INTRODUCTION:

The desirable properties of an orthodontic wire depend on the requirements set by mechanotherapy at a speciﬁc treatment stage, and thus, selection of the appropriate wire is often complex. Criteria such as the degree of torque control, the desired load-deﬂection ratio, and the need for a speciﬁed elastic or plastic zone must be taken into account in the process.

In general, three factors determine the rigidity of the wire: the length, the cross-section, and the elastic modulus of the alloy.

The traditional method to modify the rigidity consists of varying the dimensions of the wire by engaging incrementally larger cross-section wires in the slot, or adjusting the conﬁguration of the loops. The use of materials with a low elastic modulus, such as titanium alloys, was introduced as an alternative way to advance treatment, namely, ‘variable modulus orthodontics’ (Goldberg et al. , 1977 ; Burstone and Goldberg, 1979, 1980 ; Goldberg and Burstone, 1979; Burstone, 1981). The use of alloys with different rigidities provides a range of force during deactivation, which is independent of the wire cross-section. Orthodontic wires are made from different alloys and now offer alternative sequences of wire usage during all phases of orthodontic treatment. It is at present possible to match phases of treatment with orthodontic wires according to the mechanical properties of the wire. On this criteria, the selection of orthodontic wire should be based not only on the transverse section of the wire, but also on an understanding of the deactivation characteristics of the wire required for different phases of the orthodontic treatment.^[1–3]

The beta-titanium (b-Ti) wires are of titanium molybdenum alloys . These investigators envisioned this alloy for orthodontic use after recognizing few advantages such as (1) elastic modulus below stain steel and near to nickel-titanium (NiTi) conventional alloy, (2) excellent formability, (3) weldability, and (4) low potential for hypersensitivity.^[4,5]However, the use of b-Ti wire has disadvantages such as (1) high surface roughness, which increases friction at the wire-bracket interface during the wire sliding process, and (2) susceptibility to fracture during bending.^[6]moreover To reduce surface roughness, a nitrogen ion implantation technique has been used. However, some authors have questioned the effectiveness of this process in the reduction of friction. ^[7-8]Initially, b-Ti wires were used for specific application in a segmented arch technique for making of the retraction loops. Recently, b-Ti wires have been widely used in the construction of an intrusion arch and an uprighting molar spring. Also, b-Ti wire is useful in cantilevers for intrusion or extrusion of the teeth. All of these applications make it possible to individualist tooth movements and still provide a controlled force system all over. Mechanical properties of beta-titanium wires

Initially, β-Ti wires were used for specific application in a segmented arch technique for making of retraction loops. Recently, β-Ti wires have been used in the construction of an intrusion arch^[9] and an uprighting molar spring. Also, β-Ti wire is useful in cantilevers for intrusion or extrusion of teeth. All of these applications make it possible to individualize tooth movement and still provide a controlled force system. In 1992, Hilgers^[10] described the pendulum appliance for distal molar movement performed with 0.032-inch β-Ti wire. This wire was chosen because it had stiffness of about one-half that of stainless steel. The pendulum springs increased the working range for molar distillation without permanent deformation, and the amount of force used was less than that of steel for the same activation. For the past 20 years, Ormco (Glendora, Calif) has had the exclusive patent on β-Ti wire, which was sold as TMA (titanium molybdenum alloy). However, since 2000, other companies have introduced β-Ti wires.^{[11, 12 13}]. A major concern is now activation-deactivation behaviour of each of the new β-Ti wires being marketed. The mechanical properties of other wires from different alloys have been evaluated in several studies.[14, 15]These evaluations represent an important parameter in achieving optimal tooth movement. It is important for orthodontists to have reliable information about the mechanical properties of commercial β-Ti wires.

