Comparison of the effects of rapid maxillary expansion caused by treatment with either a memory screw or a Hyrax screw on the dentofacial structures--transversal effects.

The aim of the present study was to investigate and compare the effects of conventional Hyrax screw treatment and memory screw treatment on skeletal and dentoalveolar structures. Thirty-two patients with maxillary transversal deficiency were divided into two groups. The memory-screw group included 17 patients (nine females and eight males), while the Hyrax-screw group comprised 15 patients (eight females and seven males). Mean ages of the subjects in the memory-screw and Hyrax-screw groups were 13.00 +/- 1.29 and 12.58 +/- 1.50 years, respectively. Plaster models and postero-anterior cephalograms were taken from the patients at the beginning of the treatment (T1) and at the end of expansion (T2) and retention periods (T3). The mean expansion period was 7.76 +/- 1.04 days in the memory-screw group and 35.46 +/- 9.39 days in the Hyrax-screw group. 'Shapiro-Wilk Normality test' was used to determine whether the investigated parameters were homogeneous or not. To determine the treatment changes within the group, 'paired t-test' and 'Wilcoxon signed-ranks test' were applied to the homogeneous and non-homogeneous parameters, respectively. Comparison between the groups was carried out using 'Student's t-test' for homogeneous parameters and 'Mann-Whitney U-test' for the rest. Rapid maxillary expansion was carried out successfully in both the groups. However, the use of memory screw may be advantageous because it shortens the maxillary expansion period, provides additional expansion in the retention period, and generates light forces relative to the conventional Hyrax screw.