3Orthodontic Archwires Key considerations 1-Stiffness ( Spring rate): magnitude of force at a given deflection?2-Springback ( range of action): Will it deflect that far?3-Strength: The highest amount of force delivered by the wire.
4Factors affects the force wire exerts: ThicknessLengthMaterial
51-Effect of thickness round wires 1420Stiffness is proportional to (diameter)4Diameter StiffnessSmall increment in size= big increment in force
6Effect of thickness Rectangular wires Stiffness is proportional to w x h3Wh3
7Stiffness of 19x25 > 18x2519x2518x25KEY POINT – Full engagement is as important as low friction, regarding treatment efficiencyElastic ligature OR metal clip, fails to give FULL ENGAGEMENT → Poor Control and Less Effective TorqueThe ligature or clip becomes distorted, the Damon slide cannot be distorted, therefore “full engagement” is always possible
82-Effect of Length Stiffness is inversely proportional to L3 Span Stiffness6 mm5 mm4 mm3 mm2 mmCritical areas: smallest interbracket span
13The Chronological Development of Archwires ( Evans,1996) Phase l : Gold and Stainless steel ( ’s)Phase ll: Stabilized NiTi “ Stabilized Martensitic” ( 1970’s)Phase lll : Superelastic NiTi “ Active Austenitic” ( 1980’s)Phase lV : Thermodynamic NiTi “Active Martensitic”( Early 1990’s)Phase V : Graded thermodynamic ( Late 1990’s)
14Stainless steel archwires SS was developed in World War l, only in the 1940’s was introduced to orthodontics.Very rigid wire, good for space closure but not for alignment .This was solved by: Wire bending and loops, the use of multistrand SS.Multistrand SS has 20% of the stiffness and twice as range as SS.
15Development of the High Technology Alloys -NiTi alloys were developed in early1960’s for space programs by W.Buehler in USA.-This metal was called “ The Memory Metal”-Very complex structure and mechanical behavior.-Mechanical properties and thermal behavior are highly affected by composition, machining characteristics and heat treatment during manufacturing.
17NiTi Transformation Austenite Martensite High TemperatureTTRMartensiteLow TemperatureIn response to temp variation, the crystal structure undergoes deformations in which the molecular arrangement is modified without a change of atomic composition.
21Properties of different phases Martensite NiTiAustenite NiTiHexagonalCubicCrystalline structure31 GPa98 GPaElastic Modulus138 MPa379 MPaYield Strength
22NiTi Alloys-Martensitic NiTi is responsible for the lowering of the delivery force.-Austenitic NiTi is responsible for elasticity.-Modulus of elasticity of Austenitic NiTi is 3-4 times than Martensitic NiTi.
23Transitional Transformation Range (TTR) 100 %Austenite0 %Temperature
24NiTi Alloys Development Stage l : Nitinol “Stabilized Martensetic”(1970’s)Stage ll : Superelastic NiTi “ Active Austenite”( Mid 1980’s)Stage lll: Thermal Wires “ Active Martensite”(Early 1990’s)Stage lV: Development of Copper NiTi “CuNiTi”(Late 1990’s)
25Stage l: Stabilized Martensetic “ Nitinol” -Composed of 55 Ni:45 Ti-Introduced to Orthodontic by Dr.Andreasen mid 1970’s.-No shape memory or superelasticity.-Deformation occurring during processing( work hardening) suppress SME-It is passive “ Stabilized” alloy
26Cont. Stabilized Martensitic wires ( Nitinol) Advantages:-Low stiffness( 20% of SS)-Springy( range 2.5 as SS)-Light, continuous and linear force delivery.S.S.StressNiTiStrain
27Stage ll: Superelastic NiTi (Japanese or Chinese Wires) -Developed by Dr.Burstone and Muira mid 1980’s-TTR below room temperature ( Cr, Nb additions)-Active Austenitic at room temperature-Af is lower than oral temperature so no thermoelastic properties.
