Space closure /certified fixed orthodontic courses by Indian dental academy


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Space closure /certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. SWA Space Closure, Cuspid, Incisor & En-masse Retraction
  3. 3. Introduction Space closure is an important step in mechanotherapy, solely dictated by clinician trt. objective, irrespective of method employed Space closure should be individually tailored based on the diagnosis & trt. plan Selection of any method should be based on desired tooth movement
  4. 4. Goals for any space closure method • Differential space closure capability • Axial inclination control • Control of rotation & arch width • Optimum biological response • Minimum patient cooperation • Operator convenience
  5. 5. Anchorage classification Maximum (A, Critical) anchorage situation • Critical maintenance of pos. teeth position • 75% or more space req. for ant. retraction Moderate (B) anchorage situation • Relatively symm. space closure(50:50 or 60:40) • Least diff. Minimum (C, Noncritical) anchorage situation • 75% or more space closure- by mesial movement of pos. teeth
  6. 6. Single cuspid retrn. Vs En-masse retrn. Two schools of thoughts Separate canine & incisors retraction – less detrimental to anchorage (enhance anchorage by adding teeth to pos. segment but anchorage is taxed twice) May be true in some methods of s.c , not necessarily true in all En- masse retraction adequately designed appliances, based on desired biomechanics significantly ↓ trt. Time
  7. 7. Method of anchorage is based on type of tooth movement on pos. & ant. seg. & does not entirely depend on no. of teeth (translation of post. seg. Vs controlled tipping of ant. seg.) Differential tooth movement is accomplished by unequal moments on ant. & pos. seg. Separate canine retraction- moderate to severe ant. crowding, after achieving incisor alignment, en-masse closure completes the space closure
  8. 8. Extn. of PMs is commonly believed to be necessary for proper management of some malocclusions. 6-7 mm space gained in each quadrant can be used for • Relief of crowding • Retraction of incisors • Mesial movement of molars Determinants of space closure • Many details of diag. & trt. objectives determine tooth movement req. during space closure
  9. 9. Determinants of space closure Amount of crowding Anchorage Axial inclination of canine & incisors Midline discrepancy & L/R symmetry Vertical dimensions
  10. 10. Amount of crowding : • in case of severe crowding maintenance of anchorage is necessary while creating space for incisor aling. Anchorage: • Anchorage classification & concept of differential anchorage is imp. • Using the same mechanics for diff. anchorage need limits the results • Reinforcement methods can be used in critical anchorage sit. • Using a force system determined appliance design can improve chances of success.
  11. 11. Axial inclination of canines & incisors
  12. 12. Midline discrepancy & L/R symmetry • Mid line discrepancies with or without an asymmetric L/R occ. Relationship- corrected as early as possible • Asymm. Forces on L/R could result – unilateral vertical force, skewing of dental arch or asymm. Anchor loss. Vertical dimensions • Undesired vertical force ass. with class II elastics may result in ↑ LFH, ↑ interlabial gap & gummy smile.
  13. 13. Minor & major cuspid retraction • Depend upon severity of crowding in ant. Seg., anchorage req. & axial inclination of canine Minor – refers to uncontrolled tipping of canine when 1-2 mm arch length is req. per side (lace back) Major –controlled tipping or translation of canine when more than 3 mm arch length is req. per side. if canine inclination is ideal then translation is preferred
  14. 14. Retraction mechanics divided into • Sliding (Frictional) mechanics involves either moving the brackets along the arch wire or sliding the arch wire through bracket & tube • Loop (Frictionless) mechanics involves movement of teeth without the brackets sliding along the arch wire but with the help of loops
  15. 15. Moderate Anchorage situation Treatment with 18- slot• either sliding or loop mechanics can be used. • Single or narrow twin brackets on canine & PM is ideally suited for use of closing loops in continuous arch wire Treatment with 22- slot• As a general rule s.c done in two steps • First retracting the canine usually with sliding mechanics • 2nd retracting four incisors usually with closing loop • Enmasse – using Opus or T loop but less than ideal
  16. 16. Maximum Anchorage situations Treatment with 18- slot• Friction from sliding is usually avoided, by employing closing loops. • Anchorage is augmented & anchorage strain is reduced by: • Adding stabilizing lingual arch –enmasse retrn. (2:1) • Reinforce max. post. anchorage with EO force & class III elastics from high pull head gear to supplement retrn. force in lower arch- enmasse retrn. (3: 1 - 4:1)
  17. 17. • Retraction of canine independently, prf. using a segmental closing loop & then retracting incisors with 2nd closing loop. Using with stabilizing lingual arch will produce 3:1 Treatment with 22- slot• Like 18 – slot Anchorage is augmented & anchorage strain is reduced • Canine can be retracted with sliding by • Reinforcing pos. anchorage with extra oral force • Application of EO force directly against canine to slide them posteriorly.
