Semirapid maxillary expansion--a study of long-term transverse effects in older adolescents and adults.

A new approach, namely, semirapid maxillary expansion (SRME) was introduced with the hypothesis that SRME may stimulate the adaptation process in the nasomaxillary complex and thus would result in reduction of relapse in the postretention period. The aim of this study was therefore to evaluate the short- and long-term effects of SRME on dentofacial structures in older adolescents and adults. The study sample consisted of 40 individuals, 20 orthodontic patients who required maxillary expansion and 20 control cases who received no orthodontic treatment. The mean ages were 14.57 and 13.83 years at the start of treatment and control periods, respectively, and ranged between MP3cap and Ru hand-and-wrist maturation stages. A rigid acrylic maxillary expander was used for SRME (RME of 5-7 days, followed by slow maxillary expansion). The mean expansion time was 0.34 years, and the mean follow-up period was 2.68 years after retention. PA cephalometric film measurements were performed, and the data were analyzed statistically by using paired and Student's t-tests. Lower nasal and maxillary base widths, and upper intermolar and incisor interapex widths were significantly increased compared with the control group (P < .05, P < .001) and remained unchanged during the retention and follow-up stages. Moreover, significant amount of increases occurred in zygomatic and lower nasal widths during the follow-up period. The findings of this study suggested that the dentoskeletal changes after the use of SRME were maintained satisfactorily in the long term in older adolescents and adults.