28Superelasticity -Occurs above TTR -Wire initially austenitic -Only stressed ares transform to martensite Stress Induced Martensitic Transformation ( SIMT).-Superelasticity only exists when both phases of metal are present.-Delivery of forces will be lowered in the needed areas only.Muira et al. AJODO 90: 1-10; 1986
29Advantages of Superelastic NiTi archwires -Excellent springback (4-5 of SS)-Constant forces over large wire deflectionActivationDeactivation
30SE NiTi wires ??-The slope of the graph starts with a slope three times that of Nitinol .-2 mm deflection is necessary for the formation of SIM in austenitic wires- Austenitic alloys only behave superelastically in very severe crowding cases.Muira et al. AJODO 90: 1-10; 1986
31Effect of heat treatment on SE NiTi deformation Muira et al. AJODO 1986
32Stage lll: Thermal Wires (Martensitic Active) -For the memory property to be clinically detectable, Af has to be slightly below oral temperature.-For every 150 ppm variation in composition, a 1°C change in TTR occurs.-Mainly Martensitic at room temperature-softish, ductile with shape memoryMouth TempAUSTENIRoom Temp-Austenitic with SIMT at 37˚ C-Deliver 25-30% of the force of SE NiTi and greater range of action.
33Thermal Wires ( Af=37°) Stress Deflection Iijima et al. Dental Material 18 ( 2002) 88-93
34Thermal NiTi-The main benefit is that these wires generate lower forces at mouth temperature than the corresponding size of non-thermal wire.-Allow earlier progression to large dimension wires e.g. 18x25,20x20.-Allow control amount of force delivered to posterior and anterior teeth.
35-Allow more severely displaced brackets to be engaged by chilling the wire locally.
37But Thermal wires: -More expensive. -Very sensitive to manufacturing process.-Offer little advantages in small diameters.-May give almost no force in the unloading curve if they are not formulated correctly, so may be inefficient.-Very sensitive to temperature changes in the oral cavity.
38Effect of temperature changes on thermal archwires during activation T.Melling and J.Odegaard AJODO 2001; 119:
39Effect of temperature changes on thermal archwires during deactivation T.Melling and J.Odegard AJODO 2001; 119:
40Effect of repeated short-term exposure to ice cream on torsional stiffness of thermal archwires T.Melling and J.Odegaard Angle Orthod 1998; 68:
41Stage lV: Development of Copper NiTi “’ CuNiTi” -5% Copper, % Chromium-The addition of Cu:Increase strength, reduce energy loss and allows greater control of TTR.-Long force plateau-Better manufacturing consistency-Tolerate repeated loading better-3 Types 27°, 35°, 40°.CuNiTi 40 °CuNiTi 35 °CuNiTi 27°StressDeflection
42CuNiTi 27˚ -Af at 27˚. -Superelastic wire In patients : -with average or high pain threshold.-Normal periodontal health.-where rapid tooth movement is required
43CuNiTi 35˚ -Af at 35˚. -Thermoelastic wire In patients : -with low to normal pain threshold.-Normal to compromised periodontal health.-where relative low forces are required
44CuNiTi 40˚ -Af at 40˚. -Thermoelastic wire In patients : -who are sensitive to pain .-with compromised periodontal conditions.Good as initial rectangular wire.
45Stage V: Graded Thermodynamic NiTi archwires -Deliver different amount of force at different areas of the dentition according to the surface area of periodontium.- Controlled by specifying different TTR.-80 gm of force anteriorly and 300 gm posteriorly.
46Beta-Titanium Alloy ( TMA) -Contains 80% Ti, 11% Mo, 7% Zr and 4% Sn.-Medium stiffness ( 1/3 of SS and twice of (Nitinol)-Produce gentler linear forces than SS-Has more range and greater springback-Has rough surface
56“Clinical trials” -Superelastic NiTi vs Stabilized NiTi O’Brien et al , EJO 12 ( 1990)-Superelastic NiTi vs multistrand steelWest. Jones & Newcombe , AJODO 108 (1995)-Thermal NiTi vs graded force NiTi vs multistrand steelEvans, jones & Newcombe, AJODO 114 ( 1998) 32-39-Superelastic NiTi vs ion implanted NiTi vs multistrand steelCobb et al, clin orth Res 1 ( 1998 ) 12-19-Does the transition temperature of CuNiTi archwires affect the amount of tooth movement during alignment?Dalstra & Melsen Orthd. Craniof. Res. 7 (2004) 21-25
57Results of clinical trials Rates of tooth movement hardly affected by type of wire, any difference no clinically significant.Pain experience not affected.Results are related to the individual variations in metabolic response within the periodontal ligaments and bone.