  18. 18. • Use of segmented arch mechanics for retraction • Segmented arch mechanics for tipping/uprighting Minimum Anchorage situations • Req. anchor control, to reduce incisor retraction by • To incorporate as many in ant. Segment –locating the extn. Site more post. • Placing active lingual torque in incisor section of archwires • To breakdown pos. anchorage(moving one tooth a time) • Use of extraoral force (face mask) • Use of implants/onplants to protract pos.
  19. 19. Methods of canine retraction • Friction • Frictionless – Paul Gjessing spring, Burstone T loop, delta loop, L loop, omega loop • Extra oral – head gear Four hooked for both the arches • Other methods Retraction using earth magnets Rapid canine retraction through Distraction of PDL Methods of en-masse retraction Of four incisors • Friction
  20. 20. • Frictionless –P.G spring, Burstone T loop, delta loop, L loop, Retraction utility arch, omega loop arch wire or closing loop arch wire • Extra oral - Head gears Of six anteriors • Friction • Frictionless – closing loop, Burstone T loop continuous arch wire, opus loop (Siatkowaski) Intrusion & retraction of four incisors • Burstone three piece intrusion arch • Rickets Retraction & intrusion utility arch Simultaneous retraction & intrusion of six ant. • K-Sir Arch
  21. 21. Sliding mechanics - movement of teeth along arch wire • The most significant diff. between standard edge wise mechanics & pre adjusted appliance is in stage of space closure. • In sd. Edgewise, rectangular wire could not effectively slide through bracket slots due to 1st, 2nd & 3rd order bends in arch wire • st. wire appliance allows for level bracket slot lined up & arch wire can more effectively move through bracket slots. allows effective sliding of canine along arch wire
  22. 22. Advantages • Minimal wire bending time • More efficient sliding of arch wire through post. Bracket slots • No running out of space for activation • Patient comfort • Less time consumption for placement
  23. 23. Disadvantages • Confusion regarding ideal force level • Tendency of overactive elastic & spring force  initial tipping & inadequate rebound time for uprighting if forces are activated too frequently • Generally slower than lop mechanics due to friction
  24. 24. Role of friction in sliding mechanics • Friction occurs at bracket wire interface • Some of applied force is dissipated as friction • Maximum biological tissue response occur only when the applied force is of sufficient magnitude to adequately overcome friction & lie with in optimum range of forces necessary of tooth movement. • Friction is the function of relative roughness of 2 surfaces in contact
  25. 25. • Described by coff. of friction (constant) related to surface characterstic of material • Coff . Static F- reflect force needed to initate movement • Coff. Kinetic F – reflects force neede to perpetuate this motion • It takes more force to initiate motion than perpetuate
  26. 26. Variables affecting frictional resistance during tooth movement Physical • Arch wire • • • • Materials Cross sectional shape/ size Surface texture Stiffness • Ligation of arch wire to bracket • Ligature wires • Elastomerics • Method of ligation, method of tying, bracket design to limit the force of ligation, self ligating brackets
  27. 27. • Bracket • • • • • Material Manufacturing process: cast or sintered s.s Slot width & depth Design of bracket: Single or twin 1st, 2nd & 3rd order bends • Orthodontic appliance • Interbracket distance • Level of bracket slot between adjacent teeth • Force applied for retraction
  28. 28. Biological • • • • Saliva Plaque Acquired pellicle corrosion
  29. 29. Mechanics involved • To move a tooth bodily, the force should pass through centre of resistance of tooth. • When force is applied on crown, tooth experiences both moment (in 2 planes) & force • One moment tends to rotate the tooth mesial- out & other distal tipping.
