Let It Cook!
One of the primary advantages of additional interbracket distance afforded by the single-wing brackets is that larger-diameter, stiffer archwires can be placed earlier in treatment. When the interbracket distance is increased, the relative stiffness of the wire between the brackets is reduced by a factor of the length of the wire (L) to the third power (1/L3), making the wire more flexible and easier to engage.
When the initial flexible archwire is placed in a crowded arch, this added distance between the brackets allows the wire to be deflected without creating a permanent set in the wire. The advantages of this include (1) a reduction in patient discomfort, (2) the ability to begin with a larger-diameter archwire, and (3) the use of fewer total archwires.
To use these advantages to their fullest potential, the archwire must be given time to fully express the forces and moments within. As an archwire is engaged in the bracket slots, any deflection or distortion (nonpermanent) of the wire is stored within the wire (Fig 13-1). Depending on the properties of the wire–elastic modulus, resiliency, and springback—this stored energy is transferred to the teeth via the brackets, and the teeth move, resulting in a dissipation of the wire’s forces (Fig 13-2). The process takes time, a requirement that is conveyed in the phrase, “let it cook.” This maxim implies that orthodontists must not be too hasty in changing archwires. Rather, they should allow the time necessary for the archwire to fully express its forces and become passive in the brackets before proceeding to the next archwire.
Fig 13-1 Occlusal views, extraction case. (a) Pretreatment maxilla. (b) Six months: View showing 0.016-inch stainless steel archwire, elimination of rotations, and retraction of the canines.
Fig 13-2 Occlusal views, extraction case. (a) Mandible showing initial placement of brackets and 0.016-inch nickel-titanium archwire. (b) Four months: Mandible with the same archwire.
As discussed in detail in principle 10, most nonextraction treatment will require a sequence of no more than three archwires per arch. In the maxillary arch, placement of the first flexible archwire (0.016-inch nickel-titanium) will eliminate most rotations in 1 to 3 months (Fig 13-3). The second archwire is often 0.016-inch stainless steel, curved, heat treated, and tied back. This second archwire will improve the leveling and alignment. It will remain in place for 2 to 4 months. The third and final archwire, a 0.017 × 0.025-inch stainless steel wire, is then placed after approximately 6 months of active treatment.
Fig 13-3 Occlusal views, nonextraction case. (a) Pretreatment. (b) Three months: Maxillary 0.017 × 0.025-inch multistranded stainless steel archwire showing deflection labiolingually. (c) Five months: Maxillary 0.016-inch stainless steel archwire is used.
Early placement of the final wire has many advantages. It allows more time for the final wire (0.0175 × 0.0250-inch stainless steel) to express itself, particularly in the final detailing stage. It is critical that this archwire be bent to exact standards, because the torques, angulations, and offsets built into the brackets, as well as the curve and shape of this wire, will be almost fully expressed on the teeth.
Because the archwire is tied back, the maxillary teeth now become a single unit, rather than 12 to 14 individual teeth. The force of a facebow and/or elastics is now applied to this one unit, the entire maxillary arch. Because the teeth are moved gently and quickly to one position and then held firmly throughout the remaining treatment, there is no continuous movement or jiggling of teeth. Consequently, root resorption has not been an issue in the Alexander Discipline.
Because of the increased interbracket space and rotational wings, rotations can be eliminated, spaces closed, and arches leveled, predictably and quickly. Thus, the key principle, especially in nonextraction treatment, is to place the finishing archwire as quickly as possible and then let it cook. Figure />