Ni ti wires in orthodontics /certified fixed orthodontic courses by Indian dental academy


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Ni ti wires in orthodontics /certified fixed orthodontic courses by Indian dental academy

  2. 2. Introduction :- It refers to the ability of the material to remember its original shape after being plastically deformed while in martensite form . In typical application Certain shape is set when the alloy is maintained at an elevated temperature, above martensite – austenite transition temperature . When the alloy is cooled below the transition temperature it can be plastically deformed but when heated again and the original shape is restored.
  3. 3. HISTORYHISTORY • Classification – Orthodontic wires • Stainless steel , titanium - Beta titanium , Nickel ti , co. cr – nickel . • In 1950 – 1st material used are noble metals & alloys – Gold , Platinum , Iridium , Silver alloy. • They lacked flexibility & tensile strength hence they were replaced by Stainless Steel. • In 1919 –SS was introduced by “KRUPPS” dental clinic in Germany by Dr. F.HAUPTMEYER. • In 1930 – Angle used SS as ligature wire . • In 1947 – SS was used as orthodontic material .
  4. 4. • In 1960 “ William F. Buehler” – developed nitinol in the navel ordnance laboratory[Naval surface weapons center] Ni – nickel, Ti – Titanium, Nol – Naval ordi. Lab. . • In 1970 – “Andreasen “ – used NiTi wires for orthodontics it was marketed in a stabilized martenstic form with no application of phase transition effects . • 1st marketed by 3M Unitek corporation Monrovia ,U.S.A. • In 1980 NiTi wires with active austensitic grain structure . • Stabilized martenstitic alloy commercially available – M -NiTi . • NiTi alloys with super elasticity – A .NiTi ( sentinol) • In 1990 NiTi wires – NEO SENTALLOY with shape memory at oral environment – Intro.GAC –International .
  5. 5. In 1994 – ORMCO Corpo intro copper NiTi,wire was available in 3 varients – Corresponding to austenitic finish temp for the completion of martensite to austenite transformation. 27* c – For mouth breathers 35* c – Activated at normal body temp. 40* c – Activation only after consuming hot food & beverages.
  6. 6. NiTi wiresNiTi wires • Titanium classi. Under light metals eg. AL , MG,Berllium • Light metals – frequently used to reduce the weight of components & structure . • 1795 – GERMAN chemist “martin klaporth” named titanium after the 1st sons of earth titans . • 1825 – An impure sample of Ti idendified . • 1937 – Kroll reacted Ticl 4 with molten magnesium under an atmosphere of argon. • Basic reaction – Tio2+ 2cl2+ 2c = Ticl4 +2co . • Briquette + tar+ chlorinate at 800 * c – fractional distillation of Ticl4. • Ticl4 +2mg = Ti + 2mgcl2 special atmospheric conditions needed because alloys react with air.
  7. 7. • Sponge produced by reacting with mg is purified by leaching with Hcl. • With Na ,leaching is more efficient and Ti sponge becomes more granular . MANUFACTURING METHODS – • Milling ,Powder metallurgy, injuc. Moulding . • Advances – “Heroult” – Direct electric arc in furnace • “Kjellin” – Induction method. • Recent refinement – Argon decarburization & Widening of alloying element , Consumable electrode arc furnace. SOURCE – The mineral (rutile) – Tio2 , convenient source found in beach sand. • “ilmenite” –major source.
  8. 8. STRUCTURE & COMPOSITION – • MARTENSITIC – form stable at low temperature . • AUSTENITIC – form stable at higher temperature. • The unit cells can rearrange themselves in a zig zag pattern with congruent interfaces. Which results in a reversible E.C. bain structure transformation which is responsible for “Shape memory “ & “Super elastic” properties . • “BAIN DISTORTION” – In S.S the transformation is diffusionless occuring from any chemical change & if transition is as the result of specific crystallographic relation ship between the parent phase & new phase,a rearrangement of atoms in the unit cells occurs – Bain distortion. • Equiatomic phase is stable at higher temperature austenite & is made of lattice in which units are cubic .