  30. 30. • Mesial out rotation is undesirable side effect • Distal tipping  retraction, by binding the arch wire which in turn produces moment results in distal root movement hence uprighting of tooth. • As tooth uprights moment ↓es until wire no longer binds. • Again canine retracts along arch wire till tipping again causes binding
  31. 31. Wire selection • • • • Req. wire that produce less friction Rect.> round Larger diameter>smaller TMA,NiTi > s.s • 0.016” s.s lowest friction not ideal wire (not offer control) in three planes • 0.016X 0.022ss for 0.018 slot • 0.017x 0.022 or .019x .025 for 0.022 slot
  32. 32. Methods of canine retraction in sliding mechanics • • • • • • Elastic modules with ligature Elastomeric chains Coil springs J hook head gear Mulligan’s V bend sliding mechanics Employing tip edge bracket on canines
  33. 33. Elastic modules with ligature • Bennett, McLaughlin, • An .019"´x.025" arch wire in an .022 "-slot system. • Hooks of .024 " stainless steel or .028 " brass are soldered to the U & L arch wires The average distances between hooks— 38mm in the U & 26mm in the L • Additional sizes of 35mm & 41mm (U) and 24mm & 28mm (L) • Force required for space closure is delivered by elastic "tiebacks"
  34. 34. • Elastic module stretched by 2-3mm (to twice its normal length) delivers 0.5 - 1.5mm of space closure per month( 100- 150 g force). • About .5mm of incisor retraction and .5mm of mesial molar movement. • The tiebacks are replaced every four to six weeks. Alternate systems found to be disadv. to this in following aspects • Power chain- variable force, difficult to keep clean, some times falls off
  35. 35. • Elastic bands- Applied by patient, inconsistent results due to cooperation factor • Stainless steel coil spring- deliver excessive force,unhygenic • Niti coil spring generally achieve faster & more consistent space closure Elastomeric Chains • Introduce in 1960’s • Can be used for canine retraction, diastema closure, rotation corr.
  36. 36. Adv. • • • • Inexpansive Relatively hygienic Easily applied without arch wire removal Not depend on pt. cooperation Disadv. • Absorb water & saliva • Permanent staining after few days in oral cavity • Stretching - breakdown of internal bonds –permanent deformation • Force degradation- variable force levels-↓effectiveness • Can untie or break if not placed with care
  37. 37. Tooth movement, pH & temp. change, fluoride rinse, salivary enzymes & masticatory forces- deformation, force degradation and relaxation • When E-chain first applied produces 300- 350 gms of force but lose 50- 70% of initial force during 1st day at 3 weeks retain 30-40% of original force • To overcome the problem of rapid force decay prestretching of E-chain by this ↑in residual force after 3 weeks is only 5% Configurations • Closed loop chain • Short filament chain • Long filament chain
  38. 38. Clinical considerations • M/F is lowest at initial placement of E-chain distal crown tipping of canine • As tooth retracted M/F ↑es due to dissipation of E force & by binding the arch wire produces moment results in uprighting of tooth. • For optimize tooth movement sufficient time should be allowed for distal root movement • A common mistake to change elastic too oftenmaintaining high force & M/F which produce tipping • Hyalinization around canine & direct resorption of pos.  anchor loss • E-chain or module should be changed at interval of 46 weeks.
  39. 39. Closed coil springs • 1931 • Various materials • Stainless steel • Co-Cr-NI alloy • Ni Ti • Stainless steel coil spring • Before s.s made avail. In 1930’s – precious metals • 1854 T.W Evans- retr. Maxillary incisors precious metal c.c springs
  40. 40. Apply more predictable level of force than force elastics Easy to apply But have high LDR as compare to NiTi, so as space closes, some force degradation due to lessening activation NiTi close coil spring • Produce more consistent space closure than elastics • Indicated if large spaces need to close or infrequent adjustment opportunities • Samuels et al (1998)optimum force for space closure with this spring – 150 gm
  41. 41. Two sizes avali. – 9 mm & 12 mm Springs should not be extending beyond manuf. Recomm. (22mm for 9 mm spring, 36 mm for 12 mm springs) Deliver constant force till reach the terminal end of deactivation stage Can be easily placed & removed without Aw removal Don't reactivation at each appointment Pt. cooperation not needed Relatively unhygienic as compare to elastic system
  42. 42. Problems during sliding mechanics with elastics or coil springs • Occl. Interference can hinder distalization • Friction & binding due to improper angulation of canine bracket to wire • Cortical plate resistance • Excessive force • Rotation of canine (MB) & molar (DB)
  43. 43. Inhibitors to canine sliding retraction • • • • • • • Inadequate levelling resulting in AW binding Damaged or crushed bracket Soft tissue buid up at extn. Site Cortical plate resistance Excessive force causing tipping & binding Occlu. Interferance Insufficient or inconsistant force.
