in-out, tip & torque into bracket- “Straight Wire Appliance”.  Roth - stressed mandible should gnathologic centric relation. be in
  20. 20. Edge wise Appliance Advantages    The ability to obtain tooth movements in all 3 planes of space with a single arch wire. The philosophy of treating to an ideal arch or the angle’s concept of the line of occlusion. The use of rectangular or square edge wise arches which, if properly used; control arch widths, arch form, buccolingual crown inclinations, axial root inclinations, and incisor crown and torque.
  21. 21. Disadvantages       Operator skill is require. Bends incorporated in the arch wire should be accurate to get proper finishing of the case. Heavy forces generated: Causes pain discomfort to the patients, damage to tooth roots Anchorage control and extra oral anchorage More chair side time. Tipping of tooth crown is impossible with rectangular wires. Anterior movement of dental arches
  22. 22. Straight Wire Concept    Emphasize the term “concept” Concept- more consistent, more ideal result obtained with less physical and mental drain on the operator, less patient discomfort and less overall treatment time. SWA concept- eliminate bends (I, II & III order) by incorporating features into bracket.
  23. 23.  First order bends : 1. In-out bends 2. Bucco-lingual / Labio-lingual 3.  Rotational movements Second order bends: 1. Tip bends 2.  Mesio-distal movements Third order bends 1. Torque
  24. 24. First order bends  Purpose: To contour the arch wire to the buccal surface of teeth, which vary in their labio-lingual thickness and do not conform to an arch
  25. 25.  Amount & use depends on Clinician  May be for leveling or finishing  In severe malposition additional bends needed
  26. 26. Second order bends    Bends in the occlusogingival direction to maintain the final angulations of teeth. In incisal area- artistic bends provide ideal angulations to these teeth. Posterior teeth- maintain distal tipping of premolars and molars.
  27. 27. Third order bends  Torsional bends along the long axis of the rectangular archwire Factors influencing torque requirements Initial position of incisors  Type of mechanics  Size of archwire
  28. 28. Andrews’ Straight Wire Appliance  Story of what a motivated person could achieve with determination and perseverance.  After graduation in 1959, Laurence Andrews looking for a topic to write thesis that was required for certification by the ABO.  Theme - prevalent quality of American practice with respect to static occlusion.  Concluded – existing criteria for measuring the quality of finishing were ill
  29. 29. A study of excellent normal occlusion and of the state of the Orthodontic art- considered a good thesis subject.
  30. 30. Research categorized into   Five studies Three stages
  31. 31.  First stage- The early, impressionistic examination of completed cases display at meetings.  Second stage- The collecting of cast was supplemented by head films & extra-oral photographs over a period of 4 years.  Gathering of casts of naturally good- to excellent occlusion.
  32. 32.  As on 1988, 120 best of total sample was reexamined. Features: 1. Never subjected to orthodontic treatment. 2. Well aligned and pleasing in appearance 3. Have excellent occlusion 4. Would not benefit from orthodontic treatment  Six significant characteristics were found.
  33. 33. Special value of Six Keys to optimal occlusion    They are complete set of indicators for optimal occlusion. Can be judged from facial and occlusal surfaces of the crowns. Can be judged from tangible landmarks.
  34. 34.    Uniqueness of Andrews’ study - the tooth positions were referenced from clinically visible teeth crowns. The most important of the referents was the facial axis of clinical crown or F.A.C.C. all the teeth other than the molars- it is the most prominent ridge on the crown’s face The molars -dominant groove on the crown’s face.
  35. 35. When all the teeth are correctly positioned, the plane joining the F.A. points of all the teeth is named as Andrews’ plane.
  36. 36. Key I  Consists of 7 parts:
  37. 37. Key II Crown angulation – each tooth type have similar amount of angulation.
  38. 38. Positive FACC angulation for each tooth type
  39. 39. Key III Crown inclination- Maxillary incisors have positive inclination, mandibular incisors have a slight negative inclination. + - Occlusal plane 90°
  40. 40. +7° Occlusal plane 174° -1° INTERINCISAL ANGLE IS LESS THAN 1800
  41. 41. Key IV  Absence of rotations
  42. 42. Key V Contact points should abut unless a discrepancy exists in mesio-distal crown diameter.
