Preadjusted edgewise techniques /certified fixed orthodontic courses by Indian dental academy


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Preadjusted edgewise techniques /certified fixed orthodontic courses by Indian dental academy

  1. 1. Preadjusted Edgewise Techniques INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. Contents ♦ ♦ ♦ Development and evolution of the preadjusted appliance. Design considerations - SWA by Andrews - Roth prescription - Alexander Discipline - MBT bracket system - Level anchorage system Treatment mechanics
  3. 3. ► ► ► ► ► Misconceptions and Myths about the SWA. Pitfalls of the straight wire system Future developments Conclusions References.
  4. 4. Development of the Preadjusted appliance. ► Angle (1927) suggested angulating the bracket to free the archwire from second order bends. ► Holdaway (1952) overangulated the brackets adjacent to the extraction site for second order correction. ► Jarabak (1957) incorporated slot inclination in the brackets and recommended bracket angulation. ► Stifter (1958) introduced bracket with three dimensional control. Brackets had male and female parts.The female part was attached to the tooth.The male part was altered
  5. 5. according to the various combinations of inclination, angulation and crown prominence. ► Lawrence Andrews was credited with the scientific development of the concept and mechanotherapy of the preadjusted appliance.(1971) ► The preadjusted, preangulated appliance was based on the concept that in an ideal gnathological set up for a given patient, the bracket bases would accurately fit each tooth at a predetermined point, and the bracket slots would passively accept a straight wire.
  6. 6. ► This original straight wire appliance was a Hybrid Twin Edgewise appliance with built in tip, torque and in –out values, to achieve the six keys of normal occlusion. ► Later many straight wire techniques were introduced which were modifications of Andrew`s concept of Straight wire technique.
  7. 7. Andrew`s Straight Wire Appliance ► Andrew introduced the Straight Wire Appliance in 1972, based on the measurements of 120 non orthodontic normal cases. He used the data as a basis to design the bracket system. ► These were the first generation preadjusted brackets which were developed to overcome inadequacies in the standard edgewise brackets.
  8. 8. ► When brackets were sited on a full complement of optimally positioned teeth the final archwire requires 76 primary wire bends if it is to be placed passively into the slots of the standard edgewise brackets.
  9. 9. ► Bracket design- the fully programmed appliances incorporate all the features that were sited by Andrew`s in order to enable the use of straight unbent wires. ► The original SWA brackets were designed to treat only non extraction cases with an ANB differential of less than 5 degrees. ► Extraction series brackets were developed with two additional features, countermesiodistal tip and counterrotation to allow translation of teeth as much as
  10. 10. TIP 5 9 11 2 2 5 5 2 2 TORQUE 7 3 -7 5 2 2 2 2 -7 -7 -9 -9 -1 -1 -11 -17 -22 -30 -35
  11. 11. much as possible and to offset any relapse tendency by overcorrection. ► Translation series brackets were further classified as - minimum (>2mm) - medium (2- 4mm) - maximum (>4mm) ► Andrew`s later introduced different series and sets of brackets for different combinations of extractions, ANB differentials and different anchorage needs.
  12. 12. ► He also recommended the use of three different sets of incisor brackets with varying degrees of torque. ► Increased inclination for Class III and decreased inclination for Class II in maxilla and reverse in the mandible.
  13. 13. ► Bracket placement - Accuracy in bracket placement is essential so that the built in features of the bracket system can be fully and efficiently expressed. ► Andrew`s chose the centre of the clinical crown as a horizontal reference point for consistent I and III order expression. ► The FACC is the vertical reference plane, which refers to the centre of the middle developmental lobe.
  14. 14.
  15. 15. ► Andrew`s concept of treatment involved correction of malocclusion totally by translation of teeth without being tipped. ► He believed that some amounts of relapse is normal after appliance removal and it is not possible to precisely position the teeth into occlusion before appliance removal due to bracket interference. ► In the original SWA heavy forces were continued to be used, no special anchorage control measures were
  16. 16. ► employed. Andrew`s also emphasized on the ‘wagon wheel effect’ where tip was lost as torque was added. ► Hence additional tip was added to the anterior brackets. ► Difficulties were also encountered in the treatment mechanics due to use of heavy forces and also due to increased tip in the anterior brackets. ► This consequently led to the “roller coaster effect”.
  17. 17.