582-Archwires Sequence-A recent RCT in Manchester by Mandall N. et al. EJO in press-Three randomly allocated archwire sequence in terms of : efficiency, patient discomfort, root resorption.-A=16 NiTi, 18x25 NiTi ( n=41)-B=16 NiTi, 16 SS, 20 SS ( n= 44)-C=16x22 CuNiTi, 19x25 CuNiTi ( n=44)The endpoint was the passive placement of 19x25 SS for at least 4 weeks
59Results-No statistical difference for patient discomfort at hours 4 hrs, 24 hrs, 3 days and 1 week.-Root resorption was not statistically significant with average root resorpion between mm
60Time required to reach the working archwire No of visitsTime ( Months)Archwire sequence5.7 ( 2.1)5.4 ( 2.1)6.8 ( 2.5)6.7 ( 3.5)A LowerUpper7.5 ( 1.9)7.1 ( 2.6)9.3 ( 4.4)7.9 ( 3.5)B Lower6.4 ( 2.2)5.9 ( 2.8)8.3 ( 4.2)7.1 ( 3.4)C Lower
61Can Thermal Rectangular wires be used as first aligning archwires?
62First aligning archwires -Mild crowding: 15 Multistrand SS14 Nitinol18 Thermal(20x20 CuNiTi)-Moderate crowding: 16 Thermal14 SE NiTi-Severe crowding: 14 Thermal12 SE NiTi
63When to move to the next wire? -When the next wire can be engaged in all the slots-Look at the worst tooth to decide-Watch for rotation particularly-Give enough time for the wire to work especially the new high technology wires
72Finishing wires Options for close-fitting archwires (21x25): -Steel : Too stiff-NiTi: Not adjustablePoor torqueing-B-Titanium: Ideal stiffnessused to provide root paralleling
73Self-Ligating Brackets? KEY POINT – The high friction and binding that exists with ACTIVE or CONVENTIONAL systemsSales Tools15x D2/D3 model with ligatureCompetitor brackets on wireSelf- LigationLow Force, Low FrictionActive Ligation High Force, High Friction
74What Are The Limitations Of Conventional or Active Ligation? Poor Control – Less Effective TorqueElastic Ligature or Metal Clip19x2519x25KEY POINT – Full engagement is as important as low friction, regarding treatment efficiencyElastic ligature OR metal clip, fails to give FULL ENGAGEMENT → Poor Control and Less Effective TorqueThe ligature or clip becomes distorted, the Damon slide cannot be distorted, therefore “full engagement” is always possibleDamon 4 Solid WallsConventional Wire Out Of Slot
75Self-Ligating Brackets -Friction is increased 500% over Damon, if using a conventional bracket with steel ligatures-Friction is increased 1500% over Damon, if using an elastic ligatureThere are 70 grams of frictional force, per tooth, when using an elastic ligatureEJO 2004 KhandyKEY POINT -High Force will produceMore patient discomfort – Periodontal ligament becomes crushedLonger treatment times - Periodontal ligament becomes crushed – less blood flow – slower tooth movementMore anchorage required (to be discussed later in presentation)High forces WILL NOT work with the patients biology. Teeth are pushed into their new position rather than utilizing the light forces which exist with the Damon System, allowing a more natural (biological) tooth position
76Frictional Resistance N/m Sims, Birnie and Waters (1993)
78Archwires in Self-Ligating brackets -High Technology Wires should be used( e.g. CuNiTi).-Smaller dimensions ( Start with 14)-Give 10 weeks appointment interval.-Use 14x25 CuNiTi as second aligning archwires to correct rotations.- Then 18x25 CuNiTi to express additional torque.