THE JOURNAL OF HOKKAIDO ORTHODONTIC SOCIETY

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Rapid maxillary expansion（RME）using screw expander has long been popular in clinical orthodontics. Recently, a new RME with built-in superelastic NiTi coil spring was commercially introduced. The purpose of this study was to investigate the forces delivered by the RME with built-in superelastic NiTi coil spring. Two conventional RMEs were used for comparison. Three commercially available RMEs ware selected. The arms of the RMEs were standardized and holded with a pair of grips attached to a universal testing machine（EZ test, Shimadzu, Kyoto）．All the RMEs were first activated 1 or 2 quarter-turns and the forces delivered were measured for 10 minutes at room temperature（25℃）（n = 5）．Results were compared using ANOVA and Tukey’s test, with p set at < 0.05 for statistical significance. The forces delivered were increased with increasing activation in all the RMEs. The RME with built-in superelastic NiTi coil spring showed a significantly lower forces than the other two RMEs in all conditions of the activation. The forces delivered by RME increase with increasing each activations, but almost constant right after each activation. The RME with built-in superelastic NiTi coil spring produces significantly lower forces due to the effect of the NiTi coil spring.

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