  43. 43. Key VI CURVE OF SPEE    Flat to slightly concave. Flat – Receptive of normal occlusion Reverse curve of spee- Excessive room for upper teeth
  44. 44. Additional keys     Key VII: Intercuspal position: Intercuspal position and retruded jaw relation should be coincident. Key VIII: Anterior guidance: In mandibular protrusion, opening should be guided by the incisors. There should be disocclusion of all other teeth Key IX: Canine guidance: Lateral movements of the mandible should guided by the working side canines. There should be disocclusion of all other teeth on both working and non working sides. Key X: Cusp embrasure contact: The intercuspal position, this should be even throughout both buccal segments.
  45. 45. Third stage  Methodical examination of treated cases shown by skilled orthodontists.  1150 models studied from 1965-1971  Nature’s best Vs Orthodontist’s best  Lack of any keys predictive of other inadequacies.
  46. 46. Fourth study- lead to development of Fully programmed appliance Fifth study- occlusal characteristics of the post treatment dental casts displayed at the meeting of societies, were compared with those of untreated optimal sample.
  47. 47. Shortcomings of Edgewise appliance Andrews concluded: 1. Variability in wire bending from operator to operator and even with the same operator. 2. Deficiencies in the standard edgewise bracket design. 3. Variations in the bracket siting procedures.
  48. 48. Andrews’ study on Non- Orthodontic normal occlusion Development of appliance Conclusions of this study:  Most individuals have normal teeth regardless of whether they have normal occlusion or malocclusion.
  49. 49.  Each normal tooth type is similar in shape from one individual to another.  All the teeth in any individual’s mouth are proportionate, may vary in size from person to person -large, medium or small.
  50. 50.  The size of normal crowns within a dentition has no effect on the relative prominence of their facial surfaces, or the curvatures - both vertical and horizontal.  When the upper and lower jaws are proportionate and properly related, it is always possible for the teeth to be brought in optimal occlusion.
  51. 51. WHY “STRAIGHT WIRE” ?    The term straight wire in the present context refers to an archwire that is given the arch form -and often the curvature to open the bite- but which is free from the first, second or third order bends. It is a ‘formed’ but ‘unbent’ archwire. Transferring most of the tooth guidance functions from the archwires to the brackets -by modifying the bracket design.
  52. 52. BASED ON FOLLOWING REASONS:  Primary bends in an archwire are needed, it is difficult to make these bends precisely for effecting the exact amount of tooth movement. Hence, if precise tooth guidance is built in the brackets instead of depending on the wire bends, more consistent results could be obtained.
  53. 53.  Secondary bends are required for compensating for faulty placement of the brackets or the deficiencies in the bracket design.  Needed in all the successive archwires and in almost all the patients. For example, by having built-in torque in the brackets itself to remedy the above mentioned situation.
  54. 54.  The bends placed in the successive archwires are likely to vary.  The results from such differing bends are unpredictable and often lead to undesired tooth movements.  Additional secondary wire bends will be required for overcoming them.
  55. 55.  Some of the bends influence the actions of other bends e.g. torque in the anterior section of the archwire negates the tip by a ratio of 1:4 (wagon wheel effect). Accurate wire bending to negate such ill effects is extremely difficult but provision could be made in the bracket design to overcome them to a large extent.
  56. 56.   DEFICIENCIES IN CONVENTIONAL EDGEWISE Bracket baseAPPLIANCEthe faciois perpendicular to lingual axis, and the slot is cut parallel to the facio-lingual axis. may result in functional interferences. Bracket bases are not contoured occlusivegingivally, they can rock on the curved crown facial surfaces, which further affects the slot inclination and occluso-gingival positions.
  57. 57.  Similarly, lack of mesio-distal base contour could lead to rocking of the brackets, which will affect the rotational control.  Brackets are not angulated, second order bends in the arch wire become necessary. Angulating the brackets themselves does not solve the problem because of rocking potential of the bracket base.
