Friction mechanics /certified fixed orthodontic courses by Indian dental academy


Published on

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,
Dental implants courses.for details pls visit ,or call

Published in: Education, Technology, Business
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Friction mechanics /certified fixed orthodontic courses by Indian dental academy

  1. 1. FRICTION MECHANICS IN ORTHODONTICS INDIAN DENTAL ACADEMY Leader in continuing dental education
  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
  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
  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
  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.
  12. 12. GROUP A ANCHORAGE Maximum (A, Critical) anchorage situation Critical maintenance of pos. teeth position 75% or more space req. for ant. retraction
  13. 13. GROUP B ANCHORAGE Moderate (B) anchorage situation Relatively symm. space closure(50:50 or 60:40)
  14. 14. GROUP C ANCHORAGE Minimum (C, Noncritical) anchorage situation 75% or more space closure- by mesial movement of pos. teeth
  15. 15.
  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.
  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
  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
  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
  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
  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
  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
  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
  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 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
  27. 27. • Biological – Saliva – Plaque – Acquired Pellicle – Corrosion
  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.
  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"
  31. 31.
  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
  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
  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
  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
  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.
  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
  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
  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.
  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
  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
  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
  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)
  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)
  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 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)
  50. 50.