  18. 18. Andrew`s philosophy
  19. 19. Roth`s appliance ► The Roth prescription was introduced in 1976. Following his early experiences with the SWA, he introduced measures to overcome day to day shortcomings which he had found in clinical use. ► Roth recommended a single appliance system, consisting primarily of minimum extraction series brackets, which he felt would allow him to manage both extraction and non extraction cases. ► This was then called the second generation of preadjusted brackets.
  20. 20. Roth prescription ► Bracket design- the bracket design was similar to Andrew`s with few modifications. - torque was increased for maxillary incisors and molars, unchanged for premolars, and decreased for the canine. - torque for the mandibular teeth were unchanged. - tip was increased for the upper and lower canines and was decreased for the incisors and premolars. - counterrotation features were incorporated in the brackets in order to prevent rotation during retraction.
  21. 21. TIP TORQUE 5 9 13 0 0 0 0 2 2 7 -1 -1 -1 -1 12 8 -2 -7 1 -1 -11 -17 -22 -30 -30 -7 -14 -14
  22. 22. TIP 5 9 11 2 2 5 5 2 2 TORQUE 7 3 -7 5 2 2 2 2 -7 -7 -9 -9 -1 -1 -11 -17 -22 -30 -35
  23. 23. ► Bracket placement – Andrew`s recommended placing wires with compensating or reverse curves during the finishing phase of treatment. Variations in the bracket placement was recommended in the Roth set up to permit placement of flat, unbent full size arch wires. ► The key in determining bracket height is the canines and premolars.( 2nd premolar in an extraction case) ► The brackets should be placed at the maximum convexity of the crown of posterior teeth.
  24. 24. ► The canine bracket is placed 1mm more incisally than the lateral incisors which are at the same level as the centrals. ► Generally, the bracket position will appear to be more incisal than the FA point of Andrew`s and this allows for vertical overcorrection of tooth positions.
  25. 25. ► Arch Form- The arch wires are relatively flat around the upper and lower incisors, curve more tightly around the cuspids and bicuspids and then curve gently towards the distal . ► The most prominent point in the front curvature of the arch is the first premolar and the most prominent and widest pint in either arch is at the mesiobuccal cusp of the first molar.
  26. 26. ► Roth`s arch form was wider than Andrew`s in order to avoid damage to the canine tips during treatment and to assist in obtaining good protrusive function.
  27. 27.
  28. 28. Roth Philosophy ► Since its introduction in 1975, the Roth bracket prescription has basically remain unchanged with only modifications in the configuration of brackets and hooks. ► The most recent information from several companies is that the Roth treatment accounts for almost 70pc of bracket sales worldwide and this indicates its effectiveness.
  29. 29. ► Reason for the Roth treatment coming into being----- Andrew`s idea was a total concept –of which the appliance was one part- ‘the guidance system’. His objective was to move teeth in straight line vectors from their malpositions to their final positions by translation or bodily movement. However the ideal force system to accomplish this has not been developed. - Hence to accomplish this with the force systems currently available, different bracket values must be
  30. 30. used depending on how far a tooth or group of teeth must be moved. ► Andrew thus attempted to translate teeth throughout treatment without tipping the teeth ( use of sliding mechanics). In the Roth approach tipping of teeth is allowed but the attempt is to keep it to a minimum.
  31. 31. ► Anchorage Loss- whenever mesially angulated brackets are placed on posterior teeth the teeth tend to tip mesially and migrate forward. The original Andrew`s treatment was devised for treatment of cases less than a 5degree ANB difference and nonextraction. However the mesial inclination of buccal teeth creates an anchorage loss problem in extraction cases. ► In Roth treatment the uprighting of upper premolars and overrotation of upper molars would help maintain anchorage as would the distal rotation of lower molars.
  32. 32. ► Overcorrection- the general overcorrection built into the Roth treatment has to do with the concept of where the teeth should be at the end of appliance therapy. ► As some degree of settling of the teeth after full fixed appliance therapy takes place, it seems obvious that treatment to an ideal occlusion with appliances in place should not be done as the teeth most likely would move out of those positions after the appliances are removed. ► Hence overcorrection was employed in the treatment.
  33. 33. Roth`s treatment philosophy ► Precise individualized orthodontic and orthopedic goals. ► Treatment mechanics tailored to individual situation and individual facial type. ► The appliance should provide correct tooth position prior to appliance removal that would allow teeth to settle in normal occlusion. ► Altered bracket placement to allow for overcorrection ► Space closure by tipping –translation to allow for greater efficiency and shorter treatment duration.
