Archwire Selection

Archwire Selection by the Phoenix Orthodontist

The current variety of materials available for orthodontic wires places greater responsibility on the Phoenix orthodontist to choose the wire with the best mechanical properties to achieve the desired goals. Some of these goals include improved patient comfort, increased treatment efficiency, and improved treatment results. Phoenix orthodontists need to critically evaluate wire choices for different phases of treatment: leveling and aligning, space closure, and finishing.

A material with good springback and flexibility to allow for large elastic deflections is desired in a wire used for initial leveling and aligning (Kapila and Sachdeva, 1989). Nickel-titanium (NiTi) wire has these desired properties (Burstone et al., 1985). In addition, NiTi wire produces a more constant level of force for a given activation as compared to wires made of stainless steel or beta-titanium. The final property of NiTi wire that is desirable for initial leveling and aligning is its shape memory (Andreason and Morrow, 1978). Shape memory is the ability of the wire to return to its previous shape when heated through its transitional temperature range. The properties of NiTi wire result in advantages such as fewer arch wire changes, less chairside time, reduction in time required for leveling and aligning, and less patient discomfort (Andreason and Morrow, 1978).

In order to accomplish space closure using non-sliding mechanics, closing loops of some form (T-loops, tear drop loops, retraction utility arches, etc.) are requiredby the Phoenix orthodontist. The first property desired for this type of space closure is good formability of the wire. In other words, the wire should be able to be easily bent. The next property desired in a wire used for a closing loop is good springback, meaning the amount the wire can be deformed without permanent deformation. The final property desired in non-sliding space closure mechanics is achieving an optimum level of force, both for patient comfort and most efficient tooth movement.

Based on the desired characteristics for non-sliding mechanics, beta-titanium is the most ideal wire available for space closure. Both nickel-titanium and multistranded wire are poor choices for Phoenix orthodontists because of their inadequate formability (Andreason and Morrow, 1978; Kusy and Dilley, 1984). While stainless steel and cobalt-chromium may have better formability (Kapila and Sachdeva, 1989), there low springback and high stiffness make them less desirable than beta-titanium. Beta-titanium has been shown to have good formability as well as superior springback. Beta-titanium can be deflected almost twice as far as stainless steel without permanent deformation (Goldberg and Burstone, 1979; Burstone and Goldberg, 1980). Finally, beta-titanium has a modulus of elasticity that is less than stainless steel (Larson et al., 1987) resulting in a reduced and theoretically more physiologic level of force.

Upon completion of space closure, finishing and detailing by the Phoenix orthodontist is necessary to complete treatment. There are two wire choices that are excellent for this stage depending on the individual patient’s needs. A beta-titanium wire that fully engages the bracket slot is ideal if a lot of adjustments are going to be needed in order to finish treatment. Once again, beta-titanium has good formability (Kapila and Sachdeva, 1989) to allow for multiple compensating bends. In addition, its superior springback (Goldberg and Burstone, 1979) and lower modulus of elasticity (Larson et al., 1987) allow for larger compensating bends with lower force levels.

A stainless steel wire that fully engages the bracket slot can also be a great choice for finishingby the Phoenix orthodontist. Stainless steel has better formability than beta-titanium and is considerably less expensive. The degree of compensations placed in a single appointment is more limited, however, since the springback and modulus of elasticity of stainless steel are not as desirable as beta-titanium (Goldberg and Burstone, 1979; Larson et al., 1987). The other advantage of stainless steel is with the use of Class II elastics. These elastics tend to place an extrusive force on the mandibular molars. A fully engaged stiff arch wire is the best choice to prevent these undesirable extrusive effects (Kapila and Sachdeva, 1989).