Friction mechanics /certified fixed orthodontic courses by Indian dental academy

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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.


Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
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Friction mechanics /certified fixed orthodontic courses by Indian dental academy

  1. 1. FRICTION MECHANICS IN ORTHODONTICS INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. 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 www.indiandentalacademy.com
  3. 3. RETRACTION FRICTIONLESS TIP AND UPRIGHT STAGE 1 SLIDING CANINE FRICTIONLESS SIMULTANEOUS INTRUSION AND RETRACTION STAGE 2 ANTERIORS SLIDING FRICTIONLESS www.indiandentalacademy.com SLIDING
  4. 4. INTRODUCTION Tooth movement occurs by various mechanisms EXTRENSIC Force is basic component INTRINSIC Extrinsic - elastics, E-chain, NiTi springs e.t.c Intrinsic - Loops bend in arch wire www.indiandentalacademy.com
  5. 5. 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 www.indiandentalacademy.com
  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 www.indiandentalacademy.com
  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 www.indiandentalacademy.com
  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 www.indiandentalacademy.com
  9. 9. Determinants of space closure • Amount of crowding • Anchorage • Axial inclination of canine & incisors • Midline discrepancy & L/R symmetry • Vertical dimensions www.indiandentalacademy.com
  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. www.indiandentalacademy.com
  11. 11. ANCHORAGE CLASSIFICATION According to Ravindra Nanda GROUP A GROUP B GROUP C BIOMECHANICS IN CLINICAL ORTHODONTICS -RAVINDRA NANDA www.indiandentalacademy.com
  12. 12. GROUP A ANCHORAGE Maximum (A, Critical) anchorage situation Critical maintenance of pos. teeth position 75% or more space req. for ant. retraction www.indiandentalacademy.com
  13. 13. GROUP B ANCHORAGE Moderate (B) anchorage situation Relatively symm. space closure(50:50 or 60:40) www.indiandentalacademy.com
  14. 14. GROUP C ANCHORAGE Minimum (C, Noncritical) anchorage situation 75% or more space closure- by mesial movement of pos. teeth www.indiandentalacademy.com
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  16. 16. • Axial inclination of canines & incisors
  17. 17. • 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. www.indiandentalacademy.com
  18. 18. • 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 www.indiandentalacademy.com
  19. 19. • 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 www.indiandentalacademy.com
  20. 20. • 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 www.indiandentalacademy.com
  21. 21. • 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 www.indiandentalacademy.com
  22. 22. • 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 www.indiandentalacademy.com
  23. 23. • 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 www.indiandentalacademy.com
  24. 24. – 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 www.indiandentalacademy.com
  25. 25. • 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 www.indiandentalacademy.com ligation, self ligating brackets
  26. 26. – 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 www.indiandentalacademy.com
  27. 27. • Biological – Saliva – Plaque – Acquired Pellicle – Corrosion www.indiandentalacademy.com
  28. 28. • 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. www.indiandentalacademy.com
  29. 29. – 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.
  30. 30. • 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" www.indiandentalacademy.com
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  32. 32. • Reduced rotation control - mainly in the teeth adjacent to extn sites, which tend to roll in if spaces are closed too rapidly
  33. 33. • 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.
  34. 34. • 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 www.indiandentalacademy.com
  35. 35. • 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 www.indiandentalacademy.com
  36. 36. • 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"
  37. 37. Active Lace back Type 1 Type 2 Type 3 www.indiandentalacademy.com
  38. 38. – 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 www.indiandentalacademy.com
  39. 39. – 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. www.indiandentalacademy.com
  40. 40. • Adv. – Inexpensive – 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 www.indiandentalacademy.com
  41. 41. • 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 www.indiandentalacademy.com
  42. 42. • 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 4-6 weeks. www.indiandentalacademy.com
  43. 43. • 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 www.indiandentalacademy.com
  44. 44. • 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 www.indiandentalacademy.com
  45. 45. • 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 www.indiandentalacademy.com
  46. 46. • 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) www.indiandentalacademy.com
  47. 47. • 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 retraction 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) www.indiandentalacademy.com
  48. 48. • 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 www.indiandentalacademy.com of mouth
  49. 49. • 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) www.indiandentalacademy.com
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