  34. 34. Variations in Roth Treatment ► Several variations in Roth treatment are available for special circumstances. - Super torque - upper anterior canine to canine model. Cases when two upper premolars only are extracted and a size discrepancy is created.( because half of a molar is smaller than an upper premolar).The additional torque and tip makes the upper anteriors occupy more space. These are used in conjunction with the zero rotation upper molars as the mesial molar rotation created causes the molars to occupy more space in the arch.
  35. 35. ► In this way the tooth size discrepancy is compensated for and proper overjet and overbite can be established and the upper extraction sites remain closed. ► The Super torque device also is used in Class II div 2 cases and any case that requires 6mm or more of upper anterior retraction.
  36. 36. ► The Zero Tip canine brackets- These are used for segmental surgical cases to ensure space between the canines and premolars for the osteotomy cut. After healing from surgery has occurred the standard Roth canine brackets are placed to achieve final finishing. ► These variations are the only ones needed to treat almost any case that might arise.
  37. 37.
  38. 38. MBT system ► Mc Laughlin and Bennet worked for more than 15yrs and developed and refined the treatment mechanics based on sliding mechanics, mainly using the standard SWA brackets.( 1975-1993) ► Their treatment mechanics included adequate bracket positioning, lacebacks and bendbacks for early anchorage control and light archwire forces. ► In the period between 1993-1997 they worked with Trevisi to redesign the entire bracket system to
  39. 39. overcome the perceived inadequacies of the SWA. They re- examined Andrew`s original findings and took into account additional research input from Japanese sources when designing the MBT bracket system. ► In the period between 1997- 2001 they developed a completely modern systemized method of treatment mechanics. ► These were then called the third generation of pre adjusted brackets.
  40. 40. MBT Prescription ► Bracket design- The tip was reduced in the upper and lower anterior teeth due to the following reasons. - to prevent anchorage loss - to prevent bite deepening during the aligning stage. - to prevent over proximity of the canine root apex and the premolar root. - Torque was increased for the maxillary anteriors with a range of torque values available for the canine bracket.
  41. 41. TIP 0 TORQUE 4 0 8 0 8 3 0 2 0 2 0 0 17 10 7 -1 -6 -6 -12 -17 -20 -6 -1 0 -10 -10 -10
  42. 42. TIP 5 9 11 2 2 5 5 2 2 TORQUE 7 3 -7 5 2 2 2 2 -7 -7 -9 -9 -1 -1 -11 -17 -22 -30 -35
  43. 43. ► Brackets with three options for canine torque were needed for different patient arch forms and other clinical variables. The 0 and 7 degree options are preferred for cases with narrow maxillary bone form, prominent canine roots. ► Lower canine torque is -6, 0 degrees but even 6 degree is available for some cases.
  44. 44. ► Bracket placement- The MBT bracket placement approach is similar to the Andrew`s approach .He recommended a bracket placement chart devised on the measurement of the clinical crown height of the errupted teeth. Different bracket positioning charts are available for premolar extraction cases and molar extraction cases. The variations in extraction cases are to achieve good marginal ridge contact adjacent to the extraction site. Bracket positioning gauges also used for vertical accuracy.
  45. 45.
  46. 46.
  47. 47. ► Arch form- a medium sized standard ovoid arch form was used for majority of the cases, and the size reflected the fact that many of their patients were children with malocclusions , unlike Andrew`s sample of 120 normals ,which were non extraction adults with large arches. ► The recommended technique is to create an individualized form for all the patients based on ovoid, tapered or square arch forms.
  48. 48.
  49. 49. Versatility of the MBT Versatile bracket systemSeven areas of versatility are present in the third generation brackets which are - Options for palatally displaced upper laterals.-10 degrees - 3 torque options for upper canines.-7,0,7 - 3 torque options for lower canines.-6,0,6 - Interchangeable lower incisor and interchangeable upper premolar brackets.
  50. 50. - Use of upper 2nd molar tubes on the 1st molars in non headgear cases Use of lower 2nd molar tubes for the upper 1st and 2nd molars of the opposite side when finishing cases to a class II molar relationship.
  51. 51.
  52. 52.
