A controlled clinical study of the effects of the Ni-Ti Memoria® Leaf Spring Activated Expander

Objective: To evaluate the dental effects of the Ni-Ti Memoria® Leaf Spring Activated Expander (MLSAE) in adolescent orthodontic patients presenting with maxillary transverse constriction. Methods: This retrospective controlled clinical study included 22 patients consecutively treated with the Ni-Ti MLSAE (mean age = 12.72 ± 3.07; range = 6-16 yrs). The sample was compared with 22 untreated controls from the University of Michigan Growth Study. Controls were matched by gender, CVM stage and inter-first molar width. Digital dental casts were obtained at pretreatment, one week, monthly and post-expansion time-points. Maxillary dental arch measurements of inter-canine, interpremolar, inter-first molar, arch depth, arch perimeter and molar angulation were evaluated using 3Shape’s OrthoAnalyzer software. Data were analysed using paired sample and modified Student’s t-tests. Results: Total mean expansion duration was 4.2 ± 1.23 months. Significant increases were observed between baseline and final inter-canine, inter-first and second premolars, inter-first molar, and arch perimeter measurements within the treatment group. No significant differences were found within the controls. Between group analyses showed statistically significant differences between the treatment and control groups for all variables except for arch depth and molar angulation. Average changes for inter-canine, inter-first premolar, inter-second premolar, inter-first molar, and arch perimeter were 1.04, 5.65, 5.80, 4.70 and 2.15 mm, respectively. Conclusions: The Ni-Ti MLSAE is capable of obtaining adequate expansion in patients, 6-16 years of age, without causing significant dental tipping. It should be considered a slow expansion device that allows for calibrated expansion at a rate of 1-1.5 mm per month when following the suggested protocol.