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Abstract
Ten subjects, five in the deciduous dentition and five in the mixed dentition (mean
age = 6 years 9 months), had functional posterior cross-bites successfully corrected
with fixed lingual arch wire expansion appliances of the quad-helix design. The appliance,
in the context of "early" treatment, produced midpalatal suture separation on each
subject as evidenced on occlusal radiographs. While the relative orthopedic and orthodontic
changes were not determined, the maxillary intermolar and intercanine transverse measurements
showed significant increases in all subjects, with mean values of +5.3 mm. and +4.1
mm., respectively. The active phase of treatment averaged 30 days and 1.1 adjustments
for the desired expansion to be achieved. Incorporating a standard 6-week retention
period, the total appliance wear time had a mean value of 75 days. Following a 3-month
postretention adjustment period, relapse of the intermolar and intercanine transverse
dimensions presented mean decreases of -1.5 mm. and -1.9 mm., respectively. The relapse
potential was successfully compensated for by overexpansion of 2 to 3 mm. during the
active phase of treatment. No significant differences were demonstrated between the
deciduous- and mixed-dentition groups during the course of maxillary expansion with
the quad-helix appliance.