Dental Effects of the Ni-Ti Memoria® Leaf Spring Activated Expander: A Controlled Clinical Study
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Objective: To evaluate the dental effects of the Ni-Ti Memoria ® Leaf Spring activated expander (Ni-Ti MLSAE; Leone America, Oxnard, California) in adolescent orthodontic patients presenting with maxillary transverse constriction. Methods: This retrospective controlled clinical study was conducted using digital dental casts of 22 consecutively treated patients with the Ni-Ti MLSAE (mean age= 12.72±3.07; range= 6-16 yrs). All patients had fully erupted maxillary first molars and required transverse expansion for numerous reasons. The sample was compared with 22 untreated controls from the University of Michigan Growth Study. Controls were matched by sex, 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, inter-premolar, inter-first molar, arch depth, arch perimeter and molar angulation were evaluated using 3Shape’s OrthoAnalyzer software. Data were analyzed using paired sample and modified Student’s t-tests. Results: The total mean expansion duration with the Ni-Ti MLSAE 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 2.15mm, respectively. Conclusions: The Ni-Ti MLSAE is capable of obtaining adequate expansion in patients 6-16 years of age without causing significant buccal molar tipping. This device 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.