  58. 58.  Stems of equal prominence necessitate the first order bends such as the bends required between the upper central and lateral incisors.  Similarly, because the molar tubes or brackets have no offset built-in, first order bends become necessary mesial to the molars.
  59. 59. ANDREWS’ FULLY PROGRAMMED BRACKETS  Every tooth type had a specifically designed bracket, which had precisely built- in angulation and inclination to eliminate the second and third order bends.  The magnitude of angulations and inclinations for different teeth (‘prescription’ values in degrees) were derived from his study of normal occlusion.
  60. 60.  The slots were cut at an angle to the vertical edges for attaining the built-in angulation in the bracket.  This obviated the need to rotate the brackets for angulating them.
  61. 61.  The torque was built in the bracket bases and not in the face of the bracket. This made it possible to make the midtransverse planes of each crown and bracket stem and slot coincide.  Also to align the midtransverse planes of all the crowns and bracket slots so that they coincided with Andrews’ plane when the teeth were correctly positioned.
  62. 62.  The thickness of the brackets stem was varied according to the facial prominence of each tooth, thus eliminating the need for the first order bends.  The bracket bases were made such that the slot in every bracket was perpendicular to the mid sagittal plane of the crown.
  63. 63.  This necessitated a built-in offset in the maxillary molar tubes or brackets.  The bracket bases were contoured both occluso-gingivally and mesio-distally, (compound contouring) according to the facial surface anatomy of each tooth type to eliminate rocking of the brackets on the teeth.
  64. 64.  It was possible to use flat unbent archwires in the appliance through most part of the treatment.  The treatment could be started with small diameter wires, which would flex in the brackets on malposition teeth. The resilient wires, while regaining their original shape and form, would correct the malpositions to some extent.
  65. 65.  As one gradually moves to bigger diameter archwires, they would progressively align the teeth till a full size ‘straight’ archwire could passively fit in all the brackets.  Two types of bracket configuration were originally made available.
  66. 66.  The vertical edges were always parallel to the FACC, while the horizontal edges were perpendicular to the vertical edges in the square type brackets and at a different angle in the rhomboid shaped - or so called ‘diamond’ - brackets.  The latter type bracket became more popular since the horizontal edges could be well aligned with the incisal edges.
  67. 67. Convenience features meant for increasing the ease of the operator.  Markings on the brackets to identify them, and gingival tie wings on the posterior teeth extended laterally for ease of ligation were added to the brackets.  The facial aspects of the incisor and canine brackets being curved and parallel to the crown’s facial surface so as to reduce irritation to the lips.
  68. 68.  Auxiliary features such as power arms, hooks, face bow tubes, tubes for utility arches and rotation arms were also added.
  69. 69.  Andrews’ emphasized accurate placement of brackets, as a integral part of SWA.  Bracket siting procedure aimed at targeting the slot within 2° and 0.5mm of precise placement over the slot site.  Anyone with average skill could draw with a pencil FACC and mark mid points.
  70. 70. FACC  Importance of bracket positioning. – Torque required at gingival 1/3rd varies by 540o from that required at the occlusal 1/3rd.  Facial Axis of Clinical Crown – FACC – Easy to visualize and mark – The centre of this line was the FA point
  71. 71. FACC
  72. 72. TYPE OF BRACKETS Standard brackets Extraction series brackets or translation brackets •Minimum •Medium •Maximum Incisor brackets •A •S •C
  73. 73. Standard Brackets  Non extraction cases  Same values of built in features as normals  One bracket for each tooth, except max. molars  Max molars – 2 types of brackets – – Class I molars – Class II molars
  74. 74. Types of Brackets Tooth Maxillary Mandibul ar II molar I Molar II PM 2/-35 2/-35 Canine 2/-7 2/-7 11/-7 2/-22 5/-9 5/-9 (10o offset) (10o offset) I PM 2/-17 5/-11 Tooth II Molar I Molar Maxillary 0/-9 0/-9 Mandibular - - (Tip / Torque)
  75. 75. Types of Brackets Incisor brackets Tooth Central Lateral Maxillary 5 9 Mandibular 2 2
  76. 76. Translation brackets  Solutions → – Long lever arm – Over correction in the bracket  Anti-tip  Anti-rotation  Anti-buccolingual tip
  77. 77. Translation brackets  3 sets of brackets – Minimum – upto 2 mm of translation – Medium – 3mm to 4mm of translation – Maximum – 5mm or more
  78. 78. Translation brackets Counter tip Counter rotation Counter buccoling. tip Minimum 2 2 -4 Medium 3 4 -5 Maximum 4 6 -6
  79. 79. Appliance for different clinical situation    Standard brackets- for non- extraction cases, with an ANB differential of less than 5°. One standard bracket for every tooth except incisors and molars. Differing features built-in inclination for incisors and angulation and offset for molars.