  9. 9. • In each cell the Ni & Ti atoms are evenly distributed & made up of self accommodating coherent twins. • TWINNING – Is an angular movement of atoms parallel & symmetric towards a specific plane . • The unit cells can rearrange themselves in a zigzag pattern with congruent interfaces • Memory effect lasts only as long as the twinning & detwinning phenomenon can take place . • SHAPE MEMORY EFFECT – It refers to the ability of the material to remember its original shape after being plastically deformed in martensite form .( when the alloy is cooled below the transition temperature it can be plastically deformed & when heated again original temp. is restored .
  10. 10. • SUPER ELASTICITY – Ability to withstand much higher elastic strain than ordinary alloy before permanent set. • This property is exploited in orthodontics at body temp. to provide almost constant forces during long intervals of deformation. • COMPOSITION – Ni -55% Ti –45% • For thermally activated purpose the third metal commonly used are Cu because they reduce the hysteresis & brings TTR close to oral temperature & improves the strength of martensitic form . • Addition of carbon improves control of arch wire spring back properties . • Small amount of impurities disrupt the matrices ( 0,N,&C) • Copper - < 5% , Chromium O .3%.(cu NiTi)
  11. 11. CLASSIFICATION OF NiTi WIRES – • In 1992 water’s review classified it into three groups – Group I- Alloys with TTR bet. The room temp. & body temp. ( martensitic active alloys) Group II - TTR below the room temp. (austenitic) Group III - TTR close to body temp. which by virtue of shape memory effect spring back to their original shape when activated by body heat . Evans & Durning classification – Phase I – Alloys of gold & stainless steel Phase II – Original work hardened Nitinol. Phase III – Predominantly austenitic at room temp. with TTR below the intraoral temp. Phase IV – Thermodynamic or active martensitic alloys .
  12. 12. • In this alloys the TTR is set close to the intraoral temp. They have a great working range at room temp. because they exist in a mixed or rhobohedral phase at room temp. so they maintain the permanent deformation . • Once exposed to higher intra oral temp. the martensite form will be gradually converted into austenite with a recovery of ideal preset arch form with an increased force delivery. Eg .Cu NiTi . • Phase V – Graded thermodynamic – • Commercial Nitinol ortho. Wires contains 1.6 % Cobol to modify the tranisition temp. & mechanical properties • Shape memory phenomenon of NiTi alloys was investi. By Andreasen & Barret in 1973 that resisted permanent deformation .
  13. 13. • Forces developed as a result of contraction of pre stretched .O2O NiTi wire when heated to room temp. force ranging from 1.5 to 5 pounds is generated which aids in space closure . • Hence NiTi requires fewer arch wire changes & less chair side time & shortens treatment time required to accomplish correction of rotation & leveling. • Andreasen & Morrow in1978 performed bending & torsion test with new ADA spec. no. 32 on ortho. Wires to compare NiTi & SS .OI8 round NiTi has stiffness similar to .O14 SS. Until the deflection reaches 35 to 40 * • Comparison of rectangular NiTi & Square SS wires were done ,it was said that permanent set angle of NiTi wires is 5 – 7 * .NiTi is said to exhibit superior characteristic in torsion & stored energy in comparison with SS.
  14. 14. • NiTi wires can be used in cl.1 , cl.2 , cl.3 malocclusions in both extraction & n.ext cases . • Important benefits for NiTi rectangular wires is it can be inserted early in the treatment for rotation, leveling , tipping & torquing • Clinicians have been successful in beginning of the treatment with Rectangular wires .017 X .O25 & .O19 x .O25 which nearly fill the bracket slot , in a few case entire treatment can be done with just one arch wire . • It is ideally suited for use with most pretorqed & preangulated appliance becau.tipping & uprighiting can be initated in early stages of treatment. • Use of nitinol with pretorqued and preangulated brackets require careful monitoring of tooth movement because of wires high elasticity and more continuous force.
