Resumen de Long-term evaluation of changes in arch dimensions produced by rapid maxillary expansion and fixed appliances
James A. McNamara, Tiziano Baccetti, Lorenzo Franchi, Thomas Herberger
The purpose of this longitudinal study was to evaluate the short-term and long-term changes in dental arch dimensions in patients treated with rapid maxillary expansion (Haas-type expander) followed by fixed edgewise appliances. The treated group (TG) consisted of 112 patients, the records of whom were compared to those of 41 untreated control group (CG). Serial dental casts were available at three different intervals: pre-treatment (T1), after expansion and fixed appliance therapy (T2), and at long-term observation (T3). The mean duration of the T1-T2 and T2-T3 periods for the TG group was 3 years 2 ± 5 months, and 6 years 1 month ± 1 year 2 months, respectively. Arch widths, arch depth, arch perimeter, and molar angulation were assessed in all examined individuals at all observation times. T1-T2, T2-T3, and T1-T3 changes were compared statistically in the TG with respect to corresponding controls. Treatment by means of rapid maxillary expansion followed by fixed appliances produced significantly favorable short-term and long-term changes in almost all the maxillary and mandibular arch measurements. In comparison to controls, a net gain of 6.0 mm was achieved in maxillary arch perimeter, whereas a net gain of 4.5 mm was found for mandibular arch perimeter of treated subjects in the long term. The duration of retention with a fixed lower appliance in the post-treatment period did not appear to affect the long-term outcomes of the treatment protocol significantly. The amount of correction in both maxillary and mandibular intermolar widths equaled two-thirds of the initial discrepancy, whereas treatment eliminated completely the initial deficiency in maxillary and mandibular intercanine widths. The amount of correction for the deficiency in maxillary arch perimeter was about 80%, whereas in the mandible, a full correction was achieved.
