18/8 stainless steel wires used in orthodontics are work hardened to increase their strength and stiffness, making them suitable for effective tooth movement. Work hardening involves deforming the metal at room temperature, which increases dislocation density and enhances mechanical properties without the need for heat treatment. This process provides optimal elasticity and resilience required for maintaining consistent orthodontic forces. Unlike annealed or tempered wires, work hardened wires resist permanent deformation and maintain form during treatment. This characteristic is crucial for precise and controlled orthodontic adjustments.

Reference: Contemporary Orthodontics, 6th Edition.