  53. 53. ► Treatment mechanics – in the early stages of treatment the main threat to anchorage comes from the influence of the anterior bracket tip. ► Lacebacks are used to assist control of canine crowns in premolar extraction cases. ► Bendbacks are used at the start of treatment to prevent mesial movement of anterior teeth. ► Lacebacks and Bendbacks are the primary methods of supporting anchorage in the early phase of treatement.
  54. 54.
  55. 55.
  56. 56. ► Anchorage control for lower molars - use of lingual arches - class III elastics and headgear. ► Anchorage control for upper molars - use of cervical, combination or occipital pull headgears. - use of transpalatal bars.
  57. 57. ► The tip built into the anterior brackets caused the crowns of the anterior teeth to incline forward and deepen the bite. Also there was a tendency for lateral open bite.( roller coaster effect). This effect is seldom seen in today`s cases owing to the reduced tip in the MBT brackets. ► Also the use of light archwire forces will put less demand on anchorage and will also be comfortable to the patient.
  58. 58.
  59. 59. MBT Philosophy
  60. 60. Alexander`s Vari - Simplex Discipline ► 1. 2. 3. Vari simplex discipline was introduced by Alexander in 1978.This technique grew out of Tweed`s technique and today maintains its fundamental principles. Anchorage preparation (uprighting mandibular molars) Positioning of mandibular incisors over the basal bone Orthopedic alteration with head gear.
  61. 61. Concept of the Vari Simplex Discipline. ► This system revolves around five factors related to brackets. bracket selection, bracket height, bracket angulation, bracket torque and bracket in –out. ► Bracket selectionTwin brackets- maxillary anteriors. Lang brackets- maxillary and mandibular cuspids Lewis brackets- maxillary and mandibular bicuspids and mandibular incisors.
  62. 62.
  63. 63. ► Bracket height- the bicuspid bracket height is the key because of its Variable clinical crown height. The normal height is 4.5mm, the other bracket heights are calculated in relation to it.
  64. 64. ► Bracket angulation-
  65. 65. ► Bracket torque-
  66. 66. ► Bracket in-out-
  67. 67. ► Alexander principle however is much more than a bracket system or arch form. The technique involves specific treatment mechanics. ► The maxillary arch is treated first with the use of multi stranded, spiral round wires. The patient is given an extraoral appliance called the retractor. When the final archwires are placed in the maxillary arch then the treatment of the mandibular arch is started. The reasons for this delay in treatment
  68. 68. include - To avoid interference of the mandibular brackets with the maxillary teeth - As the maxillary arch improves the mandibular curve of spee improves naturally - It allows more time for the mandibular 2nd molars to errupt. - Allows physiological drifting of crowded lower anteriors. (driftodontics)
  69. 69. - During canine retraction there is no interference and or attrition on the cusp tips from the mandibular canine brackets. This system is best designed for .017x .025 inch arch wire in .018 inch bracket slot.
  70. 70. Level Anchorage System ► The Level anchorage system is a complete orthodontic treatment system designed to treat efficiently to a pre determined goal and to reach that goal on a routine basis.( Terrel Root 1981) ► Tweed advocated anchorage preparation by placing tip back bends in the lower arch wire. ► Root incorporated the concepts of preadjusted tip in the edgewise appliance in order to reduce
  71. 71. the wire bending needed during anchorage preparation. ► This was followed by Holdaway preangulating the edgewise appliance in the mandibular buccal segments depending on the severity of the malocclusion. ► The Level Anchorage System is described as a straight wire appliance utilizing the anchorage preparation as described by Holdaway
  72. 72. ► Pre adjustments of the level anchorage appliance – There are two choices of distal crown tip for the mandibular buccal teeth. ► Regular and Major- the choice depends on the severity of the malocclusion and is determined by the use of the analysis chart.
  73. 73.
  74. 74. TIP 4 7 6 0 0 0 15 (regular) 2 2 6 4 4 6 10 TORQUE 15 7 0 -7 -7 10 10 0 0 0 11 17 22 25
  75. 75. TIP 4 7 6 0 0 0 15 (major) 2 2 6 4 6 10 15 TORQUE 15 7 0 -7 -7 10 10 0 0 0 11 17 22 25
  76. 76. ► The Level Anchorage system has made the practice of orthodontics much more satisfying. ► Treatment plan is formulated by using the analysis chart. ► Arch wire bending is reduced due to the preadjusted appliance. Efficiency is improved because routine check ups for each step allows the progress to be monitored. ► Parents also prefer this system for they can understand
  77. 77. the importance of treatment steps to achieve an ideal goal. They like the positive approach that the orthodontist takes when the treatment steps and time sequence have been predetermined.