  15. 15. CHINESE NiTi:- • At mouth temperature this wire is work hardened martensite and hence does not reply on shape memory characteristics in clinical application. • Its very high springback and low stiffness characteristics have won wide clinical acceptance. • Chinese NiTi alloy wires was originally developed by Dr.Hua Cheng Tien and colleagues at research institute for non-ferrous metal in Beijing china in 1978. • Chinese NiTi wires posses super elasticity and shape memory. The possible use of chinese NiTi are many in that it offers low siffness and high spring back for tooth alignment. • High range of action of spring back chinese NiTi is applicable where large defection for uprighting, labial and lingual movements is needed.
  16. 16. • super elasticity among various NiTi wires is seen. • A flag shaped curve is formed when the stress deforms the alloy wire, inducing the martensite stage of transformation. In body temperature the alloy is easily transformed to martensite state in the mouth.The wire becomes activated thus using the shape memory effect. • Ex: Chinese NiTi • Burstone in 1985 – chinese Ni-Ti - Properties. • The wire has spring back that of 4.4 times that comparable stainless steel wire and is 1.6 that of NiTi. – 5mm span cantilever test.
  17. 17. • At 80 degrees of activation the average stiffness of chinese NiTi wire is 73% that stainless steel wire and 36% of NiTi wire. • A significant design feature for constant force application is seen. • The load deformation rate at small activations is considerably higher than that at large activations. • Chinese NiTi wire is highly suitable if low stiffness is required and large deflections are needed. • Higher stiffness at small activations make it more effective than wires of traditional alloys.
  18. 18. JAPANESE NICKEL TITANIUM ALLOYS:- • In 1978 Furu Kawa electric company of Japan produced Japanese NiTi alloy possessing all there properties (excellent spring back, shape memory and super elasticity). • Honma and takei have reported on martenstic temperature range changes in relation to the electrical resistance present in the NiTi alloy. Heat treatment was made to study the effect of temperature and time on super elasticity of the japanese NiTi alloy wire. • Up to 500o C in the linear portion, elastic deformation was indicted and the super elasticity level was lowered.
  19. 19. • Individualized force can be preformed in an arch wire of same diameter without fabrication of any loops. • It is possible to modify the amount of orthodontic force in an individualized segment of arch wire. Ex: by applying controlled heat with adequate temperature and time on the anterior segment of arch wire, the amount of force within anterior segment can be increased & posterior arch wires are not disturbed. Arch wire charact: • Japanese NiTi alloy wire exhibit superelastic properties indicating an area of definite amount of stress in spite of changes in strain rate. • Three point bending tests indicate that Nitinol wire provides a light force and a lesser amount of permanent deformation. • They possesses super elastic properties whereby the load deflection decreases.
  20. 20. • The relationship between the temperature and time of the heat treatment of the japanese NiTi alloy wire optimizes the super elastic properties of the alloy. It delivers a relatively constant force for a long period of time. NiTi in cross bite correction: Progressive first order offsets in the buccal segment of nitinol wire so that each tooth will be loaded in approximately equal amounts and then expands and contracts the two arch wires opposite the direction of crossbite. It produce a direction of force having a low load deflection rate that is more desirable that cross elastics.
  21. 21. Uprighting the impacted canines:- • Uprighting of impacted canines by the use of couple or torque in the second order . Torque is accomplished by inserting an auxillary nitinol wire into the bracket slot of canine. • This in turn produces a tipping action above the bracket and produces an uprighting force on the canine roots. • Also used as a sectional arch for bringing lingually displaced canines into position.
  22. 22. Opening the bite: • For opening the bite either by intruding the maxillary and mandibular anterior segments or by extruding the posterior segments. • For opening a deep bite & for complete anterior maxillary retraction one can place first order steps in the anterior segment to produce intruding forces on the anterior segment and extruding forces on the premolars and molars. NiTi in Beggs: A.J.Wilcock S.S wires are replaced by NiTi wires. • Alloy of NiTi with its flexibility and resistance to deformation hence facilitates and simplifies begg treatment by replacing looped stainles steel arch wires with plain arch wires and also used where Bite opening is not critical.