  44. 44. Effects of Overly Rapid Space Closure • can lead to loss of control of torque, rotation, and tip. • Loss of torque control  • in upper incisors being too upright • space closure with spaces distal to the canines • unaesthetic appearance. • lost torque is difficult to regain. • Rapid mesial movement of the upper molars can allow the palatal cusps to hang down, resulting in functional interferences, and rapid movement of the lower molars causes "rolling in"
  45. 45. Reduced rotation control - mainly in the teeth adjacent to extn sites, which tend to roll in if spaces are closed too rapidly
  46. 46. Reduced tip control produces unwanted movement of canines, premolars, and molars, along with a tendency for lateral open bite. In high-angle cases, where lower molars tip most freely, the elevated distal cusps create the possibility of a molar fulcrum effect.
  47. 47. • In some instances, excessive soft-tissue hyperplasia occurs at the extraction sites This is • Unhygienic, • Can prevent full space closure • Allow spaces to reopen after treatment. • Local gingival surgery may be necessary in such cases.
  48. 48. Direct Head gear retraction • J hook head gear( st. pull or high pull) Four hooked for both the arches, clipped mesial o canine • St. pull- swifer canine retn. Than high pull, may cause ant. Extrusion • High pull more bodily retraction, bite opening, not efficient for distal movement Adv. • Extremely conservative to anchorage • can be applied to both arches simult. (Hickham’s)
  49. 49. Disadv. • Force application intermittent –slower method • Pt. cooperation • Canine tipping & ant. Extrusion in st. pull Problems • Occl. Interference (bite opening, heavy wire in lower arch, ABP) • MB rotation of canines (rotation wedge) • Flaring of canine in buccal cortex (AW cons. Across canine) • One canine may retract faster than other • Trauma to corner of mouth
  50. 50. Mulligan’s V bend sliding mechanics • Principle – apply differential moments to teeth via bends in continuous AW while force is applied by aux. like E-chain, coil spring etc. • 18 – slot – 0.016” ss wire • 22 – slot - 0.016, 0.018 or 0.020 wire • Incisors are not engaged • 45 degree V bend are added to wire and 200 g force between canine & molar • V bend diff. moments on canines & molars • In max. anch. case near molar(2 PM not banded intially)
  51. 51. Employing tip edge bracket on canines • In case of upright or distally tipped canine (deepening of bite & lateral open bite) Tip edge bracket • Prevent binding between AW & slot during initial stages when major movements • After retraction is comp.- uprighting spring to correct angulation without ant. Extrusion • Full size rectangular wire can be placed for desired tip/torque specifications.
  52. 52. Retraction with frictionless mechanics Principle - When a bend is placed in middle of AW & engage in brackets 2 eq. & opp. Moments produced • When offset bend –diff. moment (as anchor bend in Begg tech.) greater clockwise moment in pos. segment (extrusion) & smaller anticlockwise moment in ant. Segment (intrusion)
  53. 53. Same principles in frictionless mechanics • Instead of bend loop is placed • Bends are placed mesial & distal leg of loop called α & β bends • Alpha (α ) bend is on ant. side produce α moment, produces distal root movement of ant. teeth • Beta (β) bend on post. side produces β moment, produces mesial root movement of pos. teeth • If β moment > α moment anchorage is enhanced by mesial root movement of pos. seg. & pos. extrusion & ant. Intrusion • If α moment > β moment ant. Extrusion • If both eq. – no vertical force
  54. 54. In this system teeth move without the brackets sliding along the AW. Retraction is by loops or springs Activation of loop is produce force by pulling the distal end of wire through molar tube and cinching back or by soldering a tie back mesial to molar tube on AW Moment is determined by loop design
  55. 55. M/F could be increase by (Burstone & Koenig) • By ↑ vertical dim. of loop (a regular 10 mm vertical loop offers 3:1 M/F when activated 1 mm, in order to get req. M/F activation should be ↓ to 0.2 mm- insuff. Force level) • ↑ horizontal dim. in apical part of loop • ↓interbracket distance • Positioning loop close to tooth to be retracted