  78. 78. Advantages of the Straight Wire Appliance ► ► ► ► Ease of arch wire construction due to the elimination of bends in the arch wires. No need of interbracket span. An interbracket span of great magnitude is unnecessary to reduce the force levels as there are no bends in the wire. Ease of arch wire placement Less round tripping of teeth as the teeth move in more direct vector lines from their maloccluded to their final positions.
  79. 79. ► ► ► ► ► Better control of tooth positions. Better and more consistent results with shorter treatment time. Patient comfort Complete space closure can be achieved with one set of wires since there are no bends in the wire to interfere with the brackets themselves during space closure. Ease of ligation
  80. 80. ► Bracket identification ► More accurate bracket placement
  81. 81. Misconceptions and Myths about the SWA ► It is usually misinterpreted that the 2 degree tip in the lower SWA brackets will end up with the crown being 2 degrees mesially inclined. The SWA will not produce this effect if properly used. The key here is in proper bracket placement. ► Using the lower molar as an example, its long axis is the dominant groove on the buccal surface which is at an angle of 2 degrees with the line perpendicular to the occlusal plane. So when SWA brackets are properly
  82. 82. located, the 2 degree tip in the bracket offsets the 2 degree distal tip of the crown`s long axis. So the molar, at the end of treatment will be as upright as with a zero angulation edgewise bracket that uses the occlusal plane as a reference point. ► Another misconception is that the SWA is wedded to a specific technique. The 1976 AAO meeting presentations related the SWA to direct bonding, Tweed mechanics, utility arches, sectional arch mechanics and
  83. 83. activator treatment for gross correction followed by SWA treatment for finished mechanics. It was demonstrated that SWA does not require specific technique . ► Another misconception is that no wire bending at all is ever necessary with the SWA. The SWA reduced the need for many primary archwire bends with their accompanying side effects. It has not however eliminated the need for reverse or accentuated curves, which produce forces that influence the curve of spee.
  84. 84. ► Another misconception is that the SWA in order to work properly, must be sited on the crown with more precision than an orthodontist can routinely achieve. ► The SWA carries its own placement guidelines the vertical tie wings, the welding tabs for the molar tubes. It is just a matter of placing the straight guidelines parallel to the long axis of the clinical crown. And if equal amounts of error are introduced in a test against edgewise, the SWA will prove to be more forgiving.
  85. 85. ► Torque in base- another straight wire myth. It is possible to incorporate torque either into the bracket base or machine it on the bracket face, but to fulfill strict straight wire design criteria only the former method is acceptable. Torque in face brackets do not fulfill the criteria of the SWA as they could lead to 2 problems.
  86. 86.
  87. 87. ► In built errors in final vertical tooth positioning and interference with sliding mechanics. ► But studies by Ferguson ( 1990) evaluating the two bracket systems concluded that the torque in face systems are capable of producing comparable results. ► It seems that the method of torque incorporation is unlikely to be of practical significance and that its importance has been greatly been exaggerated.
  88. 88. Pitfalls of the Straight Wire Appliance ► Frequently the anticipated results are not achieved by using the preadjusted appliances and straight wires. ► There are at least 5 reasons of not achieveing ideal tooth positions. ► First is the inaccurate bracket placement. Misplaced brackets in the mesiodistal plane results in rotational irregularities and those in the occlusogingival plane alters the torque. A 3mm occlusal displacement of the mandibular premolar bracket can result in 15 degree alteration of torque.
  89. 89. ► Second is the variation in tooth structure such as irregular facial surfaces, crown root angulations, unusual crown shapes . These require variations in their tip, torque and height parameters to achieve optimum results. ► Third is that the -Variations in vertical and anteroposterior jaw relations require variations in the position of maxillary and mandibular incisors. It is clear from class II and III frameworks that the concept of ‘one appliance fits all’ defies the normal biologic
  90. 90. variation. ► The fourth reason is the tendency for relapse during retention. The overcorrections which are done for tissue rebound or relapse tendencies should not be limited only to rotational movements but also include overcorrections for tip, torque and height. ► Fifth is that the edgewise appliances have 3 significant mechanical deficiencies.
