Preadjusted appliance, following the original concept of the Andrews Straight-Wire appliance, became increasingly common in the 1980s. In six phases of treatment, anchorage control, leveling and aligning, overbite control, overjet reduction,
space
closure, and finishing are very effective with using the preadjusted appliances. Space closure is the phase of treatment in which the difference between standard edgewise and preadjusted mechanics is most noticeable. Orthodontists have been able
to
reduce the use of closing loops and, because of the level slot lineup, enjjoy the advantages of sliding mechanics. In 1990, Dr. John C. Bennett and Richard P. McLaughlin introduced the new space closure system, namely. Elastic "tiebacks". They
found an
.019″×.025″working archwire most effective in ap .022″-slot system. Hooks of .024″stainless steel of .028″ brass wire are soldered to the upper and lower archwires. The force required for space closure is delivered by elastic "tiebacks". An
elastic module stretched by 2-3mm(to twice its normal length) usually delivers 0.5-1.5mm of space closure permonth. Group movement and sliding mechanics are combined for gentle, controlled space closure, so that about 0.5mm of incisor retraction
and
0.5mm of mesial molar movement can be seen each month. The tiebacks are replaced every four to six weeks.
By using the elastic "tiebacks", the next two cases were treated during space closure. Even though we found some clinical problems of this mechanics, long treatment time, hard to control of vertical dimension and anchorage, the application method
of
this system is so simple that orthodontists can manage many patients dduring short chair time. But we must apply this mecvhanics after perfect understanding of the biomechanics in tooth movement.
KOREA J ORTHOD 1993 ; 23(2) : 217-227.
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