Relative Stiffness of Beta Titanium Arch Wires :

The number of vendors of beta titanium (TMAy type) wires has recently expanded dramatically. Samples of all the available sizes were obtained from most of the major beta titanium vendors. Three new square sizes are now also available. A total of 34 wire samples were tested for stiffness using the new ADA three-point wire-testing jig. Results show that not all beta titanium wires have the same stiffness.1 The range of variation was from small to large depending on the nominal wire size.2There was also a spread of 1.67% to 4.27% in the standard deviation of the average stiffness from vendor to vendor.3 Burstone’s Vari-modulus of elasticity is discussed along with how the properties of beta titanium could be integrated with his concepts. Strategies for using the new sizes of rectangular beta titanium wires for torque are discussed, including their use as working wires and finishing wires.4 Beta titanium wires cannot be soldered.5 Hooks, springs, and other attachments made out of another piece of beta titanium can be spot welded with good success.6 These comparisons suggest that beta titanium wires can often be an effective replacement for stainless steel final finishing wires.

Beta Titanium wires are now readily available from multiple vendors under various brand names. Beta Titanium is now also available in 0.018 inch 3 0.018 inch and 0.021 inch 3 0.021 inch sizes. Beta titanium is available with a wider range of stiffness choices. Beta titanium has become a more useful class of wires for both working and finishing wires. In a 0.022 inch-slot appliance, beta titanium can replace stainless steel as a finishing wire.^[16,17]

Plastic Deformation:

Beta-titanium wires have been utilised in orthodontics because of their favourable characteristics such as low stiffness, excellent formability, and efficient working range for tooth movement. In fact, the only major disadvantage of this wire seems to be its cost. Initially used for springs and loops with segmented arches, b- Ti wires have become popular in all areas of orthodontic treatment. With an elastic modulus be-tween those of nickel-titanium and stainless steel alloys, the b-Ti wires are very efficient in situations requiring individual tooth movement. The pendulum appliance is a good example of the successful use of b-Ti wire. Although 0.032-inch stainless steel wire exhibits high stiffness, reduced spring back, and forces incompatible with optimum biological dental movement, b-Ti wire of the same size affords optimal force to promote molar distillation with normal tissue reaction. Cantilever and three-piece arch wires are other useful clinical applications of b-Ti wire. Presently, no ideal orthodontic wire is available. The ideal situation for the orthodontist is to understand the specific characteristics of each orthodontic wire and to be aware of the appropriate uses of each type of alloy. Because of the multistage processing required for b-Ti wire, few companies in the world manufacture this titanium alloy. It is important that the quality control process of b-Ti wire and other orthodontic wires be strictly maintained. All companies that market these wires should provide their activation-deactivation force range. Despite the inherent excellent formability of b-Ti wire, this wire processing can be problematic because of the reactivity of titanium that can result in some batches of b-Ti wire being susceptible to fracture during clinical manipulation.^[18] Laboratory tests do not necessarily reflect the clinical situation, but these tests provide a basis for comparison of different wires and are used in many studies in the literature.^[19-20] Although this in vitro test was designed to simulate a deflection inducing tooth movement, b-Ti wires showed plastic deformation during activation.

CONCLUSION:

Extensive use of Ti and its alloys as biomaterials is ubiquitous owing to their specific characteristics especially higher biocompatibility, superior corrosion behaviour and lower modulus of elasticity compared to other conventional biomaterials such as stainless steels, cobalt-based alloys, polymers, and composite materials. Novel β-Ti alloys free from toxic alloying elements and with relatively low elastic modulus have recently been developed and received great attention in the biomaterial scientists’ community. The merit of increasing use of β-Ti alloys as implantable materials lies, among other factors, in their low modulus of elasticity as well as their other significant properties. In order to obtain lower elastic modulus, recently, the researchers of biomedical Ti alloys focused on β-type Ti alloys that contain non-toxic elements such as Nb, Zr, Ta, Mo, Sn, Cr, Fe, etc. There is an important role of precipitates, texture orientation and porosity obtained, to develop desirable bio-compatible Young’s modulus, through various processing techniques.

The literature reveals that serious attempts from researchers have been made towards improving function and lifetime of an implant in the human body by reducing significantly the elastic modulus of the biomaterial .The field of biomedical titanium materials is one of the fastest growing areas of research for the contemporary materials scientist and engineers, as these materials can enhance the fineness and longevity of human life, and ameliorate patient health care. The development of titanium materials for biomedical applications is currently an area of active research around the globe and many serious attempts are made every year to improve different desirable requirements in this field. ^[21-22]

REFERENCES:

1. Gurgel JA, Kerr S, Powers JM, Le Crone V. Force-Deflection properties of superelastic Nickel-Titanium Archwires. Am J Orthod Dentofacial Orthop. 2001;120:378–382.