  56. 56. • Most effective method is by placing preactivation bends or gable bends (can be placed within the loop or where loop meets AW) as we engage the wire in bracket we pull the horizontal loops down producing a moment called activation moment & loop is said to be in neutral position
  57. 57. Moment to force relationship • The bracket is in an estimated position of 4 mm from edge of the cusp. This implies that an average M/ F ratio of 11:1 is required in order to prevent tipping of the canine ( antitip couple). • The antirotation couple acts in the horizontal plane The antirotation M/F ratio is estimated at 4:1, which equals the distance from bracket to tooth axis
  58. 58. Ideal properties of canine retraction spring • Promotes translation sagitally & horizontally with anti tip M/F 11:1 & antirotation M/F of 4:1 • Result in low LDR during generation of retraction force (50 -200 G) • No adverse interaction between anti tip & antirotation moments during activation • Could be used both slots • Have limited dim. • allow for faciolingual adjustment
  59. 59. Design of spring influences both M/F & LDR Addition of loop ↓ LDR without sig. affecting M/F LDR can be altered by wire composition • TMA loop have lower LDR than a same loop config. of S.S but no influence on M/F Another design consideration • Open Vs closed retracting loops- closed retracting loops have slightly lower LDR but same M/F • Major diff. Is in range of activation closed loop have greater range because of additional wire & Bauschinger effect.
  60. 60. Clinical consideration • When retraction loop or spring is placed • Two moments- α & β • Alpha (α ) is on ant. side produces distal root movement of ant. teeth • Beta (β) on post. side produces mesial root movement of pos. teeth • If β moment > α moment anchorage is enhanced by mesial root movement of pos. seg. & pos. extrusion & ant. Intrusion
  61. 61. • If α moment > β moment, anchorage of ant. Seg. ↑, ant. Extrusion • If both eq. – no vertical force
  62. 62. Distance that ant. &pos. seg. move depend on • Degree of crowding • Soft tissue profile • Molar relationship The amount of ant. Ret. Or pos. prot. needed is determined before loop is designed
  63. 63. Only ant. Retraction: placed closure to canine than molar, gable bend added near to molar large β bend ↑ pos. anchorage Symm. Closure : midway, gable bend of eq. dim. Only pos. protraction: placed closure to pos. seg., gable bend added near to ant. Seg. large α bend ↑ ant. anchorage Alpha< beta
  64. 64. Regardless of initial magnitude of α & β moment, changes in magnitude occur during retrn. As ant. Teeth retr. α moment ↓ faster than β moment ↑ in pos. anchorage and greater intrusive force on ant. & greater extrusive force on pos. there is ↑ in M/F due to ↓ in force as spring deactivated So spring should not be reactivated too often . Frequent reactivation will not allow the spring to ach. A high enough M/F to produce translation
  65. 65. Wire selection • For 18- slot- 16 x 22 ss or 17 x 25 TMA • For 22- slot -18 x 25 ss or 19 x 25 TMA TMA- modulus of elasticity app. 2/5th of s.s and have relatively high yield strength allows use of large pre activation bends generate low force & greater range of action. The high formability of titanium allows the fabrication of closing loops with or without helices. The low stiffness of the material and its high springback improve a loop of any given design
  66. 66. Burstone T loop attraction spring • Some cases require protraction of posterior teeth and others will require anterior retraction, Burstone used the general term attraction to describe the over-all process of space closure • Composite TMA 0.018-0.017 x 0.025 inch retraction spring. A 0.018 inch round T spring is welded directly to a 0.017 x 0.025 inch base arch. • the spring is activated 6 mm. and delivers approximately 201 Gm. of distal force at the start of retraction After the canine moves distally 1 mm., the force ↓ to 168 Gm.
  67. 67. Anterior retraction • two types: In one the anterior teeth are badly crowded, and separate canine retraction is indicated. In the other the anterior teeth have adequate arch length, and the movement that is needed is en masse space closure of all six anterior teeth. • En masse space closure in the segmented arch techniques uses two principles— the two-tooth concept and segmental movement.