  23. 23. Use of Nitinol Archwire • Cases with severe crowding 0.16 NiTi arch wires are used. • Anchor bends or tipbends more accentuated when SS is used in compared to NiTi. • Step up bends distal to the lateral brackets aid in intruding the four anterior teeth. • In 25 patients were treated with .016 maxillary and mandibular NiTi arch wires and SS arch wires-Compar.. • Time taken for tooth alignment in NiTi – 42 days,for SS is 49 days. NiTi arches showed 25% faster response for rotation, tipping and leveling when comp.. With SS . • Bite opening responded better to stainless steel arch wires than to NiTi arch wires, because relatively low force level is generated by NiTi than SS arch wires.
  24. 24. • Time for space opening with NiTi – 44 days, SS was 53 days. Limitations: • NiTi wires when compared to SS – has resistance to take a bend. • Hence the placement of desire in and out bends becomes difficult – It will rapidly break when bent over a sharp edge. Closing loops in particular are not practical for nitinol wire. • NiTi cannot be soldered or successfully welded to itself without annealing the wire and because the bending of tie back hooks entails a high risk of failure, crimpable hooks and stops a successful alternative. • Use of auxillary retraction forces will have the effect of opening the patient’s posterior bite, can be managed by remove the auxillary force mechanism at the completion of treatment and going to conventional posterior bite closing mechanics with SS arch wires.
  25. 25. Neo Sentalloy: • New super elastic NiTi rectangular wire can be used with extremely light force in the initial phase of treatment. • Three point bending and torque tests have shown the wire to exert light, continuous force regardless of deflection or wire size. • Three dimensional tooth control can be effected at the same time as horizontal and vertical leveling and root torquing. • They also provide greater arch wire flexibility and less patient discomfort than other NiTi wires.
  26. 26. Copper NiTi: • The NiTi in the alloy has been partially replaced by copper to produce ternary alloys. • Copper NiTi at the room temperature is in martensitic phase, it is possible to introduce relatively sharp bends on the wire. The original archform will be regained simply be heating the wire at a temperature above austenitic phase (i.e) has TTR of 40 degrees. • Forces exerted on the dento alveolar structure are remarkably low therefore the alloy is recommended for the treatment of patients with periodontal problems. • Disadvantage is the low stiffness of this wire of not allowing for complete dental alignment or full control of transverse dimensions.
  27. 27. Nickel Hypersensitivity : • Nickel is one of the most common causes of allergic contact dermatitis. • Nickel is a strong biological sensitizer and consquently may induce a delayed hypersensitivity reaction (type IV immune response). It is estimated that 4.5 % of the population have a hyper senstitivity to nickel with a higher prevalence in females. • This delayed allergic reaction can be verified by “Epi cutaneous test”, this is performed by taping to skin the suspected substance ,dissloved in an adequate medium like water, alcohol. After a period of time – 48 hours erthmatous reactions are evaluated according to a scale ranking.
  28. 28. RECENT DEVELOPMENTS: • NiTi wires with epoxy and nitride coatings have been recently marketed. • Nitride coatings were originally added to orthodontics wires to aid in surface hardending, epoxy electro coating provides improved esthetics. • Coated wires may be an important addition to the orthodontic armamentarium if corrosion can be inhibited and nickel release into the oral cavity can be prevented. • Epoxy coated NiTi exhibited low corrosive potential as compared to the regular NiTi. • NiTi – arch wires with ion-implanted surfaces to obtain reduced bracket friction have been introduced.
  29. 29. Conclusion: • Findings indicate that nitinol wires do facilitate and simplify Begg mechanotherapy, because unraveling and leveling for attaining good tooth alignment occurs faster than stainless steel looped arches & treatment time diminished. • They provide a good spring back effect and flexibility, which allows for large elastic deflections, with low forces. • Patient response is good and less discomfort is reported.
  30. 30. BIBLIOGRAPHY Contemporary orthodontics – Profit Orthodontics – Graber Clinical Handling of Dental materials Orthodontic Materials – William. A . Brantley A.J.O – 1990 sep,1995 jul,1998 aug.
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