2. McLaughlin R, Bennett J, Trevisi H. Systemized Orthodontic Treatment Mechanics. St Louis, Mo: Mosby; 2001:93–123 (Chapter 5).

3. Proffit WR, Fildes HW, Sarver DM. Mechanical Principles in Orthodontics Force Control: Contemporary Orthodontics. 4th ed. St Louis, Mo: Mosby; 2007:289–316 (Chapter 10).

4. Goldberg AJ, Burstone CJ. An evaluation of beta titanium alloys for use in orthodontic appliances. J Dent Res. 1979; 58:593–600.

5. Nelson KR, Burstone CJ, Goldberg AJ. Optimal welding of b titanium orthodontic wires. Am J Orthod Dentofacial Orthop. 1987;92:213–219.

6. Kusy RP, Whitley JQ. Thermal and mechanical characteristics of stainless steel, titanium-molybdenum, and nickeltitanium archwires. Am J Orthod Dentofacial Orthop. 2007; 131:229–237.

7. Tecco S, Tete` S, Festa F. Friction between archwires of different sizes, cross-section and alloy and brackets ligated with low-friction or conventional ligatures. Angle Orthod. 2009; 79: 111–116.

8. Kusy RP, Stush AM. Geometric and material parameters of the nickel-titanium and the beta-titanium orthodontic wire alloy. Dent Mater. 1987;3:207–217.

9. Kusy RP, Tobin EJ, Whitley JQ, Sioshansi P. Frictional coefficients of ion-implanted alumina against ion-implanted beta titanium in the low load, low velocity, single pass regime. Dent Mater. 1992;8:167–172.

10. Burstone CJ, Goldberg AJ. Beta titanium: a new orthodontic alloy. Am J Orthod. 1980;77:121–132.

11. Kapila S, Sachdeva R. Mechanical properties and clinical applications of orthodontic wires. Am J Orthod Dentofacial Orthop. 1989;96:100–109.

12. Kula K, Phillipis C, Gilbilaro A, Proffit WR. Effect of ion implantation of TMA archwires on the rate of orthodontic sliding space closure. Am J Orthod Dentofacial Orthop. 1998; 114:577–581.

13. Eliades T, Bourauel C. Intraoral aging of orthodontic materials: the picture we miss and its clinical relevance. Am J Orthod Dentofacial Orthop. 2005;127:403–412.

14. Verstrynge A, Humbeeck JV, Willems G. In-vitro evaluation of the material characteristics of stainless steel and betatitanium orthodontic wires. Am J Orthod Dentofacial Orthop. 2006; 130: 460–470.

15. Burstone CJ, Goldberg AJ. Beta titanium: a new orthodontic alloy.Am J Orthod. 1980;77:121–132.

16. Andreasen GF, Hilleman TB. An evaluation of 55 cobalt substituted Nitinol wire for use in orthodontics. J Am Dent Assoc. 1971;82:1373–1375.

17. Goldberg J, Burstone C. An evaluation of beta titanium alloys foruse in orthodontic appliances. J Dent Res. 1979;58:593–600.

18. Relative Stiffness of Beta Titanium Archwires 269 Angle Orthodontist, Vol 73, No 3, 2003

19. Burstone CJ. Variable-modulus orthodontics. Am J Orthod. 1981;80:81–16.

20. 20. Burstone CJ. Welding of TMA wire—clinical applications. J Clin Orthod. 1987;21:609–614.

21. Nelson KR, Burstone CJ, Goldberg AJ. Optimal welding of beta titanium archwires. Am J Orthod Dentofacial Orthop. 1987; 92:213–219.

22. Brantley WA, Eliades T. Orthodontic wires. In: Brantley WA, Eliades T, eds. Orthodontics Materials—Scientific and Clinical Aspects. New York, NY: Thieme; 2001:78–103.

Received on 20.06.2016 Modified on 27.06.2016

Research J. Pharm. and Tech 2016; 9(11):2020-2022.

DOI: 10.5958/0974-360X.2016.00412.1