  80. 80. Upper and lower incisor inclination for different skeletal types CLASS I Skeletal type Upper central incisors Upper lateral incisors Lower incisors II III 7 2 12 3 -2 8 -1 4 -6
  81. 81. Translation series: Brackets for extraction cases  As teeth are translated, they tend to tip mesiodistally and rotate into the extraction cases, since the forces acts at the brackets away from center of resistance, both in occlusal and lateral perspectives.  Depending on amount of translation required, the built-in angulation for canines and premolars was varied.  Teeth undergoing distal or mesial translation, 2,3 & 4°± from corresponding standard brackets 
  82. 82. 2° 2° 2° 2° 11° 5° 9° 2° 2° 5°
  83. 83. 3° 7° -1° -1°
  84. 84. -9° -35° -30° -22° -17° -11° -1°
  85. 85. Critical look at SWA Main: overlooks biologic variation in the anatomy of teeth of different individuals. Dellinger,Vardiman and Lamberts, Germane et.alused an optical comparator.  Data should have been collected from individuals with malocclusion.  The variation in the curvature of facial surfaces affect the torque values.
  86. 86.  Torque is the target!!!  Buccal inclinations of the teeth must be very close to the mean for the SWA to torque teeth correctly.  Method of calculating torque –
  87. 87. Criticism of the SWA  Andrews’ method of studying inclination of the buccal surfaces -
  88. 88.  Dellinger – Optical comparator – measurement to the nearest second.
  89. 89. Vardimon and Lambertz – Torque angle gauge.
  90. 90. Germane et al – radiographs magnified 10x
  91. 91.  Large variations of the inclination of buccal surface – large standard deviations and high range– – Dellinger – positioner setups – Vardimon and Lambertz – treated and untreated cases and postioner setups – Germane et al – 600 extracted teeth
  92. 92. Other factors – Collum angle – angle b/w crown and root. Not 0 in most teeth and large SD.
  93. 93.  Dellinger – – HOP – molar midpoints to mean of incisor midpoints
  94. 94.  Variation in HOP and relation with FA points in case of shallow and deep bites – – Andrews should have used malocclusion cases rather than untreated patients.  Variation of relation of FA point to contact points
  95. 95.  Large amount of play b/w archwire and slot
  96. 96.  The success of the SWA is not because of what it can do and the control it can achieve – but because of what it does not do, in terms of torque, and its lack of control. Otherwise  “The results would be erratic, inconsistent, and clinically unacceptable.”
  97. 97.  A great step forward for orthodontics  But wire bends will be needed for most patients  Especially 3rd order.  Differences in Skeletal Pattern must be kept in mind – SWA used with caution.
  98. 98.    The straight wire concept is just that- it’s a concept, not a dogmatic step-by-step treatment procedure. It is amenable to most treatment philosophies. This appliance laid a platform for the development of pre- adjusted appliance, which provides control of tooth in all three dimensions. This was the first generation of PEA, which was followed by Roth and MBT.
  99. 99. With the ingenuity supplied man by his Omnipotent Creator, all things are possible. If we are to survive as a specialty, we must use our every resource to continue to supply our patients with the very finest orthodontic care within our capabilities.
  100. 100.         Andrews. Straight wire appliance 2nd edition Andrews. AJO 1972 Roth. JCO 1976 Roth. JCO 1987 McLaughlin and bennet. JCO 1990 Creekmore. AJO 1993 Magness. AJO 1978 Schwaniger AJO 1978