Mechanical Properties of Various Archwires and Their Clinical Application in the PASS System

Clinical studies have revealed that maxillary molar mesialization could occur in physiological drifting and during orthodontic treatment. The straight wire appliance (SWA) using a continuous wire made of shape memory alloy (SMA) might result in an undesired maxillary molar mesialization or an anchorage loss in the initial aligning stage. Recent findings suggest that a maxillary molar tube including a –25° auxiliary tube might minimize this anchorage loss. It was theorized that this auxiliary tube serving as a reserved v bend could preclude the possibility of molar mesialization in SWA. This chapter introduces the clinical implications of this new appliance, called the PASS system. The archwire sequence for the PASS is similar to that of SWA, except that the –25° auxiliary tube is only used for SMA at the initial stage. The mechanical properties of various material types of archwires associated with the PASS system are reviewed. Analysis was completed on the interactions between the archwire and the PASS system, such as the stress-strain relationship and frictional forces. Both low-friction and distalization forces are revealed from our data.