Long-term stability of rapid palatal expansion in the mixed dentition vs the permanent dentition

Introduction: Palatal expansion has been a popular and proven technique for transverse discrepancies used in orthodontics for decades. The short-term effectiveness of the technique is understood, yet questions remain regarding the long-term stability, with much debate surrounding the optimum treatment timing to initiate expansion for the most beneficial and stable results, especially with regard to mixed dentition treatment. The purpose of this study was to determine the long-term stability of palatal expansion performed in the mixed dentition vs the permanent dentition. Methods: Fifty-four subjects were grouped as follows: 24 in the mixed dentition and 30 in the permanent dentition at the start of treatment. All patients had been treated with the Haas type of palatal expansion appliance followed by nonextraction fixed edgewise mechanics. Digitized dental casts were evaluated at 3 times: before treatment (T1), after treatment (T2), and at the long-term retention (T3). Intermolar widths were computed by subtracting measurements between time points, and comparisons between the groups were made to determine expansion and stability differences. Results: Significant intermolar width increases were observed from T1 to T2 with significant relapses from T2 to T3, and an overall net gain remained at T3 in each group. No significant differences were found for relapse between the mixed and permanent dentitions. Conclusions: There are no differences for the long-term intermolar width stability in patients treated with palatal expansion in the mixed dentition vs the permanent dentition.