Effects of rapid maxillary expansion in hyperdivergent patients.

INTRODUCTION: This retrospective cohort study was performed to evaluate the skeletal and dental changes in the short and long terms in hyperdivergent patients treated with rapid maxillary expansion and fixed appliances. METHODS: The sample consisted of 143 patients who had rapid maxillary expansion with a Haas-type expander followed by edgewise therapy. Two groups were established: a normal vertical dimension group (mandibular plane angle >20° and <27°; n = 52) and a hyperdivergent group (mandibular plane angle ≥27°; n = 91). Lateral cephalograms were taken before treatment (average age, 11.5 years in both groups) and after fixed appliance therapy (average age, 14.3 years in both groups). Subjects who exhibited opening or closing in the mandibular plane angle during treatment greater than 1.5° (opening group, n = 23; closing group, n = 26) were followed in the long term (average age, 20.3 years). Longitudinal changes in the different groups were evaluated statistically as well as the prevalence rates of hyperdivergent patients in the opening and closing groups. RESULTS: No significant differences in treatment effects were found in any sagittal or vertical dentoskeletal variables examined. The long-term evaluation of the patients at 5 or more years posttreatment showed no significant skeletal changes. The prevalence rate of hyperdivergent patients in the opening group was not significant. CONCLUSIONS: The results of this study indicate that rapid maxillary expansion can be carried out successfully in patients with increased vertical dimensions without detrimental effects on the vertical skeletal relationships. Thus, an increased mandibular plane angle is not a contraindication for rapid maxillary expansion therapy.

Rapid maxillary expansion followed by fixed appliances: a long-term evaluation of changes in arch dimensions.

The purpose of this longitudinal study was to evaluate the short- and long-term changes in dental arch dimensions in patients treated with rapid maxillary expansion (RME) followed by fixed edge-wise appliances. The records of 112 patients in the treated group (TG) were compared with those of 41 untreated controls. Serial dental casts were available at three different intervals: pretreatment (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 three years two months +/- five months and six years one month +/- one year two months, respectively. Treatment by RME followed by fixed appliances produced significantly favorable short- and long-term changes in almost all the maxillary and mandibular arch measurements. In comparison with controls, a net gain of six mm was achieved in the maxillary arch perimeter, whereas a net gain of 4.5 mm was found for the mandibular arch perimeter of treated subjects in the long term. The duration of retention with a fixed lower appliance in the posttreatment 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 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.