  68. 68. the posterior teeth are joined together to form a posterior anchorage unit. The anchorage unit consists of the right and left posterior teeth which are connected by a buccal stabilizing segment and a TPA in the U arch and a low lingual arch in the L arch only two teeth— an anterior tooth comprising the incisors and the canines & a posterior tooth which includes molars and premolars.
  69. 69. The principle of en masse space closure, using segmental movement in the first phase the anterior segment is tipped with a center of rotation near the apex of the incisors, followed by a second phase of root movement where the center or rotation is moved occlusally to the bracket or the incisal edge (en masse root movement). 
  70. 70. . En masse retraction., A 0.021 by 0.025 inch anterior segment is in place for true segmental space closure with a 0.017 by 0.025 inch TMA attraction spring., Low-stiffness multistrand wire in the anterior segment allowed canine to retract to gain space for anterior alignment. Following alignment, a rigid anterior segment was placed.
  71. 71. En masse translation for group B cases Patients who require equal displacement for both the anterior and posterior segments can take advantage of en masse translation. since en masse translation requires greater force magnitudes, and since practically the center of rotation is not constantly maintained, a greater anchorage loss of the posterior segments is inevitable.
  72. 72. A 0.017 by 0.025 inch TMA attraction spring. T loop is centrally placed between canine and molar auxiliary tubes. Total gable bend 40 - 45 degrees. Typical activation is 7 mm
  73. 73. Posterior protraction for group c posterior teeth must be brought forward through most of the extraction site Shape of 0.017 by 0.025 inch TMA attraction spring used for protraction of posterior teeth. Loop is placed off center to the distal aspect. Angulation bends are increased as the position is approached.
  74. 74. Canine retraction • The composite retraction spring is used in Group A arches, and the attraction spring is employed in Group B and C arches • Antirotation bends are placed in the retraction assemblies to prevent the canine from rotating as it retracts..
  75. 75. PG retraction spring Poul Gjessing of denmark 1985
  76. 76. Spring design made from 0.016 by 0.022 inch stainless steel wire. The predominant active element is the ovoid double helix loop extending 10 mm apically. It is included in order to reduce the load/deflection of the spring and is placed gingivally so that activation will cause a tipping of the short horizontal arm (attached to the canine) in a direction that will increase the couple acting on the tooth.
  77. 77. The smaller loop occlusally is incorporated to lower levels of activation on insertion in the brackets in the short arm (couple) and is formed so that activation further closes the loops. Activation to 140 to 160 gm is obtained by pulling distal to the molar tube until the two sections of the double helix are separated 1 mm Activation is repeated every 4 weeks, and the canine is expected to undergo approximately 1.5 mm of controlled movement with each activation.
  78. 78. Opus loop Raymond E. Siatkowski Wire sizes were 0.017 X 0.025 inch TMA primarily 0.016 X 0.022 S.S, or 0.018 X 0.025 S.S. wire. capable of delivering a nonvarying target M/F within the range of 8.0 to 9.1 mm inherently, without adding residual moments via twist or bends (commonly gable bends) anywhere in the arch wire or loop before insertion.
  79. 79. Can be used for en-masse retraction of all ant. teeth with 18- slot
  80. 80. Simultaneous retraction & intrusion of six ant. • K-Sir Arch (Kalra simultaneous intrusion & retraction) Modification of segmented loop mechan. of Burstone & Nanda It is continuous.019 x .025 TMA wire with closed 7 mm X 2 mm U- loop at extn. site
  81. 81. Adv. of frictionless mechanics • Precise control over ant. & pos. anchorage • It is fail safe; tooth will move to limit to which loop is activated • Diff. tooth movement possible • More controlled tooth movement Dis adv. • Good understanding of mechanics • Wire bending skill & chair side time • When individual tooth is retracted undesirable mesial out movement
  82. 82. Rapid canine retraction through Distraction of PDL Liou & Huang (1998) process of osteogensis in PDL during ortho tooth movement is similar to distraction in mid palatine suture during Rapid palatal expansion. Can elicit rapid canine retraction in 3 weeks called as dental distraction.
  83. 83. Conclusion New knowledge concerning the biomechanics, along with the development of new materials, has made possible improvements which simplify the mechanics, improve the biologic response, and offer a more hygienic appliance The clinician must use an appliance which delivers the required force system. He should also be aware of how root length and the nature of the periodontal support will influence the force system.
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