  91. 91. - Force applied to the teeth through brackets located away from the centre of resistance. Play between the archwire and the arch wire slot. Force diminution.
  92. 92. Future Developments ► In the 1984`s ‘Attract’ brackets were introduced which were single width brackets having rounded contours and micro molar tubes. The base of the slot was of the width of a twin bracket . They also had short ball hooks in the Roth prescription. ► The latest version of the SWA is a perfectly clear bracket grown from 100pc pure liquid alumina (sapphire) into a single crystal, which gives a unique crystal clear appearance. All SWA values of tip, torque
  93. 93. are grown integrally into the crystal. State of the art diamond machinery is used to fabricate these brackets. ► Over the years due to technological advances the appliance has become smaller, more comfortable and more esthetic. ► A variety of bracket configurations are now available in a variety of prescriptions.
  94. 94. Use of CAD- CAM in bracket designing ► Torque in base was an important issue with the 1st and 2nd generation SWA brackets because level slot line up was not possible with the brackets designed with torque in face. ► Modern MBT systems use the CAD- CAM system for more flexibility of design, to enhance bracket strength and features such as tie wings and labiolingual profile.
  95. 95.
  96. 96. Conclusion ► Is the Straight wire appliance, then the ultimate appliance concept? Is it the appliance to end all appliances? Definitely not. Perhaps at this time it is what Angle would call the ‘latest and best’ but further improvements in this and the other systems are expected. ► Development of brackets of sufficient strength which will better withstand the forces applied by ligatures and wires. With increased resiliency the bracket rather than the wire will have initial deformation and recovery.
  97. 97. ► Development of plastic wires rather than metal wires and light force applications of great range. ► Decrease in the friction by means of special bracket slot coatings. ► Development of brackets which can be adjusted once they have been attached to the teeth.
  98. 98. References 1 Andrews LF. Six keys to normal occlusion. AJO 1972;62;296-309. 2 Andrews LF. Straight wire appliance, origin, controversy and commentary .JCO 1976,10;99-114. 3 Roth. 5 years clinical evaluation of Andrew`s SWA.JCO,1976;836-850. 4 Roth. Straight wire appliance 17 years later. JCO 1987, 21;632-642.
  99. 99. 5 Mauric Bergman- Straight wire myths. BJO 1988 ; 115;57 6 Ferguson. Torque in base –Another straight wire myth.BJO;1990;15;57 7 Mc Laughlin, Bennet. Transition from Standard Edgewise to Preadjusted appliance.JCO1989;23;142153. 8 Meyer, Nelson. Preadjusted edgewise appliancestheory and practice. AJO 1978;73.5.485-498
  100. 100. 9 Creekmore. Straight wire- the next generation. AJO 1993;104;8-20. 10 Yogesh Midha, Valiathan A. Straight wire technique. KDJ;18.1;1049. 11 Randhawa G, Valiathan A. Anchorage loss with Straight wire appliance. JIDA ,1993,64(10);313 12 Sameer S, Valiathan A- Comparative analysis of Andrew`s SWA, Roth`s Technique and Vari simplex discipline. KDJ ;19;4;115.
  101. 101. 13 Joseph J, Randhawa S, Valiathan A. Class I bimaxillary protrusion treated with straight wire Andrew`s appliance.JPFA 1994;8;55 14 McLaughlin, Bennet JC. Finishing and detailing with the preadjusted appliance system.JCO1991;21;4;251264. 15 Mc Laughlin, Bennet. Controlled space closure with the preadjusted appliance.JCO 199024;251-260. 16 Mc Laughlin, Bennet, Trevisi- Systemized orthodontic treatment mechanics. Mosby 2001.
  102. 102. 17 18 19 20 AlexanderRG. The Vari Simplex Design. JCO1983;17;6;380-392. Lawrence Andrews- Straight wire, the concept and appliance. San Diego, L.A.Wells 1989. WB Magness. The Straight wire concept. AJO 1978;73;5;541-550. Terrell Root. The level anchorage system for correction of orthodontic malocclusions. AJO 1981,80;4;395-410.
  103. 103. 21 Hocevar R A. Why edgewise? A compendium of means to gentle resilient fixed appliances. AJO 1981,80;3;237-255. 22 Orthodontics – Current principles and techniques. third edition. Graber, Vanarsdall. 23 Contemporary orthodontics. third edition, Proffit.
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