Pass-System Orthodontics 2.73

Molar anchorage loss has been shown to occur during the early stages of alignment with preadjusted appliances.
The most commonly used archwires for initial alignment are made of nickel titanium, which has the elasticity to provide light, continuous forces but cannot accommodate the tipback bends needed to preserve molar anchorage.
Among the methods developed to reinforce anchorage, headgear was once widely used but has not been entirely effective, even in compliant patients.
Temporary anchorage devices (TADs) are more reliable but may be rejected by some patients and can only be placed in sites with optimal bone condition.
The Physiological Anchorage Spee-wire System (PASS)* was designed to optimize natural anchorage preservation while controlling friction and utilizing the elasticity of nickel titanium wires for initial alignment.